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1.  Solar  .spectrum  w  iili  Fraunliofor  lines.  'J.  .Absdriitiim  spectrum  of  a  coiiceiitriilcd  .soltitioii  of  oxylucmo- 
t;lol)iu;  all  tlie  light  is  absorbed  except  in  the  red  anil  orange.  S.  .•Vbs()r])tion  speclrnin  of  a  le.ss  concentrated 
solution  of  o.xyhamoglobin.  4.  Absorption  spectrum  of  a  dilute  solution  of  oxyhicmoglobin,  showing  the  two 
characteristic  bands,  b.  Absorption  spectrum  of  a  very  dilute  solution  of  oxyhicmoglobin,  showing  only  the 
a-band.  6.  Absorption  spectrum  of  a  dilute  solution  of  reduced  hivmoglobin.  showing  the  characteristic  single 
band  (to  be  compared  with  spectrum  4).  7.  Absorption  spectrum  of  a  dilute  solution  of  carlxm-monoxide- 
hiemoglobin  (to  be  compared  with  spectrum  1).  S.  Absorption  spectrum  of  nieth;>nioglol)in.  '.i.  Absorption 
spectrum  of  acid  hsematin  (alcoholic  solution).  10.  Absorption  spectrum  of  alkaline  li;iniatin  (alcoholic  solu- 
tion) (modified  from  MacMunn,  The  Spectroscope  in  Medicine). 


AN  AMERICAN  TEXTBOOK 


OF 


PHYSIOLOGY 


BY 

HENRY  P.  BOWDITCH,  M.  D.,  JOHN  G.  CUBTIS.  M.  D., 

HENRY  PL  DONALDSON,  Ph.D.,  W.  H.  HOWELL,  Ph.D.,  M.D., 

FREDERIC  S.  L^,  Ph.  D.,  WARREN   P.  LOMBARD,  M.D., 

GRAHAM  LUSK,  Ph.D.,  W.  T.  PORTER,  M.D.,  EDWARD  T.  REICHERT,  M.D., 

AND  HENRY  SE^VALL,  Ph.  D.,  M.  D. 


EDITED  BY 

WILLIAM  H.  HOWELL,  Ph.D.,  M:  D. 

Professor  of  Physiology  in  the  Johns  Hopkins  University,  Baltimore,  Md. 


FULLY  ILLUSTRATED 


PHILADELPHIA: 

W.     B.    SAUNDERS, 

925  Walnut  Street. 
189  7. 


/e97 


Copyright,  1896, 
By  VV.    B.    SAUNDERS. 


ILEOTBOTYPED    BY 
WESTOOTT    »i    THOMSON,   PHILADA. 


PRESS   OF 
W.    B.    SAUNDERS.   PHILADA. 


CONTRIBUTORS. 


HENRY   P.  BOWDITCH,  M.  D., 

Professor  of  Physiology  in  tlie  Harvard  Medical  School. 

JOHN  G.  CURTIS,  M.D., 

Professor  of  Physiology  in  Columbia  University  (College  of  Physicians  and  Surgeons). 

HENRY  H.  DONALDSON,  Ph.  D., 

Head-Professor  of  Xeurology  in  the  University  of  Chicago. 

W.  H.  HOWELL,  Ph.  D.,  M.  D., 

Professor  of  Physiology  in  the  Johns  Hopkins  University. 


FREDERIC  S.  LEE,  Ph.  D., 

Adjunct  Professor  of  Physiology  in  Columbia  University  (College  of  Physicians  and 
Surgeons). 


WARREN  P.  LOMBARD,  M.  D., 

Professor  of  Physiology  in  the  University  of  Michigan. 

GRAHAM  LUSK,  Ph.  D., 

Professor  of  Physiology  in  the  Yale  Medical  School. 

W.  T.  PORTER,  M.  D., 

Assistant  Professor  of  Physiology  in  the  Harvard  Medical  School. 

EDWARD  T.  REICHERT,  M.  D., 

Professor  of  Physiology  in  the  University  of  Pennsylvania. 

HENRY  SEWALL,  Ph.D.,  M.  D., 

Professor  of  Physiology  in  the  Medical  Department  of  the  University  of  Denver 

9 


PREFACE. 


The  collaboration  of  several  teachers  in  the  preparation  of  an  elementary 
text-book  of  physiology  is  unusual,  the  almost  invariable  rule  heretofore 
having  been  for  a  single  author  to  write  the  entire  book.  It  does  not  seem 
desirable  to  attempt  a  discussion  of  the  relative  merits  and  demerits  of  the  two 
plans,  since  the  method  of  collaboration  is  untried  in  the  teaching  of  physi- 
ology, and  there  is  therefore  no  basis  for  a  satisfactory  comparison.  It  is  a  fact, 
however,  that  many  teachers  of  physiology  in  this  countiy  have  not  been 
altogether  satisfied  with  the  text-books  at  their  disposal.  Some  of  the  more 
successful  older  books  have  not  kept  pace  with  the  rapid  changes  in  modern 
physiology,  while  few,  if  any,  of  the  newer  books  have  been  uniformly  satis- 
factory in  their  treatment  of  all  parts  of  this  many-sided  science.  Indeed,  the 
literature  of  experimental  physiology  is  so  great  that  it  would  seem  to  be 
almost  impossible  for  any  one  teacher  to  keep  thoroughly  informed  on  all 
topics.  This  fact  undoubtedly  accounts  for  some  of  the  defects  of  our  present 
text-books,  and  it  is  hoped  that  one  of  the  advantages  derived  from  the  col- 
laboration method  is  that,  owing  to  the  less  voluminous  literature  to  be 
consulted,  each  author  has  been  enabled  to  base  his  elementary  account  upon 
a  comprehensive  knowledge  of  the  part  of  the  subject  assigned  to  him.  Those 
who  are  acquainted  with  the  difficulty  of  making  a  satisfactory  elementary 
presentation  of  the  complex  and  oftentimes  unsettled  questions  of  physiology 
must  agree  that  authoritative  statements  and  generalizations,  such  as  are  fre- 
quently necessary  in  text-books  if  they  are  to  leave  any  impression  at  all  upon 
the  student,  are  usually  trustworthy  in  proportion  to  the  fulness  of  informa- 
tion possessed  by  the  writer. 

Perhaps  the  most  important  advantage  which  may  be  expected  to  follow 

the  use  of  the  collaboration  method  is  that  the  student  gains  thereby  the  point 

of  view  of  a  number  of  teachers.     In  a  measure  he  reaps  the  same  benefit  as 

would  be  obtained  by  following  courses  of  instruction  under  different  teachers. 

The  different  standpoints  assumed,  and  the  differences  in  emphasis  laid  upon 

the  various   lines  of  procedure,  chemical,  physical,  and   anatomical,  should 

give  the  student  a  better  insight  into  the  methods  of  the  science  as  it  exists 

11 


12  PREFACE. 

to-day.  A  similar  advantage  may  be  expected  to  follow  the  inevitable  over- 
lapping of  the  topics  assigned  to  the  various  contributoi-s,  since  this  has  led 
in  many  cases  to  a  treatment  of  the  same  subject  by  several  writers,  who  have 
approached  the  matter  under  discussion  from  slightly  varying  standpoints,  and 
in  a  few  instances  have  arrived  at  slightly  different  conclusions.  In  this 
last  respect  the  book  reflects  more  faithfully  perhaps  than  if  written  by  a 
single  author  the  legitimate  differences  of  opinion  which  are  held  by  physi- 
ologists at  present  with  regard  to  certain  questions,  and  in  so  far  it  fulfils 
more  perfectly  its  object  of  presenting  in  an  unprejudiced  way  the  existing 
state  of  our  knowledge.  It  is  hoped,  therefore,  that  the  diversity  in  method 
of  treatment,  which  at  first  sight  might  seem  to  be  disadvantageous,  will  prove 
to  be  the  most  attractive  feature  of  the  book. 

In  the  preparation  of  the  book  it  has  been  assumed  that  the  student  has 
previously  obtained  some  knowledge  of  gross  and  microscopic  anatomv,  or  is 
taking  courses  in  these  subjects  concurrently  with  his  physiology.  For  this 
reason  no  systematic  attempt  has  been  made  to  present  details  of  histology  or 
anatomy,  but  each  author  has  been  left  free  to  avail  himself  of  material  of 
this  kind  according  as  he  felt  the  necessity  for  it  in  developing  the  physiolog- 
ical side. 

In  response  to  a  general  desire  on  the  part  of  the  contributors,  references 
to  literature  have  been  given  in  the  book.  Some  of  the  authors  have  used 
these  freely,  even  to  the  point  of  giving  a  fairly  complete  bibliography  of  the 
subject,  while  others  have  preferred  to  employ  them  only  occasionally,  where 
the  facts  cited  are  recent  or  are  noteworthy  because  of  their  importance  or 
historical  interest.  References  of  this  character  are  not  usually  found  in  ele- 
mentary text-books,  so  that  a  brief  word  of  explanation  seems  desirable.  It 
has  not  been  supposed  that  the  student  will  necessarily  look  up  the  references 
or  commit  to  memory  the  names  of  the  authorities  quoted,  although  it  is  pos- 
sible, of  course,  that  individual  students  may  be  led  to  refer  occasionally  to 
original  sources,  and  thereby  acquire  a  truer  knowledge  of  the  subject.  The 
main  result  hoped  for,  however,  is  a  healthful  pedagogical  influence.  It  is  too 
often  the  case  that  the  student  of  medicine,  or  indeed  the  graduate  in  medicine, 
regards  his  text-book  as  a  final  authority,  losing  sight  of  the  fact  that  such 
books  are  mainly  compilations  from  the  works  of  various  investigators,  and 
that  in  all  matters  in  dispute  in  physiology  the  final  decision  must  be  made,  so 
far  as  possible,  upon  the  evidence  furnished  by  experimental  work.  To  enforce 
this  latter  idea  and  to  indicate  the  character  and  source  of  the  great  literature 
from  which  the  material  of  the  text-book  is  obtained  have  been  the  main 
reasons  for  the  adoption  of  the  reference  system.     It  is  hoped  also  that  the 


PREFACE.  13 

book  will  be  found  useful  to  many  practitioners  of  medicine  who  may  wisii  to 
keep  themselves  in  touch  with  the  development  of  modern  physiology.  For  this 
class  of  readers  references  to  literature  are  not  only  valuable,  but  frequently 
essential,  since  the  limits  of  a  text-book  forbid  an  exhaustive  discussion  of 
many  points  of  interest  concerning  which  fuller  information  may  be  desired. 

The  numerous  additions  which  are  constantly  being  made  to  the  literature 
of  physiology  and  the  closely  related  sciences  make  it  a  matter  of  difficulty  to 
escape  errors  of  statement  in  any  elementary  treatment  of  the  subject.  It  can- 
not be  hoped  that  this  book  will  be  found  entirely  free  from  defects  of  this 
character,  but  an  earnest  effort  has  been  made  to  render  it  a  reliable  repository 
of  the  important  facts  and  principles  of  physiology,  and,  moreover,  to  embody 
in  it,  so  far  as  possible,  the  recent  discoveries  and  tendencies  which  have  so 
characterized  the  history  of  this  science  within  the  last  few  years. 


CONTENTS. 


PAOK 

I.  INTRODUCTION     17 

By  W.  H.  Howell. 

II.  GENERAL  PHYSIOLOGY  OF  MUSCLE  AND  NERVE  ....     32 

By  Warren  P,  Lombard. 

III.  SECRETION 152 

By  W.  H.  Howell. 

IV.  CHEMISTRY  OP  DIGESTION  AND  NUTRITION 213 

By  W.  H.  Howell. 

V.  MOVEMENTS  OF  THE  ALIMENTARY  CANAL,  BLADDER, 

AND  URETER 307 

By  W.  H.  Howell. 

VI.  BLOOD  AND  LYMPH 331 

By  W.  H.  Howell. 

VII.  CIRCULATION 368 

Part  I. — The   Mechanics    of   the  Circulation   of    the 
Blood  and  of  the  Movement  of  the  Lymph 368 

By  John  G.  Curtis. 

Part  II. — The  Innervation  of  the  Heart 440 

Part  III. — The  Nutrition  of  the  Heart 471 

Part  IV.— The  Innervation  of  the  Blood-Vessels    .  .  .   482 
By  W.  T.  Porter. 

VIII.  RESPIRATION 503 

By  Edward  T.  Reich ert. 

IX.  ANIMAL  HEAT 575 

By  Edward  T.  Reichert. 

X.  CENTRAL  NERVOUS  SYSTEM 605 

By  Henry  H.  Donaldson. 

15 


16  CONTENTS. 

PAGE 

XI.  THE  SPECIAL  SENSES 744 

Vision 744 

By  Henry  P.  Bow  ditch. 

Hearing,  Cutaneous  and  Muscular  Sensibility,  Equilib- 
rium, Smell,  and  Taste 807 

By  Henry  Sewall. 

XII.  PHYSIOLOGY  OF  SPECIAL  MUSCULAR  MECHANISMS  .   .    855 

The  Action  of  Locomotor  Mechanisms 855 

By  Warren  P.  Lombard. 

Voice  and  Speech 861 

Bv  Henry  Sewall. 

XIII.  REPRODUCTION 878 

By  Frederic  S.  Lee. 

XIV.  THE  CHEMISTRY  OF  THE  ANIMAL  BODY 943 

By  Graham  Lusk. 


AN  AMERICAN 

TEXT-BOOK  OF  PHYSIOLOGY. 


I.  INTRODUCTION. 


The  term  "  physiology "  is,  in  an  etymological  sen.se,  synonymous  with 
"  natural  philosophy,"  and  occasionally  the  word  is  used  with  this  significance 
even  at  the  present  day,^  By  common  u.sage,  however,  the  term  is  restricted 
to  the  living  side  of  nature,  and  is  meant  to  include  the  sum  of  our  know- 
ledge concerning  the  properties  of  living  matter.  The  active  substance  of 
which  living  things  are  composed  is  supposed  to  be  closely  similar  in  all  cases, 
and  is  commonly  designated  as  protoplasm  (;r^a>roc,  first,  and  Tz)Aafia^  any- 
thing formed).  It  is  usually  .stated  that  this  word  was  first  introduced  into 
biological  literature  by  the  botani.-jt  You  Mohl  to  designate  the  granular  semi- 
liquid  contents  of  the  plant-cell.  It  seems,  however,  that  priority  in  the  use 
of  the  word  belongs  to  the  physiologi.st  Purkiuje  (1840),  who  employetl  it  to 
describe  the  material  from  which  the  young  animal  embryo  is  constructed.^ 
In  recent  years  the  term  has  been  applied  indiflPerently  to  the  soft  material 
constituting  the  substance  of  either  animal  or  plant-cells.  The  word  must  not 
be  misunderstood  to  mean  a  substance  of  a  definite  chemical  nature  or  of  an 
invariable  morphological  structure ;  it  is  applied  to  any  part  of  a  cell  which 
shows  the  properties  of  life,  and  is  therefore  only  a  convenient  abbreviation 
for  the  phrase  "  ma.ss  of  living  matter." 

Living  things  fall  into  two  great  groups,  animals  and  plants,  and  corre- 
sponding to  this  there  is  a  natural  separation  of  physiology  into  two  sciences,  one 
dealing  with  the  phenomena  of  animal  life,  the  other  with  plant  life.  In  what 
follows  in  this  introductory  section  the  former  of  these  two  divisions  is  chiefly 
considered,  for  although  the  most  fundamental  laws  of  physiology  are,  without 
doubt,  equally  applicable  to  animal  and  vegetable  protoplasm,  nevertheless  the 
structure  as  well  as  the  properties  of  the  two  forms  of  matter  are  in  some 
respects  noticeably  different,  particularly  in  the  higher  types  of  organisms  in 
each  group.  The  most  striking  contrast,  perhaps,  is  found  in  the  fact  that 
plants  exhibit  a  le.s.ser  degree  of  specialization  in  form  and  function  and 

^  See  Mineral  Physiology  and  Physiography,  T.  Sterry  Huut,  1886. 
•  '  O.  Hertwig  :  Die  Zelle  und  die  Gewebe,  1893. 
2  17 


18  AN  AMERICAN    TEXT-BOOK    OF   PIIYSIOI.OGY. 

a  much  greater  power  of  assimilalioii.  Owing  to  tlii.s  latter  property  tlie 
plant-cell  is  able,  'vvitii  the  aid  ol"  solar  energy,  to  construct  its  protoplasm 
from  very  simple  forms  of  inorganic  matter,  such  as  water,  cari)on  dioxide, 
and  inorganic  salts.  In  this  way  energy  is  stored  within  the  vegetable  cell  in 
the  form  of  complex  organic  compounds.  Animal  ])rotoplasm,  on  the  con- 
trary, has  comparatively  feeble  synthetic  properties  ;  it  is  characterized  chiefly 
by  its  destructive  jiower.  In  the  long  run,  animals  obtain  their  food  from  the 
plant  kingdom,  and  the  animal  cell  is  able  to  dissociate  or  oxidize  the  com])lex 
material  of  vegetable  protoplasm  and  thus  liberate  the  potential  energy  con- 
tained therein,  the  energy  taking  the  form  mainly  of  heat  and  muscular  work. 
"We  must  suppose  that  there  is  a  general  resemblance  in  the  ultimate  structure 
of  animal  and  vegetable  living  matter  to  wdiich  the  fundamental  similarity  in 
properties  is  due,  but  at  the  same  time  there  must  be  also  some  common  dif- 
ference in  internal  structure  between  the  two,  and  it  is  fair  to  assume  that 
the  divergent  properties  exhibited  by  the  two  great  groups  of  living  things 
are  a  direct  outcome  of  this  structural  dissimilarity ;  to  make  use  of  a  figure 
of  speech  employed  by  Bichat,  plants  and  animals  are  cast  in  different  moulds. 

It  is  difficult  if  not  impossible  to  settle  upon  any  one  property  which 
absolutely  shall  distinguish  living  from  dead  matter.  Xutrition,  that  is,  the 
power  of  converting  dead  food  material  into  living  substance,  and  repro- 
duction, that  is,  the  power  of  each  organism  to  perpetuate  its  kind  by  the 
formation  of  new  individuals,  are  probably  the  most  fundamental  charac- 
teristics of  living  things;  but  in  some  of  the  specialized  tissues  of  higher 
•  animals  the  power  of  reproduction,  so  far  as  this  means  mere  multiplication 
by  cell-division,  seems  to  be  lost,  as,  for  example,  in  the  case  of  the  nerve-cells 
in  the  central  nervous  system  or  of  the  ovum  itself  before  it  is  fertilized  i)y 
the  spermatozoon.  Nevertheless  these  cellular  units  are  indisputably  living 
matter,  and  continue  to  exhibit  the  power  of  nutrition  as  well  as  other  prop- 
erties characteristic  of  the  living  state.  It  is  possible  also  that  the  jxtwer 
of  nutrition  may,  under  certain  conditions,  be  held  in  abeyance  temporarily  at 
least,  although  it  is  certain  that  a  permanent  loss  of  this  property  is  incom- 
patible with  the  retention  of  the  living  condition. 

It  is  frequently  said  that  the  most  general  property  of  living  matter  is  its 
irritability.  The  precise  meaning  of  the  term  vital  irritability  is  hard  to 
define.  The  \yord  implies  the  capability  of  reacting  to  a  stimulus  and  usually 
also  the  assumption  that  in  the  reaction  some  of  the  inner  potential  energy  of 
the  living  material  is  liberated,  so  that  the  energy  of  the  res]M)nse  is  many 
times  greater,  it  may  be,  than  the  energy  of  the  stimulus.  This  last  idea  is 
illustrated  by  the  case  of  a  contracting  muscle,  in  Ayhich  the  stimulus  acts  as  a 
liberating  force  causing  chemical  decompositions  of  the  substance  of  the  muscle 
with  the  liberation  of  a  comparatively  large  amount  of  energy,  chiefly  in  the 
form  of  heat  or  of  heat  and  work.  It  may  be  remarked  in  ])assing,  liowever, 
that  we  are  not  justified  at  present  in  assuming  that  a  similar  liberation  of 
stored  energy  takes  place  in  all  irritable  tissues.  In  the  case  of  nerve-fibres, 
for  instance,  we  have  a  typically  irritable  tissue  which  responds  readily  to 


iXTROhrc'i  fON.  19 

external  stimuli,  hut  as  yet  it  has  not  hcen  possihle  to  show  that  the  forma- 
tion or  conduction  of  a  iiorvo  inn)ulse  is  accompanied  hy  or  dependent  upon 
the  liheration  of  potential  chemical  energy.  The  nature  of  the  reaction  of 
irritable  living  matter  is  found  to  vary  with  the  character  of  the  tissue  or 
organism  on  the  one  hand,  and,  so  I'ar  as  intensity  goes  at  least,  with  the 
natui'c  of  the  stimulus  on  the  (»ther.  Response  of  a  definite  character  to 
ajipropriate  external  stinuilation  may  be  observed  frequently  enough  in 
dead  matter,  and  in  st)me  cases  the  nature  of  the  reaction  sinmlates  closely 
some  of  those  displayed  by  living  thiugs.  For  instance,  a  dead  catgut  string 
may  be  made  to  shorten  after  the  manner  of  a  nuiscular  contraction  by  the 
appropriate  application  of  heat,  or  a  mass  of  gunpowder  may  be  exploded  by 
tlie  action  of  a  small  spark  and  give  rise  to  a  great  liberation  of  energy  which 
had  previously  existed  in  potential  form  within  its  molecules.  As  regards 
any  jiiece  of  matter  we  can  only  say  that  it  exhibits  vital  irritability  when  the 
I'eaction  or  response  it  gives  upon  stinuilation  is  one  characteristic  of  living 
matter  in  general  or  of  the  particular  kind  of  living  matter  under  observation ; 
thus,  a  muscle-fibre  contracts,  a  nerve-fibre  conducts,  a  gland-cell  secretes,  an 
entire  organism  moves  or  in  some  way  adjusts  itself  more  perfectly  to  its 
environment.  Considered  from  this  standpoint,  irritability  means  only  the 
exhibition  of  one  or  more  of  the  peculiar  properties  of  living  matter  and  can- 
not be  used  to  designate  a  property  in  itself  distinctive  of  living  structure  ; 
the  term,  in  fact,  comprises  nothing  more  specific  or  characteristic  than  is 
implied  in  the  more  general  phrase  vitality.  When  an  amoeba  dies  it  is  no 
longer  irritable,  that  is,  its  substance  no  longer  assimilates  when  stimulated  by 
the  presence  of  appropriate  food,  its  conductivity  and  contractility  disappear 
so  that  mechanical  irritation  no  longer  causes  the  protrusion  or  retraction  of 
pseudopodia — no  form  of  stimulation,  in  fact,  is  capable  of  calling  forth  any 
of  the  recognized  properties  of  living  matter.  To  ascertain,  therefore,  whether 
or  not  a  given  piece  of  matter  possesses  vital  irritability  we  must  first  become 
a('(]uainted  with  the  fundamental  properties  of  living  matter  in  order  to  recog- 
nize the  response,  if  any,  to  the  form  of  stimulation  used. 

Nutrition  or  assimilation,  in  a  wide  sense  of  the  word,  has  already  been 
referred  to  as  probably  the  most  universal  and  characteristic  of  these  proj)- 
erties.  By  this  term  we  designate  that  series  of  changes  through  which  dead 
matter  is  received  into  the  structure  of  living  substance.  The  term  in  its 
broadest  sense  may  be  used  to  cover  the  subsidiary  processes  of  digestion, 
respiration,  absorption,  and  excretion  through  which  food  material  and 
oxygen  are  prepared  for  the  activity  of  the  living  molecules,  and  the  waste 
products  of  activity  are  removed  from  the  organism,  as  well  as  the  actual 
conversion  of  dead  material  into  living  protoplasm.  This  last  act,  which  is 
presumably  a  synthetic  process  effected  under  the  influence  of  living  matter, 
is  especially  designated  as  anabolism  or  as  assimilation  in  a  narrower  sense 
of  the  Avord  as  opposed  to  disassimilation.  By  disassimilation  or  katabolism 
we  mean  those  changes  leading  to  the  destruction  of  the  complex  substance  of 
the  living  molecules,  or  of  the  food  material  in  contact  with  these  molecules. 


20  AN  AMi:RirAX    TEXT- HOOK    OF    PIIYSIOLOC  Y. 

As  was  said  before,  animal  protoplasm  is  pre-eminently  katabolic,  ami  the 
evidence  of  its  katal)()lisiii  is  t'oiind  in  the  waste  products,  such  as  CO,,  II,(), 
and  urea,  which  arc  given  off  from  animal  organisms.  Assiiiiilati(m  and  dis- 
assimilation,  or  anabolism  and  katabolism,  go  hand  in  hand  and  together 
constitute  an  cver-rccurring  cycle  of  activity  which  })ersists  as  long  as  the 
material  retains  its  living  structure  and  which  as  a  whole  is  designated  under 
the  nanu>  metabolism.  In  most  forms  of  living  matter  metabolism  is  in  some 
way  self-limited,  so  that  gradually  it  beco'mes  less  perfect,  old  age  comes  on, 
and  finally  tleath  ensues.  It  has  been  asserted  that  originally  the  metabolic 
activity  of  protoplasm  was  self-perpetuating — that,  barring  accident,  the  cycle 
of  changes  would  go  on  forever.  Resting  upon  this  assumption  it  has  been 
suggested  by  Weissmann  that  tPTe  protoplasm  of  the  reproductive  elements 
still  retains  this  primitive  and  perfect  metabolism  and  thus  provides  for  the 
continuity  of  life.  The  speculations  bearing  upon  this  point  will  be  discussed 
in  more  detail  in  the  section  on  Reproduction. 

Reproduction  in  some  form  is  also  practically  a  universal  property  of 
living  matter.  The  unit  of  structure  among  living  organisms  is  the  cell. 
Under  proper  conditions  of  nourishment  the  cell  may  undergo  separation  into 
two  daughter  cells.  In  some  cases  the  separation  takes  place  by  a  simple  act 
of  fission,  in  other  cases  the  division  is  indirect  and  involves  a  number  of 
interesting  changes  in  the  structure  of  the  nucleus  and  the  protoplasm  of  the 
body  of  the  cell,  or  cytoplasm,  as  it  is  frequently  called.  In  the  latter  case 
the  process  is  spoken  of  as  karyokinesis  or  mitosis.  This  act  of  division  was 
supposed  formerly  to  be  under  the  control  of  the  nucleus  of  the  cell,  but 
modern  histology  has  shown  that  in  karyokinetic  division  the  process,  in 
many  cases  at  least,  is  initiated  by  a  special  structure  to  which  the  name  cen- 
trosome  has  been  given.  The  many-celled  animals  arise  by  successive  divi- 
sions of  a  primitive  cell,  the  ovum,  and  in  the  higher  forms  of  life  the  ovum 
requires  to  be  fertilized  by  union  with  a  spermatozoon  before  cell-division 
becomes  possible.  The  sperm-cell  acts  as  a  stimulus  to  the  egg-cell  (see  section 
on  Reproduction)  and  rapid  cell-division  is  the  result  of  their  union.  It  must 
be  noted  also  that  the  term  reproduction  includes  the  power  of  hereditary 
transmission.  The  daughter-cells  are  similar  in  form  to  the  parent-cell  and 
the  organism  produced  from  a  fertilized  ovum  is  sid)stantially  a  facsimile  of 
the  parent  forms.  Living  matter,  therefore,  not  only  exhibits  the  power  of 
separating  off  other  units  of  living  matter,  but  of  transmitting  to  its  progeny 
its  own  peculiar  internal  structure  and  properties. 

Contractility  and  conductivity  are  properties  exhibited  in  one  form  or 
another  in  all  animal  organisms  and  we  must  believe  that  they  are  to  be 
counted  among  the  primitive  properties  of  protoplasm.  The  power  of  con- 
tracting or  shortening  is,  in  fact,  one  of  the  commonly  recognized  features  of 
a  living  thing.  It  is  generally  present  in  the  simplest  forms  of  animal  as 
well  as  vegetable  life,  although  in  the  more  specialized  forms  it  is  found  for 
the  most  part  only  in  animal  organisms.  The  opinion  seems  to  be  general 
among  physiologists  that  wherever  this  property  is  exhibited,  whether  in  the 


jyTR  OD  LCTION.  2 1 

formation  of  tho  pscudojMxlia  of  au  amoeba  or  white  blood-corpuscle,  or  in 
the  vibratilo  movements  of  ciliary  structures,  or  in  the  ])owerful  contractions 
of  voluntary  muscle,  the  underlying  mechanism  by  whieh  the  shortening  is 
produced  is  essentially  the  same  throughout.  However  general  the  property 
mav  be,  it  cannot  be  consiilered  as  distinctivelv  characteristic  of  livin<r  struc- 
ture.  As  was  mentioned  befort',  Kngelmann  '  has  been  able  to  show  that  a  dead 
catgut  string  when  surrounded  by  water  of  a  certain  temperature  and  exposed 
to  a  sudden  additional  rise  of  temperature  will  contract  or  shorten  in  a  man- 
ner closely  analogous  to  the  contraction  of  ordinary  muscular  tissue,  and  it  is 
not  at  all  impossible  that  the  molecular  processes  involved  in  the  shortening 
of  the  catgut  string  and  the  muscle-iibre  may  be  essentially  the  same. 

That  conductivity  is  also  a  fundamental  property  of  primitive  protoplasmic 
structure  seems  to  be  assured  by  the  reactions  which  the  simple  motile  forms 
of  life  exhibit  when  exposed  to  external  stimulation.  Au  irritation  applied 
to  one  point  of  a  protoplasmic  mass  may  produce  a  reaction  involving  other 
parts,  or  indeed  the  whole  extent  of  the  organism.  The  phenomenon  is  most 
clearly  exhibited  in  the  more  specialized  animals  which  possess  a  distinct 
nervous  system.  In  these  forms  a  stimulus  applied  to  one  organ,  as  for  instance 
light  acting  upon  the  eye,  may  be  followed  by  a  reaction  involving  quite 
distant  organs,  such  as  the  muscles  of  the  extremities;  we  know  that  in  these 
cases  the  irritation  has  been  conducted  from  one  organ  to  the  other  by  means 
of  the  nervous  tissues.  But  here  also  we  have  a  property  which  is  widely 
exhibited  in  inanimate  nature.  The  conduction  of  heat,  electricity,  and  other 
forms  of  energy  is  familiar  to  every  one.  While  it  is  quite  possible  that  con- 
duction through  the  substance  of  living  protoplasm  is  something  sui  generis, 
and  does  not  find  a  strict  parallel  in  dead  structures,  yet  it  must  be  admitted 
that  it  is  conceivable  that  the  molecular  processes  involved  in  nerve  conduction 
may  be  essentially  the  same  as  prevail  in  the  conduction  of  heat  through  a 
solid  body,  or  in  the  conduction  of  a  wave  of  pressure  through  a  liquid  mass. 
At  present  we  know  nothing  definite  as  to  the  exact  nature  of  vital  conduction, 
and  can  therefore  affirm  nothing. 

The  four  great  properties  enumerated,  namely,  nutrition  or  assimilation 
(including  digestion,  secretion,  absorption,  excretion,  anabolism,and  katabolism), 
reproduction,  conduction,  and  contractility, form  the  important  features  which 
we  may  recognize  in  all  living  things  and  which  we  make  use  of  in  distin- 
guishing between  dead  and  living  matter.  A  fifth  ])roperty  perhaps  should 
be  added,  that  of  sensibility  or  sensation,  but  concerning  this  property  as  a 
general  accompaniment  of  living  structure  our  knowledge  is  extremely  im- 
perfect; something  more  as  to  the  difficulties  connected  with  this  subject  will 
be  said  presently.  The  four  fundamental  properties  mentioned  are  all  ex- 
hibited in  some  degree  in  the  simplest  forms  of  life,  such  as  the  protozoa.  In 
the  more  highly  organized  animals,  however,  we  find  that  specialization  of 
function  prevails.  Hand  in  hand  with  the  diiferentiation  in  form  which  is 
displayed  in  the  structure  of  the  constituent  tissues  there  goes  a  specialization 

'  Ueber  den  Ursprung  der  Miiskelkraft,  Leipzig,  1893. 


22  .l^V  AMERICAN    TEXT-BOOK    OF   I'll  YSK )L<)(;  V. 

in  certain  pi-ojxTtics  with  a  com-oinitaDt  sin)j)re.ssi()n  of  otlier  properties,  the 
outcome  of  which  is  that  iniiseular  tissue  exhibits  pre-eniincutly  the  power  of 
contractility,  the  nerve  tissues  are  characterized  hy  a  liighly  developed  power 
of  conihictivity,  and  so  on.  While  in  the  simple  unicellular  forms  of  animal 
life  the  fundamental  properties  are  all  somewhat  equally  exhibited  within  the 
compass  of  a  sinj^le  uuit  or  cell,  in  the  higher  animals  we  have  to  deal  with 
a  vast  community  of  cells  segregated  into  tissues  each  of  which  possesses  some 
distinctive  property.  This  specialization  of  function  is  known  technicallv  as 
the  physiological  division  of  labor.  The  beginning  of  this  ])rocess  may  be 
recognized  in  the  cell  itself.  The  typical  cell  is  already  an  oi-ganism  of  some 
complexity  as  compared  with  a  simple  mass  of  undifferentiated  protoj)lasm. 
The  protoplasm  of  the  nucleus,  particularly  of  that  material  in  the  nucleus 
which  is  designated  as  chromatin,  is  differentiated,  both  histologicallv  and 
physiologically,  from  the  protoplasm  of  the  rest  of  the  cell,  the  so-called  cvto- 
plasm.  The  chromatin  material  in  the  resting  cell  is  arranged  usually  in  a 
network,  but  during  the  act  of  division  (karyokinesis)  it  is  segmented  into  a 
number  of  rods  or  lilameuts  known  as  chromosomes.  In  the  ovum  there  are 
good  reasons  for  believing  that  the  power  of  transmitting  hereditary  charac- 
teristics has  been  especially  acquired  by  these  chromosomes.  The  nucleus, 
moreover,  controls  in  some  way  the  metabolism  of  the  entire  cell,  for  it  has 
been  shown,  in  some  cells  at  least,  that  a  non-nucleated  piece  of  the  cytoplasm 
is  not  only  deprived  of  the  power  of  reproduction,  but  has  also  such  limited 
powers  of  nutrition  that  it  quickly  undergoes  disintegration.  On  the  other 
hand  contractility  and  conductivity,  and  some  of  the  functions  connected  with 
nutrition,  such  as  digestion  and  excretion,  seem  often  to  be  specialized  in  the 
cytoplasm.  As  a  further  example  of  differentiation  in  the  cell  itself  the  ex- 
istence of  the  centrosome  may  be  referred  to.  The  centrosome  is  a  body  of 
very  minute  size  which  has  been  discovered  in  numerous  kinds  of  cells.  It 
is  considered  by  many  observers  to  be  a  permanent  structure  of  the  cell,  lying 
either  in  the  cytoplasm,  or  possibly  in  some  cases  within  the  substance  of  the 
nucleus.  When  present  it  seems  to  have  some  special  function  in  connection 
with  the  movements  of  the  chromosomes  during  the  act  of  cell-division.  In 
the  many-celled  animals  the  primitive  properties  of  protoplasm  become  highly 
developed,  in  consequence  of  this  subdivision  of  function  among  the  various 
tissues,  and  in  many  ways  the  most  complex  animals  are,  from  a  physiological 
standpoint,  the  simplest  for  purposes  of  study,  since  the  properties  of  living 
matter  become  separated  and  emphasized  in  them  to  such  an  extent  that  they 
are  better  fitted  for  accurate  observation. 

We  are  at  liberty  to  suppose  that  the  various  properties  so  clearly  recognizable 
in  the  differentiated  tissues  of  higher  animals  are  all  actually  or  potentially 
contained  in  the  comparatively  undifferentiated  protoplasm  of  the  simplest  uni- 
cellular forms.  That  the  lines  of  variation,  or  in  other  words  the  direction  of 
specialization  in  form  and  function,  are  not  infinite,  but  on  the  contrary 
comparatively  limited,  seems  evident  when  we  reflect  that  in  spite  of  the 
numerous  branches  of  the  phylogenetic  stem  the  properties   as  well  as  the 


INTR  OD  UCTION.  23 

forms  of  the  differentiated  tissues  througliuiit  the  animal  kingdom  are  strikinj^dy 
alike.  Striated  luusck',  with  tlie  characteristic  property  of  sharp  and  powcrl'nl 
contraction,  is  cvcrywiiere  fonnd  ;  the  central  nervons  system  in  the  inver- 
tehrates  is  bnilt  npon  the  same  type  as  in  the  highest  manunals,  and  the 
variations  met  with  in  dilTcrcnt  animals  are  probably  bnt  varying  degrees  of 
])erte('tion  in  the  dcvelo})ment  of  the  innate  possibility  contained  in  primitive 
protoplasm.  It  is  not  too  much  to  say,  perhaps,  that  were  we  acquainted  with 
the  structure  and  chemistry  of  the  ultimate  units  of  living  substance,  the  key 
to  the  possibilities  of  the  evolution  of  form  and  finiction  would  be  in  our 
possession. 

Most  interesting  suggestions  have  been  made  in  recent  years  as  to  the 
essential  molecular  structure  of  living  matter.  These  views  are  necessarily 
very  incomplete  and  of  a  highly  speculative  character,  and  their  correctness  or 
incorrectness  is  at  })reseut  beyond  the  range  of  experimental  proof;  never- 
theless they  are  sufficiently  interesting  to  warrant  a  brief  statement  of  some 
of  them,  as  they  seem  to  show  at  least  the  trend  of  physiological  thought. 

Pfliiger/  in  a  highly  interesting  paper  upon  the  nature  of  the  vital  pro- 
cesses, calls  attention  to  the  great  instability  of  living  matter.  He  supposes 
that  living  substance  consists  of  very  complex  and  very  unstable  molecules  of 
a  proteid  nature  which,  because  of  the  active  iutra-molecnlar  movement  pre- 
sent, are  continually  dissociating  or  falling  to  pieces  with  the  formation  of 
simpler  and  more  stable  bodies  such  as  water,  carbon  dioxide  and  urea,  the  act 
of  dissociation  giving  rise  to  a  liberation  of  energy.  "  The  intra-molecular 
heat  (movement)  of  the  cell  is  its  life."  He  suggests  that  in  this  living  mole- 
cule the  nitrogen  is  contained  in  the  form  of  a  cyanogen  compouad,  and  that 
the  instability  of  the  molecule  depends  chiefly  upon  this  particular  grouping. 
Moreover  the  power  of  the  molecule  to  assimilate  dead  proteid  and  convert  it  to 
living  proteid  like  itself  he  attributes  to  the  existence  of  the  cyanogen  group. 
It  is  known  that  cyanogen  compounds  possess  the  property  of  polymerization, 
that  is,  of  combining  with  similar  molecules  to  form  more  complex  mole- 
cules, and  we  may  suppose  that  the  molecules  of  dead  proteid  when  brought 
into  contact  with  the  living  molecules  are  combined  with  the  latter  by  a  pro- 
cess analogous  to  polymerization  or  condensation.  By  this  means  the  stable 
structure  of  dead  proteid  is  converted  to  the  labile  structure  of  living  proteid, 
and  the  molecules  of  the  latter  increase  in  size  and  instability.  When  living 
substance  dies  its  molecules  undergo  alteration  and  become  incapable  of  ex- 
hibiting the  usual  properties  of  life.  Pfliiger  suggests  that  the  change  may 
consist  essentially  in  an  absorption  of  water  whereby  the  cyanogen  grouping 
passes  over  into  an  ammonia  grouping.  Loew^  assumes  also  that  the  dif- 
ference between  dead  and  living  or  active  ])roteid  lies  chiefly  in  the  fact  that 
in  the  latter  we  have  a  very  unstable  or  labile  molecule  in  which  the  atoms  are 
in  active  motion.     The  instability  of  the  molecules  he  likewise  attributes  to 

^  Archivfiir  die  f/esammie  Physiologie,  1875,  Bd.  10,  p.  251. 

*  Ibid.,  1880,  Bd.  22 ;  Loew  and  Bokorn y  :  Die  chemische  KrnftqueUe  in  lebenden  Proioplasma, 
Miinchen,  1882;  Imperial  Institute  of  Tokyo  (College  of  Agriculture),  1894. 


24  AN  AMERTCAX    TEXT-BOOK    OF  PIIYSIOIJXSY. 

the  exi.^^teiice  of  certain  t:;njii|)inji;s  of"  the  atoms.  InllMciiccd  in  part  l)V  the 
power  of  living  jnaterial  to  rednce  alkaline  .silver  solutions,  lie  supposes  that 
the  specially  important  labile  groiij)  in  the  molecule  is  the  aldehyde  radiral 

—  C_iT.     The  nitrotrcn  exists  also  in  a  lahile  amido- combination, —NHj, 

and   the  active  or  living  foi-m  of  these  two  grouj)s  may  be  exj»ressed   by  the 

-  Oil -Nil, 
formula        I  _(j-     If'  this  grouping  by  (ihemical  change  became  con- 

=  C    -C_H 

verted  to  the  grouping  _  ^,    —  C'HOH '  ^*  would  form  a  comparatively  iuert 

compound  such  as  we  have  in  dead  ])roteid.  Starting  with  foiinic  aldehyde 
Loew  and  IJokorny  give  a  schema  according  to  wliicii  there  might  be  con- 
structed a  living  molecule  coutaiuiug  the  requisite  aldehyde  and  araido- 
groups ;  thus : 

4HCOH  4  H.N  =  CJT^NO^  +  2H2O. 

Formic       Ammonia.       Aspartic 
aldehyde.  aldehyde. 

Further  possible  conden.sation  of  the  aspartic  aldehyde  would  give 

3(C,H,N02)  =  C12H17N3O,  +  2H2O, 

and  by  still  fiu'ther  condensation  with  the  addition  of  sulj)hur  and  some  re- 
duction we  would  get 

6(C.2H,,N30,)  +  12H  +  H2S  =  CV^Hi^NigSO^^  +  2HA 

which  represents,  from  theii-  standpoint,  the  simplest  expression  of  the  struc- 
ture of  a  proteid  molecule  possessing  great  lability  and  the  pow'er  of  further 
polymerization.  Latham '  proposes  a  theory  which  combines  the  ideas  of 
Pfliiger  and  of  Loew.  He  suggests  that  the  living  molecule  may  be  composed 
of  a  chain  of  cyan-alcohols  united  to  a  benzene  nucleus.  The  cyan-alcohols  are 
obtained  by  the  union  of  an  aldehyde  with  hydrocyanic  acid  ;  they  contain, 
therefore,  the  labile-aldehyde  grouping  as  well  as  the  cyanogen  nucleus  to 
which  Pfliiger  attributes  such  importance. 

It  has  been  assumed  by  many  observers  that  the  properties  of  living 
matter,  as  we  recognize  them,  are  not  solely  an  outcome  of  the  inner  .'structure 
of  the  hypothetical  living  molecules.  They  believe  that  these  latter  units  are 
fashioned  into  larger  secondary  units  each  of  which  is  a  definite  aggregate  of 
chemical  molecules  and  po.ssesses  certain  properties  or  reactions  that  dejiend 
upon  the  mode  of  arrangement.  The  idea  is  similar  to  that  advanced  by 
mineralogists  to  ex])lain  the  .structure  of  crystals.  They  suppose  that  the 
chemical  molecules  are  arranged  in  larger  or  smaller  groups  to  which  the 
name  "physical  molecules"  has  been  given.  So  in  living  protoplasm  it  may 
be  that  the  smallest  particles  caj^able  of  exhibiting  the  es.sential  jjrojierties 
of  life  are  grou]ys  of  ultimate  molecules,  in  the  chemical  .sense,  having  a 
definite  arrangement  and  definite  physical  properties.  These  secondary  units 
1  Brili&h  Medical  Journal,  1886,  p.  629. 


INTRODUCTION.  25 

of  structure  have  been  designated  by  various  iiaiiu's  such  as  "physiological 
molecules/"  "  somacules," '^  micelUe,*  etc.  Many  facts,  especially  from  the 
side  of  plant  physiology,  teach  us  that  the  ]>hysical  constitution  of  protoplasm 
is  probably  of  great  importance  in  understanding  its  reaction  to  its  environ- 
ment. Microscopic  analysis  is  insufficient  to  reveal  the  existence  or  character 
of  these  *'  physiological  molecules,"  but  it  has  abundantly  shown  that  proto- 
]>lasni  has  always  a  certain  j)hysi('al  construction  and  is  not  merely  a  struc- 
tureless fluid  or  semi-fluid  mass.  Most  interesting  in  this  connection  are  the 
recent  views  of  Bi'itschli/  who  believes  that  proto})lasm  is  an  aggregation  of 
fluid  vesicles  filled  with  fluid,  resembling  somewhat  the  structure  of  a  foam 
or  the  oily  vesicles  of  an  emulsion.  He  has  in  fact  constructed  an  artificial 
foam  of  oil  and  potassium  carbonate  which  not  only  gives  many  of  the  micro- 
scopic characters  of  protoplasm,  but  simulates  the  movements  and  currents 
observed  in  lower  forms  of  life. 

What  has  been  said  above  may  serve  at  least  to  indicate  the  prevalent 
physiological  belief  that  the  phenomena  shown  by  living  matter  are  in  the 
main  the  result  of  the  action  of  the  known  forms  of  energy  upon  a  substance 
of  a  complex  and  unstable  structure  which  possesses,  moreover,  a  physical 
organization  responsible  for  some  of  the  peculiarities  exhibited.  In  other 
words,  the  phenomena  of  life  are  referred  to  the  physical  and  chemical  struc- 
ture of  protoplasm  and  may  be  explained  under  the  general  physical  and 
chemical  laws  wdiich  control  the  processes  of  inanimate  nature.  Just  as  in 
the  case  of  dead  organic  or  inorganic  substances  we  attempt  to  explain  the 
differences  in  properties  between  two  substances  by  reference  to  the  difference 
in  chemical  and  physical  structure  between  the  two,  so  with  regard  to  living 
matter  the  peculiar  differences  in  properties  which  separate  them  from  dead 
matter,  or  for  that  matter  the  differences  which  distinguish  one  form  of  living 
matter  from  another,  must  eventually  depend  upon  the  nature  of  the  under- 
lying physical  and  chemical  structure. 

In  the  early  part  of  this  century  many  prominent  physiologists  were  still 
so  overwhelmed  with  the  mysteriousness  of  life  that  they  took  refuge  in  the 
hypothesis  of  a  vital  force  or  principle  of  life.  By  this  term  was  meant  a 
something  of  an  unknown  nature  Avhicli  controlled  all  the  phenomena  ex- 
hibited by  living  things.  Even  ordinary  chemical  compounds  of  a  so-called 
organic  nature  were  supposed  to  be  formed  under  the  influence  of  this  force, 
and  it  was  thought  could  not  be  produced  otherwise.  The  error  of  this  latter 
view  has  been  demonstrated  conclusively  within  recent  years  :  many  of  the 
substances  formed  by  the  processes  of  plant  and  animal  life  are  now  easily 
produced  within  the  laboratory  by  comparatively  simple  synthetic  methods. 
By  the  distinguished  labors  of  Emil  Fischer^  even  the  structure  of  carbohy- 

'  Meltzer :  "  Ueber  die  fundamentale  Bedeutung  der  Erschiitterung  fiir  die  lebende  Ma- 
terie,"  Zeitschrift  fiir  Biohf/ie,  Bd.  xxx.,  1894. 

^  Foster  :  Physiology  (Introduction).  ^  Niigeli :   Theorie  der  Gdhrung,  Miinchen,  1879. 

*  Investigations  on  Microscopic  Foams  and  on  Protoplasm,  London,  1894 ;  abstracted  in  Science, 
N.  S.,  vol.  ii.  No.  52,  1895. 

^  Die  Chemie  der  Kohlenhydrate,  Berlin,  1894. 


26  AN  AMERICAN    TEXT-BOOK    OF   PIIYSIOLOOY. 

drate  bodies  has  boon  (k'tcrmiiicd,  and  bodies  beloiifjinj^  to  this  group  have 
been  synthetically  eonstrueted  in  the  laborat(H-y.  Moreover,  the  work  of 
Schiitzenberger  and  of  (Jriniaux  gives  promise  that  before  long,  proteid  bodies 
may  be  produeed  by  similar  methods.  Physiologists  have  shown,  furthermore, 
that  the  digestion  which  takes  place  in  the  stomach  or  intestine  may  be  effected 
also  in  test-tubes,  and  at  the  present  day  probably  no  one  doubts  that  in  the 
act  of  digestion  we  have  to  deal  only  with  a  series  of  chemical  reactions  which 
iu  time  will  be  understood  as  clearly  as  it  is  possible  to  comprehend  anv  form 
of  chemical  activity.  Indeed,  the  whole  history  of  food  in  the  body  follows 
strictly  the  great  mechanical  laws  of  the  conservation  of  matter  and  of  energy 
which  prevail  outside  the  body.  No  one  disputes  the  pro])osition  that  the 
material  of  growth  and  of  excretion  comes  entirely  from  the  food.  It  has 
been  demonstrated  with  scientific  exactness  that  the  measurable  energy  given 
off  from  the  body  is  all  contained  potentially  within  the  food  that  is  eaten,^ 
and  may  be  liberated  outside  the  bodv  bv  ordinarv  combustion.  Livintr 
things,  so  far  as  can  be  determined,  can  only  transform  matter  and  energy  ; 
they  cannot  create  or  destroy  them,  and  in  this  respect  they  are  like  inanimate 
objects.  But,  in  spite  of  the  triumphs  which  have  followed  the  use  of  the 
experimental  method  in  physiology,  every  one  recognizes  that  our  knowledge 
is  as  yet  very  incomplete.  Many  important  manifestations  of  life  cannot  be 
explained  by  reference  to  any  of  the  known  facts  or  laws  of  physics  and 
chemistry,  and  in  some  cases  these  phenomena  are  seemingly  removed  from 
the  field  of  experimental  investigations.  As  long  as  there  is  this  residuum 
of  mystery  connected  with  any  of  the  processes  of  life,  it  is  but  natural  that 
there  should  be  two  points  of  view.  Most  physiologists  believe  that  as 
our  knowledge  and  skill  increase  these  mysteries  will  be  explained,  or  rather 
Avill  be  referred  to  the  same  great  final  mysteries  of  the  action  of  matter  and 
energy  under  definite  laws,  under  which  we  now  classify  the  phenomena  of 
lifeless  matter.  Others,  however,  find  the  difficulties  too  great, — they  perceive 
that  the  laws  of  physics  and  chemistry  are  not  completely  adequate  at  present 
to  explain  all  the  phenomena  of  life,  and  assume  that  they  never  will  be. 
They  suppose  that  there  is  something  iu  activity  in  living  matter  which  is 
not  present  in  dead  matter,  and  which  for  want  of  a  better  term  may  be  desig- 
nated as  vital  force  or  vital  energy.  However  this  may  be,  it  seems  evident 
that  a  doctrine  of  this  kind  stifles  inquiry.  Nothing  is  more  certain  than  the 
fact  that  the  great  advances  made  in  physiology  during  the  last  four  decades 
are  mainly  owing  to  the  abandonment  of  this  idea  of  an  unknown  vital  force 
and  the  determination  on  the  part  of  experimenters  to  push  mechanical 
explanations  to  their  farthest  limit.  There  is  no  reason  to-day  to  suppose  that 
Ave  have  exhausted  the  results  to  be  obtained  by  the  application  of  the  methods 
of  physics  and  chemistry  to  the  study  of  living  things,  and  as  a  matter  of 
fact  the  great  bidk  of  physiological  research  is  proceeding  along  these  lines.  It 
is  interesting,  however,  to  stop  for  a  moment  to  examine  briefly  some  of  the 
problems  which  as  yet  have  escaped  satisfactory  solution  by  these  methods. 
*  Rubner:  Ztitschrift  fur  Biologie,  Bd.  xxx.  S.  73,  1894. 


INTRODUGTIOX.  27 

Tlie  phenomena  of  sceri'tioii  and  aljsoiptiini  (unii  iinj)()rtaiit  parts  of"  the 
digestive  process's  in  hinlii'i"  animals,  and  wiihont  donWt  are  exhibited  in 
a  minor  degree  in  the  unic-elhdar  types.  In  the  higher  animals  the  seeretions 
may  he  eoUeeted  and  analyzed  and  their  composition  Ik;  compared  with  that  of 
the  Ivniph  or  blood  from  which  they  are  d(  rixcd.  It  has  been  i'ound  that 
secretions  may  contain  entirely  new  snbstances  not  fonnd  at  all  in  tlie  bh)od, 
as  for  example  the  mucin  of  saliva  or  the  ferments  and  liCl  of  gastric  juice; 
or,  on  the  other  hand,  that  they  may  e(»iitain  substances  which,  although  pres- 
ent in  the  blood,  are  found  in  much  greater  })ercentage  amounts  in  the  secre- 
tion— as,  for  instance,  is  the  case  with  the  urea  eliminated  in  the  urine.  In  the 
latter  case  we  have  an  instance  of  the  peculiar,  almost  purposeful,  elective 
action  of  gland-cells  of  which  many  other  examples  might  be  given.  With 
regard  to  the  new  material  present  in  the  secretions,  it  finds  a  sufficient  general 
explanation  in  the  theory  that  it  arises  from  a  metabolism  of  the  protoplasmic 
material  of  the  gland-cell.  It  offers,  therefore,  a  purely  chemical  problem, 
which  may  and  probably  will  be  worlvcd  out  satisfactorily  for  each  secretion. 
The  selective  power  of  gland-cells  for  particular  constituents  of  the  blood  is 
a  more  difficult  question.  We  find  no  exact  parallel  for  this  kind  of  action 
in  chemical  literature,  but  there  can  be  no  reasonable  doubt  that  the  phe- 
nomenon is  essentially  a  chemical  or  physical  reaction  dependent  upon  an  af- 
finity of  the  secreted  substance  for  some  material  within  the  gland-cell.  We 
may  indulge  the  hope  that  the  details  of  the  reaction  will  be  discovered  by 
more  complete  chemical  and  microscopical  study  of  the  structure  of  these  cells. 
If  in  the  meantime  the  act  of  selection  is  spoken  of  as  a  vital  phenomenon  it 
is  not  meant  thereby  that  it  is  referred  to  the  action  of  an  unknown  vital  force, 
but  only  that  it  is  a  kind  of  action  dependent  upon  the  living  structure  of  the 
cell-substance. 

The  act  of  absorption  of  digested  products  from  the  alimentary  canal  was 
for  a  time  supposed  to  be  explained  completely  by  the  laws  of  imbibition  and 
diffusion.  The  epithelial  lining  and  its  basement  membrane  form  a  septum 
dividing  the  blood  and  lymph  on  the  one  side  from  the  contents  of  the  ali- 
mentary canal  on  the  other.  Inasmuch  as  the  two  liquids  in  question  are  of 
unequal  composition  with  regard  to  certain  constituents,  a  diffusion  stream 
should  be  set  up  whereby  the  peptones,  sugar,  salts,  etc.  would  pass  from  the 
liquid  in  the  alimentary  canal,  where  they  exist  in  greater  concentration,  into 
the  blood,  where  the  concentration  is  less.  Careful  work  of  recent  years  has 
shown  that  the  laws  of  diffiision  are  not  adequate  to  explain  fully  the  ab- 
sorption that  actually  occurs  ;  a  more  detailed  account  of  the  difficulties  met 
with  may  be  found  in  the  section  on  Digestion  and  Nutrition.  It  has  become 
customary  to  speak  of  absorption  as  caused  in  part  by  the  physical  laws  of 
diffusion,  and  in  part  by  the  vital  activity  of  the  epithelial  cells.  It  will  be 
noticed  that  the  vital  property  in  this  case  is  again  a  selective  affinity  for 
certain  constituents  similar  to  that  which  has  been  referred  to  in  the  act  of 
secretion.  The  mere  fiict  that  the  old  mechanical  theory  has  proved  to  be  in- 
sufficient is  in  itself  no  reason  for  abandoning  all   hope  of  a  satisfactory  ex- 


28  AN  AMERICAN    TEXT-BOOK    OF    PHYSIOLOGY. 

j)lanation.  Most  |)liy.si()l()i!;i.sts  unquestionably  believe  that  lurther  experi- 
nientiil  work  will  bring  this  })henonienon  out  of  its  obscurity  and  show  that  it 
is  explicable  in  terms  of  known  physical  and  chemical  forces  acting  through 
the  peculiar  substance  of  the  absorptive  cell. 

The  i'acts  of  heredity  and  consciousness  offer  difficulties  of  a  much  graver 
character.  The  function  of  reproduction  is  two-sided.  lu  the  first  ])lace 
there  is  an  active  multiplication  of  cells,  beginning  with  (he  segmentation  of 
the  ovum  into  two  blastomeres  and  continuing  in  the  lai-gcr  animals  to  the 
formation  of  an  iniuunerable  multitude  of  cellular  units.  In  the  second  jilace 
there  is  ])resent  in  the  ovum  a  form-building  j)o\ver  of  such  a  character  that 
the  great  complex  of  cells  arising  from  it  form  not  a  heterogeneous  mass,  but  a 
definite  organism  of  the  same  structure,  organ  for  organ  and  tissue  for  tissue, 
as  the  parent  form.  The  ovum  of  a  starfish  develops  into  a  starfish,  the 
ovum  of  a  dog  into  a  dog,  and  the  ovum  of  man  into  a  human  being. 
Herein  lies  the  great  problem  of  heredity.  The  mere  multiplication  of  cells 
bv  direct  or  indirect  division  is  not  beyond  the  range  of  a  conceivable  me- 
chanical explanation.  Given  the  properties  of  assimilation  and  contractility  it 
is  possible  that  the  act  of  cell-division  may  be  traced  to  purely  physical  and 
chemical  causes,  and  already  cytological  work  is  opening  the  way  to  credible 
hvpotheses  of  this  character.  But  the  phenomena  of  heredity,  on  the  other 
hand,  are  too  complex  and  mysterious  to  justify  any  immediate  expectation 
that  they  can  be  explained  in  terms  of  the  known  properties  of  matter.  The 
crude  theories  of  earlier  times  have  not  stood  the  test  of  investigation  by 
modern  methods,  the  microscopic  anatomy  of  both  ovum  and  sperm  showing 
that  they  are  to  all  api)earauces  simple  cells  which  exhibit  no  visible  signs  of 
the  wonderful  potentialities  contained  within  them.  Histological  and  experi- 
mental investigation  has,  however,  cleared  away  some  of  the  difficulties  for- 
merly surrounding  the  subject,  for  it  has  shown  with  a  high  degree  of  prob- 
ability that  the  power  of  hereditary  transmission  resides  in  a  ])articular  sub- 
stance in  the  nucleus,  namely  in  the  so-called  chromatin  material  which  forms 
the  chromosomes.  The  fascinating  observations  which  have  led  to  this  con- 
clusion promise  to  open  up  a  new  field  of  experimentation  and  speculation. 
It  seems  to  l)e  possible  to  study  heredity  by  accepted  scientific  methods,  and 
we  may  therefore  hope  that  in  time  more  light  will  be  thrown  upon  the 
conditions  of  its  existence  and  possibly  upon  the  nature  of  its  activity. 

In  the  facts  of  consciousness,  lastly,  we  are  confronted  with  a  problem 
seemingly  more  difficult  than  heredity.  In  ourselves  we  recogni/e  difierent 
states  of  consciousness  following  upon  the  physiological  activity  of  certain 
parts  of  the  central  nervous  system.  We  know,  or  think  we  know,  that  these 
so-called  p.sychical  states  are  correlated  with  changes  in  the  ])rotoplasmic 
material  of  the  cortical  cells  of  the  cerebral  hemispheres.  When  these  cells 
are  stimulated,  psychical  states  result;  when  they  are  injured  or  removed, 
psychical  activitv  is  depressed  or  destroyed  altogether  according  to  the  extent 
of  the  injury.  From  the  physiological  standpoint  it  would  seem  to  be  as 
justifiable  to  assert  that  consciousness  is  a  property  of  the  cortical  nerve-cells 


INTR  OD  UCTION.  29 

as  it  is  to  define  contractility  as  a  property  of  ninscle-tissue.  But  the  short- 
ening of  a  innscle  is  a  })hysical  phenomenon  that  can  he  observed  with  tlie 
senses — be  measured  and  theoretically  explained  in  terms  of  the  known  pi-o|)- 
erties  of  matter.  Psychical  states  are,  however,  removed  from  such  methods  of 
study ;  they  are  subjective,  and  cannot  be  measured  or  weighed  or  otherwise  esti- 
mated with  sufficient  accuracy  and  completeness  in  terms  of  our  units  of  energy 
or  matter.  There  nnist  be  a  causative  connection  between  the  oiyective  changes 
in  the  brain-cells  and  the  corresponding  states  of  consciousness,  but  the  nature 
of  this  connection  remains  hidden  from  us ;  and  so  hopeless  does  tlie  problem 
seem  that  some  of  our  profonndcst  thinkers  have  not  hesitated  to  assert  that  it 
can  never  be  solved.  Whether  or  not  consciousness  is  possessed  by  all  animals 
it  is  impossible  to  say.  In  ourselves  we  know  that  it  exists,  and  we  have 
convincing  evidence,  from  their  actions,  that  it  is  possessed  by  many  of  the 
higher  animals.  But  as  we  descend  in  the  scale  of  animal  forms  the  evidence 
becomes  less  impressive.  It  is  true  that  even  the  simplest  forms  of  animal 
life  exhibit  reactions  of  an  apparently  purposeful  character  which  some  have 
explained  upon  the  simple  assumption  that  these  animals  are  endowed  with 
consciousness  or  a  psychical  power  of  some  sort.  All  such  reactions,  however, 
may  be  explained,  as  in  the  case  of  reflex  actions  from  the  spinal  cord,  upon 
purely  mechanical  principles,  as  the  necessary  response  of  a  definite  physical 
or  chemical  mechanism  to  a  definite  stimulus.  To  assume  that  in  all  cases  of 
this  kind  conscious  processes  are  involved  amounts  to  making  psychical  activity 
one  of  the  universal  and  primitive  properties  of  protoplasm  whether  animal 
or  vegetable,  and  indeed  by  the  same  kind  of  reasoning  there  would  seem  to 
be  no  logical  objection  to  extending  the  property  to  all  matter  whether  living 
or  dead.  All  such  views  are  of  course  purely  speculative.  As  a  matter  of 
fact  we  have  no  means  of  proving  or  disproving,  in  a  scientific  sense,  the  exist- 
ence of  consciousness  in  lower  forms  of  life.  To  quote  an  appropriate  remark 
of  Huxley's  made  in  discussing  this  same  point  with  reference  to  the  crayfish, 
"  Nothing  short  of  being  a  crayfish  would  give  us  positive  assurance  that  such 
an  animal  possesses  consciousness."  The  study  of  psychical  states  in  our- 
selves, for  reasons  which  have  been  suggested  abov^e,  does  not  usually  form 
a  part  of  the  science  of  physiology.  The  matter  has  been  referred  to  here 
simply  because  consciousness  is  a  fact  which  our  science  cannot  as  yet  explain. 
So  far,  some  of  the  broad  principles  of  physiology  have  been  considered — 
principles  which  are  applicable  with  more  or  less  modification  to  all  forms  of 
animal  life  and  which  make  the  basis  of  what  is  known  as  general  physiology. 
It  must  be  borne  in  mind,  however,  that  each  particular  organism  possesses 
a  special  physiology  of  its  ow-n,  which  consists  in  part  in  a  study  of  the 
properties  exhibited  by  the  particular  kinds  or  variations  of  protoplasm 
in  each  individual,  and  in  large  part  also  in  a  study  of  the  various  mechan- 
isms existing  in  each  animal.  In  the  higher  animals,  particularly,  the  com- 
binations of  various  tissues  and  organs  into  complex  mechanisms  such  as 
those  of  respiration,  circulation,  digestion,  or  vision,  differ  more  or  less  in 
each  group  and  to  a  minor  extent  in  each  individual  of  any  one  species.     It 


30  AX   AMKliJCAy    TKXT-HiJOK    OF   I'll  YSKjlJjd  \\ 

follows,  therefore,  that  each  animal  has  a  special  physiolotry  of  its  own,  and 
in  this  sense  we  may  sjx'ak  of  a  special  human  physiolotry.  It  need 
scarcely  be  said  thai  the  ^|)eeial  j)hysiol()gy  of  man  is  very  imperfectly  Unown. 
Books  like  the  present  one,  which  profess  to  treat  of  human  physioloi^v,  eon- 
tain  in  reality  a  large  amount  of  general  and  special  physiology  which  has 
been  derived  from  the  study  of  lower  animal  forms  upon  which  exact  experi- 
mentation is  possible.  Most  of  our  fundamental  knowledge  of  the  physiology 
of  the  heart  and  of  muscles  and  nerves  has  been  derived  from  experiments 
upon  frogs  and  similar  animals,  and  much  of  our  information  concerning  the 
mechanisms  of  circulation,  digestion,  etc.  has  been  obtained  from  a  study  of 
other  mammalian  forms.  We  transfer  this  knowledge  to  the  human  being,  and 
in  general  without  serious  error,  since  the  connection  between  man  and  related 
mammalia  is  as  close  on  the  ]>hysiological  as  it  is  on  the  morphological  side, 
and  the  fundamental  or  general  physiology  of  the  tissues  seems  to  be  every- 
where the  same.  Gradually,  however,  the  material  for  a  genuine  special 
human  physiology  is  being  acquired.  In  many  directions  special  investigation 
upon  man  is  possible;  for  instance,  in  the  study  of  the  localization  of  function 
in  the  cerebral  cortex,  or  the  details  of  body  metabolism  as  obtained  by  exam- 
ination of  the  excreta,  or  the  peculiarities  of  vaso-motor  regulation  as  revealed 
by  the  use  of  plethysmographic  methods,  or  the  physiological  optics  of  the 
human  eye.  This  special  information,  as  rapidly  as  it  is  obtained,  is  incorpo- 
rated into  the  text-books  of  human  physiology,  but  the  fact  remains  that  the 
greater  part  of  our  so-called  human  })hysiology  is  founded  upon  experiments 
upon  the  lower  aninals. 

Physiology  as  a  science  is  confessedly  very  imperfect ;  it  cannot  compare  in 
exactness  with  the  sciences  of  physics  and  chemistry.  This  condition  of  affairs 
need  excite  no  surprise  Avhen  we  remember  the  very  M'ide  field  ])hysiology 
attempts  to  cover,  a  field  co-ordinate  in  extent  with  the  physics  as  well  as  the 
chemistry  of  dead  matter,  and  the  enormous  complexity  and  instability  of  the 
form  of  matter  which  it  seeks  to  investigate.  The  progress  of  physiology  is 
therefore  comparatively  slow.  The  present  era  seems  to  be  one  mainly  of 
accumulation  of  reliable  data  derived  from  laborious  experiments  and  observa- 
tions. The  synthesis  of  these  facts  into  great  laws  or  generalizations  is  a  task 
for  the  future.  Corresponding  with  the  diversity  of  the  problems  to  be 
solved  we  find  that  the  methods  employed  in  physiological  research  are  mani- 
fold in  character.  Inasmuch  as  animal  organisms  are  composed  either  of 
single  cells  or  aggregates  of  cells,  it  follows  that  every  anatomical  detail  with 
regard  to  the  organization  of  the  cell  itself  or  the  connection  between  dif- 
ferent  cells,  and  every  advance  in  our  knowledge  of  the  arrangement  of  the 
tissues  and  organs  which  form  the  more  complicated  mechanisms,  is  of  imme- 
diate value  to  physiology.  The  microseo})ic  anatomy  of  the  cell  (a  braucli  of 
histology  which  is  frequently  designated  by  the  specific  name  of  cytology), 
general  histology,  and  gross  anatomical  dissection  are  therefore  frequently 
employed  in  jihysiological  investigations,  and  form  what  may  be  called  the 
observational  side  of  the  science.    On  the  other  hand  we  have  the  experimental 


INTRODUCTION.  31 

methods,  wliicli  seek  to  discover  the  |)i-(jpertios  and  functional  relationships  of 
the  tissues  and  organs  by  the  use  of  direct  experiments.  These  experiments 
may  be  of  a  surgical  character,  involving  the  extirpation  or  destruction  or 
alteration  of  known  parts  by  operations  ni)on  the  living  animal,  or  they 
may  consist  in  the  application  of  the  accepted  methods  of  j)hvsies  and 
chemistry  to  the  living  organism.  The  physical  methods  include  the  study  of 
the  physical  properties  of  living  matter  and  the  interpretation  of  its  activity 
in  terms  of  known  physical  laws,  and  also  the  use  of  various  kinds  of  physical 
ap]>aratus  such  as  manometers,  galvanometers,  etc.  for  recording  with  accuracy 
the  j)henomena  exhibited  by  living  tissues.  The  chemical  methods  implv  the 
a})plication  of  the  synthetic  and  analytic  operations  of  chemistry  to  the  study  of 
the  composition  and  structure  of  living  matter  and  the  products  of  its  activity. 
The  study  of  the  subjective  phenomena  of  conscious  life — in  fact,  the  whole 
question  of  the  psychic  aspects  or  properties  of  living  matter — for  reasons 
which  have  been  mentioned  is  not  usually  included  iu  the  science  of  physiol- 
ogy, although  strictly  speaking  it  forms  an  integral  part  of  the  subject.  This 
province  of  physiology  has,  however,  been  organized  into  a  separate  science, 
psychology,  although  the  boundary  line  between  psychology  as  it  exists  at 
present  and  the  scientific  physiology  of  the  nervous  system  cannot  always  be 
sharply  drawn. 

It  follows  clearly  enough  from  what  has  been  said  of  the  methods  used  in 
animal  physiology  that  even  an  elementary  acquaintance  with  the  subject  as  a 
science  requires  some  knowledge  of  general  histology  and  anatomy,  human  as 
well  as  comparative,  of  physics,  and  of  chemistry.  When  this  preliminary 
training  is  lacking,  physiology  cannot  be  taught  as  a  science ;  it  becomes 
simply  a  heterogeneous  mass  of  facts,  and  fails  to  accomplish  its  function  as  a 
preparation  for  the  scientific  stndy  of  medicine.  The  mere  facts  of  physiology 
are  valuable,  indeed  indispensable,  as  a  basis  for  the  study  of  the  succeeding 
branches  of  the  medical  curriculum,  but  in  addition  the  subject,  properly 
taught,  should  impart  a  scientific  discipline  and  an  acquaintance  with  the 
possible  methods  of  experimental  medicine;  for  among  the  so-called  scientific 
branches  of  medicine  physiology  is  the  most  developed  and  the  most  exact, 
and  serves  as  a  type,  so  far  as  methods  are  concerned,  to  which  the  others 
must  conform. 


II.  GENERAL   PHYSIOLOGY   OF  MUSCLE  AND 

NERVE. 


A.  Introduction. 

It  is  seldom  that  the  physical  and  chemical  structure  of  a  tissue,  as  revealed 
by  the  microscope  aud  the  most  careful  analysis,  gives  even  a  suggestion  as  to 
its  function.  No  one  would  conclude  from  looking  at  a  piece  of  beef,  or  even 
micro.'?copically  examining  a  muscle,  that  it  had  once  been  capable  of  motion, 
nor  would  the  most  exact  statement  of  its  chemical  constitution  give  indication 
of  such  a  form  of  activity.  The  most  thorough  histological  and  chemical 
examination  of  the  bundle  of  fibres  which  compose  a  nerve  would  fail  to  sug- 
gest that  a  blow  upon  one  end  of  it  would  cause  to  be  transmitted  to  the  other 
end  an  invisible  change  capable  of  exciting  to  action  the  cell  wnth  which  the 
nerve  communicated.  To  understand  such  a  structure  we  must  first  learn  the 
forms  of  activity  of  which  the  tissue  is  capable,  the  influences  which  excite 
it  to  action,  and  the  conditions  essential  to  its  activity,  and  then  seek  an  expla- 
nation of  these  facts  in  its  physical  and  chemical  structure. 

Contractility. — One  of  the  most  striking  properties  of  living  matter  is 
its  power  to  move  and  to  change  its  form.  At  times  the  movements  oocur 
apparently  spontaneously,  the  exciting  cau.se  .seeming  to  originate  within  the 
living  substance,  but  more  often  the  motions  are  developed  in  response  to  some 
external  influence.  This  power  finds  its  best  expression  in  muscle-sub.stance. 
In  its  resting  form  a  muscle,  such  as  the  biceps,  is  elongated,  and  when  it  is 
excited  to  action  it  assumes  a  more  spherical  shape,  i.  e.  shortens  and  thickens, 
whence  it  is  said  to  have  the  property  of  contractility.  It  is  the  shortening, 
the  contraction,  of  the  muscle  which  enables  it  to  perform  its  function  of 
moving  the  parts  to  which  it  is  attached,  as  the  bones  of  the  arm  or  leg,  and 
of  altering  the  size  of  the  .structures  of  which  it  forms  a  part,  as  the  walls 
of  the  heart,  intestine,  or  bladder.  Ordinary  nuiscle-substance  is  arranged 
in  fine  threads,  each  one  of  wiiich  is  enveloped  in  a  delicate  membrane,  the 
sarcolemma ;  these  muscle-fibres  can  be  compared  to  long  sausages  of  micro- 
scopic proportions.  A  muscle  is  composed  of  a  vast  number  of  fibres 
arranged  side  bv  side  in  bundles,  the  whole  beino;  firmlv  bound  tojjether  bv 
connective  tissue.  Since  i.solated  muscle-fibres  have  been  seen  under  the 
microso>ope  to  contract,  each  fibre  can  be  looked  upon  as  containing  true  muscle- 
substance  and  being  endowed  with  contractility.  The  movements  of  muscles 
are  the  resultant  of  the  combined  activity  of  the  many  microscopic  fibres  of 
which  the  muscles  are  composed. 

The  rate,  extent,  strength,  and  duration  of  muscular  contractions  are  adapted 

32 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND   NERVE. 


33 


to  the  needs  of  the  parts  to  be  influenced,  and  it  is  found  that  the  structure  of 
tlie  muscles  differs  according  to  the  work  which  they  liave  to  perform.  Thus 
we  find  two  hui^e  classes  of  muscles  :  the  one,  like  the  muscles  which  move  the 
bones,  remarkable  for  the  raj)idity  with  which  they  chan<re  their  form,  but 
unsuited  to  long-continued  action  ;  the  other,  occurring  in  the  walls  of  the 
intestine,  blood-vessels,  bladder,  etc.,  sluggish  of  movem(;nt,  but  possessing  great 
endurance.  The  first  of  these,  when  examined  with  the  microscope,  is  seen 
to  be  composed  of  bundles  of  fibres,  which  are  transversely  marked  by  alter- 
nating dark  and  light  bands,  and  hence  are  cidled  striated  or  striped  muscles  ; 
the  other,  though  com[)osed  of  fibres,  shows  no  such  cross  markings,  and 
tlierefore  is  known  as  smooth  or  non-striated  muscle.     Striated  muscles  are 


-m 


Fig.  1.— Amoeba  proteus,  magnified  200  times:  a,  endosarc;  6,  simple  pseudopodium ;  c,  ectosarc;  d, 
first  stage  in  the  growth  of  a  pseudopodium  ;  e,  pseudopodium  a  little  older  than  d ;  /,  branched  pseudo- 
podium; g,  food-vacuole ;  h,  food-ball;  i,  endoplast;  k,  contractile  vesicle  (after  Brooks:  Handbook  of 
Invertebrate  Zoology). 


often  called  voluntary,  because  most  of  them  can  be  excited  to  action  by  the 
will,  whereas  non-striated  muscles  are  termed  involuntary,  because  in  most 
cases  they  cannot  be  so  controlled.  Within  these  two  large  classes  of  muscles 
we  find  special  forms  presenting  other,  though  lesser,  differences  in  function 
and  structure.  The  muscle  of  the  heart,  though  striated,  differs  so  much  from 
other  forms  of  striped  muscle  as  almost  to  belong  in  a  special  class. 
3 


34 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


Since  contractility  is  possessed  hyall  forms  of  muscle-tissue,  it  is  evident  that 
it  is  independent  of  superficial  structural  differences.  Nor  is  muscle  the  only 
substance  possessing  this  property.  Even  isolated  microscopic  particles  of  liv- 
ing matter  are  capable  of  making  movements,  both  spontaneously  and  ^vhen 
excite<l  by  external  influences.  As  far  back  as  1755,  Kosel  von  Rosenhof 
described  the  apparently  spontaneous  changes  in  form  of  a  living  organism 
composed  of  a  single  cell,  a  fresh-water  ama'ba.  Moreover,  he  noted  that,  if 
quiet,  it  could  be  excited  to  action  by  mechanical  shocks. 

The  amoeba  (Fig.  1)  is  a  little  animal,  of  microscopic  size,  which  is  found 
in  the  ooze  at  the  bottom  of  pools,  or  in  the  slime  'which  dings  to  some  of  our 
fresh-water  plants.  Under  the  microscope  it  is  seen  to  be  composed  of  jelly- 
like, almost  transparent  matter,  in  which  are  a  vast  number  of  fine  granules,  a 
delicate  tracery  of  finest  fibrils,  a  small  round  body,  called  the  nucleus  or 
endoplast,  a  round  hollow  space  termed  the  contractile  vesicle,  which  is  seen  to 
change  in  size,  appearing  or  disappearing  from  time  to  time,  and  small  parti- 
cles, which  are  bits  of  food  or  foreign  bodies.  In  the  resting  state  the  body 
has  a  somewhat  flattened,  irregular  form,  which,  if  the  slide  on  which  it  rests  l^e 
kept  warm,  is  found  to  alter  from  minute  to  minute.  Little  tongue-like  projec- 
tions, pseudopods  (false  feet),  are  protruded  from  the  surface  like  feelers,  and 
are  then  withdrawn,  while  others  appear  in  new  places.  Evidently  the  little 
creature,  though  composed  of  a  single  cell,  is  endowed  with  life  and  has  the 
power  of  making  movements.     Moreover,  it  may  be  seen  to  change  its  place, 

the  method  of  locomotion  being  a  j)eculiar 
one.  One  of  the  processes,  or  pseudopods, 
may  be  extended  a  considerable  distance,  and 
then,  instead  of  being  withdrawn,  grow  in  size, 
while  the  body  of  the  animal  becomes  corre- 
spondingly smaller ;  thus  a  transfer  of  material 
takes  place,  and  this  continues  until  the  whole 
of  the  material  of  the  cell  has  flowed  over  to 
the  new  place.  This  power  of  movement  }>er- 
mits  the  animal  to  eat.  If  when  moving  over 
the  slide  it  encounters  suitable  food  material,  a 
diatom  for  instance,  it  flows  round  it,  engulf- 
ing it  in  its  semifluid  mass ;  and  in  a  similar 
manner  the  animal  gets  rid  of  the  useless  sub- 
stances which  it  may  have  surrounded,  by  flow- 
ing away  from  them.  These  movements  may 
result  from  changes  which  haveocrurred  within 
itsown  substance,and  apparently  independently 
of  any  external  influence.  On  the  other  hand, 
if  its  body  be  disturbed  by  being  touched,  by 
an  unusual  temperature,  by  certain  chemicals, 
or  by  an  electric  shock,  it  replies  by  drawing  in  all  of  its  pseudopods  and 
assuming  a  contracted,  ball  form. 


Fig.  2.— Vorticella  nebulifera,  X  600: 
a,  cilia  of  ciliated  disk;  6,  ciliated  disk; 
c,  peristome  ;  d,  vestibule  ;  e,  oesophagus ; 
/,  contractile  vesicle ;  g,  food-vacuoles ; 
h,  endoplast ;  r,  endosarc ;  Jfc,  ectosarc :  I, 
cuticle:  m,  axis  of  stem  (after  Brooks: 
Handbook  of  Invertebrate  Zoology). 


GENERAL    PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       35 

The  movements  of  the  leucocytes  of  the  blood  resemble  in  many  respects 
those  of  the  amoeba.' 

The  property  of  contractility  i.s  possessed  by  a  vast  variety  of  unicellular 
structures  in  lower  forms  of  auin)al  life.  Another  example  is  the  Vorticella 
(Fig.  2). 

The  vorticella,  like  the  amoeba,  is  a  little  animal  which,  although  consisting 
of  a  single  cell,  possesses  within  its  microscopic  form  all  the  phy.-iological  prop- 
erties essential  to  life  and  the  perpetuation  of  its  species.  It  consists  of  a  bell, 
with  ciliated  margin,  borne  upon  a  contractile  stalk.  If  touched  with  a 
hair,  or  jarred,  the  cell  rapidly  contracts ;  the  edge  of  the  Ix'll  is  drawn  in  so 
as  to  make  the  body  nearly  spherical,  and  the  stalk  is  thrown  into  a  spiral 
and  drags  the  body  back  toward  the  ])oint  of  attachment.  The  contraction  is 
rapid;  the  relaxation,  which  comes  when  the  irritation  ceases,  is  gradual.  An 
interesting  account  of  the  movements  of  Vorticella  gracilis  is  given  by  Hodge 
and  Aikins^  under  the  title  of  ''  The  Daily  Life  of  a  Protozoan." 

Other  examples  of  contractile  power  possessed  by  apparently  simple  organ- 
isms are  to  be  found  in  the  tentacles  of  Actiniae,  the  surface  sarcode  of  sponges, 
the  chromatoblasts  of  Pleuronectidse,^  which  are  controlled  by  nerves  and 
under  the  influence  of  light  and  darkness  change  their  size  and  so  alter  the 
color  of  the  skin,  and  the  vast  variety  of  ciliated  forms,  including  spermatozoa, 
and  some  of  the  cells  of  raucous  membranes.* 

Irritability. — We  have  thus  far  referred  to  but  one  of  the  vital  properties 
of  protoplasm,  viz.  contractility.  Another  property  intimately  associated  with 
it  is  irritability.  Irritability  is  the  property  of  living  protoplasm  which  causes 
it  to  undergo  characteristic  chemical  and  physical  changes  when  subjected  to 
certain  external  influences  called  irritants.  Muscle  protoplasm  is  very  irri- 
table, and  is  easily  excited  to  contraction  by  such  irritants  as  electric  shocks, 
mechanical  blows,  etc.  The  muscles  which  move  the  bones  rarely,  if  ever,  in 
a  normal  condition,  exhibit  spontaneous  alterations  in  form,  and  cannot  be  said 
to  possess  automatic  power.  By  automatism  is  meant  that  property  of  cell- 
protoplasm  which  enables  it  to  become  active  as  a  result  of  changes  which 
originate  within  itself,  and  independently  of  any  external  irritant.  Examples 
of  this  power  may  perhaps  be  found  in  the  movements  of  ciliated  organisms 
and  the  infusoria.  Possibly  the  rhythmic  movements  of  heart  muscle  are  of 
this  nature.  Still  another  property  of  protoplasm,  closely  allied  to  contractility 
and  irritability,  and  possessed  by  muscle-substance,  is  conductivity. 

Conductivity  is  the  property  which  enables  a  substance,  when  excited  in 
one  part,  to  transmit  the  condition  of  activity  throughout  the  irritable  mate- 
rial. For  example,  an  external  influence  capable  of  exciting  an  irritable 
muscle-fibre  to  contraction,  although  it  may  directly  affect  only  a  small  part  of 

1  An  excellent  description  of  these  movements,  accompanied  by  illustrations,  is  given  in 
Quain's  Anatomy,  vol.  i.,  pt.  2,  pp.  174-179. 

^  Hodge  and  Aikins:  American  Journal  of  Psychology,  1895,  vol.  vi.,  No.  4,  p.  524. 

'  Krukenberg :    Vergleichend-physiologische  Vortrdge,  1886,  Bd.  i.  p.  274. 

*  A  careful  study  of  the  different  forms  of  movement  exhibited  by  simple  organisms  has 
been  made  by  Engelmann:  Hermann's  Handbuch  der  Physiologie,  1879,  Bd.  i.,  Th.  1,  p.  344. 


36  ^^V  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

the  fibre,  may  iiKlireotly  influence  tlie  whole,  because  the  condition  of  activity 
which  it  excites  at  the  point  of"  a})itlication  is  transmitted  by  the  muscle-sub- 
stijnce  throiitjjhout  the  extent  of  the  fibre. 

Irritability  and  conductivity  are  not  confined  to  contractile  mechan- 
ism. They  are  possessed  to  a  still  higher  degree  by  nervous  tissues,  whidi  are 
not  found  to  have  the  power  of  movement.  The  nervous  system  is  composed 
of  nerve-cells  and  nerve-fibres.  The  nerve-cells  are  locatetl  chiefly  within  tlie 
brain  and  spinal  cord,  a  smaller  number  being  found  in  the  spinal  ganglia 
and  at  special  points  along  the  course  of  certain  nerve-fibres.  The  active  part 
of  the  nerve-fibre  is  the  axis-cylinder,  which  is  an  outgntwth  from  a  nerve-ct.ll, 
and  \\  hich  outside  of  the  central  nervous  system  acquires  a  delicate  membran- 
ous sheath,  the  neurilemma,  which  invests  it  as  the  sareolemma  does  the  muscle- 
fibre.  There  are  two  classes  of  nerve-fil)res,  medullated  and  non-meduUated, 
which  are  distinguished  by  the  fact  that  the  former  has  between  the  axis- 
cvlinder  and  the  neurilemma  another  covering  composed  of  fatty  material, 
called  the  medullary  sheath,  while  iu  the  latter  this  is  absent.  Just  as 
it  is  the  special  function  of  the  muscle-fibre  to  change  its  form  when  it 
is  excited,  so  it  is  the  special  function  of  the  nerve-fibre  to  transmit  the 
condition  of  activity  excitetl  at  one  end  throughout  its  length,  and  to 
awaken  to  action  the  cell  with  which  it  conmiuuicate.*.  Xerve-fibres  are 
the  paths  of  communication  between  nerve-cells  in  the  central  nervous  sys- 
tem, between  sense-organs  at  the  surface  of  the  body  and  the  nerve-cells, 
and  between  the  nerve-cells  and  the  muscle-  and  gland-cells.  Nerve- 
fibres  are  distinguished  as  afferent  and  efferent,  or  centripetal  and  centrifugal, 
according  as  they  carry  impulses  from  the  surface  of  the  body  inward  or  from 
the  central  nervous  system  outward.  Further,  they  receive  names  according 
to  the  character  of  the  activity  which  they  excite :  those  which  excite  muscle- 
fibres  to  contract  are  called  motor  nerves;  those  distributed  to  the  muscles 
in  the  walls  of  blood-vessels,  vaso-motor ;  those  which  stimulate  gland-cells  to 
action,  secretory ;  those  which  influence  certain  nerve-cells  in  the  brain  and  so 
cause  sensations,  sensory.  Still  other  names  are  given,  as  "trophic"  to  fibres 
which  are  supposed  to  have  a  nutritive  function,  and  "inhibitory"  to  those 
which  check  the  activities  of  various  organs.  The  method  of  conduction  is  the 
same  in  all  these  cases,  the  result  depending  wholly  on  the  organ  stimulated. 

Nerve-fibres  do  not  run  for  any  distance  separately,  but  always  in  company 
with  others.  Thus  large  nerve-trunks  may  be  fi»rme<l,  as  in  the  case  of  the 
nerves  to  the  limbs,  in  which  afferent  and  efferent  fibres  run  side  by  side,  the 
whole  being  bound  together  into  a  com]iact  bundle  by  connective  tissue.  The 
separate  fibres,  though  thus  grouped  together,  are  anatomically  and  physiologi- 
cally as  distinct  as  the  wires  of  an  ocean  cable ;  that  these  many  strands  are 
bound  together  is  of  anatomical  interest,  Init  has  little  physiological  significance. 

The  active  substance  of  the  nerve-fibre  does  not  show  contractility,  but  this 
does  not  prevent  it  from  being  classed  with  other  irritable  forms  of  living  cell- 
substance  as  protoplasm.  In  spite  of  differences  in  structure  and  composition, 
nerve  protoplasm  and  muscle  protoplasm  are  found  to  have  many  j)oiuts  of 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.        37 

resemblance.  An  explanation  of  the  physiological  resemblances  nuiy  be  found 
in  their  common  ancestry.  All  the  cells  of  the  many  structures  of  the  nniiiial 
body  are  descended  from  the  two  parent  cells  from  which  (he  animal  is  developed. 
The  fertilized  ovum  divides,  and  two  eells  are  formed,  tiiese  new  cells  divide, 
and  so  the  process  continues,  the  developing  cells  through  unknown  causes  be- 
coming ai'ranged  to  form  more  or  less  definite  layers  and  groups,  which  bv  means 
of  foldings  and  nnequal  growths  develop  into  the  various  structures  and  organs 
of  the  fetus.  At  the  same  time  that  the  division  is  going  on,  the  total  amount 
of  material  is  increasing.  Each  of  the  cells  absorbs  and  assimilates  dead  food- 
material,  and  this  dead  material  is  built  into  living  substance.  During  this 
process  of  development  and  growth  the  cells  of  special  tissues  and  organs 
acquire  special  anatomical  and  chemical  characters.  This  development  of 
specialized  cells  is  termed  cell-differentiation.  Hand  in  hand  with  the  ana- 
tomical and  chemical  differentiation  goes  a  physiological  differentiation.  The 
protoplasm  of  each  type  of  cell,  while  retaining  the  general  characteristics  of 
])rotoplasm,  has  certain  physiological  properties  developed  to  a  marked  degree 
and  other  properties  but  little  developed,  or  altogether  lacking.  The  fertilized 
ovum  does  not  have  all  the  anatomical  and  chemical  characteristics  of  all  the 
cells  which  are  descended  from  it,  not  at  least  in  just  the  form  in  which  they 
are  possessed  by  these  cells,  and  it  cannot  be  assumed  that  its  living  sub- 
stance possesses  all  the  physiological  properties  which  are  owned  by  its 
descendants.  Many  of  these  properties  it  must  have,  for  many  of  them  are 
essential  to  the  continuance  of  life  of  all  active  cells, — such  as  the  power  to  take 
in,  alter,  and  utilize  materials  which  are  suitable  for  the  building  up  and  repair 
of  the  cell-substance,  the  power  of  chemically  changing  materials  possessing 
potential  energy  so  that  the  form  of  actual  energy  which  is  essential  to  the  per- 
formance of  the  work  of  the  cell  shall  be  liberated,  and  the  power  to  give 
oflT  the  waste  materials  which  result  from  chemical  changes.  The  proto])lasm 
of  the  ovum,  to  have  these  powers,  has  properties  closely  allied  to  absorption, 
digestion,  assimilation,  respiration,  excretion  ;  and,  in  consideration  of  the  special 
function  of  the  ovum,  we  may  add  that  it  possesses  the  property  of  reproduc- 
tion. The  question  of  its  possessing  the  chai'acteristic  properties  of  muscle  and 
nerve  protoplasm  cannot  be  answered  off-hand.  Careful  study,  however,  has 
shown  the  ovum  of  Hydra  to  possess  irritability,  conductivity,  and  contractility. 
It  undergoes  amoeboid  movements,  as  was  first  shown  by  Kleinenberg. 
Balfour,^  in  writing  of  the  development  of  the  ova  of  Tubularidae,  which  is 
of  a  type  similar  to  Hydra,  says :  "  The  mode  of  mitrition  of  the  ovum  may 
be  very  instructively  studied  in  this  type.  The  process  is  one  of  actual  feed- 
ing, much  as  an  amoeba  might  feed  on  other  organisms."  Something  similar 
seems  to  be  true  of  the  ova  of  echinodermata.  During  impregnation  various 
movements  are  described  implying  the  properties  of  irritability,  conductivity, 
and  contractility.  Thus  in  the  case  o?  Astenai^  glacialis,  when  the  head  of  the 
spermatozoon  comes  in  contact  with  the  mucilaginous  covering  of  the  ovum,  "a 
prominence  pointing  toward  the  nearest  spermatozoon  now  rises  from  the  super- 
*  Comparative  Embryology,  pp.  17,  29. 


38  AN  AMERICAN   TEXT-BOOK    OF   PIIYSrOLOGY. 

ficial  layer  of  protoplasm  of"  the  egg  and  grows  until  it  conies  in  contact  with 
the  nearest  sperniatozuon."  "At  the  moment  of  contact  iH'twcen  the  sperma- 
tozoon and  the  egg,  the  outermost  layer  of  protoplasm  of  the  latter  raises  itself 
up  as  a  distinct  membrane,  which  separates  from  the  egg  and  prevents  the 
entrance  of  other  spermatozoa."  Some  of  the  eggs  of  arthroj)ods  and  other 
forms  have  likewise  been  observed  to  undergo  amoebcjid  movements  as  a  result 
of  the  physiological  stimulus  given  by  the  spermatozoon.* 

Although  irritability  and  contractility  of  the  ovum  have  thus  far  been  made 
out  in  but  few  forms,  it  is  probable  that  they  play  an  important  part  in  all 
during  fertilization  and  division.  It  would  seem,  then,  that  the  ovum  has  all 
the  principal  properties  which  we  ascribe  to  cell-j)rotoplasm,  and  that  these 
properties  are  inherited  more  or  less  completely  developed  by  the  many  forms 
of  cells  descended  from  it.  The  protoplasm  of  specialized  cells,  in  spite  of 
their  differences  in  structure,  still  retains  its  protoplasmic  nature.  Undoubtedly 
structural  peculiarities  are  intimately  related  to  specialized  functions, — the 
striped  muscle,  for  example,  is  especially  adapted  for  rapid  movements,  and 
the  nerve-fibre  is  remarkable  for  its  power  of  conduction. 

Physiological  methods  for  the  examination  of  individual  cells  are  as  yet  in 
their  infancy,  and  we  must,  for  the  most  part,  be  content  to  study  the  func- 
tional activity  of  cells  by  observing  the  combined  action  of  many  cells  of  the 
same  kind. 

B.    Irritability  of  Muscle  and  Nerve. 

Irritability  is  the  property  of  living  protoplasm  which  causes  it  to  undergo 
characteristic  physical  and  chemical  changes  when  it  is  subjected  to  certain 
influences,  called  irritants,  or  stimuli.  By  an  irritant  is  meant  an  external  influ- 
ence which,  when  applied  to  living  protoplasm,  as  of  a  nerve  or  muscle,  excites 
it  to  action.  Irritants  may  be  roughly  classed  as  mechanical,  chemical,  thermal, 
and  electrical.  The  normal  physiological  stimulus  is  developed  within  some 
of  the  nervous  mechanisms  of  the  body  as  the  result  of  the  activity  of  the 
nerve-protoplasm,  this  having  been  excited  as  a  rule  by  some  form  of  irritant. 
The  degree  of  irritiibility  of  a  given  form  of  protoplasm  is  measured  by  the 
amount  of  activity  which  it  displays  in  response  to  a  definite  irritant,  or  by  the 
minimal  amount  of  irritation  required  to  excite  it  to  action.  If  the  irritant  be 
applied  directly  to  a  muscle,  the  height  to  which  the  muscle  contracts  and  raises 
a  given  weight  may  be  taken  as  an  indication  of  its  activity.  As  the  nerve 
gives  no  visible  evidence  of  activity,  the  effect  of  the  irritant  upon  it  is  usually 
estimated  by  the  extent  to  which  the  organ  stimulate<l  by  the  nerve  reacts  ;  in 
the  case  of  motor  nerves,  the  strength  of  the  contraction  of  the  corresponding 
muscle  is  taken  as  an  index. 

To  determine  the  exact  relation  of  an  ii-ritant  to  its  irritating  effect  we  should 
be  able  to  accurately  measure  them.  This  we  cannot  do.  We  are  unable  to 
state  in  irritation-units  the  relative  value  of  different  kinds  of  irritanti>.     Even 

»  Korschelt:  Zoologischer  Jahrhuch,  1891,  Anat.  Abtheil.,  Bd.  iv.,  Heft  1,  p.  1.  Hertwig: 
Morphologische  Jahrhuch,  1876,  Bd.  1.     Herbst:  Biologische  Centralblatt,  1891,  xiii.  p.  22. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.        39 

if  we  could  accurately  estimate  the  aniouiit  of  energy  wliicii  eaeli  form  of  irri- 
tant can  expend  in  iritation,  we  should  have  oidy  one  of  the  many  factors 
which  determine  its  etiiciency.  It  is  e(iually  dillicudt  to  compare  the  irritating 
eifect  of  irritants  upon  different  forms  of  protoplasm ;  e.  g.  we  cannot  state 
what  degree  of  activity  of  a  nerve-fibre  corresponds  to  a  certain  amount  <jf 
activity  in  a  muscle-fibre.  In  spite  of  the  lack  of  exact  quantitative  measure- 
ments, we  have  gained  a  clear  idea  of  the  way  different  forms  of  irritants 
act  when  applied  to  nerves  and  muscles  in  certain  ways,  and  have  learned  to 
control  the  methods  of  excitation  sufficiently  to  permit  the  influences  which 
alter  the  irritability  of  nerves  and  muscles  to  show  themselves.  The  effect  of 
irritants  can  best  be  studied  upon  the  nerves  and  muscles  of  cold-blooded  ani- 
mals, because  these  retain  their  vitality  and  irritiibility  for  a  considerable  time 
after  they  have  been  separated  from  the  rest  of  the  body.  It  is  a  common 
observation  of  country  folk  that  the  body  of  a  snake  remains  alive  for  a  long 
time  after  the  head  has  been  crushed,  while  the  body  of  a  chicken  loses  all  signs 
of  life  in  a  comparatively  short  time  after  it  has  been  decapitated.  More  care- 
ful examination  would  show  that  in  neither  case  do  all  parts  of  the  body  die 
simultaneously.  Each  of  the  myriad  cells  has  a  life  of  its  own,  which  it 
loses  sooner  or  later  according  to  its  nature  and  to  the  alterations  to  which  it 
is  subjected  by  the  fatal  change.  The  cells  of  cold-blooded  animals,  as  the 
snake  and  frog,  are  much  more  resistant  than  those  of  warm-blooded  animals, 
because  the  vital  processes  within  the  cells  are  less  active,  and  the  chemical 
changes  which  precede  and  lead  to  the  death  of  the  part  occur  more  slowly. 
For  instance,  the  nerves  and  muscles  of  a  frog  remain  irritable  for  many  hours, 
or  even  days,  after  the  animal  has  been  killed  and  they  have  been  removed 
from  the  body.  This  fact  is  of  the  greatest  use  to  the  student.  It  enables  him 
to  study  the  nerve  or  muscle  by  itself,  and  under  such  artificial  conditions  as 
he  cares  to  employ.  Experience  shows  that  the  facts  learned  from  the  study  of 
the  isolated  nerve  and  muscle  hold  good,  with  but  slight  modification,  for  the 
nerves  and  muscles  when  in  the  normal  body.  Moreover,  it  has  been  found 
that  the  nerves  and  muscles  of  warm-blooded  animals,  and  even  man,  resemble 
physiologically  as  well  as  anatomically  those  of  the  frog.  The  correspondence 
is  by  no  means  complete,  but  it  is  so  great  as  to  make  the  facts  discovered  by 
a  study  of  the  nerves  and  muscles  of  the  frog  of  the  utmost  importance  to  us. 
We  are  driven  to  such  sources  of  information  because  of  the  great  difficulty  of 
keeping  the  muscles  of  warm-blooded  animals  alive  and  in  a  normal  condition 
after  removal  from  the  circulation. 

Irritability  of  Nerves. — The  following  preparation  suffices  to  illustrate 
the  more  striking  effects  of  irritants  upon  a  nerve.  A  frog  is  rapidly  killed, 
and  then  the  sciatic  nerve  is  cut  high  up  in  the  thigh  and  dissected  out  from 
its  groove,  the  branches  going  to  the  thigh-muscles  being  divided.  The  leg  is 
then  cut  through  just  above  the  knee.  This  gives  a  preparation  consisting  of 
the  uninjured  lower  leg  and  foot,  and  the  carefully  prepared  nerve  supplying 
the  muscles  of  these  parts.  The  leg  may  be  placed  foot  upward,  and  fastened 
in  this  position  by  a  clamp  which  grasps  the  bones  at  the  knee,  the  clamp 


40  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOOY. 

being  supported  by  an  upright  (see  Fig.  3).     This  preparation  can  i\\v\\  be 

subjected  to  a  variety  of"  tests, 

Mechanioal  Irritation. — If  the  nerve  be  cut,  pinched,  suddenly  stretched,  or 

subjected  to  a  blow,  the  muscles  of  the  leg  will 
contract  and  the  foot  will  be  quickly  moved. 

Chemical  IiTitation. — If  acid,  alkalies,  vari- 
ous salfc^,  glycerin,  or  some  other  chenncal  sub- 
stances be  placed  upon  the  nerve,  the  muscles 
of  the  leg  begin  to  twitch  irregularly,  and  as 
the  chemical  enters  more  and  more  deeply  into 
the  nerve  the  movements  will  become  more 
and  more  marked,  until  finally  all  the  muscles 
are  actively  contracted  and  the  foot  is  held 
straight  up. 

Fig.  3.-Experiment  for  determining  Thermal   Irritation.— l^  a  hot  iron,  or  the 

the  irritability  of  nerves. 

flame  of  a  match,  be  applied  to  the  nerve,  a 
condition  of  activity  will  be  developed  in  the  rapidly  heated  nerve-fibres,  and 
be  responded  to  by  more  or  less  vigorous  muscular  contractions. 

Electrical  Irritation. — If  the  wires  connected  with  the  two  poles  of  a 
galvanic  cell,  static  machine,  or  induction  apparatus  be  brought  in  contact 
with  the  nerve,  the  muscles  will  twitch  each  time  there  is  a  sudden  change  in 
potential. 

]VIore  exact  statements  with  reference  to  these  different  forms  of  irritation 
will  be  given  later.  By  all  these  methods  the  nerve  was  excited  by  irritants 
applied  to  it  from  without,  and  the  muscle  was  excited  to  action  by  the  physio- 
logical stimulus  coming  to  it  from  the  excited  nerve.  The  irritant  produced 
no  visible  change  in  the  nerve,  but  the  movement  of  the  muscles  was  an  evi- 
dence that  the  nerve  had  undergone  a  change  at  the  point  of  stimulation,  and 
that  the  active  state  thus  induced  had  been  transmitted  through  the  length  of 
the  nerve,  and  had  been  .suflficiently  marked  to  stinuilate  the  muscle  to  contrac- 
tion. This  condition  of  activity  which  was  transmitted  along  the  nerve  is  called 
the  nerve-impulse. 

Independent  Irritability  of  Muscle. — In  the  above  instances  the  irritants 
were  applied  to  the  nerve,  and  the  muscle  was  indirectly  stimulated.  Muscle 
protoplasm,  like  nerve  protoplasm,  may  be  directly  excited  to  action  by  various 
forms  of  irritants.  A'  nerve  after  entering  a  muscle  branches  freely,  and  the 
nerve-fibres  are  distributed  quite  generally  through  the  muscle.  An  irritant, 
if  directly  applied  to  muscle,  would  probably  excite  the  nerve-fibres  present  as 
well  as  the  muscle-fibres,  and  to  obtain  proof  of  independent  irritability  of 
muscle-substance  it  would  be  neces.sarv  to  prevent  the  nerves  from  stimulating 
the  muscle.     This  can  be  done  by  paralyzing  the  nerve-endings  with  curare. 

Curare,  the  South  American  arrow-poison,  is  used  by  the  Indians  in  hunt- 
ing. The  bird  shot  by  these  poisoned  arrows  gradually  becomes  paralyzed, 
and,  losing  power  to  move  its  muscles,  is  easily  captured.  The  following 
experiment  reveals  the  method  of  the  action  of  this  drug,  and  at  the  same 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.        41 

time  shows,  first,  that  the  nuiscle  prutophisin  can  be  irritated  directly,  and 
secondly,  tiiat  the  nerves  do  not  eonimuuicate  directly  with  the  muscles,  but 
stimulate  them  through  the  agency  of  terminal  end-organs,  called  moUn-  end- 
plaics} 

Curare  Experiment. — Rapidly  destroy  the  brain  of  a  frog  with  a  slightly 
curved,  blunt  needle,  and,  to  prevent  hemorrhage,  plug  the  wound  by  thrust- 
ing a  pointed  match  through  the  foramen  magnum  into  the  brain-cavitv. 
Expose  the  sciatic  nerve  of  the  left  thigh,  carefully  j)ass  a  ligature  under  it,  and 
tie  the  ligature  tightly  about  all  the  tissues  of  the  thigh  excepting  the  nerve, 
thus  cutting  off  the  circulation  from  all  the  leg  below  the  ligature  without  in- 
jury to  the  nerve.  Inject  into  the  dorsal  lymph-sac  or  tlie  abdominal  cavity  a 
few  drops  of  a  2  per  cent,  solution  of  curare.  In  from  twenty  to  forty  minutes 
the  drug  will  have  reached  the  general  circulation  and  produced  its  effect. 

Although  the  brain  has  been  destroyed  and  the  frog  is  incapable  of  having 
sensation,  it  will  be  found  that  muscular  moveraeuts  will  be  made  if  the  skin 
be  pinched  soon  after  the  drug  has  been  given.  These  are  reflex  movements, 
and  are  due  to  excitation  of  the  spinal  cord  by  the  nerves  connected  with  the 
skin.  As  the  paralyzing  action  of  the  drug  progresses,  these  reflex  actions  be- 
come feebler  and  feebler  until  altogether  lost  in  the  parts  exposed  to  the  drug, 
although  they  may  still  be  shown  by  the  parts  from  which  the  drug  has  been 
excluded.  The  condition  of  the  nerves  and  muscles  can  be  examined  as  soon 
as  reflex  movements  of  the  poisoned  parts  cease. 

To  ascertain  the  action  of  the  poison,  expose  the  nerves  of  the  two  legs, 
either  high  up  in  the  thigh  or  inside  the  abdominal  cavity,  where  they  have 
been  subjected  to  the  poison,  and  test  their  irritability  by  exciting  them  with 
electric  shocks.  Stimulation  of  the  motor  nerve  of  the  right  leg  (a,  Fig.  4) 
causes  no  contraction  of  the  muscles  of  that  leg,  while  stimulation  of  the  motor 
nerve  of  the  left  leg  (6),  results  in  active  movements  of  the  muscles  of  that 
leg.  The  response  of  the  left  leg  shows  that  nerve-trunks  are  not  injured  by 
the  poison,  and  that  the  paralysis  of  the  right  leg  must  find  some  other  expla- 
nation. On  testing  the  muscles  it  is  found  that  they  are  irritable  and  contract 
when  directly  stimulated.  Since  neither  nerve-trunks  nor  muscles  are  poisoned, 
it  is  necessary  to  assume  that  the  cause  of  the  paralysis  is  something  which  pre- 
vents the  nerve-impulse  from  passing  from  the  nerve  to  the  muscle.  Micro- 
scopic examination  shows  that  the  nerve-fibre  does  not  communicate  directly 
with  the  muscle-fibre,  but  ends  inside  the  sarcolemma  in  an  organ  which  is 
called  the  motor  end-plate.  It  appears  that  the  nerve  acts  on  the  muscle 
through  this  organ,  and  its  failure  to  act  on  the  side  which  was  exposed  to  the 
curare  was  because  the  end-plate  had  been  paralyzed  by  the  drug.  By  the 
use  of  curare,  therefore,  we  are  enabled  to  prevent  the  nerve-impulse  from 
reaching  the  muscles,  and,  when  we  have  done  this,  we  find  that  the  muscle 
is  still  able  to  respond  to  direct  excitation  wnth  all  forms  of  irritants,  viz. 

^  Ch.  Bernard  :  "Analyse  physiologique  des  Propri^t^s  des  Systemes  mnsculaires  et  nerveux 
au  moyen- du  Curare,"  Comptes-rendus,  1856,  p.  825.  KoUiker:  "  Physiologische  Untersuch- 
ungen  iiber  den  Wirkungen  einiger  Gifte,"  Arckiv  fur  pathologische  Anatomie,  1856. 


42 


AN  AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 


electrical,  mechanical,  thermal,  and  chemical.  Evidently  the  muscle- proto- 
plasm is  irritable  and  is  caj)able  of  developing  a  contraction  independently  of 
the  nerves. 

Other  Proofs  that  the  Muscle-protoplasm  can  be  Directly  Irritated. 
— Muscles  with  long  [)arallel  fibres,  such  as  the  sartorius  of  the  fi'og,  contain  no 
nerves  at  tiieir  extremities,  the  nerve-fibres  joining  the 
nuiscle-fibres  at  some  little  distance  from  their  ends. 
The  tip  of  such  a  muscle,  where  no  nerve-fibres  can 
be  discovered  by  the  most  careful  microscopical  exam- 
ination, is  found  to  be  irritable.  The  fact  that  in  some 
of  the  lower  animals  there  are  simple  forms  of  contrac- 
tile tissue  in  which  nerves  cannot  be  discovered,  and 
which  are  irritable,  is  interesting  as  corroborative  evi- 
dence, although  it  is  not  a  proof,  of  the  independent 
irritability  of  a  highly  diffi?rentiated  tissue  such  as 
striated  muscle.  Another  similar  piece  of  evidence  is 
to  be  found  in  the  fact  that  the  heart  of  the  embryo 
beats  rhythmically  before  nerve  appears  to  have  been 
developed.  A  proof  can  be  found  in  the  observation 
that  if  a  nerve  be  cut  it  begins  to  undergo  degenera- 
tion and  loses  its  irritability  and  conductivity  in  four 
or  five  days,  and  the  excitation  of  such  a  nerve  has 
no  effect  upon  the  muscle  although  direct  stimulation 
of  the  muscle  itself  is  followed  by  contraction.  As 
degeneration  involves  not  only  the  whole  course  of  the 
nerve,  but  also  the  nerve  end-plates,  the  contraction 
must  be  attributed  to  the  irritability  of  the  muscle- 
substance.  Another  point  of  interest  in  this  connection 
is  the  behavior  of  a  dying  muscle.  If  it  be  struck, 
instead  of  contracting  as  a  whole  it  contracts  at  the 
place  where  it  was  irritated,  the  drawing  together  of 
the  fibres  at  the  part  forming  a  local  swelling,  or  welt. 
If  such  a  muscle  be  stroked,  a  wave  of  contraction  spreads  over  it,  following 
the  instrument,  instead  of  extending,  as  under  normal  conditions,  by  means  of 
the  excited  nerve-fibres  to  other  parts.  Under  these  circumstances  the  circum- 
scribed contraction  would  seem  to  show  that  the  nerves  had  lost  their  irrita- 
bility, or  that  the  nerve-ends  no  longer  transmitted  the  stimulus  to  the  muscle, 
and  the  response  was  due  to  the  direct  excitation  of  the  dying  muscle-fibres. 
This  phenomenon  is  known  as  an  idiomuscular  contraction. 


Fig.  4.— Curare  experiment : 
the  shaded  parts  show  the  re- 
gion of  the  body  to  which  the 
drug  had  access;  theunshaded 
part,  the  portion  which  was 
protected  by  the  ligature 
from  the  action  of  the  drug. 
The  unbroken  lines  represent 
the  sensory  nerves  which 
carry  sensory  impulses  from 
the  skin  to  the  central  nerv- 
ous system ;  the  broken  lines 
indicate  the  motor  nerves, 
which  carry  motor  impulses 
from  the  central  nervous  sys- 
tem out  to  the  muscles  (after 
Lauder  Brunton:  Pharmacol- 
ogy, Therapeutics,  and  Materia 
Medica). 


Conditions  which  Determine  the  Effect  of  Excitation. 

The  result  of  the  irritation  of  nerve  and  muscle  is  dependent  on  two  sets 
of  conditions — namely,  (1)  Conditions  which  determine  the  irritability;  (2) 
Conditions  which  determine  the  efficiency  of  the  irritant. 

It  will  be  necessary  for  us  to  study  the  second  set  of  conditions  first, — for. 


GENERAL   PHYSIOLOGY  OF  MUSCLE  AND   NERVE.       43 

before  we  fan  judge  of  the  irritability  and  the  efU'ct  of  various  influences  upon 
it,  we  must  consider  how  far  the  activity  of  the  nerve  and  muscle  is  depend- 
ent on  the  cliarai'ter,  strength,  and  method  of  application  of  the  irritant. 

Conditions  which  Determine  .the  EflQciency  of  Irritants. — Some  of 
these  conditions  can  be  best  studied  on  nerves,  while  others  are  more  ap- 
parent in  their  effects  on  muscles.  The  most  useful  irritant  for  ])urposes  of 
study  is  the  electric  current.  INIechanical,  thermal,  and  chemical  irritants  are 
likely  to  injure  the  tissue,  and  are  not  manageable,  whereas  electricity,  if  not 
too  strong,  can  be  applied  again  and  again  without  producing  any  permanent 
alteration,  and  can  be  accurately  graded  as  to  strength,  place,  time,  and  dura- 
tion of  application,  etc.  Of  course  the  results  obtained  by  the  use  of  a  given 
irritant  cannot  be  accepted  for  others  until  verified.  The  conditions  which 
determine  the  eifectiveness  of  the  electric  current  as  an  irritant  may  be  classed 
as  follows : 

(a)  The  rate  at  which  the  intensity  changes. 

(6)  The  strength  of  current. 

(c)  The  density  of  current. 

{d)  The  duration  of  application. 

(e)  The  angle  of  application. 

(/)  The  direction  of  flow. 

Irritating  Effect  of  the  Electric  Current. — Galvani,  in  seeking  to  find  the 
effect  of  atmospheric  electricity  upon  the  animal  body,  suspended  frogs  by 
copper  wires  from  an  iron  balcony,  and  observed  the  remarkable  fact,  that 
when  the  wind  blew  the  legs  against  the  balcony  the  muscles  of  the  frogs 
twitched.  He  repeated  the  experiment  in  his  laboratory,  and  concluded  that 
the  frogs  had  been  excited  to  action  by  electric  currents  developed  within  them- 
selves ;  he  looked  upon  the  metals  which  he  had  used  merely  as  conductors  for 
this  current.  Volta,  Professor  of  Natural  Philosophy  at  Pavia,  repeated  Gal- 
vani's  experiment,  and  concluded  that  there  had  been  an  electric  current 
developed  from  the  contact  of  the  dissimilar  metals  with  the  moist  tissues  of 
the  frog.  In  accordance  with  this  idea  he  constructed  the  voltaic  pile,  and 
this  was  the  starting-point  of  the  electric  science  of  to-day. 

Although  it  is  true  that,  under  certain  conditions,  differences  in  electric 
potential  sufficient  to  excite  muscles  to  contraction  can  be  developed  in  the 
animal  body,  the  contractions  of  the  frog's  leg  which  Galvani  observed  were 
due  to  the  metals  which  he  employed.  The  experiment  can  be  easily  per- 
formed by  connecting  a  bit  of  zinc  to  a  piece  of  curved  copper  wire,  and  bring- 
ing the  two  ends  of  the  arc  against  the  moist  nerve  and  muscle  of  a  frog.  A 
stronger  and  more  efficient  shock  can  be  obtained  from  a  Daniell  or  some  other 
voltaic  cell. 

A  Daniell  cell  (Fig.  5)  is  composed  of  a  zinc  and  copper  plate,  the  former  dipping 
into  dilute  sulphuric  acid,  the  latter  into  a  strong  copper-sulphate  solution.  Although 
gravity  will  keep  these  liquids  separated,  if  the  cell  is  to  be  moved  about  it  is  better 
to  enclose  one  of  them  in  a  porous  cup.  A  common  form  of  cell  consists  of  a  glass  jar, 
in  the  middle  of  which  is  a  porous  cup ;  outside  the  cup  is  the  sulphuric  acid  and  the 


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zinc  plate,  and  inside  the  cup   is  the  copper  sulphate  solution  and  the  copper  plate. 

The  zinc  plate  is  acted  upon  by  the  sulphuric  acid,  and,  as  a  result  of  the  chenjical 
change,  a  difference  of  electric  potential  is  set  up  between  the 
metals,  so  that  if  the  zinc  and  copper  be  connected  by  a  piece  of 
metal,  what  we  call  an  electric  current  flows  from  the  zinc  tv  the 
copper  inside  the  cell,  and  from  the  copper  to  the  zinc  outside  the 
cell.  The  zinc  plate,  being  the  seat  of  the  chemical  change,  is 
called  the  positive  plate,  and  the  copper  the  negative  plate. 
Several  such  cells  may  be  connected  together  to  form  a  batterj', 
each  cell  adding  to  the  electro-motive  force,  and  hence  to  the 
strength  of  the  current.  As  the  current  is  always  considered  to 
flow  from  -r  to  — ,  we  call  the  end  of  the  wire  connected  with  the 
copper  (negative  plate)  the  positive  pole,  or  anode,  and  the  end 
of  the  wire  connected  with  the  zinc  (positive  plate)  the  negative 
pole,  or  kathode.  If  one  of  these  wires  be  touched  to  a  nerve, 
under  ordinary  circumstances  no  effect  is  produced  ;  but  when  the 
other  wire  is  likewise  brought  in  contact  with  the  nerve,  the 
moist  tissues  of  the  nerve  form  a  conductor,  complete  the  cir- 
cuit, and  an  electric  current  at  once  flows  through  the  nerve  from 
the  anode  to  the  kathode.  The  effect  of  the  sudden  flow  of 
electricity  into  the  nerve  is  to  give   it  a  shock — as  we  say,  it 

irritates  the  nerve — and  the  muscle  which  the  nerve  controls  is  seen  to  contract. 

In  the  place  of  using  ordinary  wires  for  applying  the  electricity,  we  vise  electrodes. 

These  are  practically  the  same  thing,  but  have  insulated  handles,  and  have  a  form  better 

suited  to  stimulate  nerves  or  other  tissues.     The  two  wires  mav  be  held  in  two  different 


Fig.  5.— Darnell  cell. 


Fig.  6.— a,  Ordinary  tk-ttrmk-  fur  excitiiiir  exposed  nerves  and  muscles,  consisting  of  two  wires 
enclosed,  except  at  their  extremities,  in  a  handle  of  non-conducting  material ;  b,  c,  non-polarizable  elec- 
trodes. When  metals  come  in  contact  with  moist  tissues  a  galvanic  action  is  likely  to  occur  and  polariz- 
ing currents  to  be  formed.  These  extra  currents  would  complicate  or  interfere  with  the  results  of  many 
forms  of  experiment,  and  they  are  avoided  by  the  use  of  non-polarizable  electrodes.  A  simple  form  con- 
sists of  a  short  glass  tube,  at  one  end  of  which  is  a  plug  of  china  clay  mixed  with  a  0,6  per  cent,  solution 
of  sodium  chloride,  and  at  the  other  end  a  cork  through  which  an  amalgamated  zinc  rod  is  thrust.  The 
zinc  rod  dips  into  a  saturated  solution  of  zinc  sulphate,  which  is  in  contact  with  the  clay.  The  clay  plugs 
touch  the  tissue  to  be  excited,  and  the  current  passes  from  the  zinc  rods  through  the  zinc-sulphate  and 
sodium-chloride  solutions  in  the  clay  to  the  tissues;  d-f,  electrodes  for  exciting  htiman  nerves  and  mus- 
cles through  the  skin  (after  Erb) :  these  may  be  of  various  forms  and  sizes,  and  are  arranged  to  screw 
into  handles  (g),  to  which  the  wires  are  attached :  they  are  usually  made  of  brass  and  covered  with 
sponge  or  other  absorbent  material  wet  with  salt-solution.  The  smaller  electrodes  are  used  when  a  dense, 
well-localized  stream  is  required,  and  the  larger  electrodes  when  little  action  is  wished  aud  it  is  of 
advantage  to  have  the  stream  ditluse. 

handles,  in  which  case  we  speak  of  the  positive  and  negative  electrodes,  or  the  anode 
and  the  kathode,  or  they  may  be  held  in  the  same  handle  (Fig.  6). 

Keys. — It  is  not  as  convenient  to  stimulate  a  nerve  by  touching  it  with  the  electrodes  as 


GENERAL    PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       45 


it  is  to  place  it  upon  tlic  electrodes  and  close  the  connection  between  the  zinc  and  copper  at 
some  other  part  of  the  circuit ;  this  may  be  done  by  what  is  called  a  key.  Any  mechanism 
which  can  be  used  to  complete  the  circuit  could 
receive  this  name,  and  there  are  a  number 
ol"  convenient  forms.  The  one  mo.^t  used  by 
physiologists  is  that  devised  by  J)u  liois-Key- 
mond,  and  whicli  bears  his  name  (.see  Fig.  7). 
This  \\Ji»  the  advantage  of  being  capable  of 
being  used  in  two  different  ways — one  simply 
as  a  means  to  close  tlie  circuit,  and  the  other 
to  short-circuit  tlie  current.  These  two  meth- 
ods are  sliown  in  Figure  8. 

By  the  former  method  the  key  supplies  a 
movable  piece  of  metal  by  which  contact  be- 
tween the  two  ends  of  the  wires  may  be  made 
as  in  a  (Fig.  8),  or  broken  as  in  6,  and  the 
current  be  sent  through  the  nerve,  or  prevented 
from  entering  it.  By  the  latter  method  the 
battery  is  all  the  time  connected  with  the 
electrodes,  and  the  key  acts  as  a  movable 
bridge  between  the  wires,  and  when  closed  gives  a  path  of  slight  resistance  by  which 
the  current  can  return  to  the  battery  without  passing  through  the  nerve.  The  current 
always  takes  the  path  of  least  resistance,  and  so,  if  the  key  be  closed  as  in  c,  all  the  cur- 
rent will  pass  through  the  key  and  none  will  go  to  the  nerve,  which  has  a  high  resistance, 
whereas  if  the  key  be  opened  as  in  </,  the  bridge  being  removed,  all  the  current  will  go 
through  the  nerve.  It  is  often  better  to  let  the  cell  or  battery  work  a  short  time  and  to 
get  its  full  strength  before  letting  the  current  enter  the  nerve,  and  the  short-circuiting  key 
permits  of  this.     Moreover,  there  are  times  when  a  nerve  may  be  stimulated  if  connected 


Fig.  7.— Electric  key. 


Fig.  8.— Electric  circuiting. 

with  the  source  of  electricity  by  only  one  wire,  the  circuit  being  completed  through  the 
earth  ;  when  the  nerve  is  so  excited,  it  is  called  unipolar  stimulation ;  this  may  be  pre- 
vented by  the  short-circuiting  key. 

As  has  been  said,  a  nerve  is  irritated  if  it  be  counected  with  a  battery  and 
an  electric  current  suddenly  passes  through  it.  Unless  the  current  be  very 
strong  the   irritation  is  transient,  however;  the  muscle  connected  with  the 


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nerve  gives  a  single  twitch  at  the  moment  that  the  current  enters  the 
nerve,  and  then  remains  quiet;  and  thus  we  meet  with  the  remari<al)le  fact 
that  an  electric  current,  though  irritating  a  nerve  at  the  moment  that  it 
enters  it,  can  flow  through  the  nerve  continuously  without  exciting  it.  Fur- 
ther, although  the  current  while  flowing  through  the  nerve  does  not  excite 
it,  a  sudden  withdrawal  of  the  current  from  the  nerve  irritates  it,  and  causes 
the  muscle  connected  with  it  to  contract.  It  is  our  custom  to  speak  of 
closing,  or  making,  the  circuit  when  we  complete  the  circuit  and  let  the 
current  flow  through  the  nerve,  and  of  opening,  or  breaking,  the  circuit 
when  we  withdraw  the  current  from  the  nerve.  Since  the  closing  of  the 
circuit  acts  as  a  sudden  irritant  to  the  nerve,  we  speak  of  this  irritant  as 
a  "making"  or  "closing"  shock,  and  the  corresponding  contraction  of  the 
muscles  as  a  making  or  closing  contraction ;  similarly  we  s})eak  of  the  effect 
of  opening  the  circuit  as  an  "opening"  or  "  breaking"  shock,  and  the  result- 
ing contraction  as  an  oi)ening  or  breaking  contraction.  As  we  shall  see  later, 
the  making  contraction  excited  by  the  direct  battery  current  is  stronger  than  the 
breaking  contraction  :  the  explanation  of  this  must  be  deferred  (see  page  53).  • 
(a)  Effect  of  the  Rate  at  tohich  an  Irritant  is  Apjdied,  llluatrated  by  the  Elec- 
tric Current. — As  has  been  said,  an  electric  current  of  constant  medium  strength 


Fig.  '.».— Rheonome. 


does  not  irritate  a  nerve  while  flowing  through  it,  but  the  nerve  is  irritated  at 
the  instant  that  the  current  enters  it,  and  at  the  instant  that  the  current  leaves 
it.  Is  it  the  change  of  condition  to  which  the  nerve  is  subjected,  or  is  it  the 
suddenness  of  the  change,  which  produces  the  excitation?  Would  it  be  possi- 
ble to  turn  an  electric  current  into  a  nerve  and  remove  it  from  a  nerve  so 
slowly  that  it  would  not  act  as  an  irritant  ? 

The  experiment  has  been  tried,  and  it  has  been  found  that  if  the  nerve  be 
subjected  to  an  electric  current  the  strength  of  which  is  increased  or  decreased 
very  gradually,  no  change  occurs  in  the  nerve  sufficient  to  cause  a  contraction 
of  the  muscle.  In  this  experiment,  instead  of  using  the  ordinary  key,  we  close 
and  open  the  circuit  by  means  of  a  rheonome  (see  Fig.  9). 

This  instrument  contains  a  fluid  resistance,  which  can  be  altered  at  will,  thereby  per- 
mitting a  greater  or  less  strength  of  current  to  pass  from  the  battery  into  the  circuit 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.        47 

containing  the  nerve.  The  wires  from  the  battery  are  connected  with  binding-posts,  a,  b 
(Fig.  9),  at  opposite  sides  of  a  circuhir  groove  containing  a  saturated  solution  of  zinc  sul- 
phate. Strips  of  amalgamated  zinc  connect  the  binding-posts  with  the  fluid,  and  so  com- 
plete a  circuit  which  ofl'ers  much  resistance  to  the  passage  of  the  current.  From  the  centre 
of  the  block  containing  the  groove  rises  an  upright  bearing  a  movaljlc  horizontal  bar,  from 
each  extremity  of  which  an  amalgamated  zinc  rod,  e  and/,  descends  and  dips  inf(j  the  zinc- 
sulphate  solution.  The  zinc  n)ds  are  connected  with  binding-posts  on  the  movable  bar,  and 
from  these  wires  pass  to  the  electrodes  on  which  the  nerve  rests.  The  bar  revolves  on  a 
pivot  on  the  top  of  the  upright,  and  thus  the  zinc  rods  can  be  readily  approached  to 
or  removed  from  the  zinc  strips,  the  poles  of  the  battery.  When  the  zinc  rods  hold  a 
position  midway  between  these  poles,  the  current  all  passes  by  the  way  of  the  fluid.  As 
the  bar  is  turned,  so  as  to  bring  the  zinc  rods  nearer  and  nearer  the  two  poles  of  the  bat- 
tery, the  current  divides,  and  more  and  mcjre  of  it  passes  through  the  path  of  le&sening 
resistance  of  which  the  nerve  is  a  part.  When  the  zinc  rods  are  brought  directly  opposite 
the  poles  of  the  battery  nearly  all  the  current  passes  by  the  way  of  the  nerve.  If  the  bar  be 
turned  more  or  less  rapidly,  the  current  is  thrown  into,  or  withdrawn  from,  the  nerve  more 
or  less  quickly. 

By  this  arraugement  we  can  not  only  observe  that  the  nerve  fails  to  be  irritated 
when  the  current  is  made  to  enter  or  leave  it  gradually,  and  when  it  is  flowing 
continuously  through  it,  but  that  sudden  variations  in  the  density  of  the  cur- 
rent flowing  through  the  nerve,  such  as  are  caused  by  quick  movements  of  the 
bar,  although  they  do  not  make  or  break  the  circuit,  serve  to  excite.  This 
experiment  shows  that  electricity,  as  such,  does  not  irritate  a  nerve,  but  that  a 
sudden  change  in  the  density  of  the  current,  whether  it  be  an  increase  or 
decrease,  produces  an  alteration  in  the  nerve-protoplasm  which  excites  it  to 
action  and  causes  the  development  of  what  we  call  the  nerve-impulse. 

Du  Bois-Reymond's  Law. — Du  Bois-Reymond  formulated  the  following 
rule  for  the  irritation  of  nerves  by  the  electrical  current :  "  It  is  not  the  abso- 
lute value  of  the. current  at  each  instant  to  which  the  motor  nerve  replies  by  a 
contraction  of  its  muscle,  but  the  alteration  of  this  value  from  one  moment  to 
another;  and,  indeed,  the  excitation  to  movement  which  results  from  this  change 
is  greater  the  more  rapidly  it  occurs  by  equal  amounts,  or  the  greater  it  is  in 
a  given  time." 

We  shall  have  occasion  to  see  that  this  rule  has  exception.?,  or  rather  that 
there  is  an  upper  as  well  as  lower  limit  to  the  rate  of  change  of  density  of  the 
electric  current  which  is  favorable  to  irritation. 

Similar  observations  may  be  made  with  other  forms  of  irritants.  Pres- 
sure, if  brought  to  bear  on  a  nerve  gradually  enough,  may  be  increased  to  the 
point  of  crushing  it  Avithout  causing  sufficient  irritation  to  excite  the  attached 
muscle  to  contract,  although,  as  has  been  said,  a  very  slight  tap  is  capable  of 
stimulating  a  nerve.  Temperature,  and  various  chemicals,  likewi.se,  must  be  so 
applied  as  to  produce  rapid  alterations  in  the  nerve-protoplasm  in  order  to  act 
as  irritants.  The  same  rule  would  seem  to  hold  good  for  the  nerve-cells  of  the 
central  nervous  system.  It  is  a  matter  of  daily  experience  that  the  nervous 
mechanisms  through  which  sensory  impressions  are  perceived  are  vigorously 
excited  by  sudden  alterations  in  the  intensity  of  stimuli  reaching  them,  and  but 
little  affected  by  their  continuous  application ;  the  withdrawal  of  light,  a  sudden 


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alteration  of  temperature,  an  uuexpeeted  noise,  or  the  cessation  of  a  monotonous 
sound,  as  exempliiied  by  the  common  experience  that  a  sleeper  is  awakened 


Fig.  10.— Induction  apparatus;  a,  primary  coil;  h,  secondarj-  coil ;  c,  the  automatic  interrupter. 

when  reading  aloud  abruptly  ceases,  attract  the  attention,  although  a  continu- 
ous sensory  irritation  may  be  unnoticed.  This  physiological  law  of  the  nervous 
system  would  seem  to  have  a  psychological  bearing  as  well. 


Fig.  11.— Schema  of  induction  apparatus. 

Irritating  Effect  of  Induced  Electric   Currents. — Within  certain  limits,  the 
more  rapid  the  change  in  intensity  of  an  electric  current  the  greater  its  power  to 

irritate.  This  })robably  accounts  in  part 
for  the  fact  that  the  induced  current  is  a 
more  powerful  irritant  to  nerves  than  the 
direct  galvanic  current.  Induced  currents 
are  usually  obtained  by  means  of  an  induc- 
tion apparatus  (sec  Fig.  10). 

The  ordinary  induction  apparatus  employed 
in  the  laboratory  (see  Fig.  1 1 )  consists  of  a  coil  of 
wire,  p,  which  may  be  connected  with  the  ter- 
minals of  a  battery,  h,  and  a  second  coil,  .s,  wholly 
independent  of  the  first,  which  is  connected  with 
electrodes,  e.  At  the  instant  that  the  key,  /r,  in 
the  primary  circuit  is  closed,  and  the  battery  cur- 
rent enters  tlie  priniarj'  coil,  an  induced  cuiTcnt 
isdevdoijcd  in  the  secondary  coil,  and  the  nerve 
resting  on  the  electrodes  is  irritated.  The  in- 
duced current  is  of  exceedinjrly  short  duration, 
suddenly  rising  to  ftill  intensity  and  falling  to 
zero.  As  long  as  the  battery  current  continues  to 
flow  constantly  through  the  primarj-  coil,  there  is 
no  change  in  the  electrical  condition  of  the  sec- 
ondary coil,  but  at  the  instant  the  primary  current  is  broken  another  mduccd  current  of  short 
duration  is  set  u])  in  the  secondary  coil,  and  again  the  nerve  receives  a  shock.     The  rise  and 


^ 

3 

l^ 

-^..^-^ 

1 

Fig.  12.— Schema  of  the  relative  intensity 
of  induction  currents  (after  Hermann,  Hand- 
buch  der  Phyniologie,  Bd.  ii.  S.  37) :  /',  abscissa 
for  the  primary  current;  S,  abscissa  for  the 
secondary  current;  1,  curve  of  the  rise  of 
intensity  of  the  primary  current  when  made ; 
2,  curve  of  the  rise  and  fall  of  intensity  of 
tiie  cnrre.sponding  induced  current;  3,  curve 
of  fall  of  the  intensity  of  the  primary  cur- 
rent when  it  is  broken  ;  4,  curve  of  the  rise 
and  fall  of  intensity  of  the  corresponding  in- 
duced current. 


GENEBAL    PHYSIOLOGY    OF   MUSCLE   AXD    NERVE.       49 

fall  of  the  density  of  the  current  in  the  secondary  coil  is  very  rapid,  and  this  raj)id  double  change 
in  density  of  the  current  causes  the  induetion  shock  to  he  a  very  effective  irritant.  The  break- 
ing induction  shock,  as  we  call  that  which  is  pruiliiced  by  breaking  the  primary  current,  is 
found  to  act  more  vigorously  than  the  niaking  shock,  which  is  the  reverse  of  what  is  found 
with  direct  battery  currents.  The  cause  of  this  lies  in  the  nature  of  the  apparatus.  At  tlie 
moment  that  the  current  begins  to  flow  into  the  primary  coil,  it  induces  not  only  a  current 
in  the  secondary  coil,  but  also  currents  in  the  coils  of  wire  of  the  i)riniary  coil.  These 
extra  induced  currents  in  the  primary  coil  have  the  opposite  direction  to  the  battery  cur- 
rent and  tend  to  oppose  its  entrance,  and  thereby  to  prevent  it  from  immediately  gain- 
ing its  full  intensity.  This  delay  affects  the  development  of  the  induced  current  in  the 
secondary  coil,  causing  it  to  be  weaker  and  to  have  a  slower  rise  and  fall  of  intensity  than 
would  otherwise  be  the  case.  When  the  primary  current  is  broken,  on  the  other  hand, 
there  is  no  opposition  to  its  cessation,  and  the  current  induced  in  the  secondary  coil  is 
intense  and  has  a  rapid  rise  and  fall.     These  differences  are  illustrated  in  Figure  12. 

To  accurately  test  the  effect  of  tlie  making  and  breaking  induction  shocks, 
it  is  necessary  to  record  the  reaction  of  the  nerve ;  this  can  be  done  by  record- 
ing the  extent  to  which  the  corresponding  muscle  contracts  in  response  to  the 
stimulus  which  it  receives  from  the  nerve.  In  such  an  experiment  it  is 
customary  to  use  what  is  known  as  a  nerve-muscle  preparation.  The  gas- 
trocnemius muscle  and  sciatic  nerve  of  a  frog,  for  instance,  are  carefully 
dissected  out,  the  attachment  of  the  muscle  to  the  femur  being  preserved,  and 
the  bone  being  cut  through  at  such  a  point  that  a  sufficiently  long  piece  of 
it  shall  be  left  to  fasten  in  a  clamp,  and  so  support  the  muscle  (see  Fig.  13). 


Fig.  13. — Method  of  recording  muscular  contraction. 

The  simplest  method  of  recording  the  extent  of  the  muscular  contraction 
is  to  connect  the  muscle  by  means  of  a  fine  thread  with  a  light  lever,  and  let 
the  point  of  the  lever  rest  against  a  smooth  surface  covered  with  soot,  so  that 
when  the  muscle  contracts  it  shall  draw  up  the  lever  and  trace  a  line  of  cor- 
responding length  upon  the  blackened  surface.     The  combination  of  instru- 

4 


50  .LV   AMERICA. \    TEXT-IIOOK    OF    PHYSIOLOGY. 

ments  omplovtHl  to  iccord  tlic  contriK'tioii  of  :i  nui.scle  is  called  ;i  intiocintjih,  and 
tlu'  ivt'onl  of  the  contraction  is  termed  a  vii/i)(/r(nii.  If,  wlien  the  ninsclc  of  a 
ncrvc-niuscle  preparation  is  tluis  arranged  to  Mrite  its 
loutractions,  the  nerve  be  irritated  with  alternating  mak- 
ing and  breaking  indnction  shocks  of  medium  strength, 
(he  muscle  will  make  a  series  of  movements,  which,  if 
the  suifaoe  be  moved  past  the  writing-point  a  short 
distance  after  each  contraction,  will  be  pictured  in  the 
record  as  a  row  of  alternatino;  long  and  short  lines   the 

Fig.  14.— Effect  of  making  ^  .  •  i  •    i  i 

and  breaking  induction  rccords  of  the  breaking  contractions  being  higher  than 
^^°^^^-  those  of  the  making  contractions  (Fig.   14).     Similar 

results  are  obtained  if,  instead  of  irritating  the  nerve,  we  irritate  the  ciirarized 
muscle  directly. 

Stimulating  Effects  of  Making  and  Breaking  the  Direct  Battery  Current. — 
On  account  of  the  construction  of  the  induction  apparatus,  breaking  induction 
shocks  are  more  effective  stimuli  than  making  induction  shocks.  The  reverse 
is  true  of  the  stimulating  effects  which  come  from  making  and  breaking  the 
direct  battery  current.  The  excitation  wdiich  results  from  sending  a  galvanic 
current  into  a  nerve  or  muscle  is  stronger  than  that  which  is  cau.sed  by  the 
withdrawal  of  the  current.  This  difference  is  due  to  the  physiological  altera- 
tions produced  by  the  current  as  it  flows  through  the  irritable  substance,  and 
is  M-itliout  doubt  closely  associated  with  changes  in  the  irritability  which  occur 
at  the  moment  of  the  entrance  and  exit  of  the  current. 

The  making  contraction  starts  from  the  kathode,  and  the  breaking  contraciion 
from  the  anode.  The  irritation  process  which  results  from  making  the  current 
is  developed  at  the  kathode,  and  that  which  results  from  breaking  the  current 
is  developed  at  the  anode.  This  was  first  demonstrated  on  normal  muscles  by 
Von  Bezold,^  and  has  since  been  substantiated  for  nerves  as  well  as  muscles 


Fig.  15.— Schema  of  Ilering's  double  myojiraph  :  C,  clamp  holding  middle  of  muscle;  P,P,  pulleys  to 
the  axes  of  which  the  recording  levers  are  attached;  p, p.  pulleys  for  the  light  weights  which  keep  the 
muscle  under  slight  tension;  ^,  positive  electrode;  if,  negative  electrode ;  r,  commutator  for  reversing 
the  current ;  k,  key  ;  6,  battery. 

by  the  experiments  of  a  great  many  observers.  Perhaps  the  most  striking 
demonstration  is  to  be  obtained  by  Engelmann's  method.  The  positive  and 
negative  electrodes  are  applied  to  the  two  extremities  of  a  long  curarized  sai*to- 

^  Untersnchunfjen  iiber  die  elcktrische  Eivegung  von  Muskeln  und  Nen-en,  1861. 


GENERAL    PHYSIOLOGY   OF   MUSCLE   AND    NERVE.        51 

rius  niusclo,  which  is  ohunpcd  in  the  middle  firndy  cnouj^h  to  prevent  the  con- 
tnietions  of  one  half  from  moving  the  otlier,  Wnt  not  en(ni<rh  to  interfere  with 
the  conduction-power  of  the  tissue.  The  record  of  the  contractions  is  best 
ohtained  by  tlie  douhle  myogra})h  of  Ilering  (Fig.  15),  wliieh  permits  the 
reeouling  levers  attached  to  the  two  ends  of  the  muscle  to  write  directly  under 
each  other,  so  that  any  diiference  in  the  beginning  of  the  contraction  of  the 
two  halves  of  the  muscle  is  immediately  recognizable  from  the  relative  posi- 
tions of  the  records  of  their  contractions. 

The  current  is  applied  to  the  two  extremities  of  the  muscle  by  non-polarizable  electrodes. 
In  all  experiments  with  the  direct  battery  current  it  is  essential  to  emi)loy  non-polarizable 
electrodes.  The  tbrm  devised  by  Hering  is  very  useful  where  the  current  has  to  be  apjdied 
d'u-ectly  to  the  muscle,  because  the  two  electrodes  are  hung  from  j^ivots  in  such  a  way  that 
they  move  with  the  movements  of  the  muscle,  and  hence  do  not  shift  their  position  when 
the  muscle  contracts.  Some  kind  of  apparatus  has  to  be  employed  for  quickly  reversing 
the  direction  of  the  current.  A  convenient  in- 
strument for  this  purpose  is  Pohl's  mercury  com- 
mutator (Fig.  16).  This  instrument  consists  of 
a  block  of  insulating  material  in  which  are  six 
little  cups  containing  mercury,  which  is  in  con- 
nection with  binding-posts  on  the  sides  of  the 
block.     Two  of  the  mercury  cups  on  the  opposite 


Figs.  16, 17.— Pohl's  mercury  commutator. 


sides  of  the  block  a  and  h  (Fig.  17,  A),  are  connected  by  wires  with  the  battery ;  two  others, 
c  and  d,  are  connected  with  wires  which  pass  to  the  electrodes ;  the  remaining  two  on  the 
opposite  side  of  the  block,  e  and  /.  are  joined  by  movable  good  conducting  wires  with  the 
cups  c  and  d  in  such  a  way  that  c  connects  with  /,  and  d  with  e.  Two  anchor-like  pieces  of 
metal  are  connected  by  an  insulated  handle,  and  are  so  placed  that  the  stocks  of  the  anchors 
dip  into  the  mercury  cups  a  and  h  (Fig.  16).  The  anchors  can  be  rocked  to  one  side  or  the 
other,  so  that  the  ends  of  the  curved  arms  shall  dip  into  the  cups  c  and  d  (in  which  case 
cup  a  will  be  connected  with  cup  c,  and  cup  h  with  cup  r? ),  or  so  that  the  other  ends  of  the 
arms  shall  dip  into  cups  e  and  /  (in  which  case  cup  a  will  be  connected  with  cup  e,  and  by 
means  of  the  cross  wire  with  cup  rf,  and  cup  h  will  be  connected  with  cup  /,  and  by  means 
of  the  cross  wire  with  cup  c).  By  the  arrangement  shown  in  Fig.  17,  ^  the  current  can 
pass  from  the  battery  by  way  of  a  and  c  down  the  nerve,  and  by  way  of  d  and  h  back  to 
the  battery ;  or  it  can  pass  from  the  battery  by  way  of  a,  e,  d,  and  in  the  reverse  direction, 
up  the  nerve  and  back  to  the  battery,  by  way  of  c,  /,  h. 

This  commutator  can  be  used  in  another  way  (see  Fig.  17,  B).  If  the  battery  be  con- 
nected with  it  as  before,  and  the  cross  wires  be  removed,  the  current  can  be  sent  at  will 
into  either  one  of  two  separate  circuits.  For  instance,  if  the  cups  c,  d  be  connected  with 
the  electrodes  on  one  part  of  the  nerve,  and  the  cups  e,  /  with  the  electrodes  on  another 


52 


AX  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


part,  the  ;uk1u)i>  liavo  only  to  be  rocked  to  one  side  or  the  other  to  complete  the  commu- 
nication between  the  battery  and  one  or  the  other  of  these  pairs  of  electrodes. 

Ill  experiiiicnts   with  the  douhle  nivogra])h,  in   which  the  makinf/  of  the 
current  is  used  to  irritate,  records  are  oWtained  such  as  an- shown  in  Fi<rure  18. 


Fig.  18.— The  making  contraction  starts  at  the  kathode  (after  Biedermann). 


In  the.se  records  the  beginning  of  the  tuning-fork  waves  shows  the  moment 
that  the  current  wa.s  made  and  the  irritation  given.  In  the  experiment  from 
which  record  a  was  taken  the  anode  was  at  the  knee-end  of  a  curarized  sartorius 
muscle  and  the  kathode  at  the  pelvic  end — i.  e.  the  current  was  ascending 
through  the  muscle.  The  lower  of  the  two  curves  was  that  got  from  the 
kathode  lialf,  the  arrangement  being  that  shown  in  Figure  15,  and  the  lower 
curve  began  before  that  got  from  the  anode  half;  /.  e.  the  contraction  originated 
at  the  kathode  and  spread  thence  over  the  muscle.  In  b  the  current  was 
reversed,  and  the  upper  curve  w^as  obtained  from  the  kathode  half  and  the 
lower  from  the  anode  half;  in  this  also  the  kathode  end  contracted  first. 
In  the  above  experiments  the  making  of  the  current  was  u.sed  to  irritate, 
and  the  muscular  contraction  began  at  the  kathode;  in  experiments  in  which 
the  breaking  of  the  current  was  employed  the  opposite  was  ob.<erved,  the 
anode  end  being  .seen  to  contract  first,  regardless  of  the  direction  of  tlie  cur- 
rent. 

If  strong  currents  be  used,  the  fleeting  contractions  which  result  from 
opening  and  closing  the  current  are  followed  by  continued  contractions,  the 
closing,  Wundt's,  and  the  opening,  Hitter's  tetanus,  a-s  they  are  called.  These 
continued  contractions,  which  last  for  a  considerable  time,  remain  strictly 
located   at  the  region  where  they  originate,  and   Engclmann   proved   by  his 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND    NERVE.       53 

experiiucnts  tluit  the  tetanus  which  results  irom  eh)sii)<;-  a  stronj^  oiUTeut 
reiiKiins  located  at  the  kathode,  and  the  tetanus  tbllowinj;  the  opening  of 
the  current   remains  located  at  the  anode. 

The  same  is  true  of  the  nerve  as  of  the  muscle;  the  irrilatinj;'  j)rocess  which 
is  callwl  out  by  the  sudden  entrance  of  a  battery  current  into  a  nerve  starts 
from  the  negative  pole,  the  kathode,  and  spreads  thence  throut^hout  the  nerve, 
while  the  irritating  process  excited  by  the  cessation  of  the  flow  of  the  current 
starts  from  the  region  of  the  positive  pole,  the  anode,  and  spreads  from  that 
point  throughout  the  nerve.  A  proof  of  this  was  obtained  by  Von  Bezold, 
who  observed  the  difference  in  the  time  between  the  moment  of  excitation  and 
the  beginning  of  the  contraction  of  the  muscle,  when  the  nerve  was  excited 
by  opening  and  by  closing  the  current,  with  the  anode  next  to  the  muscle, 
and  with  the  kathode  next  to  the  muscle.  He  found  the  time  to  be  longer 
when  the  current  was  closed  if  the  kathode  was  the  more  distant,  and  to  be 
longer  when  the  current  was  opened  if  the  anode  was  farther  from  the  muscle. 
Evidently  in  the  case  of  the  nerve  as  of  the  muscle,  the  irritable  substance 
subjected  to  the  current  is  not  all  affected  alike.  The  current  does  not 
set  free  the  irritating  process  at  every  part  of  the  nerve,  but  produces 
peculiar  and  different  effects  at  the  two  poles,  the  change  which  occurs  at  the 
kathode  when  the  current  is  closed  being  of  a  nature  to  cause  the  development 
of  the  excitatory  process  which  awakens  the  closing  contraction,  and  the 
change  which  occurs  at  the  anode  when  the  current  is  opened  being  such  a? 
to  cause  the  development  of  the  excitatory  process  which  calls  out  the  opening 
contraction. 

Closing  contractions  are  stronger  than  02:)ening  contractions.  The  irritation 
developed  at  the  kathode  is  stronger  than  that  developed  at  the  anode.  It  is 
true  of  both  striated  and  uustriated  muscles  that  an  efficient  irritation  can  be 
developed  at  the  kathode  with  a  weaker  irritant  than  at  the  anode.  Moreover, 
a  greater  strength  of  current  is  required  to  produce  opening  than  closing  con- 
tinued contractions. 

The  same  may  be  said  of  nerves.  If  one  applies  a  very  weak  battery  cur- 
rent to  the  nerve  of  a  nerve-muscle  preparation,  he  notices  when  he  closes  the 
key  a  single  slight  contraction  of  the  muscle,  and  when  he  opens  the  key,  no 
effect.  If  he  then  increases  the  strength  of  the  current  very  gradually,  and 
tests  the  effects  of  the  making  and  breaking  of  the  current  from  time  to  time, 
he  observes  that  each  time  the  strength  of  the  current  is  increased  the  closing 
contraction,  which  is  due  to  irritation  originating  in  the  part  of  the  nerve  sub- 
ject to  the  kathode,  grows  stronger,  and  finally  contractions  are  also  seen  wdien 
the  circuit  is  broken,  the  irritation  process  developed  at  the  anode  having 
become  strong  enough  to  excite  the  muscle.  These  opening  contractions  at 
first  are  weak,  but  gradually  increase  in  strength,  until  with  a  medium  strength 
of  current  vigorous  contractions  are  seen  to  follow  both  opening  and  closing  of 
the  current.  If  the  strength  of  the  current  be  still  further  increased,  it  is 
found  that  either  the  closing  or  opening  contraction  begins  to  decrease  in 
size,  and  if  a  very  strong  current  be  employed,  the  closing  or  opening  con- 


54  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

traction  will  be  absent.  It  has  been  ascertained  that  the  direction  in  which 
the  current  is  flowing  through  the  nerve  determines  which  of  these  van- 
tractions  shall  cease  to  appear.  The  cause  of  this  will  be  explained  a  little 
later. 

ib)  Effect  of  Strength  of  Irritant. — As  a  rule,  the  stronger  an  electric  current 
the  greater  its  irritating  effect.  This  can  be  readily  tested  upon  a  nerve  with 
the  induction  current,  the  strength  of  which  can  be  varied  at  jjleasure.  The 
strength  of  the  induced  current  obtained  from  a  given  apparatus  depends 
upon  the  strength  of  the  current  in  the  primary  coil,  and  on  the  distance  of 
the  secondary  from  the  primary  coil.  In  ordinary  induction  machines  (see  Fig. 
10,  p.  48)  the  secondary  coil  is  arranged  to  slide  in  a  groove,  and  can  be  easily 
approached  to  or  removed  from  the  primary  coil,  thus  placing  the  coils  of  wire 
of  the  secondary  coil  more  or  less  under  the  influence  of  the  magnetic  field 
about  the  primary  coil.  This  permits  the  strength  of  the  current  to  be  graded 
at  will.  The  strength  of  the  induced  current  does  not  increase,  however,  in 
direct  proportion  to  the  nearness  of  the  coils.  As  the  secondary  approaches 
the  primary  coil,  the  induced  current  increases  in  strength  at  first  very  slowly, 
and  later  more  and  more  rapidly,  reaching  its  greatest  intensity  when  the 
secondary  coil  has  been  pushed  over  the  primary. 

The  relation  of  the  strength  of  a  current  to  the  irritating  effect  upon  a  nerve 
can  be  readily  tested  with  such  an  induction  apparatus.  The  secondary  coils 
can  be  connected  with  a  pair  of  electrodes  on  which  the  nerve  of  a  nerve- 
muscle  preparation  rests  (as  in  Fig.  11,  page  48),  and  the  muscle  can  be 
arranged  to  record  the  height  of  its  contractions  (as  in  Fig.  13,  p.  49). 
The  experiment  can  be  begun  by  })lacing  the  secondary  coil  at  such  a  dis- 
tance from  the  primary  that  the  making  and  breaking  shocks  are  too  feeble  to 
have  any  effect  upon  the  nerve.  Then  the  secondary  coil  can  be  gradually 
approached  to  the  primary,  the  primary  current  being  made  and  broken  at 
regular  intervals.  At  a  certain  point  the  breaking  shock  will  excite  a  very 
feeble  contraction,  the  making  shock  producing  no  effect.  If  this  contraction 
is  barely  sufficient  to  be  recognized,  we  call  it  the  minimal  breaking  contraction 
(see  Fig.  19,  a).  In  seeking  the  minimal  contraction  care  must  be  taken  not 
to  excite  the  preparation  at  too  short  intervals  of  time,  for,  as  we  shall  see, 
an  irritation  too  slight  to  excite  even  a  minimal  contraction  may,  if  repeated 
at  short  intervals,  increase  the  irritability  of  the  preparation  and  so  become 
effective.  By  using  a  short-circuiting  key  in  the  secondary  circuit  we  can 
cut  out  the  making  shocks,  and  test  the  effect  of  a  liiitlur  increase  in  the 
strength  of  the  current  by  the  response  of  the  muscle  to  the  breaking  shocks. 
As  the  contractions  become  larger,  care  must  be  taken  not  to  irritate  the  muscle 
too  frequently,  lest  it  be  fatigued  and  so  fail  to  give  the  normal  response.  As 
the  current  is  strengthened  the  l^reaking  contractions  will  become  higher  and 
higher  until  a  point  is  reached  beyond  which  the  strength  of  the  current  may 
be  increased  to  a  considerable  extent  without  any  further  heightening  effect  (Fig. 
19,  b).  If  the  current  be  still  further  increased,  this  first  maximum  is  suc- 
ceeded by  a  still  further  growth  in  the  height  of  the  contractions,  until  finally 


GENERAL    PHYSIOLOGY   OF  MUSCLE  AND    NERVE.       55 

a  secoutl  maxiimuu  (Fig.  lU,  (/)  is  reached,  l)eyontl  which  no  further  increase 
is  to  be  obtained,  liowever  much  the  current  may  be  strengthened.' 


Fig.  19.— Effect  of  increase  oi  streiigtli  oi  current  on  ilie  ellicioncy  of  breftkinj;  induction  shocks  (after 
Fick):  a,  minimal  contraction ;  6-c,  first  maximum  ;  d-e,  second  maximum. 

If  both  the  making  and  breaking  contractions  be  recorded,  inasmuch  as 
the  making  shocks  are  weaker  stimuli  than  the  breaking  (see  p.  50),  the  mak- 
ing contractions  do  not  appear  until  after  the  breaking  contractions  have 
acquired  a  considerable  height.  After  the  making  minimal  contraction  lias 
been  obtained,  the  making  contractions  rapidly  gain  in  height  as  the  current 
is  strengthened,  and  finally  acquire  the  same  height  as  the  maximal  breaking 
shocks. 

The  relation  of  the  strength  of  the  electric  current  to  its  irritating  power 
can  be  demonstrated  equally  well  by  using  the  direct  galvanic  current.  The 
strength  of  the  galvanic  current  depends  upon  the  character  and  number  of  the 
cells  employed,  and  the  total  resistance  in  the  circuit.  The  strength  of  the 
current  can  be  easily  varied  by  altering  the  resistance,  and  there  are  a  number 
of  forms  of  apparatus  for  this  purpose. 


Fig.  20.— Rheostat. 

A  convenient  instrument  is  the  rheostat  (Fig.  20).  This  is  a  box  containing  coils  of 
wire  of  known  resistance.  These  coils  are  connected  with  a  series  of  heavy  brass  blocks  on  top 
of  the  box.  The  current  enters  the  box  by  a  binding-post  attached  to  the  first  of  the  brass 
blocks  and  passes  thence  from  block  to  block,  by  going  through  the  coils  of  wire  connecting 
them,  until  it  reaches  the  binding-post  at  the  other  end  of  the  series.  The  blocks  can  be 
also  connected  by  good  conducting  brass  plugs,  which  can  be  pushed  in  between  them,  and 
when  this  is  done,  as  the  current  passes  directly  from  block  to  block  instead  of  going  through 
the  resistance  coils  beneath,  the  resistance  is  reduced  to  a  corresponding  amount. 

Another  method  of  altering  the  strength  of  the  current  flowing  through  the 
nerve  is  to  employ  some  form  of  shunt  to  split  the  current  so  that  only  a  part 
of  it  shall  pa.ss  by  way  of  the  nerve.     A  current  takes  the  path  of  least  resist- 
^  Fick:  Unlersuchungen liber elektrische  Nervenreizung,  Braunschweig,  18,64. 


5G  AN  AMEIilCAN    TEXT- HOOK    OF    I'lfYSIOLOay. 

ance,  aud  if  two  paths  are  ojK-iicd  to  it,  more  or  less  can  he  sent   tliroii;^ii  one 
of  them  by  decreasing  or  increasing  tlie  resistance  in  the  other. 

A  usiliil  iiistriiiiuMit  lor  ilividiiii?  the  current  is  the  rlieouord.     The  schema  given  in 

Figure  21  iUustrates  the  way  in 
which  it  is  used  The  amount 
of  current  i)assing  to  tlie  nerve 
will  vary  with  the  relative  re- 
sistance in  II,  h.  r,  if,  e,  /,  and 
in  «,  b,  I/,  h,  t,  /.  The  bridge 
f,  d  can  be  slid  along  the  fine 
German-silver  wires  h,  !  and 
e,  j,  and  thus  the  resistance 
Fig.  21.— Rheocuid.  a,  6,  c,  f/,  e.  /,  and  the  amount 

of  current  passing  through  tlie  nerve,  can  be  varied  at  pleasure. 

With  snch  an  arranoemeut  we  sliould  find  that  the  irritating  effect  of  the 
current  is  largely  dependent  upon  its  strength.  In  tlie  case  of  strong  currents, 
however,  the  results  may  be  complicated  by  alterations  in  the  irritability  and 
conductivity,  which  we  will  consider  later.  It  is  true  also  of  other  forms  of 
irritants,  and  of  muscles  as  of  nei'ves,  that  the  effect  of  stimulation,  up  to  a 
certain  limit,  increases  with  the  strength  of  the  irritant, 

(e)  Efect  of  Density  of  the  Current. — Although  the  strength  of  the  current 
is  an  all-important  fiictor  in  its  excitatory  action,  the  effectiveness  of  the  cur- 
rent as  an  irritant  depends  very  largely  on  the  density  of  the  stream.  When 
the  current  enters  into  a  conductor,  it  spreads  widely  through  the  conducting 
substance,  and  though  the  larger  part  of  it  takes  the  path  of  least  resistance, 
which  is  usually  the  shortest  path  to  the  point  of  exit,  many  of  the  threads 
of  current  make  a  comparatively  wide  circuit  to  reach  the  outlet.  If  the  con- 
ductor is  equally  good  at  all  points,  but  is  irreguhirly  shaped,  the  density  of 
the  stream  will  be  greatest  where  the  diameter  of  the  conductor  is  least.  Thus 
it  happens  that  if  a  current  be  made  to  flow  from  end  to  end  of  a  mu.scle,  like 
the  sartorius  of  the  frog,  which  is  smaller  at  the  knee  end  than  at  the  pdvic 
end,  the  density  of  the  current  will  be  greater  at  the  lower  than  at  the  ujiper 
end,  and  the  irritating  power  of  the  current  will  be  greater  at  the  lower  end.' 

This  question  of  the  effect  of  the  density  of  the  current  is  important,  as  it 
helps  to  explain  the  peculiar  reactions  to  the  electric  stream  obtained  when  a 
current  is  applied  under  normal  conditions  to  the  human  nerve. 

{d)  Efect  of  the  Duration  of  the  Electric  Current  on  its  Power  to  Jmtate 
Nerves  and  Jfiisries. — As  we  have  seen,  a  constant  battery  current,  when  flow- 
ing uninterruptedly  through  a  motor  nerve,  does  not  ordinarily  excite  it;  very 
slow  variations  in  the  strength  of  the  current  also  fail  to  irritate ;  but  rapid 
alterations  in  the  strength,  whether  in  the  direction  of  increase  or  decrease,  act 
as  vigorous  stimuli.  For  example,  medullated  nerves  are  irritated  more  vigor- 
ously by  the  rapid  changes  of  intensity  of  induced  currents  than  by  the  some- 
what slower  changes  occurring  at  the  make  and  break  of  battery  currents. 
Within  certain  limits,  at  lea.st,  the  more  rapidly  the  intensity  of  the  current 

'  Biedormann  :   Eleklrophjisiiilnrfir,  1895,  Bd.  i.  p.  185. 


GENERAL    PHYSIOLOaV    OP'  MUSCLE   AND    NERVE.        57 

changes,  the  greater  the  irritating  ellLet  upon  nerves.  Not  all  nerves,  however, 
are  equally  susceptible  to  rapitl  alterations  of  the  intensity  of  the  current. 
Non-nu'du Hated  nerves  do  not  apjjcar  to  react  as  readily  as  medullated  to 
electric  currents  of  short  duration.  For  instance,  the  nerves  of  the  claw  mus- 
cles of  the  crab  are  not  readily  excited  by  induced  currents,  and  respond  better 
to  the  more  prolonged  influence  of  the  closing  and  opening  of  battery  currents.^ 

The  question  now  arises.  Is  the  reaction  of  muscles  to  electric  currents  the 
same  as  that  of  nerves?  Experiment  shows  that  muscles  wdiich  have  been 
removed  from  the  action  of  nerves,  by  means  of  curare,  differ  from  iiicdiillated 
nerves  in  that  they  are  excited  more  vigorously  by  the  opening  and  closing  of 
battery  currents  than  by  making  and  breaking  induction  currents.  The  max- 
imal conti-action  got  on  opening  and  closing  a  battery  current  is  both  higher 
and  more  prolonged  than  that  to  be  obtained  with  a  single  induction  shock. 
Unstriated  muscles  exhibit  this  difference  to  a  still  greater  degree  than 
striated  muscle;  they  react  well  to  the  closing  of  battery  currents  of  medium 
strength,  provided  these  last  some  little  time,  but  respond  to  induced  currents 
only  when  they  are  very  strong.  Thus  the  unstriated  muscle  which  closes  the 
shell  of  some  of  the  fresh-water  mussels,  as  the  Anodonta,  gives  larger  and 
larger  contractions  as  the  duration  of  the  current  is  increased  from  one-quarter 
of  a  second  to  three  seconds.-  Much  the  same  is  true  of  the  unstriated  muscles 
of  the  ureters;^  the  battery  current  must  remain  closed  quite  a  while  for  the 
closing  contraction  to  be  called  out,  the  length  of  time  depending  upon  the 
strength  of  the  current ;  and  induction  shocks  have  little  or  no  effect  unless 
very  strong.  Such  a  comparison  makes  it  evident  that  the  duration  of  the 
current  is  an  important  element  in  the  influence  exerted  by  electric  currents 
on  various  forms  of  protoplasm.  Unstriated  muscles  require  that  the  current 
shall  last  from  one-quarter  of  a  second  to  three  seconds  to  produce  maximum 
contractions.  Striated  muscles  require  that  a  current  shall  last  0.001  second 
(Fick),  and  even  medullated  nerves  fail  to  react  if  the  current  lasts  too  short 
a  time.  Various  forms  of  irritable  tissue  can  be  arranged  in  series  according 
to  their  ability  to  respond  to  electric  currents  of  short  duration,  viz.  medul- 
lated nerves,  non-medullated  nerves,  striated  muscles,  non-striated  muscles, 
and  the  little-differentiated  forms  of  protoplasm  of  many  of  the  protozoa. 
On  the  other  hand  these  tissues  are  found  to  respond  in  the  reverse  order  to 
currents  which  are  more  prolonged  and  which  change  their  intensity  slowly. 
It  would  seem  as  if  the  less  perfectly  differentiated  the  form  of  protoplasm, 
the  less  its  mobility  and  its  susceptibity  to  passing  influences. 

The  same  form  of  tissue  reacts  differently  in  different  animals.  For  instance, 
the  sluggish  striated  muscles  of  the  turtle  do  not  respond  as  well  to  induced 
currents  as  the  more  ra])id  striated  muscles  of  the  frog.  Further,  the  condition 
of  the  tissue  at  the  time  is  found  to  have  an  influence  on  its  irritability  and  its 
power  to  respond  to  stimuli  of  short  duration.  Yon  Kries  reports  that  nerves, 
if  cooled,  react  better  to  slow  variations  in  the  intensity  of  the  electric  current, 

^  Biedermann :  Elektrophysiologie,  1895,  Bd.  ii.  p.  546. 
»  Engelmann:  Pfluger's  Archiv,  1870,  Bd.  iii.  p.  263, 


58  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

and,  if  wariiRd,  to  rapid  variations.  Under  pathological  conditions  the  reac- 
tion of  nerve  and  muscle  to  electric  currents  may  become  blunted,  and,  as  the 
tissue  degenerates,  its  power  to  respond  to  rai)id  changes  of  the  electric  current 
is  lessened.  If  a  nerve  be  cut,  the  part  which  is  separated  from  the  influence 
of  the  nerve-cells  degenerates.  The  irritability  at  first  increases  and  then 
very  rapidly  decreases,  in  from  three  to  four  days  being  wholly  lost.  As  the 
nerve  regenerates,  the  irritability  is  recovered  very  gradually,  and  the  power 
to  respond  to  the  relatively  prolonged  action  of  ine(-hanical  stimuli  is  regained 
sooner  than  the  ability  to  reply  to  changes  as  rapid  as  those  of  induced  cur- 
rents. Howell  and  Huber  observed  that  regenerating  nerve-fibres  when  they 
have  reached  the  stage  resembling  embryonic  fibres,  i.  e.  are  strands  of  proto- 
plasm without  axis-cylinders,  fail  to  respond  to  induction  currents,  though  they 
can  be  excited  by  mechanical  stimuli.  It  was  found  that  it  is  not  until  the 
axis-cylinder  has  grown  down  into  the  regenerating  fibres  that  the  nerve  is 
capable  of  responding  to  induction  shocks. 

When  human  striated  muscle  undergoes  degeneration  as  a  result  of  an  in- 
jury to  its  nerve,  the  degenerating  muscle  comes  to  resemble  normal  unstriated 
muscle  in  its  reactions  to  electricity,  responding  feebly  to  induced  currents,  at 
a  time  when  irritability  to  mechanical  stimuli  and  to  direct  battery  currents 
is  even  increased.  This  is  used  by  clinicians  as  a  means  of  diagnosis  of  the 
condition  of  the  nerve  and  muscle. 

From  what  has  been  said  it  is  evident  that  the  rule  laid  down  by  Du  Bois- 
Reymond  (see  p.  47)  must  be  modified  in  so  far  that  there  is  for  each  tissue 
a  limit  to  the  rate  at  which  a  change  of  intensity  of  the  electric  current  acts 
as  an  irritant.  An  extreme  illustration  of  this  may  be  found  in  the  astonish- 
ing fact  lately  published  by  Tessla,  that  although  in  general  alternating  dynamo 
currents  are  very  deadly,  a  current  of  even  high  voltage  may  be  passed  through 
the  human  body  with  impunity,  provided  that  the  rate  of  alternations  be  suf- 
ficiently rapid. 

(<?)  Effect  of  the  Angle  at  ivhich  the  Current  Enters  and  Leaves  the  Muscle 
and  Nerve. — The  angle  at  which  the  current  acts  on  the  muscle-fibre  has 
been  found  to  have  a  bearing  upon  its  jiower  to  stimulate.  Leicher^  succeeded 
in  obtaining  definite  experimental  (evidence  that  when  the  current  is  so  sent 
through  a  muscle  as  to  cross  it  at  right  angles  to  its  fibres  it  has  no  irritating 
effect,  and  that  its  jwwer  to  stimulate  increases  as  the  angle  at  which  the 
threads  of  current  strike  the  muscle-fibres  decreases,  being  greatest  when  the 
current  passes  longitudinally  through  the  fibres. 

Similarly,  it  was  found  by  Albrecht  and  Meyer"  that  the  irritating  effect 
of  the  electric  current  is  most  active  when  it  flows  longitudinally  through  the 
nerve,  and  that  it  is  altogether  absent  when  it  flows  transversely  through  it. 
'This  view  is  doubted  by  some  observers,  who  would  attribute  the  difference 
observed  to  differences  in  the  electrical  resistance.  It  is  true  that  the  resist- 
ance to  cross  transmission  is  greater  than  to  longitudinal  transmission,  but  it 

^  Untersuchungen  aus  dem  physiologischen  Institut  der  Universitdt  Halle,  Hefl  i.  p.  5. 
*  Ppger's  Archiv,  1880,  Bd.  xxi.  p.  462. 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND    NERVE.       59 

is  not  likely  that  this  (lititrenco  suffices  to  explain  the  lack  ol"  response  to  cur- 
rents applied  at  right  angles  to  the  nerve-axis. 

Relative  Ejfficacii  of  the  above  Conditions  upon  the  Irritating  Power  of  the 
Electric  Current. — When  a  current  is  applied  to  an  irritable  part  of  a  nerve 
or  muscle  at  an  angle  suitable  to  excitation,  the  stimulating  effect  of  the  current 
depends  upon  the  rate  at  which  its  intensity  is  changed,  the  strength  and 
densitv  of  the  current,  /.  c.  its  intensity,  and  the  duration  of  tiie  current. 

Fick '  gives  the  following  schema  (Fig.  22)  for  the  dilferent  M'ays  in  which 
the  intensity  of  the  electric  current  may  be  varied,  and  compares  the  eifects 
of  these  diiferent  methods  of  application  of  the  current.  It  must  be  re- 
membered that  a  decrease  of  inteusity  acts  no  less  than  an  increase  to  produce 


-.'", 

a 

10- 

_______ 

0 

■ 

10 

20 

'/      40 

IDIi 

110 

.'0' 

b 

/ 

10. 

/ 

0 

/ 

10 

20 

20' 

10 

n 

d 

c 

e                    ./■ 

/      \ 

Fig.  22.— Schema  of  relation  of  the  method  of  application  of  the  electric  current  to  the 

irritating  efl'ect. 

excitation.  In  the  above  schema  the  abscissa  represents  the  time,  and  the 
ordiuates  the  strength,  of  the  current.  Suppose  the  rise  of  intensity  has  a 
form  such  as  is  represented  in  a,  Figure  22 — that  is,  that  the  strength  of  the 
current  increases  to  a  considerable  height,  but  very  slowly.  Such  a  rate  of 
change,  even  though  the  rise  of  intensity  were  continued  until  the  strength  of 
current  was  very  great,  would  have  no  exciting  eifect  upon  a  nerve  and  might 
fail  to  irritate  a  striated  or  non-striated  muscle.  A  more  rapid  rise,  such  as 
is  shown  in  6,  might  irritate  a  non-striated  muscle,  but  fail  to  irritate  a  nerve 
or  a  striated  muscle.  With  currents  which  rapidly  gain  their  full  intensity 
and  then  return  again  to  zero,  the  following  cases  would  be  possible:  A 
rapid  rise  and  fall  of  intensity  (see  c),  such  as  occurs  by  an  induction  shock 
or  by  the  momentary  closure  of  a  battery  current,  might  suffice  to  excite 
a  nerve  but  not  be  an  effective  irritant  to  a  striated,  much  less  a  non-striated 
muscle,  unless  the  short  duration  of  the  current  were  compensated  for  by 
a  considerable  increase  in  the  intensity  (see  d).  On  the  other  hand  a  form 
of  variation  such  as  is  shown  in  e,  where  the  rate  of  change  is  very  rapid, 
although  the  intensity  is  not  great,  might  act  to  irritate  nerves,  and,  because 
of  the  longer  duration  of  the  current,  striated  muscles,  though  having  no  effect 
on  non-striated  muscles;  and  the  slower  rate  of  change,  and  considerable  dura- 
^  Beitrdge  zur  vergleichende  Physiologic  der  irrilablen  Substanzen,  Braunschweig,  1863. 


60  AN  AMERICAN    TEXT- BOOK   OF  PHYSIOLOGY. 

tion,  illustrated  hy  J\  though  uot  afroding  nerves,  might  suffice  for  striated 
muscles  and  be  favorable  to  the  excitation  of  non-striated  nmscles. 

In  the  case  of  nerves,  duration  of  current  is  less  injportant  than  a  rapid 
change  of  intensity.  In  the  case  of  striated  muscles  the  advantage  to  be 
gained  by  rapid  variations  can  be  easily  overstepped,  and  the  importance  of 
the  duration  of  the  current  is  greater;  while  in  the  citse  of  non-striated  muscles 
duration  of  current  is  of  the  first  importance  and  ra])id  variation  mav  tail  to 
excite.  In  the  case  of  all  tissues,  strength  and  density  of  current,  what  we 
may  call  intensity  of  current,  is  favorable  to  excitation. 

(/)  Kfecf  of  fjir  Direction  in  which  the  Current  Jioirs  along  the  Xerre. — 
The  result  of  the  irritating  change  produced  in  a  nerve  l)y  a  battery  current 
has  been  found  to  dejiend  upon  whether  the  current  flows  toward  or  awav 
from  the  organ  stimulated  by  the  nerve.  This  fact  can  be  most  readily  ob- 
served in  the  case  of  isolated  motor  nerves.  In  the  case  of  these  nerves,  the 
effects  produced  by  opening  and  closing  the  current  are  different  according  as 
the  current  is  descending,  /.  e.  flows  through  the  nerve  in  the  direction  of  the 
muscle,  or  ascending,  i.  c.  flows  through  the  nerve  in  the  opposite  direction. 
Moreover,  by  a  given  rate  of  change  of  intensity,  the  stimulating  effect  varies 
with  the  strength  of  the  current  employed.  Pfliiger  in  his  celebrated  mono- 
graph, Untermchnngen  liber  die  Physiologie  des  Elehtrotonvs,  pui)lished  in 
Berlin,  1859,  p.  454,  formulated  the  following  rule  for  the  result  of  excitations 
under  varying  conditions : 

Pfliiger's  Law  of  Contraction. 

Ascending  Current.  Descending  Current. 

Closing.  Opening.  Closing.  Opening. 

'Weak  current Contr.  Rest.  Contr.  Rest. 

Medium    "        Contr.  Contr.  Contr.  Contr. 

Strong       "        Rest.  Contr.  Contr.  Rest. 

To  understand  this  so-called  "  law  of  contraction  "  we  must  bear  in  mind 
certain  fimdamental  facts,  namely  : 

a.  When  a  nerve  is  subjected  to  a  battery  current,  an  excitatory  process  is 
developed  in  the  part  of  the  nerve  near  the  kathode  when  the  current  is 
closed,  and  in  the  part  of  the  nerve  near  the  anode  when  the  current  is  ojx'ued 
(see  p.  53). 

b.  The  excitatory  process  developed  at  the  kathode  is  stronger  than  that 
developed  at  the  anode  (see  p.  53). 

c.  A  third  fact  which  is  of  no  less  importance,  and  which  will  be  considered 
in  detail  when  we  study  the  effects  of  the  constant  current  on  the  irritability 
and  conductivity  of  nerve  and  mu.scle  (.see  p.  95),  is  the  following:  During 
the  time  that  a  strong  constant  current  is  flowing  through  a  nerve,  the  conduct- 
ing power  is  somewhat  lessened  in  the  part  to  which  the  kathode  is  applied,  and 
is  greatly  decreased,  or  altogether  lost,  in  the  region  of  the  anode ;  moreover, 
at  the  in.stant  that  the  current  is  withdrawn  from  the  nerve  the  conducting 
power  is  suddenly  restored  in  the  region  of  the  anode,  and  greatly  lessened,  or 
lost,  in  the  region  of  the  kathode. 


QENERAL    PHYSIOLOGY   OF   MUSCLE   AND    NERVE. 


61 


The  twelve  cases  included  in  the  above  table  can  be  represented  in  the  fol- 
lowing diagram  (Fig.  23),  in  which  a  cross  is  marked  at  the  part  of  the  nerve 


Ascending  Current. 
K  A 


Weak  current. 


Medium  current. 


Strong  current 


Descending  Current. 

A  r 

» > 


Fig.  23.— Diagram  illustrating  Pfliiger's  law. 

from  which  the  irritation  which  is  effective  in  producing  a  contraction  takes 
its  rise. 

In  the  case  of  fresli  motor  nerves  of  the  frog,  when  the  current  is  weak, 
oulv  closing  contractions,  i.  e.  those  originating  at  the  kathode,  are  obtained  bv 
both  directions  of  the  current.  As  the  strength  of  the  current  is  increased,  at 
the  same  time  that  the  closing  kathodic  contractions  grow  stronger,  opening 
anodic  contractions  begin  to  appear ;  and  with  currents  of  medium  strength 
both  closing  and  oj^ening  contractions  are  obtained  with  both  directions  of  the 
current.  If  the  .strenp'th  of  the  current  be  .still  further  increased,  a  change  is 
observed ;  with  a  strong  current,  the  closing  of  the  ascending  and  the  opening 
of  the  descending  current  fails  to  excite  a 
muscular  contraction.  This  fact  is  demon- 
strated most  clearly  if  we  employ  two 
nerve-muscle  preparations,  and  lay  the  nerves 
in  opposite  directions  across  the  non-polar- 
izable  electrodes,  so  that  the  current  from 
the  battery  shall  flow  through  one  of  the 
nerves  in  an  ascending  direction  and  through 
the  other  in  the  descending  direction  (.see 
Fig.  24).  If  under  these  conditions  a  strong 
battery  current  be  employed,  muscle  a  (through 
the  nerve  of  which  the  curi-ent  is  descending) 
will  contract  only  when  the  circuit  is  closed, 
and  muscle  h  (through  the  nerve  of  which  the  current  is  ascending)  will  con- 
tract only  when  the  circuit  is  opened. 

Since  in  the  case  of  currents  of  medium  strength,  both  opening  and  clos- 
ing the  circuit,  when  the  current  is  ascending  and  when  it  is  descending, 
develops  a  condition  of  excitation  in  the  nerve  sufficient  to  cause  contractions, 
the  failure  of  the  contraction  bv  the  closing  of  the  strong  ascending  current, 


A   5-^  K 

Fig.  24.— Effect  of  direction  of  current 
as  shown  by  simultaneous  excitation  of 
two  nerve-muscle  preparations. 


G2 


AN  AMERICAN  TEXT-BOOK   OF  PHYSIOLOGY. 


aud  by  the  openiDg  of  the  strong  descending  current,  can  scarcely  be  supposed 
to  be  due  to  a  failure  of  the  exciting  process  to  be  developed  in  the  nerve ;  and 
it  would  seem  more  likely  that  the  nerve-impulse  is  for  some  reason  jirevented 
from  reac-hiiig  the  muscle — which,  as  has  been  said,  is  the  flict,  the  region  of  the 
anode  being  incapable  of  conducting  during  the  flow  of  a  strong  current,  and 
the  region  of  the  kathode  losing  its  power  to  conduct  at  the  instant  such 
a  current  is  ojiencd. 

Effect  of  Battery  Currents  upon  Normal  Human  Nerves. — In  experi- 
ments upon  normal  human  nerves,  the  current  cannot  be  applied  directly  to  the 
nerve,  but  has  to  be  applied  to  the  skin  over  the  nerve.  As  it  passes  from  the 
anode,  the  positive  electrode,  through  the  skin,  the  threads  of  current  spread 
through  the  fluids  and  tissues  beneath,  somewhat  as  the  bristles  of  a  brush 
spread  out,  and  the  current  flows  in  a  more  or  less  difliisc  stream  toward  the 
point  of  exit,  where  the  threads  of  current  concentrate  again  to  enter  the 
kathode,  the  negative  electrode.  This  spread  of  the  current  is  illustrated  in 
Figure  25. 

The  density  of  the  current  entering  any  structure  beneath  the  skin  will 
depend  in  part  upon  the  size  of  the  electrode  directly  over  it — that  is,  the 

amount  to  which  the  current  is 
concentrated  at  its  point  of  en- 
trance or  exit^ — in  part  on  the 
nearness  of  the  structure  to  the 
skin,  and  in  part  on  the  con- 
ductivity of  the  tissues  of  the 
organ  in  question  as  compared 
with  the  tissues  and  fluids 
about  it.  If  the  conditions  be 
such  as  are  given  in  Figure  25, 
the  current  will  not,  as  in  the 
case  of  the  isolated  nerve,  enter 
the  nerve  at  a  given  point,  flow 
longitudinally  through  it,  and 
then  leave  it  at  a  given  point ; 
most  of  the  threads  of  current 
will  pass  at  varying  angles  di- 
agonally through  the  part  of 
the  nerve  beneath  the  positive 
pole,  then  flow  through  the  fluids  and  tissues  about  the  nerve,  until,  at  a  point 
beneath  the  negative  pole,  the  concentrating  threads  of  current  again  pass 
through  the  nerve.  A  distinction  is  to  be  drawn  between  the  physical  and 
physiological  anode  and  kathode.  The  physical  anode  is  the  extremity  of  the 
positive  electrode,  and  the  physical  kathode  is  the  extremity  of  the  negative 
electrode;  the  physiological  anode  is  the  point  at  which  the  current  enters  the 
tissue  under  consideration,  and  the  physiological  kathode  is  the  point  where  it 
leaves  it.     There  is  a  physiological  anode  at  every  point  where  the  current 


Fig.  25.— Rough  schema  of  active  threads  of  current  by 
the  ordinary  application  of  electrodes  to  the  skin  over  a 
nerve  (ulnar  nerve  in  the  upper  arm).  The  inactive  threads 
are  given  in  dotted  lines  (after  Erb :  ZiemssetCs  Pathologie  und 
Therapie,  Bd.  iii.  S.  76). 


GENERAL    PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       63 

enters  the  nerve,  and  a  physiological  kathode  at  every  point  where  it  leaves  the 
nerve;  therefore  there  is  a  physiological  anode  and  kathode,  or  groups  of 
anodes  and  kathodes,  for  the  part  of  the  nerve  beneath  the  positive  electrode, 
and  an()tli(>r  physiological  anode  and  kathode,  or  collection  of  anodes  and 
kathodes,  for  the  part  of  the  nerve  beneath  the  negative  electrode. 

To  understand  the  effect  ui)on  the  normal  human  nerve  of  opening  and 
closing  the  battery  current,  it  is  necessary  to  bear  in  mind  three  facts,  viz. : 

1.  At  the  moment  that  a  battery  current  is  closed,  an  irritating  process  is 
developed  at  the  physiological  kathode,  and  when  it  is  opened,  at  the  physio- 
logical anode. 

2.  The  irritating  process  developed  at  the  kathode  on  the  closing  of  the 
current  is  stronger  than  that  developed  at  the  anode  on  the  opening  of  the 
current. 

3.  The  effect  of  the  current  is  greatest  where  its  density  is  greatest. 

The  amount  of  the  irritation  process  developed  in  a  motor  nerve  is  esti- 
mated from  the  amount  of  the  contraction  of  the  muscle.  The  contraction 
which  results  from  closing  the  current,  the  closing  contraction  as  it  is  called, 
represents  the  irritating  change  which  occurs  at  the  physiological  kathode,  while 
the  contraction  which  results  from  opening  the  current,  the  opening  contrac- 
tion, represents  the  irritating  change  developed  at  the  physiological  anode. 
Since  there  are  physiological  anodes  and  kathodes  under  each  of  the  two  elec- 
trodes— the  physical  anode  and  physical  kathode  (see  Fig.  26) — four  possible 
cases  may  arise,  namely: 

1.  Anodic  closing  contraction — i.  e.  the  effect  of  the  change  developed  at 
the  physiological  kathode,  beneath  the  physical  anode  (the  positive  pole). 

2.  Anodic  ojjemng  contraction — i  e.  the  effect  of  the  change  developed  at 
the  physiological  anode,  beneath  the  physical  anode  (the  positive  pole). 


Fig.  26.— Diagram  showing  physical  and  physiological  anodes  and  kathodes:  ^,  the  physical  anode, 
or  positive  electrode ;  A',  the  physical  kathode,  or  negative  electrode  -,0,0,0,  physiological  anodes ;  k,  k,  k, 
physiological  kathodes. 

3.  Kathodic  dosing  contraction — i.  e.  the  effect  of  the  change  developed  at 
the  physiological  kathode,  beneath  the  physical  kathode  (the  negative  pole). 

4.  Kathodic  opening  contraction — i.  e.  the  effect  of  the  change  developed  at 
the  physiological  anode,  beneath  the  physical  kathode  (the  negative  pole). 


64  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

For  convenience  these  four  cases  are  represented  by  the  abbreviations  ACC, 
AOC,  KCC,  and  KOC. 

These  oases  may  be  arnuigcd  in  order  according  to  the  strengtii  of  the 
irritation  whicli  is  developed. 

Since  the  irritation  process  developed  at  a  physiological  kathode  by 
closing  a  current,  is,  other  things  being  equal,  stronger  than  that  developed 
at  a  physiological  anode  by  opening  the  current,  we  should  expect  that  tiie 
two  closing  contractions,  KCC  and  ACC,  would  be  stronger  than  the  two 
opening  contractions,  KOC  and  AOC.  This  is  the  case,  and  as  the  current  is 
more  dense  in  the  region  of  the  physiological  kathode,  beneath  the  physical 
kathode,  than  at  the  physiological  kathode,  beneath  the  physical  anode,  KCC 
is  stronger  than  ACC. 

Of  the  two  opening  contractions,  AOC  is  stronger  than  KOC  because 
of  the  greater  density  of  the  current  in  the  region  of  the  physiological  anode, 
beneath  the  physical  anode,  than  in  the  region  of  the  physiological  anode, 
beneath  the  physical  kathode. 

These  differences  in  the  strength  of  the  irritation  process  developed  in  these 
different  regions  is  well  shown  by  examining  the  reaction  of  nerves  to  cur- 
rents of  gradually  increasing  strength.  The  effect  of  the  opening  and  closing 
irritation  is  seen  to  be  as  follows  : 

Weak  currents.  Medium  currents.  Strong  currents. 

KCC  KCC  KCC 

ACC  ACC 

AOC  AOC 

KOC 

The  natural  order,  therefore,  would  be  KCC,  ACC,  AOC,  KOC.  Some- 
times, however,  AOC  is  stronger  than  ACC;  this  hapj^ens  when  on  account 
of  the  relation  of  the  surrounding  tissues  to  the  nerve  the  density  of  the  cur- 
rent at  the  physiological  anode  is  great  as  compared  with  the  density  at  the 
physiological  kathode. 

When  the  currents  employed  are  strong,  it  not  infrequently  hap]>ens  in  the 
case  of  men  that  not  only  are  the  make  and  break  followed  by  the  usual  rapid 
contractions  of  short  duration,  but  during  the  closure  of  the  current  there  is 
a  continued  contraction — galvanotonus,  as  it  is  sometimes  called. 

Conditions  which  Determine  the  Irritability  of  Nerves  and  Muscles. 
— We  have  thus  far  considered  the  conditions  which  determine  the  efficiency 
of  such  an  irritant  as  the  electric  current.  Other  irritants  are  subject  to  like 
conditions,  their  activity  being  controlled  to  a  consiihM-able  extent  by  the  sud- 
denness, strength,  density,  duration,  and,  possibly,  direction  of  ajiplication.  It 
is  not  necessary  for  us  to  consider  how  each  special  form  of  irritant  is  affected 
by  these  conditions ;  it  will  be  more  instructive  for  us  to  study  how  different 
irritants  alter  the  irritability  of  nerve  and  muscle,  and  the  relation  of  irri- 
tability to  the  state  of  excitation. 

The  power  to  irritate  is  intimately  connected  with  the  power  to  heighten 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       65 

ii'ritability — for  ii  coiulition  of"  hcij2;htened  irritability  is  difficult  to  distin- 
guisjj  tVoiii  a  state  of  excitation.  The  irritability  of  cell-protoplasm  is  very 
dependent  upon  its  physical  and  chemical  constitution,  and  even  slight  altera- 
tions of  this  constitution,  such  as  may  be  induced  by  various  irritants, 
will  modify  the  finely  adjusted  molecular  structure  upon  which  the  normal 
response  to  irritants  depends.  If  this  change  be  in  the  direction  of  increased 
irritability,  the  result  may  be  irritation.  But  we  must  defer  the  discussion  of 
the  relation  of  irritability  to  irritation  until  we  have  considered  the  conditions 
upon  which  the  irritability  of  nerve  and  muscle  depends.  These  conditions 
ciiu  be  best  studied  in  connection  with  the  influences  which  modify  them — 
namely : 

(a)  Irritants. 

{h)  Influences  which  favor  the  maintenance  of  the  normal  physiological 
condition. 

(c)  The  effects  of  functional  activity. 

(«)  The  Influence  of  Irritants  upon  the  Irritability  of  Nerve  and  3Iuscle. — 
Effect  of  llechanical  Agencies. — A  sudden  blow,  pinch,  twitch,  or  cut  excites 
a  nerve  or  muscle.  All  have  experienced  the  effect  of  a  mechanical  stimulation 
of  a  sensory  nerve,  through  accidental  blow\s  on  the  ulnar  nerve  where  it  passes 
over  the  elbow,  "  the  crazy  bone."  The  amount  of  mechanical  energy  required 
to  cause  a  maximal  excitation  of  an  exposed  motor  nerve  of  a  frog  is  estimated 
by  Tigerstedt^  to  be  7000  to  8000  milligrammillimeters,  which  would  corre- 
spond roughly  to  a  weight  of  0.500  gram  falling  fifteen  millimeters — at  least 
a  hundred  times  less  energy  than  that  given  out  by  the  muscles  in  response  to 
the  nerve-impulse  developed.  Such  stimuli  can  be  repeated  a  great  many 
times,  if  not  given  at  too  short  intervals,  without  interfering  with  the  activity 
of  the  nerve.  A  nerve  can  be  irritated  thirty  to  forty  times,  at  intervals  of 
three  to  four  minutes,  by  blows  from  a  weight  of  0.485  gram,  falling  1  to  20 
millimeters,  the  contractions  of  the  muscle,  weighted  with  30  to  50  grams, 
varying  from  minimal  to  from  3  to  4  millimeters  in  height.  Rapidly  following 
light  blows  or  twitches  applied  to  a  motor  nerve,  by  the  tetanomotor  of  Heiden- 
hain  or  Tigerstedt,  excite  a  series  of  contractions  in  the  corresponding  muscles 
which  fuse  more  or  less  into  a  form  of  continuous  contraction,  known  as 
tetanus. 

Mechanical  applications  to  nerve  and  muscle  first  increase  and  later  lessen 
and  destroy  the  irritability.  Thus  pressure  gradually  applied  first  increases 
and  later  reduces  the  power  to  respond  to  irritants.  Stretching  a  nerve  acts  in 
a  similar  way,  for  this  also  is  a  form  of  pressure ;  as  Valentin  said,  the  stretch- 
ing causes  the  outer  sheath  of  the  nerve  to  compress  the  myelin,  and  this  in 
turn  to  compress  the  axis-cylinder.  Tigerstedt  states  :^  "  From  a  tension  of 
0  up  to  20  grams  the  irritability  of  the  nerve  is  continually  increased,  but 
it  lessens  as  soon  as  the  weight  is  further  increased." 

Surgically  the  stretching  of  nerves  is  sometimes  employed  to  destroy  their 

'"Studien  iiber  mechanische  Nervenreizung,"  Acta  Sodetati's  Scientiarum  Fennicce,  1880, 
lorn.  xi.  p.  32.  ^  Op.  cit,  p.  43. 


66  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

excitability.  Slight  stretching  heightens  the  excitability  and  even  (juite  vigor- 
ous stretching  has  only  a  ternjxjrary  depressing  effect  unless  it  be  carried  to 
the  point  of  doing  positive  injury  to  the  axis-cylinder,  and  of  causing  degen- 
eration. As  nerves  have  the  power  to  regenerate  tiny  may  recover  from  even 
such  an  iiijury. 

The  irritability  of  muscles  is  likewise  increased  by  moderate  stretching  and 
destroyed  if  it  be  excessive.  Thus  slight  stretching  produced  by  a  weight 
causes  a  muscle  to  respond  more  vigorously  to  irritants.  Similarly  tension  of 
the  muscles  of  the  leg,  produced  by  slight  over-flexion  or  extension,  makes 
them  more  irritable  to  reflex  stimuli,  as  in  the  case  of  the  knee-jerk  and  ankle- 
clonus.  Tension  must  be  very  marked  to  permanently  alter  the  irritability  of 
the  mascles. 

Effect  of  Temperature. — Changes  in  temperature,  if  sudden  and  extreme, 
irritate  nerv^es  and  muscles.  If  the  nerve  or  muscle  be  quickly  frozen  or 
plunged  into  a  hot  fluid  it  will  be  excited  and  the  muscle  be  seen  to  contract 
The  cause  of  the  irritation  has  been  attributed  to  mechanical  or  chemical 
alterations  produced  by  the  change  of  temperature.  The  ulnar  nerve  at  the 
elbow  is  excited  if  the  part  be  dipped  into  ice-water  and  allowed  to  remain 
there  until  the  cold  has  had  time  to  penetrate ;  as  is  proved  by  the  fact  that  in 
addition  to  the  sensations  from  the  skin,  pain  is  felt  which  is  attributed  by  the 
subject  of  the  experiment  to  the  region  supplied  by  the  nerve.  As  the  effect 
of  the  cold  becomes  greater  the  pain  is  replaced  by  numbness,  both  the  irrita- 
bility and  power  of  conduction  of  the  nerve  being  reduced.  Gradual  cooling 
of  motor  nerves  or  muscles,  and  gradual  heating,  even  to  the  point  of  death 
of  the  tissue,  fails  to  excite  contractions.  It  is  stated  that  if  a  frog  whose 
brain  has  been  destroyed  is  placed  in  a  bath  the  temperature  of  which  is  very 
gradually  increased,  the  heating  may  be  carried  so  far  as  to  boil  the  frog  without 
active  movements  having  been  called  out.  If  a  muscle  be  heated  to  45°  C. 
for  frogs  and  50°  C.  for  mammals,  it  undergoes  a  chemical  change,  which  is 
accompanied  by  a  form  of  shortening  different  from  the  contraction  induced  by 
irritants.  This  form  of  contraction,  though  extensive,  is  feeble  and  is  asso- 
ciated with  a  stiffening  of  the  muscle,  known  as  ric/or  oalork. 

In  general  it  may  be  said  that  raising  the  temperature  above  the  usual  tem- 
perature of  the  animal  increases,  \vhile  cooling  decreases  the  irritability  of  the 
nerves  and  muscles.  Cold,  unless  excessive  and  long  continued,  though  it 
temporarily  suspends  does  not  destroy  the  irritability,  while  heat,  if  at  all  great, 
so  alters  the  chemical  constitution  of  the  cell-protoplasm  as  to  destroy  its  life. 

The  higher  the  temperature,  the  more  rapid  the  chemical  changes  of  the 
body  and  the  less  its  power  of  resistance ;  low  tem])erature,  on  the  other  hand, 
slows  chemical  processes  and  increases  the  endurance.  It  is  noticeable  that 
nerves  and  muscles  remain  irritable  much  longer  than  ordinarily  in  case  the 
body  l)e  cooled  before  their  removal.  In  the  case  of  a  mammal  the  irritability 
may  last  from  six  to  eight  hours  instead  of  two  and  a  half,  while  in  the  case 
of  frogs  it  may  be  preserved  at  0°  for  ten  days,  although  at  summer  heat  it  lasts 
onlv  twenty-four  hours.     In  the  case  of  frogs  which  have  been  kept  at  a  low 


GENERAL    PHYSIOLOGY   OF  MUSCLE  AND    NERVE.       67 

temperature  the  irritahility  becomes  abnormally  high  when  they  are  warmed 
to  ordinary  room-teniiKTatiirc 

Effecl  of  Chemicak  and  iJrugs. — The  activity  of  nerve  and  muscle  proto- 
plasm is  markedly  influenced  by  even  slight  changes  in  its  constitution.     If 
a  nerve  or  muscle  be  allowed  to  lie  in  a  liquid  of  a  different  constitution  from 
its  own  fluid,  and  especially  if  such  a  liquid  be  injected  into  its  blood-vessels, 
an  interchange  of  materials  takes  place  which  results  in  an  alteration  of  the 
constitution  of  the  tissue,  and  a  change  in  its  irritability.     Indeed,  the  only 
solutions  which  fail  to  alter  the  irritability  are  those  which  closely  resemble 
serum  and  lymph.     Fluids  having  other  than  the  normal  percentage  of  salts 
have  a  marked  effect,  while  the  absence  of  proteids  appears  to  have  little 
influence  unless  continued  for  a  considerable  time.    These  facts  have  been  most 
clearly  demonstrated  in  experiments  upon  the  nature  of  fluids  essential  to  the 
maintenance  of  the  activity  of  isolated  heart  muscle.     Most  drugs  and  chemicals 
capable  of  influencing  the  irritability  of  nerves  first  increase  and  later  destroy 
the  irritability.     It  is  said  that  sensory  fibres  are  less  susceptible  to  chemical 
stimulation  than  motor,  but  this  is  not  certain.     If  the  change  in  the  chemical 
condition  of  the  nerve  or  muscle  be  a  rapid  one,  it  is  usually  accompanied  by 
the  phenomenon  of  excitation  ;  if  more  gradual,  the  irritability  alone  is  altered. 
The  simple  withdrawal  of  water  from  a  motor  nerve,  by  drying,  or  by  strong 
solutions  of  neutral  alkaline  salts,  urea,  glycerin,  etc.,  causes  first  an  increase 
and  later  a  decrease  and  loss  of  irritability.     The  increase  of  irritability  is 
frequently  accompanied  by  active  irritation,  the  muscle  in  connection  with  the 
nerve  showing  rapid  irregular  contractions  as  different  fibres  of  the  nerve  are 
one  after  the  other  affected.     If  the  drying  has  not  been  too  long  continued, 
the   irritability  may  be   restored  by  supplying  water.     On  the  other  hand, 
imbibition  of  distilled  water  may,  by  altering  the  relative  amount  of  salts,  or 
from    mechanical   causes,  produce   a  lessening   of  irritability.     If  water  be 
applied  to  the  tissues  by  being  injected  into  the  blood-vessels,  it  first  excites 
contractions   and    later   causes    a   decline   of    irritability.      Veratria,   eserin 
digitalis,  alcohol,  chloroform,  ether,  sublimate,  mineral  acids  (except  phosphoric), 
many  organic  acids,  free  alkalies,  most  salts  of  the  heavy  metals,  destroy  the 
irritability  of  nerves  and  muscles,  as  a  rule  after  first  producing  increased 
excitability.     Carbon  dioxide,  either  because  it  is  an  acid  or  because  of  some 
specific  effect,  acid  potassium  phosphate,  and  lactic  acid,  lessen  the  irritability. 
Neutral  potash  salts,  if  concentrated,  rapidly  kill  but  excite  less  than  do  soda 
compounds.     Many  gases  and  fumes  chemically  irritate  and  kill  nerve  and 
muscle  protoplasm. 

Ammonia,  neutral  salts,  carbon  bisulphide,  and  ethereal  oils  may  destroy 
the  irritability  of  nerves  without  causing  excitation,  at  least  not  sufficiently  to 
produce  visible  contractions  of  the  muscle.  If  directly  applied,  however, 
these  substances  excite  muscles. 

A  sodium-chloride  solution,  of  a  strength  of  6  parts  per  1000  of  distilled 
water,  has  been  called  the  physiological  solution  because  it  was  supposed  to 
have  no  effect  on  the  irritability  of  nerves  and  muscles ;  but  late  experiments 


68  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

have  .shown  that  even  tliis  if  hjnji;  euutiiiued  lirst  iuoreases  and  hiter  deereases 
the  irritability  of  tnusc'le.s.  Tlie  cause  of  this  is,  however,  probably  the  removal 
of  other  salts  whiih  are  essential  to  the  irritability,  or  the  presence  of  carbonic 
acid. 

From  all  these  results  it  becomes  evident  that  the  normal  irritability  of 
nerves  and  muscles  requires  that  a  certain  chemical  constitution  be  maintained, 
and  that  even  slight  variations  from  this  suffice  to  alter,  and  if  continued  to 
destroy,  the  irritability.  Further,  it  is  noticeable  that  in  most  cases  the  first 
step  toward  deterioration  is  a  rise  of  irritability,  which,  if  marked,  is  accom- 
panied by  a  condition  of  irritiition.  If  the  cause  of  the  increase  in  irritability 
and  excitation  be  continued,  sooner  or  later  exhaustion  supervenes,  the  irrita- 
bility lessens,  and  finally  is  lost. 

Effect  of  the  Electnc  Current  upon  3Iasdes. — If  a  constant-battery  current 
of  medium  strength  be  sent  through  a  muscle  for  a  short  time,  the  muscle  will 
give  a  single  short  contraction  at  the  moment  that  the  current  enters  it,  and 
again  when  the  current  leaves  it.  If  a  strong  current  be  used,  the  short 
closing  contraction  may  be  followed  by  a  prolonged  contraction  (Wundt's  closing 
tetanus),  which,  though  gradually  decreasing,  may  last  as  long  as  the  current 
is  closed ;  and  when  the  current  is  broken,  the  usual  opening  contraction  may 
be  likewise  followed  by  a  prolonged  contraction  (Rittcr's  opening  tetanus), 
which  only  gradually  passes  off.  The  closing  contraction  originates  at,  and 
the  closing  continued  contraction  may  be  limited  to,  the  region  of  the  kathode; 
and  the  opening  contraction  originates  at,  and  the  opening  continued  contrac- 
tion may  be  limited  to,  the  region  of  the  anode. 

In  case  a  very  weak  current  is  used,  no  contraction  will  be  observed ; 
nevertheless,  while  the  current  is  flowing  through  the  muscle  it  modifies  its 
condition  ;  a  state  of  latent  excitation  is  produced  at  the  kathode,  which  shows 
itself  in  an  apparent  increase  of  irritability  of  that  part  of  the  muscle.  On 
the  other  hand,  the  irritability  of  the  muscle  at  the  kathode  will  be  found  to 
be  lessened  after  the  withdrawal  of  the  polarizing  current,  because  the  condi- 
tion of  excitation  which  it  causes  fatigues  that  part  of  the  muscle. 

The  effects  of  the  battery  current  at  the  region  of  the  anode  are  just  oppo- 
site to  those  produced  at  the  kathode.  While  the  current  is  flowing,  the  irri- 
tability at  the  anode  is  lessened,  and  when  the  polarizing  current  is  removed, 
irritability  at  the  anode  is  found  to  be  greater  than  it  was  before  the  battery 
current  was  applied. 

The  lessened  irritability  which  is  produced  at  the  anode  during  the  flow 
of  the  battery  current  may  be  shown  by  an  inhibition  of  a  condition  of  exci- 
tation which  may  be  present  at  the  time  that  the  current  is  ap})lied  to  the 
muscle.  For  example,  in  the  case  of  unstriated  muscles,  not  only  does  closing 
the  battery  circuit  never  cause  a  contraction  at  the  anode,  but  if  the  ]>art  of 
the  muscle  exposed  to  the  influence  of  the  anode  happens  to  be  at  the  time  in 
a  condition  of  tonic  contraction,  the  entrance  of  the  current  causes  that  part 
of  the  muscle  to  relax.  The  inhibitory  influence  exerted  by  the  anode,  as  a 
result  of  the  lowering  of  the  irritability,  is  seen  to  a  remarkable  degree  in  its 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.       69 

eifect  upon  the  heart.'  If  tlie  anode  rest  on  the  ventricle  of  the  frog's  heart, 
and  the  kathode  at  some  indifferent  point,  relaxation  is  seen  in  the  region  of  the 
anode  with  each  systole  of  the  ventricle.  Inasmuch  as  the  rest  of  the  ventricle 
contracts,  the  pressure  of  the  blood  causes  the  wall  of  the  ventricle  to  bulge 
out,  anil  make  a  little  vesicle  at  the  region  of  the  anode.  A  similar  inhibitory 
intlu(Mice  may  be  observed  upon  an  ordinary  striated  muscle  at  the  point  of 
ap[)lication  of  the  anode,  if  it  be  in  a  condition  of  tonic  contraction  when  the 
battery  current  is  sent  into  it.  During  the  flow  of  the  constant  current  through 
a  muscle,  the  irritability  is  increased  in  the  region  of  the  kathode  and  decreased 
in  the  region  of  the  anode.  When  the  current  is  withdrawn  from  the  muscle, 
on  the  other  hand,  the  irritability  of  the  kathode  is  found  to  be  decreased,  and 
at  the  anode  to  be  increased. 

Effect  of  the  Eleetiic  Current  upon  Nerves. — The  polarizing  eifects  of  a  con- 
tinuous constant  current  are  the  same  upon  a  nerve  as  upon  a  muscle,  with  the 
exception  that  in  the  case  of  the  nerve  the  condition  of  altered  irritability  is 
not  so  strictly  limited  to  the  point  of  application  of  the  anode  and  kathode,  but 
spreads  thence  throughout  the  part  of  the  nerve  between  the  two  electrodes,  the 
intrapolar  region,  as  it  is  called,  and  for  a  considerable  distance  into  the  parts 
of  the  nerve  through  which  the  current  does  not  flow,  i.  e.  the  extrapolar  region. 
The  term  electrotouus  has  been  applied  to  the  effects  of  battery  currents  on 
nerves  and  muscles,  and  includes  two  sets  of  changes — (1)  physiological,  mani- 
fested by  the  alterations  of  irritability  which  we  are  considering;  (2)  physical, 
exhibited  in  changes  of  the  electrical  condition  of  the  tissue.  The  most  im- 
portant work  on  the  influence  of  the  constant  current  on  the  irritability  of  nerves 
was  done  by  Pfliiger.  He  ascertained  the  electrotonic  effects  of  the  polarizing 
current  to  be  most  vigorous  in  the  immediate  vicinity  of  the  anode  and  kathode, 
and  to  spread  thence  in  both  directions  along  the  nerve.  He  called  the  change 
produced  in  the  nerve  in  the  region  of  the  anode  "  anelectrotonic,"  and  the 
condition  itself  "  anelectrotonus,"  while  the  change  at  the  kathode  was  termed 
"  katelectrotonic,"  and  the  condition  "  katelectrotonus."  The  same  names  are 
given  to  the  effects  of  battery  currents  upon  muscles. 

To  test  the  effect  of  a  constant  battery  current  upon  the  irritability  of  a 
nerve,  put  the  nerve  of  a  nerve-muscle  preparation  upon  two  non-polarizable 
electrodes  (A,  K,  Fig.  27)  which  are  placed  at  some  little  distance  apart  and 
at  a  considerable  distance  from  the  muscle.  Connect  these  electrodes  with  a 
battery,  introducing  into  the  circuit  a  key  (k),  which  permits  the  current  to 
be  quickly  thrown  into  or  removed  from  the  nerve,  and  a  commutator  ((7), 
which  allows  the  current  to  be  reversed  and  to  be  sent  through  the  nerve  in 
either  the  ascending  or  descending  direction.  Connect  the  nniscle  with  a  myo- 
graph lever,  arranged  so  as  to  record  the  height  of  tiie  muscle  contractions. 
Then  apply  to  the  nerve  at  some  point  between  the  polarizing  electrodes  and 
the  muscle  a  pair  of  electrodes  (I)  connected  with  the  secondary  coil  of  an 
induction  apparatus,  which  is  placed  near  enough  to  the  primary  coil  to  cause 
excitations  of  medium  strength,  and  introduce  into  the  secondary  circuit  a 
^  Biedermann :  Elektrophysioiogie,  1895,  p.  195. 


70 


A.y  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 


short-circuitiug  key  (N),  by  which  the  closing  sliocks  can  be  prevented  from 
reaching  the  nerve. 

If,  with  this  arrangenjt'ut,  a  breaking  induction  shock  of  medium  strength 
be  given,  the  nerve  will  be  excited,  and  the  height  of  the  muscular  contraction 
which  results  may  be  taken  as  a  test  of  the  irritability  of  the  nerve  at   /. 


Fig.  27.— Method  of  testing  anelectrotonic  and  katelectrotonic  alterations  of  irritability  in  nerves. 

Now  send  the  polarizing  current  through  the  nerve,  in  the  ascending  direction, 
that  is,  with  the  anode  nearer  the  muscle.  At  the  moment  the  current  is 
closed,  if  it  be  of  medium  strength,  a  closing  contraction  will  be  observed ; 
then  comes  a  period  during  which  the  muscle  is  not  contracting  and  the  polar- 
izing current  is  apparently  producing  no  effect  on  the  nerve;  if,  however,  after 
the  current  has  acted  a  short  time,  the  irritability  of  the  nerve  at  the  point 
/  be  again  tested  with  a  breaking  induction  shock,  it  will  be  found  to  be  de- 
creased, on  account  of  the  condition  of  anelectrotonus  which  has  been  induced. 
If  the  key  in  the  polarizing  current  be  then  opened,  the  usual  opening  con- 
traction will  be  recorded.  After  the  polarizing  current  has  been  removed,  the 
condition  of  the  nerve  at  I  can  be  again  tested,  and  it  will  be  seen  that  the 
jrritabilitv  has  returned  to  the  normal,  or  is  even  greater  than  it  was  at  the 
start. 

The  effect  of  the  kathode  on  the  irritability  may  be  tested  in  a  similar  way, 
by  reversing  the  polarizing  current  and  again  sending  it  into  the  nerve.  This 
time  the  current  will  be  descending,  i.  e.  the  kathode  nearest  the  mu.'^cle.  As 
before,  a  closing  contraction  will  be  seen  when  the  circuit  is  made,  but  on  test- 
ing the  irritability  at  /with  an  induction  shock  of  the  same  strength  as  before, 


GENERAL    PHYSIOLOGY    OF  MUSCLE   AND    NERVE.       71 

it  will  be  luiuul  to  he  iiicreuscd,  the  shock  eaiirtiiig-  u  larger  contraction.  On 
opening  the  polarizing  current  the  usual  opening  contraction  will  be  seen,  and 
if  after  the  current  has  been  removed  the  irritability  be  again  t^'.sted,  it  will 
be  found  to  have  returned  to  the  normal,  or  to  be  decrea.sed.  The  changes 
in  irritability  dcscribeil  can  be  ascertained  by  using  mechanical  or  chemical 
stimuli  as  well  as  induction  shocks.  Alterations  of  the  irritability  induced  by 
anelectrotonic  and  katelectrotouic  changes  of  the  nerve-substance  are  to  be 
found  not  only  in  the  part  of  the  nerve  between  the  point  to  which  the  polar- 
izing current  is  applied  and  the  muscle,  but  in  the  extrapolar  region  at  the 
ceutral  end  of  the  nerve,  and  in  the  intrapolar  region.  The  experimental 
evidence  of  this  is  not  so  readily  obtained,  but  there  is  no  doubt  of  the  fact. 
The  effect  of  the  polarizing  current  is  the  greater,  the  better  the  condition 
of  the  nerve;  moreover,  the  stronger  the  current  employed,  the  more  of  the 
nerve  influenced  by  it.  Of  course,  in  the  intrapolar  region  there  is  a  point 
where  the  effect  of  the  anode  to  decrease  the  irritability  comes  into  conflict  with 
the  effect  of  the  kathode  to  increase  it,  and  where,  in  consequence,  the  irrita- 
bility remains  unchanged.  This  indifferent  point  may  be  observed  to  approach 
the  kathode  as  the  strength  of  the  current  is  increased.  The  following  schema 
is  given  by  Pfliiger  to  illustrate  the  way  in  which  the  irritability  is  changed  in 
the  anelectrotonic  and  katelectrotouic  regions  as  the  strength  of  the  current  is 
increased : 


Fig.  28.— Electrotonic  alterations  of  irritability  caused  by  weak,  medium,  and  strong  battery 
currents :  A  and  B  indicate  the  points  of  application  of  the  electrodes  to  the  nerve,  A  being  the  anode, 
B  the  kathode.  The  horizontal  line  represents  the  nerve  at  normal  irritability ;  the  curved  lines  illus- 
trate hovir  the  irritability  is  altered  at  different  parts  of  the  nerve  with  currents  of  different  strengths. 
Curve  2/1  shows  the  effect  of  a  weak  current,  the  part  below  the  line  indicating  decreased,  and  that  above 
the  line  increased  irritability,  at  x^  the  curve  crosses  the  line,  this  being  the  indifferent  point  at  which 
the  katelectrotouic  effects  are  compensated  for  by  anelectrotonic  effects :  if  gives  the  effect  of  a  stronger 
current,  and  y^,  of  a  still  stronger  current.  As  the  strength  of  the  current  is  increased  the  effect  becomes 
greater  and  extends  farther  into  the  extrapolar  regions.  In  the  intrapolar  region  the  indifferent  point  is 
seen  to  advance  with  increasing  strengths  of  current  from  the  anode  toward  the  kathode. 

As  in  the  case  of  the  muscle,  so  of  the  nerve,  the  constant  current  leaves 
behind  it  important  after-effects.  In  general  it  may  be  stated  that  wherever 
during  the  flow  of  the  current  the  irritability  is  increased,  there  is  a  decrease 
of  irritability  immediately  after  the  removal  of  the  current,  and  vice  versa. 
When  the  current  is  withdrawn  from  the  nerve,  the  irritability  in  the  region 
of  the  kathode  is  lowered,  and  in  the  region  of  the  anode  raised.  It  must  be 
added,  however,  that  the  decrease  of  irritability  seen  at  the  kathode  gradually 
passes  over  into  a  second  increase  of  irritability,  while  the  increase  seen  at  the 


72  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

anode  upon  the  reiiioval  of  the  current  continues  a  considerable  time  and  is 
not  reconverted  to  a  decrease;  therefore  the  total  after-effect  is  an  increase  of 
irritability. 

The  lact  that  when  the  current  is  closed  the  irritation  starts  from  the  kathode, 
and  when  the  current  is  opened  from  the  anode,  may  well  be  associated  with  the 
chauires  in  irritability  wiiich  take  place  at  the  kathode  and  anode  upon  the  closing 
and  the  ojicning  of  the  current.  The  setting  free  of  an  irritation  appears  to  be 
associated  only  with  an  increase  of  irritability.  When  the  current  is  closed  the 
establishment  of  the  condition  of  katelectrotonus  is  accompanied  by  a  rise  of 
irritai)ilitv  at  the  kathode,  and  when  the  current  is  opened  the  cessation  of  the 
condition  of  anelectrotonus  is  likewise  accompanied  by  a  rise  of  irritability.  In 
the  first  case  the  irritability  rises  from  the  normal  to  something  above  the 
normal,  and  in  the  second  case  the  irritability  rises  from  the  condition  of 
decreased  irritability  up  to  something  above  the  normal  irritability.  The  change 
from  the  normal  to  the  anelectrotonic  condition  of  decreased  irritability,  or 
from  the  katelectrotonic  condition  of  increased  irritability  down  to  normal 
irritability,  does  not  irritate.  As  has  often  been  said,  it  is  hard  to  distinguish 
between  increase  of  irritability  and  irritation. 

The  effects  produced  by  battery  currents  upon  irritability  are  found  to  be 
associated  with  peculiar  alterations  in  the  electrical  condition  of  nerves  and 
muscles.  The  relation  is  a  suggestive  one,  but  cannot  be  taken  as  a  definite 
explanation  of  the  changes  of  irritability. 

Efect  of  Frequency  of  Application  of  the  Stimulus  on  Irritability. — We  have 
seen  that  influences  which  act  as  irritants  may  also  have  an  effect  upon  the  irri- 
tabilitv  of  the  nerve  or  muscle.  In  order  to  produce  this  change  they  must  be 
as  a  rule  powerful,  or  act  for  a  considerable  time.  Nevertheless,  in  the  case 
of  muscles,  at  least,  even  a  weak  irritant  of  short  duration,  if  repeated  fre- 
quently, tends  to  heighten  irritability.  For  example,  if  a  muscle  be  stimulated 
bv  separate  weak  induction  shocks  at  long  intervals,  the  effect  of  each  shock  is 
slight,  and  the  change  produced  by  it  is  compensated  for  by  restorative  pro- 
cesses which  occur  within  the  living  protoplasm  during  the  following  interval 
of  rest,  and  each  of  the  succeeding  irritations  finds  the  mechanism  in  much  the 
same  condition  ;  if,  however,  the  shocks  follow  each  other  rapidly,  each  stimu- 
lation leaves  an  after-effect  which  may  have  an  influence  upon  the  effectiveness 
of  the  stimulus  following  it.  As  a  result  of  this,  induction  shocks  too  feeble  to 
excite  contractions  may,  if  frequently  repeated,  after  a  little  time  cause  a  visible 
movement,  and  shocks  of  medium  strength,  if  given  at  short  intervals,  may 
each  cause  a  larger  contraction  than  its  predecessor,  until  a  certain  height  of 
contraction  has  been  reached,  beyond  which  there  is  no  further  increase  pos- 
sible. It  is  not  known  whether  the  irritability  of  nerves  is  similarly  increased, 
nor  is  it  known  whether  physiological  stimuli  exert  such  an  influence.  We 
shall  consider  these  so-called  "  staircase  contractions  "  more  carefully  later  (see 
page  110).  When  irritations  follow  each  other  very  rapidly,  the  whole  cha- 
racter of  the  contraction  is  changed,  and  the  muscle,  instead  of  making  rapid 
single  contractions,  enters  into  the  condition  of  apparently  continuous  contrac- 


GENERAL    PHYSIOLOGY    OF  MUSCLE   AND    NERVE.       73 

tion  Uiiowii  ;i8  tetanus,  diiriji};-  which  it  shurtfiis  (•(tn>i(lerably  more  thuii  it  cl(X'.s 
when  inakiiijr  single  contractions.  Increase  in  irritability  plays  only  a  com- 
paratively small  ])art  in  the  production  of  tiiis  remarkable  ])henomenon,  which 
we  shall  study  more  ciiref'ully  when  we  come  to  the  mechanical  ])r()blems 
involved  in  muscular  contractions. 

Rapidly  repeated  stimuli,  though  at  first  favorable  to  activity  of  a  muscle, 
soon  exert  an  unfavorable  influence  by  causing  the  h'ssenod  irritability  which 
is  associated  with  fati}j:ue. 

{h)  Influences  which  favor  the  Maintenance  of  the  Normal  FhymAofjical 
Condition  of  Nerve  and  Muscle. — Effect  of  Blood-sujypl y  on  Nerve  and  Muscle. 
— The  vascular  system  is  a  i)ath  of  communication  between  the  several  organs 
and  tissues,  and  the  circulating  blood  is  a  medium  of  exchange.  Tlie  blood 
carries  nutritive  materials  from  the  digestive  organs  and  oxygen  from  the 
lungs  to  all  the  tissues  of  the  body,  and  it  transports  the  waste  materials  which 
the  cells  give  off  to  the  excretory  organs.  In  addition  to  these  functions  it 
has  the  power  to  neutralize  the  acids  which  are  produced  by  the  cells  during 
action,  and  so  maintain  the  alkalinity  essential  to  the  life  of  the  cell ;  it  su})- 
plies  all  parts  with  moisture ;  by  virtue  of  the  salts  which  it  contains,  it  secures 
the  imbibition  relations  which  are  necessary  to  the  preservation  of  the  normal 
chemical  constitution  of  the  cell-protoplasm  ;  it  distributes  the  heat,  and  so 
equalizes  the  temperature  of  the  body ;  finally,  in  addition  to  these  and  other 
similar  functions,  it  is  itself  the  seat  of  important  chemical  changes,  in  which 
the  living  cells  which  it  contains  play  an  active  part.  It  is  not  strange  that 
such  a  fluid  should  exert  a  marked  influence  upon  the  irritability  of  the  nerves 
and  muscles.  Since  the  metabolism  of  muscles  is  best  understood,  we  will 
first  consider  the  importance  of  the  circulation  to  the  muscle.  Muscles,  even 
in  the  so-called  state  of  rest,  are  the  seat  of  chemical  changes  by  which  energy 
is  liberated,  and  when  they  are  active  these  changes  may  be  very  extensive. 
If  the  cell  is  to  continue  its  work,  it  must  be  at  all  times  in  receipt  of  mate- 
rials to  replenish  the  continually  lessening  store  of  energy-holding  compounds; 
moreover,  as  the  setting  free  of  energy  is  largely  a  process  of  oxidation,  a  free 
supply  of  oxygen  ls  likewise  indispensable  to  action.  These  oxidation  pro- 
cesses result  in  the  formation  of  waste  products — such  as  carbon  dioxide,  water, 
lactic  acid — and  these  are  injurious  to  the  muscle  protoplasm,  and  if  allowed 
to  accumulate  would  finally  kill  it.  Of  the  services  Mhich  the  blood  renders 
to  the  muscle  there  are,  therefore,  two  of  paramount  importance,  viz.  the 
bringing  of  nutriment  and  oxygen  and  the  removal  of  waste  matter  and  sur- 
plus energy. 

A  classical  experiment  illustrating  the  effect  of  depriving  tissues  of  blood 
is  that  of  Stenson,  which  consists  in  the  closure  of  the  abdominal  aorta  of  a 
warm-blooded  animal  by  a  ligature,  or  by  compression.  In  the  case  of  a 
rabbit,  for  example,  the  blood  is  shut  off,  not  only  from  the  limbs  but  from  the 
lower  part  of  the  spinal  cord.  The  effect  is  soon  manifested  in  a  complete 
paralysis  of  the  lower  extremities,  sensation  as  well  as  power  of  voluntary  and 
reflex  movements  being  lost.     The  paralysis  is  due,  in  the  first  instance,  to  the 


74  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

I0&5  of  fuuction  of  tlie  uerve-celLs  iu  the  cord  by  which  the  muscles  are  nor- 
mally excited  to  action.  Later,  however,  the  nerves  and  muscles  of  the  limbs 
lose  their  irritability.  Of  the  peripheral  mechanisms  the  motor  nerve-ends 
are  found  to  succumb  before  the  nerves  and  muscles.  This  is  shown  by  the 
fact  that  although  the  muscles  are  still  capable  of  responding  to  direct  irrita- 
tion, they  are  not  aflPected  by  stimuli  applied  to  the  nerve,  although  the  nerve 
at  the  time,  to  judge  from  electrical  changes  which  occur  when  it  is  excited, 
is  still  irritable.  Since  the  nerve  and  muscle  are  irritable,  the  lack  of  response 
must  be  attributed  to  the  nerve-ends.  The  response  to  indirect  stimulation 
(/.  e.  excitation  of  a  muscle  by  irritating  its  nerve)  is  lost  in  about  twenty 
minutes,  while  the  irritability  of  the  muscle,  as  tested  by  direct  excitation,  is 
not  lost  for  four  or  five  hours.  Iu  this  as  in  so  many  instances  the  loss  of 
irritability  of  the  muscle  is  due  primarily  to  the  disturbance  of  the  respira- 
tion of  the  muscle.  Of  the  substances  supplied  to  the  muscle  by  the  blood, 
oxygen  is  one  the  want  of  which  is  soonest  felt.  The  muscle  contains  within 
itself  a  certain  store  of  oxygen,  but  one  which  is  by  no  means  equal  to  the 
amount  of  oxidizable  substances.  Of  this  oxygen,  that  which  is  in  the  least 
stable  combinations,  and  which  is  available  for  immediate  needs,  is  soon 
exhausted.  A  continual  supply  of  oxygen  is  required  even  for  the  chem- 
ical changes  which  occur  iu  the  quiet  muscle.  Of  the  waste  substances  which 
the  blood  removes  from  the  cell,  carbon  dioxide  is  the  one  which  accumu- 
lates most  rapidly  and  is  the  first  to  lessen  the  irritability.  Lactic  acid  and 
waste  products  from  the  breaking  down  of  nitrogenous  materials  of  the  cell 
are  also  injurious. 

The  dependence  of  nerve-fibres  upon  the  blood-supply  is  by  no  means  so 
well  understood.  The  nerve-fibre  is  a  branch  of  a  nerve-cell,  and  it  seems  as 
if  the  nourishment  of  the  fibre  was  largely  dependent  upon  that  of  the  cell 
(see  Fatigue  of  Xerve,  p.  79).  Nevertheless,  the  nerve-fibre  requires  a  con- 
stant supply  of  blood  for  the  maintenance  of  its  irritability.  The  irritability 
of  the  nerve  cannot  long  continue  without  oxygen,  and  a  nerve  which  has 
been  removed  from  the  i)o(ly  is  found  to  remain  irritable  longer  in  oxygen 
than  in  air,  and  in  air  than  in  an  atmosphere  containing  no  oxygen.  Waste 
products  liberated  by  active  muscles  have  a  deleterious  effect  on  nerves ; 
whether  such  substances  are  produced  in  the  nerves  themselves  will  be  con- 
sidered later. 

The  efficacy  of  the  blood  to  preserve  the  irritability  is  to  be  seen  in  such 
experiments  as  those  of  Ludwig  and  Schmidt;'  they  succeeded  in  maintaining 
the  artificial  circulation  of  defibrinated,  aerated  blood  through  the  muscles 
of  a  dog,  and  kept  them  irritable  for  many  hours  after  death  of  the  animal. 
If  such  an  experiment  is  to  be  successful,  the  blood  must  be  maintained  at  the 
normal  temperature,  be  plentifully  supplied  with  oxygen,  and  be  kept  as  free 
from  carbon  dioxide  as  possible.     Von  Frey  ^  made  an  elaborate  experiment  of 

*  Sitzungsberichte  der  math.-phys.  CUutse  der  k.  sacks.  Gesellschaft  der  Wissenschfiffen,  vol.  xx.,  1868. 

*  "  Versiiche  iiber  den  Stoffwechsel  des  Muskeb,"  Archiv  fur  Anatomie  und  Physiologic, 
1885;  physiologische  Abtheilung,  p.  533. 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       75 

this  nature.  A  dog  was  killed,  the  body  was  cut  in  halves,  ami  the  aorta  aud 
inferior  vena  cava  were  quickly  connected  with  an  apparatus  for  pumping  the 
blood  at  a  regular  rate  through  the  hind  part  of  the  bcjdy.  Before  the  blood 
entered  the  arteries  it  passed  through  coils  in  which  it  was  warmed  to  the  nor- 
mal temperature,  and  an  artiticial  lung,  where  it  received  a  supply  of  oxygen 
and  was  relieved  of  its  carbon  dioxide.  Under  these  conditions  the  muscles 
were  kept  alive  for  more  than  seven  hours,  and  so  far  retained  their  normal 
condition  that  throughout  this  period  they  were  able  to  respond  to  stimuli 
sent  to  them  through  their  nerves  aud  contract  with  sufficient  vigor  to  raise  a 
considerable  weight.  H.  N.  Martin  ^  made  a  similar  experiment  on  the  heart 
of  a  dog.  The  heart  and  lungs  were  isolated  from  the  rest  of  the  b<jdy,  the 
lieart  was  fed  with  defibrinated  blood  from  a  Mariotte's  flask,  and  the  lungs 
were  supplied  with  air  by  an  artificial  respiration  apparatus.  The  heart,  which 
was  kept  moist  and  at  the  normal  temperature,  contirmed  to  beat  for  four  hours 
and  more. 

Normally  the  blood-supply  to  the  muscle  is  varied  according  to  its  needs. 
When  the  muscle  is  stimulated  to  action,  its  blood-vessels  are  at  the  same  time 
dilated  so  that  it  receives  a  free  supply  of  blood.^  Moreover,  if  muscular  work 
is  extensive,  the  heart  beats  faster  and  the  respiratory  movements  are  quicker, 
so  that  a  larger  amount  of  oxygen  is  provided  and  the  carbon  dioxide  is 
removed  more  rapidly.  The  importance  of  the  blood-supply  to  a  muscle  can 
be  best  understood  if  we  consider  it  in  relation  to  the  eflPects  of  fatiguing  work 
upon  the  muscles.  The  relation  of  other  substances  in  the  blood  to  the 
needs  of  the  muscle  can  be  best  considered  together  with  the  chemistry  of 

the  muscle. 

Effect  of  Separation  from  the  Central  Net'vous  System.— If  a  motor  nerve  be 
cut,  or  if  some  part  of  it  be  so  injured  that  the  fibres  lose  their  power  of  conduc- 
tion, the  portion  of  the  nerve  thus  separated  from  the  central  nervous  system 
sooner  or  later  completely  degenerates.  Each  of  the  motor  nerve-fibres  is  a 
branch  of  a  motor  cell  in  the  anterior  horns  of  the  spinal  cord.  These  nerve- 
cells  are  supposed  to  govern  the  nutrition  of  their  processes,  though  how  a 
microscopic  cell  can  thus  influence  a  nerve-fibre  a  meter  or  so  long  is  by  no 
means  clear.  Soon  after  the  nerve  is  separated  from  its  cell  it  exhdnts  an 
increase  of  excitabilitv  near  the  point  of  section,  and  this  change  progresses 
down  the  fibre  toward  the  periphery.  The  rule  that  the  change  in  irritability 
progresses  centrifugallv  along  the  motor  nerves  is  known  as  the  Ritter-Yalli 
law.  The  increase  is  soon  followed  by  a  decrease  of  irritability.  In  the  case 
of  mammalian  nerves  loss  of  irritability  may  be  complete  at  the  end  of  three 
or  four  days,  but  the  nerves  of  cold-blooded  animals  may  retain  their  irri- 
tabilitv  for  several  weeks.  The  immediate  cause  of  the  loss  of  irritability  is 
the  change  in  the  chemical  and  physiological  structure  of  the  axis-cylinder. 
The  degenerative  changes  result  finally  in  the  complete  destruction  of  the 
nerve-fibres,  and  involve  the  motor  end-organs  as  well,  but  do  not  imme- 

1  Stmlip,  from  the  Biological  Laboratory  of  Johns  Hopkins  University,  1882,  vol.  ii.  p.  188. 
»  Sczelkow:  Sitzungsber.  d.  k.  Akad.  Wien,  1862,  vol.  xlv.  Abth.  1. 


76  ^^V  AMERICAN  TEXT-BOOK   OF  PHYSIOLOGY. 

diately  iuvatlt-  the  luusele,  which  iimy  be  considered  a  proof"  that  nerve  and 
muscle  j)rotopla.siu  are  not  continuous. 

Though  wo  ininietliate  cliangc  in  the  structure  of  the  muscle  is  ohservahle, 
the  irritability  ol"  the  muscle  soon  begins  to  alter.  At  the  end  of  a  fortnight 
the  irritability  of  the  muscle  for  all  forms  of  stimuli  is  lessened.  From  this 
time  on,  the  irritability  gradually  undergoes  a  remarkable  change,  the  excita- 
bility for  mechanical  irritants  and  for  direct  battery  currents  beginning  to 
increase,  but  the  power  to  respond  to  electric  currents  of  short  duration, 
as  induction  shocks,  continuing  to  lessen ;  indeed,  the  reactions  of  the 
muscle  appear  to  take  on  more  of  the  character  of  those  of  smooth  muscle- 
fibres.  The  condition  of  increasing  irritability  to  direct  battery  currents  and 
mechanical  irritants  reaches  its  maximum  by  the  end  of  the  seventh  week, 
and  from  that  time  on  the  power  to  respond  to  all  forms  of  stimuli  lessens, 
the  excitability  being  wiiolly  lost  by  the  end  of  the  seventh  or  eighth  month. 
During  the  stage  of  increased  excitability  fibrillary  contractions  are  often 
observed. 

As  in  the  case  of  a  nerve  so  in  the  muscle  the  loss  of  irritability  is  due  to 
degenerative  changes  which  gradually  lead  to  the  destruction  of  the  muscle 
protoplasm.  The  cause  of  the  change  in  the  muscle  is  still  a  matter  of  doubt, 
some  regarding  it  as  due  to  the  absence  of  some  nutritive,  trophic  influence 
from  the  central  nervous  system,  while  others  consider  it  to  be  the  result  of 
circulatory  disturbances,  consequent  upon  the  lack  of  a  proper  regulation  of 
the  blood-supply,  due  to  the  division  of  the  vaso-motor  nerves.  As  regards 
the  latter  view,  it  may  be  said  that  muscles  whose  vaso-motor  nerves  are  intact, 
the  vessels  being  innervated  through  other  nerves  than  those  which  supply  the 
muscle-tissue  proper,  as  is  the  case  with  some  of  the  facial  muscles,  undergo 
similar  changes  in  irritability  when  their  motor  nerves  are  cut.  As  regards 
the  former  view,  it  may  be  said  that  if  the  muscles  be  artificially  excited,  as  by 
electric  stimuli,  and  thus  are  exercised  daily,  the  coming  on  of  degeneration  can 
be  at  least  greatly  delayed.  The  question  as  to  whether  the  anabolic  processes 
within  the  nmscle-cell  are  dependent  on  the  central  nervous  system,  in  the  sense 
of  there  being  specific  trophic  influences  sent  from  the  nerve-cells  to  the  mus- 
cles, is  still  under  discussion  and  need  not  be  considered  further  in  this  place. 
Without  doubt  the  reflex  tonus  impulses  which  during  waking  hours  are  all 
the  time  coming  to  the  muscles  are  productive  of  katabolic  changes  and, 
indirectly  at  least,  favor  anabolism. 

(c)  Effect  of  Infiuences  which  remdt  from  the  Functional  Actimty  of  Nei^ea 
and  Muscles. — Fatigue  of  Muscles. — The  condition  of  muscular  fatigue  is  cha- 
racterized by  lessened  irrital)ility,  decrease  in  the  rate  and  vigor  with  which 
the  muscle  conti-acts  and  liberates  energy,  and  a  still  greater  decrease  in  the 
rate  with  which  it  relaxes  and  recovers  its  normal  form.  In  a  sense,  whatever 
induces  such  a  state  can  be  said  to  cause  fatigue,  but  it  is  ])erhaps  best  to 
restrict  the  term  to  the  form  of  fatigue  which  is  produced  by  excessive 
functional  activity.  The  cause  of  exhaustion  which  results  from  over- 
work is  much   the  same  as  the  cause  of  the   loss  of  irritability  and  power 


GENERAL   PHYSIOLOGY   OF  MUSCLE   AND    NERVE.       11 

which  follows  the  cutting  ott'  of  the  blood-siii)i)ly.  The  working  cell  liberates 
energy  at  the  expense  of  its  store  of  nutriment  and  oxygen,  and  through  oxi- 
dation processes  forms  waste  products  which  arc  poisonous  to  its  protoplasm. 
The  fatigue  which  results  from  functional  activity  has,  therefore,  a  twofold 
cause,  the  decreiise  in  energy-holding  compounds  and  the  accumulation  of 
poisonous  waste  matters. 

It  is  evident  that  the  leno;th  of  time  that  the  cell  can  continue  to  work  will 
dej)end  very  much  upou  the  rapidity  with  which  the  energy-holding  exijlosive 
compounds  are  formed  by  the  cell-protoplasm  and  the  waste  products  are 
excreted.  If  a  muscle  is  made  to  contract  vigorously  and  continuously,  as 
when  a  heavy  weight  is  held  up,  fatigue  comes  quickly  ;  on  the  other  hand,  a 
muscle  may  be  contracted  a  great  many  times  if  eacii  contraction  is  of  short 
duration  and  considerable  intervals  of  rest  intervene  between  the  succeeding 
contractions.  The  best  illustration  of  this  is  the  heart,  which,  though  making 
contractions  in  the  case  of  man  at  the  rate  of  seventy  or  more  times  a  minute, 
is  able  to  beat  without  fatigue  throughout  the  life  of  the  individual.  Each 
of  the  vigorous  contractions,  or  systoles,  is  followed  by  an  interval  of  rest, 
diastole,  during  which  the  cells  have  time  to  recuperate.  The  same  is  true  of 
the  skeletal  muscles.  It  was  found  in  an  experiment  that  if  a  muscle  of  the 
hand,  the  abductor  incUcis,  were  contracted  at  regular  intervals,  a  weight  being 
so  arranged  that  it  was  lifted  by  the  finger  each  time  the  muscle  shortened,  a 
light  weight  could  be  raised  at  the  rate  of  once  a  second  for  two  hours  and  a 
half,  i.  e.  more  than  9000  times,  without  any  evidence  of  fatigue.  If,  however, 
the  weight  was  increased,  which  required  a  greater  output  of  energy,  or  if  the 
rate  of  contractions  was  increased,  which  shortened  the  time  of  repose,  the  mus- 
cle fatigued  rapidly.  In  general,  the  greater  the  weight  which  the  muscle  has 
to  lift,  the  shorter  must  be  the  periods  of  contraction  in  proportion  to  the  inter- 
val of  rest  if  the  muscle  is  to  maintain  its  power  to  work.  Maggiora,^  in  his 
interesting  experiments  in  Mosso's  laboratory  at  Turin,  made  a  very  careful  study 
of  this  subject,  and  ascertained  that  for  a  special  group  of  muscles  there  is  for 
each  individual  a  definite  weight  and  rate  of  contraction  essential  to  the  accom- 
plishment of  the  greatest  possible  work  in  a  given  time.  Either  increasing 
the  weight  or  the  rate  of  contraction  hastens  the  coming  on  of  fatigue  and  so 
lessens  the  power  and  the  total  amount  of  work.  In  such  an  exercise  as 
walking  the  muscles  are  not  continually  acting,  but  intervals  of  rest  alternate 
with  the  periods  of  work,  and  the  time  for  recu])eration  is  sufficiently  long  to 
permit  the  protoplasm  of  the  muscle-cells  to  prepare  the  cliemical  compounds 
from  Avhich  the  energy  is  liberated,  as  fast  as  they  are  used,  and  get  rid 
of  the  waste  products  of  contraction,  so  that  vigorous  muscles  can  be  em- 
ployed many  hours  before  any  marked  fatigue  is  experienced.  Sooner 
or  later,  however,  the  vigor  of  the  muscle  begins  to  decrease.  The  reason 
for  this  is  not  wholly  clear.  It  is  noticeable,  however,  that  not  only  the 
muscles  employed  in  the  work,  but  other  muscles,  such  as  those  of  the 
arms  for  instance,  even  when  purposely  kept  quiet,  have  their  irritability 
'  Archiv  fur  Analmiie  und  Physiologie,  1890  ;  physiologische  Abtheilnng,  p.  191. 


78  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

reduced.  This  would  .•^uj^gest  that  tlie  fatigue  wliich  finally  asserts  itself  is 
due  to  some  general  rather  than  local  influence.  To  understand  this  we  must 
recall  the  fact  tluit  all  parts  of"  the  body  are  in  c()mnuiui(;ation  by  means  of 
the  circulatory  system.  The  ever-circulating  blood  as  it  is  thrown  out  by  the 
heart  is  divided  into  minute  streams,  which,  after  passing  through  the  many 
organs  of  the  body,  unite  again  on  their  return  to  the  heart.  If  materials  l)e 
taken  from  the  blood  by  one  l)art,  they  are  lost  to  all  the  rest,  and  if  materials 
be  added  to  the  blood  by  any  part,  tliey  are  sooner  or  later  carried  to  all  the  rest. 
During  the  course  of  a  long  march,  the  muscles  of  the  leg  take  up  a  great  deal 
of  nutriment,  and  give  off  many  waste  products,  and  all  the  organs  suffer  in  con- 
sequence. Mosso,*  in  his  experiments  upon  soldiers  taking  long  forced  marches, 
found  that  lack  of  nutriment  is  not  the  only  cause  of  the  general  fatigue 
produced  by  long-continued  muscular  work.  The  soldiers,  though  somewhat 
refreshed  bv  the  taking  of  food,  did  not  recover  completely  until  after  a  pro- 
longed interval  of  rest.  He  attributed  this  to  the  fatigue-products  which  he 
supposed  the  muscles  to  have  given  off,  and  concluded  .hat  they  were  only 
gradually  eliminated  from  the  blood.  To  see  if  there  were  fatigue-products 
in  the  blood  of  a  tired  animal  capable  of  lessening  the  irritability  of  organs 
other  than  those  which  had  been  working,  he  made  the  following  experiment : 
He  drew  a  certain  weight  of  blood  from  the  veins  of  a  dog,  and  then  put  back 
into  the  animal  an  equal  amount  of  blood  from  another  completely  rested  dog. 
The  dog  which  was  the  subject  of  the  experiment  appeared  to  be  all  right  after 
the  operation.  On  another  day  he  repeated  the  experiment,  but  this  time  the 
blood  which  was  put  back  was  taken  from  a  dog  that  was  completely  tired  out 
by  running.  The  effect  of  the  blood  from  the  fatigued  animal  was  very 
marked  ;  the  dog  receiving  it  showed  all  the  signs  of  fatigue,  and  crept  off  into 
a  corner  to  sleep.  Mosso  concluded  from  this  experiment,  that  duriug  muscular 
work  fatigue-products  are  generated  in  the  muscles,  pass  from  thence  into  the 
blood,  and  are  conveyed  to  other  muscles,  where  they  produce  the  lowered 
irritability  and  loss  of  power  characteristic  of  fatigue.  Many  years  before. 
Von  Ranke  extracted  from  the  tired  muscles  of  frogs  substances  which  he 
considered  fatigue  materials.  We  know  many  of  the  waste  products  formed 
by  muscles,  and  have  learned  that  some  of  them  lower  the  irritability,  but 
what  the  exact  substances  are  which  produce  the  effects  observed  in  the  above 
experiments  is  not  known. 

Maggiora,  in  his  experiments  upon  the  fatigue  of  special  groups  of  muscles, 
likewise  found  that  the  taking  of  food  causes  only  a  partial  recovery  of  the 
tired  muscles,  and  that  an  interval  of  rest  is  essential  to  complete  recovery. 
In  these  experiments  the  irritability  of  the  muscles  was  tested  not  only  by 
volitional  impulses,  lint  by  the  strength  of  the  electric  current  required  to 
cause  direct  excitation.  In  the  case  of  vigorous  men,  one  and  a  half  horn's 
suffices  to  restore  the  muscles  of  the  forearm  which  have  been  com]>letely  tire^l 
out  by  raising  a  heavy  weight  many  times.  He  also  observed  that  the  time 
required  for  recovery  can  be  greatly  shortened  if  the  circulation  of  the  blood 
'  Archiv  fiir  Anatmnie  und  Physiologic,  1890 ;  phvsiologische  Abtheilung. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.       79 

and  Ivn,,,!,  in  the  muscles  be  increasal  l.y  .nas^ige.     Tl.is  suggests  ^.at  the 
power  of  the  cell  to  give  off  its  waste  procluds  to  the  blood  >s  sufficcntly 
Lid  to  keep  pace  with  the  ordinary  prcKlucti.m,  but  not  with  the  n>„re  rap.d 
formation  ulklng  place  during  iatigniug  work.     This  would  s..,n  to  be  th 
case  in  spite  of  the  fact  that  circulation  of  the  blo,xl  n,  the  n,ns<:lcs  ,s  increased 
,l„,.ing  action.     When  nm.scles  arc  stimulated  to  action  l,y  nnpnlscs  conung 
to  the™  from  the  ..cntral  nervous  system,  the  muscles  m  the  walls  of  the  blood- 
vessels of  the  umsclc  are  also  irritated  by  their  vaso-dilator  nerves  and,  relax- 
ing, permit  a  greater  flow  of  blood  through  the  muscle;  when  the  muscles 
ceSe  to  be  exdtcd  the  muscles  iu  the  vessel  walls  are  gradually  eontraet«^ 
again  through  the  action  of  the  vaso-coostrietor  nerves,  and  the  blood-snpp  y 
to  the  muscle  tissue   is  correspondingly  lessened.     Tins  arrangement  would 
seem  to  suffice  for  the  bringing  of  nutriment  and  oxygen  and  the  removal  of 
waste  matters  under  ordinary  conditions. 

Normally  the   muscles   are   never   con.pletcly  fatigued.     It  won  d   seem 
that  as  the  muscles  tire  and  their  irritability  is  lessene<l,  the  central  nei-ve- 
eells  which  send  the  stimulating   impulses   to  them  have   to  work  harder 
and  that  the  nerve-cells  give   out  sooner  than  the  muscles      On  the  o  he 
hand    certain  exi«riments  seem  to   show  that  the  nervc-eells   recover  from 
fat   ™  more  rapidly  than   the  muscles  do,  so   that  it  is  an  advantage   to 
;  fo  g  n   m  that  they  should  eease  to  excite  the  mt,seles  before  muscular 
fetieue  .s  complete.     With  the  decreasing  irritability  of  the  mu.scle,  a  feelmg 
rf  dslomfort  in  the  muscle  and  an  increasing  sense  of  effort  are  expenenced 
S   he"  *Wual,  both  of  which  tend  to  cause  a  cessation  of  coutract.o,,  and 
prevent  a  harmful  amount  of  work.     That  such  an  arrangemen   -0"U   '    of 
LrvL  was  apparent  in  the  experiments  of  Maggiora,  m  winch  he  found  that 
^  mils  a.' 'forced  to  work  after  fatigue  ha.  developed,  the^me  of  recovery 
is  prolonged  out  of  all  proportion  to  the  extra  work  accomplished. 

Ta^W  y.,«..-Mnscle-,  gland-  and  nerve-cells-m  fact,  almost  eyety 
fori  o     ;;fto;iasm_if  excited'to  vigorotts   long-continued   -t.on,  deter. 
oZ  and   exhbit   a  decline  of  functional   activity.     As  we   have  seen,  n 
leea"  of  muscle  there  is  a  using  up  of  energy-holdmg  compounds  and 
a  productL  of  poisonous  waste  matters,  and  these  two  effects  mdnce  he  con- 
liS  nCvn  as  Ligue.     A  priori,  we  should  exj^ct  sim.lar  d-ges  o  -nr 
in  the  active  nerve-fibre;  alnmst  all  the  experimental  evide,  ee  ,s  however 
om   sir  o  this  view.    tLc  form  of  activity  which  is  most  character.sfe  of 
n  usee  s  CO    Ltion  ;  that  which  is  ntost  characteristic  of  nerve  tseonducttm. 
In  the  in    the  m;sele  it  is  exceedingly  difficult  to  distingu.sh  between  the 
in  tiie  case  oi  me  chansre  of  form  and  those 

effects  produced  by  the  processes  associated  -;''  *  «  f  ^^ge.     There  is  little 
which  result  from  *e  .transm,ss.m  of  the  ex«  ^^^^,^^^ 

doubt  but  that  fat,gue  ts  --»-*«^j"  ^™  ;;,,here  the  transmi^ion 
''^   Apparently  the  same  may  be  said  of  the  processes  which  result  in  the 


80  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

development  ot"  what  we  call  the  nerve-impulse.  We  have  already  seen  that 
the  nerve  may  undergo  an  alteration  of  irritability  if  subjected  to  artificial 
irritants.  Such  a  change  at  the  point  of  application  of  the  irritant  is  hardly 
to  be  regarded  as  a  latigue  effect,  however,  for  in  many  cases,  at  least,  it  is 
due  to  the  direct  effect  of  the  irritant  on  the  physical  or  chemical  structure  of 
the  nerve-protoplasm  rather  than  to  molecular  changes  which  are  j^eculiar  to 
the  development  of  the  nerve-impulse.  Thus  the  change  of  irritability  which 
results  from  a  series  of  light  blows,  such  as  may  be  given  to  a  nerve  by 
Tigerstedt's  tetanomotor,  cannot  properly  be  said  to  be  the  result  of  fatigue.  It 
has  been  found  that  a  medullary  nerve  may  be  excited  many  times  a  second 
for  houi*s,  by  an  induced  current,  and  still  be  capable  of  developing  at  the 
stimulated  point  what  we  call  the  nerve-impulse.  The  change  which  is  de- 
veloped at  the  point  of  excitation  and  which  passes  thence  the  length  of  the 
nerve,  would  seem  to  be  the  expression  of  a  form  of  energy  liberated  within 
the  nerve,  and  since  the  liberation  of  energy  implies  the  breaking  down  of 
chemical  combinations,  the  apparent  lack  of  fatigue  of  the  nerve  is  incompre- 
hensible. It  is  the  more  remarkable  since  the  nerve-fibre  is  to  be  considered  a 
branch  of  a  nerve-cell,  and  nerve-cells  appear  to  fatigue  if  frequently  excited 
to  vigorous  action.  Inasmuch  as  we  have  as  yet  no  definite  knowledge  of  the 
nature  of  what  we  c^ll  the  nerve-impulse,  or  of  the  character  of  the  jwocesses 
by  which  it  is  transmitted  along  the  nerve,  we  can  afford  to  leave  this  question 
open,  and  simply  state  that  the  evidence  thus  far  obtained  is  opposed  to  the 
view  that  nerve-fibres  fatigue. 

Effect  of  Use  and  Disuse. — Different  kinds  of  muscle- tissues  possess  very 
different  degrees  of  endurance.  By  endurance  we  mean  the  capacity  to  liber- 
ate energy  during  long  periods  of  time.  This  capacity  is  intimately  associated 
with  irritability,  for  one  of  the  first  marks  of  failure  of  power  is  a  decline  of 
irritability.  In  general,  the  more  irritable  a  muscle  the  less  its  endurance, 
because  with  an  increase  of  irritability  there  is  associated  a  more  rapid  and 
extensive  liberation  of  energy  in  response  to  irritants.  For  example,  the  rap- 
idly responding  and  acting  pale  striated  muscles  of  the  rabbit  have  le&s  resist- 
ing power  than  the  red  striated  muscles,  while  the  sluggish  unstriated  muscle- 
fibres  can  contract  a  long  time  without  suffering  from  fatigue. 

The  endurance  of  muscles  of  even  the  same  kind  may  differ  very  considera- 
bly in  the  same  individual,  but  the  differences  are  more  striking  in  the  case  of 
different  individuals.  One  of  the  causes  of  this  is  the  extent  to  which  the 
muscles  are  employed.  Use,  exercise,  is  the  most  effective  method  of  increasing 
not  only  the  strength,  but  the  endurance  of  the  muscle.  Though  this  fact  is 
so  well  known  as  to  scarcely  need  repeating,  the  explanation  of  it  is  by  no 
means  so  clear.  Undoubtedly  one  of  the  causes  is  a  more  perfect  circulation 
in  a  muscle  which  is  often  used,  but  this  is  not  all.  It  would  seem  as  if  the 
protoplasm  of  the  muscle-cell  was  educated,  so  to  speak,  to  be  more  expert  in 
assimilating  materials  containing  energy,  in  building  up  the  explosive  compounds 
employed  in  its  work,  and  in  excreting  deleterious  waste  matters. 

The  effect  of  exercise  upon  irritability  has  not  been  thoroughly  worked  out. 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND    NERVE.       81 

It  would  seem  as  if  there  were  a  normal  degree  of  irritability  for  each  special 
form  of  muscle-tissue,  and  as  if  either  an  increase  or  decrease  of  the  irritability 
above  or  below  this  level  was  a  sif2;n  of  det<!rioration.  J^xercise,  if  not  excess- 
ive, is  favorable  to  the  maintenance  of  this  normal  physiological  condition. 
Without  doubt  many  of  the  differences  which  we  attribute  to  the  muscles  of 
different  men  arc  really  due  to  differences  in  the  central  nerve-cells,  the  action 
of  muscles,  rightly  inter[)reted,  being  rather  an  expression  of  central  nervous 
activity  than  the  result  of  peculiarities  of  the  muscles  themselves.  To  exercise 
the  muscles  is  to  exercise  the  nerve-cells,  and  the  effects  of  exercise  upon  these 
nervous  mechanisms  is  of  as  much  importance  as  the  effect  upon  the  muscles. 
In  admiring  visible  proportions  we  must  always  bear  in  mind  "the  power 
behind  the  throne."  "Beef"  is  of  use  to  the  athlete,  but  the  muscles  are 
merely  the  servants,  and  can  accomplish  nothing  if  the  master  is  sick.  The 
nerve-cells  always  give  out  before  the  muscles,  and  the  man  preparing  for  a 
contest  should  watch  his  nervous  system  more  than  his  muscles.  He  who 
forgets  this  can  easily  over-train,  and  do  himself  a  permanent  injury,  besides 
failing  in  the  race. 

Effect  of  Enforced  Rest. — Not  only  is  the  strength  of  the  muscles  greatly 
increased  by  exercise,  but  a  lack  of  exercise  soon  results  in  a  loss  of  strength. 
This  is  seen  when  an  individual  is  confined  to  his  bed  for  even  a  comparatively 
short  time,  or  when  a  limb  is  subjected  to  enforced  rest  by  being  placed  in  a 
splint.  The  cause  is  to  be  sought  in  changes  peculiar  to  the  muscle  proto- 
plasm itself,  although  reduced  circulation  may  also  play  a  part.  The  effect  of 
prolonged  rest  on  the  irritability  of  muscles,  is  seen  most  markedly  when  they 
are  separated  from  the  central  nervous  system  by  injuries  of  their  nerves  (see 
13.  79).  The  lowered  irritability  which  results  from  prolonged  rest  is  not 
peculiar  to  muscles,  but  is  shared  by  all  forms  of  protoplasm. 

0.  Conductivity. 

Conductivity  is  that  property  of  protoplasm  by  virtue  of  which  a  condition 
of  activity  aroused  in  one  portion  of  the  substance  by  the  action  of  a  stimulus 
of  any  kind  may  be  transmitted  to  any  other  portion.  For  example,  if  the 
edge  of  the  bell  of  a  vorticella  (see  Fig.  2,  p.  34)  be  irritated  by  a  hair,  not 
only  do  the  movements  of  the  cilia  cease,  but  the  contractile  substance  of  the 
bell  draws  it  into  a  more  compact  shape,  and  the  fibrillae  of  the  stalk  shorten 
and  pull  the  bell  away  from  the  offending  irritant.  In  such  a  case  an  exciting 
process  must  have  been  transmitted  throughout  the  cell,  and  through  several  more 
or  less  differentiated  forms  of  protoplasm.  This  property  of  conductivity  is  not 
known  to  be  limited  to  any  one  peculiar  structural  arrangement  of  protoplasm 
distinguishable  with  the  microscope,  but  is  exhibited  by  a  vast  variety  of  forms 
of  cell-protoplasm,  and  by  plants  as  well  as  animals.  The  cytoplasm  of  cells, 
the  part  of  the  protoplasm  surrounding  the  nucleus,  appears  to  be  composed 
of  a  semifluid  granular  material,  traversed  in  all  directions  by  finest  fibrillse 
which  in  some  cases  appear  to  form  an  irregular  meshwork,  the  reticulum,  and 
in  others  to  be  arranged  side  by  side  as  more  or  less  complete  fibrils.    It  is  not 


82  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

known  whether  the  power  of  conduction  is  possessed  by  the  whole  of"  the  pro- 
toplasmic substance  or  is  confined  to  the  reticular  substance,  but  there  are  cer- 
tain reasons  why  the  former  view  may  be  considered  the  more  probable.  The 
rate  and  the  strcng:tli  of  the  conduction  process  varies  greatly  in  different  forms 
of  prot()i)lasm,  and  there  aj)pear  to  be  dififcrences  in  the  facility  with  which 
the  exciting  process  spreads  through  different  jiarts  of  even  the  same  cell.'  Not 
only  are  such  differences  to  Ijc  noticed  in  many  of  tiie  ciliated  infusoria,  but 
even  the  substance  of  striated  muscles  seems  to  conduct  in  two  different  ways, 
the  sarcoplasm  appearing  to  conduct  slowly,  and  the  more  highly  differentiated 
fibrilldry  jiortion  of  the  fibre  rapidly.  In  general  the  })r()cess  appears  to  be 
more  rapid  and  vigorous  where  a  fibrillated  structure  is  observable.  Smooth 
muscle-tissue,  which  has  a  somewhat  simple  structure,  conducts  comparatively 
slowly;  striated  muscle,  which  is  more  highly  differentiated,  more  rapidly,  and 
the  fibrillated  axis-cylinder  of  the  nerve-fibre,  most  rapidly  of  all. 

Protoplasmic  Continuity  is  Essential  to  Conduction. — Effect  of  a 
Break  in  Protoplasmic  Continuity. — A  break  of  protoplasmic  continuity  in  any 
part  of  a  nerve-  or  muscle-fibre  acts  as  a  barrier  to  conduction.  If  a  nerve  be  cut 
through,  the  irritability  and  conductivity  remain  for  a  considerable  time  in  the 
severed  extremities,  but  communication  between  them  is  lost,  and  remains  absent 
however  well  the  cut  extremities  may  be  adjusted.  The  nerve-impuLse  is  not 
transmitted  through  the  nerve-substance  as  electricity  is  transmitted  along  a 
wire :  join  the  cut  ends  of  a  wire,  and  the  contact  suffices  for  the  passage  of 
the  current ;  join  the  cut  ends  of  a  nerve,  and  the  nerve-impulse  cannot  pass. 
Any  severe  injury  to  a  nerve  alters  the  proto})lasmic  structure  and  prevents 
the  chemical  and  physical  processes  through  which  conductivity  is  made 
possible.  It  is  probable  that  the  same  may  be  said  of  all  forms  of  liv- 
ing cells,  and  the  absence  of  protoplasmic  continuity  would  .seem  to  be  an 
explanation  of  the  fact  that  nerve-  and  muscle-fibres  which  lie  close  together 
may  physiologically  act  as  separate  mechanisms. 

Even  in  the  case  of  apparently  homogeneous  protoplasm  there  is  probably 
a  definite  structural  relation  of  the  finest  particles,  and  upon  this  the  physi- 
ological properties  of  the  substance  depends.  Slight  physical  and  chemical 
alterations  suffice  to  change  the  rate  and  stretigth  of  the  conduction  })roccss, 
and  the  power  to  conduct  is  altogether  lost  if  the  protoplasm  is  so  altered  that 
it  dies. 

The  relation  of  conductivity  to  .structure  of  cell-protoplasm  is  illustrated  in 
the  effects  of  degeneration  and  regeneration  upon  the  physiological  jiroperties  of 
the  nerve-fibre.  The  life  of  the  nerve-fibre  is  dependent  on  influences  exerted 
upon  it  by  the  nerve-cell  of  which  it  is  a  branch.  When  any  part  of  the  fibre  is 
injured  it  loses  its  power  to  conduct,  and  the  portion  of  the  fibre  separated  by 
this  block  from  its  cell  soon  dies.  The  irritability  and  conductivity  are  wholly 
lo.st  at  the  end  of  three  or  four  days,  and  the  fibre  begins  to  undergo  degenera- 
tion. The  axis-cylinder  and  the  myelin  are  seen  to  break  up  and  are  then 
absorbed,  apparently  Mith  the  assistance  of  the  nuclei  which  normally  lie  just 
'  Biedernianii :  Elektrophysiologie,  1895,  p.  137. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NEJiVE.       83 

inside  the  neurilcmina,  and  Avliifh  at  this  time  proliferate  greatly  and  eonie  to 
occupy  most  of  the  lumen  of  the  tube.  The  process  of  absorption  is  nearly  com- 
plete at  the  end  of  a  fortnight  after  the  injury.  Under  suitable  conditions,  how- 
ever, regeneration  may  occur,  and  as  this  takes  place  there  is  a  recovery  of  physi- 
ological activities.  The  order  in  which  conductivity  and  irritability  return  is 
instructive,  llowcll  and  Huber'  made  a  careful  study  of  this  subject.  They 
found  that  the  many  nuclei  which  develop  during  degeneration  are  apparently 
the  source  of  new  pr()t()])lasm,  which  is  seen  to  accumulate  in  the  old  sheath  until 
a  continuous  band  of  protoplasm  is  ibrmed.  About  this  thread  of  protoplasm 
a  new  membranous  sheath  develops,  and  thus  is  built  up  what  closely  resembles 
an  embryonic  nerve-fibre.  The  embryonic  fibre  formed  in  the  peri])heral  end 
of  the  regenerating  nerve  joins  that  of  the  central  end  in  the  cicatricial  tissue 
Avhich  has  been  deposited  at  the  point  of  injury.  Thus  a  temporary  nerve- 
fibre  is  formed  and  united  to  the  undegenerated  part  of  the  old  fibre,  and  this 
new  structure,  though  possessing  neither  myelin  nor  axis-cylinder,  is  found  to 
be  capable  of  conduction  and  to  have  a  low  form  of  irritability,  being  ex- 
citable to  violent  mechanical  stimuli  but  not  to  induction  currents.  The  power 
of  conduction  appears  to  return  before  irritability,  and  may  be  observed  first 
at  the  end  of  the  third  week.  Apparently  sensation  is  recovered  before  the 
power  of  making  voluntary  movements ;  this  difference  may  w^ell  be  due,  not 
to  any  essential  difference  between  sensory  and  motor  fibres,  but  to  the  fact 
that  extra  time  is  required  for  the  motor  fibres  to  make  connection  with  the 
muscle.  The  embryonic  fibre  gradually  gives  place  to  the  adult  fibre,  new 
myelin  being  formed  all  along  the  fibre,  and  a  new  axis-cylinder  growing  down 
from  the  old  axis-cylinder.  As  the  axis-cylinder  grows  down,  the  irritability 
for  induction  shocks  is  recovered.  Many  months  may  be  necessary  for  the 
complete  recovery  of  function. 

The  same  is  true  of  muscle  as  of  nerve  protoplasm, — the  power  of  con- 
duction ceases  with  the  life  of  the  cell-substance ;  thus,  if  the  middle  part  of 
a  muscle-fibre  be  killed,  by  pressure,  heat,  or  some  chemical,  the  dead  proto- 
plasm acts  as  a  block  to  prevent  the  state  of  activity  which  may  be  excited  at 
one  end  from  being  transmitted  to  the  other,  and  the  conduction  power  is  only 
recovered  on  the  regeneration  of  the  injured  tissue. 

Isolated  Conduction  is  the  Rule. — (a)  Conduction  in  Kerve-trunks. — The 
axis-cylinders  of  the  many  fibres  which  run  side  by  side  in  a  nerve-trunk  are 
separated  from  each  other  by  the  neurilemma,  and  in  the  case  of  the  medullary 
nerves  by  the  myelin  substance  as  well,  so  that  there  is  not  even  contiguity, 
much  less  continuity  of  nerve-substance.  Thus  the  many  fibres  of  a  nerve- 
trunk,  some  afferent  and  others  efferent,  though  running  side  by  side,  conduct 
independently  of  one  another.  For  example.  If  the  skin  of  the  foot  be  pricked, 
the  excitation  of  its  sense-organs  is  communicated  to  sensory  nerve-fibres,  and 
is  transmitted  along  them  to  the  spinal  cord,  where  the  stimulus  awakens  cer- 
tain groups  of  cells  to  activity;  these  cells  in  turn,  by  means  of  their  branches, 
the  motor  nerve-fibres,  transmit  the  condition  of  excitation  down  to  the  mus- 
^  Journal  of  Physiology,  1892,  vol.  xiii.  p.  361. 


84  AN  AMERICAN    TEXT-BOOK    OF   PllWSlOLOGY. 

cle-fibres  of  the  legs,  wliich,  when  stimulated,  contract  and  withdraw  the  foot 
from  the  offending  irritant.  The  sensory  and  motor  nerves  concerned  in  this 
reflex  act  run  for  a  considerable  part  of  their  course  in  the  same  nerve-trunk, 
but  the  sensory  impulses  have  no  direct  effect  on  the  motor  nerve-fibres,  and 
the  roundabout  course  which  has  been  described  is  the  only  way  by  which 
they  can  influence  them. 

It  is  probable  that  isolated  conduction  by  separate  fibres  and  their  branches 
holds  gootl  within  the  central  nervous  system,  as  elsewhere,  otherwise  we  could 
scarcely  explain  the  localization  of  sensations,  or  co-ordinated  movements.  It 
is  possible  that  within  the  central  nervous  system  the  neuroglia  may  act  to 
secure  isolated  conduction.     This  question  will  be  considered  elsewhere. 

(6)  Distribidioii  of  Excitation  by  Branches  of  Nerves. — Nerve-fibres  rarely 
branch  in  their  passage  along  the  peripheral  nerves.  The  branches  which  are 
seen  to  be  given  off  from  the  nerve-trunks  are  composed  of  bundles  of  nerve- 
fibres  which  have  separated  off  from  the  rest,  but  which  remain  intact.  After 
the  nerves  have  entered  a  peripheral  organ,  or  the  central  nervous  system,  the 
axis-cylinders  may  give  off  branches.  Thus  in  muscles,  and  to  a  still  greater 
degree  in  the  electric  organs  of  certain  fish,  the  nerve-fibre  and  its  axis-cylinder 
may  divide  again  and  again,  or  after  entering  the  spinal  cord  the  fibre  may  be 
seen  to  give  off  a  great  many  lateral  branches — collaterals,  as  they  are  called. 
It  is  not  known  whether  in  such  cases  the  fibrilhe  of  the  axis-cylinder  give 
off  branches,  or  whether  they  simply  separate,  a  part  of  them  entering  the 
branch  while  the  rest  of  them  continue  on  in  the  main  fibre.  Though  the 
exciting  process  does  not  pass  from  fibre  to  fibre,  it  probably  involves  in  a 
greater  or  less  degree  all  the  elements  of  the  same  fibre,  and  passes  into  all  its 
branches.  It  is  evident  that  where  it  is  necessary  for  the  irritation  to  be 
localized,  branching  could  not  occur ;  but  where  a  more  general  distribution 
is  permissible,  especially  where  several  parts  of  an  organ  ought  to  act  at  the 
same  instant,  conduction  through  a  single  fibre  wliich  branches  freely  near  its 
termination  would  be  useful. 

(c)  Conduction  in  3lHscles. — Each  fibre  of  the  muscles  which  move  the 
bones — the  skeletal  muscles,  as  they  are  sometimes  called — is  physiologically 
independent  of  the  rest.  The  sarcolemma  prevents  not  only  continuity,  but 
contiguity  of  the  muscle-substance  of  the  separate  fibres,  and  there  is  no  cross 
conduction  from  fibre  to  fibre.  Each  of  the  separate  muscle-fibres  is  sup]>lied 
by  at  least  one  nerve-fibre,  and,  under  normal  conditions,  only  acts  when 
stimulated  by  the  nerve.  In  the  case  of  ])lant-cells,  and  of  certain  forms  of 
muscle-cells,  about  which  there  is  a  more  or  less  definite  wall  or  sheath,  there 
are  little  bridges  of  protoplasm  binding  the  cells  together.  For  example, 
Engelmann  describes  the  muscle  of  the  intestines  of  the  fly  as  composed  of 
striated  cells,  sheathed  by  sarcolemma,  except  whore  bound  together  by  little 
branches  of  sarcoplasma,  which  may  act  as  conducting  wires  between  the  cells. 

There  are  certi\in  cells,  however,  which  have  been  supposed  to  be  exceptions 
to  the  rule  that  protoplasmic  continuity  is  essential  to  conduction.  The  stri- 
ated  muscle-fibres  of  the  heart  are  quite  different   from   those  of  ordinary 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.       85 

skeletal  muscles,  physiologically  as  well  as  anatomically.  They  are  stumpy, 
quadrantrular  colls,  wiiich  are  not  known  to  have  a  sarculemma,  and  which  are 
united  not  only  by  their  broad  ends,  but  by  lateral  branches.  Engelniann 
and  others  have  considered  conduction  to  take  place  in  the  heart  from  cell  to 
cell,  without  the  intervention  of  nerves,  and  in  all  directions  with  equal  readi- 
ness. This  view  was  held  because  the  irritation  was  found  to  spread  in  all 
directions  through  the  muscle-substance,  and  no  nerves  had  been  discovered 
which  could  account  for  this  free  communication.  Quite  lately,  however, 
Hegmans  and  Demoor  claim  to  have  discovered  in  the  heart  of  the  frog,  by 
the  Golgi  staining  method,  an  anastomosing  network  of  nerve-fibres  which 
extends  over  the  whole  heart.  This  nervous  network  would  appear  to  give 
ample  means  of  communication  between  the  different  parts  of  the  heart,^  but 
it  is  possible  that  it  has  only  a  regulatory  function. 

The  cells  of  the  contractile  substance  of  some  of  the  medusae  (as  Aurelia), 
have  been  supposed  to  communicate  by  contiguity  rather  than  by  continuity. 
The  same  has  been  thought  to  be  the  case  with  many  forms  of  unstriated 
muscle-tissue  ;^  moreover,  there  are  groups  of  ciliated  cells,  the  members  of 
which  act  in  unison  although  they  have  not  been  found  to  be  connected  either 
directly  or  by  nerves.  These  cells  have  apparently  no  membranous  covering, 
and  though  living  as  independent  units,  are  so  related  that  a  condition  of 
activity  excited  in  one  seems  to  be  transmitted  to  the  rest  by  means  of  contact, 
or  through  the  mediation  of  cement-substance. 

From  what  has  been  said  it  will  be  seen  that  protoplasmic  continuity 
ensures  free  communication  between  different  cells ;  that  protoplasmic  con- 
tiguity, either  directly  or  through  the  mediation  of  the  cement-substance,  may 
possibly  permit  of  conduction;  but  that  the  intervention  of  a  different  tissue, 
even  as  delicate  as  the  sarcolemma,  suffices  to  cause  complete  isolation  of  the 
cell  from  its  neighbors. 

Transmission  of  Excitation  by  means  of  End-organs. — The  latest 
researches  on  the  anatomy  of  the  spinal  cord  seem  to  show  that  the  incoming  fibres 
do  not  communicate  directly  with  nerve-cells,  but  terminate  in  brush-like  end- 
ings in  the  immediate  vicinity  of  the  cells.  A  similar  arrangement  is  found 
wherever  nerve-cells  are  excited  to  action  by  nerve-fibres.  It  is  doubtful 
whether  the  brush-like  endings  should  be  regarded  as  special  exciting  mechan- 
isms, or  whether  the  brush  endings  should  be  considered  to  be  in  contact  with  the 
nerve-cells  or  their  protoplasmic  processes,  and  this  relation  to  be  sufficiently 
close  to  permit  the  cells  to  be  stimulated.  The  former  view  is  favored  by  the 
fact  that  though  the  end-brush  can  excite  the  cell,  the  cell  does  not  seem  to  be 
able  to  excite  the  brush.  Much  the  same  can  be  said  of  the  end-plates  by 
which  the  condition  of  excitation  of  nerve-fibres  is  conveyed  to  muscle-fibres, 
for  they  seem  to  be  in  contact  with,  rather  than  continuous  with  the  muscle- 
substance.  Though  the  nerve  end-organ  can  excite  the  muscle,  the  muscle 
does  not  appear  to  be  able  to  excite  the  nerve. 

'  Archives  de  Biologie,  1895,  vol.  xiii.,  No.  4,  p.  619. 
^  Engelmann:  Pfliiger^s  Archiv,  1871,  Bd.  iv. 


86  A.y  AMERICAN   TEXT-HOOK    OF   PHYSIOLOGY. 

Wa  liuve  little  knowledge  of  the  j)liysi()l()o;i('al  activities  of  the  eiul-hiiishcs. 
We  know  that  much  more  time  is  lost  in  the  central  nervous  processes  than 
would  be  required  to  transmit  the  excitation  through  nerve-fibres,  and  that  the 
time  occu])ied  is  apparently  the  greater  the  longer  the  chain  of  nerve-cells  en- 
tering into  the  act.  A  i)art  of  this  time  is  undoubtedly  sjKMit  in  the  processes 
occurring  within  the  nerve-cells,  but  it  is  not  unlikely  that  a  |)ortion  of  it  may 
be  spent  bv  the  nerve  end-brushes  in  the  excitation  of  the  cells. 

It  is  certain  that  the  motor  end-plates  use  up  more  time  in  the  excitation  of 
the  nuiscles  than  would  be  recpiired  for  the  transmission  of  the  irritation 
through  a  corresponding  amount  of  nerve-substance.  It  is  found  by  experi- 
ment that  a  nniscle  does  not  contract  so  quickly  if  it  be  excited  through  its 
nerve  as  when  directly  stimulated.  Part  of  the  lost  time  is  spent  in  transmis- 
sion of  the  excitation  through  the  nerve,  but  after  allowance  has  been  made  for 
this  loss  there  is  a  balance  to  be  accounted  for,  and  this  is  credited  to  the  motor 
end-plates.  The  average  time  used  by  the  motor  end-plate  is  found  to  be 
0.0032  second.^  There  are  many  facts  which  go  to  show  that  the  motor  end- 
organ  is  different  physiologically  from  the  nerve ;  viz.  the  latent  period 
of  the  motor  end-plate,  the  effect  of  curare  on  the  nerve  end-plate  as  dis- 
tinguished from  nerve  and  muscle,  the  fact  that  the  end-organ  loses  its  vitality 
quicker  than  do  nerve  and  muscle  when  the  blood-supply  is  cut  off,  and  the 
very  existence  of  an  end-organ  distinguishable  with  the  microscope. 

Conduction  in  Both  Directions. — [a)  In  Muscle. — Wherever  proto- 
plasmic continuity  exists,  conductivity  would  seem  to  be  possible;  moreover, 
the  active  change  excited  by  an  irritant  would  seem  to  be  able  to  pass  in  all 
directions,  though  whether  with  the  same  facility  is  not  known.  Where  the 
spread  of  the  excitatory  process  is  accompanied  by  a  change  in  form,  as  is  the 
case  in  many  of  the  lower  organisms  and  in  muscle-tissue,  it  is  not  difficult  to 
trace  the  process.  The  rate  at  which  the  excitation  spreads  through  the  ifrita- 
ble  substance  is  very  rapid,  and  special  arrangements  have  to  be  employed  to 
follow  it,  but  the  change  is  not  so  swift  that  its  course  cannot  be  accurately 
determined.  It  has  been  found  that  if  a  muscle-fibre  be  stimulated,  as  nor- 
mally, by  a  nerve-fibre,  the  active  condition  produced  at  the  })oint  of  stimula- 
tion spreads  along  the  muscle-fibre  in  both  directions  to  its  extremities  ;  if  the 
fibre  be  artificially  irritated  at  either  end,  the  exciting  change  runs  the  length 
of  the  fibre,  regardless  of  the  direction,  and  stimulates  every  part  of  it  to  con- 
traction. 

(6)  In  Nei'ves. — In  the  cases  of  nerves  where  excitation  is  accompanied  by 
no  visible  manifestation  of  activity,  a  definite  answer  to  the  question  is  not  so 
readily  obtained.  As  long  as  a  nerve  is  within  the  normal  body,  the  activity 
of  the  nerve-fibre  can  only  be  estimated  from  the  response  of  the  cell  which  the 
nerve-fibre  excites,  and  there  is  such  an  organ  only  at  one  extremity  of  the  fibre. 
Efforts  have  been  made  to  elucidate  the  pn^blem  by  attempting  to  unite  the 
central  part  of  a  cut  sensory  nerve  with  the  perijiheral  part  of  a  divided  motor 
nerve,  and  observing,  after  the  healing  was  complete,  whether  excitation  of  the 

^  Bernstein  :  Archiv  fur  Anutomie  unci  Phijxiolocjir,  1882,  p.  329. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND   NERVE.       87 

sensory  nerve  caused  movements  in  the  part  ^uj)i)lietl  by  the  niotcn-  nerve, 
Whh  a  simihir  j)urpose  Paul  Bert  made  a  well-known  experiment,  in  which 
he  succeeded  in  bringing  about  union  of  the  end  of  the  tail  of  a  rat  witii 
the  tissues  of  the  back,  and  found,  when  the  union  was  complete,  after  the  tail 
was  cut  oif  at  its  base,  it  was  still  capable  of  giving  sensations  of  pain.  Ail 
such  experiments  fail  to  throw  light  on  the  problem,  for  we  now  know  that  the 
]KM"ipheral  part  of  the  cut  nerve  dies,  and  the  conduction  power  manifested 
later  is  dependetit  on  new  axis-cylinders  which  have  grown  down  from  the 
central  nerve-stump. 

There  is,  however,  an  entirely  different  method  of  experimentation  which 
seems  to  prove  that  nerve-,  like  muscle-protoplasm,  can  conduct  in  both  direc- 
tions.   This  method  is  based  on  the  fact  that  though  nerve-fibres  rarely  branch 
in  the  peripheral  nerve-trunks  on  their  way  to  an  organ,  they  may  divide  very 
freely  after  reaching  it.    Such  branchings  of  fibres  occur  in  muscle,  and  Kuehne^ 
found  that  if  one  of  these  branches  was  stimulated,  the   irritation  passed  up 
the  branch  to  the  nerve-fibre  and  then  down  the  other  branches  to  tlic  muscle. 
For  example,  he  split  the  end  of  the  sartorius  muscle  of  a 
frog  by  a  longitudinal  cut,  and  then  found  on  exciting  one 
of  the  slips  that  the  other  contracted  (see  Fig.  29).     Since 
cross  conduction  between   striated  muscle-fibres  does  not 
occur,  no  other  explanation  presents  itself.     Perhaps  a  still 
more  striking  example  is  to  be  found  in  an  experiment  of 
Babuchin  ^  on  the  nerve  of  the  electric  organ  of  an  electric 
fish,  the  Malopterurus.     The    organ,  consisting  of  many 
thousand  plates,  is  supplied  by  a  single  enormous  nerve- 
fibre  which  after  entering  the  organ  divides  very  freely  so         ^^^  29.-Kuehnes 
as  to  supply  every  plate.     In  this  case  mechanical  stirau-      preparation  of  sarto- 
lation  of  the  central  end  of  one  of  the  cut  branches  of  the      conduct  ion  Ln?rye^ 
nerve  sufficed  to  cause  an  electric  discharge  of  the  whole 
organ.     The  irritation  must  have  passed  backward  along  the  irritated  branch 
until  the  main  trunk  w^as  reached  and  then  in  the  usual  direction  down  the 
other  branches  to  the  electric  plates. 

Still  another  method  is  that  which  was  employed  by  Du  Bois-Reymond,^ 
on  the  fibres  of  the  spinal  nerve-roots.  When  a  nerve  is  excited  to  action  it 
underiroes  a  change  in  electrical  condition,  and  this  change  progresses  along 
the  fibre  at  the  same  rate  and  in  same  direction  as  the  nerve-impulse.  This 
electrical  change,  though  entirely  different  from  the  nerve-impulse  itself,  can 
be  taken  as  an  indication  of  the  direction  of  movement  of  the  process  of 
conduction.  Du  Bois-Reymond  found  that  if  he  stimulated  the  afferent  fibres 
of  the  posterior  spinal  nerve-roots  of  the  sciatic  nerve  of  the  frog,  a  "  nega- 
tive variation  current,"  as  the  current  resulting  from  the  change  in  the  elec- 
trical condition  of  the  nerve  is  called,  passed  down  the  nerve  in  a  direction 

1  Archivfilr  Anatomie  und  Physiologie,  1859,  p.  595. 

2  Ibkl,  1877,  p.  262. 

»  Thierische  Electriciidt,  1849,  Bd.  ii.  S.  587. 


88  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

opposite  to  tliat  whicli  the  noriual  iiiij)ul.st'  takes.  Furtlier,  it  was  louud 
that  if  the  sciatic  nerve  was  excited,  a  negative  variation  current  could  be 
detected  in  the  anterior  as  well  as  the  posterior  roots.  Normally  the  irritation 
only  passes  up  the  posterior  roots  and  down  the  anterior,  for  normally  the 
sensory  fibres  of  the  posterior  roots  are  excited  only  at  the  })eripheral  end  and 
the  motor  fibres  of  the  anterior  roots  only  at  the  central  end.  The  ex|)eriment 
showed  both  sensory  and  motor  fibres  to  be  capable  of  conducting  in  both 
directions. 

There  is  no  doubt  but  that  uerve-protoj)lasm  can  conduct  in  both  directions, 
although  normally  the  nerve  is  stimulated  only  at  one  end  and  therefore  con- 
ducts in  only  one  direction.  This  question  is  of  considerable  importance,  not 
only  with  reference  to  the  possil)ility  of  the  central  nervous  .system  being 
influenced  by  stimuli  passing  from  the  muscles,  for  instance,  back  along  the 
motor  nerves,  but  more  especially  with  reference  to  the  spread  of  impulses 
through  the  central  nervous  system, — a  problem  which  will  be  considered  later 
with  others  of  a  similar  character. 

Rate  of  Conduction. — The  activity  of  the  conduction  process  varies 
greatly  in  different  tissues.  The  nerves  of  warm-blooded  animals  conduct  more 
rapidly  than  those  of  cold ;  in  a  given  animal  the  nerve-fibres  conduct  more 
rapidly  than  muscle-fibres ;  striated  muscle  conducts  more  rapidly  than  smooth 
muscle;  and  even  within  a  single  cell  different  portions  may  transmit  the  ex- 
citing process  at  different  rates ;  thus  the  jiiyoid  substance  of  the  contractile  fibres 
of  one  of  the  rhizopods  conducts  more  rapidly  than  the  less  highly  differen- 
tiated protoplasm  of  the  cell.  In  general,  it  may  be  said  that,  "  the  power  to 
conduct  increases  with  increase  of  mobility  and  sensitiveness  to  external  irri- 
tants, a  fact  which  reveals  itself  in  the  protozoa,  by  a  comparison  of  the  slowly 
moving  rhizopods  with  the  lively  flagellata  and  ciliata."*  A  study  of  different 
classes  of  muscle-tissue  supports  this  view. 

(a)  Rale  of  Conduction  in  Muscles. — The  conduction  process  is  invisible, 
hence  we  estimate  its  strength  and  rate  by  its  effects.  It  is  most  readily  fol- 
lowed in  such  mechanisms  as  muscle,  where  the  conducting  medium  itself 
undergoes  a  change  of  form  as  the  exciting  influence  passes  along  it. 

Rate  of  Transmission  of  Wave  of  Contraction. — If  a  muscle  be  excited  to 
action  by  an  irritant  applied  to  one  end,  it  does  not  contract  at  once  as  a  whole, 
but  the  change  of  form  starts  at  the  point  which  is  irritated  and  spreads  thence 
the  length  of  the  fibres.  At  the  same  time  that  the  muscle  shortens  it 
thickens,  and  under  certain  conditions  the  swelling  of  the  muscle  can  be  seen 
to  travel  from  the  end  which  is  excited  to  the  further  extremity.  In  the  case 
of  normal,  active,  striated  muscle,  the  rate  at  which  the  change  of  form  spreads 
over  the  muscle  is  far  too  rapid  to  be  followed  by  the  eye,  and  hence  the 
muscle  ajipears  to  act  as  a  whole.  By  suitable  recording  mechanisms,  evidence 
can  be  obtained  of  the  rate  at  which  the  exciting  influence  and  contraction  ]iro- 
cess  pass  along  the  fibre.  Thus  two  levers  can  be  so  placed  as  to  rest  on  the 
two  extremities  of  a  muscle,  at  the  same  time  that  the  free  ends  of  the  levers 
^  Biedermann :  FAektrophysiologie,  1895,  Bd.  i.  S.  124. 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       89 


touch  a  revolving  cylinder,  the  surface  of  wiiich  is  covered  with  paj)er  black 
eued  with  lampblack.  If,  when  the  cylinder  is  revolving,  one  end  of  the  mus 
cle  be  stimulated,  the  record  will 
show  that  the  lever  resting  on  that 
part  is  the  first  to  move,  making 
it  evident  that  that  part  of  the  mus- 
cle begins  to  thicken  first,  and  that 
the  contraction  does  not  begrin  at 
the  further  extremity  of  the  mus- 
cle until  somewhat  later.  The  re- 
cord given  in  Figure  30  was  ob- 
tained in  a  similar  experiment,  but 
one  in  which  the  contraction  of 
the  muscle  was  registered  by  the 
pince  myographique  and  recording  tambour  of  Marey  (see  Fig.  31). 

Bernstein  ^  measured  the  rate  at  which  the  irritating  process  is  transmitted 
along  the  muscle  by  recording  the  latent  period,  the  time  elapsing  between  the 


Fk;.  30.— Rate  of  conduction  of  the  fontraetion  pro- 
cess along  a  muscle,  as  shown  by  the  difl'erence  in  the 
time  of  thickening  of  the  two  extremities.  The  tuning- 
fork  waves  record  ^Jj  second  (after  Marey). 


Fig.  31.— Method  of  recording  the  rate  of  passage  of  the  contraction  process  along  a  muscle  (after 
Marey).  The  movements  of  the  muscle  are  recorded  by  means  of  air-transmission.  The  pince  myo- 
graphique consists  of  two  light  bars,  the  upper  of  which  acts  as  a  lever,  moving  freely  on  an  axis  sup- 
ported by  the  lower.  When  the  free  end  of  the  upper  bar  is  raised,  the  other  end  presses  down  on  a 
delicate  rubber  membrane  which  covers  a  little  metal  capsule,  which  is  carried  on  the  corresponding 
extremity  of  the  lower  bar.  The  capsule  is  in  air-communic.ation,  by  a  stiff-walled  rubber  tube,  with 
another  capsule  which  is  similarly  covered  with  rubber  membrane.  A  light  lever  is  connected  with  the 
membrane  of  the  second  tambour,  and  records  its  movements  on  the  surface  of  a  revolving  cylinder. 
The  muscle  is  placed  between  the  free  ends  of  the  bars  of  the  pince  myographique,  and,  when  the  muscle 
thickens  in  contraction,  it  raises  one  end  of  the  lever,  depresses  the  membrane  at  the  other  end,  and 
drives  air  into  the  recording  tambour,  and  thus,  by  automatically  raising  the  writing-point,  records  its 
change  in  form  on  the  cylinder. 

moment  of  irritation  and  the  beginning  of  the  contraction  (see  p.  101).  A 
lever  was  so  connected  with  one  end  of  the  muscle  as  to  record  the  instant  that 
it  began  to  thicken.  The  muscle  was  stimulated  in  one  experiment  at  the  end 
from  which  the  record  of  its  contraction  was  taken,  and  in  another  immediately 
'  Untersuchungen  iiber  die  ekktrische  Erregung  von  Muskeln  und  Nerven,  1871,  p.  79. 


90  AiX  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

lolloping  exjx'rinient  it  was  stiiniilatcd  near  the  uther  en<l.  'Die  distance 
between  the  .stimulated  points  being-  known,  tlie  rate  of  transmission  was 
reckoned  from  the  difference  in  the  hitent  j)eriods.  Jn  his  experiments  he 
found  the  rate  of  conduction  in  the  semimembranosus  of  the  frog  to  be  from 
3.2  to  4.4  meters  per  second.  Hermann  found  the  rate  to  be  2.7  meters  for 
the  curarized  sartorius  of  the  frog.  The  results  obtained  l)y  A  bey  and  some 
others  are  a  little  lower,  but  probably  3  meters  per  second  can  be  accepted  as 
the  average  normal  rate  for  frog's  muscle. 

Length  of  Wave. — By  such  experiments  it  becomes  obvious  that  the  con- 
traction process  passes  over  the  muscle,  in  the  form  of  a  wave.  In  an  experi- 
ment, such  as  Bernstein's,  in  which  the  thickening  of  the  muscle  is  recorded, 
we  can  determine  from  the  length  of  tlie  curve  written  by  the  contracting 
muscle  how  long  the  contraction  remains  at  a  given  place.  Knowing  this, 
and  the  rate  at  which  the  process  passes  along  the  fibre,  we  can  estimate  the 
length  of  the  contraction  wave,  just  as  we  could  reckon  the  length  of  a  train 
of  cars  if  we  knew  how  fast  it  was  moving  and  how  long  it  required  to  pass 
a  given  station.  Thus,  if  the  contraction  is  found  to  last  at  a  given  point 
on  the  muscle  0.1  second,  and  the  rate  at  Avhich  the  contraction  process  is 
travelling  is  3000  millimeters  per  second,  the  length  of  the  wave  is  300  milli- 
meters. According  to  Bernstein's  determinations,  the  length  of  the  wave  of 
contraction  in  a  frog's  striated  muscle  is  from  198-380  millimeters.  The 
length  of  a  striated  muscle-fibre  is,  at  the  most,  scarcely  more  than  40  milli- 
meters, and  normally  the  muscle-fibre  is  stimulated,  not  as  in  the  above  ex- 
periment at  one  end,  but  near  its  centre,  at  the  point  wdiere  the  nerve  joins 
it ;  the  irritation  process  spreads  along  the  fibre  in  both  directions  from  this 
point,  and  would  pass  over  the  distance  20  millimeters  so  quickly  that  practi- 
cally the  whole  muscle-fibre  would  be  in  the  same  phase  of  contraction  at  the 
same  time. 

Rate  of  Conduction  in  Different  Kinds  of  Muscle. — The  rate  of  conduction 
varies  veiy  considerably  in  the  muscles  of  different  animals,  and  in  different 
kinds  of  muscle  in  the  same  animal,  just  as  the  contraction  process  itself  dif- 
fers in  its  rate  and  strength. 

Meters  per  second. 

Smooth  muscle-fibres  of  the  ureters  of  the  rabbit  .    .    .    0.02-0.03    (Engelmann). 

Muscle  of  the  heart-ventricle  of  the  frog 0.1  (Waller). 

Contractile  substance  of  medusae 0.5  (Waller). 

Neck-muscles  of  the  turtle 0.1  -0.5      (Hermann  and  Abey). 

Gracilis  and  semimembranosus  of  the  frog  ....    3.2  -4.4      (Bernstein). 

Cruralis  (red  muscle)  of  the  rabbit 3.4  ( Rollet). 

Sterno-mastoid  of  the  dog .3.     -6         (Bernstein  and  Steiner). 

Semimembranosus  (white  muscle)  of  the  rabbit      ...    5.4  -11.4    (Rollet). 

Human  muscle 10.     -13        (Ilermannl. 

(6)  Rate  of  Conduction  in  Nerves. — Conduc-tivity  is  most  highly  developed 
in  the  case  of  the  nerve-fibre.  The  distances  through  which  it  acts  and  the 
rapidity  of  the  process  excite  our  wonder.  The  process  is  accompanied  by  no 
visible  change  in  the  nerve-fibre  it.<elf,  and  the  strength  and  rate  have  to  be 


GENERAL   PHYSIOLOGY   OF  MUSCLE   AND    NERVE.       91 

estimated  by  tlie  t'llect  [)fi)ducc'd  on  llic  organ  wliidi  tlie  nerve  excites  to  action, 
or  by  the  change  which  takes  phice  iu  the  electrical  condition  of"  the  nerve  as 
the  wave  of  excitation  sweeps  over  it. 

Rate  in  Motor  Nerves. — J  lelniholtz  was  the  first  to  measure  the  rate  of  con- 
duction in  nerves.*  Originally  he  employed  Pouillet's  method  for  measuring 
short  intervals  of  time.  The  arrangement  is  illustrated  in  Figure  32.  The 
moment  that  the  current  in  the  primary  coil  of  an  induction  apparatus  was 
broken  and  the  nerve  connected  with  the  secondary  coil  received  a  shock, 
a  current  was  thrown  into  the  coils  of  a  galvanometer  (see  p.  136).  An  instant 
after,  the  contraction  of  the  muscle  wiiich  resulted  from  the  stimulation  of  the 
nerve  broke  the  galvanometer  circuit.  The  amount  of  deviation  of  the  magnet 
of  the  galvanometer  varied  with  the  time  that  the  circuit  remained  closed,  and 
therefore  could  be  taken  as  a  measure  of  the  interval  elapsing  between  the 
stinmlation  of  the  nerve  and  the  contraction  of  the  muscle.  The  nerve  was 
excited  in  two  succeeding  experiments  at  two  points,  at  a  known  distance  apart, 
and  the  difference  in  the  time  records  obtained  was  the  time  required  for  the 
transmission  of  the  nerve-impulse  through  this  distance. 


Fig.  32.— Method  of  estimating  rate  of  conduction  in  motor  nerve  of  frog,  as  used  by  Helmholtz. 
The  horizontal  bar  a-b  is  supported  on  an  axis  in  such  a  manner  that  when  the  contact  is  made  at  a  it  is 
broken  at  b,  therefore  at  the  same  instant  a  current  is  made  in  the  galvanometer  circuit  and  opened  in 
the  primary  circuit  of  the  induction  apparatus.  When  the  muscle  contracts,  the  galvanometer  circuit 
is  broken  at  c.    The  nerve  was  stimulated  in  two  successive  experiments  at  d  and  e. 

Later,  Helmholtz  devised  a  method  of  directly  recording  the  contractions 
of  the  muscle,  and  employed  this  to  measure  the  rate  of  conduction  in  motor 
nerves.  He  stimulated  the  nerve  as  near  as  possible  to  the  muscle  and  re- 
corded the  contraction,  then  he  stimulated  the  nerve  as  far  as  possible  from  the 
muscle  and  again  recorded  the  contraction.  The  difference  in  time  between 
the  moment  of  excitation  and  the  beginning  of  the  contraction  in  the  two 
experiments  was  due  to  the  difference  in  the  distance  that  the  nerve-impulse 
had  to  pass  in  the  two  cases,  and,  this  distance  being  known,  the  rate  of  con- 
duction could  be  readily  calculated.  By  this  means  he  found  the  rate  of  trans- 
mission in  the  motor  nerves  of  the  frog  to  be  27  meters  per  second.  In 
similar  experiments  upon  men  he  recorded  the  contractions  of  the  muscles  of 
the  ball  of  the  thumb,  and  noted  the  difference  in  the  time  of  the  beginning 
of  the  contractions  when  the  median  nerve  was  excited  through  the  skin  at  two 
1  Helmholtz:   Archiv  fur  Anatomic  und  Physiologie,  1850,  p.  71-276;  1852,  p.  199. 


92  AN  AMERICAN   TEXT- HOOK    OF  PHYSIOLOGY. 

different  places.  Ho  found  the  average  normal  rate  lor  man  to  he  nhont  .'i4 
meters  per  second,  a  rate  which  is  considerably  (juicker  than  that  of  our 
fastest  express  trains,  but  a  million  times  less  than  the  rate  at  which  an  electric 
current  is  transmitted  along  a  wire.  These  determinations  are  still  accc|)tc(l 
as  approximately  correct  for  human  nerves,  although  they  are  found  to  varv 
very  considerably  under  different  conditions,  a  high  temperature  and  stront:; 
irritation  quickening  the  rate  to  90  or  more  meters  per  second.  Moreover, 
considerable  differences  exist  in  nerves  controlling  different  functions,  even  in 
the  same  animal.  Thus  Chauveau  gives  the  rate  for  the  fibres  of  the  vagus 
nerve,  which  su})ply  the  rapidly  contracting  striated  muscles  of  the  larynx,  as 
66.7  meters  ])cr  second ;  and  the  rate  for  vagus  fibres,  controlling  the  slower 
smooth  muscles  of  the  €eso})hagus,  ag  8.2  meters  per  second.  The  rate  of 
transmission  in  the  non-medullated  nerves  of  invertebrates  appears  to  be  still 
slower ;  the  nerve  for  the  claw-muscles  of  the  lobster  conducts  at  a  rate  of 
from  6  to  12  meters  per  second,  according  as  the  temperature  is  high  or  low 
(Fredericq  and  Vandervelde). 

Rate  in  Sensory  Nerves. — We  have  no  definite  knowledge  of  the  rate  of 
conduction  in  sensory  nerves.  The  attempt  has  been  made  to  measure  it,  by 
stimulating  the  sensory  fibres  of  a  nerve-trunk  at  two  different  points  and 
noting  the  difference  in  the  time  of  the  beginning  of  the  resulting  reflex  acts; 
or,  in  experiments  on  men,  the  difference  in  the  length  of  the  reaction  time 
has  been  taken  as  an  indication.  By  reaction  time  is  meant  the  interval  which 
elapses  between  the  moment  that  the  irritant  is  applied  and  the  signal  which  is 
made  by  the  subject  as  soon  as  he  feels  the  sensation.  Oehl  found  the  mean 
normal  rate  of  conduction  in  the  sensory  nerves  of  men  to  be  36.6  meters  per 
second.^  Dolley  and  Cattell,^  by  employing  the  reaction-time  method,  found 
the  rate  for  the  sensory  fibres  of  the  median  nerve  of  one  of  them  to  be  21.1 
meters  per  second,  and  for  the  other  49.5  meters  per  second,  while  the  posterior 
tibial  nerve  gave  rates,  for  one  of  them  31.1  meters,  and  for  the  other  64.9 
meters.  They  attribute  these  wide  variations  in  part  to  differences  in  the 
effectiveness  of  the  irritant  at  different  ])arts  of  the  skin,  but  chiefly  to  difler- 
ences  in  the  activity  of  the  central  nervous  processes  involved  in  the  act. 

In  spite  of  the  great  difficulty  of  getting  definite  measurements  on  men, 
we  may  conclude  from  the  work  of  these  and  other  observers  that  the  rate  of 
conduction  in  sensory  fibres  is  about  the  same  as  in  motor  fibres ;  in  the  case 
of  man  about  35  meters  ])er  second. 

Influences  ■which  Alter  the  Rate  and  Strength  of  the  Conduction  Pro- 
cess.— (a)  Effect  of  Death-processes. — Normally,  the  rate  of  conduction  in  mus- 
cle-fibres is  so  rapid  that  the  whole  muscle  appears  to  contract  at  the  same  time; 
but  there  are  certain  conditions  under  which  the  transmission  of  the  exciting 
influence  is  very  much  slowed,  or  even  altogether  prevented,  so  that  the  stinui- 
lation  of  a  given  part  of  the  muscle  results  in  a  local  swelling,  or  welt,  limited 
to  the  excited  area.     When  a  muscle  is  dying,  the  rate  of  conduction  as  well 

'  Oehl  :  Archives  italiennes  de  Biologie,  1895,  xxi.,  3.  p.  401. 
*  Psychological  Review,  New  York  and  London,  1894,  i.  p.  159. 


GENERAL    PHYSIOLOGY   OF   MUSCLE   AND    NERVE.       93 

as  the  rapidity  of  contraction  is  lessened.  The  muscles  of  warm-blooded  ani- 
mals exhiWit  more  strikiiit^  dilferemjes  than  tlu)se  of  cold-blooded,  but  both  are 
affe<!tcd  by  th(  in.  If  a  dying  muscle  be  mechanically  .stimulated,  as  by  adirect 
blow,  a  locali/t(l  swcUino-  develops  at  the  place;  and  if  the  muscle  be  stroked 
with  a  dull  instrument,  a  wave  of  contraction  maybe  seen  to  follow  the  instru- 
ment, the  contraction  beinji;  quite  strictly  limited  to  the  excited  area,  so  that 
one  can  write  on  the  nuiscle.  The  strict  localization  of  the  contraction  to  the 
irritated  parts  makes  it  evident  that  the  nerves  take  no  part  in  it,  hence  Schiff 
called  it  an  idio-muscular  contraction,  in  distinction  from  the  normal  neuro- 
muscular contraction.  In  the  dying  nerve  as  in  the  dying  muscle  the  rate  of 
transmission  is  found  to  be  slowed. 

(6)  Effeet  of  Mechanical  Conditions. — The  effect  of  pressure  to  lessen  the 
conduction-power  of  nerves  is  one  which  everyone  has  had  occasion  to  demon- 
strate on  himself.  For  example,  if  pressure  be  brought  to  bear  on  the  ulnar 
nerve  where  it  crosses  the  elbow,  the  region  su})plied  by  the  nerve  becomes  numb, 
"  goes  to  sleep,"  so  to  speak.  It  is  noticeable  that  only  a  slightly  greater 
effort  is  required  to  move  the  muscles,  at  a  time  when  no  sensations  are  received 
from  the  hand.  For  some  unexplained  reason  the  sensory  nerve- fibres  appear 
to  be  less  resistant  than  the  motor.  Gradually  applied  pressure  may  paralyze 
the  nerve  without  exciting  it,  but  on  the  removal  of  the  pressure  the  recovery 
of  function  of  the  sensory  fibres  is  accompanied  by  excitation  processes,  which 
are  felt  as  pricking  sensations  referred  to  the  region  supplied  by  the  nerve.  The 
exact  reason  of  the  loss  of  functional  power  caused  by  pressure  which  is  insuf- 
ficient to  produce  permanent  injury  is  not  altogether  clear.  Stretching  a  nerve 
may  act  to  lessen,  and  if  severe  destroy,  conductivity.  It  is  in  one  sense  another 
way  of  applying  pressure,  since  the  calibre  of  the  sheath  is  lessened  and  through 
the  fluids  pressure  is  brought  to  bear  on  the  axis-cylinder.  Of  course,  if  the 
stretching  were  excessive,  the  nerve-fibres  would  be  ruptured  and  degenerate. 

(c)  Effect  of  Tempei'oture  on  Conduction. — Helmholtz  and  Baxt  found  that 
by  cooling  motor  nerves  they  could  lower  the  rate  of  conduction,  and  by  heat- 
ing them  they  could  increase  it  even  more  markedly.  By  altering  the  tem- 
perature of  the  motor  nerves  of  man,  they  observed  rates  varying  from  30  to 
90  meters  per  second.  The  rate  of  the  motor  nerves  of  other  animals  is  like- 
wise greatly  altered  by  heat  and  cold.  This  is  true  of  the  invertebrates  as  well 
as  the  vertebrates ;  the  rate  in  the  nerves  of  the  claw-muscles  of  the  lobster, 
for  example,  changes  from  6  to  12  meters  per  second  as  the  temperature  is 
varied  from  10°  to  20°  C.  Sensory  nerve-fibres  are  similarly  influenced  by 
temperature.  Oehl  found  by  cooling  and  heating  the  nerves  of  men,  variations 
of  from  34  to  96  meters  per  second,  and  in  some  cases  even  greater  differences 
were  observed.  Both  the  sympathetic  and  vagus  nerve-fibres  in  the  frog  have 
their  influence  on  the  heart-beat  decreased  by  cold  and  increased  by  heat.^  The 
favorable  influence  of  heat  on  the  conduction  power  seems  common  to  all 
nerves,  but  only  within  certain  limits.  The  motor  fibres  of  the  sciatic  of  the 
frog  lose  their  power  to  conduct  at  41°  to  44°  C,  but  may  recover  the  power 
^  Stewart:  Journal  of  Physiology,  1891,  vol.  xii.,  No.  3,  p.  22. 


94  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

if  quiokly  cooled;   if  tlie  temperature  has  reached  50°  ('.  oondin-tivilv  is  per- 
manently lost. 

Nerves  of  like  function  in  diHerent  animals  may  lose  the  power  of  cimkIuc- 
tion  at  different  temperatures.  Thus  the  motor  fibres  of  the  sciatic  nerve  of 
the  dog  cease  to  conduct  at  G°  ('.,  those  of  the  cat  at  o°  to  3°  C,  of  the  frog  at 
about  0°  C.  The  inhibitory  fibres  of  the  vagus  nerve  of  the  dog  show  dimin- 
ished activity  at  3°  C,  and  bi'come  Mliolly  inactive  at  0°  C. ;  the  inhii)itorv 
fibres  of  the  vagus  of  the  rabbit  become  inactive  at  15°  C. 

Different  kinds  of  fibres  in  the  same  nerve-trunk  may  be  differentlv  affected 
by  temperature,  and  this  difference  may  be  sufficiently  marked  in  some  cases  to 
be  used  as  a  means  of  distinguishing  thcm.^  For  example,  the  temperature 
limits  at  which  the  vaso-coustrictor  fibres  of  the  sciatic  of  the  cat  can  conduct 
are  2°-3°  C.  to  47°  C,  while  the  limits  for  the  dilator  fibres  are  both  lower 
and  higher  than  for  the  constrictors.  If  cold  be  a])plied  to  the  sciatic  nerve, 
the  fibres  suj)plying  the  extensor  muscles  seem  to  fail  before  those  M'hich  in- 
nervate the  flexors. 

Further,  it  has  been  observed  that  if  cold  be  applied  locally  to  a  nerve,  the 
part  affected  loses  its  power  to  conduct,  and  acts  as  a  block  to  the  passage  of 
the  nerve-impulse  generated  in  another  part  of  the  nerve ;  on  the  other  hand, 
the  strength  of  an  impulse  is  increased  by  passage  through  a  region  which  has 
been  warmed.  These  facts  remind  us  of  the  effect  of  heat  and  cold  on  the 
activity  of  other  forms  of  protoplasm  and  would  find  a  comparatively  easy 
explanation  were  we  content  to  look  upon  conduction  as  the  result  of  chemical 
change  in  the  axis-cvlinder.  The  fact  that  conduction  does  not  cause  fatisrue 
is  opposed  to  such  an  explanation,  and  so  we  take  refuge  in  the  idea  that  heat 
is  favorable  and  cold  unfavorable  to  molecular  activity  in  general. 

{d)  Effect  of  Chemicals  and  Drugs. — The  conductivity,  like  the  irritabilitv, 
of  nerve  and  muscle  is  greatly  influenced  by  anything  which  alters  the  chemical 
constitution  of  active  substance.  In  general  it  may  be  said  that  influences 
w-hich  increase  or  decrease  the  one  have  a  similar  effect  upon  the  other,  but 
there  are  important  exceptions  to  the  rule.  Thus  the  dii-ect  application  of 
alcohol,  ether,  etc.,  may  destroy  the  conductivity  without  greatly  lessening  the 
irritabilitv,  while  carbon  dioxide  mav  destrov  the  irritabilitv,  thouirh  leavinsr 
the  conductivity  unimpaired. 

(e)  Effect  of  a  Constant  Battery  Current. — A  constant  electric  current,  if  al- 
lowed to  flow  through  a  nerve  or  muscle,  not  only  alters  the  irrital)ility  but  also 
the  conductivity.  The  change  in  the  conductivity  affects  both  the  strength 
and  rate  of  the  conduction  process.  Von  BezokP  found  that  weak  and 
medium  currents  have  little  effect  on  the  conductivity,  but  that  strong  currents 
completely  destroy  the  power  of  the  nerve  to  transmit  the  nerve-impulse.  As 
the  strength  of  the  current  is  increased  the  first  effect  is  observed  at  the  anode, 
and  shows  itself  in  a  slowing  of  the  passage  of  the  exciting  imj)ulse.  This 
action  is  the  greater  the  more  of  the  nerve  exposed  to  the  current,  the  stronger 

'  Howell,  Budgett,  and  Leonard  :  Journal  of  Physiology,  vol.  xvi.,  Nos.  3  and  4,  1894. 
*  Untersuchungeyi  iiber  die  elektrische  Erregung  den  Nerven  und  Muskeln,  Leipzig,  1861. 


GENERAL    PHYSIOLOGY    OF   MUSCLE    AND    NERVE.       95 

the  curi'cnt,  and  the  l(,)iiii('i'  it  is  closed.  The  loss  of  conduction  ])owcr  is  asso- 
ciated with  cliauges  at  the  j)Iace  wlicre  the  cun-cnt  enters  and  where  it  leaves 
the  nerve  ratlier  than  with  alterations  witiiin  the  intrapolar  re<:;ion.  Engclniann, 
in  his  experiments  on  the  smooth  muscle-fibres  ot"  the  ureter,  saw  a  decline  of 
j)ower  of  conduction  at  tlie  anode  by  weak  currents,  which  when  the  strength 
of  the  current  was  increased  appeared  also  at  the  kathode ;  the  conductivity 
was  wholly  lost  at  botii  poles  when  the  current  was  very  strong.  In  the  case 
of  a  striated  muscle,  such  as  the  sartorius  of  the  frog,  the  kathode  has  been 
found  to  become  impassable  after  strong  currents  have  flowed  through  a  nuiscle 
for  a  considerable  time.     The  same  is  true  of  nerves. 

It  is  not  surprising  that  a  current  which  can  greatly  decrease  the  ii-ritability 
at  the  anode,  and  even  inhibit  a  contraction  which  may  be  present  wlien  it  is 
applied,  should  be  found  to  decrease  the  conductivity  as  well,  but  that  the  con- 
ductivity should  be  decreased  at  the  kathode,  where  the  irritability  is  greatly 
increased,  was  not  to  be  expected.  Rutherford  ^  found  that  with  M^eak  currents 
the  rate  of  the  conduction  power  at  the  kathode  was  increased  rather  than 
diminished,  and  that  it  was  only  when  strong  currents  acted  a  considerable 
tin)e  that  the  conduction  power  lessened  at  the  kathode.  Biedermann  explains 
this  on  the  ground  that  the  increased  excitability  at  the  kathode  leads  in  the 
muscle  to  a  condition  of  latent  contraction  and  therefore  to  fatigue,  and  that 
it  is  this  which  lessens  the  conductivity.  The  lessened  power  to  conduct  con- 
tinues at  the  kathode  after  the  removal  of  the  current.  There  is  little  doubt 
that  fatigue  interferes  with  the  conduction  power  of  muscle,  but  this  explana- 
tion would  hardly  apply  to  nerves  which  are  not  known  to  fatigue  at  the  point 
of  stimulation,  i.  e.  if  we  limit  the  term  fatigue  to  changes  resulting  from 
physiological  activity.  Undoubtedly  chemical  and  j)hysical  alterations  may 
occur  in  nerves  as  a  result  of  the  passage  of  an  electric  current  through  them, 
and  it  would  seem  as  if  the  loss  of  conductivity  which  they  show  when  sub- 
jected to  strong  currents  is  to  be  accounted  for  by  such  changes. 

The  changes  produced  in  the  conductivity  of  nerves  by  strong  currents 
explain  the  failure  of  the  closing  of  the  ascending  current  and  opening  of  the 
descending  current  to  irritate  the  muscle  (see  Pfliiger's  law,  p.  60).  In  the 
former  case  the  anode  region  of  decreased  conductivity  intervenes  between  the 
kathode,  wdiere  the  closing  stimulus  is  developed,  and  the  muscle.  In  the 
latter  case  the  irritation  developed  at  the  anode,  on  the  opening  of  the  current, 
is  unable  to  pass  the  region  of  decreased  conductivity  which  is  formed  at  the 
kathode,  and  which  persists  after  the  current  is  opened. 

Practical  A-pplkation  of  Alterations  produced  by  Battery  Currents, — The 
alterations  produced  by  strong  battery  currents  in  the  irritability  and  conduc- 
tivity of  nerves  and  muscles  may  be  made  use  of  by  the  physician.  If  the 
effect  of  only  one  pole  is  desired,  it  may  be  applied  as  a  small  electrode  im- 
mediately over  the  region  to  be  influenced,  while  the  other  pole  may  be  a  large 
electrode  placed  over  some  distant  part  of  the  body  where  there  are  no  import- 
ant organs.  The  size  of  the  electrodes  used  determines  the  density  of  the 
'  Journal  of  Anatomy  and  Physiologic,  1867,  vol.  2,  p.  87. 


96  AX  AMEBICAX   TEXT-BOOK   OF   PHYSIOLOGY. 

current  leaving  or  entering  the  Ixxly  and  consequently  the  intensity  of  its 
action.  The  application  of  the  anode  to  a  region  of  increased  excitai)ility,  hy 
decreasing  the  irritability,  may  for  the  tinie  lessen  irritation;  on  the  other 
hand  the  kathode  may  heighten  the  irritability  of  a  region  of  decreased 
excitability.  The  sending  of  a  strong  polarizing  current  through  a  motor 
nerve,  by  lessening  the  conductivity,  may  prevent  abnormal  motor  impulses 
from  reaching  muscles,  and  so  stop  harmful  ''  cramps ; "  or  the  sending  of 
such  a  current  through  a  sensory  nerve  may,  during  the  flow  of  the  cur- 
rent, keep  painful  impulses  from  reaching  the  central  nervous  system.  In 
applving  a  strong  battery  current  to  lessen  irritability  or  conductivity  it 
must  be  remembered  that  the  after-effect  of  such  a  current  is  increa.sed 
irritability. 

(/)  Effect  of  Conduction. — Many  experiments  have  been  made  in  the  hope 
of  detecting  some  form  of  chemical  change  as  a  result  of  conduction.  The 
nerve  has  been  stimulated  for  many  hours  in  succession  with  an  electric  cur- 
rent, and  then  been  examined  with  the  utmost  care  to  find  whether  there  had 
been  an  accumulation  of  some  waste  product,  as  carbon  dioxide,  or  some  other 
acid  body.  The  gray  matter  of  the  spinal  cord,  which  is  largely  composed  of 
nerve-cells,  is  found  to  become  acid  as  a  result  of  activity,^  but  this  cannot  be 
found  to  be  the  case  w^ith  the  white  matter  of  the  cord,  which  is  chiefly  made 
up  of  nerve-fibres,  nor  has  an  acid  reaction  been  obtained  with  certainty  in 
nerve-trunks.^ 

Not  only  has  an  attempt  to  discover  this  or  other  waste  products  which 
might  be  supposed  to  result  from  chemical  changes  within  the  nerve-fibre 
failed,  but  observers  have  been  unable  to  obtain  evidence  of  the  liberation 
of  heat,  which  one  would  expect  to  find  were  the  nerve-fibre  the  seat  of  chem- 
ical changes  during  the  process  of  conduction.^  Stewart  writes  :  "  Speaking 
quite  roughly,  I  think  we  may  say  that  in  the  nerves  of  rabbits  and  dogs  there 
is  not  even  a  rise  of  temperature  of  the  general  nerve-sheath  of  -^ijy^  of  a 
degree  during  excitation." 

Many  experiments  have  been  made  to  ascertain  whether  a  nerve  would 
fatigue  if  made  to  conduct  for  a  long  time.  Most  of  these  have  been  made 
upon  motor  nerves,  the  amount  of  contraction  of  the  muscle,  in  response  to  a 
definite  stimulus  applied  to  the  nerve,  being  taken  as  an  index  of  the  activity 
of  the  nerve.  Since  the  muscle  would  fatigue  if  stimulated  continuously  for 
a  long  time,  various  means  have  been  employed  to  block  the  nerve-impulse 
and  prevent  it  from  reaching  the  muscle,  except  at  the  beginning  and  end  of 
the  experiment.  This  block  has  been  established  by  passing  a  continuous 
current  through   the   nerve   near  the   muscle,  thus   inducing  an   electrotonic 

'  Funke:  Archivfiir  Anatomie  unci  Physioloyie,  1859,  p.  835.  Ranke:  Centralblatt  fiir  medicin- 
ische  Winsenschafl,  1868  and  1869. 

^  Heidenhain:  Studien  aus  dem  physiologischen  Institut  zu  Breslau,  ix.  p.  248;  Centralblatt  Jiir 
Medicin,  1868,  p.  833.  Tigerstedt:  "Studien  iiber  meclianische  Nervenreizung,"  Acta  Socielatis 
Scienliarnm  Fennmz,  1880,  torn.  xi. 

^Helmholtz:  ArcMv  fiir  Anatomie  und  Phymologie,  1848,  p.  158.  Heidenhain:  op.  cit. 
RoUeston :  Journal  of  Physiology,  1890,  vol.  xi.  p.  208.     Stewart :  ihid.,  1891,  vol.  xii.  p.  424. 


GENERAL    PHYSIOLOGY    OF   MUSCLE   AND    NERVE.       9? 

cluuit^o  aud  uun-conclucting  aiva ; '  or  the  nerve-eiids  were  poisoned  with 
curare  (see  p.  41),  and  tiie  nerve  excited  until  the  effect  of  the  dru«r  wore  off", 
and  the  nerve-impulse  was  able  to  reach  the  muscle;^  or  the  part  of  the  nerve 
near  the  muscle  was  temporarily  deprived  of  its  conducting  power  by  an 
anaesthetic,  such  as  ether.  Another  method  of  experimentation  consisted  in 
using  the  negative  variation  current  of  a  nerve  (see  p.  140)  as  an  indication 
of  its  activity,  the  presence  of  the  current  being  observed  with  the  galvanom- 
eter.^ Other  experimenters  have  examined  the  vagus  nerve,  to  see  if  after 
long-continued  stimulation  it  was  still  capable  of  inhibiting  the  heart,  the 
effect  of  the  stimulation  being  prevented  from  acting  on  the  heart  muscle 
during  the  experiment  by  atropin/  or  by  cold,  applied  locally  to  the  nerve.* 
Still  another  method  was  to  study  the  effect  of  long-continued  stimulation  on 
the  secretory  fibres  of  the  chorda  tympani,  the  exciting  impulse  being  kept 
from  the  gland-cells  by  atropin.*'  Most  of  these  experiments  have  yielded  nega- 
tive results,  aud  it  is  doubtful  whether  nerves  are  fatigued  by  the  process  of 
conduction. 

These  results,  of  course,  do  not  show  that  the  nerve-fibres  can  live  and 
function  independently  of  chemical  changes.  As  has  been  said,  nerves  lose  their 
irritability  in  time  if  deprived  of  the  normal  blood-supply,  and  undoubtedly 
they  are,  like  all  protoplasmic  structures,  continually  the  seat  of  metabolic 
processes.  The  normal  function  of  the  nerve,  however,  the  conduction  of  the 
nerve-impulse,  seems  to  take  place  without  any  marked  chemical  change. 

Nature  of  the  Conduction  Process. — There  have  been  a  great  many 
views  as  to  the  nature  of  the  conduction  process,  one  after  the  other  being 
advanced  and  combated  as  physiological  facts  bearing  on  the  question  have 
been  accumulated.  It  has  been  suggested  that  the  whole  nerve  moved  like  a 
bell-rope ;  that  the  nerve  w'as  a  tube,  and  that  a  biting  acid  flowed  along  it ; 
that  the  nerve  contained  an  elastic  fluid  which  was  thrown  into  oscillations ; 
that  it  conducted  an  electric  current,  like  a  wire;  that  it  was  composed  of 
definitely  arranged  electro-motor  molecules  which  exerted  an  electro-dynamic 
effect  on  each  other ;  that  it  was  made  up  of  chemical  })articles,  which  like 
the  particles  of  powder  in  a  fuse,  underwent  an  explosive  change,  each  in 
turn  exciting  its  neighbor ;  that  the  irritant  caused  a  chemical  change,  which 
produced  an  alteration  of  the  electrical  condition  of  such  a  nature  as  to  excite 
neighboring  parts  to  chemical  change  aud  thereby  to  electrical  change,  and 
so  alternating  chemical  and  electrical  changes  progressed  along  the  fibre  in  the 
form  of  a  w^ave ;  finally,  tliat  the  molecules  of  the  nerve-substance  underwent 
a  form  of  physical  vibration  analogous  to  that  assumed  for  light. 

^  Bernstein:  Pfliicjei-'s  Archiv,  \^11,  xv.  p.  289.  Wedenski :  CentralblaU  fur  die  medicinischen 
Wi'-semrhaften,  1884. 

'^  Bowditch :  Journal  of  Phi/siolof/y,  1885,  vi.  p.  133. 

^  Wedenski :  loc.  cit.    Maschek  :  Sitzungsberichte  dcr  Wiener  Academie,  1887,  Bd.  xcv.  Abthl.  3. 

*  Szana:  Archiv  fiir  Anatnmie  und  Physiologie,  1891,  p.  315. 

*  Howell,  Budgett,  and  Leonard:  Journal  of  Physiolo(/ij,  1894,  xvi.  p.  312. 
^  Lambert :  Comptes-rendus  de  la  Societe  de  Biolofjie,  1894,  p.  511. 

7 


98  ^l.V  AMERICAN   TEXT- BOOK    OF   PHYSIOLOGY. 

A  discussion  of  these  different  theories,  none  ot"  whicii  can  be  regarded 
as  entirely  satisfactory,  cannot  be  entered  upon  here. 

D.  Contractility. 

Contractility  is  the  property  of  protoplasm  by  virtue  of  which  the  cell  is 
able  to  change  its  form  when  subjected  to  certain  external  influences  called 
irritants,  or  when  excited  by  certain  changes  occurring  within  itself.  The 
change  of  form  does  not  involve  a  change  of  size.  The  contraction  is  the 
result  of  a  change  in  the  position  of  the  more  fluid  parts  of  the  cell-protoplasm, 
and  the  effect  is  to  cause  the  cell  to  approach  a  sjihcrical  sha|>e.  In  the  case  of 
an  amwba,  for  instance,  excitation  causes  a  drawing  in  of  the  pseudopods,  and 
as  the  material  in  them  flows  back  into  the  cell  the  body  of  the  cell  expands 
and  acquires  a  globular  form.  In  the  simpler  forms  of  contractile  protoplasm 
the  movement  does  not  appear  to  be  limited  to  any  special  direction,  but  in  the 
case  of  the  highly  difJ'erentiated  forms,  such  as  muscle,  both  contraction  and 
relaxation  occur  on  definite  lines. 

When  a  muscle  is  excited  to  action,  energy  is  liberated  through  chemical 
change  of  certain  constituents  of  the  muscle-substance,  and  this  energy  in  some 
unknown  way  causes  a  rearrangement  of  the  finest  particles  of  the  muscle-sub- 
stance, and  the  consequent  change  of  form  ])eculiar  to  the  contracted  stjite. 
When  the  irritation  ceases  and  relaxation  takes  place,  there  is  a  sudden  return 
of  the  muscle-substance  to  the  position  of  rest,  either  because  of  elastic  recoil  or 
of  some  other  force  at  work  within  the  muscle  itself.  That  the  recovery  of 
the  elongated  form  peculiar  to  the  resting  muscle  is  not  dependent  on  external 
influences  is  evidenced  by  the  fact  that  a  muscle  floating  on  mercury,  and 
subjected  to  no  extending  force,  will  on  the  cessation  of  irritation  assume  its 
resting  form.  The  relaxation  no  less  than  the  contraction  must  be.  regarded 
as  an  active  process,  but  on  account  of  their  flexibility  muscle-fibres  are  incap- 
able of  exerting  an  expansion  force,  therefore  cannot  by  relaxing  do  external 
work. 

Both  the  histological  structure  and  physiological  action  of  the  striated  mus- 
cles which  move  the  bones  show  them  to  be  the  most  highly  differentiated,  the 
most  perfect  form  of  contractile  tissue.  It  is  by  means  of  these  structures  that 
the  higher  animals  perform  all  those  voluntary  movements  by  which  they  change 
their  position  with  reference  to  external  objects,  acquire  nourishment,  protect 
themselves,  and  influence  their  surroundings.  Aii  exact  knowledge  of  the 
method  of  action  of  these  mechanisms  and  the  influences  which  affect  them  is 
therefore  of  the  greatest  importance  to  us. 

1.  Simple  Muscle -Contractions  Studied  by  the  Graphic  Method. — 
When  a  mu.-icle  makes  a  single  contraction,  in  respon.se  to  an  electric  shock  or 
other  irritant,  the  change  of  form  is  too  rapid  to  be  followed  by  the  eye.  To 
acquire  an  adequate  idea  of  the  character  of  the  movement  it  is  necessary  that 
we  should  obtain  a  continuous  record  of  the  alterations  in  shajie  which  it  un- 
dergoes. This  can  be  done  by  connecting  the  muscle  with  a  mechanism  which 
enables  it  automatically  to  record  its  movements. 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       99 


If  one  moves  a  pencil  vertically  up  and  down  on  a  piece  of  paper,  a  straight 
line  is  written  ;  if  while  the  vertical  movements  are  continued  the  paper  be 
drawn  along  at  a  regular  rate  in  a  direction  at  right  angles  to  the  move- 
ment of  the  pencil,  a  curve  will  be  traced.  If  the  paper  be  moved  at  a  regular 
rate,  the  shape  of  the  curve  will  depend  on  the  rate  at  which  the  pencil  is 
moved,  and,  if  the  speed  of  the  paper  be  known,  the  rate  of  movement  of  the 
pencil  can  be  readily  determined.  This  princi})le  is  employed  in  recording  the 
movements  of  muscles.  The  muscle  is  connected  with  a  mechanism  which 
rises  and  falls  as  the  muscle  contracts  and  relaxes,  and  records  the  movement 
of  the  muscle  on  a  surface  which  passes  by  the  writing-point  at  a  regular 
speed  (see  Fig.  35) ;  such  a  record  is  called  a  myogram. 

The  Myograph. — The  writing  mechanism,  together  with  the  apparatus 
which  moves  the  surface  on  which  the  record  of  the  movement  of  a  contracting 
muscle  is  taken  is  called  a  myograph.  The  writing  mechanism  has  usuallv  the 
form  of  a  light,  stitf  lever,  which  moves  very  easily  on  a  delicate  axis ;  the 
lever  is  so  connected  w^ith  the  muscle  as  to  magnify  its  movements.  The  point 
of  the  lever  rests  very  lightly  against  a  glass  plate,  or  surface  covered  with 
glazed  paper,  which  is  coated  with  a  thin  layer  of  soot.  The  point  of  the  lever 
scratches  oflP  the  soot,  and  the  movements  are  recorded  as 
a  very  fine  white  line.  At  the  close  of  the  experiment 
the  record  is  made  permanent  by  passing  it  through  a 
thin  alcoholic  solution  of  shellac.  The  recording  surface 
in  some  cases  is  in  the  form  of  a  plate,  in  others  of  a  cyl- 
inder, and  is  moved  at  a  regular  rate  by  a  spring,  pendu- 
lum, falling  weight,  clockwork,  electric  or  other  motor.^ 

The  record  which  is  traced  with  the  myograph  lever 
by  the  muscle  has  the  form- of  a  curve.  From  the  height 
of  the  curve  we  can  readily  estimate  the  amount  that 
the  muscle  changes  its  length,  but  in  order  to  accu- 
rately determine  the  duration  of. the  contraction  process 
and  the  time  relations  of  different  parts  of  the  curve, 
it  is  necessary  to  know  the  exact  rate  at  which  the 
recording  surface  is  moving.  The  shape  of  the  curve 
drawn  by  the  muscle  will  depend  very  largely  on  the 
rate  of  the  movement  of  the  surface  on  which  the  record 
is  taken.  This  is  illustrated  by  the  four  records  repro- 
duced in  Figure  33.  These  were  all  taken  from  the 
same  muscle  within  a  few  minutes  of  each  other  and 
under  exactly  the  same  conditions,  except  that  in  the 
successive  experiments  the  speed  of  the  drum  on  which 
the  record  was  traced  was  increased. 

A  glance  at  these  records  shows  that  a  knowledge 
of  the  rate  of  movement  of  the  surface  on  which  the  record  is  taken  is  indis- 
pensable to  an  understanding  of  the  time  relations  of  the  different  parts  of  the 
^  See  O.  Langendorff;  Physiologische  Graphik,  Franz  Deuticke,  Leipzig,  1891. 


Fig.  33.— Records  of  four 
contractions  of  a  gas- 
trocnemius muscle  of  a 
frog:  a,  recording  sur- 
face at  rest;  b,  surface 
moving  slowly ;  c,  sur- 
face moving  more  rapidly ; 
d,  surface  moving  even 
faster. 


100 


AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


curve  written  by  the  muscle.     The  rate  of  movement  of  the  reconlin*;  surface 
can  be  registered  by  an  instrument  called  a  chronograph. 

The  chronograph  [g,  Fig.  34),  consists  of  one  or  two  coils  of  wire  wound 
round  cores  of  soft  iron,  and  a  little  lever  bearing  a  strip  of  iron,  which  is 
attracted  to  the  soft-iron  cores  whenever  they  are  magnetized  by  an  elec- 
tric current  flowing  through  the  coils  of  wire  about  them.  When  the  current 
ceases  to  flow  and  the  iron  cejises  to  be  magnetized,  a  spring  draws  the  lever 
away  from  the  iron.     Many  of  the  instruments  employed  for  this  purpose  are 

rfr 


Fig.  34.— Method  of  interrupting  an  electric  circuit  by  a  tuning-fork,  and  of  recording  the  interrup- 
tions by  means  of  an  electro-magnet:  a,  battery:  b,  tuning-fork,  with  platinum  wire  at  the  extremity 
of  one  of  its  arms,  which  with  each  vibration  of  the  fork  makes  and  breaks  contact  with  the  mercury 
in  the  cup  below:  c,  mercury  cup:  c,  electro-magnet  which  keeps  the  fork  vibrating;  ^,  chronograph. 
The  current  from  the  battery  a,  passes  to  the  fork  h,  then,  by  way  of  the  platinum  wire,  to  the  mercury 
in  cup  c,  then  to  the  binding-post  d,  where  it  divides,  a  part  going  through  the  coils  of  wire  of  the 
chronograph  g,  and  thence  to  the  binding-post  /,  the  rest  through  the  coil  of  wire  of  electro-magnet 
e,  and  then  to  the  post/,  from  which  the  united  threads  of  current  flow  back  to  the  battery.  The 
electro-magnet  e  keeps  the  fork  in  vibration,  because  when  the  platinum  wire  enters  the  mercury 
at  c,  the  circuit  is  completed  and  the  electro-magnet  magnetizes  its  soft-iron  core,  which  attract.^  the 
arms  of  the  fork,  and  thus  draws  the  wire  out  of  the  mercury  and  so  breaks  the  circuit.  When  the 
current  is  broken  the  fork,  being  released,  springs  back,  dips  the  wire  into  the  mercury,  and  by 
closing  the  circuit  causes  the  process  to  be  repeated. 

very  delicate,  and  are  capable  of  responding  to  ver^'  rapid  interruptions  of  the 
current.  The  electric  current  is  made  and  broken  at  regular  intervals  by  a  clock, 
tuning-fork  (6,  Fig.  34),  or  other  interrupting  mechanism,  and  the  lever  of  the 
chronograph,  which  has  a  writing-point  at  its  free  end,  moves  correspondingly 


a 

Ir 

C                    c 

f. 

rv,.-V.,VA.-A-..V..VtfJtfJ-/';'J-/AW« 

wwwwwJ 

hN\tj\t\t\rN\tjv\i 

^^^w^^^^^w^^A^^^WA^^^^^^;  y 

Fig.  35. — Myogram  from  gastrocnemiii?  muscle  of  frog ;  beneath,  ihe  time  is  recorded  in  0.005  second : 
a,  moment  of  excitation  ;  b,  beginning  of  contraction  ;  c,  height  of  contraction  ;  d,  end  of  contraction. 

and  traces  an  interrupted  line  on  the  recording  surface  of  the  myograph  (see 
Fig.  35).  The  space  between  the  succeeding  jogs  marked  by  the  chronograph 
lever  is  a  measure  of  the  amount  of  the  surface  which  passed  the  point  of  the 
chronograph  in  one  second,  ^^  second,  or  jl^  second,  as  the  ca.se  may  be. 


GENERAL    PHYSIOLOGY    OF  MUSCLE   AND    NERVE.       101 

Myogram  of  Simple  Muscle-contraction. — 'J'lic  rate  of  the  movement  of  the 
muscle  during  every  part  of  its  contraction  can  he  loadily  determined  hv  com- 
paring  the  record  it  has  (h'awii  witli  that  of  the  chronograph. 

Figure  35  is  the  repnuUK'tion  of  a  single  contraction  of  a  gastrocnemius 
muscle  of  a  frog.  The  rise  of  the  curve  shows  that  the  contraction  began 
comparatively  slowly,  soon  became  very  rapid,  but  toward  its  close  was  again 
gradual ;  the  relaxation  began  almost  immediately,  and  took  a  similar  course, 
though  occupying  a  somewhat  longer  time.  The  electric  current  which 
actuated  the  chronograph  was  made  and  broken  by  a  tuning-fork  which 
made  200  complete  vibrations  per  second,  therefore  the  s]>aces  between  the 
succeeding  peaks  of  the  chronograph  curve  each  represents  0.005  second.  A 
comparison  of  the  movements  of  the  muscle  with  the  tuning-fork  curve 
reveals  that  about  yfg-  second  elapsed  between  the  point  />,  at  which  the  muscle 
curve  began  to  rise,  and  c,  the  point  at  which  the  full  height  of  the  contraction 
was  reached,  and  that  about  ^^  second  was  occupied  by  the  return  of  the 
muscle  curve  from  c  to  point  d,  at  the  level  from  which  it  started.  The  muscle 
employed  in  this  experiment  was  slightly  fatigued,  and  the  movements  were 
in  consequence  a  little  slower  than  normal. 

Latent  Period. — The  time  that  elapses  between  the  moment  that  a  stim- 
ulus reaches  a  muscle  and  the  instant  the  muscle  begins  to  change  its  form  is 
called  the  latent  period.  In  the  experiment  recorded  in  Fig.  35  the  muscle 
received  the  shock  at  the  point  a  on  the  curve,  but  the  lever  did  not  begin  to 
rise  until  the  point  h  was  reached.  The  latent  jieriod  as  recorded  in  this  ex- 
periment was  about  0.006  second.  The  latent  period  and  the  time  relations  of  the 
muscle-curve  were  first  measured  by  Helmholtz,  Avho  introduced  the  use  of  the 
myograpli.^  Helmholtz  concluded  from  his  experiments  that  the  latent  period 
for  a  frog's  muscle  is  about  y^  second,  that  the  rise  of  the  curve  occupies 
about  yI^,  and  the  fall  about  -^^  second,  the  total  time  occupying  about  -^ 
second.  These  rates  (^an  be  considered  approximately  correct,  excepting  for 
the  latent  period,  which  has  been  found  by  more  accurate  methods  to  be  con- 
siderably shorter.  Tigerstedt  connected  a  curarized  frog's  muscle  with  a  myo- 
graph lever,  which  was  so  arranged  as  to  break  an  electric  contact  at  the 
instant  that  the  muscle  made  the  slightest  movement ;  the  break  in  the  electric 
circuit  was  recorded  on  a  rapidly  revolving  drum,  by  an  electro-magnet  similar 
to  the  chronograph.  By  this  means  he  found  the  latent  period  of  a  frog's 
muscle  may  be  as  short  as  0.004  second.  Tigerstedt^  did  not  regard  this  as 
the  true  latent  ])eriod,  however ;  he  expressed  the  belief  that  the  muscle  proto- 
plasm must  have  begun  to  respond  to  the  excitation  much  sooner  than  this. 
The  contraction  of  the  whole  muscle  is  the  result  of  a  shortening  of  each  of  the 
myriad  of  light  and  dark  disks  of  which  each  of  the  muscle-fibres  is  composed 
(see  Fig.  36).  The  distance  to  be  traversed  by  the  finest  particles  of  muscle- 
substance  is  microscopic,  hence  the  raj^idity  of  the  change  of  form  of  the  M^hole 
muscle.     Even  such  a  change  would  require  time,  however,  and  it  is  probable 

*  Archiv  fur  Anatomie  und  Pltysiologie,  1850,  p.  308. 
^llnd.,  1885,  Suppl.  Bd.,  p.  111. 


102  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

tliat  the  imiscle  protoplasm  becomes  active  before  any  outward  manifestation 
occurs.     Tliat  this  view  is  correct  has  been  proved  by  electrical  observations. 

When  mnsclt'  protoplasm  jiasst'S  from  a  state  of  rest  to  one  of  acti(»n  it 
undergoes  an  alteration  in  electrical  condition.  This  change  can  be  detected  by 
the  galvanometer  (Fig.  58,  p.  135)  or  by  the  capillary  electrometer  (Fig.  59, 
p.  136).  Burdon  Sanderson^  has  foinid  that  by  the  aid  of  the  latter  instru- 
ment an  alteration  of  the  electrical  condition  of  the  muscle  of  a  frog  can  be 
detected  within  0.0025  second  after  the  stimulus  has  been  applied  to  it.  Since 
some  slight  interval  of  time  nuist  have  been  lost  even  by  this  delicate  method, 
it  would  seem  that  muscle  protoplasm  begins  to  be  active  at  the  instant  it  is 
stimulated. 

According  to  this  view,  muscle-substance  has  no  latent  period ;  neverthe- 
less we  can  still  speak  of  the  latent  period  of  the  muscle  as  a  whole.  It  will 
be  necessary,  however,  to  distinguish  between  the  electrical  latent  j)criod  and 
the  mechanical  latent  period  :  by  the  former  we  mean  the  time  which  ela])ses 
between  the  moment  of  excitation  and  the  first  evidence  obtainable  of  a  change 
in  the  electrical  condition  of  the  muscle ;  by  the  latter,  the  time  between  exci- 
tation and  the  earliest  evidence  of  movement  which  can  be  observed.  In  the 
case  of  the  striated  muscles  of  a  frog  the  electrical  latent  period  is  about  0.0025 
second,  and  the  mechanical  about  0.004  second.  Mendelssohn^  estimated  the 
mechanical  latent  period  of  the  muscles  of  man  to  be  about  0.008  second. 
There  can  be  little  doubt,  however,  that  this  figure  is  too  large. 

Bernstein^  found  that  if  a  normal  frog's  muscle  be  excited  indirectly, 
by  the  stimulation  of  its  nerve,  the  mechanical  latent  period  is  somewhat 
longer  than  when  it  is  directly  excited.  Of  course  a  certain  length  of  time  is 
required  to  transmit  the  excitation  through  the  length  of  nerve  intervening 
between  the  point  stimulated  and  the  muscle  fibres.  If  this  time  be  deducted, 
there  still  remains  a  balance  of  about  0.003  second,  which  can  only  be  ac- 
counted for  on  the  assumption  that  the  motor  nerve  end-plates  require  time  to 
excite  the  muscle-fibres.  The  motor  end-plates  are  therefore  said  to  have  a 
latent  period  of  0.002-0.003  second. 

The  latent  period,  and  the  time  required  for  the  rise  and  fall  of  the  myo- 
graph curve,  are  found  to  be  very  different  not  only  for  the  nmscles  of  differ- 
ent animals,  but  even  for  the  different  muscles  of  the  same  animal.  Moreover, 
the  time  relations  of  the  contraction  process  in  each  muscle  are  altered  by  a 
great  variety  of  conditions. 

Before  considering  the  effect  of  various  influences  upon  the  character  of  the 
muscle  contraction,  let  us  give  a  glance  at  the  finer  structure  of  the  muscle, 
and  the  change  of  form  which  the  microscopic  segments  of  the  mnsclc-fibre 
undergo  during  contraction. 

2.  Optical  Properties  of  Striated  Muscle  during  Rest  and  Action. — 
An  ordinary  striated   muscle  is  composed  of  a  great  number  of  very  long 

*  Centralblatl  fur  Physiologic,  July  5,  1890,  vol.  iv. 

*  Archiv  de  Physiologie,  1880,  2d  series,  vol.  vii.  p.  197. 

'  TJntertuchungen  iiber  den  Erregungsvorgang  im  Nerven  und  MiisktlsifStem,  1871. 


GENERAL    PHYSIOLOGY    OP  MUSCLE    AND    NERVE. 


103 


muscle-cells,  fibres  as  they  are  called,  arranged  side  by  side  in  hiindles,  the 
whole  being  bound  together  by  a  fine  connective-tissue  network.  Kik  li  muscle- 
fibre  consists  of  a  very  delicate  elastic  sheath,  the  sarcolennna,  wiiich  is  com- 
pletely filled  with  the  muscle-substance.  Under  the  microscope  the  fibres  are 
seen  to  be  striped  by  alternating  light  and  dark  transverse  bands,  and  on  (bcus- 
ing,  the  difference  in  textiu'c  which  this  suggests  is  found  to  extend  through 
the  fibres,  /.  c.  the  light  and  dark  bands  correspond  to  little  disks  of  substances 
of  diifereut  degrees  of  translucency.  More  careful  study  with  a  high  power, 
shows  under  certain  circumstances  other 

cross  markings  (see  Fig.  36,  ^1),  the  light  ^  -^ 

band  is  found  to  be  divided  in  halves  by 
a  fine  dark  line,  Z,  and  parallel  to  it  is  z- 
another  faint  dark  line,  n,  while  the  dark  q 
baud,  Q,  is  found  to  have  a  barely  per-  ^I 
ceptible  light  line  in  its  centre. 

The  fine  dark  lines,  Z,  which  run 
through  the  middle  of  the  light  bauds, 
were  for  a  time  supposed  to  be  caused  by 
delicate  membranes  (Krause's  membrane), 
which  were  thought  to  stretch  through  o 
the  fibre  and  to  divide  it  into  a  series  of  q.. 

little  compartments,  each  of  which  had  . 

exactly  the  same  construction.     Kuehne 

chanced  to  see  a  minute  nematode  worm      fig.  36— schema  of  histological  structure  of 

•I  •      "J  1     ui  1    muscle-fibre:  ^,  resting  fibre  as  seen  bv  ordinary 

moving  along  inside   a    muscle-fibre,  and    ug^t;  U.  resting  fibre  seen  by  polarized  light;  c, 
observed  that  it  encountered    no  obstrUC-    contracting  fibre  by  ordinary  light ;  D,  contract- 
ing fibre  by  polarized  light. 

tion,  such  as  a  series  of  membranes,  how- 
ever delicate,  would  have  caused.  As  it  moved,  the  particles  of  muscle-sub- 
stance closed  in  behind  it,  the  original  structure  being  completely  recovered. 
This  observation  did  away  with  the  view  that  the  fibre  is  divided  into  com- 
partments, but  the  arrangement  shown  in  Figure  36,  A,  repeats  itself  through- 
out the  length  of  the  fibre  and  indicates  that  it  is  made  up  of  a  vast  succession 
of  like  parts. 

Muscle-substance  consists  of  two  materials,  which  differ  in  their  optical 
peculiarities  and  their  reaction  to  stains.  If  a  muscle-fibre  be  examined  by 
polarized  light,  it  is  found  that  there  is  a  substance  in  the  dark  bands  which 
refracts  the  light  doubly,  is  anisotropic,  while  the  bulk  of  the  substance  in  the 
light  bands  is  singly  refractive,  isotropic  {B,  Fig.  36).  The  anisotropic  sub- 
stance is  found  to  stain  with  haematoxylin,  while  the  isotropic  is  not  thus 
stained ;  on  the  other  hand,  the  isotropic  substance  is  often  colored  by  chloride 
of  gold,  which  is  not  the  case  with  the  anisotropic.  By  means  of  these  reac- 
tions it  has  been  possible  to  ascertain  something  as  to  the  arrangement  of  these 
substances  within  the  muscle-fibre,  though  the  ultimate  structure  has  not  been 
definitely  decided.  It  appears  that  the  isotropic  material  is  the  sarcoplasma, 
which  is  distributed  throughout  the  fibre  and  holds  imbedded  within  it  the 


104  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

particles  of  the  anisotropic  substance,  these  particles  liaviug  a  definite  arrange- 
ment. Striate<^l  inuscle-fihros  jircst'iit  not  only  cross  markings,  but  under 
favorable  conditions  longitudinal  striations,  these  being  most  evident  in  the 
dark  bands.  These  longitudinal  striations  are  looked  upon  with  great  interest 
as  indicating  that  the  particles  of  anisotropic  material  are  arranged  in  long 
chains  as  incomplete  fibrillae.  According  to  this  view  the  muscle-fibre  is  com- 
j)Ose(i  of  semifluid  isotropic  substance,  in  which  are  the  j)articles  of  anisotropic 
material,  arranged  to  form  vast  numbers  of  parallel  fibrillae  of  like  structure, 
and  so  placed  as  to  give  the  effect  of  transverse  disks  (Z,  n,  Q,  Fig.  36). 

AVhen  a  striated  muscle  contracts,  each  of  its  fibres  becomes  shorter  and 
thicker,  and  the  same  is  true  of  the  dark  and  light  disks  of  which  the  fibres 
are  composed.  If  we  examine  a  muscle-fibre  which  has  been  fixed  by  osmic 
acid  at  a  time  when  part  of  it  was  contracting,  we  see  that  in  the  contracted 
part  the  light  and  dark  bauds  have  both  become  shorter  and  wider,  but  that 
the  volume  of  the  dark  bands  (Q,  Fig.  36,  C)  has  increased  at  the  expense  of 
the  light  bands. 

Further,  the  dark  bands  are  seen  to  be  lighter  and  the  light  bands  darker 
in  the  contracted  part,  while  examination  with  polarized  light  shows  that 
though  the  anisotropic  substance  does  not  seem  to  have  changed  its  position, 
(Fig.  36,  D),  the  original  dark  bands  have  less  and  the  lighter  bands  greater 
refractive  power.  These  appearances  would  seem  to  be  explained  by  Engel- 
mann's  view  that  contraction  is  the  result  of  imbibition  of  tiie  more  fluid  part 
of  the  sarcoplasm  by  the  anisotropic  substance ;  the  cause  of  the  imbibition  is 
the  liberation  of  heat  by  chemical  changes  which  occur  at  the  instant  the 
muscle  is  excited.  Eno-elmann  ^  has  shown  that  dead  substance  containing: 
anisotropic  material,  such  as  a  catgut  string,  can  change  its  form,  by  imbi- 
bition of  fluid  under  the  influence  of  heat,  and  give  a  contraction  curve  in 
many  respects  similar  to  that  to  be  obtained  from  muscle.  This  theory  of 
the  method  of  action  of  the  muscle-substance,  though  attractive,  can  be 
accepted  only  as  a  working  hypothesis,  and  is  not  to  be  regarded  as  proved. 
Various  other  theories  have  been  advanced  to  explain  the  connection  between 
the  chemical  changes  which  undoubtedly  occur  during  contraction  and  the 
alteration  of  form,  but  none  have  been  generally  accepted.  Enough  has  been 
said  to  show  that  the  contraction  of  the  muscle  as  a  whole  is  the  result  of 
a  change  in  the  minute  elements  of  the  fibrilla",  and  that  the  various  condi- 
tions which  influence  the  activity  of  the  process  of  contraction  must  act  chiefly 
through  alterations  produced  in  these  little  mechanisms. 

3.  Elasticity  of  Muscle. — The  elasticity  and  extensibility  of  muscle  are 
of  great  importance,  for  by  every  form  of  muscular  work  tlie  muscle  is  sub- 
jected to  a  stretching  force.  Elasticity  of  muscle  is  the  property  by  virtue  of 
which  it  tends  to  preserve  its  normal  form,  and  to  resist  any  external  force 
w'hich  would  act  to  alter  that  form.  The  shape  of  muscles  may  be  altered  by 
pressure,  but  the  change  is  one  of  form  and  not  of  bulk ;  since  muscles  are 
largely  made  up  of  fluid,  their  compressibility  is  inconsiderable.     The  elasticity 

*  Ueber  den  Ursprung  der  Muskelkraft,  Leipzig,  1R93. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.       105 


of  muscles  is  slight  hiit  (jiiito  perfect,  by  which  is  meant  that  a  muscle  yields 
reiidily  to  a  stretching  force,  but  on  the  removal  of  the  force  quickly  recovers 
its  normal  form.  Most  of  the  experiments  upon  muscle  elasticity  have  been 
made  after  the  muscle  had  been  removed  from  the  body,  hence  under  abnormal 
conditions.  Under  these  circumstances  it  is  found  that  if  a  number  of  equal 
weights  be  added  to  a  suspended  muscle,  one  after  the  other,  the  extension  pro- 
duce<l  is  not,  like  that  of  an  inorganic  body 
such  as  steel  spring,  proportional  to  the  weight, 
but  each  weight  stretches  the  nuiscle  less  than 
the  preceding.  If  the  weights  be  removed 
in  succession,  an  elastic  recovery  is  observed, 
which,  although  considerable,  is  incomplete. 
li  the  change  in  the  length  be  recorded  by 
a  lever  attached  to  the  muscle,  the  surface 
being  moved  along  just  the  same  amount  after 
each  weight  is  added  or  removed,  a  curve  is 
obtained  such  as  is  shown  in  Fig.  37,  h. 
Above  this  is  a  record  taken  in  a  similar  way 
from  a  piece  of  rubber  (a).  The  rubber  resem- 
bles a  steel  spring  in  that  equal  weights  stretch 
it  to  like  amounts,  but  the  elastic  recovery, 
though  more  complete  than  that  of  the  muscle, 
is  imperfect. 

In  such  an  experiment  it  is  found  that  the 
full  effect  of  adding  the  weights,  or  removing 
them  from  the  muscle,  does  not  occur  immedi- 
ately, but  when  a  weight  is  added  there  is  a 
gradual  yielding  to  the  stretching  force,  and,  on  the  removal  of  a  weight,  a 
gradual  I'ecovery  of  form  under  the  influence  of  the  elasticity.  This  slow 
after-action  makes  it  difficult  to  say  just  what  is  to  be  considered  the  proper 
curve  of  elasticity  of  muscle,  especially  as  the  physiological  condition  of  the 
muscle  is  always  changing.  The  elasticity  of  muscles  is  dependent  on  normal 
physiological  conditions,  and  is  altered  by  death,  or  by  anything  which  causes 
a  change  in  the  normal  constitution  of  the  muscles,  as  the  cutting  off  of  the 
blood-supply.  The  dead  muscle  is  less  extensible  and  less  elastic  than  the 
normal  living  muscle.  Heating,  within  limits,  increases,  and  cooling  decreases 
the  elasticity.  Contraction  is  accompanied  by  increased  extensibility,  i.  e. 
lessened  elasticity,  and  the  changes  caused  by  fatigue  lessen  the  elasticity.  It 
is  interesting  to  note  in  this  connection  that  the  elasticity  is  decreased  by  weak 
acid  solutions  and  increased  by  weak  alkaline  solutions  (Brunton  and  Cash).^ 

The  elasticity  of  a  muscle  within  the  normal  body  is  witiiout  doubt  more 

perfect  than  that  of  an  isolated  muscle,  and  suffices  to  preserve  the  tension  of 

the  muscle  under  all  ordinary  conditions.     The  muscles  are  attached  to  the 

bones  under  elastic  tension,  as  is  shown  by  the  separation  of  the  ends  in  case 

^  Philosophical  Transactions,  1884,  p.  197. 


Fig.  37. — a,  Curve  of  extensibility 
and  elasticity  of  a  rubber  band ;  6,  curve 
of  extensibility  and  elasticity  of  a  sar- 
torius  muscle  of  a  frog.  The  weights 
employed  were  10  grams  each.  The 
same  length  of  time  was  allowed  to 
pass  between  the  adding  and  subtract- 
ing of  the  weights. 


106  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

a  muscle  be  cut.  This  elastic  tension  is  veiy  l:iv<)ral)le  to  tlic  acti(jn  of  (he 
muscle,  as  it  takes  up  the  slack  and  ensures  that  at  the  instant  tiic  muscle 
begins  to  shorten  the  effect  of  the  change  shall  be  (juickly  inij)artccl  to  the 
bones  which  it  is  its  function  to  move.  The  extensibility  of  the  nniscle  is 
a  great  protection,  lessening  the  danger  of  ruj)ture  of  the  nmscle-fibres  and 
ligaments,  and  the  injury  of  joints  Avhen  tiie  nuiscles  contract  suddenly  and 
vigorously,  or  when  they  are  subjected  to  sudden  strains  by  external  foi-ces. 
The  importance  of  extensibility  and  elasticity  to  muscles  which  act  as  antag- 
onists is  evident,  ^yhen  a  muscle  suddenly  contracts  against  a  resisting  ft)rce 
such  as  the  inertia  of  a  heavy  weight,  the  energy  of  contraction,  wdiich  puts  the 
muscle  on  the  stretch,  is  temporarily  stored  in  it  as  elastic  force,  and  as  the 
weight  yields  to  the  strain,  is  given  out  again  ;  thus  the  effect  of  the  contrac- 
tion force  is  tempered,  the  application  of  the  suddenly  developed  energy  being 
prolonged  and  softened. 

4.  Influences  which  Afi'ect  the  Activity  and  Character  of  the  Con- 
traction.— ((/)  The  Character  of  the  Musdc. — Attention  has  been  called  to 
the  fact  that  irritability  and  conductivity  may  be  different  not  only  in  different 
kinds  of  muscle-tissue,  and  in  muscles  of  different  animals,  but  even  in  similar 
kinds  of  muscle-tissue  in  the  different  muscles  of  the  same  animal;  the  same 
may  be  said  of  contractility.  Although  irritability,  conductivity,  and  contrac- 
tility are  to  be  regarded  as  different  properties  of  muscle  protoplasm,  they  are 
usually  found  to  be  developed  to  a  corresponding  degree  in  each  muscle. 
Those  forms  of  muscle  which  require  for  their  excitation  irritants  of  slow  and 
prolonged  action,  are  found  to  conduct  slowly  and  to  make  slow  and  long- 
drawn-out  contractions,  and  muscles  which  are  excited  by  irritants  acting 
rapidly  and  briefly  are  noted  for  the  quickness  with  which  they  contract 
and  relax. 

Differences  in  the  activity  of  the  contraction  process  are  made  evident 
by  the  duration  of  single  contractions  of  different  forms  of  muscle-tissue. 
The  duration  of  the  contraction  of  the  striated  muscles  of  different  animals 
differs  greatly,  e.  g.  of  the  frog  -^  second,  of  the  turtle  1  second,  of  certain 
insects  only  ^^  second.     Even  muscles  of  apparently  the  same  kind  in  the 

Ppctornlis  major 

Omohyoid //[^\ — ..(^intvUh  ^^^^ 


i   ••••'•-•«•■•'•••  1 

Fig.  38.— Records  of  maximal  isotonic  contractions  of  four  diflerent  muscles  from  a  turtle,  each 
weighted  with  30  grams  :  Pectoralis  major ;  omohyoid ;  gracilis ;  palmaris.  The  dots  mark  i  second,  and 
the  longer  marks  seconds  (after  Cash). 2 

same  animal  exhibit  different  degrees  of  activity.  Cash  ^  reports  the  following 
differences  in  the  duration  of  the  contractions  of  different  striated  muscles  of 
a  frog  in  fractions  of  a  second:  Hyoglo.'^sus,  0.205;  rectus  abdominis,  0.170; 
gastrocnemius,  0.120  ;  semimembranosus,  0.108  ;  triceps  femoris,  0.104.  Sim- 
»  Arcldv  fur  Anatntnie  und  Physiologic,  1880,  suppl.  VA.,  p.  147.  *  Op.  cit.,  p.  157. 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       107 

ilar  differences  are  found  to  exi.st  between  different  muscles  in  other  aninuds 
— in  tlio  turtle,  for  instance,  as  is  shown  by  tlic  niyoj^ranis  in  Fig.  38. 

It  is  interesting;  to  eoiniect  the  rate  of  the  contraction  ])rocess  in  different 
muscles  with  their  function.  The  omohyoid  muscle  of  the  turtle  is  capable  of 
comparatively  rapid  contractions,  and  the  action  of  this  muscle  is  to  draw  back 
the  head  beneath  the  i)rojecting  shell;  the  pectoralis,  on  the  other  hand, 
although  strong,  contracts  slowly ;  it  is  a  muscle  of  locomotion  and  has  to 
move  the  heavy  body  of  the  animal.  Unstriated  muscles,  which  are  remark- 
able for  the  slowness  and  the  duration  of  their  contractions,  are  found  chiefly 
in  the  walls  of  the  intestines,  blood-vessels,  etc.,  which  require  to  remain  in  a 
state  of  continued  contraction  for  considerable  periods  and  do  not  need  to  alter 
rapidly.  It  is  the  business  of  the  heart-muscle  to  drive  fluids  often  against 
considerable  resistance,  and  a  strong,  not  too  rapid,  slightly  prolonged  contrac- 
tion, such  as  is  peculiar  to  it,  would  be  best  adapted  to  its  function.  The  bulk 
of  the  muscles  of  ihQ  bodies  of  warm-blooded  animals  are  capable  of  rapid 
contraction  and  relaxation,  but  the  rate  normal  to  the  muscle  is  found  to  vary 
with  the  form  of  work  to  be  done.  The  muscles  which  control  the  vocal 
organs,  for  instance.,  have  a  very  rapid  rate  of  relaxation  as  well  as  of  con- 
traction. The  muscles  which  move  the  bones  appear  to  have  different  rates 
of  contraction  and  relaxation  according  to  the  weight  of  the  parts  to  be  moved ; 
those  which  control  the  lighter  parts,  as  the  hand,  being  capable  of  rapid  con- 
tractions, while  those  which  have  to  overcome  the  inertia  of  heavier  parts,  to 
which  rapidity  of  action  would  be  a  positive  disadvantage,  react  more  slowly. 
In  general,  where  rapid,  brief,  and  vigorous  contractions  are  required,  pale 
striated  muscles  are  found;  where  more  prolonged  contractions  are  needed, 
red  striated  muscles  occur.     The  accompanying  myograms  (Fig.  39)  illustrate 


Fig.  39.— .4,  maximal  contractions  of  the  gastrocnemius  medialis  of  the  rabbit  (pale  muscle),  weighted 
■with  50, 100,  300,  and  500  grams  ;  B,  maximal  contractions  of  the  soleus  of  the  rabbit  (red  muscle),  weighted 
with  50, 100,  and  200  grams  (after  Cash). 


the  difference  in  the  rate  of  contractions  of  pale  and  red  striated  muscles  of 
the  rabbit. 

Pale  and  red  striated  fibres  are  found  united  in  the  same  muscle  in  certain 
instances,  and  in  these  cases  it  is  supposed  that  the  former,  which  are  capable 


108 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


of"  very  rapid  and  powerful  but  short-lived  contractions  start  the  moveiueiit, 
while  the  slower  red  muscles  continue  it. 

(6)  Effect  of  Tension  on  the  Extent  and  Course  of  the  Contraction. — As  we 
have  seen,  the  rate  of  the  contraction  of  an  ordinary  striated  muscle  is  much 
too  rapid  to  be  followed  by  the  eye,  and  to  study  the  course  of  the  chan<re  in 
form  it  is  necessary  to  employ  some  i<ind  of  recordini;  mechanism.  Every 
mechanical  device  for  recording  the  movements  of  the  muscle  has  inertia,  and, 
if  given  motion,  acquires  momentum.  Both  of  these  factors  would  tend  to 
alter  the  shape  of  the  record,  and  the  more,  the  greater  the  weight  of  the  re- 
cording apparatus. 

A  weight,  or  tension,  can  be  applied  to  a  muscle  in  various  ways,  and  the 
form  of  the  contraction  will  be  correspondingly  changed.  If  a  muscle  is  made 
to  work  with  a  considerable  weight  hanging  on  it,  we  speak  of  it  as  loaded ; 
if  the  weight  be  connected  with  the  muscle,  but  so  supported  that  it  does 
not  pull  on  it  until  the  muscle  begins  to  siiorten,  the  muscle  is  said  to  be  after- 
loaded ;  if  the  weight  is  the  same  throughout  the  contraction,  as  when  the 
muscle  has  only  to  lift  a  light  weight,  ajiplied  close  to  the  axis  of  the  lever,  the 
contraction  is  said  to  be  isotonic  ;  if  on  the  other  hand  the  contracting  muscle 
is  made  to  work  against  a  strong  s]^ring,  so  that  it  can  shorten  very  little,  i.  e. 
has  almost  the  same  length  throughout  the  contraction,  the  contraction  is  said 

to  be  isometric.  The  shape  of  the 
myogram  recorded  as  a  residt  of 
the  same  stimulus  would  evidently 
be  very  different  in  these  four 
cases.  The  effect  of  a  weight  to 
alter  the  myogram  is  illustrated  in 
the  record  given  in  Figure  40. 
Increasing  the  weight  prolonged 
the  latent  period,  and  lessened  the 
height  and  duration  of  the  con- 
tractions. 

The  alterations  liable  to  occur 
in  the  form  of  the  myogram  as  a 
result  of  the  mechanical  condi- 
tions under  wiiicli  the  work  is 
done  are — 

(1)  Prolongation  of  fJie  latent 
2')eriod.  There  can  be  no  move- 
ment of  the  lever  until  the  inertia 
of  the  weight  has  been  overcome, 
and  the  first  effect  of  the  contrac- 
tion is  to  stretch  the  muscle,  a 
part  of  the  energy  of  contraction  being  changed  to  elastic  force,  which  on  the 
recoil  assists  in  raising  the  weight. 

(2)  Alteration  in  the  shape  of  the  ascending  limb  of  the  myograph  curve.    The 


Fig.  40— Effect  of  the  weight  upon  the  form  of  tlie 
myogram.  The  gastrociieinius  muscle  of  a  frog  excited 
by  maximal  breaking  induction  shocks  five  times,  tlie 
weight  being  increased  after  each  contraction,  and  in  the 
intervals  supported  at  the  normal  resting  length  of  the 
muscle;  i.e.  the  muscle  was  after-loaded:  1,  muscle 
weighted  only  with  very  liglit  lever;  2,  weight  five 
grams ;  3,  ten  grams  ;  4,  twenty-five  grams ;  5,  fifty  grams. 
The  perpendicular  line  marks  the  moment  of  excitation. 
The  time  is  recorded  at  the  bottom  of  the  curve  by  a 
chronograph,  actuated  by  a  tuning-fork  vibrating  r>0  times 
per  second. 


GENERAL   PHYSIOLOGY   OF  MUSCLE   AND   NERVE.       109 

weight  will  either  lessen  the  rate  at  which  the  curve  rises  and  decrease  the 
height,  or,  if  the  weight  be  not  great,  it  may  acquire  a  velocity  from  the  energy 
suddenly  imparted  to  it  by  the  muscle,  which  will  carry  the  record  higher  than 
the  absolute  contraction  of  the  muscle. 

(3)  lliefdll  of  the  curve  may  be  altered.  The  weight,  suddenly  i'reed  by  the 
rapidly  relaxing  muscle,  may  acquire  a  velocity  in  falling  which  will  stretch 
the  muscle-tissue,  carry  the  record  lower  than  the  actual  relaxation  of  the 
muscle  would  warrant,  and  lead  to  the  development  of  artificial  elastic  after- 
oscillations. 

These  sources  of  error  can  be  in  part  overcome  by  the  employment  of  an 
exceedingly  light,  stiif  writing-lever,  and  by  bringing  the  necessary  tension  on 
the  muscle  by  placing  the  extending  weight  very  near  the  axis  of  the  lever,  so 
that  it  shall  move  but  little  and  hence  acquire  little  velocity. 

(c)  Effect  of  Rate  of  Excitation  on  Height  and  Form  of  Muscular  Contrac- 
tion.— If  a  muscle  be  excited  a  number  of  times  by  exactly  the  same  irritant 
and  under  the  same  external  conditions,  the  amount  and  course  of  each  of 
the  contractions  should  be  exactly  the  same,  provided  the  condition  of  the 
muscle  itself  remains  the  same.  The  condition  of  the  muscle  is,  however, 
altered  every  time  it  is  excited  to  contraction,  and  each  contraction  leaves 
behind  it  an  after-effect.  This  altered  condition  is  not  permanent ;  as  we  have 
seen,  increased  katabolism  is  accompanied  by  increased  anabolism,  and,  if  the 
excitations  do  not  follow  each  other  too  rapidly,  the  katabolic  changes  occur- 
ring in  contraction  are  compensated  for  by  anabolic  changes  during  the  suc- 
ceeding interval  of  rest.  Normally,  a  muscle,  under  the  restorative  influence 
of  the  blood,  rapidly  recovers  from  the  alterations  produced  by  the  contraction 
process,  and,  therefore,  if  not  excited  too  frequently,  will  give,  other  things 
being  equal,  the  same  response  each  time  it  is  called  into  action.  The  best 
illustration  of  this  is  the  heart,  which  continues  to  beat  at  a  regular  rate 
throughout  the  life  of  the  individual.  Tiegel  found  that  one  of  the  skeletal 
muscles  of  a  frog,  while  in  the  normal  body,  can  make  more  than  a  thousand 
contractions  in  response  to  artificial  stimuli  without  showing  fatigue;  finally 
the  effect  of  the  work  shows  itself  in  a  lessening  of  the  power  to  contract. 
Every  muscle  contains  a  surplus  of  energy-holding  compounds  and  also  sub- 
stances capable  of  neutralizing  waste  products,  and  even  a  muscle  which  has 
been  separated  from  the  rest  of  the  body  retains  for  a  considerable  time  the 
ability  to  recover  from  the  effects  of  excitation.  It  is  evident  that  when  a 
muscle  is  excited  repeatedly,  a  certain  interval  of  rest  must  be  permitted 
between  the  succeeding  excitations  if  its  normal  condition  is  to  be  maintained, 
and  that  the  more  extensive  the  chemical  changes  produced  by  the  excita- 
tions the  longer  must  be  the  periods  allowed  for  recovery.  This  being  the 
case,  the  rate  of  excitation  and  consequent  length  of  the  interval  of  rest  Mill 
have  a  great  effect  upon  the  condition  of  the  muscle  and  its  capacity  for  work. 

(1)  Effect  of  Frequent  Excitations  on  the  Height  of  Separate  Muscular 
Contractions. — Other  things  being  equal,  the  height  to  Avhich  a  muscle  can  con- 
tract Avheu  excited  by  a  given  irritant  can  be  taken  as  an  index  of  its  capacity 


110 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


to  do  work,  and  if  a  muscle  be  excited  many  times  in  succession,  the  eifect  of 
action  upon  the  strengtli  of  the  contraction  process,  the  endurance,  and  the 
coming  on  of  fatigue  can  be  estimated  from  tlie  lieight  of  the  succeeding  con- 
tractions. One  might  expect  that  ev'cry  contraction  would  tend  to  fatigue  and 
to  leaseu  the  power  of  the  muscle,  but  almost  tiie  first  effect  of  action  is  to 
increase  the  irritability  and  mobility  of  muscle  protoplasm. 

Introdndovy  and  Staircase  Coni factions. — The  jjcculiar  effect  of  action  to 
increase  muscular  activity  was  first  observ^ed  by  Bowditch,'  when  studying 
the  effect  of  excitations  upon  the  heart.  He  found  that  repeated  excitations 
of  equal  strength  applied  to  the  ventricle  of  a  frog's  heart  caused  a  series  of 
contractions  each  of  which  was  greater  than  the  preceding.  If  the  contrac- 
tions were  recorded  on  a  regularly  moving  surface,  the  summits  of  the  succes- 
sive contractions  were  seen  to  rise  one  above  the  other  like  a  flight  of  steps. 
This  peculiar  phenomenon  received  the  name  of  the  "  staircase  contractions  " 
(see  Fig.  41). 


■^           -^-g^- 

FiG.  41.— staircase  contractions  of  a  frog's  ventricle  in  response  to  a  series  of  like  stimuli,  written  on 
a  regularly  revolving  drum  by  the  float  of  a  water  manometer  connected  with  the  chamber  of  the 
ventricle  (after  Bowditch).    The  record  is  to  be  read  from  right  to  left. 

This  effect  of  repeated  excitations  was  later  observed  by  Tiegel,^  on  the 
skeletal  muscles  of  frogs;  by  Rossbach,^  on  the  muscles  of  warm-blooded 
animals,  and  by  many  others  on  various  forms  of  contractile  protoplasm. 

The  following  series  of  contractions  (Fig.  42),  which  closely  resembles  the 
above,  was  obtained  from  the  gastrocnemius  muscle  of  a  frog,  excited  at  a 
regular  rate  by  a  series  of  equal  breaking  induction  shocks. 


Fig.  42.— Staircase  contractions  of  gastrocncmins  muscle  of  a  ft'og,  excited  once  every  two  seconds  by 
strong  breaking  induction  shocks. 

The  contractions  in  Figure  42  did  not  begin  to  increase  in  height  imme- 
diately ;  on  the  contrary,  each  of  the  first  four  contractions  was  slightly  lower 
than  the  one  which  preceded  it.     A  decline  in  the  height  of  the  first  three  or 

*  Berichte  der  kbniglichen  sdchsischen  Gesellschafl  der  Wissenschaft,  1871.  '  Ibid.,  1875. 

'  Pfluger's  Archiv,  1882,  1884,  Bd.  xiii.,  xv. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.        Ill 


four  contractions  is  the  rule  when  a  normal  resting  nuisele  is  called  into  action 
(see  Figs.  43  and  46),  and  these  contractions  at  the  beginning  of  a  series  have 
received  the  name  of  the  "  introductory  contractions."  The  introductory  con- 
tractions appear  to  indicate  that  the  first  effect  of  action  is  to  lessen  irritability, 
or  that  anabolic  changes  are  too  slow  to  compensate  for  katabolic  changes,  and 
each  of  the  first  few  contractions  leaves  behind  it  a  fatigue  effect.  It  is  not 
long,  however,  before  the  influence  of  activity  to  heighten  anabolism  and 
increase  irritability  shows  itself  in  the  growth  of  the  height  of  the  succeeding 
contractions,  and  the  "  staircase  contractions"  are  observed.  This  growth  of  the 
height  of  contractions  nuist  necessarily  reach  a  limit,  and  the  amount  of 
increase  is  found  to  gradually  lessen  until  the  succeeding  contractions  have  the 
same  height.  Sometimes  the  full  height  of  the  staircase  is  not  reached  before 
more  than  a  hundred  contractions  have  been  made.  These  maximal  contractions 
may  be  repeated  many  times ;  sooner  or  later,  however,  an  antagonistic  effect  of 
the  work  manifests  itself  and  the  height  of  the  contractions  begins  to  lessen. 

Effect   of  Fatigue.— A.   decline   in    the   height  of  the   contractions   is   an 
evidence  of  fatigue,  and  indicates  that  anabolism  is  failing  to  keep  pace  with 


66  contractions. 


Rest.        1-30  100  200  300  400  500 


600 


700 


800 


900 


1000 


1100 


1200 


1300 


1400 


1500 


1600 


1700 


Fig.  43.— Effect  of  fatigue  on  the  height  of  muscular  contractions.  The  figure  is  a  reproduction  of 
parts  of  a  record  of  over  1700  contractions  made  by  an  isolated  gastrocnemius  muscle  of  a  frog.  The  con- 
tractions were  isotonic,  the  weight  being  about  20  grams.  The  stimuli  were  maximal  breaking  induction 
shocks,  and  were  applied  directly  to  the  muscle,  at  the  rate  of  25  per  minute.  Between  the  first  group  of 
66  contractions  and  the  following  groups  a  rest  of  five  minutes  was  given ;  after  this  rest  the  work  was 
continued  without  interruption  for  about  one  and  a  half  hours.  The  second  group  of  contractions,  that 
immediately  following  the  period  of  rest,  contains  the  first  twenty  contractions  of  the  new  series;  the 
next  group  the  100th  to  the  110th  ;  the  next  the  200th  to  the  210th,  and  so  on. 

katabolism.     From  this  time  on,  the  height  of  the  succeeding  contractions 
continually  lessens,  and  often  with  great  regularity,  so  that  a  line  drawn  so  as  to 


112  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

connect  the  .summits  of  the  declining  contractions,  the  "curve  of  fatigue,"  as 
it  is  called,  may  be  a  straight  line.  In  the  experiment,  parts  of"  tiie  record  of 
which  are  reproduced  in  Figure  43,  an  isolated  gastrocnemius  mascle  of  a  frog 
Mas  excited  with  maximal  breaking  induction  shocks  at  the  rate  of  25  times 
a  minute  for  about  one  and  one-half  hours ;  the  contractions  were  isotonic,  and 
the  total  weight  of  lever  and  load  did  not  exceed  20  grams ;  the  records  of 
the  succeeding  contractions  were  recorded  on  a  slowly  moving  cylinder.  The 
experiment  consisted  of  two  parts — in  the  first  G6  contractions,  in  the  second 
over  1700  contractions  were  made;  an  interval  of  rest  of  five  minutes  was 
permitted  between  the  two  series. 

In  the  fii'st  part  of  the  experiment  there  was  a  decline  in  the  height  of  the 
contractions  for  the  first  five  contractions,  the  "  introductory  contractions," 
then  during  the  next  sixty-one  contractions  a  gradual  rise  in  the  height  of  the 
contractions,  the  "  staircase  contractions."  These  phenomena  repeat  themselves 
in  the  second  part  of  the  experiment,  that  following  the  interval  of  rest.  The 
contractions  at  the  beginning  of  the  second  series  were  not  so  high  as  those  at 
the  end  of  the  first  series,  though  somewhat  higher  than  those  seen  at  the 
beg-innint;  of  the  first  series ;  the  rest  of  five  minutes  was  not  sufficient  to 
entirely  do  away  with  the  stimulating  influence  of  the  preceding  work.  The 
contractions  of  the  second  series  took  the  following  course:  The  first  four 
introductory  contractions  gradually  declined,  then  eame  the  staircase  contrac- 
tions, which  continued  to  rise  until  the  100th  contraction,  when  a  gradual 
lessening  of  the  height  of  the  contractions  began.  This  decline  continued 
throughout  the  long  series  of  more  than  1 700  contractions  given  in  the  record, 
and,  had  the  experiment  been  continued,  would  have  undoubtedly  gone  on 
until  the  power  was  completely  lost.  The  curv'e  of  fatigue  was  not  a  straight 
line,  but  fell  somewhat  more  rapidly  during  the  early  part  of  the  work  than 
toward  the  end. 

That  the  peculiar  changes  in  the  height  of  the  contractions  which  occur  in 
the  early  part  of  an  experiment  such  as  that  which  we  have  described  are  not 
abnormal,  and  the  result  of  the  artificial  conditions  under  which  the  work  is 
done,  is  shown  not  only  by  the  fact  that  they  are  observed  when  a  muscle 
which  has  its  normal  blood-supply  is  rhythmically  excited  to  a  large  number 
of  contractions,  but  by  the  personal  experience  of  every  one  accustomed  to 
violent  nuiscular  exercise.  E%'eryone  is  conscious  that  he  cannot  put  out  the 
greatest  muscular  effijrt  until  he  has  "warmed  up  to  the  Mork."  The  runner 
precedes  the  race  by  a  short  run  ;  the  oarsman  takes  a  short  pull  before  going 
to  the  line ;  in  all  the  sports  one  sees  the  contestants  making  movements  to 
"  limber  up  "  before  they  enter  upon  the  work  of  the  game.  These  prelim- 
inarv  movements  are  performed  not  only  to  put  the  muscles  in  better  condition 
for  action,  but  to  ensure  more  accurate  co-ordination — that  is  to  say,  the  facts 
ascertained  for  the  muscle  can  be  carried  over  to  the  central  nervous  system. 
The  finelv  adjusted  activities  of  the  nerve-cells  which  control  the  muscles  reach 
their  perfection  only  after  repeated  action. 

In  such  experiments  as  that  recorded  in  Figure  43  the  record  shows  to 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       113 

a  remarkable  degree  the  fact  tliat  at  any  given  time  the  muscle  has  a  definite 
capacity  tor  work.  A  suitable  explanation  of  this  is  lacking.  The  corre- 
spondence in  the  height  of  the  contractions  of  the  same  gronj),  and  the  difFer- 
euce  in  the  height  of  ditlerent  groups  of  contractions,  must  be  attributed  to  the 
existence  within  the  muscle-cell  of  some  automatic  mechanism  which  regulates 
the  liberation  of  energy  and  which  has  its  activity  greatly  influenced  by  the 
alterations  which  result  from  action.  Whether  this  supposed  automatic  regu- 
latory mechanism  controls  both  the  preparation  of  the  final  material  from 
which  the  energy  displayed  by  the  muscle  is  liberated,  and  the  amount  of  the 
explosive  change  which  results  from  the  application  of  the  irritant,  cannot  be 
definitely  said. 

(2)  Effect  of  Frequent  Excitations  upon  the  Form  of  Separate  Contractions. 
— The  effect  of  activity  is  not  only  observable  in  the  change  in  the  height 
of  the  muscular  contractions,  but  in  the  length  of  the  latent  period,  in  the  rate 
at  which  the  muscle  shortens,  and,  above  all,  in  the  rate  at  which  the  muscle 
relaxes.  The  effect  of  a  large  number  of  separate  contractions,  made  in  quick 
succession,  upon  the  rate  at  which  the  muscle  changes  its  form  during  contrac- 
tion, is  illustrated  in  the  myograms  reproduced  in  Figure  44. 


Fig.  44.— Effect  of  excitation  upon  the  form  of  separate  contractions.  In  this  experiment  the  records 
of  the  muscular  contractions  were  taken  upon  a  rapidly  revolving  drum.  The  muscle  was  the  gas- 
trocnemius of  the  frog ;  the  contractions  were  isotonic ;  the  weight  was  very  light,  about  10  grams ;  the 
stimuli  were  maximal  breaking  induction  shocks ;  and  the  rate  of  stimulation  was  twenty-three  per 
minute.  1  marks  the  first  contraction ;  2,  the  100th ;  3,  the  200th  ;  4,  the  300th.  The  muscle  was  excited 
automatically  by  an  arrangement  carried  by  the  drum,  and  the  excitation  was  always  given  when  a 
definite  part  of  the  surface  of  the  drum  was  opposite  the  point  of  the  lever  Avhich  recorded  the  con- 
tractions. 


In  Figure  44  only  the  l.st,  100th,  200th,  and  300th  contractions  were  re- 
corded. The  perpendicular  line  marks  the  point  at  which  the  stimulus  was 
given.  In  this  experiment  the  latent  period  for  each  of  the  succeeding  con- 
tractions is  seen  to  be  longer ;  the  height  is  lessened  ;  the  rise  of  the  curve  of 
contraction  is  slowed  and  the  curve  of  relaxation  is  even  more  prolonged.  These 
and  certain  other  changes  are  to  be  observed  in  the  records  of  Figure  45,  which 
were  taken  in  an  experiment  made  under  the  same  conditions  as  the  last,  except 

8 


114  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

that  the  rate  of  excitation  was  80  per  minute,  instead  of  23,  as  in  the  preced- 
ing experiment,  and  the  record  of  every  50th  contraction  was  recorded. 


Fig.  45.— Effect  of  frequent  excitation  on  the  form  of  separate  contractions.  The  method  employed 
to  obtain  this  record  is  the  same  as  in  the  preceding  experiment,  except  that  the  drum  is  revolving  more 
rapidly,  and  every  50th  contraction  is  recorded :  1  marks  the  first  contraction ;  2,  the  50th  :  3,  the  100th ; 
4,  the  150th ;  5,  the  200th  ;  6,  the  250th  ;  7,  the  300th. 

A  comparison  of  the  first  with  tlie  50th  contraction  gives  a  number  of 
points  of  interest.  The  stimulating  effect  of  action  upon  the  contraction  pro- 
cess is  shown  by  the  fact  that  the  latent  period  of  the  50th  (2  of  Fig.  45)  is 
shorter  than  that  of  the  first,  the  rise  of  the  curve  is  somewhat  steeper,  and  the 
height  is  considerably  greater.  It  is  noticeable,  however,  that  the  crest  is  pro- 
longed, and  consequently  the  total  length  of  the  contraction  is  increased.  In 
considering  the  greater  activity  of  the  contraction  process  of  this  50th  con- 
traction as  compared  with  the  first,  we  must  recall  that  it  represents  one 
of  a  series  of  staircase  contractions,  such  as  we  noticed  in  Figure  43.  If 
we  examine  the  100th  contraction  (3  of  Fig.  45)  we  see  the  evidences  of  the 
beginning  of  fatigue;  although  the  latent  period  is  nearly  as  quick  as  in  the 
first,  the  rise  of  the  curve  is  less  rapid,  the  height  is  less,  and  rate  of  relaxation 
is  very  much  slowed.  Tiie.se  changes  are  to  be  seen  in  a  more  mark(>d  degree 
in  the  150th  contraction  (4  of  Fig.  45),  and  the  prolongation  of  the  crest  of 
the  contraction  and  the  decreased  rate  of  relaxation  are  particularly  noticeable. 
The  same  sort  of  differences  are  to  be  observed  in  the  later  contractions.  By 
still  more  rapid  rates  of  excitation  these  alterations  in  the  contraction  curve 
are  not  only  exaggerated,  but  develop  more  quickly,  and  play  a  very  important 
part  in  producing  the  peculiar  form  of  continued  contraction  known  as  tetanus. 

(3)  Effect  of  Frequent  Excitations  to  Produce  Tetanus. — As  we  have  seen,  the 
normal  muscle  the  first  time  that  it  is  excited  relaxes  almost  as  quickly  as  it 
contracts,  but  if  it  be  excited  rhythmically  a  number  of  times  a  minute,  gradu- 
ally loses  its  power  of  rapid  relaxation.  The  tendency  to  remain  contractefl 
begins  to  show  itself  in  a  prolongation  of  the  crest  of  the  contraction  curve, 
even  before  fatigue  comes  on,  and  increases  for  a  considerable  time  in  spite  of 
the  effect  of  fatigue  in  lessening  the  height  of  the  contractions.  If  a  skeletal  mus- 
cle of  a  frog  be  excited  many  times,  at  a  rate  of  about  once  every  two  seconds, 
the  gradual  increase  in  the  duration  of  the  contractions  will  have  the  effect  of 
preventing  the  muscle  from  returning  to  its  normal  length  in  the  intervals  be- 


GENERAL   PHYSIOLOGY   OF  MUSCLE   AND   NERVE.       115 

tween  the  suocecdiug  stimuli,  for  contraction  will  be  excited  before  relaxation 
is  complete.  As  is  shown  in  the  record  of  the  experiment  reproduced  in  Figure 
46,  there  will  come  a  time  in  the  work  when  the  base-line  connecting  the  lower 
extremities  of  the  succeeding  myograms  will  be  seen  to  rise  in  the  form  of  a 
curve,  the  change  being  at  first  gradual,  then  more  and  more  rapid,  and  then 
again  gradual  (see  6,  Fig.  46).  The  eifect  of  the  change  in  the  power  to  relax 
is  to  make  it  appear  as  if  the  muscle  were  the  seat  of  two  contraction  j)rocesses, 
the  one  acting  continuously,  the  other  intermittently  in  response  to  the  suc- 
cessive excitations.  Such  a  condition  as  that  exhibited  in  section  c,  Figure  46, 
is  spoken  of  as  an  incomplete  tetanus,  complete  tetanus  being  a  condition  of 
continuous  contraction  caused  by  rhythmical  excitations,  in  which  none  of  the 
separate  contraction  movements  are  visible.  In  complete  tetanus  the  muscle 
writes  an  unbroken  curve. 


Fig.  -16.— Effect  of  frequent  stimuli  to  gradually  produce  incomplete  tetanus.  Series  of  isotonic  con- 
tractions of  a  gastrocnemius  muscle  of  a  frog,  excited  once  every  two  seconds  by  strong  breaking  induc- 
tion shocks.  Only  a  part  of  the  record  is  shown,  70  contractions  have  been  omitted  between  the  end  of  the 
section  marked  a  and  the  beginning  of  section  b,  and  200  contractions  between  the  end  of  section  6  and  the 
beginning  of  e.  The  increase  in  the  extent  of  the  relaxations  seen  at  the  close  of  the  record  was  due 
to  the  slowing  of  the  rate  of  excitations  at  that  time. 

The  slowing  of  the  relaxation  of  the  muscle  and  consequent  state  of  con- 
tinued shortening  which  is  to  be  seen  in  the  latter  part  of  the  above  experiment 
is  termed  "  contracture."  The  amount  of  contracture  increases,  within  limits, 
with  the  increase  in  the  strength  and  rate  of  excitation.     The  intensity  and 


116  AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

rate  of  stinuilatiou  required  for  the  production  of  tiiis  condition  depends  \tx^ 
largely  u])on  tlie  character  of  the  muscle,  and  its  condition  at  the  time.  In 
the  experiment  recorded  in  Figure  47  the  deviloj^nent  of  the  condition  of  con- 


FiG.  47.— Effect  of  frequent  excitations  to  gradually  produce  tetanus.  Experiment  on  a  gastrocnemius 
muscle  of  a  frog,  similar  to  the  last.  The  weight  was  only  in  grams.  The  rate  of  excitation  was  100  per 
minute.  Tliis  muscle  had  been  worked  a  short  time  before  this  series  of  contractions  was  taken,  and,  as 
a  result,  the  introductory  and  staircase  contractions  were  absent  and  contracture  began  much  sooner 
than  in  the  experiment  recorded  in  Figure  45.  The  record  in  section  6  is  a  continuation  of  that  in 
section  a. 

tracture  was  more  marked  than  in  the  above  experiment,  and  the  resulting  con- 
dition of  continued  contraction  caused  first  incomplete  and  finally  complete 
tetanus. 

Although  frequent  excitations  appear  to  be  essential  to  the  development  of 
contracture,  it  is  doubtful  whether  it  is  to  be  considered  a  fatigue  effect,  since 


Fig.  48.— Development  and  fatigue  of  contracture.  Exi>eriment  on  a  gastrocnemius  muscle  of  a  frog. 
The  weight  was  10  grams.  As  in  the  preceding  experiments  strong  maximal  breaking  induction  shocks 
were  used  to  excite.  The  rate  of  excitation  was  5  per  second.  The  record  appears  as  a  silhouette  for  the 
reason  that  the  drum  was  moving  very  slowly. 

the  contracted  state  which  it  produces  may  be  increasing  at  the  time  that  fatigue 
is  lessening  the  height  of  the  ordinary  contraction  movements,  and  since  the 


GENERAL   PHYSIOLOGY   OF  MUSCLE   AND   NERVE.       117 

form  of  coutraction  peculiar  to  contracture  is  itself  seen  to  lessen  as  fatigue 
becomes  excessive.  Both  of  these  facts  are  illustrated  in  Figure  47,  but  are 
more  strikingly  shown  in  Figure  48,  in  which  a  more  rapid  rate  of  excitation 
was  used. 

The  record  in  Figure  48  shows  many  points  of  interest :  a  to  h,  a  rapidly 
developing  staircase,  which  is  accompanied  by  a  rising  of  the  base  line,  which 
indicates  that  contracture  began  to  make  itself  felt  from  the  moment  the  work 
began ;  6  to  c,  a  rapid  and  then  a  gradual  fall  in  the  height  of  contractions 
due  to  fatigue  effects ;  c  to  d,  a  rise  in  the  top  of  the  curve  in  spite  of  the 
lessening  height  of  the  contractions,  due  to  the  increasing  contracture ;  d  to  e, 
a  gradual  fall  of  the  curve  of  incomplete  tetanus,  due  to  the  effect  oi  fatigue 
on  the  contracture ;  e,  complete  tetanus,  but  continued  gradual  decline  in  the 
height  of  the  curve  under  the  influence  of  fatigue. 

The  following  experiment.  Figure  49,  differs  from  those  whicli  have  preceded 
it,  in  that  the  muscle,  instead  of  being  directly  excited,  was  stimulated  indirectly 
by  irritation  of  its  nerve.  Each  shock  applied  to  the  nerve  was  represented 
by  a  separate  contraction  process  in  the  muscle.  The  experiment  illustrates 
well  the  combined  effect  of  the  staircase  and  the  contracture  to  raise  the  height 


Fig.  49.— Development  of  incomplete  tetanus  and  contracture,  by  indirect  stimulation.  A  gas- 
trocnemius muscle  of  a  frog  was  indirectly  stimulated  by  breaking  induction  shocks,  of  medium 
strength,  applied  to  the  sciatic  nerve.  The  rate  was  about  8  per  second,  as  shown  by  comparison  of  the 
seconds  traced  at  the  bottom  of  the  figure  with  the  oscillations  caused  by  the  separate  contractions.  The 
weight  was  somewhat  heavier  than  in  the  preceding  experiment.  The  drum  was  revolving  much  faster 
than  in  the  other  experiments,  hence  the  difference  in  the  apparent  duration  of  the  contractions. 

of  the  contractions.  On  account  of  the  more  rapid  rate  of  excitation,  the 
contracture  came  on  more  quickly  than  in  the  preceding  experiments ;  it  did 
not  become  sufficient  during  the  few  seconds  that  this  experiment  lasted  to 
prevent  the  separate  relaxations  from  being  seen,  and  an  incomjjlete  tetanus 
was  the  result. 

In  the  experiment  the  record  of  which  is  given  in  Figure  50,  the  muscle  was 
directly  stimulated,  and  the  rate  of  excitation  was  rapid,  33  per  second.  Not 
even  this  rate  sufficed  to  cause  complete  tetanus,  and  the  crest  of  the  curve 
shows  fine  waves,  which  represent  the  separate  contractions  the  combined  effect 
of  which  resulted  in  the  almost  unbroken  curve  seen  in  the  record.  Had  the 
rate  been  a  little  more  rapid,  no  waves  could  have  been  detected  and  the  tetanus 
would  have  been  complete  from  the  start.  The  effects  of  the  staircase  and  con- 
tracture are  merged  into  one  another,  and  a  very  rajiid  high  rise  of  the  curve 
of  contraction  is  the  re.sult.  It  is  noticeable  that  the  summit  of  the  curve  is 
rising  throughout  the  experiment,  owing  to  the  increasing  contracture. 


118  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

It  is  evident  that  the  condition  of  contracture  whidi   is  developcHl   in  a 
rapidlv  stimulated  muscle  will  tend  to  maintain  a  condition  of  continuous  oon- 


FiG.  50.— Effect  of  rapid  excitations  to  produce  tetanus.  Experiment  with  a  gastrocnemius  muscle 
of  a  frog,  excited  directly,  with  breaking  induction  shocks  of  medium  strength,  at  the  rate  of  33  per 
second.  The  weight  was  about  15  grams.  The  drum  was  moving  much  more  slowly  than  in  the  pre- 
ceding experiment.    The  time  record  gives  fiftieths  of  a  second. 

traction,  there  being  no  opportunity  for  the  muscle  to  relax  in  the  intervals 
between  the  succeeding  excitations. 

4.  Explanation  of  the  Great  Height  of  Tetanic  Contractions. — We  have 
now  to  seek  an  explanation  of  the  fact  that  a  muscle  when  tetanized  will  con- 
tract much  higher  than  it  will  as  a  result  of  a  single  excitation.  As  we  have 
seen,  repeated  excitations  cause,  in  the  case  of  a  fresh  muscle,  a  gradual  increase 
in  irritability  and  consequently  a  gradual  rise  in  the  height  of  the  succeeding 
contractions,  but  the  staircase  sooner  or  later  reaches  its  upper  limit,  and  will 
not  alone  account  for  the  great  shortening  which  occurs  in  tetanus. 

Efect  of  Two  Rapidli/  Following  Excitations. — Helmholtz  was  the  first  to 
investigate  the  effect  of  rate  of  excitation  on  the  height  of  combined  contrac- 
tions. For  the  sake  of  simplicity,  he  excited  a  muscle  with  only  two  breaking 
induction  shocks,  of  the  same  strength,  and  observed  the  effect  of  varying  the 
interval  between  these  two  excitations.  He  concluded  that  if  the  second  stim- 
ulus is  given  during  the  latent  period  of  the  first  contraction,  the  effect  is  the 
same  as  if  the  muscle  has  received  but  one  shock ;  if  the  second  shock  be  applied 
at  some  time  during  the  contraction  excited  by  the  first,  the  second  contraction 
behaves  as  if  the  amount  of  contraction  present  when  it  begins  were  the  resting 
.state  of  the  muscle,  i.  e.  the  condition  of  activity  caused  by  the  first  shock  has 
no  influence  on  the  amount  of  activity  cau.sed  by  the  second,  but  the  lieight 
of  the  second  contraction  is  simply  added  to  the  amount  of  the  first  contraction 
present.  Were  this  rule  correct,  as  a  result  of  this  summation,  if  the  second 
contraction  occurred  when  the  first  was  at  its  height,  the  sum  of  the  two  con- 
tractions would  be  double  the  height  of  either  contraction  taken  by  itself. 

Helmholtz'  conclusion,  that  the  condition  of  activity  awakened  by  the  first 

excitation  has  no  effect  upon  that  caused  by  the  second  excitation,  has  not  been 

substantiated  by  later  observers.     Von  Kries '  has  found  that  the  presence  of 

the  first  contraction  hastens  the  development  of  the  contraction  process  result- 

*  Archil'  fiir  Anatomic  und  Physiologic,  1888. 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       119 


ing  from  the  second  excitation ;  and  Von  Frey  ^  has  ascertained  that  Helm- 
holtz's  rule  of  summation  applies  only  to  weighted  muscles.  In  the  case  of 
unweighted  muscles  the  summation  effect  is  greatest  when  the  second  contrac- 
tion starts  during  the  period  of  developing  energy  caused  by  the  first  excita- 
tion, /.  €.  during  the  rise  of  tiie  first  contraction.     If  the  second  contraction 


Fig.  51.— a  schema  of  the  effect  of  double  excitations  upon  the  gracilis  muscle  of  a  frog,  by  differ- 
ent intervals  of  excitation.  To  obtain  this  figure,  the  results  of  diflerent  experiments  were  super- 
imposed (after  Von  Frey). 

starts  during  the  period  of  relaxation  of  the  first,  the  second  may  be  not  even 
as  high  as  when  occurring  alone  (see  Fig.  51). 

The  fact  that  the  second  contraction  is  higher  if  it  starts  during  the  ascent 
of  the  first,  may  be  explained  as  due  to  a  summation  of  the  condition  of  ex- 


FiG.  52.— Effect  of  support  on  height  of  contractions  (after  Von  Frey) :  o,  gastrocnemius  muscle  of  a 
frog,  separate  contractions,  tetanus,  separate  contractions,  and  group  of  supported  contractions  ;  weight 
10.5  grams ;  6,  the  same,  by  weight  of  0.5  grams. 

citation  awakened  by  the  two  irritants,  and  hence  the  liberation  of  a  greater 
amount  of  energy.  Nevertheless,  the  increased  irritability,  indicated  by  stair- 
case contractions,  and  the  summation  of  excitation  effects  which  occur  by  rapidly 
repeated  excitations,  shown  by  the  above  experiment,  do  not  suffice  to  wholly 
explain  the  great  shortening  of  the  muscle  seen  in  tetanus.  Helmholtz'  idea, 
'  Archiv  fiir  Awxtomie  und  Physiologic,  1888,  p.  213. 


120  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

that  there  is  a  support  atfordeJ  by  the  first  contraction  to  the  second,  nuist 
also  phiy  an  important  part,  and  we  mnst  turn  to  this  for  the  completion  of  the 
explanation  of  the  great  height  acquired  by  the  tetanus  curve. 

Efed  of  Support  on  the  Heic/ht  of  Contractions. — Von  Kries '  and  Von 
Frey  -  found  that,  in  general,  the  shorter  the  distance  the  muscle  has.  to  raise 
a  .weight,  the  higher  it  can  contract,  and  that  if  a  muscle  be  excited  at  a  regu- 
lar rate,  and  the  support  for  the  weight  be  raised  between  each  of  the  succeed- 
ing contractions,  at  a  certain  height  of  the  support  the  contractions  may  be 
as  high  as  during  tetanus  (see  Fig.  52).  This  effect  can  be  got  with  a  fresh 
muscle  when  the  interval  between  the  excitations  is  such  that  there  can  be  no 
summation  in  Helmholtz'  sense. 

The  importance  of  this  discovery  to  our  understanding  of  tetanus  is  very 
great,  for  it  has  been  found  that  if  an  unsupported  muscle  be  rapidly  excited, 
effects  are  observed  which  closely  resemble  those  obtained  by  the  aid  of  a  sup- 


FiG.  53.— Effect  of  a  gradually  Increasing  rate  of  excitation.  Excitation  of  a  gastrocnemius  muscle 
of  a  frog  with  breaking  induction  shocks  of  medium  strength.  Tlic  time  was  recorded  directly,  by  a 
tuning-fork  making  100  vibrations  per  second.  The  rate  of  excitation  was  gradually  increased,  and 
then  gradually  decreased.  The  ascending  curve,  a-b,  shows  the  effect  of  increasing,  and  the  descending 
curve,  c-d,  of  decreasing  the  rate  of  stimulation.  Excitation  was  given  by  means  of  a  special  mechanism 
•for  interrupting  the  primary  circuit  of  an  induction  apparatus  and  at  the  same  time  short-circuiting  the 
making  shocks.  This  interrupter  was  run  by  an  electric  motor  which  was  allowed  to  speed  up  slowly, 
and  was  slowed  down  gradually. 

port;  this  we  have  seen  in  the  experiments  recorded  in  Figures  47,  48,  p.  llf). 
After  a  certain  amount  of  excitation,  a  change  occurs  in  the  condition  of  a 
muscle,  owing  to  which  it  acts  as  if  it  had  received  an  upward  push,  and  as 
if  a  new  force  had  been  developed  within  it,  which  aids  the  ordinary  con- 
^  Archivfiir  Anatomic  und  Physiologic,  1886.  ^  Ibid.,  1887. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.       121 

traction  process  in  raising  the  weight.     The  new  aid  to  high  contraction  is 
the  support  afforded  by  the  developing  condition  of  contracture. 

5.  Effect  of  Gradually  Increasing  the  Rate  of  Excitation. — One  of  the 
most  instructive  methods  of  exciting  tetanus  is  to  send  into  the  nmscle  a  series 
of  breaking  induction  shocks  of  medium  intensity,  at  a  gradually  increasing 
rate.     The  record  of  such  an  experiment  has  been  reproduced  in  Figure  53. 

At  the  beginning  of  the  experiment,  a,  one  complete  contraction  with  a 
wave  of  elastic  after-vibration  was  recorded ;  this  was  followed  by  two  con- 
tractions of  less  height,  "  introductory  contractions  ;"  then  came  three  contrac- 
tions each  of  which  was  higher  than  the  preceding,  "staircase  contractions;" 
these  were  followed  by  three  contractions,  which,  in  spite  of  the  developing 
contracture,  were  of  less  height,  "  fatigue  eflfect."  The  rate  of  excitation  at 
this  place  was  about  17  per  second.  From  this  point  on,  the  developing  con- 
tracture supported  the  muscle  more  and  more  and  the  contraction  waves  became 
less  and  less,  until  finally,  when  the  rate  had  become  36  a  second,  the  effect 
of  the  separate  stimuli  could  scarcely  be  detected,  although  the  curve  continued 
to  rise.  This  is  as  far  as  the  record  shows,  but  the  rate  was  increased  still 
further,  and  the  contraction  curve  continued  to  rise,  although  less  and  less, 
until  finally  an  almost  straight,  unbroken  line  was  drawn.  After  a  little  time 
this  was  seen  to  begin  to  fall,  the  contracture  yielding  to  the  effect  of  fatigue. 

As  the  drum  had  nearly  revolved  to  the  place  at  which  the  experiment  had 
been  begun,  the  rate  of  excitation  was  then  slowly  decreased.  With  the  lessen- 
ing rate,  the  curve  fell  more  and  more  rapidly,  and  oscillations  began  to  show 
themselves.  The  character  of  the  record  during  the  rest  of  the  experiment  is 
shown  in  the  curve  e^,  Figure  53.  At  c  the  rate  was  about  1 7,  and  at  d  it 
was  so  slow  that  separate  contractions  were  recorded,  nevertheless  the  curve  as 
a  whole  kept  up.  Indeed,  even  after  the  excitation  had  altogether  ceased,  the 
muscle  maintained  a  partially  contracted  state  for  a  considerable  time,  on 
account  of  the  contracture  effect,  which  only  gradually  passed  off. 

6.  Summary  of  the  Effects  of  Rapid  Excitation  ichich  produce  Tetanus. — 
Muscle-tetanus  is  the  result  of  the  combined  action  of  a  great  many  different 
factors,  but  the  essential  condition  is  that  the  muscle  shall  be  excited  at  short 
intervals,  so  that  the  eflPect  of  each  contraction  shall  have  an  influence  on  the 
one  to  follow  it.  This  influence  is  exerted  in  several  different  ways:  1.  In- 
crease of  irritability  resulting  from  action,  and  leading  to  the  production  of 
staircase  contractions ;  2.  Summation  of  excitation  effects,  as  when  each  of  the 
succeeding  stimuli  begins  to  act,  before  the  contraction  process  excited  by  its 
predecessor  has  ceased ;  3.  Support  given  by  the  contracting  muscle  to  itself, 
especially  the  support  offered  by  contracture. 

7.  Number  of  Excitations  required  to  Tetanize. — The  number  of  stimuli  per 
second  required  to  tetanize  a  muscle  depends  largely  on  the  nature  of  the 
muscle,  for  this  decides  the  character  of  the  separate  contractions,  and,  through 
them,  the  effect  of  their  combined  action. 

The  duration  of  the  separate  contractions,  and  the  tendency  of  the  muscle 
to  enter  into  contracture,  are  the  predominant  factors  in  determining  the  result. 


122  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

Complete  tetanus  can  only  be  obtained  in  the  ease  of  a  fresh  muscle,  when  the 
interval  between  succeeding  stimuli  is  shorter  than  is  required  for  the  muscle 
to  reach  its  maximal  contraction  by  a  single  stimidus.  Thus  the  prolonged 
contractions  of  smooth  muscles  permit  of  the  development  of  a  form  of  tetanus 
by  successive  closures  of  the  galvanic  current  at  intervals  of  several  seconds. 
Tlie  contraction  of  some  of  the  muscles  of  the  turtle  may  last  nearly  a  second, 
and  two  or  three  excitations  a  second  suffice  to  tetanize.  Tetanus  of  the  red 
(slowly  contracting)  striated  muscles  of  the  rabbit  can  be  obtained  by  10  exci- 
tations per  second,  while  20-30  per  second  are  required  to  tetanize  the  pale 
(active)  striated  muscles  (Kronecker  and  Sterling).  100  stimuli  per  second 
are  needed  to  tetanize  the  muscles  of  some  birds  (Richet),  and  over  300  per 
second  would  be  required  to  tetanize  the  muscles  of  some  insects  (Marey). 
Strange  to  say,  the  heart-muscle  cannot  be  tetanized ;  if  it  replies  at  all  to 
frequent  excitations,  it  gives  the  simple  contractions  characteristic  of  the  heart- 
beat. Any  influence  which  will  prolong  the  contraction  process  will  lessen  the 
rate  of  excitation  required  to  tetanize. 

8.  Effect  of  Exceedingly  Rapid  Excitations. — The  question  arises.  Is  there  an 
upper  limit  to  the  rate  of  excitation  to  which  muscles  wall  respond  by  tetanus? 
There  is  no  doubt  that  this  is  the  case,  but  there  is  a  difference  of  opinion  as 
to  what  the  limit  is,  and  how  it  shall  be  explained. 

Striated  muscles  and  nerves  can  be  excited  by  rates  at  which  our  most  deli- 
cate chronographs  fail  to  act.  The  muscle  ceases  to  be  tetanized  by  direct  exci- 
tation at  a  rate  by  w'hich  it  can  still  be  indirectly  excited  through  its  nerve. 
The  highest  rate  for  the  nerve  has  been  placed  at  from  3000  to  22,000  by  differ- 
ent observers,^  and  this  wide  difference  is  probably  attributable  to  the  methods 
of  excitation  employed.  That  such  different  results  should  have  been  reached 
is  not  strange,  if  we  recall  the  many  conditions  upon  which  the  exciting  power 
of  the  irritant  depends.  As  a  rule,  when  the  rate  of  excitation  is  so  high  that 
tetanus  fails,  a  contraction  is  observed  when  the  current  is  thrown  into  the 
nerve,  and  often  another  when  it  is  withdrawn  from  the  nerve.  A  satisfactory 
explanation  for  this,  as  well  as  for  the  failure  of  the  tetanus,  is  at  present  lack- 
ing. 

9.  Relative  Intensity  of  Tetanus  and  Single  Contractions. — The  amount  that 
a  muscle  is  capable  of  shortening,  when  tetanized  by  maximal  excitations,  and 
the  strength  of  the  tetanic  contraction,  depends  very  largely  on  tiie  kind  of 
muscle.  For  example,  pale  striated  muscles,  although  capal)le  of  higher  and 
more  rapid  single  contractions  than  the  red  striated,  do  not  show  as  great  an 
increase  in  the  height  and  strength  of  contractions  when  tetanized  as  do  the 
red ;  the  latter,  which  are  very  rich  in  sarcoplasma,  liave  likewise  the  greater 
endurance.  Gruetzner  has  called  them  "  tetanus  muscles,"  since  they  seem  to 
be  particularly  adapted  to  this  form  of  contraction.  Fick  found  that  human 
muscles  when  tetanized  develop  ten  times  the  amount  of  tension,  by  isometric 

'  Kronecker  and  Sterling:  Archiv  fiir  Anatomic  und  Phijsiologie,  1878,  and  Jouinial  nf  Phi(i^i- 
ology,  1880,  vol.  i.  Von  Fray  und  Wiedermann :  Berichte  der  sdchsischen  Gesellschafi  der  H'tsse/i- 
sctuift,  1885.     Roth  :  PflUget^s  Archiv,  1888. 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       12.] 

contractions,  tluit  they  give  by  single  contractions;  and  in  this  respect  they 
can  be  said  to  resemble  red  striated  muscles.  The  following  relations  have 
been  found  to  exist  between  separate  contractions  and  tetanus  in  certain  muscles  : 
triceps  and  gastrocnemius  of  the  frog,  1  :  2  or  3  ;  the  corresponding  muscles  of 
the  turtle,  1:5;  hyoglossus  and  rectus  abdomiualis  of  the  frog,  1 : 8  or  9.^  It 
is  evident  that  no  just  estimate  of  the  part  played  by  different  groups  of  muscles 
in  the  movement  of  the  body  can  be  reached  without  a  careful  analysis  of  the 
nature  of  the  contractions  peculiar  to  each  of  the  muscles  participating  in  the 
movement. 

Both  the  height  and  strength  of  the  tetanus  is  controlled  by  the  intensity 
of  the  stimulus.  A  strong  stimulus  not  only  causes  the  separate  contractions 
of  which  the  tetanus  is  composed  to  be  higher,  but  is  favorable  to  the  develop- 
ment of  all  the  other  factors  which  have  been  described  as  entering  into  the  pro- 
duction of  tetanus.  All  normal  physiological  contractions  are  supposed  to  be 
tetani,  and  everyone  is  conscious  of  the  wonderful  accuracy  with  wdiich  he  can 
grade  the  extent  and  strength  of  his  voluntary  movements.  The  remarkable 
shading  of  the  intensity  of  action  observable  in  co-ordinated  movements  must 
find  its  explanation  in  the  adjustment  of  protoplasmic  acti\'ity  in  the  nerve- 
cells  of  the  central  nervous  system. 

10.  Continuous  Contractions  caused  by  Continuous  Excitation. — Attention 
has  been  already  called  to  the  fact  that  under  certain  circumstances  a  form  of 
continuous  contraction  may  be  excited  by  a  continuous  constant  electric  current. 
If  the  current  be  very  strong,  the  short  closing  contraction  may  be  followed  by 
a  more  or  less  continuous  contraction — the  closing  (or  Wundt's)  tetanus,  and 
the  short  opening  contraction  may  be  follow^ed  by  another  continuous  contrac- 
tion, which  only  gradually  passes  off — the  opening  (or  Hitter's)  tetanus.  This 
form  of  contraction  is  quite  readily  excited  in  normal  human  muscles,  both  by 
direct  and  indirect  excitation.  The  term  "  galvanotdnus  "  is  sometimes  em- 
ployed for  the  continuous  contraction  of  human  muscles  excited  by  the  con- 
tinuous flow  of  a  constant  current. 

The  closing  tetanus  originates  at  the  kathode,  and  the  opening  tetanus  at 
the  anode.  The  contraction  process  may  spread  rapidly  from  the  point  of 
origin  to  the  rest  of  the  muscle,  or,  if  the  muscle  be  in  an  abnormal  state,  or  be 
dying,  the  contraction  may  remain  localized  as  a  circumscribed  swelling,  or 
welt.  Although  a  continuous  contraction  caused  by  the  constant  current  is 
spoken  of  as  tetanus,  it  is  a  matter  of  doubt  wliether  it  is  a  true  tetanic  condi- 
tion, for  the  term  tetanus  is  limited  to  an  apparently  continuous  contraction 
resulting  from  many  frequently  repeated  stimuli.  Von  Frey  ^  expresses  the 
view  that  the  continuous  contraction  which  follows  the  closing  of  the  contin- 
uous constant  current  is  a  form  of  tetanus.  It  is  certainly  true  that  the 
closing  tetanus  often  shows  irregular  oscillations,  suggestive  of  a  more  or  less 
intermittent  excitation.  This  might  be  attributed  to  irregular  chemical  changes 
produced  in  the  muscle-substance  by  the  electricity  and  leading  to  irregular 

^  Biedermann :  Ekktrophysiologie,  p.  109. 

*  Archiv  fiir  Anatomie  und  Physiologic,  1885,  p.  55. 


124  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

contractions  ot"  the  diliercnt  iibres,  the  combined  action  of  which  produces  a 
more  or  less  regular  continued  contraction.  Another  view  w(Hild  be  that  con- 
tracture niitjht  be  produced  under  tiie  influence  of  the  changes  caused  by  the 
electric  current,  and  a  condition  result  similar  to  that  which  causes  the  pro- 
longed contractions  which  are  characteristic  of  poisoning  with  veratria,  etc. 
(see  p.  128). 

{d)  Normal  Fhysiologkal  Contractions. — All  normal  physiological  contrac- 
tions of  muscles  are  regarded  as  tetani.  Even  the  shortest  possible  voluntary 
or  reflex  movements  are  considered  to  be  too  long  to  be  single  contractions. 
Inasmuch  as  we  can  artificially  excite  muscles  to  continuous  contraction  only 
by  means  of  a  series  of  rapidly  following  stimuli,  we  find  it  hard  to  explain 
continuous  contractions  on  any  otiier  basis,  and  hence  the  view  that  tlie  exci- 
tation sent  by  the  nerve-cells  to  muscles  has  always  a  rhythmic  character,  and 
that  the  normal  motor-nerve  impulse  is  a  discontinuous  rather  than  continuous 
form  of  excitation.  The  view  is  probably  correct,  but  cannot  be  considered  as 
proved.     The  evidence  in  favor  of  it  is  as  follows. 

Muscle-sounds,  Tremors,  etc. — During  voluntary  muscular  contractions  the 
muscle  gives  out  a  sound,  which  would  imply  that  its  finest  particles  were  not 
in  a  state  of  equilibrium,  but  vibrating.  By  delicate  mechanisms  it  has  been 
possible  to  obtain  records  of  voluntary  and  reflex  contractions  which  showed 
oscillations,  although  the  contraction  of  the  muscle  appeared  to  the  eye  to  be 
continuous.  If  the  surface  of  a  muscle  be  exposed  and  be  wet  and  glistening, 
the  light  reflected  from  it  duriftg  continued  contractions  is  seen  to  flicker,  as 
if  the  surface  were  shaken  by  fine  oscillations.  The  tired  muscle  passes  from 
apparently  continuous  contraction  to  one  exhibiting  tremors,  and  muscular 
tremors  are  observed  under  a  variety  of  pathological  conditions. 

With  these  facts  in  mind,  a  number  of  observers  have  endeavored  to  dis- 
cover the  rate  at  which  the  muscle  is  normally  stimulated.  Experiments  in 
which  muscles  have  been  excited  to  incomplete  tetanic  contractions  by  induced 
currents,  interrupted  at  different  rates,  have  shown  that  the  muscle  follows  the 
rate  of  excitation  with  a  corresponding  number  of  vibrations,  and  dot>s  not 
show  a  rate  of  vibration  peculiar  to  itself.  Further,  it  has  been  ascertained 
that  the  sound  given  out  by  a  muscle  excited  to  complete  tetanus,  i.  e.  an 
apparently  continuous  contraction,  corresponds  to  the  rate  at  which  it  is  ex- 
cited. Apparently,  any  rate  of  oscillations  detected  in  a  muscle  during  normal 
physiological  excitation  would  be  an  indication  of  the  rate  of  discharge  of 
impulses  from  the  central  nerve-cells. 

Wollaston  was  the  first  to  observe  that  a  muscle  gives  a  low  dull  sound 
when  it  is  voluntarily  contracted,  and  that  this  sound  corresponds  to  a  rate  of 
vibration  of  36  to  40  per  second.  It  may  be  heard  with  a  stethoscope  placed 
over  the  contracting  biceps  muscle,  for  instance,  or  if,  when  all  is  still  and  the 
ears  are  stopped,  one  vigorously  contracts  his  masseter  muscles.  Helmholtz 
placed  vibrating  reeds  consisting  of  little  strips  of  paper,  etc.,  on  the  muscle, 
and  found  that  only  those  which  had  a  rate  of  vibration  of  18  to  20  per 
second  were 'thrown  into  oscillation  when  tlie  muscle  was  voluntarily  contracted. 


GENERAL    PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       125 

This  observation  imlicatcd  iJiat  the  iiiiLsele  had  a  rate  ol"  vibration  of"  18  to  20 
per  second,  a  rate  too  slow  to  be  recognized  as  a  tone.  He  conclnded  that  the 
tone  heard  from  the  voluntarily  contracted  muscle  was  the  overtone,  instead 
of  the  true  muscle-tone.  The  consideration  that  the  resonance  tone  of  the 
ear  itself  corresjx^nds  to  36  to  40  vibrations  per  second,  makes  it  question- 
able whether  the  muscle-sound  should  be  accepted  as  evidence  of  the  rate  of 
normal  physiological  excitation ;  nervetheless,  the  experiments  with  the 
vibrating  reeds  remain  to  indicate  18  to  20  per  second  to  be  the  normal 
rate. 

Within  the  last  few  yeai-s  a  number  of  researches  bearing  upon  this  question 
have  been  publisiied,  and  the  results  of  these  point  to  a  still  slower  rate  of  vol- 
untiiry  excitation,  varying  from  8  to  12  per  second  according  to  the  muscle  on 
which  the  experiment  is  made.  Loven'  discovered  in  the  tetanus  excited  in 
frogs  poisoned  with  strychnia,  and  in  voluntary  contractions,  both  by  mechani- 
cal methods  and  by  recording  the  electrical  changes  occurring  during  action 
with  the  capillary  electrometer,  rates  of  7  to  9  per  second.  Horsley  and 
Schafer^  excited  the  brain  cortex  and  motor  tracts  in  the  corona  radiata  and  the 
spinal  cord  of  mammals  by  induction  shocks,  at  widely  differing  rates,  and 
recorded  the  resulting  muscular  contractions  by  tambours  placed  over  the 
muscles.  They  observed  oscillations  in  the  myograms  obtained  which  had  a 
rate  of  8  to  12  per  second,  the  average  being  10.  The  rate  of  oscillations  was 
quite  independent  of  the  rate  of  excitation,  and  oscillations  of  the  same  rate 
were  seen  by  voluntary  and  by  reflex  contractions.  TunstalP  found  by  the  use 
of  tambours,  in  experiments  on  voluntary  contractions  of  men,  a  rate  of  8  to  13 
per  second,  with  an  average  of  10.  Griffiths*  likewise  used  the  tambour 
method,  and  studied  the  effect  of  tension  on  the  rate  of  oscillations  in  voluntarily 
contracted  human  muscles.  He  observed  rates  varying  from  8  to  19,  the  rate 
being  increased  with  an  increase  of  weight  up  to  a  certain  point,  and  beyond  this 
decreased.  The  oscillations  became  more  extensive  as  fatigue  developed.  Von 
Kries  by  a  similar  method  found  rates  varying  with  different  muscles,  but 
averaging  about  10. 

It  is  not  easy  to  harmonize  the  view  that  8  to  13  excitations  per  second 
can  cause  voluntaiy  tetani,  when  it  is  possible  for  the  expert  pianist  to  make 
as  many  as  10  or  11  separate  movements  of  the  finger  in  a  second.  It  is, 
indeed,  a  common  observation  that  a  muscle  can  be  slightly  and  continuously 
voluntarily  contracted,  and,  at  the  same  time,  be  capable  of  making  additional 
short  rapid  movements.  Von  Kries  would  explain  this  as  due  to  a  peculiar 
method  of  innervation,  while  Biedermann  favors  Gruetzner's^  view  that  the 
muscle  may  contain  two  forms  of  muscle-substance,  one  of  which  is  slow  to 
react,  resembling  red  muscle-tissue,  and  maintains  the  continuous  contraction, 
the  other,  of  more  rapid  action,  being  responsible  for  the  quicker  movements. 
Although  the  evidence  is,  on  the  whole,  in  favor  of  the  view  that  all  normal 

*  Centralblatt  fiir  medicinische  Wissenschaft,  1881.         ^  Journal  of  Physiology,  1886,  vii.  p.  96. 
^  Journal  of  Physiology,  1886,  vii.  p.  114.  *  Journal  of  Physiology,  1888,  ix.  p.  39. 

'"  Pfliigers  Archiv,  1887,  Bd.  41,  S.  277. 


126  ^iV^  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

contractions  of  voluntary  nniscles  are  tetanic  in  character,  there  is  a  great  deal 
which  remains  to  be  explainetl. 

Efect  of  Arflficial  compared  ivlth  Normal  Stimulation. — Experiment  shows 
that,  with  the  same  strength  of  irritant,  a  muscle  contracts  more  vigorously 
when  irritated  indirectly,  through  its  nerve,  than  when  it  is  directly  stimulated. 
Rosenthal  describes  the  following  experiment :  If  the  nerve  of  muscle  A  be 
allowed  to  rest  on  a  curarized  muscle  B,  and  an  electric  shock  be  applied  in 
such  a  way  as  to  excite  nerve  A  and  muscle  B  to  the  same  amount,  muscle  A 
will  be  found  to  contract  more  than  muscle  B. 

Further,  it  has  been  found  that  muscles  respond  more  vigorously  to  volun- 
tary excitations  than  to  any  artificial  stimulus  which  can  be  applied  to  either 
the  nerve  or  muscle.  This  shows  itself,  not  only  in  the  fact  that  a  muscle  can 
by  voluntary  stimulation  lift  much  larger  weights  than  by  electrical  excitation, 
but  that  after  a  human  muscle  has  been  fatigued  by  electrical  excitations  it 
can  still  respond  vigorously  to  the  will.  An  illustration  of  this  is  given  in 
Figure  54, 


<,<'»<'<»«; 


Fig.  54.— Voluntary  excitations  are  more  effective  than  electrical.  The  flexor  muscles  of  the  second 
finger  of  the  left  hand  of  a  man  were  excited  first  voluntarily,  a,  then  electrically,  a-h,  and  then  volun- 
tarily, h.  The  electrical  excitation  consisted  of  series  of  induction  shocks,  which  were  applied  once 
every  two  seconds,  during  about  half  a  second,  the  spring  interrupter  of  the  induction  coil  vibrating 
23  times  per  second.  Each  time  the  muscle  contracted  it  raised  a  weight  of  one  kilogram.  Each  of  the 
contractions  recorded,  whether  the  result  of  electrical  or  voluntary  excitation,  was  a  short  tetanus. 

Fatigue  of  Voluntary  Muscular  Contractions. — Mosso  and  his  pupils  have 
done  a  large  amount  of  work  upon  the  fatigue  of  human  muscles  when  excited 
by  voluntary  and  artificial  stimuli  under  varying  conditions.  The  results  at 
which  they  arrived  all  favor  the  view  that  human  muscles  differ  but  little  from 
thase  of  warm-blooded  animals,  and  that  the  facts  which  have  been  ascertained 
by  experiments  upon  cold-blooded  animals,  such  as  the  frog,  can  be  accej)ted 
with  but  slight  modifications  for  the  muscles  of  man.  In  the  experiment 
recorded  in  Figure  55  we  see  the  effect  of  repeated  tetanic  contractions,  excited 
by  electricity,  to  fatigue  a  human  muscle.  Normal  voluntary  contractions,  if 
frequently  repeated,  provided  the  muscle  has  to  raise  a  considerable  weight, 
likewi.se  cause  fatigue. 

It  is  doubtful  whether,  in  an  experiment  such  as  is  shown  in  Figure  55,  the 
loss  of  the  power  to  rai.se  the  weight  is  due  to  fatigue  of  the  muscles.  It  is 
more  likely  that  the  decline  in  power  is  really  due  to  fatigue  of  the  central 


GENERAL    PHYSIOLOGY   OF  MUSCLE    AND    NERVE.       127 

nerve-cells  by  which  the  muscles  are  excited  to  action  duriug  voluntary  mus- 
cular work.^  This  fact,  that  the  nerve-cells  give  out  before  the  muscles,  ex- 
plains the  apparent  contradiction,  that  a  muscle  fatigued  by  electric  excitations 
can  be  voluntarily  contracted,  and  when  the  power  to  voluntarily  contract  the 


< mmfn 

Fig.  55.— EflFect  of  fatigue  on  voluntary  muscular  contractions.  The  flexor  muscles  of  the  second 
finger  of  left  hand  were  voluntarily  contracted  once  every  two  seconds,  and  always  with  the  utmost 
force.    The  weight  raised  was  four  kilograms. 

muscles  has  been  stopped  by  fatiguing  voluntary  work  the  mu.scles  will  respond 
to  electrical  excitation.  It  is  undoubtedly  of  advantage  to  the  body  that  the 
nerve-cells  should  fatigue  before  the  muscles,  for  the  muscles  are  thereby  pro- 
tected from  the  injurious  effects  of  overwork,  and  are  always  ready  to  serve  the 
brain.^  It  may  be  added  that  nerve-cells  not  only  fatigue  more  quickly,  but 
recover  from  fatigue  more  rapidly  than  the  muscles. 

(e)  Effect  of  Temperature  upon  3fuscular  Contraction. — Heat,  within  certain 
limits,  increases  the  irritability  and  conductivity  of  muscle-tissue,  and  at  the 
same  time  has  a  favoring  influence  upon  those  forms  of  chemical  change  which 
liberate  energy.  The  effect  of  a  rise  of  temperature,  as  shown  by  the  myo- 
gram, is  a  shortening  of  the  latent  period,  an  increase  in  the  height  of  contrac- 
tion, and  a  quickening  of  the  contraction  and  relaxation,  the  whole  curve  being 
shortened.  Of  course  there  is  an  upper  limit  to  this  favoring  action,  since,  at  a 
certain  temperature,  about  45°  C.  for  frog's  muscle  and  about  50°  C.  for  the 
muscles  of  warm-blooded  animals,  heat-rigor  begins,  and  this  change  is  accom- 
panied by  a  loss  of  all  vital  properties.  Cold  can  be  said,  in  general,  to  pro- 
duce effects  the  opposite  of  those  of  heat;  as  the  muscle  is  cooled,  the  latent 
period,  the  contraction,  and  the  relaxation,  are  all  prolonged. 

Nevertheless,  the  effect  of  temperature  is  not  a  simple  one  (see  Fig.  56).     If 

^  Lombard :  Archives  Italiennes  de  Biologie,  xiii.  p.  1 ;   or  American  Journal  of  Psychology, 
1890,  p.  1 ;  Journal  of  Physiolocjy,  1892,  p.  1 ;  1893,  p.  97. 
=■  Waller :  Brain,  1891,  p.  179. 


128 


.l.V   AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


durinu:  tliu  cooling  process  a  striated  muscle;  ot'  a  irog  ho  irritated  from  lime  to 
time  with  single  induction  shocks,  the  height  of  tiie  contractions  (h)es  not  con- 
tinually grow  less  as  one  would  expect.'  The  maximal  height  is  obtained  at 
30°  C,  the  height  above  this  point  l)eing  somewhat  less,  the  irritabilitv  les- 
sening as  the  coagulatiou-point  is  approached;  from  30°  C.  to  19°  C.  the 
height  continually  decreases,  but  from  19°  to  0°  C.  the  height  increases,  while 
below  0°  C.  it  again  becomes  less,  until  at  the  freezing-point  of  muscle  no  con- 
traction is  obtained.  The  cause  of  these  peculiar  phenomena  is  not  definitely 
understood. 


Fig.  56.— Schema  of  effect  of  temperature  on  height  and  form  of  contraction  curve  :  a,  contraction  at 
19°  C. ;  b,  c,  d,  e,f,  contractions  made  at  intervals,  each  one  at  a  lower  temperature;  g,  h,  contractions 
at  higher  temperatures  than  19°  C,  h  being  made  when  the  temperature  was  30°  C. ;  i,  k,  I,  show  a  different 
series  of  contractions,  made  as  the  temperature  was  increased  from  30°  C.  toward  the  point  at  which  the 
muscle-substance  coagulates  (after  Gad  and  Heymans). 

(J)  Effect  of  Drugs  and  Chemicals  upon  Jfuscular  Contraction. — Certain  drugs 
and  chemicals  have  a  marked  effect  upon  the  irritability  and  conductivity  of 
mu.scles,  and  these  effects  must  nece.ssarily  find  expression  in  the  amount  of  con- 
traction which  would  be  excited  by  a  given  irritant.  In  addition  to  this,  it  is 
worthy  of  notice  that  the  character  of  the  contraction  may  be  altered. 

The  drug  which  has  the  rao.st  striking  effect  upon  the  form  of  contraction  is 
veratria.  A  few  drops  of  a  one  per  cent,  solution  of  the  acetate  of  veratria,  in- 
jected beneath  the  skin  of  a  frog  whose  brain  has  first  been  destroyed,  in  a  few 
minutes  alters  qompletely  the  character  of  the  reflex  movements ;  the  muscles 


Fig.  57.— Myogram  of  muscle  poisoned  with  veratria  and  that  of  a  normal  muscle ;  a,  myogram  from  a 
normal  gastrocnemius  muscle  of  a  frog— the  waves  at  the  close  are  due  to  the  recoil  of  the  recording  lever; 
b,  myogram  from  a  gastrocnemius  muscle  poisoned  with  veratria,  recorded  at  the  same  part  of  the  drum. 

are  still  capable  of  rapidly  contracting,  but  the  contractions  are  cramp-like, 
the  power  to  relax  being  greatly  lessened.     The  poison  acts  upon  the  muscle- 
substance.     If  a  muscle  poi.soned  with  veratria  be  isolated  and  connected  with 
^  Gad  und  Heymans:  Archivfur  Anatomic  und  Physiologic,  1890,  p.  73. 


GENERAL    PHYSIOLOGY   OF  MUSCLE  AND    NERVE.        129 

a  inyograpli,  a  contraction  excited  by  a  single  induction  shock  will  show  a  rise 
as  rapid  and  as  high  as  normal,  but  the  fall  of  the  curve  will  be  greatly  pro- 
longed (see  Fig.  57). 

Often  the  crest  of  the  curve  will  exhibit  a  notch,  which  shows  that  relaxa- 
tion may  begin  and  be  checked  by  a  second  contraction  process  which  carries 
the  curve  up  again  and  holds  it  there  for  a  considerable  time.  In  the  above 
experiment  the  contracture  etiect  followed  the  primary  contraction  immediately. 
If  the  muscle  be  frequently  excited,  the  characteristic  prolongation  of  the 
contraction  disappears,  and  the  curve  becomes  normal ;  but  if  the  muscle  be 
allowed  to  rest,  there  is  a  return  of  the  condition.  Both  high  and  low  tempera- 
tures act  like  exercise  to  prevent  this  peculiar  effect  of  veratria  from  showing 
itself. 

Barium  salts,  and  to  a  less  degree  calcium  and  strontium,  act  similarly  to 
veratria  to  prolong  the  relaxation  of  the  muscle  without  lessening  the  rapidity 
and  height  of  the  contraction.  Potassium  and  ammonium  salts  act  to  kill  the 
muscle,  and,  as  the  death-process  develops,  excitation  produces  prolonged  local- 
ized contractions.  This  effect  seems  to  be  quite  different  from  that  of  veratria, 
being  accompanied  by  a  rapid  lessening  of  the  power  of  the  muscle.  Sodium 
salts  in  strong  solution  may  increase  the  irritability  and  induce  fatigue,  which 
is  always  accompanied  by  a  prolongation  of  the  curve  of  relaxation. 

The  condition  of  continued  contraction  caused  by  veratria  is  a  form  of 
"contracture."  The  true  natm*e  of  the  condition  is  still  under  discussion; 
the  fact  that  the  veratria  contracture  passes  off  if  the  muscle  is  worked,  shows 
that  it  is  not  in  the  nature  of  a  fatigue  effect.  Since  more  heat  is  produced 
during  contracture  than  during  rest  (Fick  and  Boehme),  it  is  to  be  regarded  as 
an  active  contraction  process  and  not  an  increase  of  elasticity.  The  fact 
that  the  crest  of  the  veratria  curve  often  exhibits  a  notch,  and  that  the  second 
rise,  leading  to  the  prolonged  ridge,  may  be  higher  than  the  primary  rise,  has 
been  interpreted  to  mean  that  the  muscle  contains  two  different  forms  of  muscle- 
tissue  which,  like  the  pale  (rapid)  and  red  (slower)  striated  muscles  of  the  rab- 
bit, have  different  rates  of  contraction.  The  first  rise  is  supposed  to  be  due  to 
the  quicker  and  the  second  to  the  slower  form  of  muscle.  A  similar  double 
crest  is  seen  in  the  contraction  curves  of  muscles  the  irritability  of  which 
has  been  heightened  by  sodium  carbonate,  and  indeed  in  the  curves  from 
muscles  of  normal  frogs  after  their  irritability  has  been  increased  by  frequent 
excitations. 

Liberation  of  Energy  by  the  Contracting'  Muscle. — The  law  of  con- 
servation of  energy  applies  no  less  to  the  living  body  than  to  the  inanimate 
world  in  which  it  dwells.  Every  manifestation  of  life  is  the  result  of  the 
liberation  of  energy  which  was  stored  in  the  body  in  the  form  of  chemical 
compounds.  When  a  muscle  is  excited  to  action  it  undergoes  chemical 
changes,  which  are  accompanied  by  the  conversion  of  potential  to  kinetic  en- 
ergy. This  active  energy  leaves  the  muscle  in  part  as  thermal  energy,  in  part 
as  mechanical  energy,  and,  to  a  slight  extent,  under  certain  conditions,  as  elec- 
trical energy.  In  general,  the  sum  of  the  liberated  energy  is  given  off  as  heat 
9 


130  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

or  niotiou.  The  proportion  in  whicii  these  two  forms  of  energy  shall  be  pro- 
duced by  a  muscle  may  vary  within  wide  limits,  according  to  the  state  of  the 
muscle  and  the  conditions  under  which  the  work  is  done.  Fick  *  states  that 
if  the  nmscle  works  against  a  very  heavy  weight,  ])ossibly  \  of  the  liberated 
energy  may  be  obl^iiucd  as  mechanical  work,  but  if  the  weight  be  light  not 
more  than  ^^  of  the  chemical  energy  is  given  off  in  this  form,  the  muscle 
working  no  more  economically  than  a  steam  engine.  The  flict  that  always  a 
part,  and  often  the  whole,  of  the  mechanical  energy  developed  by  the  muscle 
is  converted  to  thermal  energy  within  the  nuiscle,  and  leaves  it  as  heat,  makes 
it  the  more  difficult  to  determine  in  what  proportion  these  two  forms  of 
energy  were  originally  produced.  Moreover,  if  Engelmann's  view  be  correct, 
that  the  change  of  form  exhibited  by  the  muscle  is  the  result  of  the  imbibition 
of  the  fluid  of  the  isotropic  substance  by  the  anisotropic  material,  this  change 
being  brought  about  by  the  heat  which  is  liberated  within  the  muscle,  we  nmst 
consider  potential  energy  to  be  set  free  first  as  heat,  a  part  of  which  is  after- 
ward changed  to  mechanical  energy,  which  in  part,  at  least,  is  again  changed 
to  heat. 

lAbeixdion  of  Mechanical  Energy. — In  estimating  the  amount  of  mechanical 
energy  liberated  by  a  muscle,  we  observe  the  amount  of  physical  work  which 
it  accomplishes,  /.  e.  the  amount  of  mechanical  energy  which  it  imparts  to  ex- 
ternal objects.  If  a  muscle  by  contracting  raises  a  weight,  it  gives  energy  to 
the  weight,  the  amount  being  exactly  that  which  the  weight  in  falling  through 
the  distance  which  it  was  raised  by  the  muscle  can  impart  as  motion,  heat,  etc., 
to  the  objects  with  which  it  comes  in  contact.  The  measure  of  the  mechanical 
work  done  by  the  contracting  muscle  is  the  product  of  the  weight  into  the  height 
to  which  it  is  lifted.  For  example,  if  a  muscle  raises  a  weight  of  5  grams, 
10  millimeters,  it  does  50  grammillimeters  of  work. 

The  amount  of  work  which  a  muscle  can  do  depends  on  the  following  con- 
ditions : 

(rt)  The  kind  of  muscle.  The  muscles  of  warm-blooded  animals  are  stronger 
than  those  of  cold-blooded  animals ;  a  human  muscle  can  do  two  to  three 
times  the  amount  of  work  of  an  equal  amount  of  frog's  muscle.  The  muscles 
of  certain  insects  have  even  greater  strength.^ 

(6)  nie  quantity  of  muscle-substance  and  the  arrangement  of  the  fibres.  The 
power  of  a  muscle  to  do  mechanical  work,  the  absolute  muscular  force,  is  esti- 
mated by  the  weight  which,  brought  upon  the  muscle  at  the  instant  it  begins  to 
contract,  prevents  it  from  shortening  but  does  not  stretch  it,  /.  e.  one  which  ex- 
actly balances  the  contractile  force  of  the  muscle  when  it  is  excited  to  a  maxi- 
mal tetanic  contraction.  It  is  evident  that  the  amount  of  force  which  can  be 
developed  will  depend  on  the  amount  of  contractile  substance  and  on  the 
arrangement  of  the  fibres.  Since  the  force  which  can  be  developed  by  a  contract- 
ing muscle  depends  largely  on  the  arrangement  of  the  microscopic  contractile 
mechanisms  of  which  it  is  composed,  it  is  found  best,  for  purposes  of  compari- 

*  Fick:  Pfluger's  Archiv,  1878,  xvi.  p.  85. 

*  Hermann  :  Handbuch  der  Physiologie,  1879,  Bd.  i.  p.  64. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.        131 

son,  to  state  tlie  strength  ot'u  tnusclc  and  its  capacity  to  do  work,  fur  tlie  unit 
of  bulk,  one  cubic  centimeter,  or  the  unit  of  weight  of  muscle-substance,  one 
gram.  Thus,  the  absolute  nuiscular  force  of  frog's  muscle  is  estimated  to 
be  about  3  kilograms  per  cubic  centimeter,  and  of  human  muscle  to  be  8  to  10 
kilograms  per  cubic  centimeter.  Fick  states  that  the  maximal  amount  of  ex- 
ternal work  of  which  frog's  muscle  is  capable  is  1  grammeter  per  gram  of 
m  uscle-substance. 

(c)  The  condition  of  the  muscle.  Any  of  the  influences  which  lessen  the 
irritability  of  the  muscle — lack  of  blood,  fatigue,  cold,  etc. — decreases  the  power 
to  liberate  energy,  and  any  influence  which  heightens  the  irritability  is  favora- 
ble to  the  work.  The  effect  of  tension  to  heighten  irritability  has  already  been 
referred  to  and  is  of  especial  interest  in  this  connection,  since  the  very  re- 
sistance of  the  weight  is,  within  limits,  a  condition  favorable  to  the  liberation 
of  the  energy  required  to  overcome  the  resistance.  This  will  be  referred  to 
again. 

(d)  The  strength  and  character  of  the  stimulus.  The  liberation  of  energy  is, 
up  to  a  certain  point,  the  greater,  the  stronger  the  excitation.  Furthermore, 
rapidly  repeated  excitations  are  much  more  effective  than  single  excitations, 
because  a  series  of  rapidly  following  stimuli,  both  by  altering  the  irritability  and 
by  inducing  the  form  of  contraction  known  as  tetanus,  act  to  produce  powerful 
and  high  contractions.  Bernstein  states  that  the  energy  developed  by  the 
muscle  increases  with  the  increase  of  the  rate  of  excitation  from  10  to  50  per 
second,  at  which  rate  the  contraction  power  may  be  double  that  called  out  by  a 
single  excitation. 

(e)  The  method  of  contraction  and  the  mechanical  conditions  under  which  the 
work  is  done.  Inasmuch  as  mechanical  work  is  measured  by  the  product  of 
the  weight  into  the  height  to  which  it  is  lifted,  an  unweighted  muscle  in  con- 
tracting does  no  work ;  a  muscle,  however  vigorously  it  may  contract,  if  it  be 
prevented  from  shortening,  does  no  work;  finally,  a  muscle  which  raises  a 
weight  and  then  lowers  it  again  when  it  relaxes,  does  not  alter  its  surround- 
ings as  the  tot  result  of  its  activity,  and  hence  does  no  work.  Although  no 
mechanical  work  is  accomplished  under  these  circumstances,  physiological  work 
is  being  done,  as  is  evidenced  by  the  fatigue  produced.  Unquestionably  mechani- 
cal energy  is  developed  within  the  muscle  in  all  these  cases,  but  it  is  all  con- 
verted to  heat  before  it  leaves  the  muscle. 

The  amount  of  weight  is  an  important  factor  in  determining  the  extent  to 
which  a  muscle  will  shorten  when  excited  by  a  given  stimulus,  and,  therefore, 
the  quantity  of  work  which  it  will  accomplish.  If  a  muscle  be  after-loaded, 
i.  e.  if  the  weight  be  supported  at  the  normal  resting  length  of  the  muscle,  and 
the  muscle  be  excited  to  a  series  of  maximal  contractions,  the  weight  being  in- 
creased to  a  like  amount  before  each  of  the  succeeding  excitations,  there  is,  in 
general,  a  gradual  lessening  in  the  height  of  the  contractions,  but  the  de- 
crease in  height  is  not  proportional  to  the  increase  of  the  weight.  The 
decrease  in  the  height  of  contractions  is,  as  a  rule,  more  rapid  at  the  beginning 
of  the  series  than  later,  though  at  times  an  opposite  tendency  may  show  itself 


132  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

aud  the  increasing  weights  temporarily  increase  the  irritability  and  therefore 
increase  the  amount  of  shortening.  The  effect  of  tension  to  increase  the  activ- 
ity of  the  contraction  process  is  seen  if  a  muscle  which  is  connected  with  a 
strong  spring  or  heavy  weight  be  excited  to  isometric  contractions  and  in 
the  midst  of  a  contraction  be  suddenly  released  ;  the  muscle  under  such  cir- 
cumstances is  found  to  contract  higher  than  when  excited  by  the  same  stimulus 
without  bcintr  sul))ected  to  tension.  The  effect  of  tension  on  the  activitv  of 
muscular  contractions  is  to  be  clearly  seen  in  the  case  of  the  heart  muscle. 
A  rise  of  pressure  of  the  fluid  within  the  isolated  heart  of  a  frog  increases 
the  strength  as  well  as  the  rate  of  the  beat. 

If  the  weight  be  gradually  increased,  although  the  height  of  the  contrac- 
tions is  lessened,  the  work  will  for  a  time  increase,  and  a  curve  of  work  (con- 
structed by  raising  ordinates  of  a  length  corresponding  to  the  work  done, 
from  points  on  an  abscissa  at  distances  proportional  to  the  weights  em- 
ployed), will  be  seen  to  rise.  After  the  weight  has  been  increased  to  a  cer- 
tain amount  the  decline  in  the  height  of  contractions  will  be  so  great  that  the 
product  of  the  weight  into  the  height  will  begin  to  decrease,  and  the  curve  of 
work  will  fall,  until  finally  a  weight  will  be  reached  which  the  contracting 
muscle  can  just  support  at,  but  not  raise  above,  its  normal  resting  length.  As 
has  been  said,  this  weight  will  be  a  measure  of  the  absolute  muscular  force. 

Example. 

Load  Height  of  lift  Work 

(grams).  (millimeters).  (grammillimeters). 

0 13 0 

30 11 330 

60 9 540 

90 7 630 

120 5 600 

150 3 450 

180 2 360 

210 0 0 

In  the  above  experiment  30  grams  Avas  added  to  the  muscle  after  each 
contraction ;  as  the  weight  was  increased  up  to  90  grams  the  amount  of 
work  was  increased,  with  greater  weights  the  amount  of  work  was  lessened. 

Liberation  of  Thermal  Energy. — Energy  leaves  the  body  as  mechanical 
energy  only  when  by  its  movements  the  body  imparts  energy  to  surrounding 
objects.  Most  of  the  energy  liberated  within  the  body  leaves  it  as  heat ;  even 
during  violent  muscular  exercise  five  times  more  energy  may  be  expended  as 
heat  than  as  mechanical  energy,  and  the  dispro])ortion  may  be  even  greater 
than  this.  So  great  is  the  production  of  heat  during  exercise,  that,  in  spite 
of  the  great  amount  leaving  the  body,  the  temperature  of  an  oarsman  has  been 
found  to  be  increased,  during  a  race  of  2000  meters,  from  37.5°  C.  to  39° 
or  40°  C 

It  is  exceedingly  difficult  to  ascertain  M'ith  accuracy  on  the  warm-blooded 
animal  the  exact  relation  of  heat-production  to  muscular  contraction.     The 

^  Geo.  Kolb:  Physiology  of  Sport,  translated  from  the  German,  2d  edition,  London,  1892. 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND    NERVE.       133 

best  results  have  been  obtained  by  experiments  on  isolated  muscles  of  cold- 
blooded animals.  Helmholtz  observed  the  temperature  of  a  muscle  of  a 
frog  to  be  increased  by  tetanus  lasting  a  couple  of  minutes  0.14°  to  0.18° 
C. ;  Heidenhain  saw  a  change  of  0.005°  C.  result  from  a  single  contraction ; 
and  Fick  ascertained  that  a  fresh,  isolated  muscle  of  a  frog  can  by  a  single 
contraction  produce  per  gram  of  muscle-substance  enough  heat  to  raise 
3  milligrams  of  water  1°  C*  To  obtain  evidence  of  the  slight  changes 
of  temperature  which  occur  in  such  small  masses  of  muscle-tissue  it  is 
necessary  to  employ  a  very  delicate  instrument,  such  as  a  thermopile  or  a 
bolometer. 

The  thermopile  consists  of  strips  of  two  dissimilar  metals,  united  at  their  extremities, 
so  as  to  form  a  series  of  thermo-electric  junctions.  If  there  be  a  difference  of  temperature 
at  two  such  junctions,  a  difference  of  electric  potential  is  developed,  which  causes  the 
flow  of  an  electric  current.  If  the  current  be  passed  through  the  coils  of  wire  of  a 
galvanometer  its  amount  can  be  measured,  and  the  extent  of  the  change  in  tempera- 
ture at  one  of  the  junctions,  the  other  remaining  constant,  can  be  estimated.  In  the 
more  sensitive  instruments,  several  thermo-electric  junctions  are  used.  The  amount  of 
current  depends  largely  on  the  metals  employed,  antimony  and  bismuth  being  a  very 
sensitive  combination. 

The  action  of  the  bolometer  is  based  on  the  fact  that  the  resistance  of  a  wire  to  the 
passage  of  an  electric  current  changes  with  its  temperature. 

The  amount  of  heat  developed  within  the  muscle  by  direct  conversion  of 
potential  to  thermal  energy,  and  the  amount  formed  indirectly,  through  con- 
version of  mechanical  to  thermal  energy,  has  been  made  a  subject  of  careful 
study  by  Heidenhain,^  Fick  and  his  pupils,^  and  others,  the  experiments  being 
made  chiefly  with  isolated  muscles  of  frogs. 

In  general,  the  stronger  the  stimulus  and  the  greater  the  irritability  of  the 
muscle — in  other  words,  the  more  extensive  the  chemical  changes  excited  in 
the  muscle — the  greater  the  amount,  not  only  of  mechanical,  but  of  thermal 
energy  liberated.  Increase  of  tension,  which  is  very  favorable  to  muscular 
activity,  greatly  increases  the  heat-production.  As  the  weight  is  increased, 
both  the  amount  of  heat  developed  and  the  work  are  increased,  but  the  libera- 
tion of  heat  reaches  its  maximum  and  begins  to  decline  sooner  than  the  amount 
of  work,  i.  e.  with  large  weights  the  muscle  works  more  economically ;  similarly, 
as  the  muscle  is  weakened  by  fatigue  the  heat-production  lessens  sooner  than 
the  work. 

Muscle-tonus  and  Chemical  Tonus. — During  waking  hours,  the  cells 
of  the  central  nervous  system  are  continually  under  the  influence  of  a  shower 
of  weak  nervous  impulses,  coming  from  the  sensory  organs  all  over  the  body;* 
moreover,  activity  of  brain-cells,  especially  emotional  forms  of  activity,  leads 

1  Fick  :  Pfluger's  Archiv,  1878,  xvi.  p.  89. 

*  Mechanische  Leistung,  Wdrmeentwicklung  und  Stoffumsatz  bei  der  Muskelthdtigkeit,  Leipzig, 
1864. 

^  Myothermische  Untersuchungen  aus  den  physiologischen  Laboratorium  zu  Zurich  und  Wurzburg, 
Wiesbaden,  1889. 

*  Brondgeest :  Archiv  fur  Anatomic  und  Physiologic,  1860,  p.  703;  Hermann,  Ibid.,  1861, 
p.  350. 


134  AN  AMERICAN   TEXT-BOOK   OF    PHYSIOLOGY. 

to  au  ovorliow  ot"  nervous  impuLses  to  the  spinal  cord  and  an  increased  irrita- 
bility, o)',  if  stronger,  excitation  of  motor  uerve-cells.  If,  when  one  is  quietly 
sitting  and  reading,  he  turns  his  attention  to  the  sensory  impressions  which 
are  coming  at  every  moment  from  all  over  the  body  to  the  brain,  notes  the 
temperature  of  different  parts  of  the  skin,  the  pressure  of  the  clothes,  etc., 
upon  different  parts,  the  light  reflected  from  neighboring  objects,  and  the  slight 
sounds  about  him,  he  will  recognize  that  the  central  nervous  system  is  all  the 
time  subject  to  a  vast  number  of  excitations,  which,  because  of  their  very 
repetition,  are  ordinarily  disregarded  by  the  mind,  but  which  arc,  nevertheless, 
all  the  time  influencing  tiic  nerve-cells.  The  effect  of  this  multitude  of  affer- 
ent stimuli,  in  spite  of  their  feebleness,  is  to  cause  the  motor  cells  of  the  cord 
to  continually  send  delicate  motor  stimuli  to  the  muscles.  These  cause  the 
muscle  to  keep  in  the  state  of  slight  but  continued  contraction  which  gives  the 
tension  ])eculiar  to  waking  hours,  and  which  is  called  viusclc-tonus.  That 
such  a  tension  exists  is  made  evident  by  the  change  in  attitude  which  occurs 
when  the  relaxation  accompanying  sleep  comes  on.  The  effect  of  brain  activ- 
ity to  cause  muscular  tension  is,  likewise,  most  easily  recognized  by  observing 
the  relaxation  of  the  muscles  which  occurs  when  mental  excitement  ceases. 

Muscle-tonus,  like  every  form  of  muscular  contraction,  is  the  result  of  chem- 
ical change,  and  the  liberation  of  energy.  But  little  of  this  energy  leaves  the 
body  as  mechanical  energy,  most  of  it  being  given  off  as  heat. 

This  view  is  by  no  means  universally  accepted,  and  many  physiologists 
believe  in  a  production  of  heat  by  the  muscles,  as  a  result  of  nervous  influences, 
independent  of  contraction.  It  is  thought  that  a  condition  of  slight  but  con- 
tinuous chemical  activity  resulting  in  the  production  of  heat  may  be  maintained 
in  the  muscles  by  intermittent  but  frequent  reflex  excitations,  a  condition  which 
has  been  called  chemical  tonus}  That  the  chemical  activity  of  muscles  is  kept 
up  by  small  stimuli  from  the  spinal  cord  is  shown  by  the  fact  that  if  the  nerves 
be  severed,  or  the  nerve-ends  be  poisoned  by  curare,  the  muscle  absorbs  less 
oxygen  and  gives  off  less  carbon  dioxide  than  when  at  rest  under  normal 
conditions.^ 

The  theory  of  a  reflex  chemical  tonus  independent  of  contraction  implies 
the  existence  of  special  nervous  mechanisms  for  the  exciting  of  chemical 
changes  in  the  muscles  which  shall  result  in  the  liberation  of  energy  as  heat, 
independent  of  the  change  of  form  of  the  muscle.  The  question  of  the  exist- 
ence of  special  nervous  mechanisms  controlling  heat-production — heat-centres, 
as  they  are  called — will  be  considered  in  another  part  of  this  book. 

E.  Electrical  Phenomena  in  Muscle  and  Nerve. 

The  active  muscle  liberates  three  forms  of  energy  :  mechanical  work,  heat, 
and  electricity.  The  active  nerve  makes  no  visible  movements,  gives  off  no 
recognizable  quantity  of  heat,  but  exhibits  changes  in  electrical  condition  quite 

^  Roehrig  und  Zuntz:  Pfluger's  Archiv,  1871,  Bd.  iv. ;  Pfliiger:  PiUUjei^s  Archiv,  1878,  xviii. 
p.  247. 

'^  Zuntz:  Pfluger's  Archiv,  1876,  xii.  522;  Colasanti,  Ibid.,  1878,  xvi.  p.  57. 


GENERAL   PHYSIOLOGY  OF  MUSCLE  AND    NERVE.       135 


comparahk'  to  those  observed  in  the  aetive  niusele.  The  electrieal  changes  in 
nerves  are  the  only  evidence  of  activity  which  we  can  observe,  aside  from  the 
effect  of  the  nerve  on  the  organ  whicli  it  excites ;  tliey  are  therefore  of  great 
interest  to  ns. 

Electrical  energy,  like  all  forms  of  active  energy,  is  the  result  of  a  trans- 
formation of  potential  or  some  form  of  kinetic  energy.  In  the  case  of  the 
muscle,  as  of  an  electric  battery,  we  find  electricity  to  be  associated  with  chemi- 
cal change,  and  believe  it  to  be  liberated  from  stored  potential  energy.  In  the 
case  of  nerves  no  chemical  change  can  be  detected  during  action,  and  hence  we 
are  at  a  loss  to  explain  the  devolopment  of  electricity.  We  can  only  say  that 
it  is  the  result  of  some  chemical  or  physical  process  which  we  have  as  yet  failed 
to  discover. 

Although  activity  of  nerve  and  muscle  is  found  to  be  associated  with  elec- 
trical change,  we  must  not  suppose  functional  activity  to  be  in  any  sense  an 
electrical  process.  The  movements  of  a  man  may  be  interpreted  from  the  move- 
ments of  his  shadow,  but  they  are  very  different  phenomena;  the  activity  of 
the  nerve  and  muscle  is  indicated  by  the  electrical  changes  accompanying  it, 
but  they  may  be  independent  processes.  Certainly  the  irritating  change  which 
is  transmitted  along  the  nerve  and  which 
excites  the  muscle  to  action,  although  ac- 
companied by  electrical  changes,  is  not 
itself  an  electric  current. 

Electrical  energy  is  exhibited  not  only 
by  active  nerve  and  muscle,  but  during 
the  activity  of  a  great  variety  of  forms 
of  living  matter.  It  may  be  detected  in 
gland-cells,  in  the  cells  of  many  of  the 
lower  animal  organisms,  and  even  plant- 
cells.  The  amount  of  electrical  energy 
developed  in  animal  tissues  may  be  far 
from  trivial.  Although  delicate  instru- 
ments are  necessary  to  observe  the  elec- 
trical changes  in  nerve  and  muscle,  as 
the  great  internal  resistance  of  the  tissues 
causes  the  currents  to  be  small,  we  find  in 
certain  fish  special  electric  organs,  which 
appear  to  be  modified  muscle-tissue,  and 


Fig.  58.— Schema  of  galvanometer:  n,  s,  north 
and  south  poles  of  astatic  pair  of  magnets ;  m, 
compensating  magnet,  held  by  friction  on  the 
which  are  capable  of  discharging  a  great     staff,  and  capable  of  being  approached  to,  or  ro 

amount  of  electrical  energy  when  excited 
through  their  nerves.  So  intense  is  the 
action  of  this  electrical  apparatus  that  it 
can  be  used  as  a  weapon  of  defence  and 
offence. 

1.  Methods  of  Ascertaining  the  Electrical  Condition  of  a  Muscle  or  a  Nerve.— 
If  the  electric  tension  of  any  two  parts  of  an  object  differs,  the  instant  they  are  joined  an 


tated  with  reference  to,  the  suspended  magnet ; 
X,  mirror;  /,  fibre  supporting  the  magnets;  c,  c, 
c,  c,  coils  of  wire  to  carry  the  electric  current 
near  to  the  magnets,  the  upper  coils  being  wound 
in  the  opposite  direction  to  the  lower ;  e,  e,  non- 
polarizable  electrodes  applied  to  the  longitudinal 
surface  and  cross  section  of  a  muscle. 


136 


A^^  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


electric  current  will  flow  from  the  point  where  the  tension  is  greater  to  that  where  it  is  less. 
The  presence,  direction  of  flow,  and  strength  of  an  electric  current  can  be  detected  by  an 
instrument  calleil  a  iralvanometer.  If  any  two  parts  of  a  muscle  or  nerve,  as  e,  e,  Figure 
58,  be  connected  by  suitable  conductors  witli  the  coils,  c,  c,  of  a  galvanometer,  and  if  there 
be  a  difiereiice  in  the  electric  potential  of  the  twu  jiarts  examined,  an  electric  airrent  will 
be  indicated  by  the  instrument.  In  such  tests  all  extra  sources  of  electricity  are  to  be 
avoided,  therefore  the  electrodes  applied  to  the  muscle  must  be  non-polarizable. 

The  Galvanometer — An  ordinary  form  of  galvanometer  consists  of  a  magnet  suspended 
bj'  an  exceedingly  delicate  fibre  of  silk,  or  quartz,  and  one  or  more  coils,  composed  of  many 
windings  of  pure  copper  wire,  placed  vertically  near  the  magnet  and  in  the  plane  of  the  mag- 
netic meridian.  If  an  electric  current  be  allowed  to  flow  through  the  wire,  it  influences  the 
magnetic  field  about  it,  and,  if  the  coils  be  close  to  the  suspended  magnet,  cau.ses  the 
magnet  to  deviate  from  the  plane  of  the  magnetic  meridian  in  one  or  the  other  direction, 
according  to  the  direction  of  the  flow  of  the  current.  In  the  more  delicate  instruments  the 
influence  of  the  earths  magnetism  is  lessened  by  the  use  of  two  magnets  of  as  nearly  as  pos- 
sible the  same  strength,  placed  so  as  to  point  in  opposite  directions,  and  fastened  at  the 
extremities  of  a  liglit  rod.  As  each  magnet  tends  to  point  toward  the  north,  they  mutually 
oppose  each  other,  and  therefore  the  effect  of  the  earth's  magnetism  is  partly  compensated. 
Still  another  magnet  may  be  brought  near  this  "astatic"  combination,  and  by  opposing  the 
action  of  the  earth's  magnetism  make  the  arrangement  even  more  delicate.  In  the  Thomp- 
son galvanometer,  the  rod  connecting  the  needles  bears  a  slightly  concave  mirror,  from 
which  a  beam  of  liglit  can  be  reflected  on  a  scale.  Or  a  scale  may  be  placed  so  that  its 
image  falls  on  the  mirror,  and  the  shghtest  movement  of  the  magnet  may  be  read  in  the 
mirror  by  a  telescope. 

The  galvanometer  is  very  sensitive  to  the  presence  of  electric  currents.  Another  appa- 
ratus which  is  even  more  responsive  to  changes  in  electric  potential  of  short  duration  is 
the  capillary  electrometer. 

The  capillarrj  electrometer  (Fig.  59)  consists  of  a  glass  tube  ia)  drawn  out  to  form 
a  very  fine  capillary,  the  end  of  which  dips  into  a  glass  cup  with  parallel  sides  (/)  contain- 
ing a  10  per  cent,  solution  of  sulphuric  acid.  The 
upper  part  of  the  tube  is  connected  bj'  a  thick- 
walled  rubber  tube  with  a  pressure-bulb  containing 
mercury  (c).  As  the  pressure-bulb  is  raised,  the 
mcrcurj'  is  driven  into  the  capillary,  the  flow  being 
opposed  by  the  capillary  resistance.  By  a  suffi- 
cientlj'  great  pres.sure.  mercury  may  be  driven  to  the 
extremity  of  the  capillar^'  and  all  the  air  expelled. 
When  the  pressure  is  relieved  the  mercurj'  rises 
again  in  the  tube,  drawing  the  sulphuric  acid  after 
it.  The  colunm  of  mercur>'  will  come  to  rest  at  a 
point  where  the  pressure  and  the  capillary  force  just 
balance.  Seen  through  the  microscope  (e),  the  end 
of  the  column  of  mercury,  where  it  is  in  contact 
with  the  sulphuric  acid  appears  as  a  convex  menis- 
cus (d).  Any  alteration  of  the  surface  tension  of 
the  meniscus  causes  the  mercury  to  move  with 
great  rapidity  in  one  direction  or  the  other  along 
the  tube ;  and  a  verj'^  slight  difference  of  electric 
potential  suffices  to  cause  a  change  in  surface  ten- 
sion of  the  mercurj'-sulphuric  acid  meniscus.  A  i)latinum  wire  ftised  into  the  glass  tube 
(a),  and  another  dipped  into  a  little  mercury  at  the  bottom  of  the  cup  holding  the  acid, 
permit  the  mercury  in  the  capillary  and  the  acid  to  be  connected  with  the  body  the  elec- 
tric condition  of  which  is  to  be  examined.  If  the  mercury  and  acid  be  connected  with 
two  points  of  different  electric  potential,  as  g  and  /;  of  muscle  M,  the  mercury  will  instantly 


Fig.  59.— Schema  of  capillary  electrometer. 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       137 

move  from  tlie  direction  of  greater  to  that  of  lesser  tension,  descending  deeper  into  the 
tube  if  the  pressure  be  raised  on  tlie  mercury  side,  or  lowered  on  the  acid  side,  and  vice 
versa.  As  seen  through  the  micnjscope  the  picture  is  reversed  {d),  and  the  movements 
of  the  mercury  appear  to  be  in  the  opposite  direction  to  that  stated.  The  extent  of  the 
movements  of  the  mercury  column  can  be  estimated  by  a  scale  in  the  eyepiece.  More- 
over, the  movement  of  the  mercury  can  be  recorded  ijhotographicully,  \>y  placing  a  strong 
light  behind  the  column  of  mercury,  and  letting  its  shadow  fall  thnjugh  a  slit  in  the  wall 
of  a  dark  chamber,  upon  a  sheet  of  sensitized  i)aper  stretched  over  the  surface  of  a  revolv- 
ing drum  or  a  sensitized  plate  moved  by  clockwork  or  other  suitable  mechanism.  This 
instrument,  of  which  there  are  a  number  of  different  forms  besides  that  originally  devised 
by  Lippmann,  is  very  delicate,  recording  exceedingly  slight  differences  in  electrical  poten- 
tial. 


2.  Currents  of  Rest. — A  normal  resting  nerve  or  muscle  presents  no  dif- 
ferences in  electric  tension  and  gives  no  evidence  of  electric  currents,  wherefore 
we  say  it  is  iso-electric.  If  any  part  of  the  structure  be  injured,  its  electrical 
condition  is  forthwith  changed,  and  if  the  injured  portion  and  some  normal 
part  be  connected  with  a  galvanometer,  an  electric  current  is  observed  to  flow 
from  the  normal  region  to  the  point  of  injury.  These  muscle-currents  were 
discovered  at  about  the  same  time  by  Matteucci  and  Du  Bois-Reymond,  and 
the  latter  wrote  a  now  celebrated  treatise  upon  the  electrical  phenomena  to  be 
observed  in  the  nerve  and  muscle  undei'  varying  conditions.^ 

Directions  of  Currents  of  Rest. — If  a  striated  muscle,  with  long  parallel 
fibres,  such  as  the  sartorius  or  the  semimembranosus  of  a  frog,  be  prepared 
with  care  not  to  injure  the  surface,  and  then  be  given  a  cylindrical  shape  by 
cutting  off  the  two  ends  at  right  an- 
gles to  the  long  axis,  the  piece  will 
present  two  cross  sections  of  injured 
tissue  and  a  normal  longitudinal  sur- 
face (see  Fig.  60).  If  non-polarizable 
electrodes,  connected  with  the  coils  of 
wire  of  a  galvanometer,  be  applied  to 
various  parts  of  such  a  piece  of  mus- 
cle, it  will  be  found  that  all  points  on 
the  longitudinal  surfaces  are  positive 
in  relation  to  all  points  on  the  cross 
sections,  but  that  the  differences  of 
tension  will  differ  according  to  the 
points  which  are  compared.  Suppose 
that  the  cylinder  be  divided  into 
equal  halves  by  a  plane  parallel  to  the 
cut  ends.  Points  on  the  line  bound- 
ing this  plane,  the  equator,  show  the 

greatest  positive  tension,  and  the  forther  other  points  on  the  longitudinal  sur- 
face are  from  the  equator  the  less  their  tension.     Points  on  the  cross  section 
show  a  negative  tension,  and  this  lessens  from  the  centre  to  the  periphery  of 
'  Untersuchungen  vber  thierische  Ekktricitdt,  Berlin,  1849. 


Fig.  60.— Schema  to  show  the  direction  of  cur- 
rents to  be  obtained  from  muscle.  The  schema 
represents  a  cylindrical  piece  of  muscle  with  nor- 
mal longitudinal  surface  (a,  c  and  6,  d),  and  two 
artificial  cross  sections  (a,  b  and  c,  d).  The  position 
of  the  equator  is  shown  by  line  e.  The  unbroken 
lines  connect  points  of  different  potential,  and  the 
arrows  show  the  direction  which  the  currents 
would  take  were  these  points  connected  with  a 
galvanometer.  The  broken  lines  connect  points 
of  equal  potential  from  which  no  current  would  be 
obtained. 


138  AN  AMERICAN    TEXT-BOOK    OF   I'HV.SIOLOaY. 

the  cross  section.  Points  on  the  cross  section  equidistant  from  the  centre,  or 
on  the  longitudinal  surface  equidistant  from  the  equator,  have  the  >amc  poten- 
tial and  give  no  current,  while  points  placed  nnsymmetrieally  give  a  current. 
Splitting  the  cylinder  by  separation  of  the  parallel  fibres  gives  j)ieces  of  nuis- 
cle  M Inch  show  the  same  electrical  juMuliarities,  and  without  doubt  the  same 
would  be  true  of  separate  muscle-fibres  or  pieces  of  fibres. 

Theories  as  to  Cause  of  Ounrnts  of  Best — Du  Bois-Reymond,  impressed  by 
the  facts  which  he  had  ascertained  as  to  the  direction  of  action  of  the  electro- 
motive forces  exhibited  by  the  muscle,  tried  to  explain  the  difference  in  elec- 
trical tension  of  the  surface  and  cross  section  on  the  supjiosition  that  the 
muscle  was  composed  of  electro-motive  molecules  which  presented  differences 
in  electric  tension  similar  to  those  shown  by  the  smallest  particles  of  muscle 
which  it  is  possible  to  study  experimentally.  Further,  he  considered  these  dif- 
ferences in  tension,  and  the  consequent  electric  currents,  to  exist  within  the 
normal  muscle — the  longitudinal  surface  and  normal  cross  section,  i.  e.  the 
point  where  the  muscle-fibre  joins  the  tendon,  having  the  same  sort  of  differ- 
ence in  electric  potential  as  the  normal  longitudinal  surface  and  the  artificial 
cross  section.  When  the  muscle  is  injured  the  balance  of  the  electro-motive 
forces  within  is  lost,  and  they  are  revealed.  It  is  difficult  to  refute  such  a 
theory  by  experiment,  because  our  instruments  only  record  differences  in  tension 
at  points  on  the  surface  of  the  muscle  to  which  we  can  apply  the  electrodes. 
We  cannot  say  that  there  is  an  absence  of  electric  tension  or  lack  of  electric 
currents  within  the  normal  resting  muscle ;  we  can  only  say  that  there  is  no 
direct  experimental  evidence  of  the  existence  of  such  currents. 

Another  theory  of  the  electrical  phenomena  observed  in  muscle,  and  one 
which  has  found  many  adherents,  was  advanced  by  Hermann.^  According  to 
Hermann's  view  there  are  no  differences  in  electric  potential  and  no  electric 
currents  within  the  normal  muscle;  the  "current  of  rest"  is  a  "current  of 
injury,"  a  "demarcation  current,"  i.  e.  it  is  due  to  chemical  changes  occurring 
in  the  dying  muscle-tissue  at  the  border  line  between  the  injured  and  living 
muscle-tissue. 

Although  the  greatest  differences  in  potential  are  observed  when  many  muscle- 
fibres  are  injured,  as  when  a  cut  is  made  completely  through  a  muscle,  injurv 
to  any  part  causes  that  part  to  become  negative  as  compared  with  the  rest. 
Even  an  injurv  to  a  tendon  causes  a  difference  in  potential.  It  is  exceedingly 
difficult,  therefore,  to  expose  a  muscle  M'ithout  injuring  it ;  but  this  can  be  done 
in  the  case  of  the  heart  ventricle,  and  Engelmann  showed  that  this  gives  no  cur- 
rent when  at  rest,  although  a  current  is  found  as  soon  as  any  part  is  hurt,  the 
part  becoming  immediately  negative  in  relation  to  other  uninjured  parts.  In 
experiments  on  isolated,  long,  parallel-fil)red  muscles,  the  current  which  is 
caused  by  the  injury  of  one  extremity  is  found  to  fade  away  only  very  gradu- 
ally (it  may  last  forty-eight  hours  or  more),  and  this  current  can  be  strength- 
ened but  little  by  new  injuries.  In  the  case  of  the  heart-muscle  the  current 
caused  by  cutting  off  a  piece  of  the  ventricle  soon  disappears,  but  another  cur- 
1  Handbuch  der  Physiologic,  1879,  Bd.  i.  p.  226. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.       139 

rent  ot"  ocuinl  strength  is  got  if  a  new  section  be  made  by  cutting  off  the  tissue 
injured  by  the  lirst  cut.  In  tiie  case  of  the  long-fibred  muscles  the  death 
process  gradually  progivsses  the  length  of  the  injured  fibres,  while  in  the  case 
of  the  heart-niuscle,  in  which  the  cells  are  very  short,  the  death  processes  are 
limited  to  the  injun-d  cells,  and  on  their  death  the  current  disappears;  when  a 
new  cut  is  made  other  cells  are  injured  and  again  a  strong  current  is  obtained. 

Dead  tissue  gives  no  current ;  normal  resting  living  tissue  gives  no  current ; 
dying  tissue  is  electrically  negative  as  compared  with  normal  living  tissue. 

Hering  has  carried  Hermann's  view  that  electrical  change  is  the  result  of 
chemical  action  still  further.  He  considers  that  the  condition  of  negativity  is 
an  evidence  of  katabolic  (breaking-down)  chemical  processes  and  that  anabolic 
(building-up)  chemical  processes  are  accompanied  by  a  positive  electrical  change. 
Like  Du  Bois-lieymond,  he  believes  that  the  normal  resting  muscle  may  be 
the  seat  of  electro-motive  forces  Avhich  do  not  manifest  themselves  as  long  as 
the  diflferent  parts  are  in  like  condition. 

Current  of  Red  of  a  Nerve. — Xerves  like  muscles  show  no  electric  currents 
if  normal  and  resting,  but  give  a  demarcation  current  if  injured,  the  dying  por- 
tion being  negative  to  normal  parts,  and  the  direction  of  the  currents  is  the 
same  as  in  injured  muscle.  Gotch  and  Horsley^  ascertained  the  electro-motive 
force  in  the  nerve  of  a  cat  to  be  0.01  of  a  Daniell  cell  and  of  an  ape  only  0.005, 
while  in  the  spinal  nerve-roots  of  the  cat  it  was  0.025,  and  in  the  tracts  of  the 
spinal  cord  of  the  cat  0.046  and  of  the  ape  0.029.  Larger  currents  are 
obtained  from  uon-medullated  nerves,  probably  because  a  non-medullated 
nerve  contains  a  larger  number  of  axis-cylinders  than  a  medullated  nerve  of 
the  same  size.  The  current  of  injury  of  a  nerve  lasts  only  a  short  time.  The 
death  process  which  is  the  immediate  result  of  the  injury  proceeds  along  the 
nerve  only  a  short  distance,  perhaps  to  the  first  node  of  Ranvier,  and  when  it 
has  ceased  to  advance  the  current  fails ;  a  new  injury  of  the  nerve  causes 
another  demarcation  current  as  strong  as  the  first. 

Hering  found  that  a  nerve  like  a  muscle  could  be  excited  by  its  own  cur- 
rent, provided  the  circuit  between  the  longitudinal  and  fresh  cross  section  of  an 
irritable  nerve  was  rapidly  closed. 

3.  Currents  of  Action  in  Muscle. — Just  as  the  dying  tissue  of  nerves  is 
electrically  negative  as  compared  with  normal  tissue,  so  active  nerve-  and 
muscle-tissue  is  electrically  negative  as  compared  with  resting  tissue. 

Du  Bois-Reymond  discovered  that  if  the  normal  longitudinal  surface  and 
injured  cut  end  of  a  muscle  were  connected  with  a  galvanometer  and  the  muscle 
were  tetanized,  the  magnet  swung  back  in  the  opposite  direction  to  the  deflec- 
tion which  it  had  received  from  the  current  of  rest.  This  backward  swing  of 
the  magnet  was  not  due  to  a  lessening  of  the  current  of  rest,  for  if  the  effect 
of  the  current  of  rest  on  the  galvanometer  were  compensated  for  by  a  battery 
current  of  equal  strength  and  of  opposite  direction,  so  that  the  needle  stood  at 
0,  and  the  muscle  were  then  tetanized,  there  was  a  deviation  of  the  needle 
in  the  opposite  direction  to  that  given  it  by  the  current  of  rest.  Du  Bois- 
1  Philosophical  Transactio7is,  1891,  B.,  vol.182,  pp.  267-526. 


Fig.  6L— Secondary  tetanus. 


140  AN  AMERICAN   TEXT- BOOK   OF  PHYSIOLOGY. 

Reymond  called  this  current  of  action  the  negative  variation  current.  This 
negative  variation  current  was  found  to  last  as  long  as  the  muscle  coiitinucd  in 
tetanus.  On  the  cessation  of  the  stimulus  the  current  subsided  more  or  less 
rapidly  and  the  needle  returned  more  or  less  completely  to  the  position  given  it 
by  the  current  of  rest  before  the  excitation.  Tiie  return  was  rarely  complete, 
and  by  repeated  excitations  there  was  a  gradual  lessening  of  the  current  of 
rest,  the  amount  varying  with  the  extent  of  the  preceding  irritation. 

Secondary  Tetanus. — Matteucci  and  Du  Bois-Reyraond  (1842)  both  dis- 
covered the  phenomenon  which  Du  Bois-Rcymond  called  secondary  tetanus. 

If  two  nerve-muscle  preparations  be 
''''•^^•~-^'' — ^  1:^  made,  and  the  nerve  of  prejiaration  B 

„._/ — r^v^^  \\^  be  laid  on  the  muscle  of  preparation 

A,  when  the  nerve  of  A  is  stimulated, 
not  only  the  muscle  of  A  but  the 
muscle  of  B  will  twitch  (see  Fig.  61). 
If  nerve  A  be  excited  by  many 
rapidly  following  induction  shocks  so 
that  muscle  A  enters  into  tetanus, 
muscle  B  will  also  be  tetanized.  The  phenomenon  is  not  due  to  a  spread  of 
the  irritating  electric  current  through  nerve  and  muscle  A  to  nerve  B,  for  the 
tetanus  of  both  muscles  stops  if  nerve  A  be  ligated ;  moreover,  a  secondary 
tetanus  is  obtained  in  case  tetanus  of  muscle  A  is  called  out  by  mechanical 
stimuli,  such  as  a  series  of  rapid  light  blows,  applied  to  nerve  A. 

Du  Bois- Reymond  considered  "  secondary  tetanus  "  a  proof  of  the  discon- 
tinuity of  the  apparently  continuous  contraction  of  tetanus,  for  muscle  B  could 
only  have  been  excited  to  tetanus  by  rhythmic  excitations  from  A.  Each  of 
the  rapidly  following  excitations  applied  to  A  was  the  cause  of  a  separate  con- 
traction process  and  a  separate  current  of  action  in  B  ;  the  separate  contractions 
combined  to  produce  the  tetanus  of  7>,  but  the  separate  currents  of  action  did 
not  fuse,  although  they  caused  a  continuous  negative  variation  of  the  slowly 
moving  magnet  of  the  galvanometer. 

The  correctness  of  this  view  has  been  shown  by  experiments  with  the  capil- 
lary electrometer,  which  approaches  the  "  physiological  rhcoscopc,"  as  the 
nerve-muscle  preparation  is  called,  in  its  sensitiveness  to  rapid  changes  in  elec- 
trical potential. 

Burdon  Sanderson  ^  has  obtained,  by  photographically  recording  the  move- 
ments of  the  column  of  mercury  of  the  capillary  electrometer  (see  Fig.  59, 
p.  136),  beautiful  records  of  the  changes  of  electric  potential  which  occur  when 
an  injured  muscle  is  tetanized. 

The  record  in  Figure  62  shows,  first,  a  series  of  negative  changes  resulting 
from  the  separate  stinmli.  It  is  these  which  cause  secondary  tetanus  and 
which  produced  the  negative  variation  current  disclosed  by  the  galvanometer 
in  the  experiments  of  Du  Bois-Reymond.  Second,  there  is  a  more  permanent 
negative  change,  likewise  opposed  to  and  lessening  the  effect  of  the  negative 
^  Journal  of  Physiology,  1895,  vol.  xviii.  p.  717. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.       141 

chan^i'  at  tlie  part  where  the  tissue  is  dying,  and  called  by  Sanderson  "  the 
diniiuntional  effect."  This  continuous  negative  change  is  probably  attributable 
to  the  presence  of  a  continuous  contraction  process,  perhaps  the  contracture 
which  we  observed  in  studying  the  tetanus  curve  (see  Fig.  49).     This  "  diniinu- 


Fin.  02. — Recc^rd  of  cliaii^es  in  eleetrif'  potential  in  a  tetanized  injured  muscle  of  a  fro^'.  The  leadiuK- 
off  non-polarizable  electrodes  connected  with  the  capillary  electrometer  touched  the  normal  longitud- 
inal and  injured  cut  surface  of  the  muscle.  The  muscle  was  tetanized  by  an  induction  current  applied 
to  its  nerve,  the  rate  of  interruptions  being  210  per  second.  A  rise  of  the  curve  indicates  an  electrical 
change  of  opposite  direction  to  that  caused  by  the  injury.  The  diminution  of  the  current  of  injury, 
which  was  less  than  in  some  other  experiments,  was  0.008  volt.  The  time  record  at  the  bottom  of  the 
curve  was  obtained  from  a  tuning  fork  making  500  double  vibrations  per  second  (after  Burdon  San- 
derson). 

tional  effect "  is  only  to  be  observed  upon  an  injured  muscle,  since  it  repre- 
sents a  difference  in  potential  between  the  normally  contracting  and  the  injured, 
imperfectly  contracting  muscle-substance.  AYhen  all  parts  of  the  muscle  are 
normal  and  contracting  to  an  equal  amount,  the  electrical  forces  would  be 
everywhere  of  the  same  nature,  balance  one  another,  and  give  no  external 
evidence.  Although  the  diminutional  effect  is  only  to  be  observed  upon  the 
injured  muscle,  the  temporary  negative  changes  which  follow  each  excitation 
are  to  be  observed  on  the  normal  muscle.  To  understand  this  we  must  con- 
sider the  diphasic  current  of  action. 

Diphasic  Current  of  Action. — If  a  normal  muscle  be  locally  stimulated  by 
a  single  irritation,  either  directly  or  indirectly  through  its  nerve,  the  part 
excited  will  be  the  first  to  become  active  and  electrically  negative,  and  this 
condition  will  be  taken  on  later  by  other  parts.  Our  methods  only  permit  us 
to  observe  the  relative  condition  of  the  parts  of  the  muscle  to  which  the  elec- 
trodes are  applied,  the  changes  in  the  intermediate  tissue  failing  to  show  them- 
selves. If  an  electrode  be  applied  near  the  place  where  the  uninjured 
muscle  is  stimulated.  A,  and  another  at  some  distant  point,  B,  and  these 
electrodes  be  connected  with  a  capillary  electrometer,  a  diphasic  electrical 
change  will  be  observed  to  follow  each  stimulation.  At  the  instant  the  irritant 
is  applied  the  muscle-substance  at  A  will  become  suddenly  negative  with 
respect  to  that  at  B ;  when  the  spreading  irritation  wave  has  reached  B,  that 
part  too  wnll  tend  to  be  negative,  and  an  electrical  equality  will  be  temporarily 
established ;  finally,  B  continuing  to  be  active  after  A  has  ceased  to  act,  B 
will  be  negative  in  respect  to  A.  Since  the  Avave  of  excitation  spreads  along 
the  fibres  in  both  directions  from  the  point  irritated,  each  excitation  will  cause 
two  such  diphasic  electrical  changes. 


142  AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

If  the  muscle  has  beeu  injured  at  i>,  the  dyiiii^  libre.s  lliere  will  react  but 
poorly  to  the  stimulus,  and  therefore  the  anta<ronistic  influence  of  the  nej^ative 
change  at  B  will  incompletely  compensate  for  the  negativity  at  A,  and  hence 
only  a  single  phase  due  to  the  condition  of  negativity  at  A  will  be  seen. 

The  normally  beating  heart  shows  diphasic  currents  of  action  :  in  the  first 
phase  the  base,  where  the  contra(;tion  process  starts,  is  negative  to  the  apex, 
and  in  the  second  phase  the  apex  is  negative  to  the  base.  In  case  the  heart  be 
injured,  the  negative  change  corresponding  to  action  fails  at  the  injiu'cd  part, 
and  therefore  a  single  and  because  not  antagonized  more  prolonged  negative 
change  is  observed.  Under  certain  conditions  a  trii)hasic  change  is  observed, 
which  need  not  be  discussed  here.  AV^aller  ^  has  succeeded  in  recording  the 
electrical  changes  which  accompany  the  beat  of  the  human  heart. 

These  diphasic  changes  of  the  electric  condition  are  sufficiently  strong  and 
rapid  in  the  mammalian  heart  to  excite  the  nerve  of  a  nerve-muscle  prepara- 
tion, and  the  muscle  will  be  seen  to  give  one,  or,  if  the  heart  is  uninjured, 
sometimes  two,  contractions  every  time  the  heart  beats. 

Bernstein  2  found  the  time  between  the  two  portions  of  diphasic  change  to 
be  proportional  to  the  distance  between  the  Icading-off  electrodes,  and  to  cor- 
respond to  a  rate  of  transmission  the  same  as  that  of  the  wave  of  excitation 
as  revealed  by  the  spread  of  the  contraction  process  (in  the  muscle  of  the  frog 
3  meters  per  second).  Hermann,'*  by  using  cord  electrodes  on  the  human  fore- 
arm, found  the  rate  of  spread  of  the  active  process  by  the  voluntary  contraction 
of  human  muscle  to  be  from  10  to  13  meters  per  second.  Du  Bois-Reymond 
dip])ed  a  finger  of  each  hand  into  fluid  contained  in  cups  connected  with  a 
galvanometer.  If  the  muscles  of  one  arm  were  vigorously  contracted,  a 
deflection  of  the  magnet  was  seen.  This  was  probably  due  to  electric  currents 
from  the  glands  of  the  skin  and  not  from  the  contracting  muscles.  Bernstein 
found  that  the  negative  change  began  at  the  instant  of  excitation,  /.  e.  during 
what  was  considered  the  latent  period,  and  hence  he  thought  that  it  preceded  the 
contraction  process  and  rei)resented  the  excitation  process.  It  is  now  believed 
that  the  katabolic  chemical  changes  which  result  in  the  development  of  the 
three  forms  of  energy,  heat,  motion,  and  electricity,  have  little  or  no  latent 
period,  but  begin  at  the  instant  the  irritant  acts,  being  practically  synchronous 
with  the  excitation  process  (see  p.  101).  The  condition  of  negativity  is  con- 
sidered not  to  result  from  an  irritation  process  preceding  the  contraction,  but 
to  be  associated  with  the  contraction  process  itself,  and  this  view  is  supported 
by  the  discovery  that  the  negative  state  continues  throughout  the  contraction. 
Sanderson  and  Page*  saw  the  diphasic  change  which  accompanies  the  beat  of 
the  heart  last  throughout  the  contraction. 

Lee^  found  the  dijihasic  change  which  occurs  when  the  skeletal  muscle  of 

'  Archiv  fiir  Anatomie  unci  Physiolor/ie,  1890;  physiol.  Abtheil.,  p.  187. 

^  Untersuchuncjen  iiber  den  Erregunfjsvorgung  im  Nerven-  und  Muskel-systeme,  1871. 

'  Handbuch  der  Physiologie,  1879,  i.  1,  p.  224. 

*  Journal  of  Physiology,  1879,  vol.  ii.,  p.  396. 

^  Archiv  fiir  Anatomie  und  Physiologic,  1887,  p.  204. 


GENERAL   PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       143 

a  frog  is  excited  by  a  single  stinmlus  to  continue  as  long  as  the  muscle  remains 
active,  including  the  period  relaxation  ;  in  some  cases  it  lasted  from  0.05  to 
0.06  second.  Sandei*son,  as  we  have  seen  (see  Fig.  62),  tetanized  injured 
skeletal  nuiscles  of  the  frog,  and  found  not  only  a  series  of  negative  variations 
corresponding  to  the  contraction  processes  which  resulted  from  the  separate 
excitations,  but  a  continuous  negative  variation,  the  diminutional  effect,  which 
developed  comparatively  slowly  and  lasted  after  the  irritant  had  ceased  to  act. 
All  these  facts  unite  to  point  to  the  conclusion  that  the  negative  electrical 
change  w'hich  develops  when  a  muscle  is  excited  to  action  is  associated  with 
the  contraction  process. 

4.  Currents  of  Action  in  Nerves. — In  general,  the  facts  which  have  been 
stated  with  regard  to  the  current  of  action  in  muscles  apply  to  nerves.  When 
a  normal  nerve  is  excited  a  negative  change  is  forthwith  developed  at  the 
stimulated  point  and  passes  thence  in  both  directions  along  the  nerve  at  the 
same  rate  as  the  nerve  impulse.  This  change  is  diphasic,  first  the  part  excited 
and  later  distant  parts  showing  the  negative  change.  If  the  nerve  be  injured, 
and  the  normal  surface  be  compared  with  the  dying  or  dead  cross  section,  the 
second  phase  is  absent.  If  the  nerve  be  frequently  excited,  each  excitation 
awakens  a  separate  current  of  action.  The  duration  of  the  negative  change 
caused  by  a  .single  stimulus  varies  in  different  conditions  from  0.007  to  0.023 
second.  The  strength  of  the  current  of  action  likewise  varies,  but  under 
favorable  conditions  may  be  twice  as  great  as  the  current  of  rest,^  and  Hering 
has  shown  that  it  is  capable  of  exciting  another  nerve  to  action.  Nerve-cells 
and  muscles  are  more  sensitive  to  nerve  impulses  than  our  instruments  are  to 
the  accompanying  electrical  changes,  nevertheless  a  negative  change  may  be 
observed  to  accompany  a  nerve  impulse  which  has  been  caused  by  the  excita- 
tion of  the  nerve  by  nerve-cells. 

Du  Bois-Reymond  observed  with  the  galvanometer  a  lessening  ("  negative 
variation")  of  the  demarcation  current  ("current  of  rest")  when  in  strychnia- 
poisoning  the  spinal  motor  nerve-cells  were  exciting  the  motor  nerves  vigor- 
ously and  causing  cramp-like  tetanic  muscular  contractions.  Gotch  and 
Horsley  ^  applied  electrodes  connected  with  a  capillary  electrometer  to  periph- 
eral nerves,  spinal  nerve-roots,  and  tracts  of  motor  fibres  within  the  spinal 
coi'd,  and  di.scovered  that  if  the  cortical  brain-cells  in  the  motor  zones  were 
excited,  the  nerves  showed  currents  of  action  corresponding  in  rate  to  the  dis- 
charge of  motor  impulses  from  these  brain-cells,  e.  g.  if  the  epileptiform  con- 
vulsions were  occurring  at  the  time,  the  capillary  electrometer  revealed  changes 
of  potential  of  like  rate  in  the  nerves. 

As  far  as  has  been  ascertained  the  nerve  impulse  has  the  same  general  cha- 
racteristics in  all  forms  of  nerves,  medullated  and  non-medullated,  sensory, 
inhibitory  and  motor,  and  except  as  regards  strength,  rhythm,  etc.  is  the  same 
whether  they  be  excited  artificially  or  normally  by  a  nerve-cell  or  sen.sory  end- 
organ.     In  every  case  the  impulse  appears  to  be  accompanied  by  a  current  of 

'  Biedermann  :  Elektrophysiologie,  1895,  p.  666. 

*  Philosophical  Transactions,  1891,  vol.  182,  pp.  267-526. 


144  AN  A3fUBICAN   TEXT-BOOK    OF   PHYSIOLOGY. 

action,  e.g.  light  falling  on  the  retina  of"  the  eye  of  a  frog  causes  a  negative 
variation  of  the  current  of  rest  of  the  optic  nerve. 

F.  Chemistry  of  Muscle  and  Nerve. 

1.  Chemistry  of  Muscji.e. 

Muscles  contain  about  75  j)art,s  water  and  25  parts  solids;  nearly  21  parts 
of  the  solids  are  proteids,  the  remaining  4  parts  consisting  of  fats,  extractives, 
and  salts. 

Little  is  known  concerning  the  chemistry  of  living  muscle;  the  instability 
of  the  complex  jnolecules  which  makes  possible  the  rapid  development  of  energy 
peculiar  to  muscles  renders  exact  analysis  impossible.  The  manipulations 
essential  to  chemical  analysis  necessarily  alter  and  kill  the  muscle  protoplasm. 

Death  of  the  muscle  is  ordinarily  associated  with  a  peculiar  chemical  change 
known  as  rigor  mortis.  To  understand  the  chemical  composition  of  muscle  it 
is  necessary  that  we  should  consider  the  nature  of  this  change. 

1.  Rigor  Mortis. — Rigor  mortis,  the  rigidity  of  death,  is  the  result  of  a 
chemical  chung(i  in  the  substance  of  a  muscle  by  which  it  is  permanently 
altered,  its  irritability  and  other  vital  properties  being  irretrievably  lost.  The 
change  is  manifested  by  a  loss  of  translucency,  the  muscle  becoming  opaque,  and 
by  a  gradual  contraction,  accompanied  by  a  development  of  heat  and  acidity, 
and  resulting  in  the  muscle  being  stiff  and  firm  to  the  touch,  less  elastic,  and 
less  extensible.     Whenever  muscle  dies  it  undergoes  this  change. 

Conditions  which  Influence  the  Development  of  Rigor. — Ordinarily  on  the 
death  of  the  body  the  muscle  enters  into  rigor  slowly — the  muscle-fibres  are 
involved  one  after  the  other,  and  through  the  gradual  contraction  and  harden- 
ing of  the  antagonistic  muscles  the  joints  become  fixed  and  the  body  acquires 
the  rigidity  which  we  associate  with  death.  Rigor  usually  affects  the  different 
parts  of  the  body  in  a  regular  order,  from  above  downward,  the  jaw,  neck, 
trunk,  arms,  and  legs  being  influenced  one  after  the  other.  The  jjosition  taken 
by  the  body  is  generally  determined  by  the  weight  of  the  parts  and  the  rela- 
tive strength  of  the  contractions  of  the  muscles. 

The  time  required  for  the  appearance  of  rigor  is  very  variable.  It  is  deter- 
mined in  part  by  the  nature  of  the  muscle,  its  condition  at  the  moment  of 
death,  and  the  temperature  to  which  it  is  subjected.  The  muscles  of  warm- 
blooded animals  enter  into  rigor  more  quickly  than  those  of  cold-blooded 
animals;  of  the  warm-blooded  animals,  pale  muscles  more  quickly  than  red, 
and  the  flexors  before  the  extensors  ;  of  the  cold-blooded  animals,  frog's  muscles 
more  quickly  than  those  of  the  turtle.  In  general,  the  more  active  the  muscle 
protoplasm,  the  more  rapid  are  the  chemical  changes  which  it  undergoes,  and 
amongst  these  the  coagulation  of  rigor  mortis. 

The  condition  of  the  muscle  plays  a  very  important  part  in  determining  the 
onset  of  rigor.  If  the  muscles  are  strong  and  vigorous  and  death  of  the  body 
has  come  suddenly,  rigor  develo])s  slowly  ;  if  the  muscles  have  been  enfeebled 
by  disease  or  fatigued  by  great  exertion  shortly  before  death,  it  comes  rapidly. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.       145 

In  till'  case  of  wasting  diseases  rigor  comes  quickly,  is  poorly  developed,  and 
passes  off'  quickly ;  when  the  muscles  are  fatigued  at  the  time  of"  death,  as  in 
the  case  of  a  hunted  animal,  it  comes  (juickly.  We  hear  of  soldiers  found  dead 
on  the  field  of  battle  grasping  the  sword,  as  if  the  muscular  contractions  of  life 
had  been  continued  by  the  contractions  of  death.  In  the  case  of  certain  dis- 
eases of  the  spinal  cord  and  brain,  too,  rigor  may  come  so  ra})idly  that  the 
limbs  may  maintain  the  position  which  they  had  at  the  time  of  death,  "  cata- 
leptic rigor,"  as  it  has  been  called.  The  coming  on  of  rigor  is  particularly 
striking  in  the  case  of  diseases  which,  like  cholera,  are  accompanied  by  violent 
muscular  cramps  and  lead  to  a  rapid  death.  It  is  not  uncommon,  in  such 
cases,  for  the  contractions  of  rigor  to  cause  movements  which  may  mislead  a 
watcher  into  supposing  the  dead  man  to  be  still  alive.  This  idea  is  favored  by 
the  fact  that  the  body  may  remain  warm,  owing  to  the  heat  which  is  produced 
in  the  muscles  as  a  result  of  the  chemical  changes  occurring  during  rigor. 
The  post-mortem  muscular  contractions  and  the  rise  of  temperature  observed 
in  such  eases  are  only  excessive  manifestations  of  what  always  occurs  on  the 
death  of  the  muscle.  The  movements  are  probably  due,  in  part,  to  the  rapidity 
with  which  the  muscles  contract  in  rigor,  and  in  part  to  the  fact  that  the 
antagonistic  muscles  are  not  affected  at  the  same  time  to  the  same  degree. 
Whether  the  contractions  are  partly  excited  by  changes  accompanying  the 
death  of  the  motor  nerve-cells  in  the  central  nervous  system  is  uncertain,  but 
not  impossible.  Muscles  are  still  able  to  respond  by  contractions  to  stimuli 
coming  to  them  through  the  nerve,  even  after  rigor  has  become  quite  pro- 
nounced, probably  because  the  coagulation  process  attacks  the  different  fibres 
at  different  rates,  and  certain  of  the  fibres  are  still  alive  and  irritable  after  the 
others  are  dead  and  coagulated. 

Many  observers  favor  the  view  that  the  central  nervous  system  influences 
muscles  after  the  death  of  the  body  as  a  whole,  and  by  weak  stimuli  resulting 
from  the  changes  in  the  nerve-cells  excites  chemical  changes  in  the  muscles 
which  favor  the  coming  on  of  rigor.^  In  proof  of  this  it  is  stated  that  cura- 
rized  muscles  enter  into  rigor  more  slowly  than  non-curarized.  Undoubtedly 
stimulation  of  the  nerve,  or,  indeed,  anything  which  would  excite  a  muscle  to 
action,  tends  to  put  it  in  a  condition  favorable  to  the  coming  on  of  rigor ; 
whether  the  influence  exerted  by  the  central  nervous  system  is  more  than  this 
is  very  questionable. 

Temperature  has  a  marked  influence  on  the  development  of  rigor  mortis. 
Cold  delays  and  warmth  favors,  38°-40°  C.  being  most  favorable.  Since  rigor 
is  the  result  of  a  chemical  change,  these  effects  of  temperature  are  what  one 
would  have  expected.  Other  forms  of  chemical  change  which  are  attributable 
to  ferment  action  are  found  to  be  the  most  vigorous  at  a  temperature  of  about 
40°  C. 

In  general,  it  may  be  said   that  rigor  in  warm-blooded  animals  comes  on 
in  from  ten  minutes  to  seven   hours  after  death,  although  some  state  that  it 
may  come  as  late  as  eighteen  hours.     It  lasts  anywhere  from  one  to  six  days. 
^  Brown-Sequard  :  Archives  de  Physiologie,  1889,  p.  675. 
10 


146 


AN  AMERICAN    TEXT- BOOK   OF  PHYSIOLOGY. 


The  sooner  it  conies  on,  the  sooner  it  goes  off.  The  stiffness  can  be  broken  up 
artificially  by  forced  movements  of  the  part?^,  and  when  thus  destroyal  does 
not  return,  provided  the  rigor  was  complete  at  the  time. 

The  Clause  and  Xature  of  the  Contraction  of  Rigor  3Ior( is. — Tlie  most  likely 
explanation  of  the  contraction  of  the  dying  muscle  is  that  it  is  the  result  of 
the  coagulation  of  a  part  of  the  semi-fluid  muscle-substance  within  the  sarco- 
lemma.  This  was  suggested  by  Bruecke,  and  Kuehne  proved  that  such  a 
coagulation  change  takes  place,  by  showing  that  the  semi-fluid  muscle-sub- 
stance, "  the  muscle-plasma,"  if  expressed  from  the  frozen  muscle,  coagulates  on 
being  warmed.  The  coagulation  is  a  chemical  change  attributed  to  the  action 
of  a  ferment,  the  myosin  ferment,  which  is  thought  to  be  formed  at  the  death 
of  the  muscle. 

Another,  though  less  generally  accepted  view,  is  that  the  contraction  of  the 
muscle  seen  in  rigor  is  of  the  same  nature  as  ordinary  muscular  contractions.^ 
Prolonged  muscle  ct)ntractions  are  ol)served  when  a  muscle  is  greatly  fatigued 
or  subjected  to  such  a  drug  as  veratria  (see  p.  128),  and  there  are  many  points 
of  resemblance  between  the  contraction  of  normal  and  dying  muscle — viz.  the 
change  of  form,  the  production  of  heat,  the  formation  of  sarcolactic  acid,  the 
using  up  of  oxygen  and  the  production  of  carbon  dioxide,  and  the  fact  that 
the  dying  and  presumably  coagulating  muscle  is,  like  normal  contracting  mus- 
cle, electrically  negative  as  compared  with  normal  resting  muscle.  To  this 
may  be  added  that,  as  has  been  said,  the  muscle  continues  to  be  irritable  even 
when  rigor  is  quite  advanced,  and  that  it  enters  into  rigor  more  quickly  if  left 
in  connection  with  the  central  nervous  system. 

On  the  other  hand,  one  cannot  fail  to  be  impressed  with  the  differences 
between  the  two  forms  of  contraction. 


Normal  Contracting  Musdc. 
Contains  uncoagulated  myosinogen. 
Is  translucent. 
Is  soft  and  flexible. 
Is  no  less  elastic  than  in  repose. 
Is  more  extensible  than  in  repose. 
Contracts  rapidly. 
Fatigues  rapidly  and  reTaxes. 


Muscle  contracting  by  Rigor  Mortis. 
Contains  coagulated  myosin. 
Is  opaque. 
Is  firm  and  stiff. 
Is  less  elastic  than  before. 
Is  less  extensible  than  before. 
Contracts  very  slowly,  as  a  rule. 
Remains  contracted  a  long  time. 


Furthermore,  it  may  be  added  that  normal  contractions  only  occur  A\hen 
the  irrital)le  muscle  is  stimulated,  while  a  mu.scle  can  enter  into  rigor  when  its 
irritability  has  been  taken  away  by  subjecting  it  to  oxalate  solutions,^  also, 
when  it  has  been  curarizod  and  so  shut  out  from  all  nervous  influences.^ 

Rigor  is  not  confined  to  the  voluntary  mu.scles,  though  it  is  less  easily 
observed  in  the  case  of  most  involuntary  muscles.  The  heart  enters  rapidly 
into  rigor,  with  the  formation  of  sarcolactic  acid.  The  non-striated  muscle 
of  the  stomach  and  ureters,  too,  has  been  .seen  to  undergo  this  change. 

'  Hermann  :  Handbuch  dtr  Physiologie,  1879,  Bd.  i.  p   146. 
*  Howell :  Journal  of  Physiology,  1893,  vol.  xiv.  p.  476. 
'  Nagel :  Pjliiger's  Archiv,  vol.  Iviii.  S.  279. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.      147 

The  passini^  ott'  of  rigor  mortis  is  usually  accompanied  by  beginning 
decomposition,  and,  indeed,  it  is  generally  supposed  that  the  decomposition  is 
the  cause  of"  softening  of  the  muscle.  This  is  denied  by  certain  observers,  and 
it  is  stated  that  rigor  may  pass  off  when  the  presence  of  putrefactive  organisms 
is  excluded  by  special  aseptic  precautions. 

The  Chemical  Changes  which  accompany  the  Development  of  Rigor. — Rigor 
mortis  is  characterized  by  the  coagulation  of  a  part  of  the  muscle-substance ; 
this  can  be  prevented  by  a  temperature  a  little  below  0°  C.  Cold,  although 
temporarily  depriving  the  muscle  of  its  irritability,  does  not,  unless  extreme  and 
long-continued,  kill  the  muscle  protoplasm.  Frogs  can  be  frozen  stiff  and 
recover  their  activity  when  they  thaw  out.  Indeed,  this  probably  happens  not 
infrequently  to  the  frogs  hibernating  in  holes  in  the  banks  of  ponds.  Since  cold 
prevents  coagulation  without  destroying  the  life  of  the  muscle  protoplasm,  we 
can  by  its  aid  isolate  the  living  muscle-substance  from  the  nerves,  blood- 
vessels, connective  tissue,  and  sarcolemna  of  the  muscle,  but  as  soon  as  we 
begin  to  analyze  it  it  loses  its  living  structure.  This  method  of  obtaining 
muscle-plasma  was  introduced  by  Kuehne^  in  the  study  of  the  muscles  of  frogs, 
and  was  later  employed  with  slight  modifications  by  Halliburton^  for  the  mus- 
cles of  warm-blooded  animals.  The  blood  was  washed  out  of  the  vessels  with 
a  stream  of  0.6  per  cent,  sodium-chloride  solution  at  5°  C. ;  the  irritable  mus- 
cles were  then  quickly  cut  out  and  frozen  in  a  mixture  of  ice  and  salt  at 
12°  C  The  frozen  muscle  was  then  cut  up  finely  in  the  cold,  and  a  yellowish, 
somewhat  viscid,  and  faintly  alkaline  muscle-plasma  was  squeezed  out.  This 
fluid  was  found  to  coagulate  in  twenty  to  thirty  minutes  at  a  temperature  of 
40°  C. ;  if  the  temperature  were  lower  the  coagulation  was  slower.  The  clot, 
which  was  jelly-like  and  translucent,  contracted  slowly  aud  in  a  few  hours 
squeezed  out  a  few  drops  of  serum.  The  coagulated  material  formed  in  the 
clot  is  called  myosin.  It  dissolves  readily  in  dilute  neutral  saline  solutions, 
as  a  10  per  cent,  solution  of  sodium  chloride  or  a  5  per  cent,  solution  of  mag- 
nesium sulphate,  and  its  saline  solutions  are  precipitated  in  an  excess  of  water 
or  by  saturation  with  sodium  chloride,  magnesium  sulphate,  or  ammonium 
sulphate ;  it  has,  in  short,  the  characteristics  of  a  globulin.  Chittenden  and 
Cummins  state  that  it  has  the  following  composition:  C  52.82,  H  7.11.  X 
16.17,  S  1.27,  O  22.03. 

Halliburton,  in  studying  the  coagulation  of  mu.scle,  followed  for  the  sake  of 
comparison  the  methods  which  have  been  employed  in  the  study  of  coagulation 
of  blood.  He  found  that  muscle-plasma,  like  blood-plasma,  is  prevented  from 
coagulating  not  only  by  cold,  but  by  neutral  salts,  such  as  magnesium  sulphate, 
sodium  chloride,  and  sodium  sulphate ;  and  further,  that  the  salted  plasma  if 
diluted  coagulates. 

The  points  of  resemblance  between  the  coagulation  of  myosin  and  fibrin 
suggest  a  similar  cause,  and  Halliburton  succeeded  in  obtaining  from  muscles 
coagulated  by  long  standing  in  alcohol  a  watery  extract,  which  greatly  hastened 

'  UntersHckungen  iiber  das  ProtopUwna,  Leipzig,  1864. 
^  Journal  of  Physiology,  1887,  vol.  viii.  p.  134. 


148  AN  AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 

the  coagulation  of  nmscle-plasina  and  myosin  solutions,  llo  cailc^d  the  sub- 
stance thus  obtained  myosin  ferment.  The  extract  obtained  contained  an 
albumose  which  was  eitluM-  the  ferment  or  held  it  in  close  combination.  The 
pure  ferment  has  not  been  isolated.  The  myosin  ferment  is  not  the  same  as 
fibrin  ferment,  since  neither  can  do  the  w(;rk  of  the  other.  Moreover,  fibrin 
ferment  is  destroyed  at  75°-80°  C.  and  myosin  ferment  is  not  destroyed  till 
100°  C. 

In  several  respects  there  is  a  close  resemblance  between  th(!  bcluivior  of 
blood-  and  muscle-plasma,  but  the  coatrulated  products  differ.  Kuehne  found 
that  myosin  could  be  dissolved  by  a  dilute  saline  solution,  and  that,  on  further 
dilution,  it  w^as  reprecipitated.  Halliburton  observed  that  a  saline  solution  of 
myosin,  diluted  twenty  times  with  water,  gave  a  precipitate  which  could  be 
dissolved  in  a  5  per  cent,  magnesium-sulphate  solution,  and  then  by  the  addi- 
tion of  water  be  made  to  recoagulate.  In  these  respects  myosin  differs  markedly 
from  fibrin.  Fil)rin  is  dissolved  only  with  difficulty  in  dilute  saline  solutions 
and  cannot  be  recoagulated.  Myosin  also  differs  from  fibrin  by  its  greater 
solubility  in  dilute  HCl. 

Moreover,  the  chemical  change  which  results  in  the  formation  of  myosin  is 
different  from  that  which  produces  fibrin.  The  clotting  of  muscle-plasma  and 
the  formation  of  myosin  is  accompanied  or  closely  followed  by  the  production 
of  an  acid,  while  no  such  change  occurs  during  the  coagulation  of  blood-plasma. 
In  the  earlier  stages  of  clotting  the  acidity  may  be  due  in  part  to  acid  potassium 
phosphate,  but  the  final  acidity  is  chiefly  due  to  lactic  acid.  The  source  of  the 
lactic  acid  has  not  been  definitely  made  put.  The  view  that  it  comes  from 
glycogen  is  made  questionable  by  Boehm's^  observation  that  the  amount  of 
glycogen  is  not  lessened  in  rigor,  and  is  corroborated  by  the  observation  that 
the  muscles  of  starving  animals  become  acid  when  entering  into  rigor,  although, 
as  Bernard  found,  they  contain  no  glycogen.  Boehme  concluded  that  the 
sarcolactic  acid  is  formed  from  the  proteids,  and  this  is  accepted  by  other  good 
observers. 

Some  writers  have  thought  the  coagulation  of  the  muscle  was  the  result  of 
the  formation  of  an  acid  by  the  dying  muscle.  This  is  unlikely,  although  the 
presence  of  acid,  like  that  of  many  other  substances,  quinine,  caflfein,  digitaliu, 
veratrin,  hydrocyanic  acid,  ether,  chlorofi)rm,  etc.,^  may  hasten  the  process. 
This  may  account  for  the  rapidity  with  which  rigor  comes  on  in  fatigued 
muscles. 

2.  Constituents  of  Muscle-serum  and  Changes  resulting  from  Con- 
traction.— Muscle-serum  can  be  most  readily  obtained  by  mincing  a  muscle 
in  rigor  mortis  and  expressing  the  fluid.  The  proteids  of  the  serum  can  be 
separated  by  the  degrees  at  which  they  undergo  heat-coagulation. 

The  method  of  fractional  heat-coagulation  was  employed  by  Halliburton' 
to  determine  the  proteids  of  muscle.     He  found  the  following : 

^  Pfiiiyer' s  Arckiv,  1880,  Bd.  xxiii.  S.  44.         "  Ilalliburton  :  Phyi^iological  Chemistry,  p.  414. 
■'  Journal  of  Physiology,  viii.  pp.  184-186. 


GENERAL    PHYSIOLOGY   OF  MUSCLE  AND   NERVE.       149 

Name.  Temperature  of  coagulation. 

Proteids  obtained  from  )  Paramyosinogen 47°  V, 

the  dissolved  clot  .    .    t-  Myosinogen 5G°  C 

Y>    J  •  1       1  ,  •      ]   ,•         (  Mvoglobulin 63°  C. 

Proteids  obtainetl  irom  ^      -    >-' 


muscle-serutn 


Myo-albiimin      73°  C. 

iMyo-albumose (not  coagulated  by  heat). 


The  proteids  of  the  serum  can  also  be  (listinguished  by  their  sohibilities  in 
neutral  salt-solutions  of  various  strengths.  The  myoglobulin  resembles  .serum- 
globulin,  although  precipitated  at  63°  C.  instead  of  73°  C.  The  myo-albumin 
is  apparently  identical  with  serimi-albumin. 

To  these  proteids  we  must  add  the  pigment  haemoglobin.  Another  })ig- 
ment,  myohsematiu,  is  also  found.  It  is  not  unlikely  that  the.se  pigments  have 
here  as  elsewhere  a  respiratory  fimction. 

Nitrogenous  Extractives. — The  chief  nitrogenous  extractive  is  creatin ;  in 
addition  to  this  we  find  small  amounts  of  creatinin  and  of  various  xanthin 
bodies,  as  xanthin,  hypoxanthin,  carnin,  and  sometimes  traces  of  urea,  uric 
acid,  taurin,  and  glycocoil.  The  chemical  nature  of  these  bodies  need  not  be 
considered  here.  Physiologically  they  may  be  regarded  as  waste  products 
which  result  from  the  partial  oxidation  of  the  proteids  of  muscle  during  the 
katabolic  processes  which  are  continually  occurring  even  in  the  resting  muscle 
protoplasm.  Monari  has  shown  that  the  amount  of  creatin  and  creatinin  is 
increased  by  the  wear  and  tear  of  muscular  work,  although  the  proteids  of  the 
well-fed  muscle  probably  supply  but  little  of  the  energy  which  is  set  free.^ 

The  non-nitrogenous  constituents  of  muscle  are  fats,  glycogen,  inosit,  sugar, 
and  lactic  acid. 

Fats  are  usually  found  in  intermuscular  connective  tissue,  but  there  is  little 
within  the  normal  fibre.  It  is  doubtful  whether  fat  plays  any  direct  part  in 
the  ordinary  metabolic  processes  involved  in  the  action  of  muscles,  although 
it  is  probable  that  if  more  available  sources  of  energy  are  lacking  it  may,  like 
the  proteids,  be  altered  and  employed.  Under  pathological  conditions  large 
amounts  of  fat  may  be  found  inside  the  sarcolemma ;  in  phosphorus-poisoning 
the  degenerated  muscle  protoplasm  may  be  replaced  by  fat  in  the  form  of  fine 
globules. 

Glycogen  is  found  in  very  variable  amounts  in  different  muscles.  The  work 
of  many  observers  has  shown  that  it  is  here,  as  in  the  liver,  a  store  of  carbo- 
hydrate material,  and  is  employed  by  the  muscle,  either  directly  or  after  con- 
version into  some  other  body,  as  a  source  of  energy.  The  quantity,  which  is 
rarely  more  than  |  per  cent.,  lessens  rapidly  during  muscle  work. 

Sugar  is  found  in  muscles  in  small  quantities  only,  nevertheless  it  probably 
plays  an  important  part,  for  Chauveau  and  Kaufmann,  by  studying  the  levator 
labii  .superioris  of  the  horse,  found  that  the  muscles  take  sugar  from  the  blood, 
and  that  they  take  more  during  action  than  rest.     The  sugar  which  the  mus- 

1  Fick  und  Wislicenns:  VierteJjahresschrift  der  Ziiricher  Nnturfornchenden  Gesellschafi,  1865, 
Bd.  X.  p.  317  ;  Pettenkofer  und  Voit :  Zeitschrift  far  Bioloc/ie,  1866,  ii. ;  Voit :  [bid.,  1876,  vi. 
S.  305. 


150  AN  AMERICAN   TEXT-BOOK  OF  PHYSIOLOGY. 

cle  takes  during  rest  is  for  the  most  part  stored  as  glycogen.'  Altliough  sugar 
is  considered  a  source  of  muscle-energy,  the  exact  way  in  which  it  is  employed 
is  doubtful. 

Inovganio  Constituents  of  Muscle. — Amongst  the  bases,  potassium  has  the 
greatest  prominence,  and  sodium  next ;  magnesium,  calcium,  and  small  amounts 
of  iron  are  also  found.  Of  the  acids,  phosphoric  is  present  in  the  largest  quan- 
tities. 

Gases  of  Muscle. — No  free  oxygen  can  be  extracted,  but  carbon  dioxide 
may  be  obtained,  in  part  free  and  in  part  in  combination.  A  little  nitrogen 
can  also  be  extracted.  The  amount  of  carbonic  acid  varies  greatly  with  the  con- 
dition of  the  muscle ;  for  instance,  it  is  much  increased  by  muscle  work.  Mus- 
cles take  up  oxygen  from  the  blood  freely,  especially  when  active,  and 
when  removed  from  the  body  may  absorb  small  amounts  from  the  air. 
More  oxygen  is  taken  up  by  the  muscle  during  rest  than  is  liberated  as 
carbon  dioxide,  but  during  action  the  reverse  is  the  case.^  Oxygen  is  not 
retained  as  free  oxygen,  but  is  stored  in  some  combination  more  stable  than 
oxyha^moglobiu.  It  is  by  virtue  of  the  combined  oxygen  that  the  muscle  is 
enabled  to  do  its  work,  but  the  process  is  not  one  of  simple  oxidation.  That 
muscles  hold  oxygen  in  available  combinations  was  shown  by  Hermann,  who 
ascertained  that  a  muscle  can  contract  hundreds  of  times  in  an  atmosphere 
free  from  oxygen,  and  produce  water  and  carbon  dioxide. 

II.  Chemistry  of  Nerves. 

Most  of  our  ideas  concerning  the  chemistry  of  nerves  are  based  on  analysis 
of  the  white  and  gray  matter  of  the  central  nervous  system.  The  white  matter 
is  largely  made  up  of  fibres  and  supporting  tissue  and  the  gray  matter  of  nerve- 
cells.  The  peripheral  nerve-fibres  are  simply  a  continuation  of  the  structures 
in  the  central  nervous  system ;  the  active  part  of  the  fibre,  the  axis-cylinder,  is 
an  outgrowth  of  the  cytoplasm  of  a  nerve-cell,  and  the  surrounding  medullary 
sheath  a  continuation  of  the  material  which  sheaths  the  axis-cylinder  while  in 
the  brain  and  cord.  It  is  ])robable,  therefore,  that  the  chemistry  of  the  axis- 
cylinder  approaches  to  that  of  the  nerve-cell  of  which  it  is  a  branch,  and  the 
chemistry  of  the  medullary  substance  is  the  same  outside  as  inside  the  central 
nervous  system. 

The  white  matter  of  the  brain  of  the  ox,  which  is  largely  made  up  of  nerve- 
fibres,  is  composed  of  about  70  parts  water  and  30  parts  solids,  about  one-half 
the  latter  being  cholesterin,  about  a  quarter  proteids  and  connective-tissue  sub- 
stance, and  about  a  quarter  complex  fatty  bodies,  neuro-keratin,  salts,  chiefly 
potassium  salts  and  phosphates,  and  traces  of  xanthin,  hypoxanthin,  etc. 

The  nerve-fibre  has  a  delicate  sheath,  the  neurilemma,  the  exact  constitution 

'  C5jn/5/e.s  rendus  de  la  Sociefe  de  Biologie,  1886,  civ. 

"  Ludwig  und  Sczelkow  :  Sitzungsberichte  den  k.  A/cad.  Wien,  1862,  Bd.  xlv.  Abthl.  1  ;  and 
Ludwig  und  Schmidt :  Silzungaberkhte  den  math.-phys.  Classe  d.  k.  Sachs.  Gesethchrtft  drr  Witsen- 
schdft.  1868,  Bd.  xx. ;  Regnault  and  Reiset:  Annates  de  Chimie  el  de  Physique,  1849,  3  me  s^r., 
xxvi. ;  Pfliiger:  Pjluger's  Archiv,  1872,  vi. ;  and  others. 


GENERAL    PHYSIOLOGY   OF  MUSCLE   AND    NERVE.       151 

of  which  is  unknown,  but  which  is  supposed  to  resemble  tlie  sarcolemma  and 
to  be  composed  of"  a  substance  similar  to  elastin.  The  fibres  are  bound  together 
by  connective  tissue  which  on  boiling  gives  gelatin.  Within  the  neurilemma  is 
the  medulkiri/  sheath,  which  is  composed  of  two  elements — viz.  (1)  neuro-kera- 
tin,  a  material  similar  to  the  horny  substance  of  epithelial  structures,  which 
forms  a  sort  of  loose  trellis,  or  network,  and  probably  acts  as  a  supporting 
framework  to  the  fibre ;  (2)  a  white,  highly  refracting,  semi-fluid  material, 
which  fills  the  meshes  of  the  ncuro-keratin  network,  and  which  is  composed 
largely  of  protagon  and  cholesterin  combined  with  fatty  bodies.  Protagon  is 
a  complex  pli()sj)horized  nitrogenous  compound,  which  many  observers  believe 
to  contain  lecithin  and  cerebrin.  Both  lecithin  and  cerebrin  are  fatty  bodies 
possessing  nitrogen,  and  the  former  phosphorus.  These  and  some  other  com- 
plex fatty  bodies  ])robably  exist  in  addition  to  protagon  in  the  medullary  sub- 
tance.  The  formation  of  the  "myelin  forms"  seen  in  the  medulla  of  dead 
nerves  is  attributed  to  lecithin.  The  axis-cylinder  probably  contains  most  of 
the  proteids  of  the  fibre,  chiefly  globulins,  mixed  with  complex  fatty  bodies. 

The  reaction  of  the  normal  living  fibre  is  neutral  or  slightly  alkaline.  It 
is  said  to  become  acid  after  death,  but  this  change  is  not  known  to  accompany 
functional  activity.  Indeed,  nothing  is  known  of  the  physiological  import  of 
the  chemical  constituents  of  the  nerve-fibre  or  of  the  chemical  changes  which 
occur  in  the  axis-cylinder  when  it  develops  or  transmits  the  nerve  impulse. 
The  peculiar  chemical  composition  of  the  medullary  substance  would  suggest 
that  it  has  a  more  important  function  than  simply  to  protect  the  axis-cylinder. 
Some  have  attributed  to  it  nutritive  powers,  and  others  have  supposed  it  helped 
to  insulate :  it  is  certain  that  the  axis-cylinder  can  develop  and  transmit  the 
nerve  impulse  without  the  aid  of  the  medullary  sheath,  for  there  is  a  large 
class  of  important  nerves — the  non-medullated  nerves — in  which  it  is  lacking. 


III.  SECRETION. 


A.  General  Considerations. 

The  term  secretion  is  meant  ordinarily  to  apply  to  the  liquid  or  semi- 
liquid  products  formed  by  glandular  organs.  On  careful  consideration 
it  becomes  evident  that  the  term  gland  itself  is  widely  applied  to  a  variety 
of  .structures  differing  greatly  in  their  anatomical  organization — .so  much  so, 
in  fact,  that  a  general  definition  of  the  term  covering  all  cases  becomes 
very  indefinite,  and  as  a  con.sequence  the  conception  of  what  is  meant  by  a 
secretion  becomes  correspondingly  extended. 

Considered  from  the  most  general  standpoint  we  might  define  a  gland 
as  a  structure  composed  of  one  or  more  gland-cells,  epithelial  in  character, 
which  forms  a  product,  the  .secretion,  which  is  discharged  either  upon  a 
free  epithelial  surface  such  as  the  skin  or  mucous  membrane,  or  upon  the 
closed  epithelial  surface  of  the  blood-  and  lymph-cavities.  In  the  former  ca.se 
— that  is,  when  the  .secretion  appears  upon  a  free  epithelial  surface  communi- 
cating with  the  exterior,  the  product  forms  what  is  ordinarily  known  as  a 
secretion ;  for  the  sake  of  contrast  it  might  be  called  an  external  secretion. 
In  the  latter  case  the  secretion  according  to  modern  nomenclature  is  designated 
as  an  internal  secretion.  The  best-known  organs  furnishing  internal  .secretions 
are  the  liver,  the  thyroid,  and  the  pancreas.  It  remains  pcssible,  however, 
that  any  organ,  even  tho.se  not  po.ssessing  an  epithelial  structure,  such  as 
the  muscles,  may  give  off'  substances  to  the  blood  comparable  to  the  internal 
secretions — a  possibility  which  indicates  how  indefinite  the  distinction  between 
the  processes  of  .secretion  and  of  general  cell-metabolism  may  become  if  the 
analysis  is  carried  sufficiently  far.  If  we  consider  only  the  external  secretions 
definition  and  generalization  become  much  easier,  for  in  these  cases  the  secret- 
ing surface  is  always  an  epithelial  structure  which,  when  it  pos.'ses.ses  a  certain 

organization,  is  designated  as 

rr^TO  W  •  /  •  )♦)•  /-T-T^JjJj  /  •/v^T^T^rr  I '  \\lL.    a  gland.  The  type  upon  which 

~~^^^^^^^^^\^^^l^^^^^^^^^=zpo^       these  secreting  surfaces  arecon- 

^^~^  structed  is  illustrated  in  Figure 

Fig.  63.— Plan  of  a  secreting  membrane.  /ir>        mi        ^  •   ^         *• 

63.  The  type  consists  or  an 
epithelium  placed  upon  a  basement  membrane,  while  upon  the  other  side  of 
the  membrane  are  blood-capillaries  and  lymph-spaces.  The  secretion  is 
derived  ultimately  from  the  blood  and  is  discharged  upon  the  free  epithelial 
surface,  which  is  suppo.sed  to  communicate  with  the  extei-ior.  The  nuicous 
membrane  of  the  alimentary  canal  from  stomach  to  rectum  may  be  considered, 

152 


SECRETION. 


153 


if  we  neglect  tlie  existence  of  tlie  villi  and  crypts,  as  representing  a  secreting 
surface  constructed  on  this  type.     If  we  suppose  such  a  membrane  to  become 


22333333^ 


M^ 


Fig.  64.— To  illustrate  the  simplest  form  of  a  tubular  and  a  racemose  or  acinous  gland. 

invaginated  to  form  a  tube  or  a  sac  possessing  a  definite  lumen  (see  Fig.  64), 
we  have  then  what  may  be  designated  technically  as  a  gland. 

It  is  obvious  that  in  this  case  the  gland  may  be  a  simple  pouch,  tubular  or 
saccular  in  shape  (Fig.  65),  or  it  may  attain  a  varying  degree  of  complexity  by 
the  elongation  of  the  involuted  portion  and  the  development  of  side  branches 


SSJJS 


Fig.  65.— Simple  alveolar  gland  of  the 
amphibian  skin  (after  Flemming). 


Fig.  66.— Schematic  representation  of  a  lobe  of  a 
compound  tubular  gland  (after  Flemming). 


(Fig.  66).  The  more  complex  structures  of  this  character  are  known  sometimes 
as  compound  glands,  and  are  further  described  as  tubular,  or  racemose  (saccular), 
or  tubulo-racemose,  according  as  the  terminations  of  the  invaginations  are 
tubular,  or  saccular,  or  intermediate  in  shape.^  As  a  matter  of  fact  we  find 
the  greatest  variety  in  the  structure  of  the  glands  imbedded  in  the  cutaneous 
and  mucous  surfaces,  a  variety  extending  from  the  simplest  form  of  crypts  or 
tubes  to  very  complicated  organs  possessing  an  anatomical  independence  and 
definite  vascular  and  nerve-supplies  as  in  the  case  of  the  salivary  glands 
or  the  kidney.  In  compound  glands  it  is  generally  assumed  that  the  terminal 
portions  of  the  tubes  alone  form  the  secretions,  and  these  are  designated  as  the 
the  acini  or  alveoli,  while  the  tubes  connecting  the  alveoli  with  the  exterior  are 
known  as  the  ducts,  and  it  is  supposed  that  their  lining  epithelium  is  devoid 
of  secretory  activity. 

The  secretions  formed  by  these  glands  are  as  varied  in  composition  as  the 
glands  are  in  .structure.     If  we  neglect  the  case  of  the  so-called  reproductive 

'  Flemming  has  called  attention  to  the  fact  that  most  of  the  so-called  compound  racemose 
glands,  salivary  glands,  pancreas,  etc.,  do  not  contain  terminal  sacs  or  acini  at  the  ends  of  the 
system  of  ducts ;  on  the  contrary,  the  final  secreting  portions  are  cylindrical  tubes,  and  such 
glands  are  better  designated  as  compound  tubular  glands. 


154  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

glands,  the  ovary  and  testis,  whose  I'ight  to  the  desiguutiou  of"  glauds  is  doubt- 
ful, we  may  say  that  the  secretions  in  the  mammalian  body  are  liquid  or  semi- 
liquid  in  character  and  are  composed  of  water,  inorganic  salts,  and  various 
organic  compounds.  With  regard  to  the  last-mentioned  constituent  the  secre- 
tions differ  greatly.  In  some  cases  the  organic  substances  present  are  not  found  in 
the  blood,  and  furthermore  they  may  be  specific  to  a  particular  secretion,  so  that 
we  must  suppose  that  these  constituents  at  least  are  constructed  in  the  gland 
itself.  In  other  cases  the  organic  elements  may  be  present  in  the  blood,  and 
are  merely  eliminated  from  it  by  the  gland,  as  in  the  case  of  the  urea  found  in 
the  urine.  Johannes  MUller  long  ago  made  this  distinction,  and  spoke  of  secre- 
tions of  the  latter  kind  as  excretions,  a  term  which  we  still  use  and  which  car- 
ries to  our  minds  also  the  implication  that  the  substances  so  named  are  waste 
products  whose  retention  would  be  injurious  to  the  economy.  Excretion  as 
above  defined  is  not  a  term,  however,  which  is  capable  of  exact  aj)plication  to 
any  secretion  as  a  whole.  Urine,  for  example,  contains  some  constituents  which 
are  probably  formed  within  the  kidney  itself,  e.  g.  hij)puric  acid;  while,  on 
the  other  hand,  in  most  secretions  the  water  and  inorganic  salts  are  derived 
directly  from  the  blood  or  lymph.  So,  too,  some  secretions — for  example,  the 
bile — carry  off  waste  products  which  may  be  regarded  as  mere  excretions,  and 
at  the  same  time  contain  constituents  (the  bile  salts)  which  are  of  immediate 
value  to  the  whole  organism.  Excretion  is  therefore  a  name  which  we  may 
apply  conveniently  to  the  process  of  removal  of  waste  products  fi-om  the  botly, 
or  to  particular  constituents  of  certain  secretions,  but  no  fundamental  distinc- 
tion can  be  made  between  the  method  of  their  elimination  and  that  of  the 
formation  of  secreted  products  in  general.  Owing  to  the  diversity  in  com- 
position of  the  various  external  secretions  and  the  obvious  difference  in  the 
extent  to  which  the  glandular  epithelium  participates  in  the  process  in  different 
glands,  a  general  theory  of  secretion  cannot  be  formulated.  The  kinds  of 
activity  seem  to  be  as  varied  as  is  the  metabolism  of  the  tissues  in  general. 

It  was  formerly  believed  that  the  formation  of  the  secretions  was  de- 
pendent mainly  if  not  entirely  upon  the  physical  processes  of  filtration,  im- 
bibition, and  diffusion.  The  basement  membrane  Avitli  its  liuing  epithelium 
was  supposed  to  constitute  a  membrane  through  which  various  products  of  the 
blood  or  lymph  passed  by  filtration  and  diffusion,  and  the  variation  in  com- 
position of  the  secretions  was  referred  to  differences  in  structure  and  chemical 
properties  of  the  dialyzing  membrane.  The  significant  point  about  this  view 
is  that  the  epithelial  cells  were  supposed  to  play  a  passive  part  in  the  process ; 
the  metabolic  processes  within  the  cytoplasm  of  the  cells  were  not  believed  to 
affect  the  composition  of  the  secreted  product.  As  compared  with  this  view 
the  striking  peculiarity  of  modern  ideas  of  secretion  is,  perhai)S,  the  import- 
ance attributed  to  the  living  structure  and  properties  of  the  epithelial  cells. 
It  is  believed  generally  now  that  the  glandular  epithelium  takes  a  direct  part 
in  the  production  of  some  if  not  all  of  the  constituents  of  the  secretions.  The 
reasons  for  this  view  will  be  brought  out  in  detail  further  on  in  describing  the 
secreting  processes  of  the  separate  glands.     Some  of  the  general  facts,  how- 


SECRETION.  155 

ever,  whidi  infiiieiiced  physiologists  in  coming  to  this  conclusion  are  as 
follows  : 

Microscopic  examination  has  demonstrated  clearly  that  in  many  cases  parts 
of  the  epithelial  cell-substance  can  be  followed  into  the  secretion.  In  the 
sebaceous  secretion  the  cells  seem  to  break  down  completely  to  form  the  mate- 
rial of  the  secretion  ;  in  the  formation  of  mucus  by  the  goblet  cells  of  the 
mucous  membrane  of  the  stomach  and  intestines  a  portl(^n  of  the  cytoplasm 
after  undergoing  a  mucoid  degeneration  is  extruded  bodily  from  the  cell  to 
form  the  secretion  ;  in  the  mammary  glands  a  portion  of  the  substance  of  the 
epithelial  cells  is  likewise  broken  off  and  disintegrated  in  the  act  of  secretion, 
while  in  other  glands  the  material  of  the  secretion  is  deposited  within  the  cell 
in  the  form  of  visible  granules  which  during  the  act  of  secretion  may  be 
observed  to  disappear,  apparently  by  dissolution  in  the  stream  of  water  passing 
through  the  cell.  Facts  like  these  show  that  some  at  least  of  the  products  of 
secretiou  arise  from  the  substance  of  the  gland-cells,  and  may  be  considered  as 
representing  the  results  of  a  metabolism  within  the  cell-substance.  From 
this  standpoint,  therefore,  we  may  explain  the  variations  in  the  organic 
constituents  of  the  secretions  by  referring  them  to  the  different  kinds  of 
metabolism  existing  in  the  different  gland-cells.  The  existence  of  distinct 
secretory  nerves  to  many  of  the  glands  is  also  a  fact  favoring  the  view  of 
an  active  participation  of  the  gland-cells  in  the  formation  of  the  secretion. 
The  first  discovery  of  this  class  of  nerve-fibres  we  owe  to  Ludwig,  who  (in 
1851)  showed  that  stimulation  of  the  chorda  tympani  nerve  causes  a  strong 
secretion  from  the  submaxillary  gland.  Later  investigations  have  demon- 
strated the  existence  of  similar  nerve-fibres  to  many  other  glands — for 
example,  the  lachrymal  glands,  the  sweat-glands,  the  gastric  glands,  the 
pancreas.  It  is  asserted  also  that,  in  some  cases  at  least,  the  increased 
secretion  is  accompanied  by  an  elevation  in  temperature  of  the  gland,  \vhich 
speaks  for  an  increased  metabolic  activity.  Moreover,  there  is  considerable 
evidence,  which  will  be  given  in  the  proper  place,  to  show  that  the  secretory 
fibres  are  of  two  kinds,  one  controlling  the  production  of  the  organic  elements, 
and  one  increasing  the  flow  of  water  and  inoi'ganic  salts.  Recent  microscopic 
work  indicates  that  the  secretory  fibres  end  in  a  fine  plexus  between  and  round 
the  epithelial  cells,  and  we  may  infer  from  this  that  the  action  of  the  nerve- 
impulses  conducted  by  these  fibres  is  exerted  directly  upon  the  gland-cells. 

The  formation  of  the  water  and  inorganic  salts  present  in  the  various 
secretions  offers  a  problem  the  general  nature  of  which  may  be  referred  to  ap- 
propriately in  this  connection,  although  detailed  statements  must  be  reserved 
until  the  several  secretions  are  specially  described.  The  problem  involves, 
indeed,  not  only  the  well-recognized  secretions,  but  also  the  lymph  itself  as 
well  as  the  various  normal  and  pathological  exudations.  Formerly  the  occur- 
rence of  these  substances  was  explained  by  the  action  of  the  physical  processes 
of  filtration  and  diffusion  through  membranes.  With  the  blood  under  a  con- 
siderable pressure  and  with  a  certain  concentration  in  salts  on  one  side  of  the 
basement  membrane,  and  on  the  other  a  liquid  under  low  pressure  and  differ- 


156  .l.V    AMEIilCAX    TEXT- HOOK    OF   PHYSIOLOGY. 

ing  iu  chemical  coniposititm,  it  would  s^eein  inevitable  that  water  .should  Hltor 
through  the  membrane  and  that  processes  of  osmosis  would  be  set  up,  further 
ehanjxinix  the  nature  of  the  secretion.  Upon  this  theory  the  water  and  salts  iu 
all  secretions  were  regarded  merely  as  transudatory  products,  and  so  far  as  they 
were  concerned  the  epithelium  was  supposed  to  act  simply  as  a  dead  membrane^ 
This  theory  has  not  proved  entirely  acceptable  for  various  reasons.  It  has 
been  shown  that  living  membranes  offer  considerable  resistance  to  filtration 
even  when  the  liquid  pressure  on  one  side  is  much  greater  than  on  the  other. 
Tigerstedt  ^  and  Santessen,  for  instance,  found  that  a  lung  taken  fi-om  a  frog 
just  killed  gtive  no  filtrate  when  its  cavity  was  distended  l)y  liquid  under  a 
pressure  of  18  to  20  centimeters,  providetl  the  liquid  used  was  one  that  did 
not  injure  the  tissue.  If,  however,  the  lung-tissue  was  killed  by  heat  or  other- 
wise, filtration  occurred  readily  under  the  same  pressure.  In  some  glands, 
also,  the  formation  of  the  water  and  salts,  as  has  been  said,  is  obviously  under 
the  control  of  nerve-fibres,  and  this  fact  is  difficult  to  reconcile  with  the  idea 
that  the  epithelial  cells  are  merely  passive  filters.  In  glands  like  the  kidney, 
and  in  other  glands  as  well,  it  has  been  shown  that  the  amount  of  water  and 
salts  does  not  increase  in  proportion  to  the  rise  of  blood-pressure  within  the 
capillaries,  as  should  happen  if  filtration  were  the  sole  agent  at  work,  and 
furthermore,  certain  chemical  substances  when  injected  into  the  blood  may 
increase  the  flow  of  water  in  the  secretion  to  an  extent  that  cannot  be  well 
accounted  for  in  any  other  way  than  by  supposing  that  they  act  as  chemical 
stimuli  to  the  epithelial  cells. 

While,  therefore,  it  cannot  be  denied  that  the  anatomical  conditions  pre- 
vailing in  the  glands  are  favorable  to  the  processes  of  filtration  and  osmosis, 
and  while  no  one  is  justified  in  denying  that  these  processes  do  actually  occur 
and  seem  to  account  in  part  for  the  appearance  of  the  water  and  inorganic 
salts,  it  seems  to  be  clear  that  iu  the  present  condition  of  our  knowledge  these 
factors  alone  do  not  suffice  to  explain  all  the  phenomena  connected  with  the 
secretion  of  water  and  salts.  We  must  suppose  that  the  epithelial  cells  are 
actively  concerned  in  the  process.  The  way  in  which  they  act  is  not  known ; 
various  hypotheses  have  been  advanced,  but  none  of  them  meets  all  the  facts 
to  be  explained,  and  at  present  it  is  customary  to  refer  the  matter  to  the  vital 
projjerties  of  the  cells — that  is,  to  the  peculiar  j)hysical  or  chemical  properties 
connected  with  their  living  structure. 

We  may  now  pass  to  a  consideration  of  the  facts  known  with  regard  to  the 
physiology  of  the  different  glands  considered  merely  as  secretory  organs. 
The  functional  value  of  the  secretions  will  be  found  described  in  the  sections 
on  Digestion  and   Nutrition. 

B.  Mucous  AND  Albuminous  (Serous  )  Types  of  Glands  ;  Salivary 

Glands. 

Mucous  and  Albuminous   Glands. — Heidenhain  rwognized  two  types 
of  glands,  the  mucous  and  the  ali)umin()us,  basing  his  distinction   upon   the 
'  Mittheil.  vom  physiol.  Lab.  de.s  Carol,  mfrl.-chir.  InstittUs  in  Stockholm,  1885. 


SECRETION.  157 

character  of"  tlie  secretion  uiul  u[)()n  the  histological  appearance  of  the  secreting 
cells.  The  classification  as  originally  made  was  applied  only  to  the  salivary 
glands  and  to  similar  glands  fonnd  in  the  mucous  membranes  of  the  mouth 
and  (esophagus,  the  air-passages,  conjunctiva,  etc.  The  chemical  difference 
in  the  secretions  of  the  two  types  consists  in  the  fact  that  the  secretion  of  the 
albuminous  (or  serous)  glands  is  thin  and  watery,  containing  in  addition  to 
possible  enzymes  only  water,  inorganic  salts,  and  small  quantities  of  albumin  ; 
while  tluit  of  the  mucous  glands  is  stringy  and  viscid  owing  to  the  presence 
of  mucin.  As  examples  of  the  albuminous  glands  we  have  the  parotid  in 
man  and  the  mammalia  generally,  the  submaxillary  in  some  animals  (rabbit), 
some  of  the  glands  of  the  mucous  membrane  of  the  mouth  and  nasal  cavities, 
and  the  lachrymal  glands.  As  examples  of  the  mucous  glands,  the  submaxil- 
lary in  man  and  most  mammals,  the  sublingual,  the  orbital,  and  some  of  the 
glands  of  the  mucous  membrane  of  the  mouth-cavity,  oesophagus,  and  air- 
passages.  The  histological  appearance  of  the  secretory  cells  in  the  albuminous 
glands  is  in  typical  cases  markedly  different  from  that  of  the  cells  in  the 
mucous  glands.  In  the  albuminous  glands  the  cells  are  small  and  densely 
filled  with  granular  material,  so  that  the  cell  outlines,  in  preparations  from  the 
fresh  gland,  cannot  be  distinguished  (see  Figs.  70  and  72).  In  the  mucous 
glands,  on  the  contrary,  the  cells  are  larger  and  much  clearer  (see  Fig.  73). 
In  microscopic  preparations  of  the  fresh  gland  the  cells,  to  use  Langley's 
expression,  present  the  appearance  of  ground  glass,  and  granules  are  only 
indistinctly  seen.  Treatment  with  proper  reagents  brings  out  the  granules, 
which  are,  however,  larger  and  less  densely  packed  than  in  the  albuminous 
glands,  and  are  imbedded  in  a  clear  homogeneous  substance.  Histological 
examination  shows,  moreover,  that  in  some  glands,  e.  g.  the  submaxillary 
gland,  cells  of  both  types  occur.  Such  a  gland  is  usually  spoken  of  as  a 
mucous  gland,  since  its  secretion  contains  mucin,  but  histologically  it  is  a 
mixed  gland.  The  terms  mucous  and  albuminous  or  serous,  as  applied  to  the 
entire  gland,  are  not  in  fact  perfectly  satisfactory,  since  not  only  do  the  mucous 
glands  usually  contain  some  secretory  cells  of  the  albuminous  type,  but  albu- 
minous glands,  such  as  the  parotid,  may  also  contain  cells  belonging  to  the 
mucous  type.  The  distinction  is  more  satisfactory  when  it  is  applied  to  the 
individual  cells,  since  the  formation  of  mucin  within  a  secreting  cell  seems  to 
present  a  definite  histological  picture,  and  we  can  recognize  microscopically  a 
mucous  cell  from  an  albuminous  cell  althouo-h  the  two  mav  occur  together  in 
a  single  alveolus. 

Goblet  Cells. — The  goblet  cells  found  in  the  epithelium  of  the  intestine 
afford  an  interesting  example  of  mucous  cells.  The  epithelium  of  the  intes- 
tine is  a  simple  columnar  epithelium.  Scattered  among  the  columnar  cells  are 
found  cells  containing  mucin.  These  cells  are  originally  columnar  in  shape 
like  the  neighboring  cells,  but  their  protoplasm  undergoes  a  chemical  change 
of  such  a  character  that  mucin  is  produced,  causing  the  cell  to  become  swollen 
at  its  free  extremity,  whence  the  name  of  goblet  cell.  It  has  been  shown  that 
the  mucin  is  formed  with  the  substance  of  the  protoplasm  as  distinct  granules 


158 


AN  AMERICAN    TEXT- BOOK    OF  PHYSIOLOGY. 


of  a  large  size,  and  that  the  ainount  ui'  iniicin  iiiereases  gradually,  forcing  the 
micleus  aud  a  small  part  of  the  unchanged  protoplasm  toward  the  base  of  the 
cell.  Eventually  the  mucin  is  extruded  bodily  into  the  lumen  of  the  intestine, 
leaving  behind  a  partially  empty  cell  with  the  nucleus  and  a  small  remnant  of 
protoplasm  (see  Fig.  67).     The  complete  life-history  of  these  cells  is  imper- 


FiG.  67.— Formation  of  secretion  of  mucus  in  the  goblet  cells:  ^,  cell  containing  mucin;  5,  escape  of 
the  mucin  ;  C,  after  escape  of  the  mucin  (after  Paneth). 

fectly  known.  According  to  Bizzozero^  they  are  a  distinct  variety  of  cell  and 
are  not  genetically  related  to  the  ordinary  granular  epithelial  cells  by  which 
they  are  surrounded.  According  to  others,  any  of  the  columnar  epithelial  cells 
may  become  a  goblet  cell  by  the  formation  of  mucin  within  its  interior,  and 
after  tiie  mucin  is  extruded  the  cell  regenerates  its  proto])lasm  and  becomes 
again  an  ordinary  epithelial  cell.  However  this  may  be,  the  interesting  fact 
from  a  physiological  standpoint  is  that  these  goblet  cells  are  genuiue  unicellular 
mucous  glands;  moreover,  the  deposition  of  the  mucin  in  the  form  of  definite 
granules  within  the  protoplasm  gives  histological  proof  that  this  material  is 
produced  by  a  metabolism  of  the  cell-substance  itself.  It  will  be  found  that 
the  mucin  cells  in  the  secreting  tubules  of  the  salivary  glands  exhibit  similar 
appearances.  So  far  as  is  known,  the  goblet  cells  do  not  possess  secretory 
nerves. 

Salivary  Glands. 

Anatomical  Relations. — The  salivary  glands  in  man  are  three  in  num- 
ber on  each  side — the  parotid,  the  submaxillary,  and  the  sublingual.  The 
parotid  gland  communicates  with  the  mouth  by  a  large  duct  (Stenson's  duct) 
which  opens  upon  the  inner  surface  of  the  cheek  opposite  the  second  molar 
tooth  of  the  upper  jaw.  The  submaxillary  gland  lies  below  the  lower  jaw, 
and  its  duct  (Wharton's  duct)  opens  into  the  mouth-cavity  at  the  side  of  the 
frsenum  of  the  tongue.  The  sublingual  gland  lies  in  the  floor  of  the  mouth 
to  the  side  of  the  frseuum  and  opens  into  the  mouth-cavity  by  a  number  (8  to 
20)  of  small  ducts,  known  as  the  ducts  of  Rivinus.  One  larger  duct  which 
runs  parallel  with  the  duct  of  Wharton  aud  opens  separately  into  the  mouth- 
cavity  is  sometimes  present  in  man.  It  is  known  as  the  duct  of  Bartholin 
and  occurs  normally  in  the  dog.  In  addition  to  these  three  pairs  of  large 
glands  a  number  of  small  glands  belonging  both  to  the  albuminous  and  the 
*  Arckivfiir  mihroskopische  Anatomie,  1893,  vol.  42,  p.  <S2. 


SECRETION. 


159 


mucous  types  are  found  imbedded  in  the  mucous  membrane  of  the  mouth  and 
tongue.  The  secretions  of  these  glands  contribute  to  the  formation  of  the 
saliva. 

The  course  of  the  nerve-fibres  supplying  the  large  salivary  glands  is  interest- 
ing in  view  of  the  physiological  results  of  their  stimulation.  The  description 
here  given  applies  especially  to  their  arrangement  in  the  dog.  The  parotid  gland 
receives  its  fibres  from  two  sources — first,  cerebral  fibres  which  originate  in  the 
glosso-pharyugeal  or  ninth  cranial  nerve,  pass  into  a  branch  of  this  nerve  known 
as  the  tympanic  branch  or  nerve  of  Jacobson,  thence  to  the  small  superficial 
petrosal  nerve,  through  which  they  reach  the  otic  ganglion.  From  this  gan- 
glion they  pass  by  way  of  the  auriculo-temporal  branch  of  the  inferior  max- 


Inferior  maxillary 
'    branch  of  fifth 


Glosso-pharyngeal 
nerve 


Fig.  68. 


Petroii^ 
ganglion 

-Schematic  representation  of  the  course  of  the  cerebral  fibres  to  the  parotid  gland. 


illary  division  of  the  fifth  cranial  nerve  to  the  parotid  gland.     (A  schematic 
diagram  showing  the  course  of  these  fibres  is  given  in  Figure  68.)     A  second 


FariaJ 


Inferior  maxillary 
branch  of  fifth 


Branches 
to  tongue 


Branches  to  submaxil- 
lary and  sublingual  ganglion 

Fig.  69.— Schematic  representation  of  the  course  of  the  chorda  tympani  nerve  to  the  submaxillary  gland. 

supply  of  nerve-fibres  is  obtained  from  the  cervical  sympathetic  nerve,  the 
fibres  reaching  the  gland  ultimately  in  the  coats  of  the  blood-vessels.     The 


160  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

submaxillary  (and  tiic  subliumial)  uiaiuls  receive  their  nerve-lihro  also  from 
two  sources.  The  cerebral  fibres  arise  from  the  brain  in  the  facial  nerve  and 
pass  out  in  the  chorda  tympani  branch  (Fij^.  69).  This  latter  nerve,  after 
emerging  from  the  tympanic  cavity  throntrh  the  Glaserian  fissure,  joins  the 
lingual  nerve.  After  running  with  this  nerve  for  a  >hort  distance,  the  secre- 
tory (and  vaso-dilator)  norve-Hbres  destined  for  the  sul)maxillarv  and  sublin- 
gual glands  branch  off  and  pass  to  the  glands,  following  the  course  of  the 
ducts.  Where  the  chorda  tympani  fibres  leave  the  lingual  there  is  a  small 
ganglion  which  has  received  the  name  of  submaxillary  ganglion.  The  nerve- 
fibres  to  the  glands  pass  through  this  ganglion,  but  Langley  has  shown  that 
only  those  destined  for  the  sublingual  gland  really  connect  with  the  nerve- 
cells  of  the  ganglion,  and  he  suggests  therefore  that  it  should  be  called  the 
sublingual  instead  of  the  submaxillary  ganglion.  The  nerve-fibres  for  the 
submaxillary  gland  make  connections  with  nerve-cells  within  the  hilus  of  the 
gland  itself.  The  submaxillary  and  sublingual  glands  receive  also  sympa- 
thetic nerve-fibres,  which  after  leaving  the  superior  cervical  ganglion  pass  to 
the  glands  in  the  coats  of  the  blood-vessels. 

Histolog-ical  Structure. — The  salivary  glands  belong  to  the  type  of  com- 
pound tubular  glands,  as  Flemming  has  pointed  out.  That  is,  the  secreting 
portions  are  tubular,  in  shape,  although  in  cross  sections  these  tubes  may 
present  various  outlines  according  as  the  plaue  of  the  section  passes  through 
them.  The  parotid  is  described  usually  as  a  typical  serous  or  albuminous 
gland.  Its  secreting  epithelium  is  composed  of  cells  which  in  the  fresh  con- 
dition as  well  as  in  preserved  specimens  contain  numerous  fine  granules  (see 
Figs.  70  and  72,  A).  Heideuhain  states  that  in  exceptional  cases  (in  the 
dog)  some  of  the  secreting  cells  may  belong  to  the  mucous  type.  The  base- 
ment membrane  is  composed  of  flattened  branched  connective-tissue  cells,  the 
interstices  between  which  are  filled  by  a  thin  membrane.  The  submaxillary 
gland  differs  in  histology  in  different  animals.  In  some,  as  the  dog  or  cat, 
all  the  secretory  tubes  are  composed  chiefly  or  exclusively  of  epithelial  cells 
of  the  mucous  type  (Fig.  73).  In  man  the  gland  is  of  a  mixed  type,  the 
secretory  tubes  containing  both  nuicous  and  albuminous  cells.  The  sublingual 
gland  in  man  also  contains  both  varieties  of  cells,  although  the  mucous  cells 
predominate.  It  follows  from  these  histological  characteristics  that  the  secre- 
tion from  the  submaxillary  and  sublingual  glands  is  thick  and  mucilaginous  as 
compared  with  tl.at  from  the  j)arotid. 

In  the  mucous  glands  another  variety  of  cells,  the  so-called  demilunes  or 
crescent  cells,  is  frequently  met  with  ;  and  the  physiological  significance  of 
these  cells  has  been  the  subject  of  much  discussion.  The  demilunes  are  cres- 
cent-shaped granular  cells  lying  between  the  mucous  cells  and  the  basement 
membrane,  and  not  in  contact,  therefore,  with  the  central  lumen  of  the  tube 
(see  Fig.  73).  According  to  Heideuhain  these  demilunes  are  for  the  purpose 
of  replacing  the  nuicous  cells.  In  consecjuence  of  long-continued  activity  the 
raucous  cells  may  disintegrate  and  disappear,  and  the  demilunes  then  develop 
into  new   mucous  cells.     According  to  other  views  the  demilunes  represent 


SECRETION.  161 

merely  an  inactive  stage  of  ordinary  mucous  cells,  or  the  basal  protoplasmic 
part  of  a  mucous  cell,  or,  finally,  a  distinct  secretory  cell  of  the  albuminous 
type. 

The  secreting  tubules  of  the  salivary  glands  each  possess  a  distinct  lumen 
round  which  the  cells  are  arranged.  In  addition  a  number  of  recent  observers, 
making  use  of  the  Golgi  method  of  staining,  have  apparently  demonstrated 
that  in  the  albuminous  glands  the  lumen  is  continued  as  fine  capillary  spaces 
running  between  the  secreting  cells.^  The  statement  is  also  made  that  from 
these  secretion  capillaries  small  side-branches  are  given  oif  which  penetrate 
into  the  substance  of  the  cell,  making  an  intracellular  origin  of  the  system  of 
ducts;  this  point,  however,  needs  confirmation.  In  the  mucous  glands  similar 
secretion  capillaries  are  found  only  in  connection  with  the  demilunes.  This 
latter  fact  supports  the  view  that  the  demilunes  are  not  simply  inactive  forms 
of  mucous  cells,  but  cells  with  a  specific  functional  activity.  It  is  an  un- 
doubted fact  that  the  salivary  glands  possess  definite  secretory  nerves  which 
when  stimulated  start  the  formation  of  secretion.  This  fact  indicates  that 
there  must  be  a  direct  contact  of  some  kind  between  the  gland-cells  and  the 
terminations  of  the  secretory  fibres.  The  nature  of  this  connection  has  been 
the  subject  of  numerous  investigations,  the  results  of  which  were  for  a  long  time 
negative  or  untrustworthy.  Quite  recently,  however,  the  application  of  the 
useful  Golgi  method  has  led  to  satisfactory  results.  The  ending  of  the  nerve- 
fibres  in  the  submaxillary  and  sublingual  glands  has  been  described  by  a  num- 
ber of  observers.^  The  accounts  differ  somewhat  as  to  details  of  the  finer 
anatomy,  but  it  seems  to  be  clearly  established  that  the  secretory  fibres  from 
the  chorda  tympani  end  first  round  the  intrinsic  nerve-ganglion  cells  of  the 
glands,  and  from  these  latter  cells  axis-cylinders  are  distributed  to  the 
secreting  cells,  passing  to  these  cells  along  the  ducts.  The  nerve-fibres  termi- 
nate in  a  plexus  upon  the  membrana  propria  of  the  alveoli,  and  from  this 
plexus  fine  fibrils  pass  inward  to  end  on  and  between  the  secreting  cells.  A 
more  elaborate  description  of  the  final  termination  of  the  secretory  fibres  is 
given  by  DogieP  for  the  lachrymal  gland,  which  is  a  gland  belonging  to  the 
albuminous  type.  It  would  seem  from  these  observations  that  the  nerve- 
fibrils  do  not  penetrate  or  fuse  with  the  gland-cells,  as  was  formerly  supposed, 
but  form  a  terminal  network  in  contact  with  the  cells,  following  thus  the 
general  schema  for  the  connection  between  nerve-fibres  and  peripheral  tissues. 

Composition  of  the  Secretion, — The  saliva  as  it  is  found  in  the  mouth 
is  a  mixed  secretion  from  the  large  salivary  glands  and  the  numerous 
smaller  glands  scattered  over  the  mucous  membrane  of  the  mouth.  It  is  a 
colorless  or  opalescent,  turbid,  and  mucilaginous  liquid  of  weakly  alkaline  re- 
action and  a  specific  gravity  of  about  1003.  It  may  contain  numerous  flat 
cells  derived  from  the  epithelium  of  the  mouth,  and  the  peculiar  spherical  cells 
known  as  salivary  corpuscles,  which  seem  to  be  altered  leucocytes.     The  im- 

^  Laserstein:  Pfluger's  Archiv  fur  die  r/esammte  Physiologic,  1893,  Bd.  55,  p.  417. 
^  See  Huber :  Journal  of  Experimental  Medicine,  1896,  vol.  i.  p.  281. 
^Archiv  fiir  mihroscopische  Anatomic,  1893,  Bd.  xlii.  S.  632. 
11 


162  AN  AMERICAN    TEXT- BOOK    OF   PHYSIOLOGY. 

purtimt  coustituents  of  the  secretion  are  mucin,  a  diastatic  enzyme  known  as 
ptyaliu,  traces  of  albumin  and  of  potassium  sulphocyanide,  and  inorganic  salts 
such  as  potassium  and  sodium  chloride,  potassium  sulphate,  sodium  carbonate, 
and  calcium  carbonate  and  ])hospluite.  The  average  jjroportions  of  these  con- 
stituents is  given  in  the  following  analysis  by  Hanunerbaeher : 

Water, 994.203 

Solids : 

Mucin  and  epithelial  cells, 2.202 

Ptvalin  and  albumin, 1.390 

Inorganic  salts, 2.205 

5.797 

1.000.000 
(Potassium sulphocyanide,  0.041.) 

Of  the  organic  constituents  of  the  saliva  the  albumin  exists  in  small  and  varia- 
ble quantities,  and  its  exact  nature  is  not  determined.  Tlie  mucin  gives  to  the 
saliva  its  roi)y,  mucilaginous  character.  This  substance  belongs  to  the  group 
of  combined  proteids,  glyco-proteids  (see  section  on  Chemistry),  consisting  of  a 
proteid  combined  with  a  carbohydrate  group.  The  physiological  value  of  this 
constituent  seems  to  lie  in  its  ])hysical  pro})erties,  as  described  in  the  section  on 
Digestion.  The  most  interesting  constituent  of  the  mixed  saliva  is  the  pty- 
alin.  This  body  belongs  to  the  group  of  enzymes  or  unorganized  ferments, 
whose  general  and  .specific  properties  are  described  in  the  section  on  Digestion. 
It  suffices  here  to  say  only  that  ptyalin  belongs  to  the  dia.static  group  of  enzymes, 
whose  specific  action  is  to  convert  the  starches  into  sugar  by  a  process  of 
hydrolysis.  In  some  animals  (dog)  jityalin  seems  to  be  normally  absent  from 
the  fresh  saliva.  An  interesting  fact  with  reference  to  the  saliva  is  the  large 
quantity  of  gases,  particularly  COg,  which  may  be  obtained  from  it  when 
freshly  secreted.  In  an  analysis  by  Pfliiger  of  the  saliva  from  the  submaxil- 
lary gland  the  following  figures  were  obtained  :  COj,  65  per  cent.,  of  which 
42.5  per  cent,  was  in  the  form  of  carbonates ;  N,  0.8  per  cent. ;  O,  0.6  per 
cent.  For  the  parotid  secretion  Kiilz  reports  :  CO2,  66.7  per  cent.,  of  which 
62  per  cent,  was  in  combination  as  carbonate ;  N,  3.8  per  cent.  ;  O,  1.46  per 
cent. 

The  secretions  of  the  parotid  and  submaxillary  glands  can  be  obtained  easily 
by  inserting  a  cannula  into  the  openings  of  the  ducts  in  the  mouth.  The  secre- 
tion of  the  sublingual  can  only  be  obtained  in  sufficient  quantities  for  analysis 
from  the  lower  animals.  Examination  of  the  separate  secretions  shows  that  the 
main  difference  lies  in  the  fact  that  the  parotid  saliva  contains  nonuicin,  while 
that  of  the  submaxillary  and  especially  of  the  sublingual  gland  is  rich  in 
mucin.  The  parotid  saliva  of  man  seems  to  be  particularly  rich  in  ptyalin  as 
compared  with  that  of  the  submaxillary,  while  the  secretion  of  the  latter  and 
of  the  sublingual  gland  give  a  stronger  alkaline  reaction  than  the  parotid 
saliva. 

The  Secretory  Nerves. — The  exi.stence  of  secretory  nerves  was  discovered 
by  Ludwig  in  1851.  He  found  that  stimulation  of  the  chorda  tympani  nerve 
caused  a  flow  of  saliva  from   the  submaxillary  gland.     He  established  also 


SECRETION.  163 

several  important  facts  with  regard  to  the  pressure  and  composition  of  the 
secretion  whicli  will  be  referred  to  presently.  It  was  afterward  shown  that 
the  salivary  glands  receive  a  double  nerve-supply,  in  part  by  way  of  the 
cervical  sympathetic  and  in  part  through  cerebral  nerves,  as  briefly  described 
on  {).  159.  It  was  discovered  also  that  not  only  are  secretory  fibres  carried 
to  the  glands  by  these  paths,  but  that  the  vaso-raotor  fibres  are  contained  in 
the  same  nerves,  and  the  arrangement  of  these  latter  fibres  is  such  that  the 
cerebral  nerves  contain  vaso-dilator  fibres  which  cause  a  dilatation  of  the  small 
arteries  in  the  glands  and  an  accelerated  blood-flow,  while  the  sympathetic 
carries  vaso-constrictor  fibres  whose  stimulation  causes  a  constriction  of  the 
small  arteries  and  a  diminished  blood-flow.  The  eflect  upon  the  secretion  of 
stimulation  of  these  two  sets  of  fibres  is  found  to  vary  somewhat  in  different 
animals.  For  purposes  of  description  we  may  confine  ourselves  to  the  effects 
observed  on  dogs,  since  most  of  our  fundamental  knowledge  upon  the  subject 
is  derived  from  Heidenhain's '  experiments  upon  this  animal.  If  the  chorda 
tympani  nerve  is  stimulated  by  weak  induction  shocks  the  gland  begins  to 
secrete  promptly,  and  the  secretion,  by  proper  regulation  of  the  stimuli,  may 
be  kept  up  for  hours.  The  secretion  thus  obtained  is  thin  and  watery,  flows 
freely,  is  abundant  in  amount,  and  contains  not  more  than  1  or  2  per  cent,  of 
total  solids.  At  the  same  time  there  is  an  increased  flow  of  blood  through 
the  gland.  The  whole  gland  takes  on  a  redder  hue,  the  veins  are  distended, 
and  if  cut  the  blood  that  flows  from  them  is  of  a  redder  color  than  in  the 
resting  gland,  and  may  show  a  distinct  pulse — all  of  which  points  to  a  dilata- 
tion of  the  small  arteries.  If  now  the  sympathetic  fibres  are  stimulated,  quite 
different  results  are  obtained.  The  secretion  is  relatively  small  in  amount, 
flows  slowly,  is  thick  and  turbid,  and  may  contain  as  much  as  6  per  cent,  of 
total  solids.  At  the  same  time  the  gland  becomes  pale,  and  if  the  veins  be 
cut  the  flow  from  them  is  slower  than  in  the  resting  gland,  thus  indicating 
that  a  vaso-constriction  has  occurred. 

The  increased  vascular  supply  to  the  gland  accompanying  the  abundant 
flow  of  "chorda  saliva"  and  the  diminished  flow  of  blood  during  the  scanty 
secretion  of  "  sympathetic  saliva "  suggest  naturally  the  idea  that  the  whole 
process  of  secretion  may  be  at  bottom  a  vaso-motor  phenomenon,  the  amount 
of  secretion  depending  only  on  the  quantity  and  pressure  of  the  blood  flowing 
through  the  gland.  It  has  been  shown  conclusively  that  this  idea  is  erro- 
neous and  that  definite  secretory  fibres  exist.  The  following  facts  may  be 
quoted  in  support  of  this  statement :  (1)  Ludwig  showed  that  if  a  mercury 
manometer  is  connected  with  the  duct  of  the  submaxillary  gland  and  the 
chorda  is  then  stimulated  for  a  certain  time,  the  pressure  in  the  duct  may 
become  greater  than  the  blood-pressure  in  the  gland.  This  fact  shows  that 
the  secretion  is  not  derived  entirely  by  processes  of  filtration  from  the  blood. 
(2)  If  the  blood-flow  be  shut  off  completely  from  the  gland,  stimulation  of 
the  chorda  will  still  give  a  secretion  for  a  short  time.     (3)  If  atropin  is 

^  Pfliiger's  Archiv  fiir  die  gesammte  Physiologie,  1878,  Bd.  xvii.  p.  1 ;  also  in  Hermann's  Haml- 
huch  der  Physiologie,  1883,  Bd.  v.  Th.  1. 


164  AN  AMEIUCAN    TEXT-BOOK    OF  PHYSIOLOGY. 

injected  into  tlie  gland,  stimulation  of  the  chorda  will  cause  vascular  dilata- 
tion but  no  secretion.  This  may  he  explained  by  supposing  that  the  atropiu 
paralyzes  the  secretory  but  not  the  dilator  fibres.  (4)  Hydrochlorate  of  qui- 
nine injected  into  the  gland  gives  vascular  dilatation  but  no  secretion.  In 
this  case  the  secretory  fibres  are  still  irritable,  since  stimulation  of  the  chorda 
gives  the  usual  secretion. 

A  still  more  marked  diffei'ence  between  the  effect  of  stimulation  of  the 
cerebral  and  the  sympathetic  fibres  may  be  observed  in  the  case  of  the  parotid 
gland  in  the  dog.  Stimulation  of  the  cerebral  fibres  alone  in  any  part  of 
their  course  (see  Fig.  68)  gives  an  abundant  thin  and  watery  saliva,  poor  in 
solid  constituents.  Stimulation  of  the  sympathetic  fibres  alone  (provided  the 
cerebral  fibres  have  not  been  stimulated  shortly  before  (Langley)  and  the  tym- 
panic nerve  has  been  cut  to  prevent  a  reflex  effect)  gives  usually  no  perceptible 
secretion  at  all.  But  in  this  last  stimulation  a  marked  effect  is  jn-oduced  upon 
the  gland,  in  spite  of  the  absence  of  a  visible  secretion  ;  this  is  shown  by  the 
fact  that  subsequent  or  simultaneous  stimulation  of  the  cerebral  fibres  gives  a 
secretion  very  unlike  that  given  by  the  cerebral  fibres  alone,  in  that  it  is  very 
rich  indeed  in  organic  constituents.  The  amount  of  organic  matter  in  the 
secretion  may  be  tenfold  that  of  the  saliva  obtained  by  stimulation  of  the 
cerebral  fibres  alone. 

Another  important  and  suggestive  set  of  facts  with  regard  to  the  action  of 
the  secretory  nerves  is  obtained  from  a  study  of  the  differences  in  composition 
of  the  secretion  following  upon  variations  in  tlie  strength  of  stimulation  of  the 
nerves. 

Relation  of  the  Composition  of  the  Secretion  to  the  Strength  of  Stimulation. — 
If  the  stimulus  to  the  chorda  be  gradually  increased  in  strength,  care  being 
taken  not  to  fatigue  the  gland,  the  chemical  composition  of  the  secretion  is 
found  to  change  with  regard  to  the  relative  amounts  of  the  water,  the  salts, 
and  the  organic  material.  The  water  and  the  salts  increase  in  amount  with  the 
increased  strength  of  stimulus  up  to  a  certain  maximal  limit,  which  for  the 
salts  is  about  0.77  per  cent.  Increase  of  stimulus  beyond  this  point  has  no 
further  effect,  the  amount  of  water  and  salts  remaining  constant.  It  is  im- 
portant to  observe  that  this  effect  may  be  obtained  from  a  perfectly  fresh 
gland  as  well  as  from  a  gland  which  had  previously  been  secreting  actively. 
With  regard  to  the  organic  constituents  the  precise  result  obtained  depends 
on  the  condition  of  the  gland.  If  previous  to  the  stimulation  the  gland  was 
in  a  resting  condition  and  unfiitigued,  then  increased  strength  of  stimulation 
is  followed  at  first  by  a  rise  in  the  ])ercentage  of  organic  constituents,  and  this 
rise  in  the  beginning  is  more  marked  than  in  the  case  of  the  salts.  But 
with  continued  stimulation  the  increase  in  organic  material  soon  ceases,  and 
finally  the  amount  begins  actually  to  diminish,  and  may  fall  to  a  low  point 
in  spite  of  the  stronger  stimulation.  On  the  other  hand,  if  the  gland  in  the 
beginning  of  the  experiment  had  been  previously  worked  to  a  considerable 
extent,  then  an  increase  in  the  stimulating  current,  while  it  increases  the 
amount  of  water  and  salts,  may  have  either  no  effect  at  all  upon  the  organic 


SECRETION.  165 

constituents  or  cause  only  a  temporary  increase,  quickly  followed  by  a  fall. 
Similar  results  may  be  obtained  from  stimulation  of  the  cerebral  nerves  of 
the  parotid  gland.  The  above  facts  led  Heidenhain  to  believe  that  the  con- 
ditions determining  the  secretion  of  the  organic  material  are  different  from 
those  controlling  the  water  and  salts,  and  he  gave  a  rational  explanation  of 
the  differences  observed,  in  his  theory  of  trophic  and  secretory  fibres. 

Theory  of  Trophic  and  Secretory  Nerve-fibres. — This  theory  supposes 
that  two  physiological  varieties  of  nerve-fibres  are  distributed  to  the  salivary 
glands.  One  of  these  varieties  controls  the  secretion  of  the  water  and  inor- 
ganic salts  and  its  fibres  may  be  called  secretory  fibres  proper,  while  the  other, 
to  which  the  name  trophic  is  given,  causes  the  formation  of  the  organic  con- 
stituents of  the  secretion,  probably  by  a  direct  influence  on  the  metabolism  in 
the  cell.  Were  the  trophic  fibres  to  act  alone,  the  organic  products  would  be 
formed  within  the  cell  but  there  would  be  no  visible  secretion,  and  this  is 
the  hypothesis  which  Heidenhain  uses  to  explain  the  results  of  the  experi- 
ment described  above  upon  stimulation  of  the  sympathetic  fibres  to  the  parotid 
of  the  dog.  In  this  animal,  apparently,  the  sympathetic  branches  to  the  parotid 
contain  exclusively  or  almost  exclusively  trophic  fibres,  while  in  the  cerebral 
branches  both  trophic  and  secretory  fibres  proper  are  present.  The  results  of 
stimulation  of  the  cerebral  and  sympathetic  branches  to  the  submaxillary  gland 
of  the  same  animal  may  be  explained  in  terms  of  this  theory  by  supposing  that 
in  the  latter  nerve  trophic  fibres  preponderate,  and  in  the  former  the  secretory 
fibres  proper. 

It  is  obvious  that  this  anatomical  separation  of  the  two  sets  of  fibres  along  the 
cerebral  and  sympathetic  paths  may  be  open  to  individual  variations,  and  that 
dogs  may  be  found  in  which  the  sympathetic  branches  to  the  parotid  glands 
contain  secretory  fibres  proper,  and  therefore  give  some  flow  of  secretion  on 
stimulation.  These  variations  might  also  be  expected  to  be  more  marked  when 
animals  of  different  groups  are  compared.  Thus  Langley  ^  finds  that  in  cats  the 
sympathetic  saliva  from  the  submaxillary  gland  is  less  viscid  than  the  chorda 
saliva,  just  the  reverse  of  what  occurs  in  the  dog.  To  apply  Heidenhain's 
theory  to  this  case  it  is  necessary  to  assume  that  in  the  cat  the  trophic  fibres 
run  chiefly  in  the  chorda.  An  interesting  fact  with  reference  to  the  secretion 
of  the  parotid  in  dogs  has  been  noted  by  Langley  and  is  of  special  interest, 
since,  although  it  may  be  reconciled  with  the  theory  of  trophic  and  secretory 
fibres,  it  is  at  the  same  time  suggestive  of  an  incompleteness  in  this  theory. 
As  has  been  said,  stimulation  of  the  sympathetic  in  the  dog  causes  usually  no 
secretion  from  the  parotid.  Langley  ^  finds,  however,  that  if  the  tympanic 
nerve  is  stimulated  just  previously,  stimulation  of  the  sympathetic  causes 
a  secretory  flow  from  the  parotid.  One  may  explain  this  in  terms  of  the 
theory  by  assuming  that  the  sympathetic  does  contain  a  few  secretory  fibres 
proper,  but  that  ordinarily  their  action  is  too  feeble  to  start  the  flow  of  water. 
Previous  stimulation  of  the  tympanic  nerve,  however,  leaves  the  gland-cells  in 

1  Journal  of  Physiology,  1878,  vol.  i.  p.  96. 

2  Ibid.,  1889,  vol.  X.  p.  291. 


166  ^.V  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

a  more  irritable  condition,  so  that  the  few  secretory  fibres  proper  in  the  sym- 
pathetic branches  are  now  effective  in  producing  a  flow  of  water. 

Theories  of  the  Action  of  Trophic  and  Secretory  Fibres. — The  way 
in  which  the  trophic  fibres  act  has  been  briefly  indicated.  Tiiey  may  be  sup- 
posed to  set  up  metabolic  changes  in  the  protoplasm  of  the  cells,  leading  to  the 
formation  of  certain  definite  products,  such  as  mucin  or  ptyalin.  That  such 
changes  do  occur  is  abundantly  showu  by  microscopic  examination  of  the  rest- 
ing and  the  active  gland,  the  details  of  which  will  be  given  presently.  In 
general  these  changes  may  be  supposed  to  be  katabolic  in  nature  ;  that  is,  to 
consist  in  a  disassociation  or  breaking  down  of  the  complex  living  material 
with  the  formation  of  the  simpler  and  more  stable  organic  constituents  of  the 
secretion.  There  is  evidence  to  show  that  these  gland-cells  during  activity 
form  fresh  material  from  the  nourishment  supplied  by  the  blood ;  that 
is,  that  anabolic  or  building-up  processes  occur  along  with  the  katabolic 
changes.  The  latter  are  the  more  obvious  and  are  the  changes  which  are 
usually  associated  with  the  action  of  the  trophic  nerve-fibres.  It  is  possible, 
also,  that  the  anabolic  or  growth  changes  may  be  under  the  control  of  separate 
fibres  for  which  the  name  anabolic  fibres  would  be  appropriate.  Satisfactory 
proof  of  the  existence  of  a  separate  set  of  anabolic  fibres  has  not  yet  been 
furnished. 

The  method  of  action  of  the  secretory  fibres  proper  is  difficult  to  under- 
stand. At  present  the  theories  suggested  are  very  speculative,  and  a  detailed 
account  of  them  is  scarcely  appropriate  in  this  place.  Heidenhain's  own  view 
may  be  mentioned,  but  it  should  be  borne  in  mind  that  it  is  only  an  hy- 
pothesis, the  truth  of  which  is  far  from  being  demonstrated.  The  theory  starts 
from  the  fact  that  no  more  water  leaves  the  blood-capillaries  than  afterward 
appears  in  the  secretion ;  that  is,  no  matter  how  long  the  secretion  continues, 
the  gland  does  not  become  oedematous  nor  does  the  velocity  of  the  lymph- 
stream  in  the  lymphatics  of  the  gland  increase.  This  being  the  case,  we  must 
suppose  that  the  stream  of  water  is  regulated  by  the  secretion,  that  is,  by  the 
activity  of  the  gland-cells.  If  we  suppose  tiiat  some  constituent  of  these  cells 
has  an  attraction  for  water,  then,  while  the  gland  is  in  the  resting  state,  water 
will  be  absorbed  from  the  basement  membrane ;  this  in  turn  supplies  its  loss 
from  the  surrounding  lymph,  and  the  lymph  obtains  the  same  amount  of 
water  from  the  blood.  As  the  amount  of  water  in  the  cell  increases  a  point  is 
reached  at  which  the  osmotic  tension  comes  to  an  equilibrium,  and  the  diffu- 
sion stream  from  blood  to  cells  is  at  a  standstill.  The  water  in  the  cells 
does  not  escape  into  the  lumen  of  the  tubule  or  of  the  secretion  capillaries, 
because  the  periphery  of  the  cell  is  modified  to  form  a  layer  offering 
considerable  resistance  to  filtration.  The  action  of  the  secretory  fibres 
proper  consists  in  so  altering  the  structure  of  this  limiting  layer  of  the  cells 
that  it  offers  less  resistance  to  filtration  ;  consequently  the  water  under  tension 
in  the  cells  escapes  into  the  lumen,  and  the  osmotic  pressure  of  its  substance 
again  starts  up  a  stream  of  water  from  capillaries  to  cells,  which  continues  as 
long  as  the  nerve-stimulation  is  effective. 


SECRETION.  167 

Recent  work  by  Runvicr,  Drasch,  Biedenniinn,  and  others  lias  called  atten- 
tion to  an  interesting  phenomenon  occurring  in  gland-cells  during  secretion 
which  when  better  known  will  possibly  throw  light  upon  the  formation  of  the 
water  stream  under  the  influence  of  nerve-stimulation.  Ranvier^  describes 
in  both  serous  and  mucous  cells  the  formation  of  vacuoles  within  the  proto- 
plasmic substance.  These  vacuoles  are  particularly  abundant  after  nerve- 
stimulation.  They  seem  to  contain  water,  and  if  they  behave  as  they  do  in 
the  protozoa — and  this  is  indicated  by  the  observations  of  Drasch  ^  upon  the 
glands  in  the  nictitating  membrane  in  the  frog — they  would  seem  to  form  a 
mechanism  sufficient  to  force  water  from  the  cells  into  the  lumen. 

Histological  Changes  during  Activity. — The  cells  of  both  the  albu- 
minous and  mucous  glands  undergo  distinct  histological  changes  in  conse- 
quence of  prolonged  activity,  and  these  changes  may  be  recognized  both  in 
preparations  from  the  fresh  gland  and  in  preserved  specimens.  In  the  parotid 
gland  Heidenhain  studied  the  changes  in  stained  sections  after  hardening  in 
alcohol.     In  the  resting  gland  (Fig.  70)  the  cells  are  compactly  filled  with 


Fig.  70.— Parotid  of  the  rabbit,  in  the  resting  condition  (after  Heidenhain), 

granules  which  stain  readily  and  are  imbedded  in  a  clear  ground  substance 
which  does  not  stain.  The  nucleus  is  small  and  more  or  less  irregular  in  out- 
line. After  stimulation  of  the  tympanic  nerve  the  cells  show  but  little  altera- 
tion, but  stimulation  of  the  sympathetic  produces  a  marked  change  (Fig.  71). 
The  cells  become  smaller,  the  nuclei  more  rounded  and  the  granules  are  more 
closely  packed.  This  last  appearance  seems,  however,  to  be  due  to  the  hard- 
ening reagents  used.  A  truer  picture  of  what  occurs  may  be  obtained  from  a 
study  of  sections  of  the  fresh  gland.     Langley,^  who  first  used  this  method, 

^  Ccmiptes  rendus,  cxviii.,  4,  p.  168.        ^  Archivfiir  Anatomie  und  Physiologie,  1889,  S.  96. 
^Journal  of  Physiology,  1879,  vol.  ii.  p.  260. 


168 


AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 


describes  his  results  as  follows:    When  the  animal  is  in  a  fasting  condition  the 
cells  have  a  granular  appearance  throughout  their  substance,  the  outlines  of 


Fig.  71.— Parotid  of  the  rabbit,  after  stimulation  of  the  sympathetic  (after  Heidenhain). 

the  different  cells  being  faintly  marked  by  light  lines  (Fig.  72,  ^1).  When 
the  gland  is  made  to  secrete  by  giving  the  animal  food,  by  injecting  pilocarpin, 
or  by  stimulating  the  sympathetic  nerves,  the  granules  begin  to  disappear  from 


■^#^         ^^^0^" 


C  D 

Fig.  72.— Parotid  gland  of  the  rabbit  in  a  fresh  state,  showing  portions  of  the  secreting  tubules :  .i4,  in 
a  resting  condition ;  B,  after  secretion  caused  by  pilocarpin ;  C,  after  stronger  secretion,  pilocarpin  and 
stimulation  of  sympathetic  ;  D,  after  long-continued  stimulation  of  sympatlietic  (after  Langley). 

the  outer  borders  of  the  cells  (Fig,  72,  B),  so  that  each  cell  now  shows  an  outer 
clear  border  and  an  inner  granular  one.  If  the  .stimulation  is  continued  the 
granules  become  fewer  in  number  and  are  collected  near  the  lumen  and  the  mar- 


SECRETION. 


169 


gins  of  the  cells,  the  oloar  zone  increases  in  extent  and  the  cells  become  smaller 
(Fig.  72,  C,  D).  Evidently  the  granular  material  is  used  up  in  some  way  to 
make  the  organic  material  of  the  secretion.  Since  the  ptyalin  is  a  conspicuous 
organic  constituent  of  the  secretion,  it  is  assumed  that  the  granules  in  the  rest- 
ing gland  contain  the  ptyalin,  or  rather  a  preliminary  material  from  which  the 
ptyalin  is  constructed  during  the  act  of  secretion.  On  this  latter  assumption 
the  granules  are  frequently  spoken  of  as  zymogen  granules.  During  the  act 
of  secretion  two  distinct  processes  seem  to  be  going  on  in  the  cell,  leaving  out 
of  consideration  for  the  moment  the  formation  of  the  water  and  the  salts.  In 
the  first  place  the  zymogen  granules  undergo  a  change  such  that  they  are  forced 
or  dissolved  out  of  the  cell,  and,  second,  a  constructive  metabolism  or  an- 
abolism  is  set  up,  leading  to  the  formation  of  new  protoplasmic  material  from 
the  substances  contained  in  the  blood  and  lymph.  The  new  material  thus 
formed  is  the  clear,  non-granular  substance,  which  appears  first  toward  the 
basal  sides  of  the  cells.  We  may  suppose  that  the  clear  substance  during  the 
resting  periods  undergoes  metabolic  changes,  whether  of  a  katabolic  or  anabolic 
character  cannot  be  safely  asserted,  leading  to  the  formation  of  new  granules, 
and  the  cells  are  again  ready  to  form  a  secretion  of  normal  composition.  It 
should  be  borne  in  mind  that  in  these  experiments  the  glands  were  stimulated 
beyond  normal  limits.  Under  ordinary  conditions  the  cells  are  probably  never 
depleted  of  their  granular  material  to  the  extent  represented  in  the  figures. 

In  the  cells  of  the  mucous  glands  changes  equally  marked  may  be  observed 
after  prolonged  activity.  In  stained  sections  of  the  resting  gland,  according 
to  Heidenhain,  the  cells  are  large  and  clear  (Fig.  73),  with  flattened  nuclei 


Fiu.Tii.— Mucous  gland;  Submaxillary  .jf  dog,  rest-        Fiu.  74.— Mucous  gland,  submaxillary  of  dog 
ing  stage.  after  eight  hours'  stimulation  of  the  chorda  tym- 

pani. 

placed  well  toward  the  base  of  the  cell.  When  the  gland  is  made  to  secrete 
the  nuclei  become  more  spherical  and  lie  more  toward  the  middle  of  the  cell, 
and  the  cells  themselves  become  distinctly  smaller.  After  prolonged  secretion 
the  changes  become  more  marked  (Fig.  74)  and,  according  to  Heidenhain, 
some  of  the  mucous  cells  may  break  down  completely,  the  demilune  cells 
increasing  in  size  and  forming  new  mucous  cells.     According  to  most  of  the 


170  AN  AMERICAN    TEXT-BOOK    OF   PIIYHIOLOGY. 

later  observers,  however,  the  mucous  cells  do  not  actually  disintegrate,  but 
form  again  new  material  during  the  ])eriod  of  rest  as  was  described  for  the 
goblet  cells  of  the  intestine.  In  the  mucous  as  in  the  allmminous  cells  ob- 
servations upon  pieces  of  tiic  fresh  gland  seem  to  give  more  rcliabh;  results 
than  those  uj>on  preserved  specimens.  Langley '  has  shown  that  in  the  fresh 
mucous  cells  of  the  submaxillary  gland  numerous  large  granules  may  be 
discovered,  about  125  to  250  to  a  cell.  These  granules  are  comparable  to 
those  found  in  the  goblet  cells,  and  may  be  interpreted  as  consisting  of 
mucin  or  some  ])reparatory  material  from  which  mucin  is  formed.  The 
granules  are  sensitive  to  reagents ;  addition  of  water  causes  them  to  swell  up 
and  disappear.  It  may  be  assumed  that  this  happens  during  secretion,  the  gran- 
ules becoming  converted  to  a  mucin-mass  which  is  extruded  from  the  cell. 

Action  of  Atropin,  Pilocarpin,  and  Nicotin  upon  the  Secretory 
Nerves. — The  action  of  drugs  upon  the  salivary  glands  and  their  secretions 
belongs  properly  to  pharmacology,  but  the  effects  of  the  three  drugs  men- 
tioned are  so  decided  that  they  have  a  peculiar  physiological  interest.  Atro- 
pin in  small  doses  injected  either  into  the  blood  or  into  the  gland-duct 
prevents  the  action  of  the  cerebral  fibres  (tympanic  nerve  or  chorda  tympani) 
upon  the  glands.  This  effect  may  be  explained  by  assuming  that  the  atropin 
paralyzes  the  endings  of  the  cerebral  fibres  in  the  glands.  That  it  does  not 
act  directly  upon  the  gland-cells  themselves  seems  to  be  assured  by  the  inter- 
esting fact  that  with  doses  sufficient  to  throw  out  entirely  the  secreting  action 
of  the  cerebral  fibres,  the  sympathetic  fibres  are  still  effective  when  stimulated. 
Pilocarpin  has  directly  the  opposite  effect  to  atropin.  In  minimal  doses  it 
sets  up  a  continuous  secretion  of  saliva,  which  may  be  explaiued  upon  the 
supposition  that  it  stimulates  the  endings  of  the  secretory  fibres  in  the  gland. 
Within  certain  limits  these  drugs  antagonize  each  other — that  is,  the  effect  of 
pilocarpin  may  be  removed  by  the  subsequent  application  of  atroj)in  and  vice 
veisa.  Nicotin,  according  to  the  experiments  of  Langley,^  prevents  the  action 
of  the  secretory  nerves,  not  by  action  on  the  gland-cells  or  the  endings  of  the 
nerve-fibres,  but  by  paralyzing  the  nerve-ganglion  cells  through  which  the 
fibres  pass  on  their  way  to  the  gland.  If,  for  example,  the  superior  cervical 
ganglion  is  painted  with  a  solution  of  nicotin,  stimulation  of  the  cervical 
sympathetic  below  the  gland  will  give  no  secretion  ;  stimulation,  however,  of 
the  fibres  in  the  ganglion  or  between  the  ganglion  and  gland  will  give  the 
usual  effect.  By  the  use  of  this  drug  Langley  is  led  to  believe  that  the  cells 
of  the  so-called  submaxillary  ganglion  are  really  intercalated  in  the  course 
of  the  fibres  to  the  sublingual  gland,  while  the  nerve-cells  with  which  the 
submaxillary  fibres  make  connection  are  found  chiefly  in  the  hilus  of  the 
gland  itself. 

Paralytic  Secretion. — A  remarkable  phenomenon  in  connection  with  the 
salivary  glands  is  the  so-called  paralytic  secretion.  It  has  been  known  for  a 
long  time  that  if  the  chorda  tympani  is  cut  the  submaxillary  gland  after  a  cer- 

'  Journal  of  Physiology,  1889,  vol.  x.  p.  433. 

*  Proceedings  of  the  Royal  Society,  London,  1889,  vol.  xlvi.  p.  423. 


SECRETION.  171 

taiu  lime,  one  to  three  days,  begins  to  secrete  slowly  and  the  secretion  contin- 
ues uninterruptedly  for  a  long  period — as  long,  perhaps,  as  several  weeks — and 
eventually  the  gland  itself  undergoes  atrophy.  Langley  ^  states  that  section  of 
the  chorda  on  one  side  is  followed  by  a  continuous  secretion  from  the  glands 
on  both  sides ;  the  secretion  from  the  gland  of  the  opposite  side  he  designates 
as  the  auti paralytic  or  anti lytic  secretion.  He  believes  that  this  continuous 
secretion  is  due  to  the  fact  that  the  irritability  of  the  nerve-cells  in  the  secretion 
centre  (see  below)  in  the  medulla,  as  well  as  of  the  nerve-cells  in  the  gland 
itself,  is  so  much  increased  that  the  venosity  of  the  blood  itself  is  sufficient  to 
throw  them  into  continuous  activity.  It  is  difficult,  however,  to  understand 
why  section  of  the  chorda  should  have  any  such  effect  as  this  upon  the  medul- 
lary centre,  especially  as  it  is  kuown  that  section  of  the  secretory  fibres  in  the 
sympathetic  docs  not  give  a  similar  result.  A  more  plausible  explanation  is 
the  one  suggested  by  Bradford,^  namely,  that  the  salivary  glands  receive  through 
their  cerebral  nerves  certain  fibres  which  may  be  called  anabolic,  whose  action 
is  to  cause  suspension  or  inhibition  of  the  katabolic  changes  in  the  gland-cells — 
probably,  according  to  Bradford,  by  acting  on  the  local  nerve-ganglion  cells  in 
the  gland.  When  these  fibres  are  removed  by  section  there  is  nothing  to 
hold  the  katabolic  processes  in  the  gland  in  check,  and  as  a  result  we  get  a 
continuous  secretion  and  a  wasting  of  the  gland. 

Normal  Mechanism  of  Salivary  Secretion. — Under  normal  conditions 
the  flow  of  saliva  from  the  salivary  glands  is  the  result  of  a  reflex  stimulation  of 
the  secretory  nerves.  The  sensory  fibres  concerned  in  this  reflex  must  be 
chiefly  fibres  of  the  glosso-pharyngeal  and  lingual  nerves  supplying  the  mouth 
and  tongue.  Sapid  bodies  and  various  other  chemical  or  mechanical  stimuli 
applied  to  the  tongue  or  mucous  membrane  of  the  mouth  will  produce  a  flow 
of  saliva.  The  normal  flow  during  mastication  must  be  effected  by  a  reflex  of 
this  kind,  the  sensory  impulse  being  carried  to  a  centre  and  thence  transmitted 
through  the  efferent  nerves  to  the  glands.  It  is  found  that  section  of  the 
chorda  prevents  the  reflex,  in  spite  of  the  fact  that  the  sympathetic  fibres  are 
still  intact.  No  satisfactory  explanation  of  the  normal  functions  of  the  secre- 
tory fibres  in  the  sympathetic  has  yet  been  given.  Since  the  flow  of  saliva  is 
normally  a  definite  reflex,  we  should  expect  a  distinct  salivary  secretion  centre. 
This  centre  has  been  located  by  physiological  means  in  the  medulla  oblon- 
gata ;  its  exact  position  is  not  clearly  defined,  but  possibly  it  is  represented  by 
the  nuclei  of  origin  of  the  secretory  fibres  which  leave  the  medulla  by  way  of 
the  facial  and  glosso-pharyngeal  nerves.  Owing  to  the  wide  connections 
of  nerve-cells  in  the  central  nervous  system  we  should  expect  this  centre  to  be 
affected  by  stimuli  from  various  sources.  As  a  matter  of  fact  it  is  known  that 
the  centre  and  throuo-h  it  the  o-lands  mav  be  called  into  activitv  bv  stimula- 
tion  of  the  sensory  fibres  of  the  sciatic,  splanchnic,  and  particularly  the  vagus 
nerves.  So,  too,  various  psychical  acts,  such  as  the  thought  of  savory  food  and 
the  feeling  of  nausea  preceding  vomiting,  may  be  accompanied  by  a  flow  of  saliva, 

^  Proceedings  of  the  Royal  Society,  I^ondon,  1 885,  No.  236. 
^  Journal  of  Physiology,  1888,  vol.  ix.  p.  287. 


172  AN  AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 

the  effect  in  this  case  being  due  probably  to  stimulation  of  tiie  secretion  centre 
bv  nervous  impulses  descending  from  the  higher  nerve-centres.  Lastly,  the 
medullary  centre  may  be  inhibited  as  well  as  stimulated.  The  well-known 
effect  of  fear,  embarrassment,  or  anxiety  in  producing  a  parched  throat  may 
be  supposed  to  arise  in  this  way  by  the  inhibitory  action  of  nerve-impulses 
arisino-  in  the  cerebral  centres. 

Electrical  Changes  in  the  Gland  during  Activity. — It  has  been  shown 
that  the  salivary  as  well  as  other  glands  suffer  certain  changes  in  electric 
potential  during  activity  which  are  comparable  in  a  general  way  to  the 
"  action  currents  "  observed  in  muscles  and  nerves  (see  section  on  Muscle  and 
Nerve).  Bradford '  has  apparently  shown  that  stimulation  of  the  secretory 
fibres  proper  causes  the  surface  of  the  gland  to  become  negative  to  the  hilus, 
while  stimulation  of  the  trophic  fibres  gives  the  reverse  effect.  Stimulation 
of  a  mixed  nerve,  therefore,  such  as  the  chorda,  gives  a  diphasic  effect.  The 
theories  bearing  upon  the  causes  of  these  electrical  changes  are  too  intricate 
and  speculative  to  enter  upon  here.  The  reader  is  referred  to  a  recent  account 
by  Biedermann^  for  further  details. 

0.  Pancreas  ;   Glands  of  the  Stomach  and  Intestines. 

Anatomical  Relations  of  the  Pancreas. — The  pancreas  in  man  lies  in 
the  abdominal  cavity  behind  the  stomach.  It  is  a  long,  narrow  gland,  its 
head  lying  against  the  curvature  of  the  duodenum  and  its  narrow  extremity 
or  tail  reaching  to  the  spleen.  The  chief  duct  of  the  gland  (duct  of  Wirsung) 
usually  opens  into  the  duodenum,  together  with  the  common  bile-duct,  about 
eight  to  ten  centimeters  below  the  pylorus.  In  some  cases,  at  least,  a  smaller 
duct  may  enter  the  duodenum  separately  somewhat  lower  down.  The  points  at 
which  the  ducts  of  the  pancreas  open  into  the  duodenum  vary  considerably  in 
different  animals.  For  instance,  in  the  dog  there  are  two  ducts,  the  larger  of 
which  enters  the  duodenum  separately  about  six  to  seven  centimeters  below 
the  pylorus,  while  in  the  rabbit  the  main  duct  opens  into  the  duodenum  over 
thirty  centimeters  below  the  pylorus.  The  nerves  of  the  pancreas  are  derived 
from  the  solar  plexus,  but  physiological  experiments  which  will  be  described 
presently  show  that  the  gland  receives  fibres  from  at  least  two  sources,  through 
the  vagus  nerve  and  through  the  sympathetic  system. 

Histological  Characters. — The  pancreas,  like  the  salivary  glands,  belongs 
to  the  compound  tubular  type.  The  cells  in  the  secreting  portions  of  the 
tubules,  the  so-called  alveoli,  resemble  the  serous  or  albuminous  type,  and  are 
usually  characterized  by  the  fact  that  the  outer  portion  of  each  cell,  that  is, 
the  part  toward  the  basement  membrane,  is  composed  of  a  clear  non-granular 
substance  which  takes  stains  readily,  while  the  inner  portion  turned  toward 
the  lumen  is  filled  with  conspicuous  granules.  In  addition  to  this  type  of 
cell,  which  is  the  characteristic  secreting  element  of  the  organ,  the  pancreas 
contains  a  number  of  irregular  masses  of  cells  of  a  different  character  (bodies 
of  Langerhans).  These  latter  cells  are  clear  and  small,  frequently  have  ill- 
^  Journal  of  Physiology,  1887,  vol.  viii.  p.  86.  ^  Elektrophysiologie,  Jena,  1895- 


SECRETION.  173 

defined  cell-bodies,  but  coutain  nuclei  whicii  stain  readily  with  ordinary 
reagents.  By  some  these  cells  are  supposed  to  be  immature  secreting  cells  of 
the  ordinary  pancreatic  type.  By  others  it  is  thought  that  they  are  a  separate 
type  of  cell  and  take  some  special  part  in  the  secretory  functions  of  the  pan- 
creas. Nothing  definite,  however,  is  known  as  to  their  physiological  import- 
ance. 

In  the  pancreas,  as  in  the  salivary  glands,  the  latest  histological  methods 
have  apparently  demonstrated  that  the  lumen  of  each  secreting  tubule  is  con- 
tinuous with  a  system  of  intercellular  secretion  capillaries  lying  between  the 
secretory  cells,  and  according  to  some  observers  sending  terminal  capillaries 
into  the  very  substance  of  the  gland-cells. 

Composition  of  the  Pancreatic  Secretion. — The  pancreatic  secretion  is 
a  clear  alkaline  liquid  which  in  some  animals  (dog)  is  thick  and  mucilaginous. 
Its  physical  characters  seem  to  vary  greatly,  even  in  the  same  animal,  accord- 
ing to  the  duration  of  the  secretion  or  the  time  since  the  establishment  of  the 
fistula  by  which  it  is  obtained  (see  p.  238).  In  a  newly  made  fistula  in  the 
dog  the  secretion  is  thick,  but  in  a  permanent  fistula  it  becomes  much  thinner 
and  more  watery.  The  main  constituents  of  the  secretion  are  three  enzymes, 
a  large  percentage  of  proteid  material  the  exact  nature  of  which  is  not  known, 
some  fats,  soaps,  a  slight  amount  of  lecithin,  and  inorganic  salts.  The  strongly 
alkaline  nature  seems  to  be  due  chiefly  to  sodium  carbonate,  which  may 
be  present  in  amounts  equal  to  0.2  to  0.4  per  cent.  The  three  enyzmes  are 
known  respectively  as  trypsin,  a  proteolytic  ferment ;  amylopsin,  a  diastatic 
ferment,  and  steapsin,  a  fat-spliting  ferment.  The  action  of  these  enzymes 
in  digestion  is  described  in  the  section  on  Digestion. 

Action  of  the  Nerves  on  the  Secretion  of  the  Pancreas. — In  animals 
like  the  dog,  in  which  the  process  of  digestion  is  not  continuous,  the  secretion 
of  the  pancreas  is  also  supposed  to  be  intermittent.  A  study  of  the  flow  of 
secretion  as  observed  in  cases  of  pancreatic  fistula  indicates  that  it  is  connected 
with  the  beginning  of  digestion  in  the  stomach,  and  is  therefore  probably  a 
reflex  act.  Until  recently,  however,  little  direct  evidence  had  been  obtained 
of  the  existence  of  secretory  nerves.  Stimulation  of  the  medulla  was  known 
to  increase  the  flow  of  pancreatic  juice  and  to  alter  its  composition  as  regards 
the  organic  constituents,  but  direct  stimulation  of  the  vagus  and  the  sympa- 
thetic nerves  gave  only  negative  results.  Lately,  however,  Pawlow'  and  some 
of  his  students  have  been  able  to  overcome  the  technical  difficulties  in  the  w.ay, 
and  have  given  what  seems  to  be  perfectly  satisfactory  proof  of  the  existence  of 
distinct  secretory  fibres  comparable  in  their  nature  to  those  described  for  the 
salivary  glands.  The  results  that  they  have  obtained  may  be  stated  briefly  as 
follows  :  Stimulation  of  either  the  vagus  nerve  or  the  sympathetic  causes,  after 
a  considerable  latent  period,  a  marked  flow  of  pancreatic  secretion.  The  failure 
of  other  experiments  to  get  this  result  was  due  apparently  to  the  sensitiveness  of 
the  gland  to  variations  in  its  blood-supply.     Either  direct  or  reflex  vaso-con- 

^Pawlow:  Dii  Bois-Reymond's  Archiv  fiir  P%s^ioio^ie,  1893,  Suppl.  Bd. ;  Mett:  76;^/.,  1894; 
Kudrewetsky :  Ibid.,  1894. 


174  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

strictiou  of  the  pancreas  prevents  the  action  of  tlio  secretory  nerves  uj)on  it. 
Thus  stimulation  of  the  sympathetic  j^ives  usually  no  effect  upon  the  secretion, 
because  vaso-constrictor  fibres  are  stimulated  at  tiie  same  time,  but  if  the  sym- 
pathetic nerve  is  cut  five  or  six  days  previously,  so  as  to  give  the  vaso-con- 
strictor fibres  time  to  degenerate,  stimulation  will  cause,  after  a  long  latent 
period,  a  distinct  secretion  of  the  ])ancreatic  juice. 

Accepting  the  theory  of  secretory  and  trophic  fibres  j)roposed  for  the  sali- 
vary glands,  the  experiments  upon  the  variations  in  pancreatic  secretion  follow- 
ing upon  stimulation  of  the  vagus  and  sympathetic  respectively  seem  to  indi- 
cate that  in  the  sympathetic  trophic  fibres  are  more  abundant,  and  in  the  vagus 
the  secretory  fibres  proper.  The  long  latent  period  elaj)sing  between  the  time 
of  stimulation  and  the  effect  upon  the  flow  is  not  easily  understood.  The 
authors  quoted  give  no  satisfactory  explanation  of  this  curious  fact,  but  sug- 
gest that  it  may  be  due  to  the  presence  of  definite  inhibitory  fibres  to  the 
gland,  which  are  stimulated  simultaneously  with  the  secretory  fibres  and  thus 
hold  the  secretion  in  check  for  a  time.  No  indepeudent  proof  of  the  presence 
of  inhibitory  fibres  is  furnished. 

Histological  Changes  during  Activity. — The  morphological  changes  in 
the  pancreatic  cells  have  long  been  known  and  have  been  studied  satisfac- 
torily in  the  fresh  gland  as  well  as  in  preserved  specimens.  The  general 
nature  of  the  changes  is  the  same  as  that  described  for  the  salivary  gland, 
and  is  illustrated  in  Figures  75,  76,  and  77.  If  the  gland  is  removed  from 
a  dog  which  has  been  fasting  for  about  twenty-four  hours  and  is  hardened 
in  alcohol  and  sectioned  and  stained,  it  will  be  found  that  the  cells  are  filled 
with  granules  except  for  a  narrow  zone  toward  the  basal  end,  which  is  marked 
off  more  clearly  because  it  stains  more  deeply  than  the  granular  portion  (Fig. 
75).     If,  on  the  contrary,  the  gland  is  taken  from  a  dog  which  had  been  fed 


Fig.  7.').— Pancreas  of  the  dog  during  hunger ;  preserved  in  alcohol  and  stained  in  carmine 

(after  Heidenhain). 

six  to  ten  hours  previously,  the  non-staining  granular  zone  is  nuich  reduced  in 
size,  while  the  clearer  non-granular  zone  is  enlarged  (Fig.  76).  The  increase 
in  size  of  the  non-granular  zone  does  not,  however,  entirely  compensate  for 


8ECBETION. 


175 


the  loss  of  the  granular  material,  so  that  the  cell  as  a  whole  is  smaller  in 
size  than  in  the  gland  from  the  fasting  animal.  It  seems  evident  that  during 
the  honi-s  immediately  following  a  meal — that  is,  at  the  time  when  we  know 


Fig.  76.— Pancreas  of  dog  during  first  stage  of  digestion ;  alcoiiol,  carmine  (after  Heidenliain). 

that  the  gland  is  discharging  its  secretion,  the  granular  material  is  being  used 
up.  After  the  period  of  most  active  secretion — that  is,  during  the  tenth  to 
the  twentieth  hour  after  a  meal  in  the  case  of  a  dog  fed  once  in  twenty-four 


Fig.  77.— Pancreas  of  dog  during  second  stage  of  digestion;  alcohol,  carmine  (after  Heidenhain). 

hours — the  gland-cells  return  to  their  resting  condition  (Fig.  77).  New  gran- 
ules are  formed,  and  finally,  if  the  gland  is  left  unstimulated  they  fill  the 
entire  cell  except  for  a  narrow  margin  at  the  basal  end. 

Similar  results  are  reported  by  Kiihne*  and  Lea  from  observations  made 
upon  the  pancreas  cells  in  a  living  rabbit.     In  the  inactive  gland  the  outlines 

^  TJnter«ux.hungen  aus  dem  physiologischen  Insiitut  des  Universitdts  Heidelberg,  1882,  Bd.  ii. 


176  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

of  the  iudividiial  cells  are  not  clearly  distinguishable,  but  it  can  be  seeu  that 
there  are  two  zones,  one  clear  and  homogeneous  on  the  side  toward  the  basement 
membrane,  and  one  granular  on  the  side  toward  the  lumen.  During  activity 
the  secretory  tubules  show  a  notched  appearance  corresponding  to  the  positions 
of  the  cells,  the  outlines  of  the  cells  become  more  distinct,  the  granular  zone 
becomes  smaller,  and  the  homogeneous  zone  increases  in  width.  It  should  Im; 
stated  also  tiiat  in  this  latter  condition  the  basal  zone  of  the  cells  shows  a  dis- 
tinct striation.  From  these  appearances  we  must  believe  that,  as  in  the  case 
of  the  salivary  gland,  a  part  at  least  of  the  organic  material  of  the  secretion  is 
formed  from  the  granules  of  the  inner  zone,  and  that  the  granules  in  turn  are 
formed  within  the  cells  from  the  homogenous  material  of  the  outer  zone. 

Enzyme  and  Zymogen. — The  observations  just  described  indicate  that  the 
enzymes  of  the  pancreatic  secretion  are  derived  from  the  granules  in  the  cells, 
but  other  facts  show  that  the  granules  do  not  contain  the  enzymes  as  such,  but 
a  preparatory  material  or  mother-substance  to  which  the  name  zymogen 
(enzyme-maker)  is  given.  This  belief  rests  upon  facts  of  the  following  kind  : 
If  a  pancreas  is  removed  from  a  dog  which  has  fasted  for  twenty-four  hours, 
when,  as  we  have  seen,  the  cells  are  heavily  loaded  with  granules,  and  a  glycerin 
extract  is  made,  very  little  active  enzyme  will  be  found  in  it.  If,  however, 
the  gland  is  allowed  to  stand  for  twenty-four  hours  in  a  warm  spot  before  the 
extract  is  made,  or  if  it  is  first  treated  with  dilute  acetic  acid,  the  glycerin  ex- 
tract will  show  very  active  tryptic  or  amylolytic  properties.  Moreover,  if  an 
inactive  glycerin  extract  of  the  perfectly  fresh  gland  is  treated  by  various 
methods,  such  as  dihition  with  water  or  shaking  with  finely  divided  platinum- 
black,  it  becomes  converted  to  an  active  extract  capable  of  digesting  proteid 
material.  These  results  are  readily  explained  upon  the  hypothesis  that  the 
granules  contain  only  zymogen  material,  which  during  the  act  of  secretion,  or 
by  means  of  the  methods  mentioned,  may  be  converted  into  the  corresponding 
enzymes.  As  the  three  enzymes  of  the  pancreatic  secretion  seem  to  be  distinct 
substances,  one  may  suppose  that  each  has  it  own  zymogen  to  which  a  distinc- 
tive name  might  be  given.  The  zymogen  which  is  converted  into  trypsin  is 
frequently  spoken  of  as  trypsinogen. 

Normal  Mechanism  of  Pancreatic  Secretion. — After  the  establishment 
of  a  pancreatic  fistula  it  is  possible  to  study  the  flow  of  secretion  in  its  rela- 
tions to  the  ingestion  of  food.  Experiments  of  this  kind  have  been  made, 
and  show  that  in  animals  like  the  dog,  in  which  sufficient  food  may  be  taken 
in  a  single  meal  to  last  for  a  day,  the  flow  of  secretion  is  intimately  connected 
with  the  reception  of  food  into  the  stomach  and  its  subsequent  digestive 
changes.  The  time  relations  of  the  secretion  to  the  ingestion  of  food  are 
shown  in  the  accompanying  chart  (Fig.  78).  The  secretion  begins  immedi- 
ately after  the  food  enters  the  stomach,  and  increases  in  velocity  up  to  a  cer- 
tain maximum  which  is  reached  some  time  between  the  first  and  the  third  hour 
after  the  meal.  The  velocity  then  diminishes  rapidly  to  the  fifth  or  sixth 
hour,  after  which  there  may  be  a  second  smaller  increase  reaching  its  maxi- 
mum about  the  ninth  to  the  eleventh  hour.     From  this  point  the  secretion 


SECRETION. 


177 


diminishes  in  quantity  to  the  sixtoentli  or  seventeenth  hour,  when  it  has 
practically  reaclucl  the  zero  point.  In  man,  in  whom  the  meals  normally 
occur  at  intervals  of  five  to  six  hours,  this  curve  of  course  would  have  a  dif- 
ferent form.     The  interestincr  fact,  however,  that  the  secretion  starts  very  soon 


o — ,   -^  3  -^ — s — b — y    s     9    'io~^'    /2   15   /v  15  Jb   17  a 

Fig  78  -Curve  of  the  secretion  of  pancreatic  juice  during  digestion.  The  figures  along  the  abscissa 
represent  hours  after  the  beginning  of  digestion;  the  figures  along  the  ordinate  represent  the  quantity 
of  this  secretion  in  cubic  centimeters.    Curves  of  two  experiments  are  given  (after  Heidenhain). 

after  the  beginning  of  gastric  digestion  is  probably  true  for  human  beings,  and 
gives  strong  indication  that  the  secretion  is  a  reflex  act. 

Recently  a  number  of  experiments  have  been  reported  which  strengthen 
the  view  that  the   normal  secretion  of  the  pancreas  is  reflexly  excited  by 
stimuli  acting   upon    the   mucous   membrane  of  the   stomach    or   intestine. 
Gottlieb^  finds  that  in  rabbits  the  pancreatic  secretion  is  very  greatly  accel- 
erated by  stimulants  such  as  oil  of  mustard,  pepper,  acids,  or  alkalies  intro- 
duced into  the  stomach  or  duodenum,  and  Dolinsky,^  working  upon  dogs 
under  more  favorable. experimental  conditions  finds  that  acids  are  particularly 
eifective   in   arousing  the  pancreatic  flow ;   on   the  contrary,  alkalies  in  the 
stomach  diminish  the  pancreatic  secretion.     Dolinsky  believes  that  the  normal 
acidity  of  gastric  secretion  is  perhaps  the  most  effective  stimulus  to  the  pan- 
creatic gland,  and  that  in  this  way  the  flow  of  gastric  juice  in  ordinary  diges- 
tion starts  the  pancreatic  gland  into  activity.     Whether  the  acid  acts  after 
absorption  into  the  blood,  or  stimulates  the  sensory  fibres  of  the  raucous  mem- 
brane and  thus  reflexly  affects  the  pancreas  through  its  secretory  nerves,  is  not 
definitely  known,  but  the  probabilities  are  in  favor  of  the  latter  view.     It  is 
probable  also  that  the  acid  acts  mainly  upon  the  sensory  fibres  of  the  mucous 
membrane  of  the  duodenum  rather  than  upon  the  gastric  membrane. 
1  Arehiv  flir  ejcperimentelle  Pathologic  und  Phainimkologie,  1894,  Bd.  33,  p.  273. 
*  Archives  des  Sciences  biologiques,  St.  Petersburg,  1895,  vol.  iii.  p.  399. 
12 


178  J.V    AMERICAN    TEXT-BOOK    OF    PHYSIOLOGY. 

AVe  are  justitied  from  these  experiments  in  believing  that  tlie  nieclianisra 
of  the  pancreatie  secretion  is  closely  analogous  to  that  c(mtrolling  the  salivary 
glands.  It  is  usually  stated,  however,  that  the  pancreas  still  continues  to 
secrete  after  all  its  extrinsic  nerves  have  been  severed.  The  experiments 
uj)c)n  which  this  statement  rests  are  not  entirely  satisfactory,  since,  owing  to 
the  way  in  which  the  nerve-fibres  reach  the  organ  in  the  walls  of  the  blood- 
vessels, it  is  difficult  to  be  sure  that  all  the  nerve-fibres  are  actually  severed, 
and  moreover  it  is  probable  that  if  the  gland  contiiuies  to  secrete  after  removal 
of  its  extrinsic  nerves,  the  flow  is  of  the  nature  of  a  paralytic  secretion,  which 
in  time  would  be  followed  by  a  wasting  of  the  gland.  More  experimental 
work  is  required  upon  this  point. 

Glands  of  the  Stomach. 

Histolog-ical  Characteristics. — The  glands  of  the  gastric  mucous  mem- 
brane belong  practically  to  tlie  type  of  simple  tubular  glands ;  for,  although 
two  or  more  of  the  simple  tubes  may  possess  a  common  opening  or  mouth, 
there  is  no  system  of  ducts  such  as  prevails  in  the  compound  glands,  and  the 
divergence  from  the  simplest  form  of  tubular  gland  is  very  slight.  Each  of 
these  glands  possesses  a  relatively  wide  mouth,  lined  with  the  columnar  epi- 
thelium found  on  the  free  surface  of  the  gastric  membrane,  and  a  longer,  nar- 
rower secreting  part,  which  penetrates  the  thickness  of  the  mucosa  and  is  lined 
by  cuboidal  cells.  The  glands  in  the  pyloric  end  of  the  stomach  differ  in  gen- 
eral appearance  from  those  in  the  fundic  end,  and  are  especially  characterized 
by  the  fact  that  they  possess  only  one  kind  of  secretory  cell,  while  the  fundic 
glands  contain  two  apparently  distinct  types  of  cells  (Fig.  81).  The  lumen  in  the 
latter  glands  is  lined  by  a  continuous  layer  of  short  cylindrical  cells  to  which 
Heidenhain  gave  the  name  of  chief-cells.  These  cells  are  apparently  concerned 
in  the  formation  of  pepsin,  the  proteolytic  enzyme  contained  in  the  gastric  secre- 
tion. In  addition  there  are  present  a  number  of  cells  of  an  oval  or  triangular 
shaj)e  which  are  placed  close  to  the  basement  membrane  and  do  not  extend  quite 
to  the  main  lumen  of  the  gland.  These  cells,  which  are  not  found  in  the  pyloric 
glands,  are  known  by  various  names,  such  as  border-cells,  parietal  cells,  oxyntic 
cells,  etc.  The  last-mentioned  name  has  been  given  to  ihem  because  of  their 
supposed  connection  with  the  formation  of  the  acid  of  the  gastric  secretion.  The 
nature  and  function  of  these  border-cells  have  been  the  subject  of  much  discus- 
sion. From  the  histological  side  they  have  been  interpreted  as  representing 
either  immature  forms  of  the  chief-cell,  or  else  the  active  modification  of  this 
cell.  Recent  work,  however,  seems  to  have  demonstrated  that  they  form  a 
specific  type  of  cell,  and  probably  therefore  have  a  specific  function.  An 
interesting  histological  fact  in  connection  with  the  parietal  cells  is  that,  in  the 
human  stomach  at  least,  they  frequently  contain  several  nuclei,  five  or  six, 
and  some  of  these  seem  to  be  derived  from  ingested  leucocytes.  They  are 
interesting  also  in  the  fact  that  they  contain  distinct  vacuoles  which  seem  to 
appear  some  time  after  digestion  has  begun,  reach  a  maximum  size,  and  then 
gradually  grow  smaller  and  finally  disappear.     I^ike  the  similar  phenomenon 


SECRETION.  179 

described  for  other  oland-cells  (p.  167),  tliis  appearance  is  possibly  connected 
with  the  formation  of  the  secretion. 

The  duct  of  a  gastric  gland  was  formerly  supposed  to  be  a  simple  tube 
extending  the  length  of  the  gland.  A  number  of  recent  observers,  however, 
have  shown,  by  the  use  of  the  Golgi  stain,  that  this 
view  is  not  entirely  correct,  at  least  not  for  the  glands 
in  the  fundus  in  which  border-cells  are  present.  In 
these  glands  the  central  lumen  sends  offside  channels 
which  pass  to  the  border-cells  and  there  form  a  net- 
work of  small  capillaries  which  lie  either  in  or  round 
the  cell.'  An  illustration  of  the  duct-system  of  a 
fundic  gland  is  given  in  Figure  79.  If  this  work 
is  correct  it  would  seem  that  the  chief-cells  com- 
municate directlv  with  the  central  lumen,  but  that  fig.  tu— Ducts  and  secretion 
the  border-cells  have  a  system  of  secretion  capillaries     ^f  "f  ^«  ^o  parietal  oeiis. 

J  i  Gland  from  the  fundus  of  cat  s 

of  their  own,  resembling  in  this  respect  the  demi-  stomach  (after  Langendorff 
lunes  of  the  mucous  salivary  glands  (p.  161).     This 

fact  tends  to  corroborate  the  statement  previously  made,  that  the  border-cells 
form  a  distinct  type  of  cell  whose  function  is  jirobably  different  from  that 
of  the  chief-cells. 

Composition  of  the  Secretion  of  the  Gastric  Mucous  Membrane. — 
The  secretion  as  it  is  poured  out  on  the  surface  of  the  mucous  membrane  is 
composed  of  the  true  secretion  of  the  gastric  glands  together  with  more  or  less 
mucus,  which  is  added  by  the  columnar  cells  lining  the  surface  of  the  mem- 
brane and  the  mouths  of  the  glands.  In  addition  to  the  mucus,  water,  and 
inorganic  salts,  the  secretion  contains  as  its  characteristic  constituents  hydro- 
chloric acid  and  two  enzymes — namely,  pepsin  which  acts  upon  proteids,  and 
reuniu  which  has  a  specific  coagulating  effect  upon  tiie  casein  of  milk.  For  an 
analysis  of  the  gastric  secretion  of  the  dog  see  p.  161.  According  to  Heiden- 
hain,^  the  secretion  from  the  pyloric  end  of  the  stomach  is  characterized  by  the 
absence  of  hydrochloric  acid,  although  it  still  contains  pepsin.  This  statement 
rests  upon  careful  experiments  in  which  the  pyloric  end  was  entirely  resected 
and  made  into  a  blind  pouch  which  was  then  sutured  to  the  abdominal  wall 
to  form  a  fistula.  In  this  way  the  secretion  of  the  pyloric  end  could  be  obtained 
free  from  mixture  with  the  secretion  of  any  other  part  of  the  alimentary  canal. 
By  this  means  Heidenhaiu  found  that  the  pyloric  secretion  is  an  alkaline  liquid 
containing  pepsin.  This  fact  forms  the  strongest  evidence  for  Heidenhain's 
hypothesis  that  the  HCl  of  the  normal  gastric  secretion  is  produced  by  the 
"border-cells"  of  the  fundic  glands  and  the  pepsin  by  the  "chief-cells,"  since 
HCl  is  formed  only  in  parts  of  the  stomach  containing  border-cells,  whereas 
the  pepsin  is  produced  in  the  pyloric  end,  where  only  chief-cells  are  present. 

Evidence  of  this  character  is  naturally  not  very  convincing,  and  the  hypoth- 

1  Langendorff  and  Laserstein  :  Pflugei-'s  Archiv  fur  die  gesammte  Physiohgie,  1894,  Bd.  Iv.  S. 
578. 

*  Archiv  fiir  die  gesammte  Physiologic,  1878,  Bd.  xviii.  S.  169,  also  Bd.  xix. 


180  AN   AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

esis,  especially  that  part  ooniiectinj^  the  border-eell.s  with  the  turmatiou  of 
HCl,  cau  ouly  be  accepted  provisionally  until  further  investigation  confirms 
or  disproves  it.  It  should  be  stated  that  the  alkalinity  of  the  secretion  obtained 
from  the  pyloric  glands  by  Heidenhain's  method  has  been  attributed  by  some 
authors  to  the  abnormal  conditions  j)revailing,  especially  to  the  section  of  the 
vagus  fibres  which  necessarily  results  from  the  operation.  Contejean  '  asserts 
that  the  reaction  of  the  pyloric  membrane  under  normal  conditions  is  acid  in 
spite  of  the  absence  of  border-cells. 

Influence  of  the  Nerves  upon  the  Gastric  Secretion. — It  has  been  very 
difficult  to  obtain  direct  evidence  of  the  existence  of  extrinsic  secretory  nerves 
to  the  gastric  glands.  In  the  hands  of  most  experimenters,  stimulation  of  the 
vagi  and  of  the  syrapathetics  has  given  negative  results,  and,  on  the  other 
hand,  section  of  these  nerves  does  not  seem  to  prevent  the  formation  of  the 
gastric  secretion.  There  are  on  record,  however,  a  number  of  observations 
which  point  to  a  direct  influence  of  the  central  nervous  system  on  the  secre- 
tion. Thus  Bidder  and  Schmidt  found  that  in  a  hungry  dog  with  a  gastric 
fistula  (page  225)  the  mere  sight  of  food  caused  a  flow  of  gastric  juice ;  and 
Richet  reports  a  case  of  a  man  in  whom  the  oesophagus  was  completely  oc- 
cluded and  in  whom  a  gastric  fistula  was  established  by  surgical  operation. 
It  was  then  found  that  savory  foods  chewed  in  the  mouth  produced  a  marked 
flow  of  gastric  juice.  There  would  seem  to  be  no  other  way  of  explaining  the 
secretions  in  these  cases  except  upon  the  supposition  that  they  were  caused  by  a 
reflex  stimulation  of  the  gastric  mucous  membrane  through  the  central  nervous 
system.  These  cases  are  strongly  supported  by  some  recent  experimental 
work  on  dogs  by  Pawlow  ^  and  Schumowa-Simanowskaja.  These  observers 
used  dogs  in  which  a  gastric  fistula  had  been  established,  and  in  which,  more- 
over, the  oesophagus  had  been  divided  in  the  neck  and  the  upper  and  lower 
cut  surfaces  brought  to  the  skin  and  sutured  so  as  to  make  two  fistulous 
openings.  In  these  animals,  therefore,  food  taken  into  the  mouth  and  subse- 
quently swallowed  escaped  to  the  exterior  through  the  upper  oesophageal 
fistula,  without  entering  the  stomach.  Nevertheless  this  "  fictitious  meal," 
as  the  authors  designate  it,  in  the  case  of  certain  foods  (meats),  brought  about 
an  increased  formation  of  gastric  juice,  although,  curiously  enough,  other  foods, 
such  as  milk  and  soup,  gave  negative  results.  If  in  such  animals  the  two 
vagi  were  cut,  the  "  fictitious  meal  "  no  longer  caused  a  secretion  of  the  gas- 
tric juice,  and  this  fact  may  be  considered  as  showing  that  the  secretion 
obtained  when  the  vagi  were  intact  was  due  to  a  reflex  stimulation  of  the 
stomach  through  these  nerves.  Finally,  these  observer  were  able  to  show 
that  direct  stimulation  of  the  vagi  under  proper  conditions  causes,  after  a  long 
latent  period  (six  or  seven  minutes),  a  marked  secretion  of  gastric  juice.  A 
satisfactory  explanation  of  the  unusually  long  latent  period  is  not  given. 

Taking  these  results  together,  we  nuist  believe  that  the  vagi  send  secretory 
fibres  to  the  gastric  glands,  and  that  these  fibres  may  be  stimulated  reflexly 

*  Archives  de  Physiologic,  1892,  p.  554. 

'  Du  Bois-Reymond^ s  Archiv  fiir  Physiologic,  1895,  S.  53. 


SECRETION.  181 

through  the  sensory  nerves  of  i\w.  numtli,  unci  probably  also  by  psychical 
states. 

Normal  Mechanism  of  Secretion  of  the  Gastric  Juice. — Our  know- 
ledge of  the  means  by  which  the  flow  of  gastric  secretion  is  caused  during 
normal  digestion,  and  of  the  varying  conditions  which  influence  the  flow,  is 
as  yet  quite  incomplete.  Some  notable  experiments  recently  made  by  Pawlow  ' 
and  Khigine,  together  with  older  experiments  by  Heidenhain,^  have,  however, 
thrown  some  light  upon  this  difficult  problem,  and  have,  moreover,  opened 
the  way  for  further  experimental  study  of  the  matter.  Heidenhain  cut  out 
a  part  of  the  fundus  of  the  stomach,  converted  it  into  a  blind  sac,  and  brought 
one  end  of  the  sac  to  the  abdominal  wall  so  as  to  form  a  fistulous  opening  to 
the  exterior.  The  contiiuiity  of  the  stomach  was  established  by  suturing  the 
cut  ends,  but  the  fundic  sac  was  completely  separated  from  the  rest  of  the 
alimentary  canal.  He  found  that  under  these  conditions  the  ingestion  of 
ordinary  food  caused  a  secretion  in  the  isolated  and  empty  fundic  sac,  the 
secretion  beginning  fifteen  to  thirty  minutes  after  the  food  was  taken,  and 
continuing  until  the  stomach  was  empty.  The  ingestion  of  water  caused  a 
temporary  secretion  in  the  fundus,  while  indigestible  material  such  as  liga- 
mentum  nuchse  gave  no  secretion  at  all.  Heidenhain's  interpretation  of  these 
experiments  as  applied  to  normal  secretion  was  that  in  ordinary  digestion  we 
must  distinguish  between  a  primary  and  a  secondary  secretion.  The  pri- 
mary secretion  depends  upon  the  mechanical  stimulus  of  the  ingested  food, 
and  is  confined  to  the  spots  directly  stimulated  ;  the  secondary  secretion  begins 
after  absorption  from  the  stomach  is  in  progress,  and  involves  tiie  whole 
secreting  surface.  In  the  experiments  related  above,  the  secretion  from  the 
isolated  fundus  was  a  part  of  this  secondary  secretion.  The  stimulus  in  this 
case  would  seem  to  be  a  chemical  one,  consisting  of  some  of  the  })roducts 
absorbed  from  the  stomach,  which  either  acts  directly  on  the  gastric  glands 
or  indirectly  on  the  intrinsic  nerve-centres  of  the  stomach. 

Khigine  has  made  similar  experiments,  but  altered  the  operation  so  that  the 
isolated  fundic  sac  retained  its  normal  nerve-supply,  which  in  Heidenhain's 
operations  was  apparently  injured.  The  results  which  he  obtained  are  much 
more  complete  than  any  hitherto  reported.  He  was  able  in  the  first  place  to 
determine  the  effect  of  various  diets  upon  the  amount  of  gastric  secretion,  upon 
its  acidity,  and  upon  its  digestive  power,  using  the  secretion  from  the  isolated 
fundic  sac  as  typical  of  what  was  going  on  in  the  rest  of  the  stomach  in  which 
the  food  was  actually  in  process  of  digestion.  One  of  his  curves  showing  the 
effect  of  a  mixed  diet  (milk,  600  cubic  centimeters ;  meat,  100  grams ;  bread,  100 
grams)  is  reproduced  in  Figure  80.  It  will  be  seen  that  the  secretion  began 
shortly  after  the  ingestion  of  food  (seven  minutes)  and  increased  rapidly  to  a 
maximum  which  it  reached  in  two  hours.  After  the  second  hour  the  flow 
decreased  rapidly  and  nearly  uniformly  to  about  the  tenth  hour.  The  acidity 
also  rose  slightly  between  the  first  and  second  hours,  and  then  fell  gradually. 

*  Khigine:  Archives  des  Sciences  biologiques,  St. Petersburg,  1895,  vol.  iii.  p.  461. 
^  Hermann's  Hanclbuch  der  Physiologic,  1883,  Bd.  v.  S.  114. 


182 


^.Y  AMEBICAy    TEXT-BOOK    OF   PHYSIOLOGY. 


The  digestive  power  showed  ii  striking  increase  between  the  second  and 
third  hours.  The  author  gives  other  tables  showing  the  effect  of  a  meat  diet, 
a  milk  diet,  a  bread  diet,  etc.,  which  .seem  to  .sliow  that  a  meat  diet  j)romotes 

th(i  greatest  flow  of  .secretion, 
while  the  bread  diet  gives  a 
secretion  of  more  than  usual 
digestive  power. 

Khigine  attempted  to  deter- 
mine the  effect  of  various  chemi- 
cal substances,  found  in  food 
or  occurring  during  digestion, 
upon  the  flow  of  the  secretion, 
hoping  by  this  means  to  throw 
.some  light  upon  the  nature  of 
the  normal  .stimulus  in  ordinary 
gastric  digestion.  lie  obtained 
practiciilly  negative  results  with 
acids,  alkalies,  and  neutral  .salts; 
none  of  these  substances  when 
introduced  into  the  stomach  had 
any  decisive  effect  upon  the  se- 
cretion in  the  isolated  fundus. 
Water,  however,  was  quite  ef- 
fective ;  the  ingestion  of  500 
cubic  centimeters  produced  a 
marked  and  fairly  long-con- 
tinned  secretion  of  gastric  juice. 

Fig.  80.— Diagram  showing  the  variation  in  quantity  of  But,  SO  far  as  his  experiments 
gastric  secretion  in  the  dog  after  a  mixed  meal :  also  the  . 

variations  in  acidity  and  in  digestive  power  (after  Khigine).       "^^'^"1 5  peptone  IS,  yWT  excellence, 

the  chemical  .stimulus  to  the 
gastric  glands.  The  peptones  caused  an  unusual  secretion  of  gastric  juice, 
although  the  closely  related  products  of  digestion  known  as  proteoses  (see  p. 
230)  had  little  or  no  effect.  It  remains  unsettled,  however,  how  the  water 
and  the  peptones  act— whether  they  arc  ab.sorbed,  as  Heidenhain  thought,  and 
act  as  chemical  stimuli  to  the  glands  or  the  intrin.sic  ganglia  of  the  stomach,  or 
whether,  as  Khigine  believes,  they  are  direct  and  as  it  were  .specific  nerve- 
stimuli  to  the  .sen.sory  nerve-fibres  of  the  mucous  membrane,  and  thus  produce 
a  reflex  effect  upon  the  efferent  secretory  nerves  to  the  gastric  glands.  The 
latter  view  would  be  more  in  accord  with  the  mechanism  of  .secretion  as  we 
know  it  in  the  salivary  glands  and  pancreas,  but  it  cannot  be  .^aid  to  have 
been  demonstrated  as  yet. 

Histological  Changes  in  the  Gastric  Glands  during  Secretion.— The 
cells  of  the  ga.stric  glands,  especially  the  .'^o-called  chief-cells,  show  di.^^tinct 
changes  as  the  result  of  ])rolonged  activity.  Upon  preserved  specimens  taken 
from  dogs  fed  at  intervals  of  twenty-four  hours,  Heidenhain  found  that  in  the 


e 

50.3 

1- 

Quantity  in 
cubic  centi- 
meters. 

Milk,        Meat,        Bread, 
600  c.c.        100  gr.         100  gr. 

10 
8 
6 
4 
2 

0.576 
0.528 
0.480 
0.432 

18 

_ 

/ 

s 

\ 

s 

r« 

\ 

0.384    1      16 

/ 

\ 

0.336 
0.288 
0.240 
0.192 
0.144 
0.0% 
0.048 

14 
\1 
10 
8 
6 
4 
2 
0 

; 

', 

( 

1 

^ 

1 

\ 

\ 

\ 

1 

1 

^^ 

■' 

k 

1 

^ 

; 

X 

; 

'\ 

1' 

\ 

I 

_ 

y 

K 

'r~ 

/' 

/ 

— 

"^ 

\ 

0      1          0 

1 

. 

i  z  s  4  d  6  Y  8  ^  wniz 

Quantity  of  secretion. 
Acidity. 



ige 

su\ 

ep 

\i\\ 

er 

SECRETION. 


183 


fasting  condition  the  chief-cells  were  large  and  clear,  that  during  the  first  six 
hours  of  digestion  the  chief-cells  as  well  as  the  border-cells  iiicreased  in  size, 
but  that  in  a  second  period  extending  from  the  sixth  to  the  fifteenth  hour,  the 
chief-cells  became  gradually  smaller,  svhile  the  border-cells  remained  large  or 
even  increased  in  size.  After  the  fifteenth  hour  the  chief-cells  increased  in 
size,  gradually  passing  back  to  the  fasting  condition  (see  Fig.  81). 


FIG.  81.-Glands  of  the  fundus  (clog) :  A  and  A\  during  hunger  resting  condition ;  B  ^"^^"f  f  ^ /^^ 
stage  of  digestion ;  C  and  D,  the  second  stage  of  digestion,  showing  the  diminution  m  the  sue  of  the 
"  chief"  or  central  cells  lafter  Heidenhain). 

Langley '  has  succeeded  in  following  the  changes  in  a  more  satisfactory 
way  by  observations  made  directly  upon  the  living  gland.  He  finds  that  the 
chief-cells  in  the  fasting  stage  are  charged  with  granules,  and  that  during 
digestion  the  granules  are  used  up,  disappearing  first  from  the  base  ot  the 
cell,  which  then  becomes  filled  with  a  non-granular  material.  Observations 
similar  to  those  made  upon  the  pancreas  demonstrate  that  these  granules 
represent  in  all  probabilitv  a  preliminary  material  from  which  the  gastric 
enzymes  are  made  during  the  act  of  secretion.  The  granules,  therefore,  as  in 
the  other  glands,  mav  be  spoken  of  as  zymogen  granules,  the  preliminary 
material  of  the  pepsin  being  known  as  pepsinogen  and  that  of  the  rennin 
sometimes  as  pexiuogen. 

1  Journal  of  Physiology,  1880,  vol.  iii.  p.  269. 


184  ^iV'  AMERICAN  TEXT- BOOK    OF  PHYSIOLOGY. 

Glands  of  the  Intestine. — At  the  very  beginiiiug  of  the  intestine  in  the 
immediate  neighborhood  of  the  pylorus  is  found  a  small  area  of  mucous  mem- 
brane containing  distinct  tubular  glands  known  usually  as  the  glands  of 
Bruuuer.  These  glands  resemble  closely  in  arrangement  those  of  the  pyloric 
end  of  the  stomach,  with  the  exception  that  the  tubular  duct  is  more  branched. 
The  secreting  cells  are  similar  to  those  of  the  pyloric  glands  of  the  stomach. 
Little  is  known  of  their  secretion.  According  to  some  authors  it  contains 
pepsin.  The  amount  of  secretion  furnished  by  these  glands  would  seem  to 
be  too  small  to  be  of  great  importance  in  digestion.  Throughout  the  length 
of  the  small  and  large  intestine  the  well-known  crypts  of  Lieberkiihn 
are  found.  These  structures  resemble  the  gastric  glands  in  general  appear- 
ance, but  not  in  the  character  of  the  epithelium.  The  epithelium  lining  the 
crypts  is  of  two  varieties — the  goblet  cells,  whose  function  is  to  form  nmcus, 
and  columnar  cells  with  a  characteristic  striated  border.  The  chany;es  in  the 
goblet  cells  during  secretion  and  the  probability  of  a  relationship  between  them 
and  the  neighboring  epithelial  cells  has  been  discussed  (see  p.  157). 
Whether  or  not  the  crypts  form  a  definite  secretion  has  been  much  debated. 
Physiologists  are  accustomed  to  speak  of  an  intestinal  juice,  "  succus  entericus," 
as  being  formed  by  the  glands  of  Lieberkiihn,  but  practically  nothing  is  known 
as  to  the  mechanism  of  the  secretion.  The  succus  entericus  itself,  however  it 
may  be  formed,  can  be  collected  by  isolating  small  loops  of  the  intestine  and 
bringing  the  ends  to  the  abdominal  wall  to  form  fistulous  openings.  The 
secretion  thus  obtained  contains  diastatic  and  also  inverting  ferments,  the  action 
of  which  is  described  on  p.  247.  Histologically,  the  cells  in  the  bottom  of 
the  crypts  do  not  possess  the  general  characteristics  of  secreting  cells. 

D.  Liver  ;  Kidney. 

The  liver  is  a  gland  belonging  to  the  compound  tubular  type.  The 
hepatic  cells  represent  the  secretory  cells  and  the  bile-ducts  carry  off  the 
external  secretion,  which  is  designated  as  bile.  In  addition  it  is  known  that 
the  liver-cells  occasion  important  changes  in  the  material  brought  to  them 
in  the  blood,  and  that  two  important  compounds,  namely,  glycogen  and  urea, 
are  formed  under  the  influence  of  these  cells  and  afterward  are  given  off  to 
the  blood-stream.  The  liver,  then,  furnishes  a  conspicuous  example  of  a 
gland  which  forms  simultaneously  an  external  and  an  internal  secretion.  In 
this  .section  we  have  to  consider  only  certain  facts  in  relation  to  the  external 
secretion,  the  bile. 

Histological  Structure. — The  general  histological  relations  of  the  hepatic 
lobules  need  not  be  repeated  in  detail.  It  will  be  remembered  that  in  each 
lobule  the  hepatic  cells  are  arranged  in  columns  radiating  from  the  central 
vein,  and  that  the  intralobular  capillaries  are  .so  arranged  with  reference  to 
the.se  columns  that  each  cell  is  practically  brought  into  contact  with  a  mixed 
blood  derived  in  part  from  the  portal  vein  and  in  jiart  from  the  hepatic 
artery. 

As  a  gland  making  an  external  secretion,  the  relations  of  the  liver-cells  to 


SECRETION.  185 

the  ducts  and  to  the  nervous  system  are  important  j)oints  t(j  be  determined. 
The  bile-ducts  can  be  traced  without  difficulty  to  the  fine  interhjbular  branches 
running  round  the  periphery  of  the  lobules,  but  the  finer  branches  or  bile- 
capillaries  springing  from  the  interlobular  ducts  and  jjenetrating  into  the  in- 
terior of  the  lobules  luive  been  difficult  to  follow  with  exactness,  especially  as  to 
their  connection  with  the  interlobular  ducts  on  the  one  hand,  and  with  the 
liver-cells  on  the  other.  The  bile-capillaries  have  long  been  known  to  pene- 
trate the  columns  of  cells  in  the  lobule  in  such  a  way  that  each  cell  is  in  con- 
tact with  a  bile-capillary  at  one  point  of  its  periphery,  and  with  a  blood-capil- 
lary at  another,  the  bile-  and  blood-cai)illaries  being  separated  from  each  other 
by  a  portion  of  the  cell-substance.  But  whether  or  not  intracellular  branches 
from  these  capillaries  actually  penetrate  into  the  substance  of  the  liver-cells 
has  been  a  matter  in  dispute.  Kuppfer  contended  that  delicate  ducts  arising 
from  the  capillaries  enter  into  the  cells  and  end  in  a  small  intracellular  vesicle. 
As  this  appearance  was  obtained  by  forcible  injections  through  the  bile-ducts, 
it  was  thought  by  many  to  be  an  artificial  product ;  but  recent  observations 
with  staining  reagents  tend  to  substantiate  the  accuracy  of  Kuj)pfer's  obser- 
vations and  confirm  the  belief  that  normally  the  system  of  bile-ducts  begins 
within  the  liver-cells  in  minute  channels  which  connect  directly  with  the 
bile-capillaries. 

Two  questions  with  reference  to  the  bile-ducts  have  given  rise  to  considerable 
discussion  and  investigation  :  first,  the  relationship  existing  between  the  liver- 
cells  and  the  lining  epithelium  of  the  bile-ducts;  second,  the  presence  or  ab- 
sence of  a  distinct  membranous  wall  for  the  bile-capillaries.  Different  opin- 
ions are  still  held  upon  these  points,  but  the  balance  of  evidence  seems  to  show 
that  the  bile-capillaries  have  no  proper  wall.  They  are  simply  minute  tubular 
spaces  penetrating  between  the  liver-cells  and  corresponding  to  the  alveolar  lu- 
men in  other  glands.  Where  the  capillaries  join  the  interlobular  ducts  the  liver- 
cells  pass  gradually  or  abruptly,  according  to  the  class  of  vertebrates  examined, 
into  the  lining  epithelium  of  the  ducts.  From  this  standpoint,  then,  the  liver- 
cells  are  homologous  to  the  secreting  cells  of  other  glands  in  their  relations  to 
the  general  lining  epithelium.  Several  observers  (MaCallum,^  Berkeley,^  and 
Korolkow^)  have  claimed  that  they  are  able  to  trace  nerve-fibres  to  the 
liver-cells,  thus  furnishing  histological  evidence  that  the  complex  processes  oc- 
curring in  these  cells  are  under  the  regulating  control  of  the  central  nervous 
system.  According  to  the  latest  observers  (Berkeley,  Korolkow)  the  terminal 
nerve-fibrils  end  between  the  liver-cells,  but  do  not  actually  penetrate  the  sub- 
stance of  the  cells,  as  was  described  in  some  earlier  papers.  If  these  observa- 
tions prove  to  be  entirely  correct  they  would  demonstrate  the  direct  effect  of 
the  nervous  system  on  some  at  least  of  the  manifold  activities  of  the  liver- 
cells.  So  far  as  the  formation  of  the  bile  is  concerned  we  have  no  satisfactory 
physiological  evidence  that  it  is  under  the  control  of  the  nervous  system. 

Composition  of  the  Secretion. — The  bile   is  a  colored    secretion.     In 

'  MaCalluru  :   Quarterly  Journal  of  the  Microscopical  Sciences,  1887,  vol.  xxvii.  p.  439. 

^  Berkeley :  Anatomvicher  Anzeiger,  1893,  Bd.  viii.  S.  769.  ^  Korolkow  :  Ibid.,  S.  750. 


186  AN   AMERICAN    TEXT-BOOK    OF    I'll  YSIOLOGY. 

luotit  caruivorous  aninmls  it  is  golden  red,  while  in  the  herbivora  it  is  green, 
the  diflPerence  depending  on  the  character  and  quantity  of  the  pigments.  In 
man  the  bile  is  usually  stated  to  f()lk)\v  the  carnivorous  ty})e,  showing  a  red- 
dish or  brownish  color,  although  in  some  cases  apparently  the  green  predomi- 
nates. The  characteristic  constituents  of  the  bile  are  the  pigments,  bilirubin  in 
carnivorous  bile  and  bilivcnlin  in  herbivorous  bile,  and  the  bile  acids  or  bile- 
salts,  the  sodium  salts  of  glycocholic  or  taurocholic  acid,  the  relative  proportions 
of  the  two  acids  varying  in  different  animals.  In  addition  there  is  present  a 
considerable  quantity  of  a  mucoid  nucleo-albumin,  a  constituent  which  is  not 
formed  in  the  liver-cells,  but  is  added  to  the  secretion  by  the  mucous  membrane 
of  the  bile-ducts  and  gall-bladder;  and  small  quantities  of  cholesterin,  lecithin, 
fats,  and  soaps.  The  inorganic  constituents  comprise  the  usual  salts — chlorides, 
phosphates,  carbonates  and  sulphates  of  the  alkalies  or  alkaline  earths.  Iron 
is  found  in  small  quantities,  combined  probably  as  a  phosphate.  The  secre- 
tion contains  also  a  considerable  though  variable  quantity  of  COg  gas,  held  in 
such  loose  combination  that  it  can  be  extracted  Avith  the  gas-pump  without  the 
addition  of  acid.  The  presence  of  this  constituent  serves  as  an  indication  of 
the  extensive  metabolic  changes  occurring  in  the  liver-cells.  Quantitative 
analyses  of  the  bile  show  that  it  varies  greatly  in  composition  even  in  the  same 
species  of  animal.  Examples  of  this  variability  are  given  in  the  analyses 
quoted  in  the  section  on  Digestion  (p.  261),  where  a  brief  account  will  also  be 
found  of  the  origin  and  physiological  significance  of  the  different  constituents. 
The  Quantity  of  Bile  Secreted. — Owing  to  the  fact  that  a  fistula  of  the 
common  bile-duct  or  gall-bladder  may  be  established  upon  the  living  animal 
and  the  entire  quantity  of  bile  be  drained  to  the  exterior  without  serious  detri- 
ment to  the  animal's  life,  we  possess  numerous  statistics  as  to  the  daily  quantity 
of  the  secretion  formed.  Surgical  operations  upon  human  beings  (see  p.  261 
for  references),  made  necessary  by  occlusion  of  the  bile-passages,  have  furnished 
similar  data  for  man.  In  round  numbers  the  quantity  in  man  varies  from  600 
to  800  cubic  centimeters  per  day,  or,  taking  into  account  the  weight  of  the 
individuals  concerned,  about  8  to  16  cubic  centimeters  for  each  kilogram  of 
body-weight.  Observations  upon  the  lower  animals  indicate  that  the  secretion 
is  proportionally  greater  in  smaller  animals.  This  fact  is  clearly  shown  in  the 
following  table,  compiled  l)y  Ileidenhain  '  for  three  herbivorous  animals: 

Sheep.  Rabbit.        Guinea-pig. 

Ratio  of  bile-weight  for  24  liours  to  body-weiglit   .    .    .  1 :  37.5  1 :  8.2  1 :  5.6 

Ratio  of  bile-weight  for  24  hours  to  liver-weight  .    .    .  1.507  : 1         4.064  :  1         4.467  : 1 

There  .seems  to  be  no  doubt  that  the  bile  is  a  continuous  secretion,  although 
in  animals  possessing  a  gall-bladder  the  .secretion  may  be  stored  in  this  reser- 
voir and  ejected  into  the  duodenum  only  at  certain  intervals  connected  with 
the  processes  of  digestion.  The  movement  of  the  bile-stream  within  the 
system  of  bile-ducts — that  is,  its  actual  ejection  from  the  liver,  is  al.^o  probably 
intermittent.     The  observations  of  Copeman  and  Winston  on  a  human  patient 

^  Hermann's  Handbuch  dei-  Physiologie,  vol.  v.  Thl.  1,  p.  253. 


SECRETION.  187 

with  a  biliary  fistula  showed  that  the  secretion  was  ejected  in  spirts,  owing 
doubtless  to  contractions  of  the  muscular  walls  of  the  larger  bile-ducts.  But 
though  continuously  formed  within  the  liver-cells,  the  flow  of  bile  is  subject 
to  considerable  variations.  According  to  most  observers  the  activity  of  secre- 
tion is  definitely  connected  with  the  period  of  digestion.  Somewhere  from  the 
third  to  the  fifth  hour  after  the  beginning  of  digestion  there  is  a  very  marked 
acceleratit)n  of  the  flow,  and  a  second  maximum  at  a  later  period,  ninth  to 
tenth  hour  (Iloppe-Seyler),  has  been  observed  in  dogs.  The  mechanism  con- 
trolling the  accelerated  flow  during  the  third  to  the  fifth  hour  is  not  perfectly 
understood.  It  would  seem  to  be  correlated  with  the  digestive  changes  occur- 
ring in  the  intestine,  but  whether  the  relationship  is  of  the  nature  of  a  reflex 
nervous  act,  or  whether  it  depends  on  increased  blood-flow  through  the  organ 
or  upon  some  action  of  the  absorbed  products  of  secretion  remains  to  be  deter- 
mined. It  has  been  shown  that  the  presence  of  bile  in  the  blood  acts  as  a 
stimulus  to  the  liver-cells,  aud  it  is  highly  probable  that  the  absorption  of  bile 
from  the  intestine  which  occurs  during  digestion  serves  to  accelerate  the  secre- 
tion ;  but  this  circumstance  obviously  does  not  account  for  the  marked  increase 
observed  in  animals  with  biliary  fistulas,  since  in  these  cases  the  bile  does  not 
reach  the  intestine  at  all.  Some  imperfect  observations  by  Bidder  and  Schmidt 
indicate  that  the  total  quantity  of  bile  varies  with  the  character  of  the  food, 
being  larger  upon  a  meat  diet  than  when  the  subject  is  fed  exclusively  upon 
fats.     Exact  data  as  to  the  effect  of  the  different  food-stuffs  are  lacking. 

Relation  of  the  Secretion  of  Bile  to  the  Blood-flow  in  the  Liver. — 
Numerous  experiments  have  shown  that  the  quantity  of  bile  formed  by  the 
liver  varies  more  or  less  directly  with  the  quantity  of  blood  flowing  through 
the  organ.  The  liver-cells  receive  blood  from  two  sources,  the  portal  vein 
and  the  hepatic  artery.  The  supply  from  both  these  sources  is  probably  essen- 
tial to  the  perfectly  normal  activity  of  the  cells,  but  it  has  been  shown  that  bile 
continues  to  be  formed,  for  a  time  at  least,  when  either  the  portal  or  the  arterial 
supply  is  occluded.  However,  there  can  be  little  doubt  that  the  material  actually 
utilized  by  the  liver-cells  in  the  formation  of  their  external  and  internal  secre- 
tions is  brought  to  them  mainly  by  the  portal  vein,  and  that  variations  in  the 
quantity  of  this  supply  influences  directly  the  amount  of  bile  produced.  Thus, 
occlusion  of  some  of  the  branches  of  the  portal  vein  diminishes  the  secretion ; 
stimulation  of  the  spinal  cord  diminishes  the  secretion,  since,  owing  to  the  large 
vascular  constriction  produced  thereby  in  the  abdominal  viscera,  the  quantity  of 
blood  in  the  portal  circulation  is  reduced  ;  section  of  the  spinal  cord  also  dimin- 
ishes the  flow  of  bile  or  may  even  stop  it  altogether,  since  the  result  of  such  an 
operation  is  a  general  paralysis  of  vascular  tone  and  a  general  fall  of  blood- 
pressure  aud  velocity  ;  stimulation  of  the  cut  splanchnic  nerves  diminishes  the 
secretion  because  of  the  strong  constriction  of  the  blood-vessels  of  the  abdom- 
inal viscera  and  the  resulting  diminution  of  the  quantity  of  the  blood  in  the 
portal  circulation  ;  section  of  the  splanchnics  alone,  however,  is  said  to  increase 
the  quantity  of  bile,  in  dogs,  since  in  this  case  the  paralysis  of  vascular  tone 
is  localized  in  the  abdominal  viscera.     The  effect  of  such  a  local  dilatation  of 


188  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

the  blood-vessels  would  be  to  diniinish  the  resistance  alonj:;  the  intestinal 
paths,  and  thus  lead  to  a  greater  flow  of  blood  to  that  area  and  the  portal 
circulation. 

In  all  these  cases  one  might  suppose  that  the  greater  or  less  quantity  of 
bile  formed  depended  oidy  on  the  blood-pressure  in  the  capillaries  of  the  liver 
lobules — that  so  far  at  least  as  the  water  of  the  bile  is  concerned  it  is  produced 
by  a  process  of  filtration  and  rises  and  fiills  with  the  blood-pressure.  That 
this  simple  mechanicid  explanation  is  not  sufficient  seems  to  be  proved  by  the 
fact  that  the  pressure  of  bile  within  the  bile-ducts,  although  comparatively 
low,  may  exceed  that  of  the  blood  in  the  portal  vein.  While  it  is  not  possible, 
therefore,  to  exclude  entirely  the  factor  of  filtration,  it  is  evident  that  the 
quantity  of  secretion  depends  largely  on  the  mere  quantity  of  blood  flowing 
by  the  cells  in  a  unit  of  time. 

The  Existence  of  Secretory  Nerves  to  the  Liver. — The  numerous 
experiments  that  have  been  made  to  ascertain  whether  or  not  the  secretion 
of  bile  is  under  the  direct  control  of  secretory  nerves  have  given  unsatisfactory 
results.  The  experiments  are  difficult,  since  stimulation  of  the  nerves  supply- 
ing the  liver,  such  as  the  splanchnic,  is  accompanied  by  vaso-motor  changes 
which  alter  the  blood-flow  to  the  organ  and  thus  introduce  a  factor  which  in 
itself  influences  the  amount  of  the  secretion.  So  far  as  our  actual  knowledge 
goes,  the  physiological  evidence  is  against  the  existence  of  secretory  nerve- 
fibres  controlling  the  formation  of  bile.  On  the  other  hand,  there  are  some 
experiments,'  although  they  are  not  perfectly  conclusive,  which  indicate  that 
the  glycogen  formation  within  the  liver-cells  is  influenced  by  a  special  set  of 
glyco-secretory  nerve-filn-es.  This  fact,  however,  does  not  bear  directly  upon 
the  formation  of  bile. 

Motor  Nerves  of  the  Bile-vessels. — Doyon  ^  has  recently  shown  that  the 
gall-bladder  as  well  as  the  bile-ducts  is  innervated  by  a  set  of  nerve-fibres 
comparable  in  their  general  action  to  the  vaso-constrictor  and  vaso-dilator 
fibres  of  the  blood-vessels.  According  to  this  author,  stimidatiou  of  the 
peripheral  end  of  the  cut  splanchnics  causes  a  contraction  of  the  bile-ducts 
and  gall-bladder,  while  stimulation  of  the  central  end  of  the  same  nerve,  on 
the  contrary,  brings  about  a  reflex  dilatation.  Stimulation  of  the  central  end 
of  the  vagus  nerve  causes  a  contraction  of  the  gall-bladder  and  at  the  same 
time  an  inhibition  of  the  sphincter  muscle  closing  the  opening  of  the  common 
bile-duct  into  the  duodenum.  These  facts  need  confirmation,  perhaps,  on  the 
part  of  other  observers,  although  they  are  in  accord  with  what  is  known  of 
the  actual  movement  of  the  bile-stream.  The  ejection  of  bile  from  the  gall- 
bladder into  the  duodenum  is  produced  by  a  contraction  of  the  gall-bladder, 
and  it  is  usually  believed  that  this  contraction  is  brought  about  reflexly  from 
some  sensory  stimulation  of  the  mucous  membrane  of  the  duodenum  or 
stomach.  The  result  of  the  experiments  made  by  Doyon  would  indicate  that 
the  afferent  fibres  of  this  reflex  pass  upward  in  the  vagus,  while  the  efferent 

'  Moral  and  Dufoiirt:  Archives  de  Physiologit,  1894,  p.  371. 
"^  Archives  de  Physiologic,  1894,  p.  19. 


SECRETION.  189 

fibres  to  the  ^all-bladdor  riiii  in  tho  splanchnics  and  reach  the  liver  through 
the  seniihuiar  plrxns. 

Normal  Mechanism  of  the  Bile-secretion. — Bearing  in  mind  the  fact 
tliat  our  knowledge  of  the  secretion  of  bile  is  in  many  respects  incomplete, 
and  that  any  theory  of  the  act  is  therefore  only  provisional,  wa  might  picture 
the  processes  concerned  in  the  secretion  and  ejection  of  bile  as  f<)llo\vs:  The 
bile  is  steadily  formed  by  the  liver-cells  and  turned  out  into  the  bile-capil- 
laries ;  its  quantity  varies  with  the  quantity  and  composition  of  the  blood 
flowing  through  the  liver,  but  the  formation  of  the  secretion  depends  upon 
the  activities  taking  place  in  the  liver-cells,  and  these  activities  are  independ- 
ent of  direct  nervous  control.  During  the  act  of  digestion  the  formation  of 
bile  is  increased,  owing  probably  to  a  greater  blood-flow  through  the  organ 
and  to  the  generally  increased  metabolic  activity  of  the  liver-cells  occasioned 
by  the  inflow  of  the  absorbed  products  of  digestion.  The  bile  after  it  gets 
into  the  bile-ducts  is  moved  onward  partly  by  the  accumulation  of  new  bile 
from  behind,  the  secretory  force  of  the  cells,  and  partly  by  the  contractions 
of  the  walls  of  the  bile-vessels.  It  is  stored  in  the  gall-bladder,  and  at  inter- 
vals during  digestion  is  forced  into  the  duodenum  by  a  contraction  of  the 
muscular  walls  of  the  bladder,  the  process  being  aided  by  the  simultaneous 
relaxation  of  a  sphincter-like  layer  of  muscle  which  normally  occludes  the 
bile-duct  at  its  opening  into  the  intestine;  both  these  last  acts  are  under  the 
control  of  a  nervous  reflex  mechanism. 

Efifect  of  Complete  Occlusion  of  the  Bile-duct. — It  is  an  interesting 
fact  that  wdien  the  flow  of  bile  is  completely  prevented  by  ligation  of  the  bile- 
duct,  the  stagnant  liquid  is  not  reabsorbed  by  the  blood  directly,  but  by  the 
lymphatics  of  the  liver.  The  bile-pigments  and  bile-acids  in  such  cases  may 
be  detected  in  the  lymph  as  it  flows  from  the  thoracic  duct.  In  this  way  they 
get  into  the  blood,  producing  a  jaundiced  condition.  The  way  in  which  the 
bile  gets  from  the  bile-ducts  into  the  hepatic  lymphatics  is  not  definitely  known, 
but  probably  it  is  due  to  a  rupture,  caused  by  the  increased  pressure,  at  some 
point  in  the  course  of  the  delicate  bile-capillaries. 

Kidney. 

Histology. — The  kidney  is  a  compound  tubular  gland.  The  constituent 
uriniferous  tubules  composing  it  may  be  roughly  separated  into  a  secreting 
part  comprising  the  capsule,  convoluted  tubes,  and  loop  of  Henle,  and  a  col- 
lecting part,  the  so-called  straight  collecting-tube,  the  epithelium  of  Avhich  is 
assumed  not  to  have  any  secretory  function.  AVithin  the  secreting  part  the 
epithelium  differs  greatly  in  character  in  different  regions ;  its  peculiarities 
may  be  referred  to  briefly  here  so  far  as  they  seem  to  have  a  physiological 
bearing,  although  for  a  complete  description  reference  must  be  made  to  some 
work  on  Histology. 

The  arrangement  of  the  glandular  epithelium  in  the  capsule  with  reference 
to  the  blood-vessels  of  the  glomerulus  is  worthy  of  special  attention.  It  will 
be  remembered  that  each  Malpighiau  corpuscle  consists  of  two  principal  parts, 


190 


AN   AMERICAN    TEXT-BOOK    OF    PHYSIOLOGY. 


a  tuft  of  blood-vessels,  the  glonierulu.s,  ami  an  onvel()j)iiii^  exj)an.sion  of  the 
uniferous  tubule,  the  capsule.  The  glomerulus  is  a  remarkable  structure  (see 
Fig.  82,  A).  It  consists  of  a  small  afferent  artery  which  after  entering  the 
glomerulus  breaks  up  into  a  number  of  capillaries,  which,  though  twisted 
together,  do  not  anastomose.  These  capillaries  unite  to  form  a  single  etlerent 
vein  of  a  smaller  diameter  than  the  afferent  artery.     The  whole  structure, 


Fig.  S2.— Portions  of  the  various  divisions  of  the  uriniferous  tubules  drawn  from  sections  of  human 
kidney :  A,  Malpighian  body ;  x,  squamous  epithelium  lining  the  capsule  and  reflected  over  the  glomer- 
ulus ;  I/,  :,  afferent  and  efferent  vessels  of  the  tuft :  e.  nuclei  of  capillaries ;  n,  constricted  neck  marking 
passage  of  capsule  into  convoluted  tubule  ;  B,  proximal  convoluted  tubule ;  C,  irregular  tubule ;  D  and 
F,  spiral  tubules ;  E,  ascending  limb  of  Henle's  loop;  G,  straight  collecting  tubule  (Piersol). 

therefore,  is  not  an  oidinary  capillary  area,  but  a  rete  mirabile,  and  the  phys- 
ical factors  are  such  that  within  the  capillaries  of  the  rete  there  must  be  a 
greatly  diminished  velocity  of  the  blood-stream  owing  to  the  great  increase 
in  the  width  of  the  stream-bed  and  a  high  blood-pressure  as  compared  with 
ordinary  capillaries.  Surrounding  this  glomerulus  is  the  double-walled  capsule. 
One  wall  of  the  caj>sule  is  closely  adherent  to  the  capillaries  of  the  glomerulus; 
it  not  only  covers  the  structure  closely,  but  dips  into  the  interior  between  the 
small  lobules  into  which  the  glomerulus  is  divided.  This  layer  of  the  capsule 
is  composed  of  flattened  ondothelial-like  cells,  the  glomerular  epithelium,  to 
which  great  imjiortance  is  now  attached  in  the  formation  of  the  secretion.  It 
will  be  noticed  that  between  theinteriorof  the  blood-vessels  of  the  glomerulus  and 
the  cavity  of  the  capsule  which  is  the  beginning  of  the  uriniferous  tubule  there 
are  interposed  only  two  very  thin  layers,  namely,  the  epithelium  of  the  capil- 
lary wall  and  the  glomerular  epithelium.  The  apparatus  would  seem  to  afford 
most  favorable  conditions  for  filtration  of  the  liquid  ]>arls  of  the  blood.  The 
epithelium  clothing  the  convoluted  portions  of  the  tubule,  including  under  this 
designation  the  so-called  irregular  and  spiral  portions  and  the  loop  of  Henle,  is 
of  a  character  quite  different  from  that  of  the  glomerular  epithelium  (Fig.  82,  B, 
C,  D,  E,  F,  G).  The  cells,  speaking  generally,  are  cuboidal  or  cylindrical,  proto- 
plasmic, and  granular  in  appearance  ;  on  the  side  toward  the  basement  mem- 
brane they  often  show  a  peculiar  striation,  while  on  the  lumen  side  the  extreme 


SECRETION.  191 

periphery  presents  a  compact  border  wliicli  in  some  cases  shows  a  cilia-like 
striation.  These  cells  have  the  general  appearance  of  active  secretory  struc- 
tures, and  recent  theories  of  urinary  secretion  attribute  this  importance  to  them. 

Composition  of  Urine. — The  chemical  composition  of  the  urine  is  very 
complex,  as  we  should  expect  it  to  be  when  we  remember  that  it  contains  most 
of  the  end-products  of  the  varied  metabolism  of  the  body,  its  importance  in 
this  respect  being  greater  than  the  other  excretory  organs  such  as  the  lungs,  skin, 
and  intestine.  The  secretion  is  a  yellovvish  liquid  which  in  carnivorous  ani- 
mals and  in  man  has  normally  an  acid  reaction,  owing  to  the  presence  of  acid 
salts  (acid  sodium  and  acid  calcium  phosphate),  and  an  average  specific  gravity 
of  1017  to  1020.  The  quantity  formed  in  twenty-four  hours  is  about  1200  to 
1700  cubic  centimeters.  In  the  very  young  the  amount  of  urine  formed  is 
proportionately  much  greater  than  in  the  adult.  The  normal  urine  contains 
about  3.4  to  4  per  cent,  of  solid  material,  of  which  over  half  is  organic  mate- 
rial. Among  the  important  organic  constituents  of  the  urine  are  the  follow- 
ing :  urea,  uric  acid,  hippuric  acid,  xanthin,  hypoxanthin,  guanin,  creatinin 
and  aromatic  oxy-  acids  (para-oxypheuyl  ])ropionic  acid  and  para-oxyphenyl 
acetic  acid,  as  simple  salts  or  combined  with  sulphuric  acid) ;  phenol,  paracre- 
sol,  pyrocatechin  and  hydrochinon,  these  four  substances  being  combined  with 
sulphuric  or  glycuronic  acid ;  indican  or  indoxyl  sulphuric  acid  ;  skatol  sul- 
phuric acid  ;  oxalic  acid  ;  sulphocyanides,  etc.  These  and  other  organic  con- 
stituents occurring  under  certain  conditions  of  health  or  disease  in  various 
animals,  are  of  the  greatest  importance  in  enabling  us  to  follow  the  metab- 
olism of  the  body.  Something  as  to  their  origin  and  significance  will  be 
found  in  the  section  on  Nutrition,  while  their  purely  chemical  relations 
are  described  in  the  section  on  Chemistry. 

Among  the  inorganic  constituents  of  the  urine  may  be  mentioned  sodium 
chloride,  sulphates,  phosphates  of  the  alkalies  and  alkaline  earths,  nitrates,  and 
carbon  dioxide  gas  partly  in  solution  and  partly  as  carbonate.  In  this  section 
we  are  concerned  only  with  the  general  mechanism  of  the  secretion  of  urine, 
and  in  this  connection  have  to  consider  mainly  the  water  and  soluble  inorganic 
salts  and  the  typical  nitrogenous  excreta,  namely,  urea  and  uric  acid. 

The  Secretion  of  Urine. — The  kidneys  receive  a  rich  supply  of  nerve- 
fibres,  but  most  histologists  have  been  unable  to  trace  any  connection  between 
these  fibres  and  the  epithelial  cells  of  the  kidney  tubules.  Berkeley^  has,  how- 
ever, recently  discovered  nerve-fibres  passing  through  the  basement  membrane 
and  ending  between  the  secretory  cells. 

The  majority  of  purely  physiological  experiments  upon  direct  stimulation  of 
the  nerves  going  to  the  kidney  are  adverse  to  the  theory  of  secretory  fibres,  the 
marked  effects  obtained  in  these  experiments  being  all  explicable  by  the  changes 
produced  in  the  blood-flow  through  the  organ.  Two  general  theories  of  urinary 
secretion  have  been  proposed.  Ludwig  held  that  the  urine  is  formed  by  the 
simple  physical  processes  of  filtration  and  diffusion.  In  the  glomeruli  the 
conditions  are  most  favorable  to  filtration,  and  he  supposed  that  in  these  struc- 
'  The  Johns  Hopkins  Hospital  Bulletin,  vol.  iv.,  No.  28,  p.  1. 


192  AN  AMERICAN    TEXT-BOOK    OF    PHYSIOLOGY. 

tares  water  filtered  tlirough  from  tlie  blood,  earrying  with  it  not  only  the  iu- 
orgauic  salts,  but  also  the  specific  elements  (urea)  of  the  secretion.  There  was 
thus  formed  at  the  beginning  of  the  uriniferous  tubules  a  complete  but  diluted 
urine,  and  in  the  subsequent  passage  of  this  liquid  along  the  convoluted  tubes 
it  became  concentrated  by  ditfusion  with  the  lymph  surrounding  the  outside 
of  the  tubules.  So  far  as  the  latter  part  of  this  theory  is  concerned  it  has 
not  been  supported  by  actual  experiments;  recent  histological  work  (see  below) 
seems  to  indicate  that  the  epithelial  cells  of  the  convoluted  tubules  have  a 
distinct  secretory  function,  and  that  they  give  material  to  the  secretion  rather 
than  take  from  it. 

Bowman's  theory  of  urinary  secretion,  which  has  since  been  vigorously 
supported  and  extended  by  Heidenhain,  was  based  apparently  mainly  on  his- 
tological grounds.  It  assumes  that  in  the  glomeruli  water  and  inorganic  salts 
are  produced,  while  the  urea  and  related  bodies  are  eliminated  through  the 
activity  of  the  epithelial  cells  in  the  convoluted  tubes. 

Elmiinaiion  of  Urea  and  Related  Bodies. — Numerous  facts  have  been 
discovered  which  tend  to  support  the  latter  part  of  Bowman's  theory — namely, 
the  participation  of  the  cells  of  the  convoluted  tubules  in  the  secretion  of  the 
specific  nitrogenous  elements.  In  birds  the  main  nitrogenous  element  of  the 
secretion  is  uric  acid  instead  of  urea,  and  it  is  possible,  owing  to  the  small  solu- 
bility of  the  urates,  to  see  them  as  solid  deposits  in  microscopic  sections  of  the 
kidney.  When  the  ureters  are  ligated  the  deposition  of  the  urates  in  the  kid- 
ney may  become  so  great  as  to  give  the  entire  organ  a  whitish  appearance. 
Nevertheless  histological  examinations  of  a  kidney  in  this  condition  shows  that 
the  urates  are  found  always  in  the  tubes  and  never  in  the  Malpighian  corpus- 
cles. From  this  result  we  may  conclude  that  the  uric  acid  is  eliminated 
through  the  epithelial  cells  of  the  tubes.  Heidenhain  has  shown  by  a  striking 
series  of  experiments  that  the  cells  of  the  tubes  possess  an  active  secretory 
power.  In  these  experiments  a  solution  of  indigo-carmine  was  injected  into 
the  circulation  of  a  living  animal  after  its  spinal  cord  had  been  cut  to  reduce 
the  blood-pressure  and  therefore  the  rapidity  of  the  secretion.  After  a  certain 
interval  the  kidneys  were  removed  and  the  indigo-carmine  precipitated  in  situ 
in  the  kidney  by  injecting  alcohol  into  the  blood-vessels.  It  was  found  that 
the  pigment  granules  were  deposited  in  the  convoluted  tubes,  but  never  in  the 
^Malpighian  corpuscles. 

Still  further  proof  of  definite  secretory  functions  on  the  part  of  the  cells 
of  the  tubules  is  given  by  the  results  of  recent  histological  work  upon  the 
changes  in  the  cells  during  activity.  Van  der  Stricht*  and  Disse'*  both 
describe  definite  morphological  changes  in  the  epithelial  cells  of  the  convoluted 
tubes  and  ascending  loop  of  Henle  which  they  connect  with  the  functional 
activity  of  the  cells.  The  details  of  the  descriptions  diifer,  but  the  two  authors 
agree  in  finding  that  the  material  of  the  secretion  collects  in  the  interior  of  the 

'  Comptes  rendua,  1891,  and  Travail  du  Lahoratoire  d'Histolugie  de  I'  Unircrsile  dr  Gand,  1892. 
"  Referate  und  Beitrage  zur  ATiatomie  und  Entwickelungsgesckichte  (anatomische  Hefte),  Merkel 
and  Bonnet,  1893. 


SECRETION.  193 

cell  to  form  a  vesicle  wliicii  is  alterwurcl  (iiseliarged  into  the  lumen  of  the  cell. 
According  to  Disse  the  inactive  cells  are  small  and  granular,  and  toward  the 
lumen  show  a  striated  border  of  minute  processes,  while  the  lumen  of  the  tube 
is  relatively  wide.  As  the  fluid  secretion  accumulates  in  the  cells  it  may  be 
distinguished  as  a  clear  vesicular  area  near  the  nucleus.  The  cells  enlarge 
and  project  toward  the  lumen,  which  becomes  smaller;  the  striated  border  dis- 
appears. Finally  the  swollen  cells  fill  the  entire  canal,  and  the  liquid  secre- 
tion is  emptietl  from  the  cells  by  filtration.  Van  dcr  Stricht  believes  that  the 
vesicles  rupture  the  cells  and  thus  are  cast  out  into  the  lumen.  In  hmgitudinal 
sections  various  stages  in  the  process  may  be  seen  scattered  along  the  length 
of  a  single  tubule. 

Seo-etion  of  the  Water  and  Salts. — There  seems  to  be  no  question  that  the 
elimination  of  N^iiter  together  with  inorganic  salts,  and  probably  still  other 
soluble  constituents,  takes  place  chiefly  through  the  glomerular  epithelium. 
This  supposition  is  made  in  both  the  general  theories  that  have  been  men- 
tioned. It  has,  however,  long  been  a  matter  of  controversy,  in  this  as  in 
other  glands,  whether  the  water  is  produced  by  simple  filtration  or  whether 
the  glomerular  epithelium  takes  an  active  part  of  some  character  in  setting  up 
the  stream  of  water.  The  problem  is  perhaps  simpler  in  this  case  than  in  the 
salivary  glands,  since  the  direct  participation  of  secretory  nerves  in  the  process 
is  excluded.  On  the  filtration  theory  the  quantity  of  urine  should  vary 
directly  with  the  blood-pressure  in  the  glomerulus.  This  relationship  has 
been  accepted  as  a  crucial  test  of  the  validity  of  the  filtration  theory,  and 
numerous  experiments  have  been  made  to  ascertain  whether  it  invariably 
exists.  Speaking  broadly,  any  general  rise  of  blood-pressure  in  the  aorta  will 
occasion  a  greater  blood-flow  and  greater  pressure  in  the  glomerular  vessels 
provided  the  kidney  arteries  themselves  are  not  simultaneously  constricted  to 
a  sufficient  extent  to  counteract  this  favorable  influence ;  whereas  a  general  fall 
of  pressure  should  have  the  opposite  influence  both  on  pressure  and  velocity  of 
flow.  It  has  been  shown  experimentally  that  if  the  general  arterial  pressure 
falls  below  40  or  50  millimeters  of  mercury,  as  may  happen  after  section  of 
the  spinal  cord  in  the  cervical  region,  the  secretion  of  the  urine  will  be  greatly 
slowed,  or  suspended  completely.  Constriction  of  the  small  arteries  in  the 
kidney,  whether  effected  through  its  proper  vaso-constrictor  nerves  or  by  par- 
tially clamping  its  arteries,  causes  a  diminution  in  the  secretion  and  at  the 
same  time  in  all  probability  a  fall  of  pressure  within  the  glomeruli  and  a 
diminution  in  the  total  flow  of  blood.  On  the  other  hand,  dilatation  of  the 
arteries  of  the  kidney,  whether  produced  through  its  vaso-dilator  fibres  or  by 
section  or  inhibition  of  its  constrictor  fibres,  augments  the  flow  of  urine  and 
at  the  same  time  probably  increases  the  pressure  within  the  glomerular  capil- 
laries, and  also  the  total  quantity  of  blood  flowing  through  them  in  a  unit  of 
time.  From  these  and  other  experimental  facts  it  is  evident  that  the  amount 
of  secretion  and  the  amount  of  pressure  wathin  the  glomerular  vessels  do  often 
vary  together,  and  this  relationship  has  been  used  to  prove  that  the  water  of 
the  secretion  is  obtained  by  filtration  from  the  blood-plasma.     But  it  will  be 

13 


194  AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

observed  that  the  qiumtity  of  secretion  varies  not  only  with  the  ])ressure  of 
the  l)K)o(l  within  the  glomeruli,  hut  also  with  the  (jnantity  ol"  blood  flowing 
through  them.  Heidenhain  has  insisted  that  it  is  this  latter  factor  and  not 
the  intracapillary  pressure  which  determines  the  quantity  of  water  secreted. 
He  believes  that  the  glomerular  epithelial  cells  possess  the  property  of  actively 
secreting  water,  and  that  they  are  not  sim])ly  passive  filters ;  that  the  forma- 
tion, in  other  w^ords,  is  not  a  simple  mechanical  process,  but  a  more  complex 
one  depending  upon  the  living  structure  and  proj)crties  of  the  epithelial  cells. 
In  support  of  this  view  he  quotes  the  fact  that  partial  compression  of  the 
renal  veins  quickly  slows  or  stops  altogether  the  flow  of  urine.  Compression 
of  the  veins  should  raise  the  pressure  within  the  vessels  of  the  glomeruli,  and 
upon  the  filtration  hypothesis  should  increase  rather  than  diminish  the  secre- 
tion. It  has  been  shown  also  that  if  the  renal  artery  is  compressed  for  a 
short  time  so  as  to  completely  shut  off  the  blood-flow  to  the  kidney  the 
secretion  is  not  only  suspended  during  the  closure  of  the  arteries  but  for  a 
long  time  after  the  circulation  is  re-established.  According  to  Tiegerstedt, 
if  the  renal  artery  is  ligated  for  only  half  a  minute  the  activity  of  the 
kidney  is  suspended  for  three-quarters  of  an  hour.  This  fact  is  difficult  to 
understand  if  the  glomerular  epithelium  is  simply  a  filtering  membrane,  but 
it  is  easily  explicable  upon  the  hypothesis  that  the  epithelial  cells  are  actively 
concerned  in  the  production  of  the  water. 

Much  of  the  recent  work  upon  the  secretion  of  urine  tends  to  support 
Heidenhain's  opinion.  Munk  ^  and  Senator  made  careful  experiments  upon 
excisecl  kidneys  which  were  kept  alive  and  in  functional  activity  by  an  arti- 
ficial supply  of  blood,  and  w^ere  able  to  show  that  the  quantity  of  the  secretion 
depended  less  on  the  blood-})ressure  than  on  the  rate  of  flow.  So,  numerous 
experiments  upon  the  action  of  diuretics  ^  such  as  NaCl,  KNO3,  and  cafFein 
seem  to  have  shown  distinctly  that  the  increased  flow  of  blood  caused  by  these 
substances  cannot  be  explained  upon  the  filtration  hy})othesis,  and  that  we 
must  suppose  that  they  have  a  specific  action  upon  the  kidney-cells,  particularly 
the  epithelial  cells  covering  the  glomeruli. 

We  may  assume,  therefore,  until  the  contrary  is  proved,  that  the  larger 
Ipart  of  the  water  and  inorganic  salts  of  the  urine  is  secreted  at  the  capsular 
[end  of  the  uriniferous  tubule  by  a  definite  action  of  the  living  epithelial  cells. 
It  must  be  borne  in  mind,  however,  that  some  water  and  probably  also  some 
of  the  inorganic  salts  are  secreted  at  other  parts  of  the  tubule  along  with  the 
elimination  of  the  nitroo-enous  wastes.  It  is  of  interest  to  add  that  the  most 
important  of  the  abnormal  constituents  of  the  urine  under  pathological  con- 
ditions, such  as  the  albumin  in  albuminuria,  the  ha?moglobin  in  htemoglo- 
biuuria,  and  the  sugar  in  glycosuria,  seem  likewise  to  escape  from  the  blood 
into  the  kidney  tubules  through  the  glomerular  epithelium. 

Theoretical  Considerations. — Granting  that  the  glomerular  epithelium 

^  Virchow's  Archiv  fur  pathologische  Anatornie  nnd  Phy^olocfie,  etc.,  M.  cxiv.,  1888. 
*  See  Von  Scliroeder:   Archiv  fur  exper.  Pathologie  und  PharmakoL,  Bd.  xxiv.  S.  85,  and 
Dreser,  Ibid.,  1892,  Bd.  xxix.  S.  303. 


SECRETION.  195 

takes  an  active  part  in  directing  the  stream  of  water  from  the  blood  to  the 
uriniferous  tubules,  it  is  natural  to  ask  by  what  mechanism  this  action  is 
effected.  The  problem  is  essentially  similar  to  that  already  encountered  in 
explaining  the  flow  of  water  in  other  glands  (see  p.  166).  There  is  as  yet  no 
satisfactory  explanation  given.  It  is  to  be  supposed  that  this  property  is 
dependent  upon  some  physical  or  chemical  reaction  of  the  substance  of  the 
cell,  and  involves  the  existence  of  no  form  of  energy  not  already  known  to  us 
in  other  ways ;  but  what  tlie  nature  of  these  reactions  is  must  be  left  for 
future  work.  The  extent  of  the  activity  seems  to  depend  mainly  on  the 
quantity  of  blood  flowing  through  the  glomeridi.  The  greater  the  quantity 
of  blood,  the  greater  will  be  the  quantity  of  water  brought  to  the  cells,  and 
the  more  complete  also  the  supply  of  needful  oxygen.  In  addition,  substances, 
such  as  the  inorganic  salts,  which  occur  normally  in  the  blood,  or  other  sub- 
stances which  may  be  introduced  therapeutically,  may  act  as  chemical  irritants 
to  these  cells,  and  thus  increase  their  secretory  activity.  The  normal  stimulus 
to  the  epithelial  cells  of  the  convoluted  tubules,  using  the  term  convoluted  to  in- 
clude the  actively  secreting  parts,  seems  to  be  the  presence  of  urea  and  related 
substances  in  the  blood  (lymph).  That  the  elimination  of  the  urea  is  not  a  simple 
act  of  diffusion  seems  to  be  clearly  shown  by  the  fact  that  its  percentage  in  the 
blood  is  much  less  than  in  the  urine.  In  some  way  the  urea  is  selected  from 
the  blood  and  passed  into  the  lumen  of  the  tubule,  and  although  we  have 
microscopic  evidence  that  this  process  involves  very  active  changes  in  the  sub- 
stance of  the  cells,  there  is  no  adequate  theory  of  the  nature  of  the  force  which 
attracts  the  urea  from  the  surrounding  lymph.  The  whole  process  must  be 
rapidly  effected  by  the  cell,  since  there  is  normally  no  heaping  up  of  urea  in 
the  kidney-cells;  the  material  is  eliminated  into  the  tubules  as  quickly  as  it 
is  received  from  the  blood.  The  rate  of  elimination  increases  normally  with 
the  increase  in  the  urea  in  the  blood,  as  would  be  expected  upon  the  assump- 
tion that  the  urea  itself  acts  as  the  physiological  stimulus  to  the  epithelial 
cells. 

The  Blood-flow  through  the  Kidneys. — It  will  be  seen  from  the  dis- 
cussion above  that,  other  conditions  remaining  the  same,  the  secretion  of  the 
kidney  varies  with  the  quantity  of  blood  flowing  through  it.  It  is  therefore 
important  at  this  point  to  refer  briefly  to  the  nature  and  especially  the  regula- 
tion of  the  blood-flow  through  this  organ,  although  the  same  subject  is  referred 
to  in  connection  with  the  general  description  of  vaso-motor  regulation  (see 
Circulation).  It  has  been  shown  by  Landergren^  and  Tiegerstedt  that  the 
kidney  is  a  very  vascular  organ,  at  least  when  it  is  in  strong  functional  activ- 
ity such  as  may  be  produced  by  the  action  of  diuretics.  They  estimate  that 
in  a  minute's  time,  under  the  action  of  diuretics,  an  amount  of  blood  flows 
through  the  kidney  equal  to  the  weight  of  the  organ ;  this  is  an  amount  from 
four  to  nineteen  times  as  great  as  occurs  in  the  average  supply  of  the  other 
organs  in  the  systemic  circulation.  Taking  both  kidneys  into  account,  their 
figures  show  that  (in  strong  diuresis)  5.6  per  cent,  of  the  total  quantity  of 
^  Skandinavisches  Archiv  fur  Physiologie,  1892,  Bd.  iv.  S.  241. 


196  AX  AMERICAN    TEXT- BOOK    OF   PHYSIOLOGY. 

blood  sent  out  ut"  the  lott  liourt  in  a  laimite  may  pass  tlirougli  tlic  kiJueys, 
although  the  coiubineil  weight  of  these  organs  makes  only  0..")6  per  cent,  of 
that  of  the  body. 

The  richness  of  the  supply  of  vaso-iuotor  nerves  to  the  kidney  and  tiie  con- 
ditions which  bring  them  into  activity  are  fairly  well  known,  owing  to  the  use- 
ful invention  of  the  oncometer  by  Roy.'  This  instrument  is  in  principle  a 
plethysmograph  especially  modified  for  use  upon  the  kidney  of  the  living 
animal.  It  is  a  kiilney-shaped  box  of  thin  brass  made  in  two  parts,  hinged  at 
the  back,  and  with  a  clasj)  in  front  to  hold  them  together.  In  the  interior  of 
the  box  thin  peritoneal  membrane  is  so  fastened  to  each  half  that  a  layer  of  olive 
oil  may  be  placed  between  it  and  the  brass  walls.  There  is  thus  formed  in 
each  half  a  soft  pad  of  oil  upon  which  the  kidney  rests.  When  tiie  kidney, 
freed  as  far  as  possible  from  fat  and  surroiniding  connective  tissue,  but  with 
the  blood-vessels  and  nerves  entering  at  the  hilus  entirely  uninjured,  is  laid  in 
one-half  of  the  oncometer,  and  the  other  half  is  shut  down  upon  it  and  tightly 
fastened,  the  organ  is  surrounded  by  oil  in  a  box  which  is  liquid-tight  at  every 
point  except  one,  where  a  tube  is  led  ofif  to  some  suitable  recorder  such  as  a 
tambour.  Under  these  conditions  every  increase  in  the  volume  of  the  kidney 
will  cause  a  proportional  outflow  of  oil  from  the  oncometer,  which  will  be 
measured  by  the  recorder,  and  every  diminution  in  volume  will  be  accompa- 
nied by  a  reverse  change.  At  the  same  time  the  flow  of  urine  during  these 
changes  can  be  determined  by  inserting  a  cannula  into  the  in-eter  and  measur- 
ing directly  the  outflow  of  urine.  By  this  and  other  means  it  has  been  shown 
that  the  kidney  receives  a  rich  supply  of  vaso-coustrictor  nerve-fibres  which 
reach  it  between  and  round  the  entering  blood-vessels.  These  fibres  emerge 
from  the  spinal  cord  chiefly  in  the  lower  thoracic  spinal  nerves  (tenth  to  thir- 
teenth in  the  dog),  pass  through  the  sympathetic  system,  and  reach  the  organ 
as  non-medullated  fibres.  Stimulation  of  these  nerves  causes  a  contraction  of 
the  small  arteries  of  the  kidney,  a  shrinkage  in  volume  of  the  whole  organ  as 
measured  by  the  oncometer,  and  a  diminished  secretion  of  urine.  AVhen,  on 
the  other  hand,  these  constrictor  fibres  are  cut  as  they  enter  the  hilus  of  the 
kidney,  the  arteries  are  dilated  on  account  of  the  removal  of  the  tonic  action 
of  the  constrictor  fibres,  the  organ  enlarges,  and  a  greater  quantity  of  blood 
passes  through  it,  since  the  resistance  to  the  blood-flow  is  diminished  while 
the  general  arterial  pressure  in  the  aorta  remains  practically  the  same.  Along 
with  this  greater  flow  of  blood  there  is  a  marked  increase  in  the  secretion  of  urine. 

Under  normal  conditions  we  must  suppose  that  these  fibres  are  brought 
into  play  to  a  greater  or  less  extent  by  reflex  stimulation,  and  thus  serve  to 
control  the  blood-flow  through  the  kidney  and  thereby  influence  its  functional 
activity.  It  has  been  shown,  too,  that  the  kidney  receives  vaso-dilator  nerve- 
fibres,  that  is,  fibres  which  when  stimidated  directly  or  reflexly  cause  a  dilata- 
tion of  the  arteries,  and  therefore  a  greater  flow  of  blood  through  the  organ. 
According  to  Bradford,^  these  fibres  emerge  from  the  spinal  cord  mainly  in  the 

>  See  Colniheini  and  Roy  :    yircho\v&  Arckiv,  1883,  Bd.  92,  S.  424. 
^  Journal  of  Physiology,  1889,  vol.  x.  p.  358. 


SECRETION.  197 

anterior  roots  ot"  the  eluveutli,  twelf'tli,  uiid  tliirtceuth  spinal  uerves.  Under 
normal  conditions  these  fibres  are  probably  thrown  into  action  by  reflex  stimula- 
tion and  lead  to  an  increased  functional  activity.  It  will  be  seen,  therefore, 
that  the  kidneys  possess  a  local  nervous  mechanism  through  which  their 
secretory  activity  may  be  increased  or  diminished  by  corresponding  alterations 
in  the  blood-supply.  So  far  as  is  known,  this  is  the  only  way  in  which  the 
secretion  in  the  kidneys  can  be  directly  affected  by  the  central  nervous  svstem. 
It  should  be  borne  in  mind,  also,  that  the  blood-flow  through  the  kidneys, 
and  therefore  their  secretory  activity,  may  ijc  affected  by  conditions  influ- 
encing general  arterial  pressure.  Conditions  such  as  asphyxia,  strychnin- 
poisoning,  or  painful  stimulation  of  sensory  nerves,  which  cause  a  great 
rise  of  blood -pressure,  influence  the  kidney  in  the  same  way,  and  tend, 
therefore,  to  diminish  the  flow  of  blood  through  it;  while  conditions  which 
lower  general  arterial  pressure,  such  as  general  vascular  dilatation  of  the  skin 
vessels,  may  also  depress  the  secretory  action  of  the  kidney  by  diminishing 
the  amount  of  blood  flowing  thrj^ugh  it. 

In  what  way  any  given  change  in  the  vascular  conditions  of  the  body  will 
influence  the  secretion  of  the  kidney  depends  upon  a  number  of  factors,  and 
their  relations  to  one  another  ;  but  any  change  which  will  increase  the  differ- 
ence in  pressure  between  the  l)lood  in  the  renal  artery  and  the  renal  vein  will 
tend  to  augment  the  flow  of  blood  unless  it  is  antagonized  by  a  simultaneous 
constriction  in  the  small  arteries  of  the  kidney  itself.  On  the  contrary,  any 
vascular  dilatation  of  the  vessels  in  the  kidney  will  tend  to  increase  the  blood- 
flow  through  it  unless  there  is  at  the  same  time  such  a  general  fall  of  blood- 
pressure  as  is  sufficient  to  lower  the  pressure  in  the  renal  artery  and  reduce  the 
driving  force  of  the  blood  to  an  extent  that  more  than  counteracts  the  favora- 
ble influence  of  diminished  resistance  in  the  small  arteries. 

Movements  of  the  Ureter  and  the  Bladder. — (See  Micturition,  p.  327.) 

E.  Cutaneous  Glands  ;  Internal  Secretions. 

The  sebaceous  glands,  sweat-glands,  and  mammary  glands  are  all  true  epider- 
mal structures,  and  may  therefore  be  conveniently  treated  together. 

Sebaceous  Secretion. — The  sebaceous  glands  are  simple  or  compound 
alveolar  glands  found  over  the  cutaneous  surface  usually  in  association  with  the 
hairs,  although  in  some  cases  they  occur  .separately,  as,  for  instance,  on  the  pre- 
puce and  glans  penis,  and  on  the  lips.  When  they  occur  with  the  hairs  the 
short  duct  opens  into  the  hair-follicle,  so  that  the  secretion  is  passed  out  upon 
the  hair  near  the  point  where  it  projects  from  the  skin.  The  alveoli  are  filled 
with  cuboidal  or  polygonal  epithelial  cells,  which  are  arranged  in  several  lay- 
ers. Those  nearest  the  lumen  of  the  gland  are  filled  with  fatty  material. 
These  cells  are  supposed  to  be  cast  off  bodily,  their  detritus  going  to  form  the 
secretion.  New  cells  are  formed  from  the  layer  nearest  the  basement  mem- 
brane, and  thus  the  glands  continue  to]iroduce  a  slow  but  continuous  secretion. 
The  sebaceous  secretion,  or  sebum,  is  an  oily  semi-liquid  material  which  sets 
upon  exposure  to  the  air  to  a  cheesy  mass,  as  is  seen  in  the  comedones  or  pim- 


198  AN  AMERICAN    TEXT-BOOK    OF    PHYSIOLOGY. 

ple.s  which  so  fivquently  occur  upon  the  skin  from  occlusion  of  the  opening'  of 
the  ducts.  The  exact  composition  of  the  secretion  is  not  known.  It  contains 
tats  and  soaps,  some  cholcstcrin,  albuminous  material,  part  of  which  is  a 
nuclco-alhumin  often  described  as  a  casein,  remnants  of  e|)ithenal  cells, 
and  inorganic  salts.  The  cholesterin  occurs  in  combination  with  a  fatty  acid 
and  is  found  in  especially  large  quantities  in  sheep's  wool,  from  which  it  is 
extracted  and  used  commercially  under  the  name  of  lanolin.  The  sebaceous 
secretion  from  different  places,  or  in  different  animals,  is  probably  somewhat 
variable  in  composition  as  well  as  in  quantity.  The  secretion  of  the  prepuce 
is  known  as  the  smegma  pneputii ;  that  of  the  external  auditory  meatus, 
mixed  with  the  secretion  of  the  neighboring  sweat-glands  or  cenuninous  glands, 
forms  the  well-known  ear-wax  or  cerumen.  The  secretion  in  this  place  con- 
tains a  reddish  ])igment  of  a  bitterish-sweet  taste,  the  composition  of  which  has 
not  been  investigated.  Upon  the  skin  of  the  newly-born  the  sebaceous  ma- 
terial is  accumidated  to  form  the  vernix  caseosa.  The  well-known  ui-opvgal 
gland  of  birds  is  homologous  with  the  mammalian  sebaceous  glands,  and  its 
secretion  has  been  obtained  in  sufficient  quantities  for  chemical  analysis. 
Physiologically  it  is  believed  that  the  sebaceous  secretion  affords  a  protection 
to  the  skin  and  hairs.  Its  oily  character  doubtless  serves  to  protect  the  hairs 
from  becoming  too  brittle,  or,  on  the  other  hand,  from  being  too  easily  satu- 
rated with  external  moisture.  In  this  way  it  probably  aids  in  making  the 
hairy  coat  a  more  perfect  protection  against  the  effect  of  external  changes  of 
temperature.  Upon  the  surface  of  the  skin  also  it  forms  a  thin  protective 
layer  which  tends  to  prevent  undue  loss  of  heat  from  evaporation,  and  possi- 
bly is  important  in  other  ways  in  maintaining  the  physiological  integrity  of 
the  external  surface. 

Sweat. — The  sweat  or  perspiration  is  a  secretion  of  the  sweat-glands. 
These  latter  structures  are  found  over  the  entire  cutaneous  surface  except  in 
the  deeper  portions  of  the  external  auditory  meatus.  They  are  particularly 
abundant  upon  the  palms  of  the  hands  and  the  soles  of  the  feet.  Krause 
estimates  that  their  total  number  for  the  whole  cutaneous  surface  is  about  two 
millions.  In  man  they  are  formed  on  the  type  of  simple  tubular  glands;  the 
terminal  portion  contains  the  secretory  cells,  and  at  this  j)art  the  tube  is 
usually  coiled  to  make  a  more  or  less  compact  knot,  thus  increasing  the  extent 
of  the  secreting  surface.  The  larger  ducts  have  a  thin  muscular  coat  of  invol- 
untary tissue  which  may  possibly  be  concerned  in  the  ejection  of  the  secretion. 
The  secretory  cells  in  the  terminal  portion  are  columnar  in  shape,  they  possess 
a  granular  cytoplasm  and  are  arranged  in  a  single  layer.  The  amount  of 
secretion  formed  by  these  glands  varies  greatly,  being  influenced  by  the  con- 
dition of  the  atmosphere  as  regards  temperature  and  moisture,  as  well  as  by 
various  physical  and  psychical  states  such  as  exercise  and  emotions.  An  aver- 
age quantity  for  twenty-four  hours  is  said  to  vary  between  700  and  900  grams, 
although  this  amount  may  be  doubled  inider  certain  conditions. 

Composition  of  the  Secretion. — The  precise  chemical  composition  of  sweat 
is  difficult  to  determine,  owing  to  the  fact  that  as  usually  obtained  it  is  liable 


SECRETION.  1^^ 


t„  1„.  mixcl  witl,  .1,0  sebaceous  secretion.     Norn.ally  ,t  ,s  a  very  thn,  scae- 
ion  of  low  specific  gravity  (1004)  and  an  all<aline  react, on  al  hong ,  when 
ftn^  secretecl  L  .-eaetion  n,ay  bo  .M  owing  t<,  adnnxtnre  vy,tl,  tl,e  .e baceou 
Lterial.     The  la,-ger  ,,art  of  the  i„o,-gauic  salts  eons,sts  of  sod.nn.  el  lor,,  e. 
tf,uall  quantities  of  the  alkaline  sulphates  an.l  phosphates  are  also  ,„-esont.    The 
o,-ga„ic  eoustitneuts,  though  present  in  ,ne>-e  traces  arc  qmte  var,e<l  ,n  nnn,- 
li      Urea    uric  acid,  e,-eatini„,  arou.atic  oxy-  acls,  etl,ereal  sulphates  of 
pbe'nol  and  skatol,  an.l  all,u„,i„,  are  said  to  o,.cur  when  the  sweat.ng  ,s  pro- 
f  .^      Ar«,ti„sky  has  shown  that  after  the  action  of  vapo,- baths,  and  as  the 
result  of  mnsenlar  work,  the  amount  of  urea  eli,nina.ed  in  tins  seeret.on  may 
be  eousidcablc  (sec  p.  299).      Under  pathologieal   c„nd,t,o„s  '"volv.ng  a 
diminished  elimination  of  urea  through  the  kidneys  ,t  has  been  obse  vol  t ha 
tl.e  amount  found  in  the  sweat  is  markedly  i„c,-eased,  so  that  crystals  of  ,t 
„,ay  be  deposited  upon  the  skin.     Under  perfectly  normal  eond,t,o„s,  how- 
ever it  is  obvious  that  the  organic  constituents  are  of  m,nor  ,mportanee.    The 
main  fact  to  be  considered  in  the  secretion  of  sweat  is  the  format,on  o    «^ ter 
Secrdory  Fibres  to  ll^  feaf-ffW^.-Definite  expcr,mental  proof  of  the 
existence  of  sweat-uerves  was  fi^t  obtained  by  Goltz'  in  some  exi»nn,ents 
npol  stimulation  of  the  sciatic  uerve  in  «,ts.     In  the  eat  and  dog,  ,n  wh.ch 
sweat-o-lands  occur  only  on  the  balls  of  the  feet,  the  presence  of  sweat-nerves 
ZZC  demonst,-atcd  with  great  ease.     Electrical  stimulat.on  of  the  penphera 
end  of  the  divided  sciatic  nerve,  if  suificiently  strong  w,U  -use  v,s,ble  drops 
of  sweat  to  form  on  the  hairless  skin  of  the  balls  of  the  feet.     When  the  el«. 
t  odrarc  kept  at  the  same  spot  on  the  nerve  and  the  stimulatron  ,s  ma,ntamed 
he  s3on  soon  ceases,  bat'  this  effect  seems  to  be  due  to  a  temporary  ,njnry 
of  some  kind  to  the  nerve-fibres  at  the  point  of  sti,nulat,on,  and  not  to  a 
1,SL  ft  igne  of  the  sweat-glands  or  the  sweat-fibres,  s.nce  mov,ng  the  elee- 
frdeT  o  a  ,' w  point  on  the  nerve  farther  toward  the  pe,-,phery  calls  forth  a 
ew  i  rction.     The  secretion  so  formed  is  thin  and  limp,d,  and  has  a  ma,-l^ 
"llal  ,e  rllion.     The  anatomical  «,u,-se  of  these  fibres  has  been  worked  out 
"Th    cat  1  great  care  by  Langley.^     He  finds  that  for  the  h,nd  fee   th  y 
ave  the  spinal'cord  chiefly  in  the  first  and  -™"'\ '7"  ^  X::  inl  gS 
sympathetic  chain,  and  emerge  fron,  this  as  "^-"^''""f  "*>;";"  t/^^^ 
rami  nroceeding  from  the  sixth  lumbar  to  the  second  sac  al  ganglion,  but 
ra,n,  proceeo,u„  ,   „  i       ,,  (lien    on  the  nerves  of 

chiefly  in  the  seventh  lumbar  and  h,->t  sacal,  ana  i,ie,  j 
the  sciatic  plexus.  For  the  fore  feet  the  fibres  leave  the  sp,nal  cord  ,n  the 
f!„-.ht^^th  tenth  thoracic  nerves,  enter  the  sympathetic  cha.n,  pass  upward 
0  l,e  first  thoracic  ganglion,  whence  they  are  continued  as  non-meduUated 
r  whi  pass  out'of  this  ganglion  by  the  gray  --/  -"-— f  ^f^ 
the  nerves  forming  the  brachial  plexus.     The  act.on  of  the  - ^  ;«^J^"  'f^ 

.he  sweat-glands  cannot  be  explained  as  »  ■;j;-^  ^    '^  J  Xlown 

rpc^nlt  of  a  variatou    n  the  blood-flow.     JLxpenmems  lune  i  i 

Tat!  in  the  cat,  stimulation  of  the  sciatic  still  calls  forth  a  secret.on  after  the 

1  Archiv  fur  die  (jesammte  Physiologie,  1875,  Bd.  xi.  S.  71. 

2  Journal  of  Phydology,  1891,  vol.  xii.  p.  347. 


200  AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

blood  lias  been  shut  otl'  Iroiii  the  leg  l)y  ligation  oi"  the  aorta,  or  indeed  al'tc^r 
the  leg  has  been  amputated  for  as  long  as  twenty  niiinites.  So  in  iiiinian 
beings  it  is  known  that  profuse  sweating  may  often  aeeomjtany  a  j)allid  skin, 
as  in  terror  or  nausea,  while  on  the  other  hand  the  ilushed  skin  of  fever  is 
characterized  by  the  absence  of  perspiration.  There  seems  to  be  no  doubt 
at  all  that  the  sweat-nerves  are  genuine  secretory  fibres,  producing  the  secre- 
tion directly  by  their  action  on  the  cells  of  the  sweat-glands.  In  accordance 
with  this  physiological  fact  recent  iiistological  work  has  demonstrated  that 
special  nerve-fibres  are  suj)plied  to  the  glandular  epithelium.  According  to 
Arnstein  '  the  terminal  fibres  form  a  small  branching  varicose  ending  in  con- 
tact with  the  epithelial  cells.  The  sweat-gland  may  be  made  to  secrete  in 
many  ways  other  than  by  direct  artificial  excitation  of  the  sweat-fibres;  for 
example,  by  external  heat,  dyspnoea,  muscular  exercise^,  strong  emotions,  and 
by  the  action  of  various  (b'ugs  such  as  pilocarpin,  muscarin,  strychnin,  nicotiu, 
picrotoxin,  and  physostigmin.  In  all  such  cases  the  effect  is  supposed  to 
result  from  an  action  on  the  sweat-fibres,  either  directly  on  their  terminations, 
or  indirectly  upon  their  cells  of  origin  in  the  central  nervous  system.  In 
ordinary  life  the  usual  cause  of  profuse  sweating  is  a  high  external  temper- 
ature or  muscular  exercise.  With  regard  to  the  former  it  is  known  that 
the  high  temperature  does  not  excite  the  sweat-glands  immediately,  but 
through  the  intervention  of  the  central  nervous  system.  If  the  nerves  going 
to  a  limb  be  cut,  exposure  of  that  limb  to  a  high  temperature  does  not  cause 
a  secretion,  showing  that  the  temperature  change  alone  is  not  sufficient  to 
excite  the  gland  or  its  terminal  nerve-fibres.  We  must  suppose,  therefore, 
that  the  high  temperature  acts  upon  the  sensory  cutaneous  nerves,  ]>ossibly 
the  heat-fibres,  and  reflexly  stimulates  the  sweat-fibres.  Although  external 
temperature  does  not  directly  excite  the  glands,  it  should  be  stated  that  it 
affects  their  irritability  either  by  direct  action  on  the  gland-cells  or,  as  is  more 
likely,  upon  the  terminal  nerve-fibres.  At  a  sufficiently  low  temperature  the 
cat's  paw  does  not  secrete  at  all,  and  the  irritability  of  the  glands  is  increased 
by  a  rise  of  temperature  up  to  about  45°  C 

Dysj)noea,  nmscular  exercise,  emotions,  and  many  drugs  aflPeet  the  secretion, 
probably  by  action  on  the  nerve-centres.  Pilocarpin,  on  the  contrary,  is 
known  to  stimulate  the  endings  of  the  nerve-fibres  in  the  glands,  while  atropin 
has  the  opposite  effect,  completely  paralyzing  the  secretory  fibres. 

Siveat-centres  in  the  Central  Nervous  Si/sfem. — The  fact  that  secretion  of 
sweat  may  be  occasioned  by  stimulation  of  afferent  nerves  or  by  direct  action 
upon  the  central  nervous  system,  as  in  the  case  of  dyspnoea,  implies  the  exist- 
ence of  physiological  centres  controlling  the  secretory  fibres.  The  precise  loca- 
tion of  the  sweat-centre  or  centres  has  not,  however,  been  satisfactorily  deter- 
mined. Histologically  and  anatomically  the  arrangement  of  the  sweat-fibres 
resembles  that  of  the  vaso-constrictor  fibres,  and,  reasoning  from  analogy,  one 
might  suppose  the  existence  of  a  general  sweat-centre  in  the  medulla  compara- 
ble to  the  vaso-constrictor  centre,  but  positive  evidence  of  the  existence  of  such 

^  Anaiomiacher  Ameiger,  1895,  Bd.  x. 


SECRETION.  201 

an  arraiii^i'ment  is  lacking.  It  lias  Ikcm  shown  than  when  the  medulla  is 
separated  t'roni  the  cord  hv  a  sctition  in  the  cervical  or  thoracie  region  the 
action  of  dyspnoea,  or  ot"  various  sudorific  drugs  suj)p(jsed  to  act  on  the  cen- 
tral nervous  system,  may  still  cause  a  secretion.  On  the  evideuce  of*  results 
of  this  character  it  is  assumed  that  there  are  spinal  sweat-centres,  but  whether 
these  arc  few  in  number  or  represent  simply  the  various  nuclei  of  origin  of  the 
fibres  to  different  regions  is  not  definitely  known.  It  is  })ossil)le  that  in  addi- 
tion to  these  spinal  centres  there  is  a  general  regulating  centre  in  the  medulla. 

Mammary  Glands. 

The  mammary  glands  are  undoubtedly  epidermal  structures  comparable  iu 
development  to  the  sweat-  or  the  sebaceous  glands.  Whether  they  are  to  be 
homologized  with  the  sweat-  or  with  the  sebaceous  glands  is  not  clearly  deter- 
mined. In  most  animals  they  are  compound  alveolar  glands,  and  their  acinous 
structure  and  the  rich  albuminous  and  fatty  constituents  of  their  secretion 
would  seem  to  suggest  a  relationship  to  the  sebaceous  glands.  But  the  histo- 
logical structure  of  their  alveoli  with  its  single  layer  of  epithelium  points 
rather  to  a  connection  with  the  sweat-glands.  Whatever  may  have  been  their 
exact  origin  in  the  primitive  mammalia,  there  seems  to  be  no  question  that 
they  were  deriv^ed  in  the  first  place  from  some  of  the  ordinary  skin-glands 
which  at  first  simply  opened  on  a  definite  area  of  the  skin,  but  without  a  dis- 
tinct mamma  or  nipple,  as  is  seen  now  in  the  case  of  the  monotremes.  Later 
in  the  phylogenetic  history  of  the  gland  the  separate  ducts  united  to  form 
one  or  more  larger  ones,  and  these  opened  to  the  exterior  upon  the  protrusion 
of  the  skin  known  as  the  nipple.  The  number  and  position  of  the  glands 
vary  much  in  the  different  mammalia.  In  man  they  are  found  in  the  thoracic 
region  and  are  normally  two  in  number.  The  milk-ducts  do  not  unite  to 
form  a  single  canal,  but  form  a  group  of  fifteen  to  twenty  separate  systems, 
each  of  which  opens  separately  upon  the  surface  of  the  nipple.  Before  preg- 
nancy the  secreting  alveoli  are  incompletely  formed,  but  during  pregnancy 
and  at  the  time  lactation  begins  the  formation  of  the  alveoli  is  greatly  acceler- 
ated by  proliferation  of  the  epithelial  cells. 

Composition  of  the  Secretion. — The  general  appearance  and  composi- 
tion of  the  milk  are  well  known.  Microscopically  milk  consists  of  a  liquid 
portion,  or  plasma,  in  which  float  an  innumerable  multitude  of  fine  fat-drop- 
lets. The  latter  elements  contain  the  milk-fat,  which  consists  chiefly  of  neutral 
fats,  stearin,  palmitin,  and  olein,  but  contains  also  a  small  amount  of  the  fats 
of  butyric  and  caproic  acid  as  well  as  slight  traces  of  other  fatty  acid  com- 
pounds and  small  amounts  of  lecithin,  cholesterin,  and  a  yellow  pigment.  Upon 
standing,  a  portion  of  these  elements  rises  to  the  surface  to  form  the  cream.  The 
milk-plasma  holds  in  solution  important  proteid  and  carbohydrate  compounds 
as  well  as  the  necessary  inorganic  salts.  The  proteids  are  casein,  belonging  to 
the  group  of  nucleo-albumins  ;  lactalbumin,  which  closely  resembles  the  serum- 
albumin  of  blood,  and  lacto-globulin,  which  is  similar  to  the  paraglobulin  of 
blood  :  the  two  latter  proteids  occur  in  much  smaller  quantities  than  the  casein. 


202 


AX  AMERICAN   TEXT-BOOK   OF    rilVSIOLOGY. 


The  chief  carbohydrate  in  niilU  is  the  iiiilk-siigar  or  hictosc.  Ilaminarsteii ' 
has  succeeded  iu  isolating  from  the  mammary  gland  a  nucleo-protcid  (-ontain- 
ing  a  reducing  group.  He  designates  this  suhstance  as  nncleo-glyco-proteid. 
It  seems  possible  that  a  compound  of  this  character  might  serve  as  the  parent 
substance  for  both  tlie  casein  and  the  lactose  of  the  secretion.  The  mineral 
constituents  are  varied  and,  considered  quantitatively,  show  an  interesting  rela- 
tionship to  the  mineral  composition  of  the  body  of  the  suckling  (see  p.  296). 
The  fact  that  the  inorganic  salts  of  the  milk  vary  so  widely  in  quantitative 
composition  from  those  of  the  blood  has  been  used  to  show  that  they  are  not 
derived  from  the  blood  by  the  simple  mechanical  processes  of  filtration  or 
dialysis,  but  are  secreted  by  the  epitlielial  (^ells  of  the  gland.  Traces  of 
nitrogeneous  excreta,  such  as  urea,  creatiu,  and  oreatinin,  are  also  found  in 
the  milk-plasma,  together  with  some  lecithin  and  cholesterin  and  a  small 
amount  of  citric  acid  occurring  as  citrate  of  calcium. 

Histolog-ical  Changes  during  Secretion. — The  simple  fact  that  sub- 
stiinces  are  foinid  in  the  milk  which  do  not  occur  in  the  blood  or  lymph  is 
sufficient  proof  that  the  epithelial  cells  are  actively  concerned  in  the  process 
of  secretion.     Histological  examination  of  the  gland  during  lactation  confirms 

fully  tliis  a  'priori  deduction,  and  enables 
us  to  understand  the  probable  origin  of 
some  of  the  important  constituents.^  In 
the  resting  gland  during  the  period  of 
gestation,  or  in  certain  alveoli  during 
lactation,  the  alveoli  are  lined  by  a  single 
layer  of  flattened  or  cuboidal  cells,  which 
have  only  a  single  nucleus,  present  a 
granular  appearance,  and  have  few  or 
no  fat-globules  in  them  (Fig.  83). 
When  such  alveoli  enter  into  the  active 
formation  of  milk  the  epithelial  cells 
increase  in  height,  projecting  in  toward  the  lumen,  the  nuclei  divide,  and  as  a 


Fig.  83.— Section  through  the  middle  of  two 
alveoli  of  the  mammary  gland  of  the  dog ;  con- 
dition of  rest  (after  Heidenhain). 


A 

Fig.  84.— Mammary  gland  of  dog,  showing  the  formation  of  the  secretion  :  A,  medium  condition  of 
growth  of  the  epithelial  cells ;  B,  a  later  condition  (after  Heidenhain). 

rule  (Steinhaus^)  each  cell  contains  two  nuclei  (Fig.  84).      Fat-droplets  de- 
velop in  the  cytoplasm,  especially  in  the  free  end  of  the  cell,  and  according  to 

'  Zeitschrift  fiir  physiologische  Chemie,  1894,  Bd.  xix.  S.  19. 

^  See  Heidenhain:  Hermann's  Handbuch  (hr  I'hj/xiologie,  18S3,  Bd.  v.  S.  381. 

^  Du  Bok-ReymoncVs  Archiv  fiir  Phi/siolnrjle,  1892,  Siippl.  Bd.,  p.  54. 


SECRETION.  203 

Steiiihaus  the  uuclous  nearest  the  lumen  uiulergoe-s  a  fatty  metamorphosis. 
According  to  the  same  author  the  granular  material  in  the  cytoplasm  also 
undergoes  a  visible  change;  the  granules,  which  in  the  resting  cell  are 
spherical,  elongate  during  the  stage  of  activity  to  threutls  that  take  on  a 
spirochneta-like  form.  The  acme  of  this  phase  of  development  is  reached  by 
the  solution  or  disintegration  of  a  portion  of  the  end  of  the  cell;  the  frag- 
ments being  discharged  into  the  lumen  of  the  alveolus.  The  debris  of  this 
disintegrated  portion  of  the  cell  helps  to  form  the  secretion  ;  part  of  it  goes 
into  solution  to  form,  probably,  the  albuminous  and  carbohydrate  constituents, 
while  the  fat-droplets  are  set  free  to  form  the  milk-fat.  Apparently  the  basal 
portion  (jf  the  cell  regenerates  its  cytoplasm  and  thus  continues  to  form  new 
material  for  the  secretion.  In  some  cases,  however,  the  whole  cell  seems  to 
undergo  dissolution,  and  its  place  is  taken  by  a  new  cell  formed  by  karyo- 
kinetic  division  of  one  of  the  neighboring  epithelial  cells.  The  origin  of  the 
peculiar  colostrum  corpuscles  found  in  the  milk  during  the  first  few  days 
of  its  secretion  has  been  explained  differently  by  different  observers.  Heid- 
enhain  traces  them  to  certain  epithelial  cells  of  the  alveoli  which  at  this 
time  become  rounded,  develop  numerous  fat-droplets,  and  are  finally  dis- 
charged bodily  into  the  lumen,  although  he  was  not  able  to  actually  trace 
the  intermediate  steps  in  the  process.  Steinhaus,  on  the  contrary,  thinks 
that  these  corpuscles  are  derived  from  the  wandering  cells  of  the  connective 
tissue  (^Mastzellen)  which  at  the  beginning  of  lactation  are  very  numerous, 
but  seem  to  undergo  fatty  degeneration  and  elimination  in  the  secretion  of 
the  newly  active  gland. 

Control  of  the  Secretion  by  the  Nervous  System. — There  are  indica- 
tions that  the  secretion  of  the  mammary  glands  is  under  the  control,  to  some 
extent  at  least,  of  the  central  nervous  system.  For  instance,  in  women  during 
the  period  of  lactation  cases  have  been  recorded  in  which  the  secretion  was 
altered  or  perhaps  entirely  suppressed  by  strong  emotions,  by  an  epileptic 
attack,  etc.  This  indication  has  not  received  satisfactory  confirmation  from 
the  side  of  experimental  physiology.  Eckhard  ^  found  that  section  of  the 
main  nerve-trunk  supplying  the  gland,  the  external  spermatic,  caused  no  dif- 
ference in  the  quantity  or  quality  of  the  secretion.  Rohrig^  obtained  more 
positive  results,  inasmuch  as  he  found  that  some  of  the  branches  of  the  exter- 
nal spermatic  supply  vaso-motor  fibres  to  the  blood-vessels  of  the  gland  and 
influence  the  secretion  of  milk  by  controlling  the  local  blood-fiow  in  the 
gland.  Section  of  the  inferior  branch  of  this  nerve,  for  example,  gave  in- 
creased secretion,  while  stimulation  caused  diminished  secretion,  as  in  the 
case  of  the  vaso-constrictor  fibres  to  the  kidney.  These  results  have  not  been 
confirmed  by  others — in  fact,  they  have  been  subjected  to  adverse  criticism — 
and  they  cannot,  therefore,  be  accepted  unhesitatingly. 

Mironow^  reports  a  number  of  interesting  experiments  made  upon  goats. 

^  See  Heidenhain :  Hermann's  Handbuch  der  Physiologic,  Bd.  v.  Thl.  1.  S.  392. 
*  Virchovfs  Archiv  far  pathologische  Anatomic,  etc.,  1876,  Bd.  67,  S.  119. 
'^  Archives  des  Sciences  biologiques,  St.  Petersburg,  1894,  vol.  iii.  p.  353. 


204  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

He  foiiud  that  artilicial  stiiuulation  of  sensory  nerves  causes  a  diiiiinution  iu 
the  amount  of  secretion,  thus  oonlinninu-  the  opinion  IjasctI  upon  observations 
upon  tlie  Imman  heinj;-,  that  in  some  way  tlie  central  nervous  system  exerts  au 
inriuenee  on  the  mammary  gland.  When  the  mammary  glands  are  com- 
pletely isolated  from  their  connections  with  the  central  nervous  system,  stimu- 
lation of  an  afferent  nerve  no  longer  influences  the  secretion.  Mirouow 
states  also  that  although  section  of  the  external  spermatic  on  one  side  does  not 
influence  the  secretion,  section  of  this  nerve  on  both  sides  is  followed  bv  a 
marked  diminution,  and  the  same  result  is  obtained  when  the  gland  cm  one 
side  is  completely  isolated  from  all  nervous  connections.  The  diminution  of 
the  secretion  in  these  cases  comes  on  very  slowly,  after  a  number  of  days,  so 
that  the  effect  cannot  be  attributed  to  the  removal  of  definite  secretory  fibres. 
Moreover,  after  apj)arently  complete  separation  of  the  gland  from  all  its 
extrinsic  nerves,  not  oidy  does  the  secretion,  if  it  was  previously  present,  con- 
tinue to  form  although  in  less  quantities,  but  in  operations  of  this  kind  upon 
pregnant  animals  the  glands  increase  in  size  during  pregnancy  and  become 
functional  after  tlie  act  of  parturition. 

Experiments,  therefore,  as  far  as  they  have  been  carried,  indicate  that 
the  gland  is  under  the  regulating  control  of  the  central  nervous  system,  either 
through  secretory  or  vaso-motor  fibres,  but  that  it  is  essentially  an  automatic 
organ.  The  bond  of  connection  between  it  and  the  uterus  seems  to  be,  in  part 
if  not  entirely,  through  the  blood  rather  tiian  through  the  nervous  system. 
It  should  be  added  that  Arnstein  '  has  described  a  definite  connection  between 
the  nerve-fibres  and  the  epithelial  cells  of  the  gland.  If  this  fact  is  corrobo- 
rated it  would  amount  to  an  histological  proof  of  the  existence  of  special 
secretory  fibres,  but  the  physiological  evidence  for  the  same  fact  is  either 
negative  or  unsatisfactory. 

Normal  Secretion  of  the  Milk. — As  was  said  in  speaking  of  the  his- 
tology of  the  gland,  the  secreting  alveoli  are  not  fully  formed  until  tiie  first 
pregnancy.  During  tlie  period  of  gestation  the  epithelial  cells  multiply,  the 
alveoli  are  formed,  and  after  parturition  secretion  begins.  At  first  the  .secre- 
tion is  not  true  milk,  but  a  liquid  differing  in  composition  and  known  as  the 
colostrum ;  this  secretion  is  characterized  microscopically  by  the  existence  of 
the  colostrum  corpuscles,  which  seem  to  be  wandering  cells  that  have  under- 
gone a  complete  fatty  degeneration.  After  a  few  days  the  true  milk  is  formed 
in  the  manner  already  described.  According  to  Rohrig  the  secretion  is  con- 
tinuous, but  this  statement  needs  confirmation.  As  the  liquid  is  formed  it 
accumulates  in  the  enlarged  galactophorous  ducts,  and  after  the  tension  has 
reached  a  certain  point  further  secretion  is  apj)arently  inhibited.  If  the  ducts 
are  emptied,  by  the  infant  or  othcrwi.se,  a  new  secretion  begins.  The  emptying 
of  the  ducts,  in  fact,  seems  to  con.stitute  the  normal  physiological  stimulus  to 
the  gland-cells,  but  how  this  act  affects  the  secreting  cells,  whether  reflexly  or 
directly,  is  not  known.  When  the  child  is  weaned  the  .secretion  under  normal 
conditions  soon  ceases  and  the  alveoli  undergo  retrograde  changes,  although 
'  Anatomischer  Anzeiger,  1895,  Bd.  x.  S.  410. 


SECRETIOiX.  205 

they  do  not  return  completely  to  the  condition  they  were  in  before  the  first 
pregnancy. 

Inteunal  Secretions. 

According  to  tiie  definition  proposed  on  p.  152,  the  term  internal  secretion 
is  here  used  to  mean  a  specific  substance  or  substances  formed  within  a  gland- 
ular organ  and  given  off  to  the  blood  or  lymph.  As  was  said  before,  it  is 
difficult  to  make  a  distinction  between  these  iuternal  secretions  and  the  waste 
products  of  metabolism  generally  so  far  as  method  and  place  of  formation 
and  elimination  are  concerned.  Every  active  tissue  gives  off  waste  products 
which  are  borne  off  in  the  lymph  and  blood,  but  as  generally  employed  the 
term  internal  secretion  is  not  meant  to  include  all  such  products,  but  only  the 
materials  produced  in  distinctly  glandular  organs  which  are  more  or  less 
specific  to  those  organs,  and  which  are  su})pose(l  to  have  a  general  value  to 
the  body  as  a  whole.  The  idea  of  an  internal  secretion  seems  to  have  been 
first  advocated  by  Brown-S^quard  in  the  course  of  some  work  upon  extracts 
of  the  testis.  Within  the  last  few  years  the  terra  has  been  frequently  used, 
especially  in  connection  with  the  valuable  and  interesting  work  done  upon  the 
pancreas  and  the  so-called  blood-vascular  or  ductless  glands,  the  thyroids, 
adrenals,  pituitary  body,  and  spleen.  In  almost  all  cases  our  knowledge  of 
the  nature  and  importance  of  these  internal  secretions  is  in  a  formative  stage ; 
the  literature,  however,  of  the  subject  is  already  very  great,  and  is  increasing 
rapidly,  while  speculations  are  numerous,  so  that  constant  contact  with  current 
literature  is  necessary  to  keep  pace  with  the  advance  in  knowledge.  In  this 
section  only  an  outline  of  the  subject  can  be  attempted. 

Liver. — It  has  not  been  customary  to  speak  of  the  liver  as  furnishing  an 
internal  secretion,  but  two  of  the  products  formed  within  this  organ  are  so 
clearly  known  and  their  method  of  production  is  so  typical  of  what  is  sup- 
posed to  be  the  mechanism  of  internal  secretion,  that  it  is  desirable  both  for 
the  sake  of  convenience  and  consistency  to  include  them  under  this  general 
heading.  Glycogen  (CgHjoOg)!!  is  formed  within  the  liver-cells  from  the 
sugars  and  proteids  brought  to  them  in  the  blood  of  the  portal  vein,  and  in 
many  cases  the  presence  of  this  glycogen  can  be  demonstrated  microscopically 
within  the  cells.  From  time  to  time,  however,  the  glycogen  within  the  cell 
is  converted  into  dextrose  by  a  process  of  hydration, 

CeHjoOg  +  H2O  =  CgHiPei 

and  the  sugar  so  formed  is  by  a  secretory  process  of  some  kind  given  off  to 
the  blood  to  serve  for  the  metabolism  of  the  other  tissues  of  the  body,  es- 
pecially the  nuiscles.  This  elimination  of  its  stored  glycogen  on  the  part  of 
the  liver  may  be  regarded  as  a  case  of  internal  secretion.  (For  further  details 
concerning  glycogen,  its  properties  and  functions,  see  p.  266  and  the  section 
on  Chemistry.)  A  second  substance  which  is  formed  under  the  influence 
of  the  liver-cells  and  is  then  eliminated  into  the  blood  is  urea.  Urea  constitutes 
the  chief  nitrogenous  end-product  of  the  metabolism  of  the  proteid  tissues ;  it 


206  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

is  eliininiited  from  the  body  bv  tlie  kidneys,  but  it  is  known  not  to  be  formed 
in  these  organs.  Modern  investigations  (see  p.  000)  have  seemed  to  show  con- 
clusively that  this  substance  is  formed  mainly  within  the  liver  from  some 
antecedent  substance  (carbamate  of  ammonia)  which  arises  in  the  proteid  tissues 
generally,  but  is  not  prepared  for  final  elimination  until  in  the  liver  or  else- 
where it  is  converted  into  urea.  Here  again  the  liver-cells  perform  a  metab- 
olism for  the  good  of  the  organism  as  a  whole,  and  the  act  of  passing  out 
the  urea  into  the  blood  may  be  regarded  as  an  internal  secretion.  It  is  quite 
possible  that  in  still  other  ways  the  liver-cells  add  to  the  blood  elements  of 
importance  to  the  tissues  of  the  body — as,  for  example,  in  the  conservation  and 
distribution  of  the  iron  of  broken-down  hiemoglobin  (see  p.  275),  or  in  the  syn- 
thetic combination  of  the  products  of  putrefaction  formed  in  the  intestines  (indol, 
skatol,  phenol,  etc.)  with  sul])huric  acid  (see  p.  263);  but  concerning  these  mat- 
ters our  knowledge  is  not  yet  sufficiently  definite  to  make  positive  statements. 
Pancreas. — The  importance  of  the  external  secretion,  the  pancreatic  juice, 
of  the  pancreas  has  long  been  recognized,  but  it  was  not  until  1889  that  Von 
Mehring'  and  Minkowski  proved  that  it  furnishes  also  an  equally  important 
internal  secretion.  These  observers  succeeded  in  extirpating  the  entire  pan- 
creas without  causing  the  immediate  death  of  the  animal,  and  found  that  in 
all  cases  this  operation  was  followed  by  the  appearance  of  sugar  in  the  urine 
in  considerable  quantities.  Further  observations  of  their  own  and  other  experi- 
menters have  corroborated  this  result  and  added  a  number  of  interesting  facts 
to  our  knowledge  of  this  side  of  the  activity  of  the  pancreas.  It  has  been 
shown  that  when  the  pancreas  is  completely  removed  a  condition  of  glycosuria 
inevitably  follows,  even  if  carbohydrate  food  is  excluded  from  the  diet.  More- 
over, as  in  the  similar  pathological  condition  of  glycosuria  or  diabetes  mellitus 
in  man  there  is  an  increase  in  the  quantity  of  urine  (])olyuria),  and  of  urea, 
and  an  abnormal  thirst  and  hunger.  These  symptoms  in  cases  of  complete 
extirpation  of  the  pancreas  are  followed  by  emaciation  and  muscular  weak- 
ness, which  finally  end  in  death  in  about  two  weeks  or  less.  If  the  pancreas 
is  incompletely  removed  the  glycosuria  may  be  serious,  or  slight  and  transient, 
or  absent  altogether,  depending  upon  the  amount  of  pancreatic  tissue  left. 
According  to  the  experiments  of  Von  Mehring  and  Minkowski  on  dogs,  a 
residue  of  one-fourth  to  one-fifth  of  the  gland  may  be  sufficient  to  prevent  the 
appearance  of  sugar  in  the  urine.  The  portion  of  pancreas  left  in  the  body 
may  suffice  to  prevent  glycosuria,  partly  or  completely,  even  though  its  con- 
nection with  the  duodenum  is  entirely  interrupted,  thus  indicating  that  the 
suppression  of  the  pancreatic  juice  is  not  responsible  for  the  glycosuria.  The 
same  fact  is  shown  more  conclusively  by  the  following  experiments:  Glycos- 
uria after  coni]>lete  removal  of  the  pancreas  from  its  normal  connections  may 
be  prevented  by  grafting  a  portion  of  the  pancreas  elsewhere  in  the  abdominal 
cavity  or  even  under  the  skin.  The  ducts  of  the  gland  may  be  completely 
occluded  by  ligature  or  by  injection  of  paraffin  without  seriously  disturbing 

'  Archiv  fur  exper.  Pathologic  uml  Pharmakoloi/ie,  1890,  Bd.  xxvi.  S.  371.     See  also  Minkow- 
ski, Ibid.,  1893,  Bd.  xxxi.  S.  85,  for  a  more  complete  account. 


SECRETION.  207 

the  healthy  eoudition  of  the  aninial.  In  the  last  experiment  it  is  said  that 
the  normal  secreting  tubules  of  the  glaud  undergo  atrophy. 

We  must  believe  from  these  experiments  that  the  pancreas  produces  a  sub- 
stance of  some  kind  which  is  given  off  to  the  blood  or  lymph  and  which  is 
either  necessary  for  the  normal  consumption  of  sugar  in  the  body,  or  else,  as 
is  held  by  some,'  normally  restrains  the  output  of  sugar  from  the  liver  and 
other  sugar-producing  tissues  of  the  body.  What  this  material  is  and  how  it 
acts  has  not  yet  been  determined  satisfactorily.  It  is  interesting  and  sugges- 
tive to  state  in  this  connection  that  post-mortem  examination  in  cases  of  dia- 
betes mellitus  in  the  human  being  has  shown  that  this  disease  is  associated  in 
some  instances  with  obvious  alterations  in  the  structure  of  the  pancreas. 

The  Thyroid  Body. — The  thyroids  are  glandular  structures  found  in 
all  the  vertebrates.  In  the  mammalia  they  lie  on  either  side  of  the  trachea 
at  its  junction  with  the  larynx.  In  man  they  are  united  across  the  front  of 
the  trachea  by  a  narrow  band  or  isthmus,  and  hence  are  sometimes  spoken 
of  as  one  structure,  the  thyroid  body.  In  some  of  the  lower  mammals 
{e.  g.  dog)  the  isthmus  is  often  absent.  The  thyroids  in  man  are  small 
bodies  measuring  about  50  millimeters  in  length  by  30  millimeters  in  width  ; 
they  have  a  distinct  glandular  structure  but  possess  no  ducts.  Histological 
examination  shows  that  they  are  composed  of  a  number  of  closed  vesicles  vary- 
ing in  size.  Each  vesicle  is  lined  by  a  single  layer  of  cuboidal  epithelium, 
while  its  interior  is  filled  by  a  homogeneous  glairy  liquid,  the  colloid  substance 
which  is  found  also  in  the  tissue  between  the  vesicles  lying  in  the  lymph- 
spaces.  This  colloid  substance  is  regarded  as  a  secretion  from  the  epithelial 
cells  of  the  vesicles,  and  Biondi,^  Laugendorff,^  and  Hiirthle*  claim  to  have 
followed  the  development  of  the  secretion  in  the  epithelial  cells  by  micro- 
chemical  reactions.  While  the  interpretation  of  the  microscopical  appearances 
given  by  these  authors  is  not  identical,  they  agree  in  believing  that  the  colloid 
material  is  formed  within  some  or  all  of  the  epithelial  cells,  and  is  eliminated 
into  the  lumen  with  or  without  a  disintegration  of  the  cell-substance.  More- 
over, Langeudorff  and  Biondi  believe  that  the  colloid  material  is  finally  dis- 
charged into  the  lymphatics  by  the  rupture  of  the  vesicles.  The  composition 
of  the  colloid  is  incompletely  known. 

Parafhi/roids. — The  parathyroids  are  a  pair  of  small  bodies  lying  lateral  or 
posterior  to  the  thyroids,  and  in  some  animals  (rat)  they  are  apparently  con- 
tained within  the  substance  of  the  thyroids.  They  are  quite  unlike  the  thyroids 
in  structure,  consisting  of  solid  masses  or  columns  of  epithelial-like  cells  which 
are  not  arranged  to  form  acinous  vesicles.  According  to  Schaper*  these  bodies 
are  not  always  paired,  but  may  have  a  multiple  origin  extending  along  the 
common  carotid  in  the  neighborhood  of  the  thyroids.  Experimental  investi- 
gations  seem   to    show  that  these   bodies  are  probably  immature  structures 

^  See  Kaufmann  :  Archives  de  Physiologie  normale  et  pathologique,  1895,  p.  210. 

"  Berliner  Klhmche  Wochenschrift,  1888.  '  Archiv  fur  Physiologie,  1889,  Suppl.  Bd. 

*  Pflilger''s  Archiv  fib-  die  gesammte  Physiologie,  1894,  Bd.  Ivi.  S.  1. 

*  Archiv  fiir  mikroskopische  Anatomic,  1895,  Bd.  xlvi.  S.  500. 


208  AN  AMERICAN    TEXT-BOOK    OF    PHYSIOLOGY. 

which  are  capable  of  Jissiiming  the  fimetions  of  the  thyroids  to  a  greater  or 
less  extent  when  tlie.se  latter  are  removed  or  injured. 

Acce^'imri/  Thyroids. —  In  addition  to  tlie  paratliyi-oids  a  variable  number  of 
accessory  thyroids  have  been  described  by  dillerent  observers,  occurring  in  the 
neck  or  even  as  far  down  as  the  heart.  Tliese  bodies  possess  the  structure  of 
the  tliyroid,  and  presumably  have  the  same  function.  After  removal  of  the 
thyroids  they  may  suffice  to  prevent  a  fatal  result. 

Functions  of  the  Thyroids. — Very  great  interest  has  been  excited  within 
recent  years  with  regard  to  the  functions  of  the  thyroids.  In  1856  SchifF 
showed  that  in  dogs  complete  extirpation  of  the  two  thyroids  is  followed  by  the 
death  of  the  animal ;  and  within  the  last  few  years  similar  results  have  been 
obtained  by  numerous  observers.  Death  is  preceded  by  a  number  of  character- 
istic symptoms,  such  as  muscular  tremors,  which  may  pass  into  spasms  and  con- 
vulsions, cachexia,  emaciation  and  a  more  or  less  marked  condition  of  apathy. 
The  muscular  phenomena  seem  to  proceed  from  the  central  nervous  system, 
since  section  of  the  motor  nerves  protects  the  muscles  from  the  irritation.  The 
metabolic  changes  may  also  be  due  primarily  to  an  alteration  in  the  condition 
of  the  cord  and  brain.  Similar  results  have  been  obtained  in  cats.  Among  the 
herbivorous  animals  it  was  at  first  stated  that  removal  of  the  thyroids  does  not 
cause  death ;  but  so  far  as  the  rabbit  is  concerned  Gley '  has  shown  that  if  care 
be  taken  to  remove  the  parathyroids  also,  death  is  as  certain  and  more  rapid 
than  in  the  case  of  the  caruivora ;  and  a  similar  result  has  been  obtained  upon 
rats  by  Christiani.  It  is  still  asserted,  however,  that  in  sheep,  horses,  and  birds 
the  glands  may  be  removed  without  serious  injury  to  the  animal.  Cases  have 
been  reported  also  in  which  dogs  have  recovered  after  complete  thyroidectomy, 
but  these  cases  are  rare  and  may  be  explained  probal)ly  by  the  presence  of  acces- 
sory thyroids  which  remain  after  the  operation.  It  has  been  observed,  too,  that 
the  operation  is  more  rapidly  and  certainly  fatal  in  young  animals  than  in  old 
ones.  In  the  monkey  as  well  as  in  man  the  evil  results  following  the  removal 
of  the  glands  develop  more  slowly  than  in  the  lower  animals,  and  give  rise  to 
a  series  of  symptoms  resembling  those  of  myxoedema  in  man.  Among  these 
symptoms  may  be  mentioned  a  pronounced  anaemia,  diminution  of  muscular 
strength,  failure  of  the  mental  powers,  abnormal  dryness  of  the  skin,  loss  of 
hairs,  and  a  peculiar  swelling  of  the  subcutaneous  connective  tissue.  Physiol- 
ogists have  shown  that  in  the  case  of  dogs  the  fatal  results  following  thyroid- 
ectomy may  be  mitigated  or  entirely  obviated  by  grafting  a  portion  of  the 
gland  under  the  skin  or  in  the  peritoneal  cavity.  If  the  piece  grafted  is  suffi- 
ciently large  the  animal  recovers  apparently  completely  from  the  operation. 
So  also  in  removing  the  thyroids,  if  a  small  portion  of  the  gland,  or  the  para- 
thyroids, be  left  undisturbed  the  fatal  symptoms  do  not  develop.  In  human 
beings  suffering  from  myxoedema  as  the  result  of  loss  of  function  of  the  thy- 
roids it  has  been  abundantly  shown  that  injections  of  thyroid  extracts,  or 
feeding  the  fresh  gland,  restores  the  individual  to  an  approximately  normal 
condition, 

'  Archives  de  Physiologic  normale  et  Palhologiqtie,  1892,  p.  135. 


SECRETION.  209 

It  follows  from  these  various  ohscrv^iitions  that  the  thyroid  glauds  play  a 
very  important  part  of  soMie  kind  in  the  general  metabolism  of  the  body. 
Two  views  prevail  as  to  the  general  nature  of  their  function.^  According  to 
some  the  office  of  the  thyroids  is  to  remove  some  toxic  substance  which  nor- 
mally accumulates  in  the  blood  as  the  result  of  the  body-metabolism.  If  the 
thyroids  are  extirpated  this  substance  then  increases  in  quantity  and  produces 
the  observed  symptoms  by  a  ])rocess  of  auto-toxicatiou.  In  support  of  this 
view  there  are  numerous  observations  to  show  that  the  blood,  or  urine,  or 
muscle-juice  of  thyroidectoraized  animals  has  a  toxic  effect  upon  sound  animals. 
These  latter  results,  however,  do  not  appear  to  be  marked  or  invariable,  and 
in  the  hands  of  some  experimenters  have  failed  altogether.  The  second  view 
is  that  the  thyroids  secrete  a  material,  a  true  internal  secretion,  which  after 
getting  into  the  blood  plays  an  important  and  indeed  essential  part  in  the 
metabolic  changes  of  some  or  all  of  the  organs  of  the  body,  but  especially  the 
central  nervous  system.  In  support  of  this  view  we  have  such  facts  as  these : 
Injections  of  thyroid  extracts  have  a  beneficial  and  not  an  injurious  influence; 
there  is  microscopic  evidence  to  show  that  the  epithelial  cells  participate 
actively  in  the  formation  of  the  colloid  secretion  and  that  this  secretion 
eventually  reaches  the  blood  by  way  of  the  lymph-vessels;  the  beneficial 
material  in  the  thyroid  extracts  may  be  obtained  from  the  gland  by  methods 
which  prove  that  it  is  a  distinct  and  stable  substance  formed  in  the  gland,  as 
we  might  suppose  would  be  the  case  if  it  formed  part  of  a  definite  secretion. 
This  latter  fact,  indeed,  amounts  to  a  proof  that  the  important  function  of  the 
thyroids  is  connected  with  a  material  secreted  within  its  substance  ;  but  it  may 
still  be  questioned,  perhaps,  whether  this  material  acts  by  antagonizing  toxic  sub- 
stances produced  elsewhere  in  the  body  or  by  directly  influencing  the  body- 
metabolism.  Much  work  has  been  done  to  isolate  the  beneficial  material  of  the 
thyroid,  particularly  in  relation  to  the  therapeutic  use  of  the  gland  in  myxce- 
deraa  and  goitre.  The  mere  fact  that  feeding  the  gland  acts  as  well  as  injecting 
its  extracts  shows  the  resistant  nature  of  the  substance,  since  it  is  evidently  not 
injured  by  the  digestive  secretions.  It  has  been  shown  also  by  Baumann  ^ 
that  the  gland  material  may  be  boiled  for  a  long  period  with  10  per  cent,  sul- 
phuric acid  without  destroying  the  beneficial  substance.  This  observer  has 
succeeded  in  isolating  from  the  gland  a  substance  to  which  the  name  thyro- 
iodin  is  given,  which  is  characterized  by  containing  a  relatively  large  per- 
centage (9.3  per  cent,  of  the  dry  weight)  of  iodine,  and  which  preserves  in 
large  measure  the  beneficial  influence  of  thyroid  extracts  in  cases  of  myxoe- 
dema  and  parenchymatous  goitre.  This  notable  discovery  shows  that  the  thy- 
roid tissue  has  the  power  of  forming  a  specific  organic  compound  of  iodine,  and 
and  it  is  possible  that  its  influence  upon  body-metabolism  may  be  connected 
with  this  fact.  In  a  later  communication  by  Baumann  and  Roos^  it  is  stated 
that  the  thyroiodin  is  contained  within  the  gland  mainly  in  a  state  of  combi- 

'  SeeSchaefer :  "  Address  on  Physiology,"  annual  meeting  of  the  British  Medical  Association, 
London.  July-A'.igiist,  1895. 

2  Zeitschr'ift  fur  physiologische  Chemie,  1896,  Bd.  xxi.  8.  319.  ^  Ibid.,  S.  481. 

14 


210  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

nation  with  protoid  bodies,  from  wliicli  it  may  be  separated  by  digestion  with 
trastric  juice  or  bv  boilintr  witii  acids.  Most  of  the  sul)stance  is  combined  with 
an  albuminous  proteid  to  wiiicii  th(y  give  the  name  thyroicxhilbiimin,  while 
a  smaller  part  is  united  with  a  globulin-like  proteid.  In  this  paper  still  more 
favorable  reports  of  the  beneficial  action  of  this  substance  are  reported,  and 
there  can  be  but  little  doubt  that  the  authors  have  succeeded  in  isolating  the 
reallv  effective  substance  of  thyroid  extracts.  A  future  ])aper  upon  the  chemi- 
cal nature  of  thyroiodiu  is  promised,  Friiukel  has  also  isolated  a  basic  body 
— thyreo-antitoxiu — to  which  he  gives  the  formula  CgHnNjOj,  which  also 
shows  to  some  extent  the  beneficial  efi'eet  of  the  thyroid  extracts.  Drechsel  ^ 
has  succeeded  in  isolating  two  crystalline  basic  bodies  one  of  which  is  apparently 
identical  with  that  described  by  Friinkel.  Both  of  these  bodies  are  said  to  have 
a  beneficial  influence  when  administered  to  thyroidectomized  animals.  Drechsel 
suggests  that  there  may  be  three  separate  substances  formed  in  the  thyroid 
which  are  of  value  to  the  body,  and  that  corresponding  to  these  the  tliyroids 
may  exert  a  threefold  effect  upon  body-metabolism.  Gourlay  states  that  he 
has  succeeded  in  proving  the  presence  of  a  nucleo-albumin  in  the  thyroids,  and 
showing  by  microchemical  reactions  that  this  substance  is  present  in  the 
colloid  secretion. 

Adrenal  Bodies. — The  adrenal  bodies — or,  as  they  are  frequently  called 
in  human  anatomy,  the  suprarenal  capsules — belong  to  the  group  of  ductless 
glands.  Their  histology  as  well  as  their  physiology  is  incompletely  known. 
It  was  shown  first  by  Brown-S6quard  (1856)  that  removal  of  these  bodies  is 
followed  rapidly  by  death.  This  result  has  been  confirmed  by  many  experi- 
menters, and  so  far  as  the  observations  go  the  effect  of  complete  removal  is 
the  same  in  all  animals.  The  fatal  effect  is  more  rapid  than  in  the  case  of 
removal  of  the  thyroids,  death  following  the  operation  usually  in  two  to  three 
days,  or,  according  to  some  accounts,  within  a  few  hours.  The  symptoms  pre- 
ceding death  are  great  prostration  and  muscular  weakness,  and  marked  dimi- 
nution in  vascular  tone.  These  symptoms  are  said  to  resemble  those  occurring 
in  Addison's  disease  in  man,  a  disease  which  clinical  evidence  has  shown  to  be 
associated  with  pathological  lesions  in  the  suprarenal  capsules.  It  has  been 
expected,  therefore,  that  the  results  obtained  for  thyroid  treatment  of  myx- 
cedema  might  be  repeated  in  cases  of  Addison's  disease  by  the  use  of  adrenal 
extracts.  These  expectations  seem  to  have  been  realized  in  part,  but  complete 
and  satisfactory  reports  are  yet  lacking.  The  physiology  of  the  adrenals  has 
usually  been  explained  upon  the  auto-toxication  theory.  The  death  that  comes 
after  their  removal  has  been  accounted  for  upon  the  supposition  that  during 
life  they  remove  or  destroy  a  toxic  substance  produced  elsewhere  in  the  body, 
possibly  in  the  nniscular  system.  Oliver  ^  and  Schaefer,  however,  have  recently 
given  reasons  for  believing  that  this  organ  forms  a  peculiar  substance  which 
has  a  very  definite  physiological  action  especially  upon  the  muscular  system. 
They  find  that  aqueous  extracts  of  the  medulla  of  the  gland  when  injected  into 

»  CeniralbluU  fiir  Pbymoloijie,  1S96,  Bd.  ix..  Xo.  24. 
^  Journcd  of  Physiology,  1895,  vol.  xviii.  p.  230. 


SECRETION.  211 

the  blood  of  a  livini;  animal  have  a  romarkal)lo  influence  upon  the  heart, 
blood-vessels,  and  skeletal  muscles.  The  contractions  of  the  latter  are  pro- 
lono-ed,  somewhat  as  after  the  action  of  veratrin.  Upon  the  blood-vessels 
the  extracts  cause  a  strong  vascular  contraction,  giving  an  enormous  increase 
in  blood-pressure,  and  upon  the  heart  muscles  also,  if  the  vagus  nerves  have 
been  previously  cut,  there  is  a  similar  stimulating  action  manifested  by  an 
increase  in  the  strength  and  frequency  of  the  beats.  These  effects  are  obtained 
with  very  small  doses  of  the  extracts.  Schaefer  states  that  as  little  as  5| 
milligrams  of  the  dried  gland  may  ])roduce  a  maximal  effect  upon  a  dog  weigh- 
ing 10  kilograms.  The  effects  produced  by  such  extracts  are  quite  temporary 
in  character.  In  the  course  of  a  few  minutes  the  blood-pressure  returns  to 
normal,  as  also  the  heart-beat,  showing  that  the  substance  has  been  destroyed 
in  some  way  in  the  body,  although  where  or  how  this  destruction  occurs  is  not 
known.  According  to  Schaefer  the  kidneys  and  the  adrenals  themselves  are 
not  responsible  for  this  prompt  elimination  or  destruction  of  the  injurious 
substance.  It  is  possible  that  the  substance  in  question  may  be  continually 
secreted  under  normal  conditions  by  the  adrenal  bodies  and  play  a  very  import- 
ant part  with  reference  to  the  functional  activity  of  the  muscular  tissue. 

Pituitary  Body. — It  is  stated  that  complete  removal  of  the  pituitary  body 
causes  death,  accompanied  by  symptoms  which  resemble  somewhat  those  fol- 
lowing thyroidectomy,  such  as  muscular  tremors  and  spasms,  apathy,  etc.  A 
number  of  observers,  therefore,  have  supposed  that  physiologically  the  pitui- 
tary body  is  related  to  the  thyroids,  and  is  able  to  vicariously  assume,  to  a 
greater  or  less  extent,  the  functions  of  the  latter.  The  work  upon  this  organ 
has  not,  however,  made  sufficient  progress  to  euable  any  satisfactory  statements 
to  be  made  concerning  its  po.-sible  functional  value. 

Testis. — Some  of  the  earliest  work  upon  the  effect  of  the  internal  secretions 
of  the  glands  was  done  upon  the  reproductive  glands,  especially  the  testis,  by 
Browu-Sequard.^  According  to  this  observer  extracts  of  the  fresh  testis  when 
injected  under  the  skin  or  into  the  blood  may  have  a  remarkable  influence 
upon  the  nervous  system.  The  general  mental  and  physical  vigor  and  espe- 
cially the  activity  of  the  spinal  centres  are  greatly  improved,  not  only  in  cases 
of  general  prostration  and  neurasthenia,  but  also  in  the  case  of  the  aged. 
Brown-Sequard  maintained  that  this  general  dynamogenic  effect  is  due  to 
some  unknown  substance  formed  in  the  testis  and  subsequently  passed  into 
th«  blood,  although  he  admitted  that  some  of  the  same  substance  may  be 
found  in  the  external  secretion  of  the  testis,  i.  e.  the  spermatic  liquid.  More 
recentlv  PoehP  asserts  that  he  has  prepared  a  substance,  spermin,  to  which  he 
gives  the  formula  CgHi^Ng,  which  has  a  very  beneficial  effect  upon  the  metab- 
olism of  the  body.  He  believes  that  this  spermin  is  the  substance  which 
gives  to  the  testicular  extracts  prepared  by  Brown-S^quard  their  stimulating 
effect.  He  claims  for  this  substance  an  extraordinary  action  as  a  physiologi- 
cal tonic.     Tiie  precise  scientific  value  of  the  results  of  experiments  with  the 

'  Sfie  Archives  de  Phyaiologie  normale  et  pathologique,  1889-92. 
^  See  Zeitschrift  fur  klinkche  Medicin,  1894,  Bd.  26,  S.  133. 


212  A.\    AMKIUCAX    TEXT-BOOK    OF   PHYSIOI.OOY. 

testicular  extracts  eaiinot  bo  estimated  at  present,  in  spite  of  tlie  large  litera- 
ture upon  the  subject;  we  must  wait  for  more  detailed  and  exact  experiments, 
which  doubtless  will  soon  be  made,  (^nite  recently  Zoth  '  tiud  alsoPregel* 
seem  to  have  obtained  exact  objective  proof,  by  means  <jf  ergograjdiic  records, 
of  the  stimulating  action  of  the  testicular  extracts  upou  the  neuro-niuscular 
apparatus  in  man.  They  find  that  injections  of  the  testicular  extracts  cause  not 
oidy  a  diminution  in  the  muscular  and  nervous  fatigue  resulting  from  muscu- 
lar work,  but  also  lessen  the  subjective  fatigue  sensations.  The  fact  that  the 
internal  secretion  of  the  testis,  if  it  exists  at  all,  is  not  absolutely  essential  to 
the  life  of  the  body  as  a  whole,  as  in  the  case  of  the  thyroids,  adrenals,  and 
pancreas,  naturally  makes  the  satisfactory  determination  of  its  existence  and 
action  a  more  difficult  task. 

*  Imager's  Arckivfur  die  gesammle  Physiologic,  1896,  Bd.  62,  8.  335.  ^  Ibid.,  S.  379. 


IV.  CHEMISTRY  OF  DIGESTION  AND  NUTRITION. 


A.    Definition  and  Composition  of  Foods-.  Nature  of  Enzymes. 

Speaking  broadlv,  what  we  eat  aud  drink  for  the  purpose  of  nourish- 
ing the  body  constitutes  our  food.     A  person  in  adult  life  who  has  reached 
his  maximum  growth,  and  whose  weight  remains  practically  constant  from 
year  to  vear,  must  eat  and  digest  a  certain  average  quantity  of  food  daily  to 
keep  himself  in  a  condition  of  health  and  to  prevent  loss  of  weight.    In 
such  a  case  we  may  say  that  the  food  is  utilized  to  repair  the  wastes  of  the  body 
—that  is,  the  destruction  of  body-material  which  goes  on  at  all  times,  even 
during  sleep,  but  which  is  increased  by  the  physical  aud  psychical  activities 
of  the  waking  hours— and  in  addition  it  serves  as  the  source  of  heat,  mechanical 
work,  and  other  forms  of  energy  liberated  in  the  body.     In  a  person  who  is 
growing— one  who  is,  as  we  say,  laying  on  flesh  or  increasing  in  stature— a 
certain  portion  of  the  food  is  used  to  furnish  the  energy  and  to  cover  the  wastes 
of  the  bodv,  while  a  part  is  converted  into  the  new  tissues  formed  during 
growtli.     The  material  that  we  eat  or  drink  as  food  is  for  the  most  part  in  an 
insoluble  form,  and,  moreover,  it  has  a  composition  differing  oftentimes  very 
widely  from  that  of  the  tissues  which  it  is  intended  to  form  or  to  repair.     The 
object  of  the  processes  of  digestion   carried  on  in  the  alimentary  tract  is  to 
change  this  food  so  that  it  may  be  absorbed  into  the  blood,  and  at  the  same 
timelo  to  alter  its  composition  that  it  can  be  utilized  by  the  tissues  of  the  body. 
For  we  shall  find,  later  on,  that  certain  foods— eggs,  for  example— which  are 
verv  nutritious  when  taken  into  the  alimentary  canal  and  digested  cannot  be 
used  at  all  by  the  tissues  if  injected  at  once,  unchanged,  into  the  blood.     Tiie 
food  of  mankind  is  most  varied  in  character.     At  different  times  of  the  year 
and  in  different  parts  of  the  world  the  diet  is  changed  to  suit  the  necessities  of 
the  occasion.     When,  however,  we  come  to  analyze  the  various  animal  and 
vegetable  foods  made  use  of  bv  mankind,  it  is  found  that  they  are  all  com- 
posed of  one  or  more  of  five  or  six  different  classes  of  substances  to  which  the 
name  food-stuff)^  or  alimentarv  principles  has  been  .given.     To  ascertain  the 
nutritive  value  of  any  food,  it  must  be  analyzed  and  the  percentage  amounts  of 
the  different  food-stuffs  contained  in  it  must  be  determined.     The  classification 
of  food-stuffs  usually  given  is  as  follows : 


^  213 


214  AX  AMERICAN    TEXT-BOOK    OF   rilV/SIOLOG  V. 

f  Wak'r; 
Inorganic  salts; 

Proteids  (or  proteid-containing  bodies) ; 
Food-stnffs.  i   Albuminoids  (a  group  of   bodies   resembling   j)rotei<ls,   but 
liaviug  in  some  respects  a  dillereut  nutritive  valuej; 
Carboliydrates; 
Fats. 

What  is  known  witli  regard  to  the  specific  nutritive  value  of  each  of  these 
substances  will  be  given  later  ou,  after  the  processes  of  digestion  have  been 
described.  A  few  general  remarks,  however,  at  this  place  will  serve  to  give 
the  proper  standpoint  froui  which  to  begin  the  study  of  the  chemistry  of 
digestion  and  nutrition. 

Wafer  and  >S(i/ts. — Water  and  salts  we  do  not  commonly  consider  as  foods, 
but  the  results  of  scientific  investigation,  as  well  as  the  experience  of  life, 
show  that  these  substances  are  absolutely  necessary  to  the  body.  The  tissues 
must  maintain  a  certain  composition  in  water  and  salts  in  order  to  function 
normally,  and,  since  there  is  a  continual  loss  of  these  substances  in  the  various 
excreta,  they  must  continually  be  replaced  in  some  way  in  the  food.  It  is  to 
be  borne  in  mind  in  this  connection  that  water  and  salts  constitute  a  part  of 
all  our  solid  foods,  so  that  the  body  gets  a  partial  supply  at  least  of  these 
substances  in  everything  we  eat. 

Proteids. — The  composition  and  different  classes  of  proteids  are  described 
from  a  chemical  standpoint  in  the  section  ou  The  Chemistry  of  the  Body. 
Different  varieties  of  proteids  are  found  in  animal  as  well  as  in  vegetable 
foods.  The  chemical  composition  in  all  cases,  however,  is  approximately  the 
same.  Physiologically,  they  are  supposed  to  have  equal  imtritive  values  out- 
side of  differences  in  digestibility,  a  detail  which  M'ill  be  given  later.  The 
e&sential  use  of  the  proteids  to  the  body  is  that  they  supply  the  material  from 
M'hieh  the  new'  proteid  tissue  is  made  or  the  old  proteid  tissue  is  repaired, 
although,  as  we  shall  find  when  we  come  to  discuss  the  subject  more  thor- 
oughly (p.  285),  proteids  are  also  extremely  valuable  as  sources  of  energy  to 
the  body.  Inasmuch  as  the  most  important  constituent  of  living  matter  is  the 
proteid  part  of  its  molecule,  it  will  l)e  seen  at  once  that  proteid  food  is  an 
absolute  necessity.  Proteids  contain  nitrogen,  and  they  are  frequently  spoken 
of  as  the  mirocjenou>^  foods;  carl )()hyd rates  and  fats,  on  the  contrary,  do  not 
contain  nitrogen.  It  follows  inunediately  from  this  fact  that  fats  and  carbo- 
hydrates alone  could  not  suffice  to  make  new  protoplasm.  If  our  diet  con- 
tained no  proteids,  the  tissues  of  the  body  woidd  gradually  waste  away 
and  death  from  starv^ation  would  result.  All  the  food-stuffs  are  necessary 
in  one  way  or  another  to  the  preservation  of  perfect  health,  but  proteids, 
together  with  a  certain  proportion  of  water  and  inorganic  salts,  are  absolutely 
necessary  for  the  bare  maintenance  of  animal  life — that  is,  for  the  formation 
and  preservation  of  living  protoplasm.  Whatever  else  is  contained  in  our 
food,  proteid    of  some  kind    must    form    a   part    of  our  diet.     The    use  of 


CHEMISTRY   OF  DIGESTION  AND    NUTRITION.  215 

the  otiier  food-stutls  is,  as  we  shall  see,  more  or  less  accessory.  It  may  be 
worth  while  to  recall  here  the  familiar  fact  that  in  respect  to  the  nutritive 
importance  of  proteids  there  is  a  wide  difference  between  animal  and  vegetable 
life.  What  is  said  above  applies,  of  course,  only  to  animals.  Plants  can, 
and  for  the  most  part  do,  build  uj)  their  living  protoplasm  upon  diets  con- 
taining no  proteid.  With  some  exceptions  which  need  not  be  mentioned  here, 
the  food-stuff's  of  the  great  group  of  chlorophyll-containing  plants,  outside  of 
oxygen,  consist  of  water,  CO2,  and  salts,  the  nitrogen  being  found  in  the  last- 
mentioned  constituent. 

Alhuminoich. — Gelatin,  such  as  is  found  in  soups  or  is  used  in  the  form  of 
table-gelatin,  is  a  familiar  example  of  the  albuminoids.  They  are  not  found 
to  any  important  extent  in  our  raw  foods,  and  they  do  not  therefore  usually 
appear  in  the  analyses  given  of  the  composition  of  foods.  An  examination  of 
the  composition  and  properties  of  these  bodies  (see  section  on  The  Chemistry 
of  the  Body)  shows  that  they  resemble  closely  the  proteids.  Unlike  the  fats 
and  carbohydrates,  they  contain  nitrogen,  and  they  are  evidently  of  complex 
structure.  Nevertheless,  tliey  cannot  be  used  in  place  of  proteids  to  build 
protoplasm.  They  are  important  foods  without  doubt,  but  their  value  is  similar 
in  a  general  way  to  that  of  the  non-nitrogenous  foods,  fats  and  carbohydrates, 
rather  than  to  the  so-called  "  nitrogenous  foods,"  the  proteids. 

Carbohydrates. — We  include  among  carbohydrates  the  starches,  sugars, 
gums,  and  the  like  (see  Chemical  section) ;  they  contain  no  nitrogen.  Their 
physiological  value  lies  in  the  fact  that  they  are  destroyed  in  the  body  and  a 
certain  amount  of  energy  is  thereby  liberated.  The  energy  of  muscular  work 
and  of  the  heat  of  the  body  comes  largely  from  the  destruction  or  oxidation 
of  carbohydrates.  Inasmuch  as  we  are  continually  giving  off  energy  from 
the  bodv,  chiefly  in  the  form  of  muscular  work  and  heat,  it  follows  that 
material  for  the  production  of  this  euergy  must  be  taken  in  the  food.  Carbo- 
hydrates form  perhaps  the  easiest  and  cheapest  source  of  this  energy.  They 
constitute  the  bulk  of  our  ordinary  diet. 

Fats. — In  the  group  of  fats  we  include  not  only  what  is  ordinarily  under- 
stood by  the  term,  but  also  the  oils,  animal  and  vegetable,  which  form  such  a 
common  part  of  our  food.  Fats  contain  no  nitrogen  (see  Chemical  section). 
Their  use  in  the  body  is  substantially  the  same  as  that  of  the  carbohydrates. 
Weight  for  weight,  they  are  more  valuable  than  the  carbohydrates  as  sources 
of  energy,  but  the  latter  are  cheaper,  more  easily  digested,  and  more  easily 
destroyed  in  the  body.  For  these  reasons  we  find  that  under  most  conditions 
fats  are  a  subsidiary  article  of  food  as  compared  with  the  carbohydrates.  From 
the  standpoint  of  the  physiologist,  fats  are  of  special  interest  because  the 
animal  body  stores  up  its  reserve  of  food  material  mainly  in  that  form.  The 
history  of  the  origin  of  the  fats  of  the  body  is  one  of  the  most  interesting 
parts  of  the  subject  of  nutrition,  and  it  will  be  discussed  at  some  length  in  its 
proper  place. 

As  has  been  said,  our  ordinary  foods  are  mixtures  of  some  or  all  of  the 
food-stuffs,  together  with  such  things  as  flavors  or  condiments,  whose  nutritive 


216 


AN   AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


value  is  of  u  .special  character.  Curefiil  analyses  have  been  luatle  of  the 
different  articles  of  food,  mostly  of  the  raw  or  uncooked  footls.  As  might 
be  expected,  the  analyses  on  recoi-d  diffei-  more  or  less  in  the  percentages 
assigned  to  the  various  constituents,  but  almost  any  of  the  tables  published 
give  a  just  idea  of  the  fundamental  nutritive  value  of  the  common  foods. 
For  details  of  separate  analyses  reference  may  be  made  to  some  of  the  larger 
works  upon  the  composition  of  foods.'  The  subjoined  table  is  one  compiled 
by  Munk  from  the  analyses  given  by  Konig : 

Composition  of  Foods. 


In  100  parts. 


Water. 


Meat 76.7 

i^gffs 73.7 

Cheese 36-60 

Cow's  milk 87.7 

Human  milk 89.7 

Wheat  dour 13.3 

Wlieat  bread 35.6 

Eye  flour 13.7 

Rye  bread ,  42.3 

Rioe      13.1 

Corn 13.1 

Macaroni j  10.1 

Pea^,  beans,  lentils     .    .    .    .  i  12-15 

Potatoes 75.5 

Carrots j  87.1 

Cabbages i  90 

Mushrooms 73-91 

Fruit !  84 


Proteid. 


Fat. 


Carbohydrate. 


Digestible.  '    Cellulose. 


20.8 

12.6 

25-33 

3.4 

2.0 

10.2 

7.1 

11.5 

6.1 

7.0 

9.9 

9.0 

23-26 

2.0 

1.0 

2-3 

4-8 

0.5 


1.5 
12.1 
7-30 
3.2 
3.1 
0.9 
0.2 
2.1 
0.4 
0.9 
4.6 
0.3 

0.2 
0.2 
0.5 
0.5 


0.3 

3-7 

4.8 

5.0 
74.8 
55.5 
69.7 
49.2 
77.4 
68.4 
79.0 
49-54 
20.6 

9.3 

4-6 

3-12 

10 


0.3 
0.3 
1.6 
0.5 
0.6 
2.5 
0.3 
4-7 
0.7 
1.4 
1-2 
1-5 
4 


Ash. 


1.3 
1.1 
3-4 
0.7 
0.2 
0.5 
1.1 
1.4 
1.5 
1.0 
1.5 
0.5 
2-3 
1.0 
0.9 
1.3 
1.2 
0.5 


An  examination  of  this  table  will  show  that  the  animal  foods,  particularlv 
the  meats,  are  characterized  by  their  small  percentage  in  cari)ohvdrate  and  bv 
a  relatively  large  amount  of  proteid  or  of  proteid  and  fat.  A\'ith  regard  to 
the  last  two  food-stuffs,  meats  differ  very  much  among  themselves.  Some 
idea  of  the  limits  of  variation  may  be  obtained  from  the  following  table, 
taken  chieflv  from  Kouitj's  analyses: 


Reef,  moderately  fat 
Veal,  fat      ..... 
Mutton,  moderately  fat 

Pork,  lean 

Ham,  salted  .  .  .  . 
Pork  (bacon),  very  fat* 
Mackerel  * 


Water. 

73.03 
72.31 
75.99 
72.57 
62.58 
10.00 
71.6 


Proteid. 


20.96 
18.88 
17.11 
20.05 
22.32 
3.00 
18.8 


Fat. 


5.41 
7.41 
5.77 
6.81 
8.68 
80.50 
8.2 


Carbohydrate. 


0.46 
0.07 


Ash. 

1.14 

1.33 

1.33 

1.10 

6.42 

6.5 

1.4 


The  vegetable  foods  are  distinguished,  as  a  rule,  by  their  large  percentage 
in  carbohydrates  and  the  relatively  small  amounts  of  proteids  and  fats,  as  seen, 
for  example,  in  the  composition  of  rice,  corn,  wheat,  and  potatoes.     Neverthe- 

'  Konig,  Die  Menschlichen  Kahrungx  und  Oemtssmittel,  3d  ed.,  1889 ;  Parke's  Manual  of  Prac- 
tical Hycjiene.  section  on  Food. 

*  .\twater:   The  Chemistry  of  Foods  and  Nutrition,  1887. 


CHEMISTRY   OF    DIGESTION  AND    NUTRITION.  217 

less,  it  will  be  nulitvd  that  the  ])ro[K)rtiuii  of  proteid  in  soiuc  oi"  the  vegetables 
is  not  at  all  iusiguiticaut.  They  are  charaeterized  by  their  excess  in  carbohy- 
drates rather  than  by  a  deficiency  in  proteids.  The  composition  of  peas  and 
other  legtiniinous  foods  is  remarkable  for  the  large  percentage  of  proteid, 
which  exceeds  that  found  in  meats.  Analyses  such  as  are  given  here  are 
indispensable  in  determining  the  true  nutritive  value  of  foods.  Nevertheless, 
it  must  be  borne  in  mind  that  the  chemical  composition  of  a  food  is  not  alone 
sufficient  to  determine  it^^  j)recise  value  in  nutrition.  It  is  obviously  true  that 
it  is  not  what  we  eat,  but  what  we  digest  and  absorb,  that  is  nutritious  to  the 
body,  so  that,  in  addition  to  determining  the  proportion  of  food-stuffs  in  any 
given  food,  it  is  necessary  to  determine  to  what  extent  the  several  constitu- 
ents are  digested.  This  factor  can  be  obtained  only  by  actual  experi- 
ments; a  number  of  results  bearing  upon  this  point  have  been  collected  which 
will  be  spoken  of  later.  It  may  be  said  here,  however,  that  in  general 
the  proteids  of  animal  foods  are  more  completely  digestible  than  are  those 
of  vegetables,  and  Mith  them,  therefore,  chemical  analysis  comes  nearer  to 
expressing  directly  the  nutritive  value. 

The  physiology  of  digestion  consists  chiefly  in  the  study  of  the  chemical 
changes  which  the  food  undergoes  during  its  passage  through  the  alimentary 
canal.  It  hajjpens  that  these  chemical  changes  are  of  a  peculiar  character. 
The  peculiarity  is  due  to  the  fact  that  the  changes  of  digestion  are  effected 
through  the  agency  of  a  group  of  bodies  known  as  enzymes,  or  unorganized 
ferments,  whose  chemical  action  is  different  from  that  of  the  ordinary  reagents 
with  which  we  have  to  deal.  It  will  save  useless  repetition  to  give  here 
certain  general  facts  that  are  known  with  reference  to  these  bodies,  reserving 
for  future  treatment  the  details  of  the  action  of  the  specific  enzymes  found  in 
the  different  digestive  secretions. 

Enzymes. — Enzymes,  or  unorganized  ferments,  or  unformed  ferments,  is 
the  name  given  to  a  group  of  bodies  produced  in  animals  and  plants,  but  not 
themselves  endowed  with  the  structure  of  living  matter.  The  term  ^inorganizcd 
or  unformed  ferment  was  formerly  used  to  emphasize  the  distinction  between 
these  bodies  and  living  ferments,  such  as  the  yeast-plant  or  the  bacteria. 
"  Enzyme,"  however,  is  a  better  name,  and  is  coming  into  general  use. 
Enzymes  are  to  be  regarded  as  dead  matter,  although  produced  in  living 
protoplasm.  Chemically,  they  are  defined  as  complex  organic  compounds  con- 
taining nitrogen.  Their  exact  composition  is  unknown,  as  it  has  not  been 
found  possible  heretofore  to  obtain  them  in  pure  enough  condition  for  analysis. 
Although  several  elementary  analyses  are  recorded,  they  cannot  be  considered 
reliable.  It  is  not  known  whether  or  not  the  enzymes  belong  to  the  group  of 
proteids.  Solutions  of  most  of  the  enzymes  give  some  or  all  of  the  general 
reactions  for  proteids,  but  there  is  always  an  uncertainty  as  to  the  purity  of 
the  solutions.  With  reference  to  the  fibrin  ferment  of  blood,  one  of  the 
enzymes,  observations  have  recently  been  made  which  seem  to  show  that  it 
at  least  belongs  to  the  group  of  combined  proteids,  uucleo-albumins  (for 
details  see  the  section  on   Blood).      But  even  should   this  be  true,  we  are 


218  AX   AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

not  justified    in   making  any  general   application   of  this   i'act   to   the   whole 
group. 

Clasfiijication  of  Enzymes. — Enzymes  are  classified  according  to  the  kind 
of"  reaction  they  produce — namely  : 

1.  Proteolytic  enzymes,  or  those  acting  upcjn  protcids,  converting  them  to  a 
soluble  modification,  peptone  or  proteose.  As  examples  of  this  group  we  have 
in  the  animal  body  pepKin  of  the  gastric  juice  and  trypsin  of  the  pancreatic 
juice.  In  plants  a  similar  enzyme  is  found  in  the  pineapple  familv  (bromelin) 
and  in  the  papaw  (papain). 

2.  Amylolytie  enzyme.s,  or  those  acting  upon  the  starches,  converting  them 
to  a  soluble  form,  sugar,  or  sugar  and  dextrin.  As  examples  of  this  group 
we  have  in  the  animal  body  pttycdin,  found  in  saliva,  amylop.S'in,  found  in 
pancreatic  juice,  and  in  the  liver  an  enzyme  capable  of  converting  glycogen 
to  sugar.  In  the  plants  the  best-known  example  is  diastase,  found  in 
germinating  seeds.  This  particular  enz\'me  has  been  known  for  a  long  time 
from  the  use  made  of  it  in  the  manufacture  of  beer.  In  fact,  the  name  "  dias- 
tase "  is  frequently  used  in  a  generic  sense,  "  the  diastatic  enzymes,"  to  cha- 
racterize the  entire  group  of  starch-destroying  ferments. 

3.  Fat-splitting  enzymes,  or  those  acting  upon  the  neutral  fats,  breaking 
them  up  into  glycerin  and  the  corresponding  fatty  acid.  The  best-known 
example  in  the  animal  body  is  found  in  the  pancreatic  secretion ;  it  is  known 
usually  as  steapsin,  altli<uigh  it  has  been  given  several  names.  Similar 
enzymes  are  known  to  occur  in  a  number  of  seeds. 

4.  Inverting  enzymes,  or  those  having  the  property  of  converting  the  double 
into  the  single  sugars — the  di-saccharides,  such  as  cane-sugar  and  maltose,  into 
the  mono-saccharides,  such  as  dextrose  and  levulose.  Two  enzymes  of  this 
character  have  been  found  in  the  animal  body,  one  acting  upon  cane-sugar  and 
one  on  maltose.  They  are  usually  spoken  of  as  invertin  or  inverting  enzymes. 
A  similar  enzyme  may  be  obtained  from  the  yeast-plant. 

5.  Coagulating  enzymes,  or  those  acting  upon  soluble  proteids,  precipitating 
thera  in  an  insoluble  form.  As  examples  of  this  class  we  have  fibrin  ferment 
(thrombin),  formed  in  shed  blood,  and  rennin,  the  milk-curdling  ferment  of  the 
gastric  juice.    An  enzyme  similar  to  rennin  ha?  been  found  in  pineapple-juice. 

These  five  classes  comprise  the  groups  of  enzymes  that  are  known  to  occur 
in  the  animal  body.  One  or  more  examples  of  each  group  take  part  in  the 
digestion  of  food  at  some  time  during  its  passage  through  the  alimentary  canal. 
Two  other  important  groups  of  enz^-mes  which  are  not  formed  in  the  animal 
body  may  be  mentioned  briefly  in  this  connection  for  the  sake  of  completeness  : 

6.  Glucoside-sjjlitting  enzymes,  or  those  acting  upon  the  glucosides,  giving  a 
carbohydrate  as  one  of  the  products  of  decomposition.  Examples:  emulsin, 
found  in  bitter  almonds ;  myrosin,  in  mustard-seeds. 

7.  Urea-splitting  enzymes,  or  those  acting  upon  urea,  converting  it  to  ammo- 
nium carbonate ;  found  in  many  bacteria,  especially  in  those  normally  occur- 
ring in  the  urine. 

A  great  number  of  general  reactions  have  been  discovered,  applicable,  with 


CHEMISriiV   OF  DIGESTION  AND   NUTRITION.  219 

ail  exct'i)ti()ii  here  and  there,  to  the  whole  j^i-oiip  of  enzymes.     Amon<r  these 
reactions  the  f'oHowing  are  the  most  useful  or  si<^nificant : 

1.  SolubUity. — The  enzymes  are  all  soluble  in  water.  They  are  also  solu- 
ble in  glycerin,  this  being  the  most  generally  useful  solvent  for  obtaining 
extracts  of  the  enzymes  from  the  organs  in  which  they  are  formed. 

2.  Effect  of  Temperature. —  In  a  moist  condition  they  are  all  destroyed  by 
temperatures  below  the  boiling-point;  60'^  to  80°  C.  are  the  limits  actually 
observed.  Very  low  temperatures  retard  or  even  suspend  entirely  (0°  C.)  their 
action,  without,  however,  destroying  the  enzyme.  For  each  enzyme  there  is 
a  temperature  at  which  its  action  is  greatest. 

3.  Incompleteness  of  Action. — With  the  exception  perhaps  of  the  coagulat- 
ing enzymes,  they  are  characterized  by  the  fact  that  in  any  given  solution  they 
never  completely  destroy  the  substance  upon  which  they  act.  It  seems  that 
the  products  of  their  activity,  as  they  accumulate,  finally  prevent  the  enzvmes 
fi'om  acting  further ;  when  these  products  are  removed  the  action  of  the  enzyme 
begins  again.  The  most  familiar  example  of  this  very  striking  peculiarity  is 
found  in  the  action  of  jiepsin  on  proteids.  The  products  of  digestion  in  this 
case  are  peptones  and  proteoses,  and  when  they  have  reached  a  certain  concen- 
tration they  prevent  any  further  proteolysis  on  the  part  of  the  pepsin. 

4.  Relation  of  the  Amount  of  Enzyme  to  the  Effect  it  Produces. — With  most 
substances  the  extent  of  the  chemical  change  produced  is  proportional  to  the 
amount  of  the  substance  entering  into  the  reaction.  With  the  enzymes  this  is 
not  so.  Except  for  very  small  quantities,  it  may  be  said  that  the  amount  of 
change  caused  is  independent  of  the  amount  of  enzyme  present,  or,  to  state  the 
matter  more  accurately,  "  with  increasing  amounts  of  enzymes  the  extent  of 
action  also  increases,  reaching  a  maximum  with  a  certain  percentage  of  enzyme; 
increase  of  enzyme  beyond  this  has  no  effect."^  This  fact  was  formerly  inter- 
preted to  mean  that  the  enzyme  is  not  used  up — that  is,  not  permanently  altered 
— by  the  reaction  which  it  causes.  This  belief,  indeed,  must  be  true  substan- 
tially, but  it  has  been  found  practically  that  a  given  solution  of  enzyme  cannot 
be  used  over  and  over  again  indefinitely.  It  is  generally  believed  now  that, 
although  an  enzyme  causes  an  amount  of  change  in  the  substance  it  acts  upon 
altogether  out  of  proportion  to  the  amount  of  its  own  substance,  neverthe- 
less it  is  eventually  destroyed  ;  its  action  is  not  unlimited.  Whether  this  using 
up  of  the  enzyme  is  a  necessary  result  of  its  activity,  or  is,  as  it  were,  an  acci- 
dental effect  from  spontaneous  changes  in  its  own  molecule,  remains  unde- 
termined. 

Theories  of  the  Manner  of  Action  of  the  Enzymes. — It  is  now^ 
known  that  with  the  possible  exception  of  the  coagulating  enzymes  the  action 
of  the  enzymes  is  that  of  hydrating  agents ;  they  produce  their  effect  by  what 
is  known  as  hydrolysis ;  that  is,  they  cause  the  molecules  of  the  substance 
upon  which  they  act  to  take  up  one  or  more  molecules  of  water;  the  resulting 
molecule  then  splits  or  is  dissociated,  with  the  formation  of  two  or  more  sim- 
pler bodies.     This  is  one  of  the  most  significant  facts  in  connection  with  the 

'  Tanimann  :  Zeitschrift  fur  physiologiache  Chemie,  xvi.,  1892,  p.  271. 


220  AN  AMERICAN    TEXT- HOOK    OF   PHYSIOLOGY. 

action  of  tlie  eDzynies;  it  is  well  illustrated  by  the  action  of  invertin  on  cane- 
sugar,  as  follows : 

C.,H,A.+H,0  =  C«H„(),  +  CJi.A 

Cane-suKar.  Dextrose.  Levulose. 

In  what  way  enzymes  cause  the  substances  they  act  u})()ii  to  take  up  water  is 
unknown.  The  fact  that  they  are  not  themselves  used  up  in  tlic  reaction  j)rc>- 
portionally  to  the  change  they  cause  formerly  influenced  physiologists  and  chem- 
ists to  explain  their  effect  as  due  to  catalyfiis,  or  contact  action.  In  its  original 
sense  this  designation  meant  that  the  molecules  of  enzyme  act  by  their  mere 
presence  or  contiguity,  but  it  need  scarcely  be  said  that  a  statement  of  this 
kind  does  not  amount  to  an  explanation  of  their  manner  of  action  ;  to  say  they 
"act  by  catalysis "  means  nothing  in  itself  Efforts  to  explain  their  action 
have  resulted  in  a  number  of  hypotheses,  a  detailed  account  of  which  would 
hardly  be  appropriate  here.  It  may  be  mentioned  that  two  ideas  have  found 
most  general  acceptance :  one,  that  the  vibrations  of  the  molecules  of  enzyme 
set  into  more  rapid  vibration  the  molecules  of  the  substance  acted  upon,  thus 
leading  to  the  taking  up  of  water  and  to  the  subsequent  splitting ;  the  other  idea 
is  that  the  enzyme  enters  into  a  definite  chemical  reaction,  in  which,  however, 
it  plays  the  part  of  a  carrier  or  go-between,  so  that,  although  the  enzyme  is 
directly  concerned  in  producing  a  chemical  change,  the  final  outcome  is  that  it 
remains  in  its  original  condition.  A  number  of  chemical  reactions  of  this 
general  character  are  known,  in  which  some  one  substance  passes  through  a 
cycle  of  changes,  aiding  in  the  production  of  new  compounds,  but  itself 
returning  always  to  its  first  condition  ;  for  example,  the  ])art  taken  by  HjSO^ 
in  the  manufacture  of  ether  from  alcohol,  or  the  successive  changes  of  haemo- 
globin to  oxyhsemoglobin  and  back  again  to  haemoglobin  after  giving  up  its 
oxygen  to  the  tissues.  Perhaps  the  most  suggestive  reaction  of  this  character 
is  the  one  quoted  by  Chittenden  ^  to  illustrate  this  very  hypothesis  as  to  the 
manner  of  action  of  enzymes,  as  follows  :  Oxygen  and  carbon  monoxide  gas, 
if  perfectly  dry,  will  not  react  upon  the  passage  of  an  electric  spark.  If, 
however,  a  little  aqueous  vapor  is  present,  they  may  be  made  to  unite  readily, 
with  the  formation  of  COj.  The  water  in  this  case,  without  doubt,  enters 
into  the  reaction,  but  in  the  end  it  is  re-formed,  and  the  final  result  is  as 
though  the  water  had  not  directly  participated  in  the  process.  The  reactions 
supposed  to  take  place  are  explained  by  the  following  equations : 

CO  +  2H2O  +  O2  =  CO  (OH),  +  HA- 

H2O,  -f  CO  =  COfOH)^. 

2CO(OH)2  =  2CO2  4-  2HoO. 

B.     Salivary  Digestion. 

The  first  of  the  digestive  secretions  with  which  the  food  comes  into  contact 
is  ftaliva.     This  liquid  is  a  mixed  secretion   from  the  six  large  salivary  glands 
(parotids,  submaxillaries,  and  sublinguals)  and  the  smaller  nuicous  and  serous 
*  Cartwright  Lectures,  Medical  Record,  New  York,  April  7,  1894. 


CHEMISTRY   OF   DIGESTION  AND    NUTRITTON.  221 

glands  which  ojx'ii  into  the  nioiitli.  The  physic )logicul  uiiattjiiiy  of  these 
ghuuls  and  the  mechanism  l)y  wliicli  the  secretions  are  produced  and  regulated 
will  be  found  described  fully  in  the  section  on  Secretion  ;  we  are  concerned 
here  only  with  the  composition  of  the  secretion  after  it  is  formed,  and  with  its 
action  upon  foods. 

Properties  and  Composition  of  the  Mixed  Saliva. — Filtered  saliva  is  a 
clear,  viscid,  transparent  liquid.  As  obtained  usually  from  the  mouth,  it  is 
more  or  less  turbid,  owing  to  the  presence  in  it,  in  suspension,  of  particles 
of  food  or  of  detached  cells  from  the  epithelium  of  the  mouth.  A  some- 
what characteristic  cell  contained  in  it  in  small  numbers  is  the  so-called 
"  salivary  corpuscle."  These  bodies  are  probably  leucocytes,  altered  in  struc- 
ture, which  have  escaped  into  the  secretion.  So  far  as  is  known,  they  have  no 
physiological  value.  The  specific  gravity  of  the  mixed  secretion  is  on  an  aver- 
age 1003,  and  its  reaction  is  normally  alkaline.  The  total  amount  of  secretion 
during  twenty-four  hours  varies  naturally  with  the  individual  and  the  condi- 
tions of  life;  the  estimates  made  vary  from  300  to  1500  grams.  Chemically,  in 
addition  to  the  water,  the  saliva  contains  mucin,  ptyalin,  albumin,  and  inor- 
ganic salts.  The  proportions  of  these  constituents  are  given  in  the  ibllowing 
analysis  (Hammerbacher) : 

In  1000  parts. 

Water 994.203 

Solids : 

Mucin  (and  epithelial  cells) 2.202 ^ 

Ptyalin  and  albumin 1.390  I  5  797 

Inorganic  salts 2.205  J 

Potassium  sulphocyanide 0.041 


[ 


The  inorganic  salts,  in  addition  to  the  sulphocyanide,  which  occurs  only  in 
traces,  consist  of  the  chlorides  of  potassium  and  sodium,  the  sulphate  of 
potassium,  and  the  phosphates  of  potassium,  sodium,  calcium,  and  magnesium  ; 
the  earthy  phosphates  form  about  9.6  per  cent,  of  the  total  ash.  Mucin  is  an 
important  constituent  of  saliva;  it  gives  to  the  secretion  its  ropy,  viscid  cha- 
racter, which  is  of  so  much  value  in  the  mechanical  function  it  fulfils  in 
swallowing.  This  substance  is  formed  in  the  salivary  glands.  Its  formation 
in  the  protoplasm  of  the  cells  may  be  followed  microscopically  (see  the  section 
on  Secretion).  Chemically,  it  is  now  known  to  be  a  combination  of  a  proteid 
with  a  carbohydrate  group  (see  section  on  The  Chemistry  of  the  Body).  So 
far  as  known,  mucin  has  no  function  other  than  its  mechanical  use.  The  pres- 
ence of  potassium  sulphocyanide  (KCXS)  among  the  salts  of  saliva  has  always 
been  considered  interesting,  since,  although  it  occurs  normally  in  urine  as  well 
as  in  saliva,  it  is  not  a  salt  found  commonly  in  the  secretions  of  the  body,  and 
its  occurrence  in  saliva  seemed  to  indicate  some  special  activity  on  the  part  of 
the  salivary  gland,  the  possible  value  of  which  has  been  a  subject  of  specula- 
tion. In  the  saliva,  however,  the  sulphocyanide  is  found  in  such  minute  traces 
and  its  presence  is  so  inconstant  that  no  special  functional  importance  can  be 
attributed  to  it.  It  is  supposed  to  be  derived  from  the  decomposition  of 
proteids,  and  it  represents,  therefore,  one  of  the  end-products  of  proteid  metab- 


222  AN  AMJJRICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

ollsni.  rutassiuiii  siilplKx-vuiiido  may  ho  detected  in  saliva  by  adding  to  the 
latter  a  (Uhite  aeiduhited  solution  of  ferric  chloride,  a  reddish  color  being 
produced. 

Ptyalin  and  its  Action. — From  a  piiysiological  standj)()int  the  most 
important  constituent  of  saliva  is  liiyaVm.  It  is  an  unorganized  ferment  or 
enzyme  belonging  to  the  amylolytic  or  diastatie  group  (p.  218)  and  possessing 
the  general  properties  of  enzymes  already  enumerated.  It  is  found  in  human 
saliva  and  in  tiiat  of  many  of  the  lower  animals — for  exam})le,  the  j)ig  and 
the  herbivora — but  it  is  said  to  be  absent  in  the  carnivora.  Ptyalin  has  not 
been  isolated  in  a  sufficiently  pure  condition  for  satisfactory  analy>is,  so  that 
its  chemical  nature  is  undetermined ;  we  depend  for  its  detection  upon  its 
specific  action — that  is,  its  effect  upon  starch.  Speaking  roughly,  we  say  that 
ptyalin  converts  starch  into  sugar,  but  when  we  come  to  consider  the  details 
of  its  action  we  find  tiiat  it  is  complicated  and  that  it  consists  in  a  series  of 
hydrolytic  splittings  of  the  starch  molecule ;  the  exact  products  of  the  reaction 
depend  upon  the  stage  at  which  the  action  is  interrupted.  To  demonstrate 
the  action  of  ptyalin  on  starch  it  is  only  necessary  to  make  a  suitable  starch 
paste  by  boiling  some  powdered  starch  in  water,  and  then  to  add  a  little  fresh 
saliva.  If  the  mixture  is  kept  at  a  proper  temperature  (30°  to  40°  C),  the 
presence  of  sugar  may  be  detected  within  a  few  minutes.  The  sugar  that  is 
formed  was  for  a  time  supposed  to  be  ordinary  grape-sugar  (dextrose,  CgH,^,Og), 
but  later  experiments  have  shown  conclusively  that  it  is  maltose  (CijHgjOj,,- 
HgO),  a  form  of  sugar  more  closely  related  in  formula  to  cane-sugar  (see 
Chemical  section).  In  experiments  of  the  kind  just  described  two  facts 
may  easily  be  noticed :  first,  that  the  conversion  of  starch  to  sugar 
is  not  direct,  but  occurs  through  a  number  of  intermediate  stages;  second, 
that  the  starch  is  not  entirely  converted  to  sugar  under  the  conditions  of 
such  experiments — namely,  when  the  digestion  is  carried  on  in  a  vessel, 
digestion  in  vitro.  The  second  fact  is  an  illustration  of  the  incomplete- 
ness of  action  of  the  enzymes,  a  general  property  which  has  already  been 
noticed.  We  may  supj)ose,  in  this  as  in  other  cases,  that  the  products  of 
digestion,  as  they  accumulate  in  the  vessel,  tend  to  retard  and  finally  to  sus- 
pend the  amylolytic  action  of  the  ptyalin.  In  normal  digestion,  however,  it 
is  usually  the  case  that  the  products  of  digestion,  as  they  are  formed,  are 
removed  by  absorption,  and  if  the  above  explanation  of  the  cause  of  the 
incompleteness  of  action  is  correct,  then  under  normal  conditions  we  should 
expect  a  complete  conversion  of  starch  to  sugar.  Lea  ^  states  that  if  the 
products  of  ptyalin  action  are  partially  removed  by  dialysis  during  digestion 
in  vitro,  a  much  larger  percentage  of  maltose  is  formed.  Ilis  experiments 
would  seem  to  indicate  that  in  the  body  the  action  of  the  amylolytic  ferments 
may  be  c()m])lete,  and  that  the  final  })roduct  of  their  action  may  be  maltose 
alone.  It  will  be  found  that  this  statement  applies  practically  not  to  the 
ptyalin,  but  to  the  similar  amylolytic  enzyme  in  the  pancreatic  secretion,  owing 
to  the  fact  that,  normally,  food  is  held  in  the  mouth  for  a  short  time  only,  and 
*  Jomiud  of  Physiology,  vol.  xi.,  1890,  p.  227. 


CHEMISTRY    OF   DIGESTION  AND    NUTRITION.  223 

that  ptyalin  tligv.stioii  is  soon  interruptecl  after  the  food  roaches  the  stomacli. 
Witli  reference  to  the  intorniediate  stages  or  pnjducts  in  the  convei'siou  of 
stardi  to  sugar  it  is  dilHcult  to  give  a  perfectly  clear  account.  It  was  formerly 
thought  that  the  starch  was  first  converted  to  dextrin,  and  this  in  turn  was 
converted  to  sugar.  It  is  now  believed  that  the  starch  molecule,  which  is  quite 
complex,  consisting  of  some  multiple  of  0^11,1,0,, — possibly  {^'^n)Or^2ii — fi^'-'^t 
takes  up  water,  thereby  becoming  soluble  (soluble  starch,  amylodcxtrin),  and 
then  splits,  with  the  formation  of  dextrin  and  maltose,  and  that  the  dextrin 
again  undergoes  the  same  hydrolytic  process,  with  the  formation  of  a  second 
dextrin  and  more  maltose ;  this  process  may  continue  under  favorable  con- 
ditions until  only  maltose  is  present.  The  difficulty  at  present  is  in  isolating 
the  diflferent  forms  of  dextrin  that  are  produced.  It  is  usually  said  that  at 
least  two  forms  occur,  one  of  which  gives  a  red  color  with  iodine,  and  is  then;- 
fore  known  as  erythrodextrin,  while  the  other  gives  no  color  reaction  M'itli 
iodine,  and  is  termed  achroodextrin.  It  is  pretty  certain,  however,  that  there 
are  several  forms  of  achroodextrin,  and,  according  to  some  observers,  erythro- 
dextrin  also  is  really  a  mixture  of  dextrins  with  maltose  in  varying  propor- 
tions. In  accordance  with  the  general  outline  of  the  process  given  above, 
Neumeister  ^  proposes  the  following  schema,  which  is  useful  because  it  gives  a 
clear  representation  of  one  theory,  but  which  must  not  be  considered  as  satis- 
factorily demonstrated  (see  also  the  section  on  Chemistry  of  the  Body). 

/Maltose. 
Starch— soluble  starch    j 

(amylodextrin).  1  .,,  ,^ 

■  'Maltose. 


Erythrodextrin. 

/Maltose. 

Achroodextrin  a.  < 

/Maltose. 

Achroodextrin  ^. .' 


/Maltose, 
(maltodextrin). 


Achroodextrin  y  j 


xMaltose. 

This  schema  represents  the  possibility  of  an  ultimate  conversion  of  all  the 
starch  into  maltose,  and  it  shows  at  the  same  time  that  maltose  may  be  pres- 
ent very  early  in  the  reaction,  and  that  it  may  occur  together  with  one  or  more 
dextrins,  according  to  the  stage  of  the  digestion.  It  should  be  said  in  conclu- 
sion that  this  description  of  the  manner  of  action  of  the  ptyalin  is  supposed  to 
apply  equally  well  to  the  amylolytic  enzyme  of  the  pancreatic  secretion,  the 
two  being,  so  far  as  known,  identical  in  their  properties.  From  the  stand- 
])oint  of  relative  physiological  importance  the  description  of  the  details  of 
amylolytic  digestion  should  have  been  left  until  the  functions  of  the  pancre- 
atic juice  were  considered.  It  is  introduced  here  because,  in  the  natural  order 
of  treatment,  ptyalin  is  the  first  of  this  group  of  ferments  to  be  encountered. 
It  is  interesting  also  to  remember  in  this  connection  that  starch  can  be  con- 
verted into  sugar  by  a  process  of  hydrolytic  cleavage  by  boiling  with  dilute 
mineral  acids.  Although  the  general  action  of  dilute  acids  and  of  amylolytic 
'  Lehrbuch  der  physiologischen  Chemie,  1893,  p.  232. 


224  J.y   AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

ciizynies  is  similar,  the  two  processes  are  not  identical,  since  in  the  first  process 
dextrose  is  the  sugar  formed,  while  in  the  second  it  is  maltose.  Moreover, 
variations  in  tcinjierature  afllect  the  two  reactions  differently. 

Conditions  Influencing-  the  Action  of  Ptyalin. — Tcmpcralare. — As  iu 
the  case  of  the  other  enzymes,  ptyalin  is  very  susceptible  to  changes  of  temper- 
ature. At  0°  C.  its  activity  is  said  to  be  sus})ended  entirely.  The  intensity 
of  its  action  increases  with  increase  of  temperature  from  this  point,  and 
reaches  its  maximum  at  about  40°  C.  If  the  temperature  is  raised  much 
beyond  this  point,  the  action  of  the  ptyalin  decreases,  and  at  from  65°  to 
70°  C.  the  enzyme  is  destroyed.  In  these  latter  points  ptyalin  differs  from 
diastase,  the  enzyme  of  malt.  Diastase  shows  a  maximum  action  at  50°  C. 
and  is  destroyed  at  80°  C. 

Efect  of  Reaction. — The  normal  reaction  of  saliva  is  slightly  alkaline. 
Chittenden'  has  shown,  however,  that  ptyalin  acts  as  well,  or  even  better,  in 
a  perfectly  neutral  medium.  A  strong  alkaline  reaction  retards  or  prevents 
its  action.  The  most  marked  influence  is  exerted  by  acids.  Free  hydrochloric 
acid  to  the  extent  of  only  0.003  per  cent.  (Chittenden)  is  sufficient  to  prac- 
tically stop  the  araylolytic  action  of  enzyme,  and  a  slight  increase  in  acidity  not 
only  stops  the  action,  but  also  destroys  the  enzyme.  The  latter  fact  is  of 
practical  importance  because  it  indica'tcs  that  the  action  of  ptyalin  on  starch 
must  be  suspended  after  the  food  reaches  the  stomach. 

Condition  of  the  Starch. — It  is  a  well-known  fact  that  the  conversion  of  starch 
to  sugar  by  enzymes  takes  place  much  more  rapidly  with  cooked  starch — for 
example,  starch  pas^e.  In  the  latter  condition  sugar  begins  to  appear  in  a 
few  minutes  (one  to  four),  provided  a  good  enzyme  solution  is  used.  With 
starch  in  a  raw  condition,  on  the  contrary,  it  may  be  many  minutes,  or  even 
several  hours,  before  sugar  can  be  detected.  The  longer  time  required  for 
raw  starch  is  partly  explained  by  the  well-known  fact  that  the  starch-grains 
are  surrounded  by  a  layer  of  cellulose  or  cellulose-like  material  which  resists 
the  action  of  ptyalin.  When  boiled,  this  layer  breaks  and  the  starch  in  the 
interior  becomes  exposed.  In  addition,  the  starch  itself  is  changed  during  the 
boiling;  it  takes  up  water,  and  in  this  hydrated  condition  is  acted  upon  more 
rapidly  by  the  ptyalin.  The  practical  value  of  cooking  vegetable  foods  is 
evident  from  these  statements  without  further  comment. 

Physiological  Value  of  Saliva. — Although  human  saliva  contains  ptyalin, 
and  this  enzyme  is  known  to  possess  veiy  energetic  amylolytic  properties,  yet 
it  is  probable  that  it  has  an  insignificant  action  in  normal  digestion.  The  time 
that  food  remains  in  the  mouth  is  altogether  too  short  to  suppose  that  the  starch 
is  profoundly  affected  by  the  ptyalin.  It  would  seem  that  whatever  change 
takes  place  must  be  confined  to  the  initial  stages.  After  the  mixed  saliva  and 
food  are  swallowed  the  acid  reaction  of  the  gastric  juice  soon  stops  completely 
all  further  amylolytic  action.  The  complete  digestion  of  the  carbohydrates 
takes  place  after  the  food  (chyme)  has  reached  the  small  intestine,  under  the 
influence  of  the  amylopsin  of  the  pancreatic  secretion.  For  these  reiisons  it  is 
'  Studies/rom  the  Laboratory  of  Physiological  Chemistry  of  Vale  Collrt/e,  vol.  i.,  1884. 


CHE3IISTBY   OF  DIGESTION  AND   NUTRITION.  225 

usually  believed  that  the  main  value  of  the  saliva,  to  the  human  being  and  to 
tiiG  carnivora  at  least,  is  that  it  facilitates  the  swallowing  of  food.  It  is  impos- 
sible to  swallow  perfectly  dry  food.  The  saliva,  by  moistening  the  food,  not 
only  enables  the  swallowing  act  to  take  place,  but  its  viscous  consistency  must 
aid  also  iu  the  easy  passage  of  the  food  along  the  oesophagus.  Among  the 
herbivora  it  is  probable  that  the  longer  retention  of  food  in  the  mouth  gives 
the  saliva  opportunity  for  more  complete  digestive  action. 

C.     Gastric  Digestion. 

After  the  food  reaches  the  stomach  it  is  exposed  to  the  action  of  the  secre- 
tion of  the  gastric  mucous  membrane,  known  usually  as  the  gastric  juice.  The 
physiological  mechanisms  involved  in  the  production  and  regulation  of  this 
secretion,  and  the  important  ])art  played  in  gastric  digestion  by  the  movements 
of  the  stomach,  will  be  found  described  in  other  sections  (Secretion,  Move- 
ments of  Alimentary  Canal).  It  is  sufficient  here  to  say  that  the  secretion 
of  gastric  juice  begins  with  the  entrance  of  food  into  the  stomach.  By  means 
of  the  muscles  of  the  stomach  the  contained  food  is  kept  in  motion  for  several 
hours  and  is  thoroughly  iliixed  with  the  gastric  secretion,  which  during  this 
time  is  exerting  its  digestive  action  upon  certain  of  the  food-stuffs.  From  time 
to  time  portions  of  the  liquefied  contents,  known  as  chyme,  are  forced  into  the 
duodenum,  and  their  digestion  is  completed  in  the  small  intestine.  Gastric 
digestion  and  intestinal  digestion  go  more  or  less  hand  in  hand,  and  usually 
it  is  impossible  to  tell  in  any  given  case  just  how  much  of  the  food  will 
undergo  digestion  in  the  stomach  and  how  much  will  be  left  to  the  action  of 
the  intestinal  secretions.  It  is  possible,  however,,  to  collect  the  gastric  secre- 
tion or  to  make  an  artificial  juice  and  to  test  its  action  upon  food-stuffs  by 
digestions  in  vitro.  Much  of  our  fundamental  knowledge  of  the  digestive 
action  of  the  gastric  juice  has  been  obtained  in  this  way,  although  this  has 
been  supplemented,  of  course,  by  numerous  experiments  upon  lower  animals 
and  human  beings. 

Methods  of  Obtaining-  Normal  Gastric  Juice. — The  older  methods  used 
for  obtaining  normal  gastric  juice  were  very  unsatisfactory.  For  instance,  an 
animal  was  made  to  swallow  a  clean  sponge  to  which  a  string  was  attached  so 
that  the  sponge  could  afterward  be  removed  and  its  contents  be  squeezed  out ; 
or  there  was  given  the  animal  to  eat  some  indigestible  material,  to  start  the 
secretion  of  juice  by  mechanical  stimulation,  the  animal  being  killed  at  the 
proper  time  and  the  contents  of  its  stomach  being  collected.  A  better  method 
of  obtaining  normal  juice  was  suggested  by  the  famous  observations  of  Beau- 
mont^ upon  Alexis  St.  Martin,  St.  Martin,  by  the  premature  discharge  of 
his  gun,  was  wounded  in  the  abdomen  and  stomach.  On  healing,  a  fistulous 
opening  remained  in  the  abdominal  wall,  leading  into  the  stomach,  so  that  the 
contents  of  the  latter  could  be  inspected.  Beaumont  made  numerous  interest- 
ing and  most  valuable  observations  upon  his  patient.  Since  that  time  it  has 
become  customary  to  make  fistulous  openings  into  the  stomachs  of  dogs  when- 

'  The  Physiology  of  Digestion,  1833. 
15 


226  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

ever  it  i.s  iR'ct'ssaiy  to  have  tlie  uuniial  juice  lor  examination.  A  .silver  e^nula 
is  placed  in  the  fistula,  and  at  any  time  the  plug  closing  the  canula  may  be 
removed  and  gastric  juice  be  obtained.  In  some  ca.ses  the  cesophagus  has 
been  occluded  or  excised  so  as  to  prevent  the  mixture  of  saliva  with  the  gastric 
juice.  Gastric  juice  may  be  obtained  from  human  beings  also  in  cases  of  vom- 
iting or  by  means  of  the  stomach-pump,  but  in  such  cases  it  is  necessarily 
more  or  less  diluted  or  mixed  with  food  and  cannot  be  used  for  exact  analvses, 
although  specimens  of  gastric  juice  obtained  by  these  methods  are  valuable  in 
the  diagnosis  and  treatment  of  gastric  troubles. 

Properties  and  Composition  of  Gastric  Juice. — The  normal  gastric  secre- 
tion is  a  thin,  colorless  or  nearly  colorless  liquid  with  a  strong  acid  reaction 
and  a  characteristic  odor.  Its  specific  gravity  varies,  but  it  is  never  great, 
the  average  being  about  1002  to  1003.  Upon  analysis  the  gastric  juice  is 
found  to  contain  a  trace  of  proteid,  probably  a  peptone,  some  mucin,  and 
inorganic  salts,  but  the  essential  constituents  are  an  acid  (HCl)  and  two 
enzymes,  pepsin  and  rennin.  A  satisfactory  analysis  of  the  human  juice  has 
not  been  reported,  owing  to  the  difficulty  of  getting  proper  specimens. 
According  to  Schmidt,^  the  gastric  juice  of  dogs,  free  from  saliva,  has  the 
following  composition,  given  in  1000  parts : 

Water 973.0 

Sulids 27.0 

Organic  substances 17.1 

Free  HCl 3.1 

NaCl      2.5 

CaClj 0.6 

KCl 1.1 

NH.Cl 0.5 

Ca3(P0J,      1.7 

Mg,(P0,)2 0.2 

FePO, 0.1 

Gastric  juice  does  not  give  a  coagulum  upon  boiling,  but  the  digestive  enzymes 
are  thereby  destroyed.  One  of  the  interesting  facts  about  this  secretion  is  the 
way  in  which  it  withstands  putrefaction.  It  may  be  kept  for  a  long  time,  for 
months  even,  without  becoming  putrid  and  with  very  little  change,  if  any,  in 
its  digestive  action  or  in  its  total  acidity.  This  fact  shows  that  the  juice 
possesses  antiseptic  properties,  and  it  is  usually  supposed  that  the  presence  of 
the  free  acid  accounts  for  this  quality. 

The  Acid  of  Gastric  Juice. — The  nature  of  the  free  acid  in  gastric  juice 
was  formerly  the  subject  of  dispute,  some  claiming  that  the  acidity  is  due  to 
HCl,  since  this  acid  can  be  distilled  off  from  the  gastric  juice,  others  contend- 
ing that  an  organic  acid,  lactic  acid,  is  present  in  the  secretion.  All  recent 
experiments  tend  to  prove  that  the  acidity  is  due  to  HCl.  This  fact  was  firet 
demonstrated  satisfactorily  by  the  analyses  of  Schmidt,  who  showed  that  if, 
in  a  given  specimen  of  gastric  juice,  the  chlorides  were  all  precipitated  by 
silver  nitrate  and  tiie  total  amount  of  chlorine  was  determined,  more  was 
*  ITammarsten :   Text-book  of  Physiological  Chemistry  (translation  by  Mandel),  1893,  p.  177. 


CHEMISTR  Y  OF  DIGESTION  AND  NUTRITION.  227 

found  tlian  could  \)o  held  in  combination  by  the  bases  present  in  the  secretion. 
Evidently,  some  of  the  chlorine  luust  have  been  present  in  combination  with 
hydroi2;en  as  iiydrochloric!  acid.  (\)uHrniat()ry  evidence  of  one  kind  or  another 
has  siuce  been  obtained.  Thus  it  lias  been  shown  that  a  number  of  color 
tests  for  free  mineral  acids  react  with  the  gastric  juice :  methyl-violet  solutions 
are  turned  blue,  contro-red  s(jlutions  and  test-paper  are  changed  from  red  to 
blue,  00  tropteolin  from  a  yellowish  to  a  pink-red,  and  so  on.  A  numl)er  of 
additional  tests  of  the  same  general  character  will  be  found  described  in  the 
laboratory  handbooks  of  physiology.^  It  must  be  added,  however,  that  lactic  acid 
undoubtedly  occurs,  or  may  occur,  in  the  stomach  during  digestion.  Its  pres- 
ence is  usually  explained  as  being  due  to  the  fermentation  of  the  carbohydrates, 
and  it  is  therefore  more  constantly  present  in  the  stomach  of  the  herbivora. 
The  amount  of  free  acid  varies  according  to  the  duration  of  digestion  ;  that  is, 
the  secretion  does  not  j)ossess  its  full  acidity  in  the  beginning,  owing  probably 
to  the  fact  (Heideuhain)  that  in  the  first  periods  of  digestion,  while  the  secre- 
tion is  still  scanty  in  amount,  a  portion  of  its  acid  is  neutralized  by  the 
swallowed  saliva  and  the  alkaline  secretion  of  the  pyloric  end  of  the  stomach 
(see  the  section  on  Secretion),  Estimates  of  the  maximum  acidity  in  the 
human  stomach  are  usually  given  as  between  0.2  and  0.3  per  cent.  The 
acidity  of  the  dog's  gastric  juice  is  greater — 0.3  to  0.58  per  cent. 

Origin  of  the  HCl. — The  gastric  juice  is  the  only  secretion  of  the  body  con- 
taining a  free  acid.  The  fact  that  the  acid  is  a  mineral  acid  makes  this  circum- 
stance more  remarkable,  although  other  instances  of  a  similar  kind  are  known; 
for  example,  Dolium  galea,  a  mollusc,  secretes  a  salivary  juice  containing  free 
H2SO4  and  free  HCl.  When  and  how  the  HCl  is  formed  in  the  stomach  is 
still  a  subject  of  investigation.  Histologically,  attempts  have  been  made  to  show 
that  it  is  produced  in  the  border  cells  of  the  peptic  glands  in  the  fundic  end 
of  the  stomach  (see  Secretion).  It  cannot  be  said,  however,  that  the  evidence 
for  this  theory  is  at  all  convincing ;  it  can  be  accepted  only  provisionally. 
Ingenious  efforts  have  been  made  to  determine  the  place  of  production  of  the 
acid  by  micro-chemical  methods.  Substances  which  give  color  reactions  with 
acids  have  been  injected  into  the  blood,  and  sections  of  the  mucous  membrane 
of  the  stomach  have  then  been  made  to  determine  microscopically  the  part  of 
the  gastric  glands  in  which  the  acid  is  produced ;  but  beyond  proving  that  the 
acid  is  formed  in  the  mucous  membrane  these  experiments  have  given  negative 
results,  the  color  reaction  for  acid  occurring  throughout  the  thickness  of  the 
membrane.^  The  chemistry  of  the  production  of  free  HCl  also  remains  unde- 
termined. No  free  acid  occurs  in  the  blood  or  the  lymph,  and  it  follows,  there- 
fore, that  it  is  manufactured  in  the  secreting  cells.  It  is  quite  evident,  too, 
that  the  source  of  the  acid  is  the  neutral  chlorides  of  the  blood  ;  these  are  in 
some  way  decomposed,  the  chlorine  uniting  with  hydrogen  to  form  HCl  which 
is  turned  out  upon  the  free  surface  of  the  stomach,  while  the  base  remains 

'  Stirling  :   Outlines  of  Practical  Physiology. 

^  Friinkel :   PjlUyer's  ArchivfUr  die  gesammtePhysiologie,  1891,  vol.  48,  p.  63. 


228  AN   AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

behiud  and  prubably  passes  back  into  the  blood.  The  latter  part  (jf  the  pro- 
cess, the  passage  of  the  base  into  the  blood-current,  enables  us  to  explain  in  part 
the  facts,  noticed  by  a  number  of  observers,  that  the  alkalinity  of  the  blood  is 
increased  and  the  acidity  of  the  urine  is  decreased  after  meals.  Attemj)ts  to 
express  the  reaction  which  takes  place  in  the  decomposition  of  the  chlorides 
are  still  too  theoretical  to  merit  more  than  a  brief  mention  in  a  book  of  this 
character.  According  to  Ileidenhain,  a  free  organic  acid  is  secreted  by  the 
cells,  which  acid  then  acts  upon  and  decomposes  the  chlorides.  According  to 
Maly,  the  HCl  is  the  result  of  a  reaction  between  the  phosphates  and  the 
chlorides  of  the  blood,  as  expressed  in  the  two  following  equations: 

NaH^PO,  +  NaCl  =  NaJTPO,  +  HCl ;  or, 
SCaCl^  +  2Na2HrO,  =  O^IVO^)^  +  4NaCl  +  2  HCl. 

A  recent  theory  by  Liebermann  supposes  that  the  mass  action  of  the  COj 
formed  in  the  tissues  of  the  gastric  raucous  membrane  upon  the  chlorides, 
with  the  aid  of  a  nucleo-albumin  of  acid  properties  which  can  be  isolated 
from  the  gastric  glands,  may  account  for  the  production  of  the  HCl.  Although 
it  is  customary  to  speak  of  the  HCl  as  existing  in  a  free  state  in  the  gastric 
juice,  certain  differences  in  reaction  between  this  secretion  and  aqueous  solu- 
tions of  the  same  acidity  have  led  to  the  suggestion  that  the  HCl,  or  a  part  of 
it  at  least,  is  held  in  some  sort  of  combination  with  the  organic  (protcid)  con- 
stituents of  the  secretion,  so  that  its  })roperties  are  modified  in  some  minor 
points  just  as  the  properties  of  luemoglobin  are  modified  by  the  combination  in 
which  it  is  held  in  the  corpuscles.  The  differences  usually  described  are  that 
in  the  gastric  juice  or  in  mixtures  of  HCl  and  proteid  the  acid  does  not  dialyze 
nor  distil  off  so  readily  as  in  simple  aqueous  solutions.  The  peptones  and 
proteoses  formed  during  digestion  seem  to  combine  with  the  acid  very  readily 
— so  much  so,  in  fact,  that  in  certain  cases  specimens  of  gastric  juice  taken 
from  the  stomach,  although  they  give  an  acid  reaction  with  litmus-paper,  may 
not  give  the  special  color  reactions  for  free  mineral  acids.  In  such  cases,  hoM'- 
ever,  the  acid  may  still  be  able  to  fulfil  its  part  in  the  digestion  of  proteids. 

Nature  and  Properties  of  Pepsin. — Pepsin  is  a  typical  proteolytic  enzyme 
which  exhibits  the  striking  peculiarity  of  acting  only  in  acid  media;  hence 
peptic  digestion  in  the  stomach  is  the  result  of  the  combined  action  of  pepsin 
and  HCl.  Pepsin  is  influenced  in  its  action  by  temperature,  as  is  the  case  with 
the  other  enzymes  ;  low  temperatures  retard,  and  may  even  suspend,  its  activity, 
while  high  temperatures  increase  it.  The  optimum  temperature  is  stated  to  be 
from  37°  to  40°  C,  while  exposure  for  some  time  to  80°  C.  results,  when  the 
pepsin  is  in  a  moist  condition,  in  the  total  destruction  of  the  enzyme.  Pepsin 
has  never  been  isolated  in  sufficient  purity  for  satisfactory  analysis.  It  may  be 
extracted,  however,  from  the  gastric  mucous  membrane  by  a  variety  of  methods 
and  in  different  degrees  of  purity  and  strength.  The  commercial  preparations  of 
pepsin  consist  usually  of  some  form  of  extract  of  the  gastric  mucous  membrane 
to  which  starch  or  sugar  of  milk  has  been  added.  Laboratory  preparations  are 
usually  made  by  mincing  thoroughly  the  mucous  membrane  and  then  extract- 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION  229 

i)i<^  Tor  a  long  time  with  glycerin.  Glycerin  extracts,  if  not  too  much  diluted 
witii  water  or  blood,  keep  I'or  an  indefinite  time.  Purer  ])re|)arations  of"  pepsin 
have  been  made  by  what  is  known  as  "  Briicke's  method,"  in  which  the  mucous 
membrane  is  minced  and  is  then  self-digested  with  a  5  per  cent,  solution  of 
phosphoric  acid.  The  phosj)horic  acid  is  j)recipitated  by  the  addition  of  lime- 
water,  and  the  pepsiu  is  carried  down  in  the  flocculent  precipitate.  This  pre- 
cipitate, after  being  washed,  is  carried  into  solution  by  dilute  hydrochloric 
acid,  and  a  solution  of  cholesterin  in  alcohol  and  ether  is  added.  The  choles- 
terin  is  jirecipitated,  and,  as  before,  carries  down  with  it  the  pepsin.  This 
precipitate  is  collected,  carefully  washed,  and  then  treated  repeatedly  with 
ether,  which  dissolves  and  removes  the  cholesterin,  leaving  the  pepsin  in 
aqueous  solution.  This  method  is  interesting  not  only  because  it  gives  the 
purest  form  of  pepsin,  but  also  in  that  it  illustrates  one  of  the  properties  of 
this  enzyme — namely,  the  readiness  with  which  it  adheres  to  precipitates  occur- 
ring in  its  solutions.  Pepsin  illustrates  very  well  two  of  the  general  properties 
of  enzymes  that  have  been  described  (p.  219):  first,  its  action  is  incomplete,  the 
accumulation  of  the  products  of  digestion  inhibiting  further  activity  at  a  certain 
stage ;  and,  secondly,  a  small  amount  of  the  pepsin,  if  given  sufKcient  time  and 
the  proper  conditions,  will  digest  a  very  large  amount  of  proteid. 

Artificial  Gastric  Juice. — In  studying  peptic  digestion  it  is  not  necessary 
for  all  })urposes  to  establish  a  gastric  fistula  to  get  the  normal  secretion.  The 
active  agents  of  the  normal  juice  are  pepsin  and  acid  of  a  proper  strength  ;  and, 
as  the  pepsin  can  be  extracted  and  preserved  in  various  ways,  and  the  HCl  can 
easily  be  made  of  the  proper  strength,  an  artificial  juice  can  be  obtained  at  any 
time  which  may  be  used  in  place  of  the  normal  secretion  for  many  purposes.  In 
laboratory  experiments  it  is  customary  to  employ  a  glycerin  extract  of  the  gastric 
raucous  membrane,  and  to  add  a  small  portion  of  this  extract  to  a  large  bulk  of 
0.2  per  cent.  HCl.  The  artificial  juice  thus  made,  when  kept  at  a  temperature  of 
from  37°  to  40°  C,  will  digest  proteids  rapidly  if  the  preparation  of  pepsin  is  a 
good  one.  While  the  strength  of  the  acid  employed  is  generally  from  0.2  to  0.3 
per  cent.,  digestion  will  take  place  in  solutions  of  greater  or  less  acidity.  Too 
great  or  too  small  an  acidity,  however,  will  retard  the  process ;  that  is,  there  is 
for  the  action  of  the  pepsin  an  optimum  acidity  which  lies  somewhere  between 
0.2  and  0.5  per  cent.  Other  acids  may  be  used  in  place  of  the  HCl — for  example, 
nitric,  phosphoric,  or  lactic — although  they  are  not  so  effective,  and  the  opti- 
mum acidity  is  different  for  each ;  for  phosphoric  acid  it  is  given  as  2  per  cent. 

Action  of  Pepsin-Hydrochloric  Acid  on  Proteids. — It  has  been  known 
for  a  long  time  that  solid  proteids,  such  as  boiled  eggs,  when  exposed  to  the 
action  of  a  normal  or  an  artificial  gastric  juice,  swell  up  and  eventually  pass 
into  solution.  The  soluble  proteid  thus  formed  was  known  not  to  be  coagu- 
lated by  heat ;  it  was  remarkable  also  for  being  more  diffusible  than  other 
forms  of  soluble  proteids,  and  was  further  characterized  by  certain  positive 
and  negative  reactions  which  will  be  described  more  explicitly  farther  on. 
This  end-product  of  digestion  was  formerly  described  as  a  soluble  proteid 
with  properties  fitting  it  for  rapid  absorption,  and  the  name  of  peptone  was 


230  AN  AM  Kit  IVAN    TEXT- BOOK    OF   J'JI  YSlOIJXlY. 

given  to  it.  It  was  quickly  found,  however,  that  the  proeess  was  complicated 
— that  in  the  convei-sion  to  so-called  "peptone"  the  proteid  under  digestion 
passed  through  a  number  of  intermediate  stages.  'J'he  intermediate  [)roducts 
were  partially  isolated  and  were  given  specific  names,  such  as  acid-albumin^ 
parapcpfone,  and  propcptone.  The  two  latter  names,  unfortunately,  have  not 
always  been  used  with  the  same  meaning  by  authors,  and  latterly  they  have 
fallen  somewhat  into  disuse,  although  they  are  still  frcijuentiy  employed  to 
indicate  some  one  or  other  of  the  intermediate  stages  in  the  formation  of  pep- 
tones. The  most  complete  investigation  of  the  products  of  pejjtic  digestion, 
and  of  proteolytic  digestion  in  general,  we  owe  to  Kiihne  and  to  those  who 
have  followed  along  the  lines  he  laid  down,  among  whom  maybe  mentioned 
Chittenden  and  IS'eumeister.  Their  work  has  thrown  new  light  upon  the 
whole  subject  and  has  developed  a  new  nomenclature.  In  our  account  of  the 
process  we  shall  adhere  to  the  views  and  terminology  of  this  school,  as  they 
seem  to  be  generally  adopted  in  most  of  the  recent  literature.  It  is  well, 
however,  to  add,  by  way  of  caution,  that  investigations  of  this  character  are 
still  going  on,  and  the  views  at  present  accepted  are  lial)le,  therefore,  to 
changes  in  detail  as  our  experimental  knowledge  increases.  Without  giving 
the  historical  development  of  Kiihne's  theory,  it  may  be  said  that  at  present 
the  following  steps  in  peptic  digestion  have  been  described :  The  proteid 
acted  upon,  whether  soluble  or  insoluble,  is  converted  first  to  an  acid-albumiu 
(see  Chemical  section)  to  which  the  name  si/ntonin  is  usually  given.  In  arti- 
ficial digestions  the  solid  proteid  usually  first  swells  up  i'rom  the  action  of  the 
acid,  and  then  slowly  dissolves.  Syntonin  has  the  general  })ropcrties  of  acid- 
albumins,  of  which  properties  the  most  characteristic  is  that  the  albumin  is 
precipitated  upon  neutralizing  the  solution  with  dilute  alkali.  If,  in  the  begin- 
ning of  a  peptic  digestion,  the  liquid  is  neutralized,  a  more  or  less  abundant 
precipitate  of  syntonin  will  form,  the  quantity  depending  upon  the  stage  of 
digestion.  The  formation  of  syntonin  is  due  mainly  to  the  action  of  the  HCl, 
although  the  acid  seems  to  be  much  more  effective  in  combination  with  pepsin 
than  in  simple  aqueous  solutions  of  the  same  strength.  Syntonin  in  turn,  under 
the  influence  of  tlie  pepsin,  takes  u})  water  and  undergoes  hydrolytic  cleavage, 
with  the  formation  of  two  soluble  proteids  known  together  as  primary  albumoses 
or  proteoses,^  and  separately  as  j^trofo-profrose  and  Jietero-pi'oteose.  Each  of  these 
proteids  again  takes  up  water  and  undergoes  cleavage,  with  the  formation  of 
a  second  set  of  soluble  proteids  known  as  secondary  proteoses,  in  contradis- 
tinction to  the  primary  proteoses,  but  to  which  the  specific  name  of  deniero- 
proteoses  is  given.  Finally,  the  deutero-proteose,  or  more  properly  the 
deutero-proteoses,  again  undergo  hydrolytic  cleavage,  with  the  formation  of 
what  are  known  as  peptones.  Peptic  digestion  can  go  no  farther  than  the 
formation  of  peptones,  but  we  shall  find  later  that  other  proteolytic  enzymes 

'  The  term  proteose  is  used  by  some  authors  in  phice  of  the  older  name  albumose,  as  it  has  a 
more  general  significance.  According  to  this  nsage  tlie  name  alhitmose  is  given  to  the  proteoses 
formed  from  albumin,  rjlobiilo.'O'  to  those  formed  from  globulin,  etc.,  while  proteose  is  a  general 
term  applying  to  the  intermediate  products  from  any  proteid. 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  231 

(trypsin,  for  example)  arc  capable  of  splitting  up  a  part  of  the  peptones  still 
further.  The  fact  that  trypsin  can  act  upon  only  a  j)art  of  the  peptone  shows 
that  this  latter  substance  is  either  a  mixture  of  at  least  two  separate  although 
closely-related  peptones,  to  which  the  names  of  anti-pcjjfonc  and  liend-peptone^ 
liave  been  given,  or  it  is  a  compound  containing  such  hemi-  and  anti-  groups, 
and  capable,  under  the  action  of  trypsin,  of  splitting,  with  llu;  formation  of 
hemi-peptone  and  anti-peptone  (Neumeister).  If  we  consider  pej)tic  digestion 
alone,  this  distinction  is  unnecessary.  The  final  products  of  peptic  digestion 
are  therefore  spoken  of  usually  simply  as  peptones,  although  the  name  ampho- 
peptone  is  also  frequently  used  to  emphasize  the  fact  that  two  distinct  varieties 
of  peptone  are  probably  present.  This  description  of  the  steps  in  peptic 
digestion  may  be  made  more  intelligible  by  the  following  schema,  which  is 
modified  somewhat  from  that  given  by  Neumeister:^ 

Proteid. 

I 
Syntonin. 


(Primary  proteoses)    =  Proto-proteose.  Hetero-proteose. 

I  I 

(Secondary  proteoses)  =  Deutero- proteose.  Deutero-proteose. 

I  I 

(Ampho-peptones)      =         Peptone.  Peptone. 

'  Kiihne's  full  theory  of  proteolytic  digestion  assumes  that  the  original  proteid  molecule 
contains  two  atomic  groups,  the  hemi-  and  the  anti-  group.  Proteolytic  enzymes  split  the  mole- 
cule so  as  to  give  a  hemi-  and  an  anti-  compound,  each  of  which  passes  through  a  proteose  stage 
into  its  own  peptone.     A  condensed  schema  of  tlie  hypothetical  changes  would  be  as  follows: 

Proteid. 


Anti-albumose.  Hemi-albumose. 

I  I 

Anti-peptone.  Hemi-peptone. 


Am  pho-peptone. 

In  the  detailed  description  of  proteolysis  given  above,  primary  and  secondary  proteoses  are  pre- 
sumably, according  to  this  schema,  mixtures  in  varying  proportions  of  hemi-  and  ami-  com- 
pounds, or,  in  other  words,  they  are  arapho- proteoses.  No  good  way  of  separating  the  anti- 
from  the  hemi-  compounds  has  been  discovered  except  to  digest  them  with  trypsin.  By  this 
means  each  compound  is  converted  to  its  proper  peptone,  and  by  the  continued  action  of  the 
trypsin  the  hemi-peptone  is  split  into  much  simpler  bodies  (p.  241),  only  anti-peptone  being  left 
in  solution.  The  conception  of  a  proteid  molecule  with  hemi-  and  anti-  groups  and  the  splitting 
into  hemi- and  anti-albumose  is  mainly  an  inference  backward  from  the  fact  that  there  are  two 
distinct  peptones,  one  of  which,  hemi-peptone,  is  acted  upon  by  trypsin,  while  the  other  is  not 
so  acted  upon.  The  details  of  the  splitting  of  the  proteid  under  the  influence  of  pepsin  are  still 
further  complicated  by  the  fact  that  in  some  cases  a  part  of  the  proteid  remains  undissolved,  form- 
ing a  highly  resistant  substance  to  which  the  name  antalhumid  has  been  given.  It  has  been  shown 
that  if  this  substance  is  dissolved  in  sodium  carbonate  and  then  submitted  to  the  action  of  trypsin, 
only  anti-peptone  is  formed,  indicating  that  it  contains  none  of  the  hemi-  group.  In  fact,  the  prop- 
erties of  antalbuniid  show  that  it  is  a  peculiar  modification  of  the  anti-  group  which  may  arise  dur- 
ing the  cleavage  of  the  proteid  molecule,  and  may  vary  greatly  in  quantity  in  different  digestions. 
^  Lehrbuch  der  physiologischen  Chemie,  1893,  p.  187. 


232  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

According  to  this  sclienia,  peptic  digestion,  after  the  syntonin  stage,  consists  in 
a  succession  of  liydrolytic  cleavages  whereby  sohible  i)roteids  (proteoses  and 
peptones)  are  produced  of  smaller  and  smaller  molecular  weights.  It  is  {jossi- 
ble,  of  course,  that  the  steps  in  this  process  may  be  moi-e  nnmenjiis  than  those 
represented  in  the  scihema,  but  the  general  nature  of  the  changes  seems  to  be 
established  beyond  question.  Moreover,  it  is  easy  to  understand  that  the 
products  of  digestion  in  any  given  case  will  vary  with  the  stage  at  which  the 
examination  is  made.  Sufficiently  early  in  the  process  one  may  find  mainly 
syntonin,  or  syntonin  and  primary  proteoses ;  later  the  deutero-proteoses  and 
peptones  may  occur  alone  or  with  mere  traces  of  the  first  i)roducts.  The  whole 
process  is  more  or  less  progressive,  although  it  must  be  understood  that  the 
first  and  the  last  products  may  coexist  in  the  same  liquid ;  that  is,  a  part  of 
the  original  proteid  may  be  well  on  toward  the  last  stages  of  the  action  while 
another  part  is  in  the  first  stages.  It  is  worth  enqohasizing  also  that  in  arti- 
ficial digestions  with  pepsin,  uo  matter  how  long  the  action  is  allowed  to  go  on, 
the  final  product  is  always  a  mixture  of  peptones  and  proteoses  (deutero-proteose). 
Even  when  provision  is  made  to  dialyze  off  the  peptone  as  it  forms,  thus  simu- 
lating natural  digestion,  the  final  result,  according  to  Chittenden  and  Amerman,' 
is  still  a  mixture  of  proteose  and  peptone.  The  extent  of  peptic  digestion  in  the 
body  will  be  spoken  of  presently  in  connection  with  a  rdsum^  of  the  ])hysiology 
of  gastric  digestion.  In  general,  it  may  be  said  that  from  a  physiological 
standpoint  the  object  of  the  whole  process  is  to  get  the  proteids  into  a  form 
in  which  they  can  be  absorbed  more  easily.  The  properties  and  reactions  of 
peptones  and  proteoses  will  be  found  stated  in  the  Chemical  section.  It  may 
serve  a  useful  end,  however,  to  give  here  some  of  their  properties,  in  order  to 
emphasize  the  nature  of  the  changes  caused  by  the  pepsin. 

Peptones. — The  name  "  peptones  "  was  formerly  given  to  all  the  })roducts 
of  peptic  digestion  after  it  had  passed  the  syntonin  stage — that  is,  to  the  pro- 
teoses as  well  as  the  true  peptones.  Commercially,  the  word  is  still  used  in  this 
sense,  the  preparations  sold  as  peptones  being  generally  mixtures  of  ])i-oteoses  and 
peptones.  True  pe])tones,  in  the  sense  used  by  Kiihne,  are  distinguished  chem- 
ically by  certain  reactions.  Like  the  proteoses,  they  are  very  soluble,  they  are 
not  precipitated  by  heating,  and  th(>y  give  a  red  biuret  reaction  (see  Reactions 
of  Proteids,  Chemical  section).  They  are  distinguished  from  the  ])rimary  pro.- 
teoses  by  not  giving  a  precipitate  with  acetic  acid  and  potassium  ferrocyanide, 
and  from  the  whole  group  of  proteoses  by  the  fact  that  they  are  not  thrown 
down  from  their  solutions  by  the  most  thorough  saturation  of  the  liquid  with 
ammonium  sulphate.  This  last  reaction  gives  the  only  means  for  the  conqilete 
separation  of  the  peptones  from  the  proteoses.  The  peptones,  indeed,  may  be 
defined  as  being  the  products  of  proteolytic  digestion  which  are  not  precipitated 
by  saturation  of  the  liquid  with  ammonium  sulphate.  The  validity  of  this 
reaction  has  lately  been  called  in  question.  It  has  been  pointed  out  that, 
although  the  primary  proteoses  are  readily  ])recipitated  by  this  salt,  the  deutero- 
proteoses,  under  certain  circumstances  at  least,  arc  not  precipitated,  and  cannot 
*  Journal  of  Physiology,  vol.  xiv.,  1893,  p.  483. 


CHEMISTRY    OF  DIGESTION  AND    NUTRITION. 


233 


therefore  be  distiiiouislied  or  separated  from  the  so-called  "  true  peptones."  We 
must  await  further  investigations  before  attempting  to  eome  to  any  conclusion 
ujwn  this  poiut.  It  is  well  to  bear  in  mind  that  the  change  from  ordinary 
proteid  to  peptone  evidently  take.^^  place  through  a  number  of  intermediate  steps, 
and  the  word  peptone  is  meant  to  designate  tiie  linal  product.  Whether  this 
final  product  is  a  chemical  individual  with  properties  separating  it  from  all  the 
intermediate  stages  is  perhaps  not  yet  fully  known,  but,  provisionally  at  least,  we 
may  adopt  Kiihne's  definition,  outlined  above,  of  what  constitutes  peptone,  as  it 
seems  to  be  generally  accepted  in  current  literature.  Peptones  are  characterized 
by  their  diffusibility,  and  this  property  is  also  possessed,  although  to  a  less 
marked  extent,  by  the  i)roteoses.  Recent  work  by  Chittenden,^  in  which  he 
corroborates  results  published  simultaneously  by  Kiihne,  shows  the  following 
relative  diffusibility  of  peptones  and  proteoses.  The  solutions  used  were  approx- 
imately 1  per  cent. ;  they  were  dialyzed  in  parchment  tubes  against  running 
water  for  from  six  to  eight  hours,  and  the  loss  of  substance  was  determined 
and  expressed  in  [percentages  of  the  original  amount.  Proto-proteose  gave  a 
loss  of  5.09  per  cent.;  deutero-proteose,  2.21  percent.;  peptone,  11  percent. 
Several  elementary  analyses  of  proteoses  and  peptones  have  been  reported, 
but  they  cannot  be  accepted  as  final,  owing  to  the  fact  that  the  substances 
analyzed  were  probably  mixtures,  and  not  chemical  individuals.  The  follow- 
ing analyses,  reported  by  Chittenden,^  will  serve  to  show  the  relative  percentage 
composition  of  these  bodies : 

Phyto-vUellin,  a  Crystallized  Proteid  extracted  from  Hemp-seed. 


Mother-proteid. 

Proto-vitellose. 

Deutero-vitellose. 

Peptone. 

c 

H 

N 

S 

0 

51.63 
6.90 

18.78 

0.90 

21.79 

51.55 
6.73 

18.90 

1.09 

•      21.73 

49.78 
6.73 

17.97 
1.08 

24.44 

49.40 
6.77 

18.40 
0.49 

24.94 

The  most  .striking  differences  in  composition  observed  in  passing  from  the 
raother-proteid  to  the  peptones  are  the  progressive  decrease  in  the  percentage 
of  carbon  and  the  increase  in  the  percentage  of  oxygen.  Both  these  facts  are 
in  accord  with  the  general  theory  that  proteolysis  consists  essentially  in  a  series 
of  hydrolytic  cleavages. 

Rennm.—lx\  addition  to  pepsin  the  gastric  secretion  contains  an  enzyme 
which  is  characterized  by  its  coagulating  action  upon  milk.  It  has  long  been 
known  that  milk  is  curdled  by  coming  into  contact  with  the  raucous  membrane 
of  the  stomach.  Dried  mucous  membrane  of  the  calf's  stomach,  when  stirred 
in  with  fresh  milk,  will  curdle  the  latter  with  astonishing  rapidity,  and  this 
property  has  been  utilized  in  the  manufacture  of  cheese.  Hammai-sten  discovered 
that  this  action  is  due  to  the  presence  of  a  specific  enzyme  which  exists  ready 
formed  in  the  membrane  of  the  sucking-calf's  stomach,  and  which  is  present 

'  Journal  of  Physiology,  vol.  xiv.,  1893,  p.  502. 

2  Cartwright  Lectures,  New  York  Medical  Record,  April,  1894. 


234  AN  AMERICAN   TEXT- BOOK   OF  PHYSIOLOGY. 

in  a  preparatory  form  (rennin-zymogen)  in  .stomachs  of  all  mammals.  This 
enzyme  has  been  given  several  names;  rcnniti  seems  preferable  to  any  other, 
and  is  the  term  most  commonly  employed.  Remiin  may  he  ol)taiiied  from 
the  stomach  by  self-digestion  of  the  nuicous  membrane  or  by  extracting  it 
with  glycerin.  Such  extracts  usually  contain  both  pepsin  and  reimin,  but  the 
two  have  been  separated  successfully,  most  easily  by  the  prolonged  action  of 
a  temperature  of  40°  C.  in  acid  solutions,  which  destroys  the  remiin,  but  not 
the  pepsin.  Good  extracts  of  rennin  cause  clotting  of  milk  with  great  rapidity 
at  a  temperature  of  40°  C,  the  milk  (cow's  milk),  if  undisturbed,  setting  first 
into  a  solid  clot,  which  afterward  shrinks  and  presses  out  a  clear  yellowish 
liquid,  the  whey;  with  human  milk,  however,  the  curd  is  much  less  firm, 
being  deposited  in  the  form  of  loose  flocculi.  The  whole  process  resembles  the 
clotting  of  blood  not  only  in  the  superficial  phenomena,  but  also  in  the 
character  of  the  chemical  changes.  Briefly,  what  happens  is  that  the  rennin 
acts  upon  a  soluble  proteid  in  the  milk  known  usually  as  casein,  but  by  some 
called  "  caseinogen,"  and  changes  this  proteid  to  an  insoluble  modification  which 
is  precipitated  as  the  curd.  The  chemistry  of  the  change  is  not  completely 
understood,  and  there  is  an  unfortunate  want  of  agreement  in  the  terminology 
used  to  designate  the  products  of  the  action.  It  has  been  shown  that,  as  in 
the  case  of  blood,  curdling  cannot  take  place  unless  lime  salts  are  present.  What 
seems  to  occur  is  as  follows:  Casein  is  a  complex  substance  belonging  to  the 
group  of  nucleo-albumins,  and  when  acted  upon  by  rennin  it  undergoes  hydro- 
lytic  cleavage,  with  the  formation  of  two  proteid  bodies,  paracasein  and  whey 
proteid.  The  first  of  these  bodies  forms  with  calcium  salts  an  insoluble  com- 
pound which  is  precipitated  as  the  curd  ;  the  second  remains  behind  in  solution 
in  the  whey.  It  will  be  seen  that  this  theory  supposes  the  action  to  be  parallel 
with  that  occurring  in  blood-coagulation,  where  fibrin  ferment  causes  a  cleavage 
of  the  fibrinogen  molecule,  a  part  uniting  with  calcium  to  form  the  insoluble 
fibrin,  and  a  part — much  the  smaller  part — remaining  in  solution  in  the  serum 
as  fibrin-globulin.  It  should  be  added  that  casein  is  also  precipitated  from 
milk  by  the  addition  of  an  excess  of  acid.  The  curdling  of  sour  milk  in  the 
formation  of  bonnyclabber  is  a  well-known  illustration  of  this  fact.  When 
milk  stands  for  some  time  the  action  of  bacteria  upon  the  milk-sugar  leads  to 
the  formation  of  lactic  acid,  and  when  this  acid  reaches  a  certain  concentration 
it  causes  the  ])recipitation  of  the  casein.  One  might  suppose  that  the  curdling 
of  milk  in  the  stomach  is  caused  by  the  acid  present  in  the  gastric  secretion, 
but  it  has  been  shown  that  perfectly  neutral  extracts  of  the  gastric  mucous 
membrane  will  curdle  milk  quite  readily. 

So  far  as  our  positive  knowledge  goes,  the  action  of  rennin  is  confined  to 
milk.  Casein  constitutes  the  chief  proteid  constituent  of  milk,  and  has  there- 
fore an  important  nutritive  value.  It  is  interesting  to  find  that  before  its 
peptic  digestion  begins  the  casein  is  acted  upon  by  an  altogether  different 
enzyme.  The  value  of  the  curdling  action  is  not  at  once  apparent,  but  we 
may  suppose  that  casein  is  more  easily  digested  by  the  proteolytic  enzymes 
after  it  has  been  brought  into  a  solid  form.     The  action  of  rennin  goes  no 


CHEMISTRY   OF   DIGESTION  AND    NUTRITION  235 

further  tlian  the  curdliiitr ;  the  digestion  of  the  curd  is  carried  on  by  the  ])ep- 
sin,  and  later,  in  the  intestines,  by  the  trypsin,  witli  the  formation  of  proteoses 
and  peptones  as  in  the  ease  of  other  proteids. 

Action  of  Gastric  Juice  on  Carbohydrates  and  Fats. — The  gastric  juice 
itself  has  no  direct  action  upon  carbohydrates;  that  is,  it  does  not  contain  an 
aniylolytic  enzyme.  It  is  possible,  nevertheless,  that  some  digestion  of  carbo- 
hydrates goes  on  in  the  stomach,  for,  as  has  been  seen,  the  masticated  food  is 
thoroughly  mixed  with  saliva  before  it  is  swallowed.  The  portion  that  enters  the 
stomach  in  the  beoinning  of  dit»;estion,  when  the  aciditv  of  the  contents  is  small 
(see  p.  227),  may  continue  to  be  acted  upon  by  the  ptyalin.  This  effect,  however, 
cannot  be  considered  important,  since  the  acidity  of  the  contents  of  the  stomach 
must  soon  reach  a  point  sufficient  to  suspend,  and  then  to  destroy,  the  ptyalin. 
It  should  be  added,  however,  that  Lusk  ^  has  shown  that  cane-sugar  can  be 
inverted  to  dextrose  and  levulose  in  the  stomach.  The  importance  of  this 
process  of  inversion,  and  the  means  by  which  it  is  accomplished,  will  be 
described  more  in  detail  when  speaking  of  the  digestion  of  sugars  in  the  small 
intestine  (p.  247).  Upon  the  fats  also  gastric  juice  has  no  direct  digestive 
action.  According  to  the  best  evidence  at  hand,  neutral  fats  are  not  split  in 
the  stomach,  nor  are  they  emulsified  or  absorbed.  Without  doubt,  the  heat 
of  the  stomach  is  sufficient  to  liquefy  most  of  the  fats  eaten,  and  the  move- 
ments of  the  stomach,  together  with  the  digestive  action  of  its  juice  on  the 
proteids  and  albuminoids  with  which  the  fats  are  often  mixed,  bring  about 
such  a  mechanical  mixture  of  the  fats  and  oils  with  the  other  elements  of  the 
chyme  as  facilitates  the  more  rapid  digestion  of  these  substances  in  the  intestine. 

Action  of  Gastric  Juice  on  the  Albuminoids. — Gelatin  is,  from  a 
nutritive  standpoint,  the  most  important  of  the  albuminoids.  Its  nutritive 
value  is  stated  briefly  on  page  215.  It  has  been  shown  that  this  substance  is 
acted  upon  by  pepsin  in  a  way  practically  identical  with  that  described  for  the 
proteids.  Intermediate  products  are  formed  similar  to  the  albumoses,  which 
products  have  been  named  gelatoses^  or  glutoses;^  these  in  turn  may  be  con- 
verted to  gelatin  peptones.  It  is  stated  that  the  action  of  pepsin  is  confined 
almost,  if  not  entirely,  to  changing  gelatin  to  the  gelatose  stage.  The  pro- 
teolytic enzyme  of  the  pancreatic  secretion,  however  carries  the  change  to  the 
peptone  stage  much  more  readily. 

"Why  does  the  Stomach  not  Digest  Itself?— The  gastric  secretion  will 
readily  digest  a  stomach  taken  from  some  other  animal,  or  under  certain  con- 
ditions it  may  digest  the  stomach  in  which  it  is  secreted.  If,  for  instance,  an 
animal  is  killed  while  in  full  digestion,  the  stomach  may  undergo  self-diges- 
tion, especially  if  the  body  is  kept  warm.  This  phenomenon  has  been  observed 
in  human  cadavers.  It  has  been  shown  also  that  if  a  portion  of  the  stomach 
is  deprived  of  its  circulation  by  an  embolism  or  a  ligature,  it  may  be  attacked 
by  the  secretion  and  a  perforation  of  the  stomach-wall  may  result.      How, 

'  Voit:  Zeitschrift  fur  Biologie,  vol.  xxviii.,  1891,  p.  269. 

"^  Chittenden  and  SoUey :  Journal  of  Phydoloriy,  vol.  xii.,  1891,  p.  23. 

^  Klug:  Pjiiiger^s  Archivfur  die  gesammte  Physiologic,  vol.  48,  1891,  p.  100. 


23(i  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

then,  under  normal  conditions,  is  the  stomacli  j^rotectod  from  corrosion  by  its 
own  secretion?  The  (juestion  has  <;iven  rise  to  much  (hscussion,  and  in  reahty 
it  deals  with  one  of  the  fundamental  properties  of  living  matter,  for  the 
same  question  nuist  be  extended  to  take  in  the  non-di<vestion  of  tlie  small 
intestine  by  the  alkaline  pancreatic  secretion,  the  non-digestion  of  the  digestive 
tracts  of  the  invertebrates,  and  the  ease  of  the  unicellular  animals  in  which 
there  is  formed  within  the  animal's  protoplasm  a  digestive  secretion  which 
digests  foreign  material,  but  does  not  att'ect  the  living  substance  of  the  cell. 
In  the  particular  case  under  consideration — namely,  the  protection  of  the 
mammalian  stomach  from  its  own  secretion — explanations  of  the  following 
character  have  been  offered  :  It  was  suggested  (Hunter)  that  the  "  princij)le 
of  life"  in  living  things  protected  them  from  digestion.  This  suggestion 
cannot  be  considered  seriously  at  the  present  day,  since  it  implies  that  living 
matter  is  the  seat  of  a  special  force,  the  so-called  "vital  principle,"  different 
from  the  forms  of  energy  acting  uj)on  matter  in  general.  Appeals  of  this 
kind  to  an  unknown  force  in  explanation  of  the  properties  of  living  matter 
are  not  now  permissible  in  the  science  of  physiology.  Moreover,  it  was 
shown  by  Bernard  that  the  hind  leg  of  a  living  frog  introduced  into  a 
dog's  stomach  through  a  fistula  undergoes  digestion.  The  same  thing  will 
happen,  it  may  be  added,  if  the  leg  is  put  into  a  vessel  containing  an  artificial 
gastric  juice  at  the  proper  temperature.  Bernard's  theory  was  that  the  c})ithe- 
lium  of  the  stomach  acts  as  a  protection  to  the  organ,  preventing  the  absorp- 
tion of  the  juice.  Others  believe  that  the  mucus  formed  by  the  gastric  mem- 
brane acts  as  a  protective  covering ;  while  still  another  theory  holds  that  the 
alkaline  blood  circulating  through  the  organ  saves  it  from  digestion,  since  it 
neutralizes  the  acid  of  the  secretion  as  fast  as  it  is  absorbed,  and  it  is  known 
that  pepsin  can  digest  only  in  an  acid  medium.  None  of  these  ex])lanations 
is  sufficient.  The  last  explanation  is  unsatisfactory  because  it  does  not  explain 
the  immunity  of  the  small  intestine  from  digestion  by  the  alkaline  pancreatic 
juice,  or  the  protection  of  the  infusoria  from  their  own  digestive  secretion. 
The  mucous  theory  is  inadequate,  as  we  cannot  believe  that  by  this  means  the 
protection  could  be  as  complete  as  it  is ;  and,  moreover,  this  theory  does  not 
admit  of  a  general  application  to  other  cases.  The  epithelium  theory  simply 
changes  the  problem  a  little,  as  it  involves  an  explanation  of  the  immunity  of 
the  living  epithelial  cells.  It  is  well  known  that  in  the  dead  stomach  the 
epithelial  lining  is  no  longer  a  protection  against  digestion,  so  that  we  are  led 
to  believe  that  there  is  nothing  j)eculiar  in  the  composition  of  ejiithelial  cells, 
as  compared  with  other  tissues,  to  account  for  their  exemption  under  normal 
conditions.  When  we  come  to  consider  all  the  evidence,  nothing  seems  clearer 
than  that  the  protection  of  the  living  tissue  is  in  every  case  due  to  the  jiroper- 
ties  of  its  living  structure.  So  long  as  the  tissue  is  alive,  it  is  protected  from 
the  action  of  the  digesting  secretion,  but  the  ultimate  physical  or  chem- 
ical reason  for  this  property  is  yet  to  be  discovered.  In  the  case  of  the 
mammalian  stomach  it  is  quite  probable  that  the  lining  epithelial  cells  are 
especially  modified  to  resist  the  action  of  the  digestive  secretion,  but,  as  has 


CHEMISTRY   OF  DldESTION  AND   NUTRITION.  237 

just  been  said,  they  lose  this  property  as  soou  as  they  undergo  the  change 
from  living  to  dead  structure.  The  digestion  of  the  living  frog's  leg  in 
gastric  juice,  and  similar  instances,  do  not  affect  this  general  idea,  since,  as 
Bernard  himself  pointed  out,  what  happens  in  this  case  is  that  the  tissue  is 
first  killed  by  the  acid  and  then  undergoes  digestion.  On  the  other  hand, 
Neuraeister  has  shown  that  a  living  frog's  leg  is  not  digested  by  strong  pan- 
creatic extracts  of  weak  alkaline  reaction,  since  under  these  conditions  the 
tissues  are  not  injured  by  the  slightly  alkaline  liquid.  When  it  is  said  that 
the  exemption  of  living  tissues  from  self-digestion  is  due  to  the  peculiarities 
of  their  structure,  it  must  not  be  supposed  that  this  is  equivalent  to  referring 
the  whole  matter  to  the  action  of  a  mysterious  vital  force.  On  the  contrary, 
all  that  is  meant  is  that  the  structure  of  living  protoplasmic  material  is  such 
that  the  action  of  the  digestive  secretion  is  prevented,  possibly  because  it  is  not 
absorbed,  this  result  being  the  outcome  of  the  physical  and  chemical  forces 
exhibited  by  matter  with  this  peculiar  structure.  While  a  statement  of  this 
kind  is  not  an  explanation  of  the  facts  in  question,  and  indeed  amounts  to  a 
confession  that  an  explanation  is  not  at  present  possible,  it  at  least  refers  the 
phenomenon  to  the  action  of  known  properties  of  matter. 

General  Remarks  upon  the  Physiology  of  the  Stomach. — From  the 
foregoing  account  it  will  be  seen  that,  speaking  generally,  the  functions  of  the 
stomach  are  in  part  to  act  chemically  upon  the  proteids,  and  in  part,  by  the 
combined  action  of  its  secretion  and  its  muscular  movements,  to  get  the  food 
into  a  physical  condition  suitable  for  subsequent  digestion  in  the  intestine. 
The  material  sent  out  from  the  stomach  (chyme)  must  be  quite  variable  in 
composition,  but  physically  the  action  of  the  stomach  has  been  such  as  to 
reduce  it  to  a  liquid  or  semi-liquid  consistency.  The  extent  of  the  true 
digestive  action  of  gastric  juice  on  proteids  is  not  now  believed  to  be  so 
complete  as  it  was  formerly  thought  to  be.  Examination  of  the  chyme 
shows  that  it  may  contain  quantities  of  undigested  or  only  partially  digested 
proteid,  complete  digestion  being  effected  in  the  intestines.  Moreover,  arti- 
ficial peptic  digestion  of  proteids  under  the  most  favorable  conditions  shows 
that  only  a  portion  is  ever  converted  to  peptone,  most  of  it  remaining  in  the 
proteose  stage.  It  has  been  suggested,  therefore,  that  gastric  digestion  of 
proteids  is  largely  preparatory  to  the  more  complete  action  of  the  pancreatic 
juice,  whose  enzyme  (trypsin)  has  more  powerful  proteolytic  properties.  In 
accordance  with  this  idea,  it  has  been  shown  that  an  animal  can  live  and 
thrive  without  a  stomach.  Several  cases  ^  are  on  record  in  ^^'llich  the  stomach 
was  practically  removed  by  surgical  operations,  the  oesophagus  being  stitched 
to  the  duodenum.  The  animals  did  well  and  seemed  perfectly  normal.  Exper- 
iments of  this  character  do  not,  of  course,  show  that  the  stomach  is  useless  in 
digestion  ;  they  demonstrate  only  that  in  the  animals  used  it  is  not  absolutely 
essential.  The  reason  for  this  will  better  be  appreciated  after  the  digestive 
properties  of  pancreatic  secretion  have  been  studied. 

^  Ludwig  and  Ogata/  Archiv  fiir  Anatomie  und  Physiologic,  1883,  p.  89;  and  Carvallo  and 
Pachon  :  Archives  dc  Physiologic  normalc  et  pathologique,  1894,  p.  106. 


238  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

D.  Intestinal  Digestion. 

After  the  fond  has  jinssed  tlir()ii<i;h  the  pylorio  orifice  of  the  stomach  and  has 
entered  the  small  intestine  it  undergoes  its  most  ])rof()und  digestive  changes. 
Intestinal  digestion  is  carried  ont  mainly  while  the  food  is  passing  through 
the  small  intestine,  althongh,  as  we  shall  see,  the  process  is  completed  during 
the  slower  passage  through  the  large  intestine.  Intestinal  digestion  is  effected 
through  the  combined  action  of  three  secretions — namely,  the  pancreatic  juice, 
the  bile,  and  the  intestinal  juice.  The  three  secretions  act  together  uimn  the 
food,  but  for  the  sake  of  clearness  it  is  advisable  to  consider  each  one  separately 
as  to  its  properties  and  its  digestive  action. 

Composition  of  Pancreatic  Juice. — Pancreatic  juice  is  the  secretion  of 
the  pancreatic  gland.  In  man  the  main  duct  of  the  gland  opens  into  the 
duodenum,  in  common  with  the  bile-duct,  about  8  to  10  cm.  below  the  opening 
of  the  pvlorus.  In  some  of  the  other  mammals  the  arrangement  is  different : 
in  dogs,  for  example,  there  are  two  ducts,  one  opening  into  the  duodenum, 
together  with  the  bile-duet,  about  3  to  5  cm.  below  the  opening  of  the 
pylorus,  and  one  some  3  to  5  cm.  farther  down.  In  rabbits  the  principal 
duct  opens  separately  into  the  duodenum  about  35  cm.  below  the  opening 
of  the  bile-duct.  For  details  as  to  the  act  of  secretion,  its  time-relations  to 
the  ingestion  of  food,  its  quantity,  etc.,  the  reader  is  referred  to  the  section  on 
Secretion.  Most  of  our  exact  knowledge  of  the  properties  of  the  pancreatic 
secretion  has  been  obtained  either  from  experiments  upon  lower  animals, 
especially  the  dog  and  the  rabbit,  in  which  it  is  possible  to  establish  a  pan- 
creatic fistula  and  to  collect  the  normal  juice,  or  from  experiments  with  arti- 
ficial pancreatic  juice  prepared  from  extracts  of  the  gland.  Various  methods 
have  been  used  in  making  pancreatic  fistuhie  :  usually  the  main  duct  of  the 
gland,  which  in  the  two  animals  named  is  separate  from  the  bile-duct,  is 
exposed  and  a  canula  is  inserted.  A  better  method,  devised  by  Heidenhain, 
consists  in  cutting  out  the  piece  of  duodenum  into  which  the  main  duct  opens 
and  sewing  this  isolated  piece  to  the  abdominal  wall  so  as  to  make  a  permanent 
fistula,  the  continuity  of  the  intestinal  tract  in  this  case  being  re-established, 
of  course,  by  sutures.  A  simple  method  of  obtaining  normal  pancreatic  juice 
from  the  rabbit  is  described  by  Ratchford.^  In  his  method  the  portion  of 
the  duodenum  into  which  the  main  duct  opens  is  resected  and  cut  open  along 
the  border  opposite  to  the  mesenteric  attachment.  The  mouth  of  the  duct  is 
seen  as  a  small  papilla  projecting  from  the  surface  of  the  mucous  membrane. 
Through  the  papilla  a  small  glass  canula  may  be  passed  into  the  duct,  and  the 
secretion,  which  flows  slowly,  may  be  collected  for  several  hours.  The  total 
quantity  olitainable  by  this  means  from  a  rabbit  is  small — about  1  c.c. — but  it 
is  sufficient  for  the  demonstration  of  some  of  the  imiiortant  properties  of  pan- 
creatic juice,  especially  its  action  upon  fats.  As  obtained  by  these  methods, 
the  secretion  is  found  to  be  a  clear,  colorless,  alkaline  liquid.  The  secretion 
obtained  from  dogs  is  thick  and  glairy,  and  forms  a  coagulum  upon  standing, 
'  Journal  of  Phymology,  vol.  xii.,  1891,  p.  72. 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION. 


239 


while  that  iVoiii  iiibbits  is  u  thin,  perf't'ctly  colorless  liquid  \vhi(;ii  duos  not  fonu 
a  clot.  Ill  dogs  the  secretiou  from  a  perniaueut  fistula  soon  becomes  thinner 
than  it  was  when  the  fistula  was  first  established,  and  this  (change  in  its  con- 
sistency is  accompanied  by  a  corresponding  variation  in  specific  gravity.  The 
specific  gravity  (dog)  of  the  juice  from  a  tem^jorary  fistula  is  given  at  1030; 
from  a  })ernianent  fistula,  at  1010  to  1011.  The  secretion  coagulates  upon 
being  heated,  owing  to  the  proteids  held  in  solution,  and  it  undergoes  putre- 
faction very  quickly,  so  that  it  cannot  be  kept  for  any  length  of  time.  The 
analysis  of  the  secretion  most  frequently  quoted  is  that  given  by  C.  Schmidt, 
as  follows : 

Pana'ealic  Juice  {Dog). 


Constituents. 


S  Water 

I  Solids 

Orfi;anic  substances 

Asli 

Sodium  carbonate 

Sodium  cbloride 

Calcium,  magnesium,  and  sodium  phosphates 


Imme.liately  after 

From  permanent 

establishing  fistula. 

fistula. 

900.76 

980.45 

99.24 

19.55 

90.44 

12.71 

8.80 

6.84 

0.58 

3.31 

7.35 

2.50 

0.53 

0.08 

The  composition  of  normal  human  pancreatic  juice  has  not  been  determined 
completely,  owing  to  the  rarity  of  opportunities  of  obtaining  the  secretion. 
Several  partial  analyses  have  been  reported.  According  to  Zawadsky,^  the 
composition  of  the  secretion  in  a  young  woman  was  as  follows : 

In  1000  parts. 

Water 864.05 

Organic  substances      132.51 

Proteids 92.05 

Salts 3.44 

The  organic  substances  held  in  the  secretion  are  in  part  of  an  albuminous 
nature,  since  they  coagulate  upon  heating,  but  the  exact  nature  of  the  proteid 
or  proteids  has  not  been  determined  satisfactorily.  The  most  important  of  the 
organic  substances — the  essential  constituents,  indeed,  of  the  whole  secretion — 
are  three  enzymes  acting  respectively  upon  the  proteids,  the  carbohydrates, 
and  the  fats.  The  proteolytic  enzyme  is  called  "  trypsin ;"  the  amylolytic 
enzyme  is  described  under  different  names :  "  amylopsin  "  is  perhaps  the  best, 
and  will  be  adopted  in  this  section  ;  for  the  fat-splitting  enzyme  we  shall  use 
the  term  "  steapsin."  Owing  to  the  presence  of  these  enzymes  the  pancreatic 
secretion  is  capable  of  exerting  a  digestive  action  upon  each  of  the  three  im- 
portant classes  of  food-stuffs. 

Trypsin. — Trypsin  is  a  more  powerful  proteolytic  enzyme  than  pepsin. 
Unlike  the  latter,  trypsin  acts  best  in  alkaline  media,  but  it  is  effective  also  in 
neutral  liquids,  or  even  in  solutions  not  too  strongly  acid.  Trypsin  is  affected 
by  changes  in  temperature  like  the  other  enzymes,  its  action  being  retarded 
by  cooling  and  being  hastened  by  warming.    There  is,  however,  a  temperature, 

'  Cenlralblatl fiir  Physiologie,  vol.5,  1891,  p.  179. 


240  AA^  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

which  nuiy  be  called  the  optimum  temperature,  at  which  the  trypsin  acts  most 
powerfully;  if,  however,  the  temperature  is  I'aised  to  as  much  as  70°  to  80°  C, 
the  enzyme  is  destroyed  entirely.  Trypsin  has  never  been  isolated  in  a  condi- 
tion sufficiently  pure  for  analysis,  so  that  its  chemical  (jomposition  is  unknown. 
Extracts  containing  trypsin  can  be  made  from  the  gland  very  easily  and  by 
a  variety  of  methods.  The  usual  laboratory  method  is  to  mince  the  gland  and 
to  cover  it  with  glycerin  for  some  time.  In  using  this  and  other  methods  for 
preparing  trypsin  extracts  it  is  best  not  to  take  the  perfectly  fresh  gland,  but 
to  keep  it  for  a  number  of  hours  before  using.  The  reason  for  this  is  that  the 
enzyme  exists  in  the  fresh  gland  in  a  preparatory  stage,  a  zymogen  (see  sec- 
tion on  Secretion),  which  in  this  case  is  called  "'  trypsinogen."  Upon  standing, 
the  latter  is  slowly  converted  to  trypsin — a  process  which  may  be  hastened  by 
the  action  of  dilute  acids  and  by  other  means.  An  artificial  pancreatic  juice 
is  prepared  usually  by  adding  a  small  quantity  of  the  pancreatic  extract  to  an 
alkaline  liquid ;  the  liquid  usually  employed  is  a  solution  of  sodium  carbonate 
of  from  0.2  to  0.5  per  cent.  To  prevent  putrefactive  changes,  which  come  on 
with  su(^h  readiness  in  pancreatic  digestions,  a  few  drops  of  an  alcoholic  solution 
of  thymol  may  be  added.  A  mixture  of  this  kind,  if  kept  at  the  proper 
temperature,  digests  proteids  very  rapidly,  and  most  of  our  knowledge  of 
the  action  of  trypsin  has  been  obtained  from  a  study  of  the  products  of  such 
digestions. 

Products  of  Tryptic  Digestion. — Tryptic  digestion  resembles  peptic  diges- 
tion in  that  proteoses  and  peptones  are  the  chief  products  formed,  but  the  two 
processes  differ  in  a  number  of  details.  The  naked-eye  appearances,  in  the  first 
place,  are  different  in  cases  in  which  the  proteid  acted  u])on  is  in  a  solid  form ; 
for  while  in  the  pepsin-hydrochloric  digestion  the;  proteid  swells  up  and  grad- 
ually dissolves,  under  the  action  of  trypsin  it  does  not  swell,  but  suffers  erosion, 
as  it  were,  the  solid  mass  of  proteid  being  eaten  out  until  finally  only  the  indi- 
gestible part  remains,  retaining  the  shape  of  the  original  mass,  but  falling  into 
fragments  when  shaken.  In  the  second  jilace,  the  hy(h'olytic  cleavages  seem 
to  be  of  a  more  intense  nature.  In  peptic  digestion,  after  the  syntonin  stage  is 
passed,  there  is  a  gradual  change  to  peptone  through  the  intermediate  primary 
and  secondary  proteoses.  Under  the  influence  of  trypsin,  according  to  the  most 
recent  experiments,  the  solid  proteid  undergoes  a  transformation  directly  to 
secondary  proteoses  (deutero-proteoses),  the  intermediate  stages  being  skipjied. 
It  was  formerly  thought  that  the  solid  proteid  was  converted  first  into  a  soluble 
proteid,  and  that  if  the  solution  was  alkaline  some  alkali-albumin  was  formed, 
precipitable  by  neutralization,  and  comparable  to  the  syntonin  of  pepsin-hydro- 
chloric digestion.  This  soluble  proteid  was  thought  to  be  split  into  proteoses 
of  the  hemi-  and  anti-  groups  which  were  then  converted  to  the  corresponding 
peptones,  according  to  Kiiline's  schema  (p.  231).  There  seems  to  be  no  doubt 
that  with  the  proteid  most  frequently  used  in  artificial  digestion — namely^ 
fibrin  from  coagulated  blood — the  first  effect  is  a  conversion  to  a  soluble 
globulin-like  form  of  proteid ;  but  Neumeister  finds  that  this  does  not  happen 
with  other  proteids,  and  he  thinks  that  in  the  case  of  fibrin  it  is  not  due  to  a 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION. 


241 


true  digestive  action  of  trvi)siu,  but  to  a  partial  solution  of  the  fibrin  by  the 
inorganic  salts  in  the  liquid.  In  general,  however,  the  preliminary  stage  of 
a  soluble  proteid  is  missed,  as  also  is  that  of  the  primary  proteoses.  The 
proteid  falls  at  once  by  hydrolytic  cleavage  into  deutero-proteoses,  and  these 
in  turn  are  transformed  to  peptones  (ampho-peptones).  Just  at  this  point 
comes  in  one  of  the  most  characteristic  differences  between  the  action  of  pepsin 
and  that  of  trypsin.  Pepsin  cannot  affect  further  the  ampho-peptones,  but 
trypsin  may  act  upon  the  supposed  hemi-  constituent  and  split  it  up,  with  the 
formation  of  a  number  of  much  simpler  non-proteid  bodies,  most  of  which  are 
amido-acids.  The  final  products  of  })rolonged  tryptic  digestion  are,  first,  a  pep- 
tone which  cannot  further  be  decomposed  by  the  enzyme  and  which  constitutes 
what  is  known  as  anti-peptone,  and,  second,  a  number  of  simpler  organic  sub- 
stances, mainly  amido-acids,  that  come  from  the  splitting  of  that  part  of  the 
peptone  which  can  be  acted  upon  by  the  trypsin,  and  which  constitutes  what 
is  known  as  henii-peptone.  It  may  be  remarked  in  passing  that  hemi-peptone 
has  not  been  isolated.  Ampho-peptones  containing  both  anti-  and  hemi-pep- 
tones  are  formed  in  peptic  digestion,  and  they  may  be  obtained  from  tryptic 
digestion  if  it  is  not  allowed  to  go  too  far ;  anti-peptone,  on  the  other  hand, 
may  be  obtained  from  tryptic  digestion  which  has  been  permitted  to  go  on  until 
the  hemi-peptone  has  been  completely  destroyed,  but  no  good  method  is  known 
by  which  hemi-peptone  can  be  isolated  from  solutions  containing  both  it  and 
the  anti-  form.  The  simpler  products  formed  by  the  breaking  up  of  the  hemi- 
peptone  molecule  under  the  influence  of  the  trypsin  can  be  formed,  in  part  at 
least,  in  the  laboratory  by  processes  which  are  known  to  cause  hydrolytic 
decompositions.  It  is  probable,  therefore,  that  these  substances  may  be  looked 
upon  as  products  of  the  hydrolytic  cleavage  of  hemi-peptone.  They  are  of 
smaller  molecular  weight  and  of  simpler  structure  than  the  peptone  molecule 
from  which  they  are  formed.  A  tabular  list  of  these  bodies,  taken  from  Gam- 
gee,^  is  given.  The  list  includes  only  those  substances  which  have  actually 
been  isolated ;  it  is  possible  that  others  exist : 


Final  Products  {other  than  Peptones)  of  the  Action  of  Trypsin  on  Albuminous  and  Albuminoid 

Bodies. 


Bodies  derived  from  the 
fatty  acids. 

Bases. 

Organic  body  of  unknown 
composition. 

Aromatic  bodies. 

Amido-caproic  acid  (leu- 

cin). 
Amido  -  valerianic     acid 

(biitalanin). 
Amido-succinic  acid  (as- 

partic  acid). 
Amido-pyrotartaric  acid 

(glutamic  acid). 
(Diamido-acetic  acid?) 

Lysin. 

Lvsatinin. 

NHa. 

Tryptophan    (gives    a 
red  color  on  the  ad- 
dition   of    chlorine- 
water,     and     violet 
with  bromine-water). 

Paroxyphenylamidopro- 
pionic  acid  (tyrosin). 

Of  these  substances,  the  ones  longest  known  and  most  easily  isolated  are  leucin 
(CgHigXOj)  and  tyrosin  (CgHuNOg).     The  chemical  composition  and  proper- 

'  A  Text-book  of  the  Physiological  Chemistry  of  the  Animal  Body,  1893,  vol.  ii.  p.  230. 
16 


242  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

ties  of  those  and  the  other  products  are  described  in  the  Chemical  section. 
Leiiciii  and  tvrosin  have  been  found  in  the  contents  of  tlie  intestines,  and  it  is 
probable,  therefore,  that  the  splitting  of  the  henii-peptone  whieii  tai<es  place  so 
readily  in  artificial  tryptic  digestions  occurs  also,  to  some  extent  at  least,  within 
the  body,  although  we  have  no  accurate  estimates  of  the  amount  of  peptone 
destroved  in  this  way  under  normal  conditions.  On  the  supposition  that  the 
production  of  leucin,  tyrosin,  and  the  other  amido-  bodies  is  a  normal  result  of 
tryptic  digestion  within  the  body,  it  is  interesting  to  inquire  what  physiological 
value,  if  any,  is  to  be  attributed  to  these  substances.  At  first  sight  the  forma- 
tion of  these  amido-  bodies  from  the  valuable  peptone  would  seem  to  be  a 
waste.  Peptone  we  know  may  be  absorbed  into  the  blood,  and  may  then  be 
used  to  form  or  n'i)air  })roteid  tissue,  or  to  furnish  energy  to  the  body  upon 
oxidation,  but  lcu('in  and  tyrosin  and  the  other  products  of  the  breaking  up 
of  the  hemi-peptone  are  far  less  valuable  as  sources  of  energy,  and  so  far  as 
we  know  they  cannot  be  used  to  form  or  rej)air  ]n"oteid  tissue.  But  m'C  must 
be  careful  not  to  jump  too  hastily  to  the  conclusion  that  the  splitting  of  the 
hemi-peptone  is  useless.  It  remains  possible  that  a  wider  knowledge  of  the 
subject  may  show  that  the  process  is  of  distinct  value  to  the  body,  although  it 
must  be  confessed  that  no  plausible  suggestion  as  to  its  importance  has  yet 
been  made.  In  addition  to  any  possible  functional  value  which  these  amido- 
bodies  may  possess,  their  occurrence  in  proteolysis  is  of  immense  interest  to 
the  physiologist.  Some  of  them  are  of  a  constitution  simple  enough  to  be  studied 
by  exact  chemical  methods,  and  the  hope  is  entertained  that  through  them 
a  clearer  knowledge  may  be  obtained  of  the  structure  of  the  proteid  molecule. 
It  should  be  added  that  not  only  are  these  amido-  bodies  found  in  the  aliment- 
ary canal  as  products  of  tryptic  digestion,  but  that  they,  or  some  of  them, 
occur  also  in  other  parts  of  the  body,  especially  under  pathological  conditions, 
and  that,  furthermore,  they  occur  among  the  products  of  the  destruction  of 
the  proteid  molecule  by  laboratory  methods  or  by  the  action  of  bacterial 
organisms.  The  theoretical  importance  of  the  base  lysatinin  will  be  referred 
to  again  later,  when  speaking  of  the  origin  of  urea  in  the  body.  The  processes 
of  tryptic  digestion  outlined  above  are  represented  in  brief  in  the  following 
schema,  taken  from  Neumeister : ' 

Proteid. 

I 
Deutero-albiimoses. 

I 
Ampho-peptone. 


Anti-peptone.  Hemi-peptone. 


Leucin.  Tyrosin.  Aspartic  acid.  Tryptophan,  etc. 

It  may  be  said  in  conclusion  that  trypsin  produces  pe])tone  from  ]>roteids  more 

readily  than  does  pepsin.     Under  normal  conditions  it  is  probable  that  most 

*  Lehrbuch  der  physiologischen  Ckemie,  1893,  p.  200. 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  243 

of  the  ]>rotei(l  of  the  food  receives  its  fiiiul  preparation  for  absorption  in  the 
small  intestine,  nnder  the  inlinenee  of  this  enzyme.' 

Albuminoids. — Gelatin  and  the  other  albuminoids  are  aeted  upon  by 
trypsin,  the  produets  being  similar  in  general  to  those  formed  from  the  pro- 
teids.  As  stated  on  page  235,  pei)sin  carries  the  digestion  of  gelatin  mainly  to 
the  gelatose  stage;  trypsin,  however,  produces  gelatin  peptones.  It  seems 
probable,  therefore,  that  the  final  digestion  of  the  albuminoids  also  is  effected 
in  the  small  intestine. 

Aniylopsin. — The  enzyme  of  the  pancreatic  secretion  which  acts  upon 
starches  is  found  in  extracts  of  the  gland,  made  according  to  the  general 
methods  already  given,  and  its  presence  may  be  demonstrated,  of  course,  in 
the  secretion  obtained  by  establishing  a  pancreatic  fistula.  The  proof  of  the 
existence  of  this  enzyme  is  found  in  the  fact  that  if  some  of  the  pancreatic 
secretion  or  some  of  the  extract  of  the  gland  is  mixed  with  starch  paste,  the 
starch  quickly  disappears  and  maltose  or  maltose  and  dextrin  are  found 
in  its  place.  Amylopsin  shows  the  general  reactions  of  enzymes  with  rela- 
tion to  temperature,  incomj)leteness  of  action,  etc.  Its  specific  reaction  is  its 
effect  upon  starches.  Investigation  has  shown  that  the  changes  caused  by  it 
in  the  starches  are  apparently  the  same  as  those  produced  by  ptyalin.  In 
fact,  the  two  enzymes  ptyalin  and  amylopsin  are  identical  in  properties  as 
far  as  our  knowledge  goes,  so  that  it  is  not  uncommon,  in  German  liter- 
ature especially,  to  have  them  both  described  under  the  name  of  ptyalin. 
The  term  amylopsin  is  convenient,  however,  in  any  case,  to  designate  the 
special  origin  of  the  pancreatic  enzyme.  As  to  the  details  of  its  action,  it  is 
unnecessary  to  repeat  what  has  been  said  on  page  223.  The  end-products 
of  its  action,  as  far  as  can  be  determined  from  artificial  digestions,  are  a  sugar, 
maltose  (Ci2H220ii,H20),  and  more  or  less  of  the  intermediate  achrobdextrins, 

'  The  details  of  the  cleavage  of  the  proteid  molecule  under  the  influence  of  pepsin 

and  trypsin  are  obviously  not  yet  completely  worked  out.     The  general  idea  of  Kiihne 

is  given  briefly  in  a  foot-note  on  .page  231.    An  important  modification  of  the  original 

conception  is  represented  in  a  theoretical  schema  given  by  Neumeister,  which  is  here 

reproduced.    According  to  this  diagram,  each  proteose,  as  well  as  the  peptone  produced 

in  an  ordinary  digestion,  contains  both  hemi-  and  anti-  groups,  and  is  therefore  an 

ami)ho-  compound.     The  relative  amount  of  hemi-  or  anti-  substance  present  at  each 

stage  is  indicated  by  thick  or  thin  lines  as  the  case  may  be.     While  proto-proteose  and 

the  deutero-proteose  and  peptone  arising  from  it  are  mainly  composed  of  the  hemi- 

group,  hetero-proteose  and  its  subsequent  stages  consist  chiefly  of  the  anti-  grouping. 

The  resistant  compound,  known  as  anti-albumid,  which  is  split  off  from  the  proteid 

molecule  in  greater  or  less  quantity,  seems  to  have  only  the  anti-  grouping;  so  far  as  it 

can  be  converted  to  peptone,  it  yields  only  anti-peptone. 

r  Proteid  molecule.  "1 

[Hemi-  group.  Anti-  group.J^^ 

Proto-proteose.  Hetero-proteose. 

(Ampho-proteose.)  {Ampho-proteose.)  Anti-albumid. 

II  II  I 

Deutero-proteose.  Deutero-proteose.  Deutero-proteose. 

(Ampho-proteose.)  (Ampho-proteose.)  (Anti-proteose.) 

II  i    I  i 

Ampho-peptone.  Ampho-peptone.  Anti-peptone. 


244  .I.V   AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

the  relative  amounts  depending  upon  the  completeness  of  digestion.  As  has 
previously  been  said,  there  are  indications  tiiat  under  tiie  favorable  conditions 
of  natural  digestion  all  tlie  starch  may  be  changed  to  maltose,  but  possibly 
it  is  not  necessary  that  the  action  should  be  so  complete  in  order  that  the 
carbohydrate  may  be  absorbed  into  the  blood,  as  will  be  shown  when  we  come 
to  speak  of  the  further  action  of  the  intestinal  secretion  upon  maltose  and  the 
dextrins.  The  amylolytic  action  of  the  pancreatic  juice  is  extremely  import- 
ant. The  starches  constitute  a  large  part  of  our  ordinary  diet.  Tlie  action  of 
the  saliva  upon  them  is  probably,  for  reasons  already  given,  of  subordinate 
importance.  Their  digestion  takes  place,  therefore,  entirely  or  almost  entirely 
in  the  small  intestine,  and  mainly  by  virtue  of  the  action  of  the  amylopsin 
contained  in  the  pancreatic  secretion.  The  action  of  the  amylopsin  is  supple- 
mented to  some  extent,  apparently,  by  a  similar  enzyme  formed  in  small 
quantities  in  the  intestinal  wall  itself,  the  nature  of  which  will  be  described 
presently  in  connection  with  intestinal  secretion. 

Steapsin. — Steapsin  is  the  name  given  to  a  fat-splitting  enzyme  occurring 
in  the  pancreatic  juice.  It  is  of  the  greatest  importance  in  the  digestion  and 
absorption  of  fats.  The  peculiar  power  of  the  pancreatic  juice  to  split  neutral 
fats  with  the  liberation  of  free  fatty  acid  was  first  described  by  Bernard.  His 
discovery  has  since  been  corroborated  for  different  animals,  including  man, 
by  the  use  of  normal  pancreatic  juice  obtained  from  a  fistula,  or  by  the  aid  of 
the  tissue  of  the  fresh  gland,  or,  finally,  by  means  of  extracts  of  the  gland. 
When  neutral  fats  (see  Chemical  section  for  the  composition  of  fats)  are 
treated  with  an  extract  containing  steapsin,  they  take  uj)  water  and  then 
undergo  cleavage  (hydrolysis),  with  the  production  of  glycerin  and  the  free 
fatty  acid  found  in  the  particular  fat  used.  This  reaction  is  exjjlained  by  the 
following  equation,  in  which  a  general  formula  for  fats  is  used : 

C3H,(aH2„,,COO)3  4-  3HP  =  C3H,(OH)3+  3(aH,„,,COOH). 

Fat.  Glycerin.  Free  fatty  acid. 

The  reaction  in  the  case  of  palmitin  would  be — 

C3H,(C\,H3,COO)3  -F  3H,0  =  C3H,(OH)3  -f-  3(C\3H3,COOH). 

Palmitin.  Glycerin.  Palmitic  acid. 

While  this  action  is  undoubtedly  caused  by  an  enzyme,  it  has  not  been  possible 
to  isolate  the  so-called  "  steapsin  "  in  a  condition  of  even  approximate  purity. 
As  a  matter  of  fact  also,  ordinary  extracts  of  pancreas,  such  as  the  laboratory 
extracts  in  glycerin,  do  Jiot  usually  siiow  the  presence  of  this  enzyme  unless 
special  precautions  are  taken  in  their  preparation.  It  would  seem  that  steapsin 
is  easily  destroyed.  With  fresh  normal  juice  or  with  pieces  of  fre.>^li  pancreas 
the  fat-splitting  effect  can  be  demonstrated  easily.  One  striking  method  of 
making  the  demonstration  is  to  use  butter  as  the  fat  to  be  decomposed.  If 
butter  is  mixed  with  normal  pancreatic  juice  or  with  pieces  of  fresh  pancreas, 
and  the  mixture  is  kept  at  the  body-temperature,  the  several  fats  contained  in 
butter  will  be  decomposed  and  the  corresponding  fatty  acids  will  be  liberated, 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  245 

amoiiii;  tlicm  butyric  acid,  which  is  readily  recognized  by  its  familiar  odor, 
that  ot"  rancid  butter.  The  action  of  steapsin,  as  in  the  case  of  the  other 
enzyiues,  is  very  much  influent-ed  l)y  the  temperature.  At  the  iKMly-temper- 
ature  the  action  is  very  rapid.  The  nature  of  the  fat  also  influences  the 
rapidity  of  the  reaction  ;  it  may  be  said,  in  general,  that  fats  with  a  high 
melting-point  are  less  readily  decomposed  than  those  with  a  low  melting- 
point.  It  has  been  shown,  however,  that  even  spermaceti,  which  is  a  body 
related  to  the  fats  and  whose  melting-point  is  53°  C,  is  decomposed,  although 
slowly  and  imperfectly,  by  steapsin.  The  fat-splitting  action  of  the  steapsin 
undoubtedly  takes  place  normally  in  the  intestines,  but  it  must  not  be  supposed 
that  all  the  fat  eaten  undergoes  this  process.  On  the  contrary,  it  is  believed 
that  a  small  portion  only  of  the  fats  and  oils  is  aifected  by  the  steapsin,  by  far 
the  larger  portion  remaining  unaffected  and  being  absorbed  into  the  blood  as 
neutral  fat.  What,  then,  is  the  physiological  value  of  steapsin  in  the  digestion 
and  absorption  of  fats?  This  question  is  difficult  to  answer  satisfactorily  if 
one  goes  into  the  details.  In  general,  however,  it  is  commonly  taught  that  the 
small  part  of  the  fat  split  by  the  steapsin  into  fatty  acid  and  glycerin  helps 
to  emulsify  the  balance  of  the  fat  and  thereby  renders  its  absorption  possible. 
The  fat-splitting  action  of  steapsin,  then,  is  of  indirect  value  in  digestion,  and 
its  importance  can  be  brought  out  best  by  describing  the  emulsification  of  fats 
and  the  conditions  bringing  this  emulsification  about. 

Emulsification  of  Fats. — An  oil  is  emulsified  when  it  is  broken  up  into 
minute  globules  which  do  not  coalesce,  but  which  remain  separate  and  more 
or  less  uniformly  distributed  throughout  the  medium  in  which  they  exist. 
Artificial  emulsions  can  be  made  by  shaking  oil  vigorously  in  viscous  solutions 
of  soap,  mucilage,  etc.  Milk  is  a  natural  emidsion  which  separates  partially 
on  standing,  some  of  the  oil  rising  to  the  top  to  form  cream.  Bernard  made 
the  important  discovery  that  when  oil  and  pancreatic  juice  are  shaken  together 
an  emulsion  of  the  oil  takes  place  very  rapidly,  especially  if  the  temperature 
is  about  that  of  the  body.  The  main  cause  of  the  emulsification  has  been 
shown  to  be  the  formation  of  free  fatty  acids  due  to  the  action  of  steapsin, 
and  the  union  of  these  acids  with  the  alkaline  salts  present  to  form  soaps. 
This  fact  has  been  demonstrated  by  experiments  of  the  following  character: 
If  a  perfectly  neutral  oil  is  shaken  with  an  alkaline  solution  (^  per  cent, 
sodium-carbonate  solution),  no  emulsion  occurs  and  the  two  liquids  soon  sepa- 
rate. If  to  the  same  neutral  oil  one  adds  a  little  free  fatty  acid,  or  if  one 
uses  rancid  oil  to  begin  with  and  shakes  it  with  \  per  cent,  sodium-carbonate 
solution,  an  emulsion  forms  rapidly  and  remains  for  a  long  time.  Oil  con- 
taining fatty  acids  when  shaken  with  distilled  water  alone  will  not  giv^e  an 
emulsion.  It  has  been  shown,  moreover,  by  Gad  and  Ratchford  that  with  a 
certain  percentage  of  free  fatty  acids  (5|  per  cent.)  rancid  oil  and  a  sodium- 
carbonate  solution  will  form  a  fine  emulsion  spontaneously — that  is,  without 
shaking.  Shaking,  however,  facilitates  the  emulsification  when  the  amount 
of  free  acid  varies  from  this  optimum  percentage.  In  what  way  the  formation 
of  soaps  in  an  oily  liquid  causes  the  oil  to  become  emulsified  is  still  a  matter 


240  ^liV"   AMERICAN    TEXT- BOOK    OF   PHYSIOLOGY. 

of  speculation.  It  lias  hccii  suf^irostod  that  the  soaj)  ioriiis  a  tliiii  n»atin<;  or 
membraiu"  round  the  small  oil-drops,  thus  ]treventing  them  I'njni  uuitin;^.  The 
splitting!;  of  the  oil  into  small  drops  seems  to  be  caused,  in  cases  of  spontaneous 
emulsification,  by  the  a<;t  of  formation  of  the  soaj) — that  is,  the  union  of  the 
alkali  with  the  fatty  acid — in  other  cases  by  the  mechanical  shaking,  or  by  these 
two  causes  combined.  The  aj)plication  of  these  facts  to  the  action  of  the  pan- 
creatic juice  normally  in  the  small  intestine  is  easily  made.  When  the  chyme, 
containing  more  or  less  of  liquid  fat,  comes  into  contact  with  the  pancreatic 
juice,  a  part  of  the  oil  is  quickly  sj)lit  by  the  steaj)sin,  with  the  formation  of  free 
fatty  acids.  These  acids  unite  with  the  alkalies  and  the  alkaline  salts  present  in 
the  secretions  of  the  small  intestine  (pancreatic  juice,  bile,  intestinal  juice)  to 
form  soaps.  The  formation  of  the  soaps,  aided,  perhaps,  by  the  peristaltic 
movements  of  the  intestine,  emulsifies  the  remainder  of  the  fats  and  thus 
renders  them  ready  for  al^sorption.  It  has  been  suggested  that  the  proteids 
in  solution  in  the  pancreatic  juice  aid  in  the  emulsification,  but  there  is  no 
experimental  evidence  to  show  that  this  is  the  case.  A  factor  of  much  more 
importance  is  the  influence  of  the  bile.  In  man  the  pancreatic;  juice  and  the 
bile  are  poured  into  the  duodenum  together,  and  in  all  mammals  the  two  secre- 
tions are  mixed  with  the  food  at  some  part  of  the  duodenum.  Now,  it  has 
been  shown  beyond  question  that  a  mixture  of  bile  and  pancreatic  juice  will 
cause  a  splitting  of  fats  into  fatty  acids  and  glycerin  much  more  rapidly  than 
will  the  pancreatic  juice  alone.'  This  effect  of  the  bile  is  not  due  to  the 
presence  in  it  of  a  fat-splitting  enzyme  of  its  own:  the  bile  seems  merely  to 
favor  in  some  way  the  action  of  the  steapsin  contained  in  the  pancreatic  secre- 
tion. Bile  aids  the  emulsification  possibly  in  another  way.  To  be  efficient  as 
emulsifiers  the  fatty  acids  must  form  soaps.  The  alkaline  salts  of  the  pancre- 
atic juice  do  not  appear  to  be  in  a  form  in  which  they  can  be  used  readily 
for  this  j)urpose.  It  is  supposed  that  the  alkaline  salts  of  the  bile  (and  the 
intestinal  juice)  are  therefore  made  use  of.  TIk;  mechanism  of  the  absorption 
of  the  emulsified  fat  and  the  importance  of  bile  in  this  j)rocess  will  be  described 
subsequently. 

Intestinal  Secretion. — The  small  intestine  is  lined  with  tubular  glands, 
the  crypts  of  Lieberkiihn,  which  are  supposed  to  form  a  secretion  of  consid- 
erable importance  in  digestion.  To  obtain  the  intestinal  secretion,  or  succus 
entericiis,  as  it  is  often  called,  recourse  has  been  had  to  an  ingenious  operation 
for  establishing  a  permanent  intestinal  fistula.  This  operation,  which  usually 
goes  under  the  name  of  the  "  Thiry-Vella  fistula,"  consists  in  cutting  out  a 
small  portion  of  the  intestine  without  injuring  its  supply  of  blood-ve&sels  or 
nerves,  and  then  sewing  the  two  open  ends  of  this  piece  into  the  abdominal 
wall  so  as  to  form  a  double  fistula.  The  continuity  of  the  intestines  is  estab- 
lished by  suture,  while  the  isolated  loop  with  its  two  openings  to  the  exterior 
can  be  used  for  collecting  the  intestinal  secreti<^n  uncontaminated  by  partially- 
digested  food.     The  secretion   is  always  small   in   quantity,  and   it  must  be 

*  Nencki :  Archiv  fur  eiperimentelle  Pathnloffie  u.  Pharmakologie,  vol.  20,  1886,  p.  367  ;  Ratch- 
ford :  Journal  of  Physiology,  1891,  vol.  12,  p.  27. 


CHEMISTRY   OF  DIGESTION  AND    NUTRITION  247 

started  by  a  stinmlus  of  some  kliul.  According  to  Rolimann,'  it  varies  in 
quantity  in  dilferent  parts  of  the  small  intestine,  being  very  scanty  in  the  upper 
])art  and  more  abundant  in  the  lower.  The  intestinal  secretion  is  a  yellowish 
liquid  with  a  strong  alkaline  reaction.  The  reaction  is  due  to  the  presence  of 
sodium  carbonate,  the  quantity  of  which  is  about  0.25  to  0.50  per  cent.  Tlier 
chemical  composition  of  the  secretion  has  not  been  satisfactorily  determined, 
but  its  digestive  action  has  been  investigated  with  success.  Upon  proteids  and 
fats  it  is  said  to  have  no  specific  action — that  is,  it  contains  neither  a  proteolytic 
nor  a  fat-splitting  enzyme.  The  possible  value  of  its  sodium  carbonate  in  aiding 
the  emulsification  of  fats  has  been  referred  to  in  the  preceding  paragraj)h. 
Upon  carbohydrates  tiie  secretion  has  an  important  action.  In  the  first  place, 
it  has  been  shown  that  it  contains  an  amylolytic  enzyme  which  is  more  abun- 
dant in  the  upper  than  in  the  lower  part  of  the  intestine.  This  enzyme  doubt- 
less aids  the  amylopsin  of  the  pancreatic  secretion  in  converting  starches  to 
sugar  (maltose)  or  sugar  and  dextrin.  What  is  still  more  important,  however, 
is  the  presence  of  inverting  enzymes  capable  of  converting  cane-sugar  (saccha- 
rose) into  dextrose  and  levulose,  and  of  a  similar  enzyme  capable  of  changing 
maltose  (or  dextrin)  to  dextrose.  Both  of  these  effects  are  examples  of  the 
conversion  of  di-saccharides  to  mono-saccharides. 

The  di-saccharides  of  importance  in  digestion  are  cane-sugar,  milk-sugar, 
and  maltose.  The  first  of  these  forms  a  common  constituent  of  our  daily  diet; 
the  second  occurs  always  in  milk ;  and  the  third,  as  we  have  seen,  is  the  main 
end-product  of  the  digestion  of  starches.  These  substances  are  all  readily 
soluble,  and  we  might  expect  that  they  would  be  absorbed  directly  into  the 
blood  without  undergoing  further  change.  As  a  matter  of  fact,  however,  it 
seems  that  they  are  first  dissociated  under  the  influence  of  the  inverting  enzymes 
into  simpler  mono-saccharide  compounds,  although  in  the  case  of  lactose  this 
statement  is  perhaps  not  entirely  justified,  our  knowledge  of  the  fate  of  this 
sugar  during  absorption  being  as  yet  quite  incomplete.  According  to  some 
authors,  lactose  is  absorbed  unchanged  (see  Chemical  section).  The  general 
nature  of  this  change  is  expressed  in  the  three  following  reactions: 

Maltose.  Dextrose.  Dextrose. 

Ci2H,,0„  -{-  H,0  =  C,H. A  +  C,H,A. 

Cane-sugar.  Dextrose.  Levulose. 

CioH2.p,i  +  H,0  =  C,n,.f),  +  CeH,  A- 

Lactose.  Dextrose.  Galactose. 

For  the  reactions  by  means  of  which  these  different  isomeric  forms  of  sugar  are 
distinguished  reference  must  be  made  to  the  Cliemical  section.  The  final  stage 
in  the  artificial  digestion  of  starches  is  the  formation  of  maltose  or  of  a  mixture 
of  maltose  and  dextrins.  In  the  intestines,  however,  the  process  is  carried 
a  step  farther  by  the  aid  of  the  inverting  enzymes,  and  the  maltose,  and  ap]iar- 
ently  the  dextrins  also,  are  converted  into  dextrose.  According  to  this  descrip- 
tion, all  of  the  starch  is  finally  absorbed  into  the  blood  in  the  form  of  dextrose  ; 

'  Pfiiigei-'s  Arehivfur  die  geaammte  Physiologie,  1887,  vol.  41,  p.  411. 


248  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

and  this  conclusion  falls  in  witli  the  iiict  that  the  sugar  found  normally  in  the 
blood  exists  always  in  the  form  of  dextrose.  With  reference  to  the  inverting 
enzymes  found  in  the  small  intestine,  it  should  he  added  that  they  occur  more 
abundantly  in  the  mucous  membrane  than  in  the  secretion  itself.  Indeed,  the 
secretion  is  normally  so  scanty,  especially  in  the  upj)cr  part  of  the  intestine, 
that  it  caiHiot  be  supposed  to  do  more  than  moisten  the  free  surface,  and  it  is 
probable  that  the  action  of  the  inverting  enzymes  takes  place  upon  or  in  the 
mucous  membrane,  as  the  last  step  in  the  series  of  digestive  changes  of  the 
carbohydrates  inimediately  pre{;eding  their  absorption. 

Digestion  in  the  Large  Intestine. — Observations  upon  the  secretions  of 
the  large  intestine  have  been  made  upon  human  beings  in  cases  of  anus  praeter- 
naturalis in  which  the  lower  portion  of  the  intestine  (rectum)  was  practically 
isolated.  These  observations,  together  with  those  made  upon  lower  animals, 
unite  in  showing  that  the  secretion  of  the  large  intestine  is  mainly  composed 
of  mucus,  as  the  histology  of  the  mucous  membrane  would  indicate,  and  that 
it  is  very  alkaline,  and  probably  contains  no  digestive  enzymes  of  its  own. 
When  the  contents  of  the  small  intestine  pass  through  the  ileo-csecal  valve  into 
the  colon  they  still  contain  a  quantity  of  incompletely  digested  material  mixed 
with  the  enzymes  of  the  small  intestine.  It  is  likely,  therefore,  that  some 
at  least  of  the  digestive  processes  described  above  may  keep  on  for  a  time  in 
the  large  intestine ;  but  the  changes  here  of  most  interest  are  the  absorption 
which  takes  place  and  the  bacterial  decompositions.  The  latter  are  described 
briefly  below. 

Bacterial  Decompositions  in  the  Intestines. — Bacteria  of  different 
kinds  have  been  found  throughout  the  alimentary  canal  from  the  mouth  to 
the  rectum.  In  the  stomach,  howxn'er,  under  normal  conditions,  the  strong 
acid  reaction  prevents  the  action  of  those  putrefactive  bacteria  which  decompose 
proteids,  and  prevents  or  greatly  retards  the  action  of  those  which  set  up 
fermentation  in  the  carbohydrates.  Under  certain  abnormal  conditions 
known  to  us  under  the  general  term  of  dyspepsia,  bacterial  fermentation  of  the 
carbohydrates  may  be  pronounced,  but  this  must  be -considered  as  pathological. 

In  the  small  intestine  the  secretions  are  all  alkaline,  and  it  was  formerly 
taken  for  granted  that  the  intestinal  contents  are  normally  alkaline.  If  this  were 
so  the  bacteria  would  find  a  favorable  environment.  It  was  supposed  that  putre- 
faction of  the  proteids  must  certainly  occur,  especially  during  the  act  of  tryptic 
digestion,  and  this  supposition  was  borne  out  by  the  extraordinary  readiness  of  ar- 
tificial pancreatic  digestions  to  undergo  putrefaction  when  not  protected  in  some 
way.  Two  recent  cases  ^  of  fistula  of  the  ileum  at  its  junction  with  the  colon  in 
human  beings  have  given  opportunity  for  exact  study  of  the  contents  of  the 
small  intestine.  The  results  are  interesting,  and  to  a  certain  extent  are  opposed 
to  the  preconceived  notions  as  to  reaction  and  proteid  putrefaction  which  have 
just  been  stated.  They  show  that  the  contents  of  the  intestine  at  the  point 
where  they  are  about  to  pass  into  the  large  intestine  are  acid,  provided  a  mixed 

'  Macfadyen,  Nencki,  and  Sieber :  Archiv  fur  expermentelle  Pathologie  u.  Pharmakologie,  1891, 
vol.  28,  p.  311 ;  Jakowski:  Archives  des  Sciences  biologiques,  St.  Petersburg,  1892,  vol.  1. 


CIIE3nSTBY  OF  DIGESTION  AND  NUTRITION.  249 

diet  is  used,  the  acidity  being  due  to  organic  acids  (acetic)  and  being  equal  to 
0.1  per  cent,  acetic  acid.  These  acids  must  have  come  from  the  bacterial  fer- 
mentation of  the  carbohydrates,  and  a  number  of  bacteria  capable  of  producing 
such  fermentation  were  isolated.  The  products  of  bacterial  i)utrefaction  of  the 
proteids,  on  the  contrary,  are  absent,  and  it  has  been  suggested  that  the  acid 
reaction  produced  by  the  fermentation  of  the  carbohydrates  serves  the  useful 
purpose,  under  normal  conditions,  of  preventing  the  putrefaction  of  the  pro- 
teids. With  reference,  therefore,  to  the  point  we  are  discussing — namely,  the 
bacterial  decomposition  of  the  contents  of  the  intestines — we  may  conclude, 
upon  the  evidence  furnished  by  these  two  cases,  that  in  the  human  being,  wdien 
living  on  a  mixed  diet,  some  of  the  carbohydrates  undergo  bacterial  decompo- 
sition in  the  small  intestine,  but  that  the  proteids  are  protected.  We  may 
further  suppose  that  in  the  case  of  the  proteids  the  limits  of  protection  are 
easily  overstepped,  and  that  such  a  condition  as  a  large  excess  of  proteid  in  the 
diet  or  a  deficient  absorption  from  the  small  intestine  may  easily  lead  to  exten- 
sive intestinal  putrefaction  involving  the  proteids  as  well  as  the  carbohydrates. 
In  the  large  intestine,  on  the  contrary,  the  alkaline  reaction  of  the  secretion 
is  more  than  sufficient  to  neutralize  the  organic  acids  arising  from  fermentation 
of  the  carbohydrates,  and  the  reaction  of  the  contents  is  therefore  alkaline. 
Here,  then,  what  remains  of  the  proteids  undergoes,  or  may  undergo,  putrefac- 
tion, and  this  process  must  be  looked  upon  as  a  normal  occurrence  in  the  large 
intestine.  The  extent  of  the  bacterial  action  upon  the  proteids  as  well  as  the 
carbohydrates  may  vary  widely  even  within  the  limits  of  health,  and  if  excessive 
may  lead  to  intestinal  troubles.  Among  the  products  formed  in  this  way,  the 
following  are  known  to  occur:  Leucin,  tyrosin,  and  other  amido-acids;  indol ; 
skatol;  phenols;  various  members  of  the  fatty-acid  series,  such  as  lactic, 
butyric,  and  caproic  acids ;  sulphuretted  hydrogen ;  methane ;  hydrogen ; 
methyl  mercaptan,  etc.  Some  of  these  products  will  be  described  more  fully 
in  treating  of  the  composition  of  the  feces.  To  what  extent  these  products 
are  of  value  to  the  body  it  is  difficult,  with  our  imperfect  knowledge,  to  say. 
It  has  been  pointed  out,  on  the  one  hand,  that  some  of  them  (skatol,  fatty 
acids,  CO2,  CH4,  and  HgS)  promote  the  movements  of  the  intestine,  and  may 
be  of  value  from  this  standpoint;  on  the  other  hand,  some  of  them  are 
absorbed  into  the  blood,  to  be  eliminated  again  in  different  form  in  the  urine 
(indol  and  phenols),  and  it  may  be  that  they  are  of  importance  in  the  metab- 
olism of  the  body  ;  but  concerning  this  our  knowledge  is  deficient.  On  the 
whole,  we  must  believe  that  the  food  in  its  passage  through  the  alimentary 
canal  is  acted  upon  mainly  by  the  digestive  enzymes,  the  so-called  "  unorgan- 
ized "  ferments,  but  that  the  action  of  the  bacteria,  or  organized  ferments,  is 
responsible  for  a  part  of  the  changes  which  the  food  undergoes  before  its  final 
elimination  in  the  form  of  feces.  These  two  kinds  of  action  vary  greatly 
within  normal  limits,  and  to  a  certain  extent  they  seem  to  be  in  inverse 
relationship  to  each  other.  When  the  digestive  enzymes  and  secretions  are 
deficient  or  ineffective  the  field  of  action  for  the  bacteria  is  increased,  and  this 
seems  to  be  the  case  in  some  pathological  conditions,  the  result  being  intes- 


250  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

tinal  troubles  of  various  kinds.  The  limits  of  normal  bacterial  action  have 
ncit  been  worked  out  satisfactorily,  but  it  is  evident  that  our  knowledge  of 
digestion  will  not  be  complete  until   this  is  accomplished. 

E.  Absorption  ;    Summary  of  Digestion   and  Absorption   op 
THE  Food-stuffs  ;  Feces. 

In  the  preceding  sections  we  have  followed  the  action  of  the  various 
digestive  secretions  upon  the  food-stuffs  as  far  as  the  formation  of  the  supposed 
end-products.  In  order  that  these  products  may  be  of  actual  nutritive  value 
to  tiie  body,  it  is  necessary,  of  course,  that  they  shall  be  absorbed  into  the 
circulation  and  thus  be  distributed  to  the  tissues.  There  are  two  jKjssible 
routes  for  the  absorbed  products  to  take:  they  may  pass  immediately  into  the 
blood,  or  they  may  enter  the  lymphatic  system,  the  so-called  "  lacteals  "  of 
the  alimentary  canal.  In  the  latter  case  they  reach  the  blood  finally  before 
being  distributed  to  the  tissues,  since  the  thoracic  duct,  into  which  the  lym- 
phatics of  the  alimentary  canal  all  empty,  opens  into  the  blood-vascular  system 
at  the  junction  of  the  left  internal  jugular  and  subclavian  veins.  The  sub- 
stances which  take  this  route  are  distributed  to  the  tissues  by  the  blood,  but 
it  is  to  be  noticed  that,  owing  to  the  sluggish  flow  of  the  lymph-circulation 
(see  section  on  Circulation),  a  relatively  long  time  elapses  after  digestion 
before  they  enter  the  blood-current.  The  products  which  enter  the  l)lood 
directly  from  the  alimentary  canal  are  distributed  rapidly ;  but  in  this  case  we 
must  remember  that  they  first  pass  through  the  liver,  owing  to  the  existence  of 
the  portal  circulation,  before  they  reach  the  general  circniation.  During  this 
})assage  through  the  liver,  as  we  shall  find,  changes  of  the  greatest  importance 
take  place.  The  physiology  of  absorption  is  con(.'erned  with  the  physical  and 
chemical  means  by  which  the  end-products  of  digestion  are  taken  up  by  the 
blood  or  the  lymph,  and  the  relative  importance  of  the  stomach,  the  small 
intestine,  and  the  large  intestine  in  this  process.  Leaving  aside  the  fats, 
whose  absorption  is  a  special  case,  the  absorption  of  the  other  products  of 
digestion  was  formerly  thought  to  be  a  simple  physical  process.  The  ])rocesses 
of  osmosis,  and  to  a  lesser  extent  of  filtration  and  iml)ibition,  as  they  are 
known  to  occur  outside  the  body,  were  supposed  to  account  for  the  absorption 
of  all  the  soluble  products.  This  belief  has  now  given  way,  in  large  part, 
to  newer  views,  according  to  which  the  living  epithelial  cells  take  an  active 
]iart  in  absorption,  acting  under  laws  peculiar  to  them  as  living  substances, 
and  different  from  the  laws  of  diffusion,  filtration,  etc.  established  for  dead 
membranes.  Since,  however,  it  is  highly  probable  that  osmosis  plays  a  ])art 
in  absorption,  it  will  be  convenient  to  give  a  brief  definition  of  this  process 
as  it  occurs  outside  the  body,  in  order  that  the  use  made  of  it  in  explain- 
ing physiological  absorption,  as  well  as  the  objections  to  its  use,  may  more 
easily  be  understood. 

Diffusion  and  Osmosis. — Certain  liquids  when  brought  into  contact  with 
each  other  gradually  mix,  owing  to  the  attraction  of  the  molecules  for  each 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  251 

other,  givino-  liiuilly  u  .solution  of  unilbrm  coinpositiou.  The  [)rocess  of  mixing 
— that  is,  of  the  passage  of  the  molecules  of  one  liquid  into  the  intermoleeular 
spaces  of  the  other — is  ealled  "diffusion."  Some  liquids — water  and  oil,  for 
example — will  not  diffuse  with  each  other,  or,  as  ordinarily  stated,  they  are  not 
miscihle.  When  two  miseible  li(|uids  are  separated  by  a  membrane,  diffusion 
still  takes  place  through  the  substance  of  the  membrane ;  the  process  under 
these  conditions  is  called  "osmosis"  or  "dialysis,"  and  it  occurs  independently 
of  any  ditierence  of  pressure  on  the  two  sides.  It  is  well  to  bear  in  mind 
that,  in  order  that  osmosis  may  occur,  it  is  not  necessary  that  there  should  be 
actual  capillary  pores  in  the  membrane.  We  may  sup[)ose  such  pores  to  be 
entirely  absent,  and  yet  osmosis  be  possible,  since  the  liquids  in  this  case,  or 
one  of  them  at  least,  may  be  imbibed  into  the  substance  of  the  membrane  and 
tlius  be  brought  into  contact.  Imbibition,  or  the  swelling  of  a  membrane  with 
water,  is,  in  fact,  always  preliminary  to  the  process  of  osmosis.  When  two 
liquids  containing  soluble  constituents  in  different  proportions  are  separated  by 
a  membrane,  the  tendency  is  for  osmosis  to  occur  until  an  equable  composition 
is  found  on  the  two  sides,  diffusion  equilibrium  being  established.  This  pos- 
sibility cannot  always  be  fulfilled,  for  the  reason  that  some  soluble  substances 
do  not  undergo  osmosis,  or,  as  we  usually  say,  are  not  dialyzable.  As  is  well 
known,  Graham  separated  soluble  substances  into  two  great  classes — the  crys- 
talloids,  comprising  most  of  the  crystalline  bodies,  which  are  dialyzable ;  and  the 
colloids,  such  as  gelatin,  which  are  not  dialyzable.  The  rapidity  of  osmosis  of 
a  crystalloid  is  measured  by  some  form  of  osmometer.  The  simplest  form  con- 
sists of  a  glass  tube  the  end  of  which  is  closed  by  a  membrane — for  example,  a 
piece  of  parchment.  If  we  place  a  strong  solution  of  sodium  chloride  in  such 
a  tube  and  then  bring  the  bottom  of  the  membrane  into  contact  with  distilled 
water,  diffusion  will  take  place,  sodium  chloride  passing  through  the  parchment 
into  the  distilled  water  outside  (exosmosis),  and  water  passing  back  into  the  tube 
(endosraosis).  The  weight  of  water  which  passes  into  the  salt  solution  is  much 
greater  than  the  weight  of  salt  which  passes  into  the  distilled  water.  If  the 
process  is  allowed  to  go  on  long  enough,  the  proportion  of  sodium  chloride 
outside  and  inside  will  be  the  same,  but  the  volume  of  liquid  inside  the  osmom- 
eter will  be  increased  greatly.  In  an  experiment  of  this  character  it  is  not 
difficult  to  determine  \vhat  weight  of  water  passes  one  way  through  the  mem- 
brane for  a  given  unit  (1  gram)  of  the  crystalloid  passing  the  other  way.  On  the 
supposition  that  this  ratio  is  constant,  it  was  determined  for  a  number  of  crys- 
talloids, and  represents  what  is  known  as  the  "endosmotic  equivalent,"  ^^^. 
As  a  matter  of  fact,  the  ratio  is  not  constant :  it  varies  among  other  things 
with  the  strength  of  solutions  used.  Still  the  term  is  often  used ;  and  it  is  a 
convenient  one,  as  it  expresses  the  approximate  rate  of  dialysis  of  different 
substances.  Colloidal  substances,  such  as  albumin  solutions,  which  dialyze 
very  slightly,  have  been  supposed  to  have  a  high  osmotic  equivalent,  but  so 
far  at  least  as  the  proteids  are  concerned  this  seems  to  be  an  error.  Recent 
work  has  shown  that  these  bodies  exert  only  a  slight  attraction  for  water.* 
'  See  Heidenhain  :  Pfl'dger's  Archiv  fiir  die  gesammte  Physiologie,  1894,  Bd.  Ivi.  S.  fi37. 


252  AN  AMERICAN  TEXT-BOOK  ON  PHYSIOLOGY. 

From  this  brief  description  it  will  l)e  seen  that  osmosis  supposes  the  existence 
of  two  miscible  liquids  lyintr  ou  opposite  sides  of  a  membrane.  In  the 
alimentary  canal  we  have  this  arrangement.  The  mucous  membrane  rep- 
resents the  dialyzing  membrane ;  on  one  side  is  the  blood  or  the  lymph,  and 
on  the  other  side  are  the  contents  of  the  stomach  or  the  intestine.  If  in 
the  latter  there  is  more  sugar,  let  us  say,  than  in  the  blood,  then,  according 
to  the  principles  of  osmosis,  the  sugar  will  tend  to  dialyze  through  the  mucous 
membrane  into  the  l)lood,  and  a  (piantity  of  water  (H)rresponding  to  its  endos- 
motic  equivalent  will  pass  back  into  the  canal.  The  facft  that  the  blood  is 
in  rapid  movement  should  promote  the  rapidity  of  dialysis,  for  the  obvious 
reason  that  it  tends  to  ])rcvent  an  equalization  in  composition;  just  as  in 
ordinary  osmosis,  if  the  parchment  tube  containing  the  substance  to  be 
dialyzed  is  swung  in  running  water,  the  osmosis  will  be  more  comj)lete 
and  more  rapid  than  when  it  is  suspended  in  a  given  bulk  of  Avater  which 
is  not  changed. 

With  this  brief  exposition  of  the  meaning  of  the  terms  diffusion,  osmosis,  and 
dialysis,  let  us  pass  on  first  to  a  consideration  of  the  facts  known  with  reference 
to  the  actual  absorption  that  occurs  in  different  parts  of  the  alimentary  canal. 

Absorption  in  the  Stomach. — In  the  stomach  it  is  possible  that  there 
might  be  absorption  of  the  following  substances:  water;  salts;  sugars  and 
dextrins,  which  may  have  been  formed  in  salivary  digestion  from  starch,  or 
which  may  have  been  eaten  as  such  ;  the  proteoses  and  peptones  formed  in 
the  })eptic  digestion  of  proteids  or  albuminoids.  In  addition,  absorption  of 
soluble  or  liquid  substances — drugs,  alcohol,  etc. — which  have  been  swallowed 
may  occur.  It  was  formerly  assumed  without  definite  proof  that  the  absorp- 
tion in  the  stomach  of  such  things  as  water,  salts,  sugars,  and  j)eptones  was 
very  important.  Of  late  years  a  number  of  actual  experiments  have  been 
made,  under  conditions  as  nearly  normal  as  possible,  to  determine  the  extent 
of  absorption  in  this  organ.  These  experiments  have  given  unexpected  results, 
showing,  upon  the  whole,  that  absorption  does  not  take  place  readily  in  the 
stomach — certainly  nothing  like  so  easily  as  in  the  intestine.  The  methods 
made  use  of  in  these  experiments  have  varied,  but  the  most  interesting  results 
have  been  obtained  by  establishing  a  fistula  of  the  duodenum  just  beyond  the 
pylorus.^  Through  a  fistula  in  this  position  substances  can  be  introduced  into 
the  stomach,  and  if  the  cardiac  orifice  is  at  the  same  time  shutoif  by  a  ligature 
or  a  small  balloon,  they  can  be  kept  in  the  stomach  a  given  time,  then  be 
removed,  and  the  changes,  if  any,  be  noted.  After  establishing  the  fistula  iu 
the  duodenum  food  may  be  given  to  the  animal,  and  the  contents  of  the 
stomach  as  they  pass  out  through  the  fistula  may  be  caught  and  examined. 
The  older  methods  of  introducing  the  substance  to  be  observed  into  the 
stomach  through  the  oesophagus  or  through  a  gastric  fistula  were  of  little  use, 
since,  if  the  substance  disappeared,  there  was  no  way  of  deciding  whether  it 
was  absorbed  or  was  simply  passed  on  into  the  intestine. 

*  Compare  V.  Mering :  Ueber  die  Function  des  3[agens,  1S9'3 ;  Edkins:  Journal  of  Physiology, 
1892,  vol.  13,  p.  445;  Brandl:  Zeitschnft  fur  Biologic,  1892,  vol.  29,  p.  277. 


CHEMISTRY  OF  DIGESTION  AND  NUTRITION.  253 

Water. — Experimeuts  of  the  character  just  described  show  that  water  when 
taken  alone  is  practically  not  absorbed  at  all  in  the  stomach.  Von  Mering's 
experinu'iits  especially  show  that  as  soon  as  water  is  introduced  into  the 
stomach  it  begins  to  pass  out  into  the  intestine,  being  forced  out  in  a  series 
of  spirts  by  the  contractions  of  the  stomach.  Within  a  comparatively  short 
time  practically  all  the  water  can  be  recovered  in  this  way,  none  or  very  little 
having  been  absorbed  in  the  stomach.  For  example,  in  a  large  dog  with  a 
fistula  in  the  duodenum,  500  cubic  centimeters  of  water  were  given  through 
the  mouth.  Within  twenty-five  minutes  495  cubic  centimeters  had  been 
forced  out  of  the  stomach  through  the  duodenal  fistula.  The  result  was  not 
true  for  all  liquids  ;  alcohol,  for  example,  was  absorbed  readily. 

Salts. — The  absorption  of  salts  from  the  stomach  has  not  been  investigated 
thoroughly.  According  to  Brandl,  sodium  iodide  is  absorbed  very  slowly  or 
not  at  all  in  dilute  solutions.  Not  until  its  solutions  reach  a  concentration  of 
3  per  cent,  or  more  does  its  absorption  become  important.  This  result,  if 
applicable  to  all  the  soluble  inorganic  salts,  would  indicate  that  under  ordi- 
nary conditions  they  are  practically  not  absorbed  in  the  stomach,  since  it  can- 
not be  supposed  that  they  are  normally  swallowed  in  solutions  so  concentrated 
as  3  per  cent.  It  was  found  that  the  absorption  of  sodium  iodide  was  very 
much  facilitated  by  the  use  of  condiments,  such  as  mustard  and  pepper,  or 
alcohol,  which  act  either  by  causing  a  greater  congestion  of  the  mucous  mem- 
brane or  perhaps  by  directly  stimulating  the  epithelial  cells. 

Sugars  and  Peptones. — Experiments  by  the  newer  methods  leave  no  doubt 
that  sugars  and  peptones  can  be  absorbed  from  the  stomach.  In  Von  Mering's 
work  different  forms  of  sugar — dextrose,  lactose,  saccharose  (cane-sugar),  maltose, 
and  also  dextrin — were  tested.  They  were  all  absorbed,  but  it  was  found 
that  absorption  was  more  marked  the  more  concentrated  were  the  solutions. 
Brandl,  however,  reports  that  sugar  (dextrose)  and  peptone  were  not  sensibly 
absorbed  until  the  concentration  had  reached  5  per  cent.  With  these  sub- 
stances also  the  ingestion  of  condiments  or  of  alcohol  increased  distinctly  the 
absorptive  processes  in  the  stomach.  On  the  whole  it  would  seem  that  sugars 
and  peptones  are  absorbed  with  some  difficulty  from  the  stomach. 

Fats. — As  we  have  seen,  fats  undergo  no  digestive  changes  in  the  stomach. 
The  process  of  emulsification  is  supposed  to  be  a  necessary  preliminary  step  to 
absorption,  and,  as  this  process  takes  place  only  after  the  fats  have  reached  the 
small  intestine,  there  seems  to  be  no  doubt  that  in  the  stomach  fats  escape 
absorption  entirely. 

Absorption  in  the  Small  Intestine. — The  soluble  products  of  digestion 
— sugars  and  peptones  or  proteoses,  as  well  as  the  emulsified  fats — are  mainly 
absorbed  in  the  small  intestine.  This  we  should  expect  from  a  mere  a  prioH 
consideration  of  the  conditions  prevailing  in  this  part  of  the  alimentary  canal. 
The  partially-digested  food  sent  out  from  the  stomach  meets  the  digestive 
secretions  in  the  beginning  of  the  small  intestine.  As  we  have  seen,  the  differ- 
ent enzymes  of  the  ])ancreatic  secretion  act  powerfully  upon  the  three  important 
classes  of  food-stuffs,  and  we  have  every  reason  to  believe  that  their  digestion 


254  AN  A3IERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

makes  rapid  progress.  The  passage  of  the  food  along  the  small  intestine, 
although  rajiid  compared  with  its  passage  through  the  large  intestine,  requires 
a  number  of  hours  for  its  completion.  According  to  the  observations  made 
upon  a  patient  with  a  fistula  at  the  end  of  the  small  intestine,'  food  begins  to 
pass  into  the  large  intestine  in  from  two  to  five  and  a  (piarter  hours  after  it 
lias  been  eaten,  and  it  requires  from  nine  to  twenty-three  hours  belbre  the  last 
portions  reach  the  end  of  the  small  intestine ;  this  estimate  includes,  of  course, 
the  time  in  the  stomach.  During  this  progress  it  has  been  converted  for  the 
most  part  into  a  condition  suitiible  for  absorption,  and  the  mucous  membrane 
with  which  it  is  in  contact  is  one  peculiarly  adapted  for  absorption,  since  its 
epithelial  surface  is  greatly  increased  in  extent  by  the  vast  number  of  villi 
as  well  as  by  the  numerous  large  folds  known  as  the  "  valvulse  conniventes." 
In  addition  to  these  considerations,  however,  we  have  abundant  experimental 
proof  that  absor])tion  takes  place  actively  in  the  small  intestine.  The  ai)sorp- 
tion  of  fats  can  be  demonstrated  microscopically,  as  will  be  described  presently. 
Experiments  made  by  Rohmann  ^  and  others  with  isolated  loo]>s  of  intestine 
have  shown  that  sugars  and  peptones  are  absorbed  readily  and  in  much  more 
dilute  solutions  than  in  the  stomach.  Moreover,  in  the  case  just  referred  to, 
of  an  intestinal  fistula  at  the  end  of  the  small  intestine,  a  determination  of 
the  proteid  present  in  the  discharge  from  the  fistula,  after  a  test-meal  contain- 
ing a  known  amount  of  proteid,  showed  that  about  85  per  cent,  had  disappeared 
— that  is,  had  been  absorbed  before  reaching  the  large  intestine.  With  refer- 
ence to  water  and  salts,  it  has  been  shown  that  they  also  are  readily  absorbed ; 
some  very  interesting  experiments  demonstrating  this  fact  have  been  reported 
recently  by  Heidenhain  in  a  paper  which  is  referred  to  briefly  on  ])age  95. 
It  must  be  remembered,  however,  that  under  normal  conditions  the  absorption 
of  water  and  salts  is  more  or  less  compensated  by  the  secretion  formed  along 
the  length  of  the  intestine,  so  that  when  the  contents  reach  the  ileo-CcTcal  valve 
they  are  still  of  a  fluid  consistency  similar  to  that  of  the  chyme  as  it  left  the 
stomach  to  enter  the  intestine.  A  consideration  of  the  mechanism  of  the 
absorption  of  flits,  sugars,  peptones,  and  water  will  be  taken  up  presently, 
after  a  few  words  have  been  said  of  absorption  in  the  large  intestine. 

Absorption  in  the  Large  Intestine. — There  can  be  no  doubt  that  absorp- 
tion forms  an  important  part  of  the  function  of  the  large  intestine.  The 
contents  pass  through  it  with  great  slowness,  the  average  duration  being  given 
usually  as  twelve  hours,  and  while  they  enter  through  the  ileo-ca?cal  valve  in  a 
thin  fluid  condition,  they  leave  the  rectum  in  the  form  of  nearly  solid  feces. 
This  fact  alone  demonstrates  the  extent  of  the  absorption  of  water.  As  for 
the  sugar  and  peptones,  examination  of  the  intestinal  contents  as  they  entered 
the  large  intestine  in  the  case  of  fistula  cited  in  the  preceding  paragraph 
showed  that  there  may  still  be  present  an  imjwrtant  percentage  of  jiroteid 
(14  per  cent.)  and   a  variable   amount  of  sugars   and    fats — more   than   is 

^  Macfadyen,  Nencki,  and  Sieber :  Arckivfiir  experimentdle  Pnthologie  u.  Phaiinakologie,  1891, 
vol.  28,  p.  311. 

"  Pfluger's  Arckivfiir  die  gesammte  Physiologie,  1887,  vol.  41,  j).  411. 


CHEMISTRY    OF  DIGESTION  AND    NUTRITION.  255 

found  normally  in  the  feces.  Some  of  this  carbohydrate  and  proteid  under- 
goes destruction  by  bacterial  action,  as  has  already  been  explained  (p.  249), 
but  some  of  it  is  absorbed,  or  may  be  absorbed,  before  decomposition  occure. 
The  power  of  absorption  in  the  large  intestine  has  been  strikingly  demon- 
strated by  the  fact  that  various  substances  injected  into  the  rectum  are 
absorbed  and  suffice  to  nourish  the  animal.  P^nemata  of  this  character  are 
frequently  used  iu  medical  j)ractice  with  satisfactory  results,  and  careful 
experimental  work  on  lower  animals  and  on  men  under  conditions  capable  of 
being  properly  controlled  has  corroborated  the  results  of  medical  experience 
and  shown  that  even  in  the  rectum  absorption  takes  place.  Without  giving 
the  details  of  this  work,  it  may  be  said  that  it  is  now  known  that  proteids  in 
solution,  or  even  such  things  as  eggs  beaten  to  a  fluid  mass  with  a  little  salt, 
are  absorbed  from  the  rectum,  and  this  notwithstanding  the  fact  that  no 
proteolytic  enzyme  is  found  in  this  part  of  the  alimentary  canal.  The 
theoretical  bearing  of  this  fact  upon  the  general  process  of  absorption  Avill  be 
brought  out  in  the  next  paragraph.  Fats  also  (such  as  milk-fat)  and  sugars 
can  be  absorbed  in  the  same  way. 

Absorption  of  Proteids. — As  we  have  seen  in  the  preceding  paragraphs, 
absorption  of  proteids  takes  place  in  the  stomach  and  the  small  and  large 
intestines,  but  in  all  probability  mainly  in  the  small  intestine.  The  end- 
products  of  the  digestion  of  proteids  by  the  proteolytic  enzymes  are  proteoses 
and  peptones.  Tryptic  digestion  produces  also  leucin,  tyrosin,  and  the  related 
amido-  bodies,  but  so  far  as  proteid  has  undergone  decomposition  to  this  stage 
it  is  no  longer  proteid,  and  does  not  have  the  nutritive  value  of  proteid.  The 
logical  conclusion  from  our  knowledge  of  proteid  digestion  should  be  that 
all  proteid  is  reduced  to  the  form  of  proteoses  or  peptones  before  absorption, 
and  that  the  great  advantage  of  proteolysis  is  that  proteids  are  more  readily 
absorbed  in  this  form  than  in  any  other.  In  the  main  we  must  accept  this 
conclusion.  The  process  of  proteid  digestion  would  seem  to  be  without  mean- 
ing otherwise.  But  we  must  not  shut  our  eyes  to  the  fact  that  proteid  may  be 
absorbed  in  other  forms  than  peptones  or  proteoses.  This  has  been  demon- 
strated most  clearly  for  the  rectum  and  the  lower  part  of  the  colon,  as  was 
stated  in  the  preceding  paragraph.  Enemata  of  dissolved  muscle-proteid 
(myosin),  egg-albumin,  etc.  are  absorbed  from  this  part  of  the  alimentary  canal 
without,  so  far  as  can  be  determined,  previous  conversion  to  peptones  and 
proteoses,  and  we  must  admit  that  the  same  power  is  possessed  by  other 
parts  of  the  intestinal  tract.  It  is  probable,  for  instance,  that  the  very  first 
product  of  pepsin-hydrochloric  digestion,  syntonin,  is  capable  of  absorption 
directly.  This  fact,  however,  does  not  weaken  the  conclusion  that  peptones 
and  proteoses  are  absorbed  more  easily  than  other  forms  of  proteids,  and  that 
they  constitute  the  form  in  which  the  bulk  of  our  proteid  is  absorbed. 
Opinions  as  to  why  these  forms  of  proteids  are  more  easily  absorbed  than  any 
other  must  vary  with  the  theory  held  as  to  the  nature  of  absorption.  It  was 
formerly  believed  that  absorption  is  entirely  a  process  of  imbibition  and 
osmosis  through  the  mucous  membrane.     The  fact  that  proteoses  and  peptones 


256  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

are  more  easily  difFusible  than  are  other  forms  of  proteids  harmonized  with 
tills  theory.  The  ohjeet  of  di<»;estion,  it  was  said,  is  to  convert  the  insolnble 
and  non-dialyzahle  j)rotci(ls  into  solnhle,  diffusible  peptones.  J5ut  a  study  of 
the  detail*^  of  j)n)teid  absorption  has  shown  that  the  process  cannot  bo 
exj)lained  by  the  hiws  of  simple  dialysis  M'hich  j^overu  tlu;  ])rocess  of  diffusion 
through  dead  mend)ranes.  l*roteids,  like  egg-albumin,  which  are  practically 
non-dialyzable  are  absorbed  readily  from  the  intestine.  Moreover,  when  one 
considers  the  rate  of  absorption  of  peptone  from  the  alimentary  tract,  it  seems 
to  be  much  too  rapid  and  complete  to  be  accounted  for  entirely  by  the  dif- 
fusibility  of  this  substance  as  determined  by  experiments  with  parchment 
dialyzers.  It  is  believed,  therefore,  that  the  initial  act  in  the  absorption 
of  proteids  is  dependent  in  some  way  upon  the  properties  of  the  living 
epithelial  cells  lining  the  mucous  membrane.  It  is  impossible  at  present 
to  make  this  statement  more  specific.  A  second  similar  suggestion  attributes 
the  absorption  of  proteids  to  the  leucocytes  found  so  abundantly  in  the 
adenoid  tissue  of  the  intestine,  but  this  has  been  shown  by  lleidenhain' 
and  others  to  be  incorrect.  We  say,  then,  in  brief,  that  the  peptones  and 
proteoses  are  absorbed  by  a  special  activity  of  the  epithelial  cells.  Are  they 
then  transferred  to  the  blood  or  to  the  lymph  ?  Experiments  have  shown 
conclusively  that  they  are  transmitted  directly  to  the  blood-capillaries :  liga- 
ture of  the  thoracic  duct,  for  example,  which  shuts  off  the  entire  lymjih-flow 
coming  from  the  intestine,  does  not  interfere  with  the  absorption  of  proteids. 
There  is  one  other  fact  of  great  significance  in  connection  with  this  sub- 
ject: the  proteids  are  absorbed  mainly,  if  not  entirely,  as  proteoses  and 
peptones,  and  they  pass  immediately  into  the  blood ;  nevertheless,  examination 
of  the  blood  directly  after  eating,  while  the  process  of  absorption  is  in  full 
activity,  fails  to  show  any  peptones  or  proteoses  in  the  blood.  In  fact,  if 
these  substances  are  injected  directly  into  the  blood,  they  behave  as  foreign, 
and  even  as  toxic,  bodies.  In  certain  doses  they  produce  insensibility  with 
lowered  blood-pressure,  and  they  may  bring  on  a  condition  of  coma  ending  in 
death.  Moreover,  when  present  in  the  blood,  even  in  small  quantities,  they 
are  eliminated  by  the  kidneys  and  are  evidently  unfit  for  the  use  of  the  tissues. 
It  follows  from  these  facts  that  while  the  peptones  and  proteoses  are  being 
absorbed  by  the  epithelial  cells  they  are  at  the  same  time  changed  into  some 
other  form  of  proteid.  What  this  change  is  has  not  been  determined. 
Experiments  have  shown  that  peptones  disappear  when  brought  into  contact 
with  fresh  pieces  of  the  lining  mucous  membrane  of  the  intestine  which  are 
still  in  a  living  condition.  The  presumption  is  that  the  peptones  and  proteoses 
are  converted  to  serum-albumin,  or  at  least  to  a  native  albumin  of  some  kind, 
but  we  have  no  definite  knowledge  beyond  the  fact  that  the  peptones  and 
proteoses,  as  such,  disappear.  It  is  well  to  call  attention  to  the  fact  that  the 
digestion  of  proteids  is  supposed,  according  to  the  schema  already  described, 
to  consist  in  a  process  of  hydration  and  splitting,  with  the  formation,  probably, 
of  smaller  molecules.  The  reverse  act  of  conversion  of  pej)tones  back  to  albu- 
'  Pji'dger's  Archivfiir  die  (jesammtc  Physiolofjie,  vol.  43,  1888,  supplement. 


CHEMISTRY   OF  DIGESTION  AND    NUTRITION.  257 

min  implies,  therefore,  a  process  of  dehydration  and  polymerization  which 
presumably  takes  place  in  the  epithelial  cells.  It  is  at  this  point  in  the  act 
of  absorption  of  protoids  that  our  knowledge  is  most  deficient. 

Absorption  of  Sugars. — The  carbohydrates  are  absorbed  mainly  in  the 
form  of  sugar  or  of  sugar  and  dextrin.  Starches  are  converted  in  the  intes- 
tine into  maltose  or  maltose  and  dextrin,  and  then  by  the  inverting  enzymes 
of  the  mucous  membrane  are  changed  to  dextrose.  Ordinary  cane-sugar 
suffers  invei'sion  into  dextrose  and  levulose  before  absorption,  and  milk-sugar 
possibly  undergoes  a  similar  inversion  into  dextrose  and  galactose,  though  less 
is  known  of  this.  So  far  as  our  knowledge  goes,  then,  we  may  say  that  the 
carbohydrates  of  our  food  are  eventually  absorbed  in  the  form  mainly  of 
dextrose  or  of  dextrose  and  levulose,  leaving  out  of  consideration,  of  course, 
the  small  part  that  normally  undergoes  bacterial  fermentation.  In  accordance 
with  this  statement,  we  find  that  the  sugar  of  the  blood  exists  in  the  form 
of  dextrose.  It  is  apparently  a  form  of  sugar  that  can  be  oxidized  very 
readily  by  the  tissues.  In  fact,  it  has  been  shown  that  if  cane-sugar  is  injected 
directly  into  the  blood,  it  cannot  be  utilized,  at  least  not  readily,  by  the  tissues, 
since  it  is  eliminated  in  the  urine ;  whereas  if  dextrose  is  introduced  directly 
into  the  circulation,  it  is  all  consumed,  provided  it  is  not  injected  too  rapidly. 
The  sugars  are  soluble  and  dialyzable,  but,  as  in  the  case  of  peptones,  exact 
study  of  their  absorption  shows  that  it  does  not  follow  the  known  laws  of 
osmosis.  The  degree  of  absorption  of  the  different  sugars  does  not  vary  directly 
with  their  diffusibility.  Moreover  in  the  small  intestine  at  least  the  rate  of 
absorption  increases  with  the  concentration  of  the  solution  only  up  to  a  certain 
point  (with  dextrose,  5  to  6  per  cent.)  at  which  the  maximum  of  absorption 
takes  place,  whereas,  if  it  were  simply  a  case  of  osmosis,  the  rapidity  of  dif- 
fusion ouo;ht  to  increase  with  an  increase  in  concentration  of  the  solution  on 
one  side  of  the  membrane.  For  these  and  for  other  reasons  it  seems  that  the 
absorption  of  sugars  is  also  a  special  act  depending,  in  all  probability,  upon 
the  living  epithelial  cells.  Their  absorption  seems  to  be  effected  by  means 
similar  to  those  used  for  the  proteids,  but  the  details  of  the  act  cannot  be 
given.  As  in  the  case  of  the  proteids,  the  absorbed  sugars — dextrose  or  dex- 
trose and  levulose — pass  directly  into  the  blood,  and  do  not  under  normal 
conditions  enter  the  lymph- vessels.  This  has  been  demonstrated  by  direct 
examination  of  the  blood  of  the  portal  vein  during  digestion  (Von  Mering  *), 
a  distinct  increase  in  its  sugar-contents  being  found.  Examination  of  the 
lymph  show^s  no  increase  in  sugar  unless  excessive  amounts  of  carbohydrates 
have  been  eaten  (Heidenhain). 

Absorption  of  Fats. — Unlike  the  sugars  and  peptones,  fats  are  absorbed 

chiefly  in  a  solid  form — that  is,  in  an  emulsified  condition.     There  can  be  no 

question  therefore,  in  this  case,  of  osmosis ;  the  process  of  absorption  must  be 

of  a  mechanical  nature.     The  details  of  the  jirocess  have  been  worked  out 

microscopically  and  have  given  rise  to  numerous  researches.     It  is  unnecessary 

to  speak  of  the  various  theories  that  have  been  held,  as  it  has  been  shown  by 

'  Du  Bois-Reymond's  Archiv  fiir  Anaiomie  und  Physiologie,  1877,  p.  413. 
17 


258  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

nearly  all  the  rocont  work  that  the  imiiuxliato  agiMit  in  the  absorption  of  fats 
is  again  the  epithelial  cells  of  the  villi  of  the  small  intestine.  The  fat-(lroj)let8 
are  taken  up  by  these  cells,  and  can  be  seen  microscopically  after  digestion  in 
the  act  of  passing,  or  rather  of  being  passed,  through  the  cell-substance.  Tiie 
epithelial  cells,  in  other  words,  ingest  the  fat-particles  lying  against  their  free 
ends,  and  then  pass  them  slowly  through  their  cytoplasm,  forcing  them  finally 
out  of  the  basal  end  of  the  cells  into  the  substance,  the  stroma,  of  the  villus. 
Reference  to  the  histology  of  the  villi  will  show  that  each  villus  possesses 
a  comparatively  large  lymphatic  capillary  lying  in  its  middle  and  ending 
blindly,  apj)areutly,  near  the  apex  of  the  villus.  Between  this  central  lym- 
phatic— or  lacteal,  as  it  is  called  here — and  the  epithelium  lies  the  stroma,  or 
main  substance  of  the  villus,  which,  in  addition  to  its  blood-capillaries  and 
plain  muscle- fibres,  consists  mainly  of  lymphoid  or  adenoid  tissue  containing 
numerous  leucocytes.  The  fat-droplets  have  to  pass  from  the  epithelium  to 
the  central  lymphatic,  for  it  is  one  of  the  jnost  certain  facts  in  absorption,  and 
one  which  has  been  long  known,  that  the  fat  absorbed  in  an  emulsified  con- 
dition gets  eventually  into  the  lacteals  and  thence  is  conveyed  through  the 
system  of  lymphatic  vessels  to  the  thoracic  duct  and  finally  to  the  blood. 
The  name  "  lacteal,"  in  fact,  is  given  to  the  lymphatic  capillaries  of  the  villus 
on  account  of  the  milky  appearance  of  their  contents,  after  meals,  caused  by 
the  emulsified  fat.  It  should  be  added,  however,  that  it  has  not  been  jiossible 
to  demonstrate  experimentally  that  all  the  absorbed  fat  passes  into  the  thoracic 
duct.  Attempts  have  been  made  to  collect  all  the  fat  passing  thiough  the 
thoracic  duct  after  a  meal  containing  a  known  quantity  of  fat,  but  even  after 
making  allowance  for  the  unabsorbed  fat  in  the  feces  there  is  a  considerable 
percentage  of  the  fat  absorbed  which  cannot  be  recovered  from  the  lymph 
of  the  thoracic  duct.  While  this  result  does  not  invalidate  the  conclusion 
.stated  above  that  the  emulsified  fat  passes  chiefly,  perhaps  entirely,  into  the 
lacteals,  it  does  indicate  that  there  are  some  factors  concerned  in  the  i)rocess  of 
fat-absorption  which  are  at  present  unknown  to  us.  The  passage  of  the  fat- 
droplets  to  the  central  lacteal  is  not  difficult  to  understand.  The  adenoid 
tissue  of  the  stroma  is  penetrated  by  minute  unformed  lyniph-channels  which 
are  doubtless  connected  with  the  central  lacteal.  In  each  villus  lymph  is 
continually  formed  from  the  circulating  blood,  so  that  there  must  be  a  slow- 
stream  of  Ivmpli  through  the  stroma  to  the  lacteal.  When  the  fat-droplets 
have  passed  through  the  epithelial  cells  (and  basement  membrane)  they  drop 
into  the  interstices  of  the  adenoid  tissue  and  are  carried  in  this  stream  into 
the  lacteal.  The  lacteals  were  formerly  designated  as  the  ''absorbents,"  under 
the  false  impression  that  they  attended  to  all  the  absorption  going  on  in  the 
intestines,  including  that  of  peptones,  sugars,  and  fats.  It  is  now  known  that 
their  action  under  ordinary  conditions  is  limited  to  the  absorption  of  fats. 

Absorption  of  "Water  and  Salts. — From  what  has  been  said  (p.  252)  it  is 
evident  that  absorption  of  water  takes  place  very  slightly,  if  at  all,  in  the 
stomach.  Whenever  soluble  substances,  such  as  peptones,  sugai's,  or  salts,  are 
absorbed  in  this  organ,  a  certain  amount  of  water  must  go  with  them,  but  the 


CIIlLMISTItV    OF   DIGESTION  AND    NUTJUTION.  259 

bulk  of  the  water  passes  out  of  the  pylorus.  In  the  small  intestine  absorption 
of  water  and  of  inor<!;anie  salts  evidently  takes  |)laee  readily,  and,  aeeording  to 
the  experiments  of  Rohmanu  and  Ileidenliain  already  referred  to,  the  laws 
governing-  their  al)sorption  are  different  from  what  we  shoidd  expect  if  the 
process  were  sim])ly  one  of  osmosis.  The  ditterences  as  regards  the  absorption 
of  salts  are  especially  emphasized  by  the  experiments  of  Heidenhain.'  Making 
use  of  an  interesting  method,  for  which  reference  must  be  made  to  the  original 
paper,  Heidenhain  has  shown  that  if  dilute  solutions  of  NaCl  (0.3  to  0.5  per 
cent.)  are  introduced  into  an  isolated  loop  of  the  small  intestine,  absorption  of 
both  water  and  salts  takes  place  readily,  in  spite  of  the  fact  that  in  this  case 
the  blood  is  the  more  concentrated  solution  and  has  therefore  the  greater 
osmotic  pressure.  Moreover,  specimens  of  the  animal's  own  blood-serum  intro- 
duced into  an  intestinal  loop  are  also  completely  absorbed,  although  in  this  case 
there  is  practically  no  diflPerence  in  composition,  as  regards  water  and  salts, 
between  the  blood  of  the  animal  and  the  serum  introduced  into  the  intestine. 
In  another  paper  by  Heidenhain*  he  proved  that  the  absorption  of  water  in 
the  small  intestine,  when  ordinary  amounts  are  ingested,  takes  place  entirely- 
through  the  blood-vessels  of  the  villus,  and  not  through  the  lacteals ;  when 
larger  quantities  of  water  are  swallowed,  a  small  part  may  be  absorbed  through 
the  lacteals,  as  shown  by  the  increased  lymph-flow,  but  by  far  the  larger 
quantity  is  taken  up  directly  by  the  blood. 

In  the  large  intestine  the  contents  become  progressively  more  solid  as  they 
approach  the  rectum ;  the  absorption  of  water  is  such  that  the  stream  is 
mainly  from  the  intestinal  contents  to  the  blood,  giving  us  a  phenomenon 
somew^hat  similar  to  the  absorption  of  water  by  the  roots  of  a  plant.  This 
process  is  difficult  to  understand  upon  the  supposition  that  it  is  caused  by 
osmosis,  using  that  term  in  its  ordinary  sense.  We  must  suppose  an  active 
attraction  of  a  peculiar  character  for  water  on  the  part  of  some  substance  in 
the  epithelial  cells  of  the  wall  of  the  large  intestine. 

Composition  of  the  Feces. — The  feces  differ  widely  in  amount  and  in 
composition  with  the  character  of  the  food.  Upon  a  diet  composed  exclu- 
sively of  meats  they  are  small  in  amount  and  dark  in  color;  with  an  ordinary 
mixed  diet  the  amount  is  increased,  and  it  is  largest  with  an  exclusively  vege- 
table diet.  The  average  weight  of  the  feces  in  twenty- four  hours  upon  a 
mixed  diet  is  given  as  170  grams,  while  with  a  vegetable  diet  it  may  amount 
to  as  much  as  400  or  500  grams.  The  quantitative  composition,  therefore,  will 
vary  greatly  with  the  diet.  Qualitatively,  we  find  in  the  feces  the  following 
things :  (1)  Indigestible  material,  such  as  ligaments  of  meat  or  cellulose  from 
vegetables.  (2)  Undigested  material,  such  as  fragments  of  meat,  starch,  or  fats 
which  have  in  some  way  escaped  digestion.  Naturally,  the  quantity  of  this 
material  present  is  slight  under  normal  conditions.  Some  fats,  however,  are 
almost  always  found  in  feces,  either  as  neutral  fats  or  as  fatty  acids,  and  to 
a  small  extent  as  calcium  or  magnesium  soaps.     The  quantity  of  fat  found  is 

^  Pjliiger's  Arehiv  fur  die  gesammte  Physiologic,  1894,  vol.  56,  p.  579. 
■■^  Ibid.,  vol.  43,  1888,  supplement. 


260  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

incrGa.«e(l  by  au  increase  of  the  fats  in  the  food.  (3)  Products  of  bacterial 
decomposition.  The  most  characteristic  of  these  pro(hicts  are  indol  and 
skatol.  Tiiese  two  substances  are  formed  normally  in  the  large  intestine  from 
the  putrefaction  of  proteid  material.  They  occur  always  together.  Indol  has 
the  formula  CgH^N,  and  skatol,  which  is  a  methyl  indol,  the  formula  CgllgN. 
They  are  crystalline  bodies  possessing  a  disagreeble  fecal  odor;  this  is  espe- 
ially  true  of  skatol,  to  which  the  odor  of  the  feces  is  mainly  due.  Indol  and 
skatol  are  eliminated  from  the  body  only  in  j)art  in  the  feces;  a  certain  ])r(>por- 
portion  of  each  is  absorbed  into  the  blood  and  is  eliminated  in  a  modified  form 
through  the  urine — indol  as  indican  (indoxyl-sulphuric  acid),  from  which  indigo 
was  formerly  made,  and  skatol  as  skatoxyl-sulphuric  acid  (see  Chemical  section 
for  further  information  as  to  the  chemistry  of  these  bodies).  (4)  Cholesterin, 
which  is  found  always  in  small  amounts  and  is  probably  derived  from  the  bile. 
(5)  Excretin,  a  crystallizable,  non-nitrogenous  substance  to  which  the  formula 
CygHjsgSOo  has  been  assigned,  is  found  in  minute  quantities.  (6)  Mucus  and 
epithelial  cells  thrown  off  from  the  intestinal  wall.  (7)  Pigment.  In  addition 
to  the  color  due  to  the  undigested  food  or  to  the  metallic  compounds  contained 
in  it,  there  is  normally  present  in  the  feces  a  pigment,  hydrobilirubin,  derived 
from  the  pigments  (bilirubin)  of  the  bile.  Hydrobilirubin  is  formed  from 
the  bilirubin  by  reduction  in  the  intestine.  (8)  Inorganic  salts — salts  of 
sodium,  potassium,  calcium,  magnesium,  and  iron.  The  importance  of  the  calcium 
and  iron  salts  will  be  referred  to  again  in  a  subsequent  chapter,  when  speaking 
of  their  nutritive  importance.  (9)  Micro-organisms.  Great  quantities  of  bac- 
teria of  different  kinds  are  found  in  the  feces. 

In  addition  to  the  feces,  there  is  found  often  in  the  large  intestine  a 
quantity  of  gas  which  may  also  be  eliminated  through  the  rectum.  This  gas 
varies  in  composition.  The  following  constituents  have  been  determined  to 
occur  at  one  time  or  another:  CH^,  CO2,  H,  N,  HgS.  They  arise  mainly 
from  the  bacterial  fermentation  of  the  proteids,  although  some  of  the  N  may 
be  derived  from  air  swallowed  with  the  food. 

F.  Physiology  of  the  Liver  and  the  Spleen. 

The  liver  plays  an  important  part  in  the  general  nutrition  of  the  body ;  its 
functions  are  manifold,  but  in  the  long  run  they  depend  upon  the  properties 
of  the  liver-cell,  which  constitutes  the  anatomical  and  physiological  unit  of  the 
organ.  These  cells  are  seemingly  uniform  in  structure  throughout  the  whole 
substance  of  the  liver,  but  to  understand  clearly  the  different  functions  they 
fulfil  one  must  have  a  clear  idea  of  their  anatomical  relations  to  one  another 
and  to  the  blood-vessels,  the  lymphatics,  and  the  bile-duets.  The  histology  of 
the  liver  lobule,  and  the  relationship  of  the  portal  vein,  the  hepatic  artery,  and 
the  bile-duct  to  the  lobule,  must  be  obtained  from  the  text-books  upon  histol- 
ogy and  anatomy.  It  is  sufficient  here  to  recidl  the  fact  that  each  lobule  is 
supplied  with  blood  coming  in  part  from  the  portal  vein  and  in  part  from  the 
hepatic  artery.  The  blood  from  the  former  source  contains  the  soluble  prod- 
ucts absorbed  from  the  alimentary  canal,  such  as  sugar  and  proteid,  and  these 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  261 

absorbed  products  are  submitted  to  the  metabolic  activity  of  the  liver-cells 
before  reaching  the  general  circulation.  The  hepatic  artery  brings  to  the  liver- 
cells  the  arterialized  blood  sent  out  into  the  systemic  circulation  from  the  left 
ventricle.  In  addition,  each  lobule  gives  origin  to  the  bile-capillaries  which 
arise  between  the  separate  cells  and  which  carry  off  the  bile  formed  within 
the  cells.  In  accordance  with  these  facts,  the  physiology  of  the  liver-cell  falls 
naturally  into  two  parts — one  treating  of  the  formation,  composition,  and  physi- 
ological significance  of  bile,  and  the  other  dealing  with  the  metabolic  changes 
produced  in  the  mixed  blood  of  the  portal  vein  and  the  hepatic  artery  as  it  flows 
through  the  lobules.  In  this  latter  division  the  main  phenomena  to  be  studied 
are  the  formation  of  urea  and  the  formation  and  significance  of  glycogen. 

Bile. — From  a  physiological  standpoint,  bile  is  partly  an  excretion  carrying 
off  certain  waste  products,  and  partly  a  digestive  secretion  playing  an  import- 
ant role  in  the  absorption  of  fats,  and  possibly  in  other  ways.  Bile  is  a  con- 
tinuous secretion,  but  in  animals  possessing  a  gall-bladder  its  ejection  into  the 
duodenum  is  intermittent.  For  the  details  of  the  mechanism  of  its  secretion, 
its  dependence  on  nerve-  and  blood-supply,  etc.,  the  reader  is  referred  to  the 
section  on  Secretion.  Bile  is  easily  obtained  from  living  animals  by  establishing 
a  fistula  of  the  bile-duct  or,  as  seems  preferable,  of  the  gall-bladder.  The 
latter  operation  has  been  performed  a  number  of  times  on  human  beings.  In 
some  cases  the  entire  supply  of  bile  has  been  diverted  in  this  way  to  the  ex- 
terior, and  it  is  an  interesting  physiological  fact  that  such  patients  may  con- 
tinue to  enjoy  good  health,  showing  that,  whatever  part  the  bile  takes  normally 
in  digestion  and  absorption,  its  passage  into  the  intestine  is  not  absolutely 
necessary  to  the  nutrition  of  the  body.  The  quantity  of  bile  secreted  during 
the  day  has  been  estimated  for  human  beings  of  average  weight  (43  to  73  kilo- 
grams) as  varying  between  600  and  850  cubic  centimeters.  This  estimate  is 
based  upon  observations  on  cases  of  biliary  fistula.'  Chemical  analyses  of  the 
bile  show  that,  in  addition  to  the  water  and  salts,  it  contains  bile-pigments, 
bile-acids,  cholesterin,  lecithin,  neutral  fats  and  soaps,  sometimes  a  trace  of  urea, 
and  a  mucilaginous  nucleo-albumin  formerly  designated  improperly  as  mucin. 
The  last-mentioned  substance  is  not  formed  in  the  liver-cells,  but  is  added 
to  the  bile  by  the  mucous  membrane  of  the  bile-ducts  and  gall-bladder.  The 
quantity  of  these  substances  present  in  the  bile  must  vary  greatly  in  different 
animals  and  under  different  conditions.  As  an  illustration  of  their  relative 
importance  in  human  bile  and  of  the  limits  of  variation  the  two  following 
analyses  by  Hammarsten  ^  may  be  quoted : 

I.  II. 

Solids      2.520  2.840 

Water 97.480  97.160 

Mucin  and  pigment 0.529  0.910 

Bile-salts 0-931  0.814 

Taurocholate 0.3034  0.053 

*  Copeman  and  Winston  :  Journal  of  Physiology,  1889,  vol.  x.  p.  213 ;  and  Kobson  :   Proceedings 
of  the  Royal  Society,  London,  1890,  vol.  47,  p.  499. 

■^  Reported  in  Centralblatt  fur  Physiologie,  1894,  No.  8. 


262  .l^V   AMEIUVAN    TEXT-BOOK    OF   PHYSIOLOGY. 

I.  ;i. 

Glycocholate 0.6276  0.761 

Fatty  acids  from  soap 0.1230  0.024 

Cliolesterin 0.003U  0.096 

^^"'•""1      0.02-20  0.1286 

Fat  -• 

Soluble  salts 0.8070  0.8051 

Insoluble  salts        0.0250  0.041 1 

The  color  of  bile  varies  in  different  animals  according  to  the  preponderance 
of  one  or  the  other  of  the  main  bile-pigments,  bilirubin  and  biliverdin.  The 
bile  of  carnivorous  animals  has  usually  a  bright  golden  color,  owing  to  the  pres- 
ence of  bilirubin,  while  that  of  the  herbivora  is  a  bright  green  from  the 
biliverdin.  The  color  of  human  bile  seems  to  vary  :  according  to  some  author- 
ities, it  is  yellow  or  brownish  yellow,  and  this  seems  especially  true  of  the  bile 
as  found  in  the  gall-bladder  of  the  cadaver :  according  to  others,  it  is  of  a 
dark-olive  color  with  the  greenish  tint  predominating.  Its  reaction  is  feebly 
alkaline  and  its  specific  gravity  varies  in  human  bile  from  1050  or  1040  to 
1010.  Human  bile  does  not  give  an  absorption  spectrum,  but  the  bile  of  some 
herbivora,  after  exposure  to  the  air  at  least,  gives  a  characteristic  spectrum. 
The  individual  constituents  of  the  bile  will  now  be  described  more  in  detail, 
but  with  reference  mainly  to  their  origin,  fate,  and  function  in  the  body.  For 
a  description  of  their  strictly  chemical  properties  and  reactions  reference  must 
be  made  to  the  Chemical  section. 

Bile-pigments. — Bile,  according  to  the  animal  from  which  it  is  obtained, 
contains  one  or  the  other,  or  a  mixture,  of  the  two  pigments  bilirubin  and 
biliverdin.  Biliverdin  is  supposed  to  stand  to  bilirubin  in  the  relation  of  an 
oxidation  product.  Bilirubin  is  given  the  formula  CjjHggN^Og,  and  biliverdin 
CjjHgeN^Og,  the  latter  being  prepared  readily  from  pure  specimens  of  the 
former  by  oxidation.  These  pigments  give  a  characteristic  reaction,  known 
as"Gmelin's  reaction,"  with  nitric  acid  containing  some  nitrous  acid  (nitric 
acid  with  a  yellow  color).  If  a  drop  of  bile  and  a  drop  of  nitric  acid  are 
brought  into  contact,  the  former  undergoes  a  succession  of  color  changes,  the 
order  being  green,  blue,  violet,  red,  and  reddish  yellow.  The  })lay  of  colors 
is  due  to  successive  oxidations  of  the  bile-pigments ;  starting  with  bilirubin, 
the  first  stage  (green)  is  due  to  the  formation  of  biliverdin.  The  pigments 
formed  in  some  of  the  other  stages  have  been  isolated  and  named.  The 
reaction  is  very  delicate,  and  it  is  often  used  to  detect  the  presence  of  bile- 
pigments  in  other  liquids — urine,  for  example.  The  bile-pigments  originate 
from  haemoglobin.  This  origin  was  first  indicated  by  the  fact  that  in  old 
blood-dots  or  in  extravasations  there  was  found  a  crystalline  product,  the 
so-called  "hseraatoidin,"  which  was  undoubtedly  derived  from  hfemoglobin, 
and  which  upon  more  careful  examination  was  proved  to  be  identical  with 
bilirubin.  This  origin,  which  has  since  been  made  probable  by  other  reac- 
tions, is  now  universally  accepted.  It  is  supposed  that  when  the  blood- 
corpuscles  go  to  jiieccs  in  the  circulation  (p.  343)  the  hfcmoglobin  is  brought  to 
the  liver,  and  then,  under  the  influence  of  the  liver-cells,  is  converted  to  an 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  263 

iron-free  compound,  bilirubin  or  biliverdin.  It  is  very  signifirant  to  find  that 
the  iron  .separated  by  this  means  from  the  haemoglobin  is  for  the  most  ])art 
r('taine<l  in  the  hver,  a  small  portion  only  being  secreted  in  the  bile.  It  seems 
probable  that  the  iron  held  back  in  the  liver  is  again  used  in  some  way  to 
make  new  ha3moglobin  in  the  hieraatopoietic  organs.  The  bile-pigments  are 
carried  in  the  bile  to  the  duodenum  and  are  mixed  with  the  food  in  its  long 
passage  through  the  intestine.  Under  normal  conditions  neither  bilirubin  nor 
biliverdin  is  found  in  the  feces,  but  in  their  place  is  found  a  reduction  pro- 
duct, hydrobilirubin.  Moreover,  it  is  believed  that  some  of  the  bile-pigment  is 
reabsorbed  as  it  passes  along  the  intestine,  is  carried  to  the  liver  in  the  portal 
blood,  and  is  again  eliminated.  That  this  action  occurs,  or  may  occur,  has 
been  made  probable  by  experiments  of  Wertheimer*  on  dogs.  It  happens  that 
sheep's  bile  contains  a  pigment  (cholohsematin)  which  gives  a  characteristic 
spectrum.  If  some  of  this  pigment  is  injected  into  the  mesenteric  veins  of  a 
dog,  it  is  eliminated  while  passing  through  the  liver,  and  can  be  recognized 
unchanged  in  the  bile.  The  value  of  this  "  circulation  of  the  bile,"  so  far  as 
the  pigments  are  concerned,  is  not  apparent. 

Bile-acids. — "  Bile-acids  "  is  the  name  given  to  two  organic  acids,  glyco- 
cholic  and  taurochoUc,  which  are  always  present  in  bile,  and,  indeed,  form 
very  important  constituents  of  that  secretion ;  they  occur  in  the  form  of  their 
respective  sodium  salts,  and  not  as  uncombined  acids,  as  the  term  "bile-acids" 
might  lead  one  to  believe.  In  human  bile  both  acids  are  usually  found,  but 
the  proportion  of  taurocholate  is  variable,  and  in  some  cases  this  latter  acnd 
may  be  absent  altogether.  Among  herbivora  the  glycocholate  predominates 
as  a  rule,  although  there  are  some  exceptions ;  among  the  carnivora,  on  the 
other  hand,  taurocholate  occurs  usually  in  greater  quantities,  and  in  the  dog's 
bile  it  is  present  alone.  Glycocholic  acid  has  the  formula  CggH^jNOg,  and 
taurocholic  acid  has  the  formula  CaeH^^NSO^.  Each  of  them  can  be  obtained 
in  the  form  of  crystals.  When  boiled  with  acids  or  alkalies  these  acids  take 
up  water  and  undergo  hydrolytic  cleavage,  the  reaction  being  represented  by 
the  following  equations : 

025H,3NO«     +   H,0    =   C^^H^oO,    -f   CH,(NH3)C00H. 

Glycocholic  acid.  Cholic  acid.  GlycocoU  (amido-acetic  acid). 

Taurocholic  acid.  Cholic  acid.  Taurin  (amido-ethyl- 

sulphonic  acid). 

These  reactions  are  interesting  not  only  in  that  they  throw  light  on  the  structure 
of  the  acids,  but  also  because  similar  reactions  doubtless  take  place  in  the  intes- 
tine, cholic  acid  having  been  detected  in  the  intestinal  contents.  As  the  for- 
mulas show,  cholic  acid  is  formed  in  the  decomposition  of  each  acid,  and  we 
may  regard  the  bile-acids  as  compounds  produced  by  the  synthetic  union  of 
cholic  acid  with  glycocoll  in  the  one  case  and  with  taurin  in  the  other. 
Cholic  acid  or  its  compounds,  the  bile-acids,  are  usually  detected  in  suspected 
'  Archives  de  Physiologie  normale  et  pathologique,  1892,  p.  577. 


264  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

liquids  by  tlic  well-known  Pettenkofer  reaction.  As  usually  ]>crfornie(l,  ti)e 
test  is  made  by  adding  to  the  liquid  a  few  drops  of  a  10  per  cent,  solution  of 
canc-su<z;ar  and  then  strong  sulj)huric  acid.  The  latter  must  be  added  carefully 
and  the  temperature  be  kept  below  70°  C.  If  bile-acids  are  present,  the  liquid 
assumes  a  beautiful  red-violet  color.  It  is  now  known  that  the  reaction  con- 
sists in  the  formation  of  a  substance  (furfurol)  by  the  action  of  the  acid  on 
sugar,  which  then  reacts  with  the  bile-acids.  The  bile-acids  are  formed 
directly  in  the  liver-cells.  This  fact,  which  was  for  a  long  time  the  subject  of 
discussion,  has  been  demonstrated  in  recent  years  by  an  im])ortant  series  of 
researches  made  upon  birds.  It  has  been  shown  that  if  the  bile-duct  is  ligated 
in  these  animals,  the  bile  formed  is  reabsorbed  and  bile-acids  and  pigments 
may  be  detected  in  the  urine  and  the  blood.  If,  however,  the  liver  is  com- 
pletely extirpated,  then  no  trace  of  either  bile-acids  or  bile-pigments  c^n  be 
found  in  the  blood  or  the  urine,  showing  that  these  substances  are  not 
formed  elsewhere  in  the  body  than  in  the  liver.  It  is  more  difficult  to  ascer- 
tain from  what  substances  they  are  formed.  The  fact  that  glycocoU  and 
taurin  contain  nitrogen,  and  that  the  latter  contains  sulphur,  indicates  that 
some  proteid  or  albuminoid  constituent  is  broken  down  during  their  })ro- 
duction. 

A  circumstance  of  considerable  physiological  significance  is  that  these  acids 
or  their  decomposition  products  are  absorbed  in  part  from  the  intestine  and 
are  again  secreted  by  the  liver:  as  in  the  case  of  the  pigments,  there  is  an 
intestinal-hepatic  circulation.  The  value  of  this  reabsorption  may  lie  in  the 
fact  that  the  bile-acids  constitute  a  very  efficient  stimulus  to  the  bile-secreting 
activity  of  the  cells,  being  one  of  the  best  of  cholagogues,  or  it  may  be  that  it 
economizes  material.  From  what  we  know  of  the  history  of  the  bile-acids 
it  is  evident  that  they  are  not  to  be  considered  as  excreta :  they  have  some 
important  function  to  fulfil.  The  following  suggestions  as  to  their  value  have 
been  made:  In  the  first  place,  they  serve  as  a  menstruum  for  dissolving  the 
cholesterin  which  is  constantly  present  in  the  bile  and  which  is  an  excretion 
to  be  removed ;  secondly,  they  facilitate  the  absorption  of  fats  from  the  intes- 
tine. The  value  of  bile  in  fat-absorption  will  ]>resently  be  referred  to  more 
in  detail.  It  is  an  undoubted  fact  that  when  bile  is  shut  off  from  the  intes- 
tine the  absorption  of  fats  is  very  much  diminished,  and  it  has  been  shown 
that  this  action  of  the  bile  is  owing  to  the  presence  of  the  bile-acids.  In  what 
way  they  act  is  unknown. 

Cholesterin. — Cliolcsterin  is  a  non-nitrogenous  substance  of  the  fornmla 
CjgH^^O.  It  is  a  constant  constituent  of  the  bile,  although  it  occurs  in  variable 
quantities.  Cholesterin  is  very  widely  distributed  in  the  body,  being  found 
especially  in  the  white  matter  (medullary  substance)  of  nerve-fibres.  It  seems, 
moreover,  to  be  a  constant  constituent  of  all  animal  and  plant  cells.  It  is 
assumed  that  cholesterin  is  not  formed  in  the  liver,  but  that  it  is  eliminated 
by  the  liver-cells  from  the  blood,  which  collects  it  from  the  various  tissues  of 
the  body.  That  it  is  an  excretion  is  indicated  by  the  fact  that  it  is  eliminated 
unchanged  in  the  feces.     Cholesterin  is  insoluble  in  water  or  in  dilute  saline 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  265 

liquids,  aiul  is  held  in  solution  in  the  bile  by  means  of  the  bile-acids.  We 
must  regard  it  as  a  waste  product  of  cell-life,  formed  probably  in  minute 
quantities,  and  excreted  mainly  throu<^li  the  liver.  It  is  partly  eliminated 
throu;4h  the  skin,  in  the  sebaceous  and  sweat  secretions,  and  in  the  milk. 

Lecithin,  Fats,  and  Nucleo-albumin. — Lecithin  also  seems  to  be  present, 
generally  in  small  quantities,  in  the  cells  of  the  various  tissues,  but  it  occure 
especially  in  the  white  matter  of  uerve-tibres.  It  is  probable,  therefore,  that, 
so  far  as  it  is  found  in  the  bile,  it  represents  a  waste  product  formed  iu 
difiPerent  parts  of  the  body  and  eliminated  through  the  bile.  The  special 
importance,  if  any,  of  the  small  proportion  of  fats  and  fatty  acids  in  the  bile 
is  unknown.  The  ropy,  mucilaginous  character  of  bile  is  due  to  the  presence 
of  a  body  formed  in  the  bile-ducts  and  gall-bladder.  This  substance  was 
formerly  designated  as  mucin,  but  it  is  now  known  that  in  ox-bile  at  least 
it  is  not  a  true  mucin,  but  is  a  nucleo-albumin  (see  Chemical  section).  Hani- 
raarsten  reports  that  in  human  bile  some  true  mucin  is  found.  Outside  the 
fact  that  it  makes  the  bile  viscous,  this  constituent  is  not  known  to  possess 
any  especial  ])hysiological  significance. 

General  Physiological  Importance  of  Bile. — The  physiological   value 
of  bile  has  been  referred  to  in  speaking  of  its  several  constituents,  but  it  will 
be  convenient  here  to  restate  these  facts  and  to  add  a  few  remarks  of  general 
interest.     Bile  is  of  importance  as  an  excretion  iu  that  it  removes  from  the 
body  waste  products  of  metabolism,  such  as  cholesterin,  lecithin,  and  bile- 
pigments.     With  reference  to  the  pigments,  there  is  evidence  to  show  that  a 
part  at  least  may  be  reabsorbed  while  passing  through  the  intestine,  and  be 
used  again  in  some  way  in  the  body.     The  bile-acids  represent  end-products 
of  metabolism  involving  the  proteids  of  the  liver-cells,  but  they  are  undoubt- 
edly reabsorbed  in  part,  and  cannot  be  regarded  merely  as  excreta.     As  a 
digestive  secretion  the  most  important  function  attributed  to  the  bile  is  the 
part  it  takes  in  the  digestion  of  fats.     In  the  first  place,  it  aids  in  the  splitting 
of  a  part  of  the  neutral  fats  and  the  subsequent  emulsification  of  the  re- 
mainder (p.  246).    More  than  this,  bile  aids  materially  in  the  absorption  of  the 
emulsified  fats.     A  number  of  observers  have  shown  that  when  a  permanent 
biliary  fistula  is  made,  and  the  bile  is  thus  prevented  from  reaching  the  intes- 
tinal canal,  a  large  proportion  of  the  fat  of  the  food  escapes  absorption  and 
is  found  in  the  feces.     This  property  of  the  bile  is  known  to  depend  upon 
the  bile-acids  it  contains,  but  how  they  act  is  not  clearly  understood.     It  was 
formerly  believed,  on  the  basis  of  some  experiments  by  Von  Westinghausen, 
that  the  bile-acids  dissolve  or  mix  with  the  fats  and  at  the  same  time  moisten 
the   mucous  membrane,  and  for  these  reasons  aid  in  bringing  the   fat  into 
immediate   contact   with  the   epithelial   cells.      It  was   stated,  for  instance, 
that  oil  rises  higher  in  capillary  tubes  moistened  with  bile  than  in  similar 
tubes  moistened  with  water,  and  that  oil  will  filter  more  readily  through 
paper  moistened  with  bile  than  through  paper  wet  with  water.     Groper,^  who 
repeated  these  experiments,  finds  that  they  are  erroneous.     AYe  must  fall  back, 
1  Archil' fur  Anatomie  u.  Physiologle  ("  Physiol.  Abtheilung"),  1889,  p.  505. 


2C,Ct  AX    A.VKRICAy    TEXT-IUJOK    OF    I'JI  YSIOLOd  V. 

therefore,  iipmi  the  ireiienil  statiiiiciit  that  the  Idle-acids  stimulate  the  epithe- 
lial eells  to  a  i^reater  activity  in  the  al>s«»rj)tioii  of"  fat,  or  possibly  accomplish 
the  same  end  In  st^me  more  indirect  way  as  yet  undis<-overed.  It  was  formerly 
believe<l  that  bile  is  also  of  great  im[)ortaiice  in  restraining  the  processes  of 
putrefaction  in  the  intestine.  It  was  asserted  that  bile  is  an  efficient  antiseptic, 
and  that  this  pi'operty  comes  into  use  normally  in  preventing  excessive  ])ntre- 
ftiction.  liacteriological  experiments  made  by  a  niunber  of  observers  have 
shown,  however,  that  bile  itself  has  very  feeble  antiseptic  ]>rojjerties,  as  is 
indi<-ated  by  the  fact  that  it  ]>utrefies  readily.  The  free  bile-acids  and  cholalic 
acid  do  have  a  direct  retarding  effect  ujiou  putrefactions  outside  the  bodv  ; 
but  this  action  is  not  very  pronounced,  and  has  not  been  demonstrated  satis- 
factorily for  bile  itself.  It  seems  to  be  generally  true  that  in  eases  of  biliary 
fistula  the  feces  have  a  very  fetid  odor  when  meat  and  fat  are  taken  in  the 
food.  But  the  increased  putrefaction  in  these  cases  may  possibly  be  due  to 
some  indirect  result  of  the  withdrawal  of  bile.  It  has  been  suggested,  for 
instance,  that  the  deficient  absorption  of  fiit  which  follows  upon  the  removal 
of  the  bile  results  in  the  proteid  and  carbohydrate  material  becoming  coated 
with  an  insoluble  layer  of  fat,  so  that  the  penetration  of  the  digestive  enzymes 
is  retarded  and  greater  opjiortunity  is  given  for  the  action  of  bacteria.  We 
may  conclude,  therefore,  that  while  there  does  not  .seem  to  be  sufficient  warrant 
at  present  for  believing  that  the  bile  exerts  a  direct  antiseptic  action  upon  the 
intestinal  contents,  nevertheless  its  presence  limits  in  some  way  the  extent  of 
putrefaction.  Lastly,  bile  takes  a  direct  part  in  suspending  or  destroying 
peptic  digestion  in  the  acid  chyme  forced  from  the  stomach  into  the  duodenum. 
The  chyme  meeting  with  bile  and  pancreatic  juice  is  neutralized  or  is  made 
alkaline,  which  alone  would  ])revent  further  peptonization.  Moreover,  when 
chyme  and  bile  are  mixed  a  ])recipitate  occurs,  consisting  j)artly  of  })roteids 
(proteoses  and  syntonin)  and  partly  of  bile-acids.  It  is  probable  that  pepsin, 
according  to  its  well-known  property,  is  thrown  «lown  in  this  floccnlent  pre- 
cipitate and,  as  it  were,  prepared  for  its  destruction. 

Glycogen. — One  of  the  most  important  functions  of  the  liver  is  the  for- 
mation of  fjli/cof/en.  This  substance  was  found  in  the  liver  in  1857  by  Claude 
Bernard,  and  is  one  of  several  brilliant  discoveries  made  by  him.  Glycogen  has 
the  formula  (C6Hio05)„,  which  is  also  the  general  formula  given  to  vegetable 
starch;  glycogen  is  therefore  frequently  spoken  of  as  "animal  starch."  It 
gives,  however,  a  port-wine-red  color  with  iodine  solutions,  instead  of  the 
familiar  deep  blue  of  vegetable  starch,  and  this  reaction  serves  to  detect  glyco- 
gen not  only  in  its  solutions,  but  also  in  the  liver-cells.  Glycogen  is  readily 
soluble  in  water,  and  the  solutions  have  a  characteristic  opalescent  appearance. 
Like  starch,  glycogen  is  acted  upon  by  amylolytic  enzymes,  and  the  end- 
products  are  apparently  the  same — namely,  maltose,  or  maltose  and  .some  dex- 
trin. For  a  more  complete  account  of  the  chemical  reactions  of  glycogen,  and 
for  the  methods  of  obtaining  it  from  the  liver,  reference  must  be  made  to  the 
Chemical  section. 

Occurrence  of  Glycogen  in  the  Liver. — Glycogen  can   be  detected   in 


CHEMISTRY   OF  DIGESTION  AND   NUTJilTION.  207 

tlu'  liver-c'L'lls  microscopically.  If  the  liver  of  a  dog  is  removed  twelve  or 
fourteen  hours  after  a  hearty  meal,  hardened  in  alcohol,  and  sectioned,  the 
liver-cells  will  be  found  to  contain  clumj)s  of  clear  material  which  give  the 
iodine  reaction  for  glycogen.  P]vcn  when  distinct  aggregations  of  the  glycogen 
cannot  be  made  out,  its  presence  in  the  cells  is  shown  by  the  red  reaction  with 
iodine.  By  this  siin])le  method  one  can  demonstrate  the  im])ortant  fact  that 
the  amount  of  glycogen  in  the  liver  increases  after  meals  and  decreases  again 
during  the  fasting  hours,  and  if  the  fast  is  sufficiently  prohmged  it  may  dis- 
appear altogether.  This  fact  is,  however,  shown  more  satisfactorily  by  quanti- 
tative determinations,  by  chemical  means,  of  the  total  glycogen  present.  The 
amount  of  glycogen  present  in  the  liver  is  quite  variable,  being  influenced  by 
such  conditions  as  the  character  and  amount  of  the  food,  muscular  exercise, 
body-temperature,  drugs,  etc.  From  determinations  made  upon  various 
animals  it  may  be  said  that  the  average  amount  lies  between  1.5  and  4  per 
cent,  of  the  weight  of  the  liver.  But  this  amount  may  be  increased  greatly 
by  feeding  upon  a  diet  largely  made  up  of  carbohydrates.  It  is  said  that  in 
the  dog  the  total  amount  of  liver-glycogen  may  be  I'aised  to  17  per  cent.,  and 
in  the  rabbit  to  27  per  cent.,  by  this  means,  while  it  is  estimated  for  man 
(Neumeister)  that  the  quantity  may  be  increased  to  at  least  10  per  cent.  It 
is  usually  believed  that  glycogen  exists  as  such  in  the  liver-cells,  being  depos- 
ited in  the  substance  of  the  cytoplasm.  Reasons  have  been  brought  forward 
recently  to  show  that  possibly  this  is  not  strictly  true,  but  that  the  glycogen  is 
held  in  some  sort  of  weak  chemical  combination.  It  has  been  shown,  for 
instance,  that  although  glycogen  is  easily  soluble  in  cold  water,  it  cannot  be 
extracted  readily  from  the  liver-cells  by  this  agent.  One  must  use  hot  water, 
salts  of  the  heavy  metals,  and  other  similar  means  that  may  be  supposed  to 
break  up  the  combination  in  which  the  glycogen  exists.  For  practical  purposes, 
however,  we  may  speak  of  the  glycogen  as  lying  free  in  the  liver-cells,  just  as 
we  speak  of  hfemoglobin  existing  as  such  in  the  red  corpuscles,  although  it  is 
probably  held  in  some  sort  of  combination. 

Orig-in  of  Glycogen. — To  understand  clearly  the  views  held  as  to  the 
origin  of  liver  glycogen,  it  will  be  necessary  to  describe  briefly  the  effect  of 
the  different  food-stuffs  upon  its  formation. 

Effect  of  Carbohydrates  on  the  Amount  of  Glycogen. — The  amount  of 
glycogen  in  the  liver  is  affected  very  quickly  by  the  quantity  of  carbohydrates 
in  the  food.  If  the  carbohydrates  are  given  in  excess,  the  supply  of  glycogen 
may  be  increased  largely  beyond  the  average  amount  present,  as  has  been  stated 
above.  Investigation  of  the  different  sugars  has  shown  that  dextrose,  levulose, 
saccharose  (cane-sugar),  and  maltose  are  unquestionably  direct  glycogen -formers, 
that  is,  that  glycogen  is  formed  directly  from  them  or  from  the  products  into 
which  they  are  converted  during  digestion.  Now,  our  studies  in  digestion  have 
shown  that  the  starches  are  converted  into  maltose,  or  maltose  and  dextrin, 
during  digestion,  and,  further,  that  these  substances  are  changed  or  inverted  to 
the  simpler  sugar  dextrose  during  absorption.  Cane-sugar,  which  forms  such 
an  important  part  of  our  diet,  is  inverted  in  the  intestine  into  dextrose  and 


268  AN  AMERICAN    TEXT- BOOK    OF    PHYSIOLOGY. 

levulose,  and  is  absorbed  in  this  loim.  Jt  is  evident,  therefore,  that  the  hulk 
of  our  carbohydrate  food  reaches  tlie  liver  as  dextrose,  or  as  dextrose  and 
levulose,  and  these  forms  of  sugar  must  be  converted  into  glycoiren  in  the 
liver-cells  by  a  process  of  dehydration  such  as  may  be  represented  in  substance 
by  the  fonnula  C,;H,^,Og  —  H/)  =  Cgll,/).,.  In  the  case  of  levulose  there  is 
reason  to  believe  that  it  is  changed  first  to  dextrose  in  the  liver  before  being 
converted  into  glycogen.  However  that  may  be,  there  is  no  doubt  that  both 
dextrose  and  levulose  increase  markedly  the  amount  of  glycogen  in  the  liver ; 
and,  since  cane-sugar  is  inverted  in  the  intestine  before  absorption,  it  also  must 
be  a  good  glycogen-former — a  fact  which  has  been  abundantly  demonstrated 
by  direct  experiment.  Lusk  ^  has  shown,  however,  that  if  cane-sugar  is  in- 
jected under  the  skin,  it  has  a  very  feeble  effect  in  the  way  of  increasing  the 
amount  of  glycogen  in  the  liver,  since  under  these  conditions  it  is  probably 
absorbed  into  the  blood  without  undergoing  inversion.  Experiments  with  sub- 
cutaneous injection  of  lactose  gave  similar  results,  and  it  is  generally  believed 
that  the  liver-cells  cannot  convert  the  double  sugars  to  glycogen,  at  least  not 
readily ;  hence  the  value  of  the  inversion  of  these  sugars  in  the  alimentary 
canal  before  absorption.  The  relations  of  lactose  to  glycogen-formation  have 
not  been  determined  satisfactorily.  If  it  contributes  at  all  to  the  direct  forma- 
tion of  glycogen,  it  is  certainly  less  efficient  than  dextrose,  levulose,  or  cane- 
sugar.  When  the  proportion  of  lactose  in  the  diet  is  much  increased,  it  quickly 
begins  to  appear  in  the  urine,  showing  that  the  limit  of  its  consumption  in  the 
body  is  soon  reached.  This  latter  fact  is  somewhat  singular,  since  in  infancy 
especially  milk-sugar  forms  a  constant  and  important  item  of  our  diet,  and 
one  would  suppose  that  it  is  especially  adapted  to  the  needs  of  the  body. 

Efcd,  of  Proteids  on  Glycogen-formation. — It  was  pointed  out  by  Bernard, 
in  his  first  studies  upon  glycogen-formation,  that  the  liver  can  produce  glycogen 
from  proteid  food.  This  conclusion  has  since  been  verified  by  more  exact 
investigations.  When  an  animal  is  fed  upon  a  diet  of  proteid  alone,  or  on 
proteid  and  gelatin,  the  carbohydrates  being  entirely  excluded,  glycogen  is  still 
formed  in  the  liver,  although  in  smaller  amounts  than  in  the  case  of  carbohy- 
drate foods.  This  is  an  important  fact  to  remember  in  studying  the  metabo- 
lism of  the  proteids  in  the  body,  for,  as  glycogen  is  a  carbohydrate  and  con- 
tains no  nitrogen,  it  implies  that  the  proteid  molecule  is  dissociated  into  a 
nitrogenous  and  a  non-nitrogenous  part,  the  latter  being  converted  to  glycogen 
by  the  liver-cells.  The  possibility  of  the  ju'oduction  of  glycogen  from  proteids 
accords  with  a  well-known  fact  in  medical  practice  with  reference  to  the  path- 
ological condition  known  as  diahetcx.  In  this  disease  sugar  is  excreted  in  the 
urine,  sometimes  in  large  quantities.  As  the  sugar  of  the  blood  is  formed 
from  the  carbohydrates  in  the  food,  it  was  thought  that  by  excluding  this 
food-stuff  from  the  diet  the  excretion  of  sugar  might  be  prevented.  It  has 
been  found,  however,  that  in  some  cases  at  least  sugar  continues  to  be  present 
in  the  urine  even  upon  a  pure  proteid  diet.  If  we  suppose  that  some  of  the 
proteid  goes  to  form  glycogen,  the  result  observed  is  explained,  for  the  gly- 

^  Voit:  Zeitschrift  fur  Biologic,  1891,  xxviii.  p.  285. 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  269 

cogeri,  as  will  be  explaiucd  presently,  is  finally  converted  to  sugar  and  is  given 

off  to  the  blood. 

Kfi'd  of  Fats  and  other  Substance.^  upon  Gli/coc/cn-formation. — It  has  been 
found  that  fats  take  no  part  in  the  formation  of  liver  glycogen.  Glycerin 
increases  the  amount  of  glycogen  in  the  liver,  but  the  evidence  goes  to  show 
that  it  is  not  a  direct  or  an  indirect  glycogen-former.  Glycerin  seems  to 
prevent  the  reconversion  of  glycogen  to  sugar  by  the  liver-cells,  and  thus 
leads  to  an  increased  percentage  of  this  substance  in  the  liver. 

The  Function  of  Glycogen  :   Glycogenic  Theory.— The  meaning  of  the 
formation  of  glycogen  in  the  liver  has  been,  and  still  is,  the  subject  of  discussion. 
The  view  advanced  first  by  Bernard  is  perhaps  most  generally  accepted.     Ac- 
cording to  Bernard,  glycogen  forms  a  temporary  reserve  supply  of  carbohydrate 
material  which  is  laid  up  in  the  liver  during  digestion  and  which  is  gradually 
made  use  of  in  the  intervals  between  meals.     During  digestion  the  carbohy- 
drate food  is  absorbed  into  the  blood  of  the  portal  system  as  dextrose  or  as 
dextrose  and  levulose.     If  these  passed  through  the  liver  unchanged,  the  con- 
tents of  the  systemic  blood  in  sugar  would  be  increased  perceptibly.     It  is  now 
known  that  when  the  percentage  of  sugar  in  the  blood  rises  above  a  certain 
low  limit,  the  excess  will  be  excreted  through  the  kidney  and  will  be  lost. 
But  as  the  blood  from  the  digestive  organs  passes  through  the  liver  the  ex- 
cess of  sugar  is  abstracted  from  the  blood  by  the  liver-cells,  is  dehydrated  to 
make  glycogen,  and  is  retained  in  the  cells  in  this  form  for  a  short  period. 
From  time  to  time  the  glycogen  is  reconverted  into  sugar  (dextrose)  and  is 
given  off  to  the  blood.     By  this  means  the  percentage  of  sugar  in  the  systemic 
blood  is  kept  nearly  constant  (0.1  to  0.2  per  cent.)  and  within  limits  best 
adapted  for  the  use  of  the  tissues.     The  great  importance  of  the  formation  of 
glycogen  and  the  consequent  conservation  of  the  sugar-supply  of  the  tissues  will 
be  more  evident  when  we  come  to  consider  the  nutritive  value  of  carbohydrate 
food.     Carbohydrates  form  the  bulk  of  our  usual  diet,  and  the  proper  regula- 
tion of  the  supply  to  the  tissues  is  therefore  of  vital  importance  in  the  main- 
tenance of  a  normal  healthy  condition.     The  second  part  of  this  theory,  which 
holds  that  the  glycogen  is  reconverted  to  dextrose,  is  supported  by  observations 
upon  livers  removed  from  the  body.     It  has  been  found  that  shortly  after  the 
removal  of  the  liver  the  supply  of  glycogen  begins  to  disappear  and  a  corre- 
sponding increase  in  dextrose  occurs.     Within  a  comparatively  short  time  all 
the  glycogen  is  gone  and  only  dextrose  is  found.     It  is  for  this  reason  that  in 
the  estimation  of  glycogen  in  the  liver  it  is  necessary  to  mince  the  organ  and  to 
throw  it  into  boiling  water  as  quickly  as  possible,  since  by  this  means  the  liver- 
cells  are  killed  and  the  conversion  of  the  glycogen  is  stopped.     How  the 
glycogen  is  changed  to  dextrose  by  the  liver  is  a  matter  not  fully  explained. 
According  to  some,  the  conversion  is  due  to  an  enzyme  produced  in  the  liver. 
Extracts  of  liver,  as  of  many  other  organs,  do  contain  a  certain  amount  of  an 
amylolvtic  enzvme,  but  this  enzvme  changes  glycogen  to  maltose,  whereas  in  the 
liver  tiie  glycogen  is  normally  changed  to  dextrose.     It  is  probable,  therefore, 
that  the  conversion  of  glycogen  to  dextrose  is  dependent  directly  upon  the 


270  AN  AMEUK'AX    TEXT- HOOK    OF    PlI YSlOLOiJ Y. 

metabolic  activity  of  tlic  livcr-cclIs,  and  so  loiif^  as  these  cells  are  in  a  living 
conditiou  they  can  effect  this  chanj^e.  In  this  description  of"  the  origin  and 
nicanini>;  of  the  liver  glycogen  reference  has  been  made  only  to  the  glvcogen 
derived  directly  from  digested  cari)ohydrates.  The  glycogen  derived  from  proteid 
foods,  once  it  is  formed  in  the  liver,  has,  of  course,  the  same  functions  to  fulfil. 
It  is  converted  into  sugar,  and  eventually  is  oxidized  in  the  tissues.  For  the 
sake  of  comj)Ieteness  it  may  be  well  to  add  that  some  of  tht;  sugar  of  the  blood 
formed  from  the  glycogen  may  under  certain  conditions  be  converted  into  fat  in 
the  adipose  tissues,  instead  of  being  burnt,  and  in  this  way  it  may  be  retained 
in  the  body  as  a  reserve  supply  of  food  of  a  more  stable  character  than  is  the 
glycogen. 

Glycogen  in  the  Muscles  and  other  Tissues. — The  history  of  glycogen  is 
not  conn)lete  without  some  reference  to  its  occurrence  in  the  muscles.  Glycogen 
is,  in  fact,  found  in  various  places  in  the  body,  and  is  widely  distributed  through- 
out the  animal  kingdom.  It  occurs,  for  example,  in  leucocytes,  in  the  placenta, 
in  the  rapidly-growing  tissues  of  the  embryo,  and  in  considerable  abundance  in 
the  oyster  and  other  molluscs.  But  in  our  bodies  and  in  those  of  the  mam- 
mals generally  the  most  significant  occurrence  of  glycogen,  outside  of  the  liver, 
is  in  the  voluntary  muscles,  of  which  glycogen  forms  a  normal  (constituent.  It 
has  been  estimated  that  the  percentage  of  glycogen  in  resting  muscle  varies 
from  0.5  to  0.9  per  cent.,  and  that  in  the  nmsculature  of  the  whole  body  there 
may  be  contained  an  amount  of  glycogen  equal  to  that  in  the  liver  itself. 
A])parently  muscular  tissue,  as  well  as  liver-tissue,  has  a  glycogenetic  func- 
tion— that  is,  it  is  capable  of  laying  up  a  supply  of  glycogen  from  the  sugar 
brought  to  it  by  the  blood.  The  glycogenetic  function  of  muscle  has  been 
demonstrated  recently  by  Kulz,^  who  has  shown  that  an  isolated  muscle  irrigated 
with  an  artificial  supply  of  blood  to  which  dextrose  had  been  added  is  capable 
of  changing  the  dextrose  to  glycogen,  as  shown  by  the  increase  in  the  latter  sub- 
stance in  the  muscle  after  irrigation.  Muscle  glycogen  is  to  be  looked  upon, 
probably,  for  reasons  to  be  mentioned  in  the  next  paragraph,  as  a  temjxirary 
and  local  reserve  supply  of  material,  so  that,  while  we  have  in  the  liver  a  large 
general  depot  for  the  temporary  storage  of  glycogen  for  the  use  of  the  body  at 
large,  the  muscidar  tissue,  which  is  the  most  active  tissue  of  the  body  from 
a  chemical  standpoint,  is  also  capable  of  laying  up  in  the  form  of  glycogen 
any  excess  of  sugar  brought  to  it.  The  fact  that  glycogen  occurs  so  widely  in 
the  rapidly-growing  tissues  of  embryos  indicates  that  this  glycogenetic  func- 
tion may  at  times  be  exercised  by  any  tissue. 

Conditions  Affecting  the  Supply  of  Glycogen  in  Muscle  and  Liver. — 
In  accordance  with  the  view  given  above  of  the  general  value  of  glycogen — 
namely,  that  it  is  a  temporary  reserve  supply  of  carbohydrate  material  which 
may  be  rapidly  converted  to  sugar  and  oxidized  with  the  liberation  of  energy — 
it  is  found  that  the  sup])ly  of  glycogen  is  grei\tly  affected  by  conditions  calling 
for  increased  oxidations  in  the  body.  Muscular  exercise  will  (piicklv  exhaust  the 
supply  of  nmselc  and  liver  glycogen,  provided  it  is  not  renewed  by  new  food. 
'  Zeltschri/t  fiir  Biologie,  1890,  p.  2'M. 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  271 

111  :i  .stiirvini;-  animal  <;lycogen  will  finally  disappear,  except  })erliaps  in  traces, 
but  tins  disappearance  will  occur  much  sooner  if  the  animal  is  made  to  use  its 
nuisc-les  at  the  same  time.  It  has  been  shown  also  by  Morat  and  Dufourt  that 
if  a  muscle  has  been  made  to  contract  vigorously,  it  will  take  up  much  more 
suo-ar  from  an  artificial  supi)ly  <»f  l>lood  sent  through  it  than  a  similar  muscle 
which  has  been  resting;  on  the  other  hand,  it  has  been  found  that  if  the  nerve 
of  one  leg  is  cut  so  as  to  paralyze  the  muscles  of  that  side  of  the  body,  the  amount 
of  glycogen  will  increase  rapidly  in  these  muscles  as  compared  with  those  of 
the  other  leg,  that  have  been  contracting  meantime  and  using  up  their  glycogen. 
Formation  of  Urea  in  the  Liver. — The  nitrogen  contained  in  the  proteid 
material  of  our  food  is  finally  eliminated,  after  the  metabolism  of  the  proteid 
is  completed,  mainly  in  the  form  of  urea.  As  will  be  explained  in  another 
part  of  this  section,  it  has  been  definitively  proved  that  the  urea  is  not  formed  in 
the  kidneys,  the  organs  which  eliminate  it.  It  has  long  been  considered  a 
matter  of  the  greatest  importance  to  ascertain  in  what  organ  or  tissues  urea  is 
formed.  Investigations  have  now  gone  so  far  as  to  demonstrate  that  it  arises 
chiefly  in  the  liver,  hence  the  property  of  forming  urea  must  be  added  to  the 
other  important  functions  of  the  liver-cell.  Schroder  ^  performed  a  number  of 
experiments  in  which  the  liver  was  taken  from  a  freshly-killed  dog  and  irri- 
gated through  its  blood-vessels  by  a  supply  of  blood  obtained  from  another 
dog.  If  the  supply  of  blood  was  taken  from  a  fasting  animal,  then  circulating 
it  through  the  isolated  liver  was  not  accompanied  by  any  increase  in  the  amount 
of  urea  contained  in  it.  If,  on  the  contrary,  the  blood  was  obtained  from  a 
well-fed  dog,  the  amount  of  urea  contained  in  it  was  distinctly  increased  by 
jiassing  it  through  the  liver,  thus  indicating  that  the  blood  of  an  animal  after 
digestion  contains  something  which  the  liver  can  convert  to  urea.  It  is  to  be 
noted,  moreover,  that  this  power  is  not  possessed  by  the  organs  generally,  since 
blood  from  the  well-fed  animals  showed  no  increase  in  urea  after  being  circu- 
lated through  an  isolated  kidney  or  muscle.  As  further  proof  of  the  urea- 
forming  power  of  the  liver  Schroder  found  that  if  ammonium  carbonate  was 
added  to  the  blood  circulating  through  the  liver — to  that  from  the  fasting  as 
well  as  from  the  well-nourished  animal — a  very  decided  increase  in  the  urea 
always  followed.  It  follows  from  the  last  experiment  that  the  liver-cells  are 
able  to  convert  carbonate  of  ammonia  into  urea.  The  reaction  may  be  ex- 
pressed by  the  equation  (NH4)2C03  —  211,0  =  CON2H4.  Schondorff  ^  in  some 
recent  work  has  shown  that  if  the  blood  of  a  fasting  dog  is  irrigated  through 
the  hind  legs  of  a  well-nourished  animal,  no  increase  in  urea  in  the  blood  can 
be  detected ;  but  if  the  blood,  after  irrigation  through  the  hind  legs,  is  subse- 
quently passed  through  the  liver,  a  marked  increase  in  urea  results.  Obviously, 
the  blood  in  this  experiment  derives  something  from  the  tissues  of  the  leg 
which  the  tissues  themselves  cannot  convert  to  urea,  but  which  the  liver-cells 
can.  Finally,  in  some  remarkable  experiments  upon  dogs  made  by  four  in- 
vestigators (Hahn,  Massen,  Nencki,  and   Pawlow),  which  will  be  described 

^  Archivfiir  experimentelle  Pathologie  und  Phai-makologie,  vols.  xv.  and  xix.,  1882  and  1885. 
^  PJlUger's  Archivfiir  die  gesammte  Phi/siologie,  1893,  vol.  liv.  p.  420. 


272  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

briefly  in  tlic  uext  section  in  connection  with  urea,  it  was  shown  that  when 
the  liver  is  practiaiUy  destroyed  there  is  a  marked  diminution  in  the  urea 
of  the  urine,  its  place  being  taken  by  carbamic  acid.  In  birds  uric  acid  takes 
the  place  of  urea  as  the  main  nitrogenous  excretion  of  the  body,  and  Minkowski 
has  shown  that  in  them  removal  of  the  liver  is  followed  by  an  important 
diminution  in  the  amount  of  uric  acid  excreted.  From  experiments  such  as  these 
it  is  safe  to  conclude  that  urea  is  formed  in  the  liver  and  is  then  given  to  the 
blood  and  excreted  by  the  kidney.  When  we  come  to  describe  the  physiological 
history  of  urea  (p.  274),  an  account  will  be  given  of  the  views  held  with  regard 
to  the  antecedent  substance  or  substances  from  which  the  liver  produces  urea. 
Physiology  of  the  Spleen. — Much  has  been  said  and  written  about  the 
spleen,  but  we  are  yet  in  the  dark  as  to  the  distinctive  function  or  functions  of 
this  organ.  The  few  facts  that  are  known  may  be  stated  briefly  without  going 
into  the  details  of  theories  which  have  been  offered  at  one  time  or  another. 
The  older  experimenters  demonstrated  that  this  organ  may  be  removed  from 
the  body  without  serious  injury  to  the  animal.  An  increase  in  the  size 
of  the  lymph-glands  and  of  the  bone-marrow  has  been  stated  to  occur  after 
extirpation  ;  but  this  is  denied  by  others,  and,  whether  true  or  not,  it  gives 
but  little  clue  to  the  normal  functions  of  the  spleen.  Laudenbach*  finds  that 
one  result  of  the  removal  of  the  spleen  is  a  marked  diminution  in  the  number 
of  red  corpuscles  and  the  quantity  of  haemoglobin.  He  infers,  therefore,  that  the 
spleen  is  normally  concerned  in  some  way  in  the  formation  of  red  corpuscles. 
These  facts  are  significant,  but  they  need,  perhaps,  further  confirmation.  The 
most  definite  facts  known  about  the  spleen  are  in  connection  with  its  move- 
ments. It  has  been  shown  that  there  is  a  slow  expansion  and  contraction  of 
the  organ  synchronous  with  the  digestion  periods.  After  a  meal  the  spleen 
begins  to  increase  in  size,  reaching  a  maximum  at  about  the  fifth  hour,  and 
then  slowly  returns  to  its. previous  size.  This  movement,  the  meaning  of  -which 
is  not  known,  is  probably  due  to  a  slow  vaso-dilatation,  together,  perhaps,  with 
a  relaxation  of  the  tonic  contraction  of  the  musculature  of  the  trabecule.  In 
addition  to  this  slow  nKjvement,  Roy^  has  shown  that  there  is  a  rhythmic 
contraction  and  relaxation  of  the  organ,  occurring  in  cats  and  dogs  at  intervals 
of  about  one  minute.  Roy  supposes  that  these  contractions  are  eflected  through 
the  intrinsic  musculature  of  the  organ — that  is,  the  plain  muscle-tissue  present 
in  the  capsule  and  trabecule — and  he  believes  that  the  contractions  serve  to 
keep  up  a  circulation  through  the  spleen  and  to  make  its  vascular  supply  more 
or  less  independent  of  variations  in  general  arterial  pressure.  These  observa- 
tions are  valuable  as  indicating  the  importance  of  the  spleen  functions.  The 
fact  that  there  is  a  special  local  arrangement  for  maintaining  its  circulation 
makes  the  spleen  unique  among  the  organs  of  the  body,  but  no  light  is  thrown 
upon  the  nature  of  the  function  fulfilled.  The  spleen  is  supplied  richly  with 
nerve-fibres  which  when  stimulated  either  directly  or  reflexly  cause  the  organ 
to  diminish  in  volume.     According  to  Schaefer,''  these  fibres  are  contained  in 

1  Ckniralblatt  fur  Physiologic,  1895,  Bd.  ix.  S.  1.     »  Journal  of  Physiology,  1881,  vol.  iii.  p.  203. 
^  Proceedings  of  the  Royal  Society,  London,  1896,  vol.  lix.,  No.  355. 


CHEMISTRY  OF  DIGESTION  AND  NUTRITION.  273 

the  splanchnic  nerves,  which  carry  also  inhibitory  fibres  whose  stimulation  pro- 
duces a  dilatation  of  the  spleen. 

The  chemical  composition  of  the  spleen  is  complicated  but  suggestive.  Its 
mineral  constituents  are  characterized  by  a  large  percentage  of  iron,  which 
seems  to  be  present  as  an  organic  compound  of  some  kind.  Analysis  shows 
also  the  presence  of  a  number  of  fatty  acids,  fats,  cholesterin,  and,  what  is 
perhaps  more  noteworthy,  a  number  of  nitrogenous  extractives  such  as 
xanthin,  hypoxanthin,  adenin,  guanin,  and  uric  acid.  The  presence  of 
these  bodies  seems  to  indicate  that  active  metabolic  changes  of  some  kind  occur 
in  the  spleen.  As  to  tbe  theories  of  the  splenic  functions,  the  following  may  be 
mentioned  :  (1)  The  spleen  has  been  supposed  to  give  rise  to  new  red  corpuscles. 
This  it  undoubtedly  does  during  fetal  life  and  shortly  after  birth,  and  in  some 
animals  throughout  life,  but  there  is  no  reliable  evidence  that  the  function  is 
retained  in  adult  life  in  man  or  in  most  of  the  mammals.  (2)  It  has  been 
supposed  to  be  an  organ  for  the  destruction  of  red  corpuscles.  This  view  is 
founded  partly  on  very  unsatisfactory  microscopic  evidence  according  to  which 
certain  large  amoeboid  cells  in  the  spleen  ingest  and  destroy  the  old  red  corpus- 
cles, and  partly  upon  the  fact  that  the  spleen-tissue  seems  to  be  rich  in  an  iron- 
containing  compound.  This  theory  cannot  be  considered  at  present  as  anything 
more  than  a  suggestion.  (3)  It  has  been  suggested  that  uric  acid  is  produced 
in  the  spleen.  This  substance  is  found  in  the  spleen,  as  stated  above,  and  it  has 
been  shown  recently  by  Horbacewsky  that  the  spleen  contains  a  substance 
from  which  uric  acid  or  xanthin  may  readily  be  formed  ;  but  further  investiga- 
tion has  shown  that  the  same  substance  is  found  in  lymphoid  tissue  generally. 
If,  therefore,  uric  acid  is  produced  in  the  spleen,  it  is  a  function  of  the  large 
amount  of  lymphoid  tissue  contained  in  it,  and  a  function  which  it  shares  with 
similar  tissues  in  the  rest  of  the  body.  The  lymphoid  tissue  of  the  spleen  must 
also  possess  the  property  of  producing  lymphocytes,  since,  according  to  the  gen- 
eral view,  these  corpuscles  are  formed  in  lymphoid  tissue  generally  wherever 
the  so-called  "  germ-centres  "  occur.  (4)  Lastly,  a  theory  has  been  supported 
by  Schiff  and  Herzen,  according  to  which  the  spleen  produces  something  (an 
enzyme)  which,  when  carried  in  the  blood  to  the  pancreas,  acts  upon  the  tryp- 
sinogen  contained  in  this  gland,  converting  it  into  trypsin.  The  experimental 
evidence  upon  which  this  view  rests  has  not  been  confirmed  by  other  observers. 

G.   The  Kidney  and  the  Skin  as  Excretory  Organs. 

The  secretion  of  the  kidneys  is  the  urine.  The  means  by  which  this  secre- 
tion is  produced,  its  relations  to  the  histological  structure  of  the  kidney,  and 
its  connections  with  the  blood-  and  nerve-supply  of  that  organ  will  be  found 
described  in  the  section  on  Secretion.  In  this  section  will  be  discussed  only 
the  chemical  composition  of  urine,  and  especially  the  physiological  significance 
of  its  different  constituents.  The  urine  of  man  is  a  yellowish  liquid  varying 
greatly  in  depth  of  color.  It  has  an  average  specific  gravity  of  1020^and  an 
acid  reaction.  The  acid  reaction  is  noLdue  to  a  free  acid,  but  to  an  ackl  salt, 
the_acid  phosphateof  sodium  (NaHaPOJ.     Under  certain  normal  conditions 

18 


274  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

human  urine  may  show  a  neutral  or  even  a  slightly  alkaline  reaction,  especially 
after  meals.  In  fact,  the  reaction  of  the  urine  seems  to  depend  directly  on  the 
character  of  the  food.  Among  carnivorous  animals  the  urine  is  uniformly 
acid,  and  among  herbivorous  animals  it  is  uniforndy  alkaline,  so  long  as 
they  are  using  a  vegetable  diet,  but  when  starving  or  when  living  upon  the 
mother's  milk — that  is,  whenever  they  are  existing  upon  a  purely  animal  diet — 
the  urine  becomes  acid.  The  exphmation,  as  given  by  Drechsel,  is  tliat  upon 
an  animal  diet  more  acids  are  produced  (from  the  sulphur  and  phosphorus) 
than  the  bases  present  can  neutrali/x',  whereius  upon  a  vegetable  diet  carbonates 
are  formed  from  the  oxidation  of  the  organic  acids  of  the  food  in  (piantities 
sufficient  to  neutralize  the  mineral  acids.  The  chemical  composition  of  urine  is 
very  complex.  Among  the  constituents  constantly  present  under  the  conditions 
of  normal  life  we  have,  in  addition  tq_water_and  inorgainc  salts,  the  folhnving 
substances:  Urea^  uric  acid;  xanthin ;  creatinin ;  hippuric  acid;  the  urinary 
pigments  (urobilin);  sulphocyanides  in  traces;  acetone;  oxalic  acid,  probably 
as  Ciilcium  oxalate ;  several  ethereal  sulphuric  acids,  such  as  phenol  and  cresol 
sulphuric  acids,  indoxyl  sulphuric  acid  (indican),  and  skatoxyl  sulphuric  acid; 
aromatic  oxy-acid ;  some  combinations  of  glycuronic  acid  ;  some  representa- 
tives of  the  fatty  acids;  and  dissolved  gases  (N  and  CO^,).  This  list  would  be 
very  nmch  extended  if  it  attempted  to  take  in  all  those  substances  occasion- 
ally found  in  the  urine.  The  complexity  of  the  composition  and  the  fact  that 
so  many  diflTerent  organic  compounds  occur  or  may  occur  in  small  quantities 
is  readily  understood  when  we  consider  the  nature  of  the  secretion.  Through 
the  kidneys  there  are  eliminated  not  only  what  we  might  call  the  normal  £nd- 
]3roducts_of  the  metabolism  of  the  tissues,  excluding  the  COg,  but  also,  in 
large  part,  the  prgducts  of  decomposition  in  the  alimentary  canal^  the  end- 
products  of  many  organic  substances  occurring  in  our  foods  and  not  usually 
classed  as  food-stuffs,  foreign  sul)stances  introduced  as  drugs,  etc.,  all  of  which 
are  eliminated  either  in  the  form  in  which  they  are  taken  or  as  derivative 
products  of  some  kind.  We  shall  speak  briefly  of  the  most  important  of  the 
normal  constituents,  dwelling  especially  upon  their  origin  in  the  body  and  their 
physiological  significance.  For  details  of  chemical  ])ropcrties,  reactions,  meth- 
ods of  ])reiiaration,  etc.  reference  must  be  made  to  the  Ciiemical  section. 

Urea. — Urea,  which  is  given  the  formula  CH^NgO,  is  usually  considered 
as  an  amide  of  carbonic  acid,   having   therefore  the  structural  formula  of 

CO<xTTT--  It  occurs  in  the  urine  in  relatively  large  quantities  (2  per  cent.  +). 

As  the  total  quantitv  of  urine  secreted  in  twenty-four  hours  by  an  adidt  male 
may  be  placed  at  from  1500  to  1700  cubic  centimeters,  it  follows  that  from  30 
to  34  grams  of  urea  are  eliminated  from  the  body  during  this  period  It  is 
the  most  important  of  the  nitrogenous  excreta  of  the  body,  the  end-product 
of  the  physiological  oxidation  of  the  proteids  of  the  body,  and  also  of  the 
albuminoids  when  they  appear  in  the  food.  If  we  know  how  much  urea  is 
secreted  in  a  given  period,  we  know  approximately  how  much  proteid  has 
been  broken  down  in  the  body  in  the  same  time.    In  round  numbers,  1  gram 


CHEMISTRY   OF   DIGESTION  AND    NUTRITION.  275 

of  proteid  M-ill  yield  \  ^I'uin  of  urea,  as  may  be  calculated  easily  from  the 
amount  of  uitrogcn  contained  in  each.  Since,  however,  some  of  the  nitrogen 
of  proteid  is  eliminated  in  other  forms — uric  acid,  creatinin,  etc. — even  aa 
exact  determination  of  all  the  urea  would  not  be  sufficient  to  determine  with 
accuracy  the  total  amount  of  proteid  broken  down.  This  fact  is  arrived  at 
more  perfectly,  as  we  shall  explain  later,  by  a  determination  of  the  total 
nitrogen  of  the  urine  and  other  excretions.  In  addition  to  the  urine,  urea  is 
found  in  slight  quantities  in  other  secretions,  in  milk  (in  traces),  and  in  sweat. 
In  the  latter  liquid  the  quantity  of  urea  in  twenty-four  hours  may  be  quite 
appreciable — as  much,  for  instance,  as  0.8  gram — although  such  a  large  amount 
is  found  only  after  active  exercise.  It  has  been  ascertained  definitely  that  urea 
is  not  formed  by  the  kidneys :  it  is  brought  to  the  kidneys  in  the  blood  for 
elimination,  the  cells  of  the  convoluted  tubules  being  especially  adapted  for 
taking  up  this  material  and  transmitting  it  through  their  substance  to  the 
lumen  of  the  tubules.  That  urea  is  not  made  in  the  kidneys  is  demonstrated 
by  such  facts  as  these :  If  blood,  on  the  one  hand,  is  irrigated  through  an 
isolated  kidney,  no  urea  is  formed,  even  though  substances  (such  as  ammonium 
carbonate)  from  which  urea  is  readily  produced  are  added  to  the  blood;  on  the 
other  hand,  urea  is  constantly  present  in  the  blood  (0.0348  to  0.1529  per  cent.), 
and  if  the  two  kidneys  are  removed,  it  continues  to  accumulate  steadily  in  the 
blood  as  long  as  the  animal  survives.  It  has  been  ascertained  that  the  urea  is 
produced  mainly  in  the  liv^er;  an  account  of  some  of  the  experiments  demon- 
strating this  fact  is  given  on  page  271.  The  most  important  questions  that 
remain  to  be  decided  are.  Through  what  steps  is  the  proteid  molecule  metab- 
olized to  the  form  of  urea?  and,  AVhat  is  the  antecedent  substance  brought 
to  the  liver,  from  which  it  makes  urea?  It  is  impossible  to  answer  these 
questions  perfectly,  but  recent  investigations  have  thrown  a  great  deal  of  light 
on  the  whole  process,  and  they  give  hope  that  before  long  the  entire  historv 
of  the  derivation  of  urea  from  proteids  and  albuminoids  will  be  known.  The 
results  of  this  work  may  be  stated  briefly  as  follows : 

1.  Urea  arises  from  proteids  by  a  process  of  hydrolysis  and  oxidation,  with 
the  formation  eventually  of  ammonia  compounds,  most  probably  the  ammo- 
nium salt  of  carbamic  acid,  which  are  then  conveyed  to  the  liver  and  there 
changed  to  urea.  The  latter  part  of  this  theory — that  the  liver  may  produce 
urea  from  carbamate  of  ammonia — rests  upon  solid  experimental  evidence,  as 
follows  :  In  the  first  place,  Drechsel  found  carbamic  acid  in  the  blood  of  dogs, 
and  Drechsel  and  Abel  have  shown  that  it  occurs  normally  in  the  urine  of 
horses  as  calcium  carbamate;  and  Abel  has  recently  shown  that  it  maybe 
found  in  the  urine  of  dogs  or  infants  after  the  use  of  lime-water.  Drechsel 
has  shown,  further,  that  ammonium  carbamate  may  be  converted  into  urea. 
If  one  compares  the  formulas  of  ammonium  carbamate  and  urea,  it  is  seen  that 
the  former  may  pass  over  into  the  latter  by  the  loss  of  a  molecule  of  water,  as — 

Ammonium  carbamate.  Urea. 


270  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

Drechsel  siippusc.-?,  however,  that  this  tlehydratiou  is?  ellected  in  an  indirect 
manner;  that  there  is  first  an  oxidation  removing  two  atoms  of  hydrogen, 
and  then  a  i-eduetion  removing  an  atom  of  oxygen.  lie  sueceeded  in  showing 
that  when  an  aqueous  sohition  of  ammonium  carbamate  is  submitted  to  elec- 
trolysis, and  the  direction  of  the  current  is  changed  repeatedly  so  as  to  get 
alternately  reduction  and  oxidation  processes  at  each  pole,  some  urea  will  be 
produced.  These  facts  show  the  existence  of  ammonium  carbamate  in  the 
body,  and  the  possibility  of  its  conversion  to  urea.  Recent  exjterinients  made 
by  Ilahn,  Pawlow,  Massen,  and  Xcncki '  show  that  in  dogs  removal  of  the 
liver  is  followed  by  the  appearance  of  carbamates  in  the  urine  and  a  marked 
decrease  in  the  amount  of  urea.  In  these  remarkable  experiments  a  fistula  was 
made  between  the  portal  vein  and  the  inferior  vena  cava,  the  result  of  which 
was  that  the  whole  portal  circulation  of  the  liver  was  abolisiied,  and  the  only 
blood  that  the  organ  received  was  through  the  hepatic  artery.  If,  now,  this 
artery  was  ligated  or  the  liver  was  cut  away,  as  was  done  in  some  of  the  ex- 
periments, then  the  result  was  practically  an  extirpation  of  the  entire  organ — an 
operation  which  has  always  been  thought  to  be  impossible  with  mammals.  The 
animals  in  these  investigations  survived  this  operation  for  some  time,  but  they 
died  finally,  showing  a  series  of  symptoms  wliich  indicated  a  deep  disturbance 
of  the  nervous  system.  It  was  found  that  the  symptoms  of  poisoning  in  these 
animals  could  be  bn)ught  on  before  they  developed  spontaneously  by  feeding 
the  dogs  upon  a  rich  meat  diet,  or  with  salts  of  ammonia  or  carbamic  acid.  Later 
investigations^  showed  that  in  normal  animals  the  ammonia  contents  of  the 
blood  in  the  portal  vein  are  from  three  to  four  times  what  is  found  in  the  arte- 
rial blood,  but  that  after  the  operation  described  the  ammonia  in  the  arterial 
blood  increases  and  at  the  time  of  the  development  of  the  fatal  symptoms 
reaches  about  the  percentage  which  is  normal  to  the  blood  of  the  portal  vein. 
It  would  seem  from  these  investigations  that  the  liver  stands  between  the 
portal  circulation  and  the  general  systemic  circulation  and  protects  the  latter 
from  the  comparatively  large  amount  of  ammonia  compounds  contained  in  the 
portal  blood  by  converting  these  compounds  to  urea.  If  the  liver  is  thrown 
out  of  function,  ammonia  (ammonium  carbamate)  accumulates  in  the  blood  and 
causes  death.  The  rich  amount  of  ammonia  in  iha  portal  blood  seems  to 
come  chiefly  from  the  decomposition  of  proteid  material  in  the  glands  of  the 
stomach  and  pancreas  during  secretion.  Similar  ammonia  salts  are  probably 
formed  in  other  active  })roteid  tissues,  since  the  percentage  of  ammonia  in  the 
tissues  is  considerably  greater  than  in  the  blood,  and  these  compounds  also  are 
doubtless  converted  to  urea  in  the  liver,  in  part  at  least.  As  to  the  origin  of 
the  ammonium  carbamate  there  is  little  direct  evidence.  It  comes  in  the  long 
run,  of  course,  from  the  nitrogenous  food-stuffs,  ])roteids  and  albuminoids. 
Drechsel's  supposition  is  that  the  proteids  first  undergo  hydrolytic  cleavage, 
with  the  formation  of  amido-  bodies  such  as  Icucin,  tyrosin,  aspartic  acid, 
glycocoll,  etc. ;  that  these  bodies  undergo  oxidation   in  the  tissues,  with  the 

*  Archivfur  experimentelle  Pathnkigie  unci  Pharmakologie,  1893,  Bd.  xxxii.  S.  161. 
«  Mencki,  Pawlow,  and  Zaleski :  Ibid.,  1895,  Bd.  xxxvii.  S.  26. 


CHEMISTR  Y  OF  DIGESTION  AND  NUTRITION.  277 

foriiiatioii  of"  NH3,  COg,  iind  H/)  ;  and  that  tlie  NII3  and  CO2  then  unite  syn- 
thetically to  form  ammonium  carbamate,  vvhieh  is  carried  to  the  liver  aud 
changed  to  urea.  There  is  reason  to  believe  that  this  formation  of  ammonium 
carbamate  may  take  place  in  the  tissues  generally.  The  carbamate  theory  i.s 
at  least  in  accord  with  the  facts  so  far  as  known,  and  it  is  more  complete  and 
satisfactory  than  others  which  have  been  offered. 

2.  Even  after  the  removal  of  the  liver  some  urea  is  still  found  in  the  urine. 
This  fact  proves  that  other  organs  are  capable  of  producing  urea,  but  what  the 
other  organs  are  and  by  what  process  they  make  urea  are  points  yet  undeter- 
mined. It  seems  probable  that  some  of  the  ammonia  compounds  which  are 
now  known  to  be  formed  in  the  tissues  generally  and  to  be  given  off  to  the 
blood  may  be  converted  into  urea  elsewhere  than  in  the  liver.  Just  as  the 
glycogenic  function  of  the  liver-cells  is  shared  to  a  less  extent  by  other  tis- 
sues— e.  g.  the  muscle-fibres — it  is  possible  that  their  power  of  converting 
ammonia  salts  to  urea  may  be  possessed  to  a  lesser  degree  by  other  cells,  and 
for  this  reason  removal  of  the  liver  is  not  followed  at  once  by  a  fatal  result. 
Concerning  this  point,  however,  we  must  wait  for  further  investigation. 
Drechsel  has  recently  called  attention  to  a  method  of  obtaining  urea  directly 
from  proteid  outside  of  the  body.  His  method  is  interesting  not  only 
because  it  is  the  first  laboratory  method  discovered  of  producing  urea  from 
proteid,  but  also  because  it  is  possible  that  substantially  the  same  process  may 
occur  inside  the  body.  The  method  consists,  in  brief,  in  first  boiling  the  pro- 
teid with  an  acid ;  HCl  was  used,  together  with  some  metallic  zinc,  so  as  to 
keep  up  a  constant  evolution  of  hydrogen  and  to  exclude  atmospheric  oxygen. 
Among  the  products  of  decomposition  of  the  proteid  thus  produced  was  a 
substance  termed  lysaUnin  (CgHuNgO),  and  when  this  body  was  isolated  and 
treated  with  boiling  baryta-water  (Ba(OH)2)  some  urea  was  obtained.  It  is  to 
be  noted  that  in  this  case  the  urea  was  obtained  not  by  the  oxidation  of  the 
proteid,  but  by  a  series  of  decompositions  or  cleavages  of  the  proteid  molecule. 
Now,  lysatinin  occurs  also  in  the  body  as  one  of  the  products  of  the  con- 
tinued action  of  trypsin  on  proteids  (seep.  241).  It  is  possible,  therefore,  that 
by  further  hydrolysis  this  substance,  when  it  occurs,  is  converted  to  urea,  and 
that  normally  a  part  of  the  urea  arises  from  proteids  by  this  process. 

Uric  Acid  and  Xanthin  Bodies. — Uric  acid,  which  has  the  formula 
C5H4N4O3,  is  found  constantly,  but  in  relatively  small  quantities,  in  human 
urine  and  in  the  urine  of  mammals  generally.  The  total  quantity  in  the  urine  of 
man  under  normal  conditions  varies  from  0.2  to  1  gram  every  twenty-four  hours. 
In  the  urine  of  birds  and  reptiles  it  forms  the  chief  nitrogenous  constituent.  In 
these  animals  it  takes  the  place  physiologically  of  urea  in  mammalia  in  that  it 
represents  the  main  end-product  of  the  metabolism  of  the  proteids  in  the  body. 
It  is  evident  that  at  some  point  in  the  process  the  katabolism  of  the  proteids  in 
mammalia  differs  from  that  in  birds  and  reptiles,  since  in  the  one  urea,  and  in 
the  other  uric  acid,  is  the  outcome.  Uric  acid  occurs  in  such  small  quantities 
in  mammals  that  its  place  of  origin  has  not  been  investigated  successfully.  It  has 
been  shown  by  Horbacewsky  that  in  the  lymphoid  tissue  generally,  including 


278  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

the  adenoid  tissue  of  the  spleen,  tlierc  is  containe<l  a  substance  which  may  he 
re<j:;ard('il  as  the  motlier-suhstanci'  of  uric  acid.  Tie  ventures  the  hvjiothesis 
that  uric  acid  represents  an  end-product  in  the  nietabolisni  of  leucocytes,  but 
the  view  at  present  can  be  regarded  only  as  an  interesting  suggestion.  Among 
birds  and  reptiles  it  has  been  shown  that  the  liver  is  the  chief  producer  of  uric 
acid,  just  as  it  is  of  urea  in  nianiinals.  Extirpation  of  the  kidneys  in  birds 
leads  to  an  accumulation  of  uric  acid  in  the  blood  and  tissues,  showing  that  the 
kidneys  do  not  produce  the  uric  acid.  Extirpation  of  the  liver,  on  the  contrary, 
leads  to  a  marked  diminution  in  the  uric  acid  of  the  urine,  and  it  is  noteworthy 
that  its  place  is  taken  by  anunoniuni  salts,  probably  aniiuonium  lactate.  This 
would  indicate  that  in  these  animals  proteid  metabolism  leads  in  some  way  to 
the  formation  of  ammonium  lactate,  which  is  then  carried  to  the  liver  and  com- 
bined synthetically  to  make  uric  acid  before  being  excreted  by  the  kidneys.  It 
is  stated  that  in  man  also,  in  certain  pathological  conditions  of  the  liver — for 
example,  acute  yellow  atrophy  and  phosphorus-poisoning — lactates  are  found  in 
the  urine.  Reasoning  from  analogy,  we  should  suppose  that  in  mammalia  too 
uric  acid  is  formed  iu  the  liver,  but  there  is  at  present  no  positive  evidence  in 
favor  of  this  view.  Although  the  quantity  of  uric  acid  ])roduced,  or  at  least 
eliminated,  during  a  day  is  so  small  in  the  mammalia,  it  is  needless  to  say  that 
the  history  of  its  formation,  when  completely  known,  will  be  of  great  import- 
ance, not  only  in  that  it  will  throw  additional  light  upon  the  metabolism  of 
the  proteids  in  the  body,  and  indeed  upon  the  structure  of  the  ])roteid  molecule, 
but  also  because  of  its  bearing  upon  the  nature  of  certain  pathological  con- 
ditions ;  for  it  has  been  found  that  in  fever,  in  leucaemia,  and  possibly  iu  other 
diseases,  there  is  an  increased  production  of  uric  acid.  Several  other  nitrogenous 
substances — xanthin,  hypoxanthiu,  guaniu,  and  adeniu — formiug  members  of 
what  is  known  as  the  xauthiu  group,  are  closely  related  in  composition  to  uric 
acid.  Some  or  all  of  these  substances  may  occur  in  the  urine,  especially  xanthin 
and  hypoxanthiu,  whose  formulas  are  respectively  CjH^X^Og  and  CjII^N^O. 
They  are  found  only  in  minute  quantities.  To  the  extent  that  they  occur  they 
represent  so  much  proteid  broken  down  in  the  body  ;  but  what  peculiarity  in 
metabolism  leads  to  their  formation  rather  than  to  that  of  uric  acid,  or  indeed 
urea,  has  not  been  discovered.  They  are  found  in  greatest  quantity  in  muscle, 
and  are  present,  therefore,  in  meat  extracts.  It  is  interesting  in  this  connection 
to  call  attention  to  the  fact  that  theobromin  (dimethyl-xanthin)  and  caifcin 
(trimethyl-xanthin)  are  closely  related  to  the  xanthin  bodies. 

Creatinin. — Creatinin  (C4H7N.5O)  is  a  crystalline  nitrogenous  substance 
constantly  found  in  urine.  It  is  closely  related  to  creatin  (CJIgNgOo),  the  two 
substances  differing  by  a  molecule  of  water;  the  creatin  changes  to  creatinin 
upon  heating  with  mineral  acids.  Creatinin  occurs  in  urine  to  the  extent 
of  about  1.12  grams  per  day  in  man.  In  dogs  it  has  been  found  that 
the  amount  may  vary  between  0.5  and  4.9  grams  per  day  according  to 
the  diet,  an  increase  in  the  amount  of  meat  in  the  diet  causing  an  increase 
in  the  creatinin.  This  is  readily  explained  by  the  fact  that  creatin  is  a 
constant   constituent   of   muscle,    and    when    taken    into   the    stomach    it    is 


CHEMISTRY   OF  DIGESTION  AND    NUTRITION.  279 

eliminated  in  tlic  urine  as  creatinin.  It  is  evident,  therefore,  that  part 
of  the  creatinin  of  the  urine  is  derived  from  tlie  meat  eaten,  and  does 
not  represent  a  metabolism  within  the  hody.  A  part,  however,  comes 
undoubtedly  from  the  destruction  of  jn'oteid  within  the  body.  In  this  con- 
nection the  following  facts  are  suggestive  and  worthy  of  consideration,  although 
they  cannot  be  explained  satisfactorily :  The  mass  of  protcid  tissue  in  the  body 
is  found  in  the  muscles,  and  the  end-product  of  the  destructive  metabolism  of 
proteid  is  supposed  to  be  chiefly  urea.  Nevertheless,  urea  is  not  found  in  the 
muscles,  while  creatin  occurs  in  considerable  quantities,  as  raucii  as  90  grams 
being  contained  in  the  body-musculature  at  any  one  time.  Only  a  small 
quantity  (1.12  grams)  of  creatin  is  eliminated  in  the  urine  as  creatinin  during 
a  day.  What  becomes  of  the  relatively  large  quantity  of  creatin  in  the  mus- 
cles? It  has  been  suggested  that  it  is  one  of  the  precursors  of  urea — that  it 
represents  an  end-product  of  the  protcid  destroyed  in  muscle  whiclj  is  subse- 
quently converted  to  urea  in  the  liver  or  elsewhere.  This  supposition  is  sup- 
ported by  the  fact  that  creatin  may  be  decomposed  readily  in  the  laboratory, 
with  the  formation  of  urea  among  other  products.  But  against  this  theory 
we  have  the  important  fact  that  creatin  introduced  into  the  blood  is  not  con- 
verted to  urea,  but  is  eliminated  as  creatinin. 

Hippuric  Acid, — This  substance  has  the  formula  C9II9NO3.  Its  molecular 
structure  is  known,  since  upon  decomposition  it  yields  benzoic  acid  and  gly- 
cocoll,  and,  moreover,  it  may  be  produced  synthetically  by  the  union  of  these 
two  substances.  Hippuric  acid  may  be  described,  therefore,  as  a  benzoyl-amido- 
acetic  acid.  It  is  found  in  considerable  quantities  in  the  urine  of  herbivorous 
animals  (1.5  to  2.5  per  cent.),  and  in  much  smaller  amounts  in  the  urine  of 
man  and  of  the  carnivora.  In  human  urine,  on  an  average  diet,  about  0.7 
gram  is  excreted  in  twenty-four  hours.  If,  however,  the  diet  is  largely 
vegetable,  this  amount  may  be  increased  greatly.  These  last  facts  are  readily 
explained.  It  has  been  found  that  if  benzoic  acid  or  related  substances  con- 
taining this  group  are  fed  to  animals,  they  appear  in  the  urine  as  hippuric 
acid.  Evidently,  a  synthesis  has  taken  place  within  the  body,  and  Bunge  and 
Schmiedeberg  proved  conclusively  that  in  dogs,  and  probably,  therefore,  in 
man,  the  union  of  the  benzoic  acid  to  glycocoll  occurs  mainly  in  the  kidney 
itself.  AVe  can  understand,  therefore,  why  vegetable  foods  which  are  known  to 
contain  substances  belonging  to  the  aromatic  series  and  yielding  benzoic  acid 
should  increase  the  output  of  hippuric  acid  in  the  urine.  Since,  however,  in 
starving  animals  or  in  animals  fed  entirely  on  meat  hippuric  acid  is  still  pres- 
ent, although  reduced  in  amount,  it  follows  that  it  arises  in  part  as  one  of  the 
results  of  body-metabolism.  Among  the  various  products  of  the  breaking- 
down  of  the  proteid  molecule,  it  is  probable  that  some  benzoic  acid  occurs, 
and,  if  so,  it  is  excreted  in  combination  with  glycocoll  as  hippuric  acid.  It 
should  be  added,  finally,  that  some  of  the  hippuric  acid  is  supposed  to  be  de- 
rived from  the  process  of  proteid  putrefaction  which  occurs  to  a  greater  or 
less  extent  in  the  large  intestine. 

Conjugated  Sulphates. — A  good  part  of  the  sulphur  eliminated  in  the 


280  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

urine  is  in  the  form  of  etliereal  salts  with  organic  compounds  of  the  aromatic 
and  indigo  series.  Quite  a  number  of  these  compounds  have  been  described  ; 
the  most  imi)ortant  are  the  compounds  with  phenol  (CgHsOSCXOlI),  eresol 
(C;H,0.S020H),  indol  (CglleXOSOpH),  and  skatol  (CgllgNOSO.OII). 
These  four  substances,  phenol,  cresol,  indol,  and  skatol,  are  formed  in  the  in- 
testine during  the  process  of  j)utrefaetive  decomposition  of  the  ])roteids  (p.  249). 
They  are  produced  iu  small  quantities,  and  they  may  be  excreted  in  part  in 
the  feces,  but  in  part  they  are  absorbed  into  the  blood.  They  are  in  them- 
selves injurious  substances,  but  in  passing  through  the  liver — which  must  of 
necessity  happen  before  they  get  into  the  general  circulation — they  are  syn- 
thetically combined  with  sulphuric  acid,  making  the  so-called  *'  conjugated  sul- 
phates," which  arc  harmless,  and  which  are  eventually  excreted  by  the  kidneys. 

"Water  and  Inorganic  Salts. —  Water  is  lost  from  the  body  through  three 
main  channels — namely,  the  liuigs,  the  skin,  and  the  kidney,  the  last  of  these 
being  the  most  important.  The  quantity  of  water  lost  through  the  lungs 
probably  varies  within  small  limits  only.  The  quantity  lost  through  the 
sweat  varies,  of  course,  w'ith  the  temperature,  with  exercise,  etc.,  and  it  may 
be  said  that  the  amounts  of  water  secreted  through  kidney  and  skin  stand  iu 
something  of  an  inverse  proportion  to  each  other;  that  is,  the  greater  the 
quantity  lost  through  the  skin,  the  less  will  be  secreted  by  the  kidneys. 
Through  these  three  organs,  but  mainly  through  the  kidneys,  the  blood  is 
being  continually  depleted  of  water,  and  the  loss  must  be  made  up  by  the 
ingestion  of  new  water.  AVhen  water  is  swallowed  in  excess  the  superfluous 
amount  is  rapidly  eliminated  through  the  kidneys.  The  amount  of  water 
secreted  may  be  increased  by  the  action  of  diuretics,  such  as  potassium  nitrate 
and  caifein,  wdiich  probably  act  directly  upon  the  secretory  cells  in  the 
glomeruli. 

The  inorganic  salts  of  urine  consist  chiefly  of  the  chlorides,  phosphates, 
and  sulphates  of  the  alkalies  and  the  alkaline  earths.  It  may  be  said  in  gen- 
eral that  they  arise  partly  from  the  salts  ingested  with  the  food,  which  salts 
are  eliminated  from  the  blood  by  the  kidney  in  the  water-secretion,  and  in  part 
they  are  formed  in  the  destructive  metabolism  which  takes  ])lace  in  the  body, 
particularly  that  involving  the  proteids  and  related  bodies.  Sodium  chloride 
occurs  in  the  largest  quantities,  averaging  about  15  grams  per  day,  of  which 
the  larger  part,  doubtless,  is  derived  directly  from  the  salt  taken  in  the  food. 
The  phosphates  occur  in  combination  Avith  Ca  and  Mg,  but  chiefly  as  the  acid 
phosphates  of  Na  or  K.  The  acid  reaction  of  the  urine  is  caused  by  these 
latter  substances.  The  phosphates  come  in  part  from  the  destruction  of  phos- 
phorus-containing tissues  in  the  body,  but  chiefly  from  the  ])hosphates  of  the 
food.  The  sulphates  of  urine  are  found  partly  conjugated  with  organic  sub- 
stances, as  described  above,  and  partly  as  simple  sulphates.  The  total  quantity 
of  sulphuric  acid  eliminated  is  estimated  to  average  about  2.5  grams  per  day. 
Sulphur  constitutes  a  constant  element  of  the  proteid  molecule,  and  the  quan- 
tity of  it  eliminated  in  the  urine  may  be  used,  as  iu  the  case  of  nitrogen,  to 
determine  the  total  destruction  of  proteid  within  a  given  period. 


CHEMISTRY   OF   DIGESTION  AND   NUTRITION.  281 

Functions  of  the  Skin. — The  pliy.siolu^ical  activities  of"  the  skin  are 
varied.  It  forms,  iu  the  first  place,  a  sensory  surface  covering  the  body,  and 
interposed,  its  it  were,  between  the  external  world  and  the  inner  mechanism. 
Nerve-fibres  of  pressure,  temperature,  and  pain  are  distributed  over  its  sur- 
face, and  by  means  of  these  fibres  reflexes  of  various  kinds  are  effected  which 
keep  the  body  adapted  to  changes  in  its  environment.  The  physiology  of  the 
skin  from  this  standj)oint  is  discussed  in  the  section  on  Cutaneous  Sensations. 
Again,  the  skin  plays  a  part  of  immense  value  to  the  body  in  regulating  the 
body-temperature.  This  regulation,  which  is  effected  by  variations  in  the 
blood-supply  or  the  sweat-secretion,  is  described  at  appropriate  places  in  the 
sections  on  Animal  Heat,  Circulation,  and  Secretion.  In  the  female,  during 
the  period  of  lactation,  the  mammary  glands,  which  must  be  reckoned  among 
the  organs  of  the  skin,  form  an  important  secretion,  the  milk ;  the  physiology 
of  this  gland  is  described  iu  the  sections  on  Secretion  and  Reproduction.  In  this 
section  we  are  concerned  with  the  physiology  of  the  skin  from  a  different  stand- 
point— namely,  as  an  excretory  organ.  The  excretions  of  the  skin  are  formed 
in  the  sweat-glands  and  the  sebaceous  glands.  The  sweat-glands  are  distrib- 
uted more  or  less  thickly  over  the  entire  surface  of  the  body,  with  the  excep- 
tion of  the  prepuce  and  glans  penis,  w  hile  the  sebaceous  glands,  usually  in  con- 
nection with  the  hairs,  are  also  found  everywhere  except  upon  the  palms  of 
the  liands  and  the  soles  of  the  feet. 

Sweat. — Sweat,  or  perspiration,  which  is  the  secretion  of  the  sweat-glands, 
is  a  colorless  liquid  with  a  peculiar  odor  and  a  salty  taste.  Its  specific  gravity 
is  given  at  1004,  and  in  man  it  usually  has  an  acid  reaction.  As  can  readily  be 
understood,  the  quantity  secreted  in  twenty-four  hours  varies  greatly,  the  secre- 
tion being  influenced  by  variations  in  temperature,  by  exercise,  and  by  psychical 
and  pathological  conditions ;  an  average  estimate  places  the  daily  secretion  at 
from  700  to  900  grams.  Chemically,  the  secretion  consists  of  water  and  inor- 
ganic salts,  traces  of  fats,  fatty  acid,  cholesterin,  and  urea.  Of  the  inorganic 
salts,  NaCl  is  by  far  the  most  abundant :  it  occurs  in  quantities  varying  from 
2  to  3.5  parts  per  thousand.  The  elements  of  the  sweat  which  are  of  import- 
ance from  an  excretory  standpoint  are  water,  inorganic  salts,  and  urea  or  related 
nitrogenous  compounds.  As  was  said  above,  sweat  constitutes  the  second  in 
importance  of  the  three  main  channels  through  which  water  is  lost  from  the 
body.  The  quantity  eliminated  in  the  sweat  is  to  a  certain  extent  inversely 
proportional  to  that  secreted  by  the  kidneys ;  but  the  physiological  value  of 
the  secretion  of  water  by  the  sweat-glands  seems  to  lie  not  so  much  in  the  fact 
that  it  is  necessary  in  maintaining  the  water-equilibrium  of  the  blood  and  tis- 
sues as  in  the  important  part  it  takes  in  controlling  the  heat-loss  from  the  skin : 
the  greater  the  evaporation  of  sweat,  the  greater  the  loss  of  heat.  The  urea  is 
described  as  occurring  in  traces.  As  far  as  it  occurs,  it  represents,  of  course,  so 
much  proteid  destroyed,  but  usually  in  calculating  the  proteid  loss  of  the  body 
this  element  has  been  neglected.  Argutinsky  demonstrated,  however,  that  in 
special  cases — namely,  during  periods  of  unusual  muscular  work  or  after  vapor- 
baths— the  total  weight  of  nitrogen  eliminated  by  the  skin  may  be  of  consider- 


282  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

able  importance,  amounting  to  as  much  as  0.7  to  0.8  gram.  Under  ordinary 
circ'uni.stanoes  the  excretion  of"  urea  and  related  conijjouuds  tlir(>u<i;h  the  skin 
must  be  regarded  as  of  very  sul)sidiary  importance,  but  the  amount  may  be 
increased  marketlly  under  pathological  conditions. 

Sebaceous  Secretion. —  The  sebaceous  secretion  is  an  oily,  semi-liquid 
material,  the  (juantity  ot"  which  cannot  be  estimated  even  approximately. 
Chemically,  it  consists  of  water  and  salts,  albumin  and  epithelium,  liits  and 
fatty  acids.  Its  excretory  importance  in  connection  with  the  metabolism  of 
the  body  must  be  slight.  Its  chief  physiological  value  nnist  be  sought  in 
its  etJ'ect  upon  the  hairs,  which  are  kept  oiled  and  pliant  by  the  secretion. 
Moreover,  it  forms  a  thin,  oily  layer  over  most  of  the  surface  of  the 
skin ;  and  we  may  suppose  that  this  layer  of  oil  is  of  value  in  two 
ways — in  preventing  too  great  a  loss  of  water  through  the  skin,  and  in 
offering  an  obstacle  to  the  absorption  of  aqueous  solutions  brought  into 
contact  Mith  the  skin. 

Excretion  of  COg. — In  some  of  the  lower  animals — the  frog,  lor  ex- 
ample— the  skin  takes  an  important  part  in  the  respiratory  exchanges,  elim- 
inating COg  and  absorbing  O.  In  man,  and  presumably  in  the  mammalia 
generally,  it  has  been  ascertained  that  changes  of  this  kind  are  very  slight. 
Estimates  of  the  amount  of  COj  given  off  from  the  skin  of  man  during 
twenty-four  hours  vary  greatly,  but  the  amount  is  small,  and  is  certainly  less 
than  one  one-hundredth  part  of  the  amount  given  off  through  the  lungs. 

H.  Body-metabolism  ;  Nutritive  Value  of  the  Food-stuffs. 

Determination  of  Total  Metabolism. — ^^'e  have  so  far  studied  the 
changes  that  the  food-stuffs  undergo  during  digestion,  the  form  in  which  they 
are  absorbed  into  the  blood,  their  history  in  the  tissues  to  some  extent,  and  the 
final  condition  in  which,  after  being  decomposed  in  the  body,  they  are  eliminated 
in  the  excreta.  To  ascertain  the  true  nutritional  value  of  the  food-stuffs  it 
is  of  the  utmost  importance  that  we  should  have  some  means  of  estimating 
accurately  the  kind  and  the  amount  of  body-metabolism  during  a  given  period 
in  relation  to  the  character  of  the  diet  used.  Fortunately,  this  end  may  be 
reached  by  a  careful  study  of  the  excreta.  The  methods  employed  can  readily 
be  understood  in  principle  from  a  brief  description.  It  has  been  made  suf- 
ficiently clear  before  this,  perhaps,  that  by  determining  the  total  amount  of  the 
nitrogenous  excreta  we  can  reckon  back  to  the  amount  of  proteid  (or  albu- 
minoid) destroyed  in  the  body.  In  the  case  of  proteids  or  albuminoids  which 
undergo  physiological  oxidation  all  the  nitrogen  appears  in  the  forms  of  urea, 
uric  acid,  creatinin,  xanthin,  etc.,  which  are  eliminated  mainly  through  the  urine, 
and  may  therefore  be  collected  and  determined.  The  following  practical  facts 
are,  however,  to  be  borne  in  mind  in  this  connection :  The  nitrogenous  excre- 
tion of  the  urine  is  mainly  in  the  form  of  urea  which  can  be  estimated  as  such, 
but  it  is  much  more  accurate  to  determine  the  total  nitrogen  in  the  urine  during 
a  given  period,  using  some  one  of  the  approved  methods  for  nitrogen-deter- 
mination, and  to  calculate  back  from  the  amount  of  nitrogen  to  the  amount  of 


CHEMISTRY    OF  DIGESTION  AND    NUTRITION.  283 

proteid.  By  this  means  all  the  nitrogenous  excreta  which  may  occur  in  the 
urine  are  allowed  for ;  and  since  the  various  proteids  differ  but  little  in  the 
amount  of  nitrogen  which  they  contain,  the  average  being  from  15.5  to  16  per 
cent.,  it  is  only  necessary  to  nuilti])ly  the  total  (quantity  of  nitrogen  found  in  the 
excretions  by  6.25  (proteid  molecule  :  N  ::  100  :  16)  to  ascertain  the  amount  of 
proteid  destroyed.  In  accurate  calculations  it  is  necessary  to  determine  the  total 
nitrogen  in  the  feces  as  well  as  in  the  urine,  and  for  two  reasons:  first,  in  ordi- 
nary diets  a  certain  proportion  of  vegetable  and  animal  proteid  escapes  digestion, 
and  this  amount  must  be  determined  and  deducted  from  the  total  proteid  eateu 
in  order  to  ascertain  what  nitrogenous  material  has  actually  been  taken  into  the 
body;  second,  the  secretions  of  the  alimentary  canal  contain  a  certain  quan- 
tity of  nitrogenous  material,  which  represents  a  genuine  excretion,  and  should 
be  included  in  estimates  of  the  total  proteid-destruction.  Practical  experience 
has  shown  that  in  man  about  29  per  cent,  of  the  total  nitrogen  of  the  feces  has 
this  latter  origin.  The  nitrogen  eliminated  as  urea,  etc,  in  the  sweat,  milk, 
and  saliva  is  neglected  under  ordinary  circumstances  because  the  amount  is 
too  small  to  affect  materially  any  calculations  made.  To  determine  the  total 
amount  of  non-nitrogenous  material  destroyed  in  the  body  during  a  given 
period,  two  data  are  required  :  first,  the  total  nitrogen  in  the  excreta  of  the 
body ;  second,  the  total  amount  of  carbon  given  off  from  the  lungs  and  in  the 
various  excreta.  From  the  total  nitrogen  one  calculates  how  much  proteid  was 
destroyed,  and,  deducting  from  the  total  carbon  the  amount  corresponding  to 
this  quantity  of  proteid,  what  remains  represents  the  carbon  derived  from  the 
metabolism  of  the  non-nitrogenous  material — that  is,  from  the  fat  or  carbo- 
hydrate. By  methods  of  this  kind  it  is  possible  to  reckon  back  from  the 
excreta  to  the  total  amount  of  material,  consisting  of  proteid,  fat,  and  carbo- 
hydrate, which  has  been  consumed  in  the  body  within  a  certain  period.  If,  now, 
by  analyzing  the  food  or  by  making  use  of  analyses  already  made  (see  p.  216),  one 
determines  how  great  a  quantity  of  proteid,  fat,  and  carbohydrate  has  been  taken 
into  the  body  in  the  same  period,  then,  by  comparison  of  the  total  ingesta  and 
egesta,  it  is  jwssible  to  strike  a  balance  and  to  determine  whether  all  the  proteid, 
fat,  and  carbohydrate  of  the  food  have  been  destroyed,  or  whether  some  of  the 
food  has  been  stored  in  the  body,  and  in  this  case  whether  it  is  nitrogenous  or 
non-nitrogenous  material,  or,  lastly,  whether  some  of  the  reserve  material  of 
the  body,  nitrogenous  or  non-nitrogenous,  has  been  destroyed  in  addition  to 
the  supply  of  food.  It  is  needless  to  remark  that  "  balance  experiments  "  of 
this  character  are  very  laborious,  particularly  as  they  must  be  made  over  long 
intervals — one  or  more  days.  Nevertheless,  a  great  deal  of  work  of  this 
kind  has  been  done  upon  man  as  well  as  upon  lower  animals,  especially  by 
Voit'  and  Pettenkofer.  In  the  experiments  upon  man  the  urine  and  feces 
were  collected  carefully  and  the  total  nitrogen  was  determined ;  at  the  same  time 
the  total  quantity  of  COg  given  off  from  the  lungs  was  estimated  for  the  entire 
period.  The  determination  of  the  CO2  was  made  possible  by  keeping  the  man 
in  a  specially-constructed  chamber  through  which  air  was  drawn  by  means  of  a 
'  Hermann's  Handbuch  der  Physiologie,  1881,  vol.  vi. 


284  J.V   AMEIilCAX    TEXT-liOOK    OF   PII YSJOLOd  Y. 

pump;  tlie  total  quantity  of  air  drawn  through  was  indicated  hy  a  gasometer, 
and  a  measured  j)ortion  of  this  air  was  drawn  off  through  a  separate  gasometer 
and  was  analyzed  for  its  CO^,  It  was  found  that  the  method  is  j)raeti('al)le  :  that 
by  the  means  described  a  nearly  perfect  balance  may  be  struck  between  the  income 
and  the  outgo  of  the  body.  Experiments  of  this  general  character  have  been 
used  to  determine  the  fate  of  tlie  food-stuffs  in  the  body  under  different  con- 
ditions, the  essential  part  that  each  food-stuff  takes  in  general  nutrition,  and 
so  on.  In  this  and  the  succeeding  sections  we  shall  have  to  consider  some  of 
the  main  results  obtained  ;  but  first  it  will  be  convenient  to  define  two  terras 
frequently  used  in  this  connection — namely,  "nitrogen  equilibrium"  and 
''carbon  equilibrium." 

Nitrogen  Equilibrium. — By  "nitrogen  equilibrium"  we  mean  that  condition 
of  an  animal  in  which,  within  a  definite  period,  the  nitrogen  of  the  excreta  is 
equal  in  amount  to  the  nitrogen  of  the  food  ;  in  other  words,  that  condition 
in  which  the  proteid  (and  albuminoid)  food  eaten  exactly  covers  the  loss  of 
proteid  (and  albuminoid)  in  the  body  during  the  same  time.  If  an  animal 
is  giving  off  more  nitrogen  in  its  excreta  than  it  receives  in  its  food,  then 
the  animal  must  be  losing  proteid  from  its  body ;  if,  on  the  contrary,  the  food 
that  it  eats  contains  more  nitrogen  than  is  found  in  the  excreta,  the  animal  nmst 
be  storing  proteid  in  its  body.  The  condition  of  nitrogen  ecpiilibrium  is  the 
normal  state  of  a  properly-nourished  adult.  It  is  important  to  remember  that 
nitrogen  equilibrium  may  be  maintained  at  different  levels;  that  is,  one  may 
begin  with  a  starving  animal  and  slowly  increase  the  amount  of  nitrogenous  food 
until  nitrogen  equilibrium  is  just  established.  If  now  the  amount  of  nitrog- 
enous food  is  increased — say  doubled — the  excess  does  not,  of  course,  continue 
to  be  stored  up  in  the  animal's  body ;  on  the  contrary,  in  a  short  time  the 
amount  of  proteid  destroyed  in  the  body  will  be  increased  to  such  an  extent 
that  nitrogen  equilibrium  will  again  be  established  at  a  higher  level,  the  animal 
in  this  case  eating  more  and  destroying  more.  The  highest  limit  at  which  nitro- 
gen equilibrium  can  be  maintained  is  determined,  apparently,  by  the  power 
of  the  stomach  and  the  intestines  to  digest  and  absorb  proteid  food.  Further 
details  upon  this  point  will  be  given  presently,  in  describing  the  nutritive 
value  of  the  food-stuffs. 

Carbon  Equilibrium. — The  term  "  carbon  equilibrium  "  is  sometimes  used 
to  describe  the  condition  in  which  the  total  carbon  of  the  excreta  (occurring  in 
the  CO,,  urea,  etc.)  is  exactly  covered  by  the  carbon  of  the  food.  As  one  can 
readily  understand,  an  animal  might  be  in  a  condition  of  nitrogen  equilibrium 
and  yet  be  losing  or  be  gaining  in  weight,  since,  although  the  consumption  of 
proteids  in  the  body  might  just  be  covered  by  the  proteids  of  the  food,  the 
consumption  of  nou-proteids,  fats  and  glycogen,  might  be  greater  or  less  than 
was  covered  by  the  supply  of  food.  In  addition,  we  might  speak  of  ixn  equi- 
librium as  regards  the  water,  salts,  etc.,  although  these  terms  are  not  generally 
used.  An  adult  in  good  health  usually  so  lives  as  to  keep  in  both  nitrogen 
and  general  body  equilibrium — that  is,  to  maintain  his  normal  weight — while 
slight  variations  in  w^eight  from  time  to  time  are  probably  for  the  most  part 


CHE3IISTRY   OF  DIGESTION  AND   NUTRITION.  285 

due  to  a  loss  or  a  gain  in  boily-lat — in  otiier  words,  to  changes  in  the  carbon 
equilibrium. 

Nutritive  Importance  of  the  Proteids. — Tlie  (Hgestion  and  absorp- 
tion of  proteids  liave  been  considered  in  previous  sections.  We  believe  that 
the  digested  proteid  is  absorbed  into  the  blood  in  a  slightly  modified  form,  with 
the  exception  of  the  variable  quantity  which  suffers  decomposition  into  the 
simpler  amido-  compounds  while  in  the  intestine  as  a  result  of  putrefaction  or  of 
the  prolonged  action  of  trypsin.  Subsequently  this  proteid  material  parses  into 
the  lymph  and  is  brought  into  contact  with  the  tissues.  Its  main  nutritive 
importance  lies  in  its  relations  to  the  tissues,  and,  speaking  generally,  we 
may  say  that  the  final  fate  of  the  proteid  molecule  is  that  it  undergoes  a  ])hys- 
iological  oxidation  whereby  the  complex  molecule  is  broken  down  to  form 
the  simpler  and  more  stable  compounds  COg,  H/),  and  urea.  This  destruction 
of  the  proteid  molectde  takes  place  in  or  under  the  influence  of  the  living  cells, 
and  it  gives  rise  to  a  liberation  of  energy  mainly  in  the  form  of  heat.  It  is 
impossible  to  follow  the  various  ways  in  which  this  physiological  oxidation 
takes  place.  It  is  probable,  however,  that  some  of  the  proteid  undergoes  de- 
struction without  ever  becoming  a  part,  an  organized  part,  of  the  living  cells, 
although  its  oxidation  is  effected  through  the  agency  of  the  cells.  It  has  been 
proposed  by  Voit  ^  to  designate  the  proteid  which  is  oxidized  in  this  way  as 
"  the  circulating  albumin  or  proteid."  According  to  Voit,  a  well-fed  animal 
has  in  its  lymph  and  tissues  always  a  certain  excess  of  proteid  which  is  to 
undergo  the  fate  of  the  circulating  proteid,  and  this  supposition  is  used  to 
explain  the  fact  that  for  the  first  day  or  so  a  starving  animal  metabolizes 
more  proteid,  as  determined  by  the  nitrogenous  excreta,  than  in  the  subse- 
quent days,  after  the  supply  of  the  circulating  proteid  has  been  destroyed. 
A  portion  of  the  proteid  food,  however,  before  its  final  destruction  is  utilized 
to  replace  the  nitrogenous  waste  of  the  tissues;  it  is  built  up  into  living  proto- 
plasm to  supply  the  place  of  organized  tissue  which  has  undergone  disassimi- 
lation  or  to  furnish  new  tissue  in  growing  animals.  To  the  proteid  which  is 
built  up  into  tissue  Voit  gives  the  name  of  "  organeiweiss,"  the  best  translation 
of  which,  perhaps,  is  "  tissue-proteid."  It  should  be  stated  that  this  division 
of  the  proteid  into  circulating  proteid  and  tissue-proteid  has  been  severely 
criticised  by  some  physiologists,  but  it  has  the  merit  at  least  of  furnishing 
a  simple  explanation  of  some  curious  facts  with  regard  to  the  use  of  proteid 
in  the  body.  To  avoid  misunderstanding,  it  is  well  to  say  that  the  sepa- 
ration into  circulating  proteids  and  tissue-proteids  does  not  mean  that  the 
proteid  which  is  absorbed  from  the  alimentary  canal  is  of  two  varieties. 
The  terms  refer  to  the  final  fate  of  the  proteid  in  the  body:  a  certain 
portion  is  utilized  to  replace  protoplasmic  tissue,  and  it  then  becomes  "tis- 
sue-proteid," while  the  balance  is  metabolized  in  various  ways  and  con- 
stitutes the  "circulating  proteid."  Any  given  molecule  of  proteid,  as  far 
as  is  known,  may  fulfil  either  function.  With  regard  to  the  general  nutri- 
tive value  of  proteids,  it  has  been  demonstrated  clearly  that  they  are  abso- 

*  Hernmnn's  Handbuch  der  Physiologic,  1881,  vol.  vi.  p.  300, 


286  AN  AMERICAN    TEXT- HOOK    OF   PHYSIOLOGY. 

lutely  neces.-^arv  for  the  fonimtion  of  protoplasmic  tissue.  An  animal  fed  only 
on  non-nitrogenous  food  such  as  fats  and  carbohydrates  will  inevitably  starve 
to  death  in  time  :  this  has  been  shown  by  actual  experiments,  and,  besides,  it 
follows  from  a  priori  considerations.  Protoplasm  contains  nitrogen;  fats  and 
carbohydrates  are  non-nitrogenous,  and  therefore  cannot  be  used  to  make  new 
protoplasmic  material.  It  is  requisite,  moreover,  not  only  that  the  food  shall 
contain  some  nitrogen,  but  that  this  nitrogen  shall  be  in  the  form  of  proteid. 
If  an  animal  is  fed  upon  a  diet  containing  fats  and  carbohydrates  and  nitrog- 
enous material  other  than  proteids,  such  as  amido-acids  or  gelatin,  nitrogenous 
equilibrium  cannot  be  maintained.  There  will  be  a  steady  loss  of  nitrogen  in 
the  excreta,  due  to  a  breaking-down  of  proteid  tissue  within  the  body,  and  the 
final  result  of  maintaining  such  a  diet  would  be  the  death  of  the  animal.  It 
may  be  said,  then,  with  certainty  of  animal  metabolism  that  jiroteid  food  is  ai)So- 
lutely  necessary  for  the  formation  of  new  protoplasm  ;  its  place  in  this  respect 
cannot  be  taken  by  any  other  element  of  our  food.  But,  in  addition  to  this  use, 
proteid,  as  has  been  described  above,  may  be  oxidized  in  the  body  without  being 
first  constructed  into  protoplasmic  material.  According  to  an  older  theory  in 
physiology,  advanced  by  Liebig,  food-stuffs  were  either  plastic  or  respirator}' ; 
by  plastic  foods  he  meant  those  which  were  built  into  tissue,  and  he  sup- 
posed that  the  proteids  belonged  to  this  class ;  by  respiratory  foods  he  meant 
those  which  were  oxidized  or  burnt  in  the  body  to  produce  heat :  the  fats  and 
carbohydrates  constituted  this  class.  We  now  know  that  proteids  are  respi- 
ratory as  well  as  plastic  in  the  terms  of  this  theory ;  they  serve  as  sources  of 
energy  as  well  as  to  replace  tissue,  and  Liebig's  classification  has  therefore 
fallen  into  disuse.  Our  present  ideas  of  the  twofold  use  of  proteid  food  may 
be  supported  by  many  observations  and  experiments,  but  perhajis  the  most 
striking  proof  of  the  correctness  of  these  views  is  found  in  the  flict  that  a  car- 
nivorous animal  can  be  kept  in  both  nitrogen  and  carbon  equilibrium  upon  a 
meat  diet  only,  excluding  for  the  time  a  consideration  of  the  water  and  iiKirganic 
salts.  Pettenkofer  and  Voit  kept  a  dog  weighing  30  kilograms  in  nitrogen 
and  carbon  equilibrium  upon  a  diet  of  1500  grams  of  lean  meat  per  day,  and 
by  increasing  the  diet  to  2500  grams  per  day  the  animal  even  gained  in  weight, 
owing  to  an  increase  in  fat.  Pfliiger  states  also  that  he  was  able  to  keep  a  dog 
in  body-equilibrium  as  long  as  eight  months  upon  a  meat  diet.  Facts  like 
these  demonstrate  that  the  animal  organism  may  get  all  its  necessary  energy 
from  proteid  food  alone,  although,  as  we  shall  see  later,  it  is  more  econom- 
ical and  more  beneficial  to  get  a  part  of  it  at  least  from  the  oxidation  of 
fats  and  carbohydrates.  Adopting  the  theory  of  "circulating  proteids,"  we 
may  say  that  any  excess  of  proteid  al)ove  that  utilized  for  tissue-repair 
or  tissue-growth  will  be  metabolized  in  the  body,  with  the  liberation  of 
energy.  It  makes  no  difference  how  much  proteid  material  we  consume : 
the  excess  beyond  that  used  to  replace  tissue  is  quickly  destroyed  in  some 
way,  and  its  nitrogen  appeal's  in  the  urine  as  urea  or  one  of  the  related 
compounds.  A  good  example  of  the  power  of  the  tissues  to  oxidize  large 
amounts  of  proteid   is  given   in   the   following  experiment,  selected   from   a 


CHEMISTRY  OF  DIGESTION  AND    NUTRITION.  287 

paper  by  Pfliiger.     Dog,  weight  28.1  kilograms,  fed  at  11  A.  m.  with  2070.7 
grams  of  meat : 

2070.7  grams  of  meat  contain 69.2  grams  N. 

Total  nitrogen  eliminated  in  urine  and  feces  in  twenty-four 

hours  (7  A.  M.  to  7  A.  M.) 71.2      "        " 

Deficit  of  N 0.9(]  grams. 

The  total  nitrogen  in  the  urine  alone  was  68.5  grams. 

In  urine  from  7  A.M.  to  11  A.M.,  the  fasting  period 6.9  grams. 

In  urine  from  11  A.  M.  to  7  A.  M.,  time  after  feeding 61.6      " 

Therefore  in  the  four  liours  of  fasting  the  animal  eliminated  in  his  urine 
1.7  grams  N  per  hour,  while  in  the  twenty  hours  after  eating  he  excreted 
3.1  grams  N  per  hour.  This  experiment  shows  not  only  the  completeness 
with  which  an  exce.?sive  proteid  diet  is  handled  by  the  tissues,  but  also  the 
rapidity  with  which  the  excess  is  destroyed.  In  so  far  as  proteid  food  is  burnt 
in  the  body  onlv  as  a  source  of  energy  and  without  being  used  to  form  new  tis- 
sue, its  place  can  be  supplied  in  part,  but  only  in  part,  by  non-nitrogenous  food- 
stuffs— carbohydrates  and  fats.  The  double  use  of  proteid  as  a  tissue-former  and 
an  energy-producer  would  seem  to  imply  that  if,  in  any  given  case,  sufficient  pro- 
teid were  used  in  the  diet  to  cover  the  tissue-waste,  the  balance  of  the  diet  might 
be  composed  of  fats  and  carbohydrates,  and  the  animal  thereby  be  kept  in  nitrog- 
enous equilibrium.  Apparently  this  is  not  the  case,  as  is  seen  from  experiments 
of  the  following  character :  When  an  animal  is  allowed  to  starve,  the  nitrogen  in 
the  urine,  after  the  first  few  days,  becomes  practically  constant,  and  represents 
the  amount  of  oxidation  of  proteid  tissue  taking  place  in  the  body.  If,  now,  the 
animal  is  given  an  amount  of  proteid  just  equal  to  that  being  destroyed  in  the 
body,  nitrogenous  equilibrium  is  not  established  ;  some  of  the  body-proteid  con- 
tinues to  be  lost,  and  to  get  the  animal  into  equilibrium  a  comparatively  large 
excess  of  proteid  must  be  given  in  the  food.  The  same  result  holds  if  carbo- 
hydrates and  fats  are  given  along  with  the  proteid,  with  the  exception  that  upon 
this  diet  nitrogen  equilibrium  is  more  readily  established — that  is,  less  proteid 
is  required  in  the  food.  Upon  the  theory  of  circulating  proteids  and  tissue- 
proteids,  this  fact  may  be  accounted  for  by  saying  that  of  the  proteid  given  as 
food,  a  part  always  undergoes  destruction  as  circulating  proteid  without  going 
to  form  tissue,  so  that  to  cover  tissue-waste  a  larger  amount  of  proteid  must  be 
taken  as  food  than  would  be  necessary  if  it  could  all  be  used  exclusively  for  the 
repair  of  tissue.  Carbohydrates  and  fats  diminish  the  amount  of  proteid 
destroyed  as  circulating  proteid,  and  thereby  enable  us  to  keep  in  nitrogen 
equilibrium  on  a  smaller  proteid  diet.  With  albuminoid  food  (gelatin)  the 
facts  seem  to  be  different.  If  albuminoids  be  given  in  the  food  together  with 
proteids  or  with  proteids  and  a  non-nitrogenous  food-stuff  (fats  or  carbo- 
hydrates), nitrogen  equilibrium  may  be  established  upon  a  much  smaller 
amount  of  proteid  than  in  the  case  of  a  diet  consisting  of  proteid  alone  or  of 
proteid  together  with  fats  and  carbohydrates.  It  seems  probable  that  albu- 
minoids can  take  the  place  entirely  of  circulating  proteids,  so  that  only  enough 


288  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

proteid  need  be  given  to  cover  actual  tissue-waste.  'J'liis  point  will  he  referred 
to  again  in  speaking  of  the  value  of  the  albuminoids. 

Luxua  Consumption. — The  fact  that  normally  more  proteid  is  eaten,  even 
in  a  mixed  diet,  than  is  necessary  to  cover  the  actual  tissue-waste  led  some  of 
the  older  physiologists  to  speak  of  the  excess  as  unnecessary,  a  luxus,  and  the 
rapid  destruction  of  the  excess  in  the  body  was  described  as  a  "  luxus  con- 
sumption." There  can  be  no  doubt  about  the  fact  that  proteid  may  be,  and 
normally  is,  eaten  in  excess  of  what  is  necessary  to  repair  tissue-waste,  c^r  in 
excess  of  what  is  requisite  to  maintain  nitrogenous  equilibrium  at  a  low 
level.  But  it  is  altogether  improbable  that  the  excess  is  really  a  "luxus." 
It  has  been  stated,  in  speaking  of  nitrogenous  equilibrium,  that  an  animal 
may  be  kept  in  this  condition  upon  a  certain  minimal  amount  of  pro- 
teid, or  upon  various  larger  amounts  up  to  the  limit  of  the  power  of  the 
alimentary  canal  to  digest  and  absorb ;  but  it  has  also  been  shown  (Munk') 
that  if  an  animal  is  fed  upon  a  diet  containing  quantities  of  proteid  barely 
sufficient  to  maintain  N  equilibrium,  it  will  after  a  time  show  signs  of  mal- 
nutrition. It  seems  to  be  necessary,  as  Pfliiger  pointed  out,  that  the  tissues 
should  have  a  certain  excess  of  proteid  to  destroy  in  order  that  their  nutri- 
tional or  metabolic  powers  may  be  kept  in  a  condition  of  normal  activity. 
Hence  we  find  that  well-nourished  individuals  habitually  consume  more  j)roteid 
than  would  theoretically  suffice  for  N  equilibrium.  For  example,  the  average 
diet  of  an  adult  contains,  or  should  contain,  from  100  to  118  grams  of  })roteid 
per  day,  but  it  has  been  shown  that  nitrogen  and  body  equilibrium  in  man 
may  be  maintained,  for  short  periods  at  least,  upon  40  grams  of  proteid  a  day, 
provided  large  amounts  of  fats  or  carbohydrates  are  eaten.  It  is  scarcely  neces- 
sary to  add  that  this  beneficial  excess  has  a  limit,  and  that  too  great  an  excess 
of  proteid  food  may  cause  troubles  of  digestion  as  well  as  of  general  nutrition. 

Nutritive  Value  of  Albuminoids. — The  albuminoid  most  frequently  oc- 
curring in  food  is  gelatin.  It  is  derived  from  collagen  of  the  connective 
tissues.  Collagen  of  bones  or  of  connective  tissue  takes  up  water  when  boiled 
and  becomes  converted  into  gelatin.  We  eat  gelatin,  therefore,  in  boiled  meats, 
soups,  etc.,  and,  besides,  it  is  frequently  employed  directly  as  a  food  in  the 
form  of  table-gelatin.  Collagen  has  the  following  percentage  comj)osition  : 
C,  50.75  per  cent. ;  H,  6.47  ;  N,  17.86  ;  O,  24.32 ;  S,  0.6.  It  resembles  the 
proteid  molecule  closely  in  chemical  composition,  and  it  would  seem  that  the 
tissues  might  use  it  as  they  do  proteid,  for  the  formation  of  new  protoi)lasm. 
Experiments,  however,  have  demonstrated  clearly  that  this  is  not  the  case. 
Animals  fed  upon  albuminoids  together  with  fats  and  carbohydrates  do  not 
maintain  N  equilibrium ;  a  certain  proportion  of  tissue  breaks  down,  giving 
an  excess  of  nitrogen  in  the  urine.  The  final  result  of  such  a  diet  would  be 
continued  loss  of  weight  and,  finally,  malnutrition  and  death.  Gelatin,  how- 
ever, is  readily  digested,  gelatoses  and  gelatin  ])eptones  being  formed ;  these 
are  absorbed  and  oxidized  in  the  body,  with  the  formation  of  CO^,  HjO,  and 
urea  or  some  related  nitrogenous  product.  Gelatin  serves,  then,  as  a  source 
*  DuBois-Reymond's  Archiv  fur  Physioloc/ie,  1891,  p.  338. 


Nourishment  (grams) 

Meat. 

Gelatin.               Fat. 

400 

—                   200 

400 

—                    — 

400 

200                 — 

CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  289 

of  energy  to  the  body  in  the  same  sense  as  do  carbohydrates  and  fats.  When 
any  one  of  these  three  substances  is  used  in  a  diet,  the  proportion  of  proteid 
necessary  for  the  maintenance  of  N  equilibrium  may  be  reduced  greatly.  Upon 
the  theory  of  circulating  proteids,  this  is  explained  by  saying  that  these  sub- 
stances are  burnt  in  place  of  proteid,  and  that  the  proportion  of  this  latter 
material  which  undergoes  the  fate  of  circulating  proteid  is  thereby  diminished. 
Actual  experiments  have  shown  that  gelatin  is  more  efficacious  than  either  fats 
or  carbohydrates  in  protecting  the  proteid  in  the  body,  and  it  has  been  sug- 
gested, therefore,  that  it  may  take  the  place,  partly  or  completely,  of  the  circu- 
lating proteid,  according  to  the  amount  fed.  If  this  suggestion  is  true,  we 
may  say  that  gelatin  has  a  nutritive  value  the  same  as  that  of  the  proteids, 
except  that  it  cannot  be  constructed  into  living  proteid.  The  relative  value 
of  fats,  carbt)liyd rates,  and  gelatin  in  protecting  proteid  from  destruction  in 
the  body  is  illustrated  by  tKe  following  experiment,  reported  by  Voit.  A  dog 
weighing  32  kilograms  was  fed  alternately  upon  proteid  and  sugar,  proteid 
and  fat,  and  proteid  and  gelatin  : 

Calculated  destruction  of  flesh 
Sugar.  in  body  (grams). 

—  450 
250  439 

—  356 

Muuk  ^  has  attempted  recently  to  determine  how  far  the  proteids  of  food  mav 
be  replaced  by  gelatin.  In  these  experiments  a  dog  was  brought  into  a  condi- 
tion of  nitrogenous  equilibrium  upon  a  diet  of  flesh-meal,  rice,  and  lard,  con- 
taining 9.73  grams  of  nitrogen.  During  the  period  this  diet  was  continued  the 
animal,  whose  weight  was  16.5  kilograms,  was  oxidizing  in  its  body  3.7  grams 
of  proteid  daily  for  each  kilogram  of  weight.  In  a  second  period  lasting  four 
days  the  quantities  of  rice  and  lard  were  the  same  as  before,  but  the  proteid  in 
its  diet  was  reduced  to  8.2  grams,  which  contained  1  gram  of  nitrogen ;  the 
balance  of  the  nitrogen  was  supplied  in  the  form  of  gelatin,  so  that  in  round 
numbers  only  one-sixth  of  the  required  daily  amount  of  nitrogen  was  given 
as  proteid.  The  result  was  that  the  animal  maintained  its  nitrogen  equilib- 
rium for  the  short  period  stated.  It  was  found  that  the  experiments  could 
not  be  continued  longer  than  four  days,  owing  to  the  growing  dislike  of  the 
animal  for  the  gelatin  food.  During  the  second  period  the  animal  was  receiving 
in  its  food  and  burning  in  its  body  only  0.5  gram  of  proteid  daily  for  each 
kilogram  of  weight,  as  against  3.7  grams  upon  a  normal  diet.  It  would  not 
be  possible  to  substitute  fats  or  carbohydrates  for  the  proteids  of  the  daily  diet 
to  anything  like  the  same  extent  without  causing  a  consumption  of  some  of  the 
store  of  proteid  material  within  the  body. 

Nutritive  Value  of  Fats. — The  fats  of  food  are  absorbed  into  the  lacteals 
as  neutral  fats.  They  eventually  reach  the  blood  in  tiiis  condition,  and  are 
afterward  in  some  way  consumed  by  the  tissues.  The  final  products  of  their 
oxidation   must  be  the  same  as  when  burnt  outside  the  body — namely,  COg 

*  Pfluger^s  Archivfiir  die  gesammfe  Physiologie,  1894,  vol.  Iviii.  p.  309. 
19 


20O  ^.V  AMERICAX    TEXT-BOOK'    OF   PHYSIOLOGY. 

and  HjO — and  a  corresjwnding  amount  of  energy  must  be  liberated.  Speak- 
ino;  (yiMierally,  then,  the  essential  nutritive  value  of  the  fats  is  that  they  furnish 
enerijy  to  tiie  biHly,  and,  from  a  chemical  standpoint,  they  must  contain  more 
available  energy,  weight  for  weight,  than  the  proteids  or  the  carbohydrates 
(st^e  p.  303).  In  a  well-nourished  animal  a  large  amount  of  fat  is  found 
normally  in  the  adipose  tissues,  particularly  in  the  so-called  "  paimiculus 
adiposus"  beneath  the  skin.  Physiologically,  this  body-fat  is  to  be  regarded 
as  a  reserve  suj^ply  of  nourishment.  AMien  food  is  eaten  and  absorbed  in 
excess  of  the  actual  metiibolic  power  of  the  body,  the  excess  is  stored  in  the 
adipose  tissue  as  fat,  to  be  drawn  upon  in  case  of  need — as,  for  instance, 
during  partial  or  complete  starvation.  A  starving  animal,  afler  its  small 
supply  of  glycogen  is  exhaustal,  lives  entirely  upon  iKxly-proteids  and  fats; 
the  larger  the  supply  of  fat,  tiie  more  effectively  will  the  proteid  tissues  be 
protected  from  destruction.  In  accordance  with  this  fact,  it  has  been  shown 
that  when  subjected  to  complete  starvation  a  fat  animal  will  survive  longer 
than  a  lean  one.  Our  supply  of  fat  is  called  upon  not  only  during  complete 
abstention  from  food,  but  also  whenever  the  diet  is  insufficient  to  cover  the 
oxidations  of  the  body,  as  in  deficient  food,  sickness,  etc. 

Formation  of  Fat  in  the  Body. — The  origin  of  body-fat  has  always  been 
an  interesting  problem  to  physiologists.  Naturally,  the  first  supposition  made 
was  that  it  comes  directly  from  the  fat  of  the  food.  According  to  this  view, 
a  certain  proportion  of  the  fat  of  the  food  was  su])posed  to  be  deposited  directly 
in  the  cells  of  adipose  tissue,  and  in  this  way  all  our  supply  of  fat  originated. 
This  theory  was  soon  disproved.  It  was  shown,  especially  upon  cows  and  pigs, 
that  the  amount  of  fat  formed  in  the  body  within  a  given  time,  including  the 
fat  of  milk  in  the  case  of  the  cow,  might  be  far  in  excess  of  the  total  amoiuit 
of  fat  taken  in  the  food  during  the  same  period,  thus  demonstrating  that  a  cer- 
tain proportion  at  least  of  the  body-fat  must  have  some  other  origin.  More- 
over, the  genesis  of  the  fat-droplets  in  fat-cells,  as  studied  under  the  microscojie, 
did  not  agree  with  the  old  view ;  and  there  was  the  further  fact  that  each  animal 
has  its  own  peculiar  kind  of  fat ;  as  Liebig  says,  "  In  hay  or  the  other  fodder 
of  oxen  no  beef-suet  exists,  and  no  hog's  lard  can  be  found  in  the  potato  refuse 
given  to  swine."  In  fact,  the  evidence  was  so  conclusive  against  this  theory  that 
physiologists  for  a  time  were  led  to  adopt  the  opposite  view  that  no  fat  at  all  can 
be  obtained  directly  from  the  fot  of  the  food.  However,  it  has  now  been  shown 
that  under  certain  conditions  fat  may  be  deposited  directly  in  the  tissues  from 
the  fat  of  food.  Lebedeff,  and  afterward  Munk,  proved  that  if  a  dog  is  first 
starved  until  the  reserve  supply  of  fat  in  the  body  is  practically  used  up,  and 
it  is  then  fed  richly  upon  foreign  fats,  such  as  rape-seed  oil,  linseed  oil,  or 
mutton  tallow,  it  will  again  lay  on  fat,  and  some  of  the  foreign  fat  may  be 
detected  in  its  body.  The  conditions  necessary  to  be  fulfilled  in  order  to  get 
this  result  make  it  probable  that  under  normal  conditions  none  of  the  fat  of 
the  body  is  derived  directly  from  the  fat  of  the  food.  On  the  contrary,  tiie 
fat  of  the  foot]  is  completely  oxidized,  and  our  body-fat  is  normally  con- 
structed anew  from  either  proteids  or  carbohydrates.    As  to  its  origin  from 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  291 

proteid,  Voit  has  devoted  Duinerou.s  researches  to  tlie  purpose  of  demon- 
strating that  this  is  the  main  source  of  body-fat.  His  belief  is  that  in  the 
course  of  metabolism  the  proteid  molecule  undergoes  a  cleavage,  with  the  for- 
mation of  a  nitrogenous  and  a  non-nitrogenous  part.  The  former,  after  further 
changes,  is  eliminated  in  the  form  of  urea,  etc. ;  the  latter  may  be  converted 
into  fat,  or  possibly  into  glycogen.  The  theoretical  maximum  of  fat  which 
can  arise  in  this  way  is  51.5  per  cent,  of  the  entire  amount  of  proteid.  Voit 
attempted  to  demonstrate  this  theory  by  actual  experiments.  He  showed  that 
dogs  fed  upon  large  amounts  of  lean  meat  did  not  give  off  as  much  carbon  in 
the  excreta  as  they  received  in  the  food.  The  excess  of  carbon  must  have  been 
retained  in  the  body,  and,  in  all  probability,  in  the  form  of  fat.  As  corrob- 
orative evidence  he  cites  the  ajiparently  direct  conversion  of  proteid  material 
into  fat  in  such  cases  as  the  formation  of  fat-droplets  in  the  fat-cells  or  cells 
of  the  mammary  glands,  and  in  muscle-fibres  and  liver-cells  undergoing  fatty 
degeneration ;  but  evidence  of  this  latter  character  is  not  conclusive,  since  we 
have  no  immediate  proof  that  the  fat  arises  directly  from  the  proteid  material 
in  the  cells.  Voit's  experimental  evidence  has  been  questioned  recently  by 
Pfliiger,  his  criticisms  being  directed  mainly  toward  the  calculations  involved 
in  Voit's  experiments.  The  result  of  this  criticism  has  been  to  make  us  more 
cautious  in  attributing  the  origin  of  body-fat  solely  or  mainly  to  ])roteids,  but 
as  regards  the  possibility  of  some  proteid  being  converted  into  fat  in  the  body 
there  can  be  no  reasonable  doubt.  It  has  been  proved  (p.  268)  that  glycogen 
may  be  formed  from  proteid,  and  since  it  is  now  generally  accepted  that  fats 
are  formed  from  carbohydrates,  the  possibility  of  an  indirect  production  of  fats 
from  proteids  seems  to  follow  necessarily. 

The  connection  between  the  carbohydrates  of  the  food  and  the  fat  of  the 
body  has  been  a  subject  of  discussion  and  investigation  among  physiologists 
for  a  number  of  years.  It  was  the  original  belief  of  Liebig  that  carbohydrates 
are  the  source  of  body-fat.  This  view  was  afterward  abandoned  under  the 
influence  of  the  work  of  Pettenkofer  and  Voit,  but  renewed  investigations  seem 
to  have  re-established  it  upon  solid  experimental  grounds.  In  some  older 
experiments  of  Lawes  and  Gilbert  it  was  shown  that  the  fat  laid  on  by  a  young 
pig  during  a  certain  period  was  greater  than  could  be  accounted  for  by  the 
total  fat  in  the  food  during  that  period,  plus  the  theoretical  maximum  obtain- 
able from  the  proteid  fed  during  the  same  time.  Of  more  recent  experiments 
demonstrating  the  same  point,  a  single  example  may  be  quoted  from  Rubner,* 
as  follows :  A  small  dog,  weighing  6.2  kilograms,  was  fed  richly  with  meat  for 
two  days  and  Avas  then  starved  for  two  days ;  its  w^eight  at  the  end  of  this  time 
was  5.89  kilograms.  The  animal  was  then  given  for  two  days  a  diet  of  cane- 
sugar  100  grams,  starch  85  grams,  and  fat  4.7  grams.  It  was  kept  in  a  respira- 
tion apparatus  and  its  total  excretion  of  nitrogen  and  carbon  was  determined : 

Total  C  excretion 87.10  grams  C. 

"       C  ingesta 176.fi         "       " 

89.5        "       "     retained  in  the  body. 

1  Zeitschri/tfur  Biologie,  1886,  vol.  22,  p.  272. 


292  AN  A^^ERICAN  TEXT-BOOK    OF  PHYSIOLOOY. 

The  total  nitrogen  excreted  ^  2.55  grams.  Tlie  oarboii  contained  in  the  pro- 
teid  thus  broken  down  plus  that  in  the  4.7  grains  of  fat  =  13  grams.  If  we 
make  the  assumption  tiiat  all  of  the  V  from  these  two  sources  was  retained 
within  the  body,  there  would  still  be  a  balance  of  76.5  grams  C  (89.5 —  13.0) 
whicii  must  have  been  stored  in  the  body  either  as  glycogen  or  as  fat.  The 
greatest  possible  storage  of  glycogen  was  estimated  at  78  grams  =  34.6  grams 
C,  so  that  76.5  —  34.6  =  41.9  grams  C  as  tiie  minimal  amount  which  must 
have  been  retained  as  fat  and  must  have  arisen  from  the  carbohydrates  of  the 
food.  Similar  experiments  have  been  made  upon  herl)ivorous  animals,  and 
as  the  result  of  investigations  of  this  character  we  are  compelled  to  admit  that 
the  carbohydrates  form  one  source,  and  possibly  the  main  source,  from  which 
the  body -fats  are  derived.  This  belief  accords  with  the  well-known  fact  that 
in  fattening  stock  tlic  best  diet  is  one  containing  a  large  amount  of  carbo- 
hydrate together  with  a  certain  quantity  of  proteid.  On  the  view  that  fats 
were  formed  only  from  proteids,  the  efficacy  of  the  carbohydrates  in  such  a  diet 
was  supposed  to  lie  in  the  fact  that  they  protected  a  part  of  the  proteid  from 
oxidation,  and  thus  permitted  the  forn)ation  of  fat  from  proteid  ;  but  it  is  now 
believed  that  the  carbohydrates  of  a  fattening  diet  are,  in  part,  converted 
directly  to  fat,  although  the  chemistry  of  the  transformation  is  not  as  yet 
understood.  Diets,  such  as  the  well-known  Banting  diet,  intended  to  reduce 
obesity  are  characterized,  on  the  contrary,  by  a  small  proportion  of  carbo- 
hydrates and  a  relative  excess  of  proteid. 

Nutritive  Value  of  Carbohydrates. — The  nutritive  importance  of  the 
carbohydrates  is  similar  in  general  to  that  of  the  fats;  they  are  oxidized  and 
furnish  energy  to  the  body.  In  addition,  as  has  been  described  in  the  pre- 
ceding paragraph,  they  may  be  converted  into  fat  and  stored  in  the  body  as 
a  reserve  supply  of  nourishment.  As  a  matter  of  fact,  the  carbohydrates  form 
the  bulk  of  ordinary  diets.  They  are  easily  digested,  easily  oxidized  in  the 
body,  and  from  a  financial  standpoint  they  form  the  cheapest  food-stuff.  The 
final  products  in  the  physiological  oxidation  of  carbohydrates  must  be  COj  and 
H.,0.  Inasmuch  as  the  H  and  O  in  the  molecide  already  exist  in  the  proper 
proportions  to  form  Wf)  (CgHjoOg,  C^J^^fi^^),  it  follows  that  relatively  less  oxy- 
gen will  be  needed  in  the  coml)ustion  <  »f  carbohydrates  than  in  the  case  of  proteids 
or  of  fats.  Whatever  may  be  the  actual  process  of  oxidation,  we  may  consider  that 
only  as  much  O  is  needed  as  will  suffice  to  oxidize  the  C  of  the  sugar  to  COj. 

Hence  the  ratio  of  O  absorbed  to  CO^  eliminated,  — — %  a  ratio  which  is  known 

as  the  respiratory  quotient,  will  approach  nearer  to  unity  as  the  quantity  of 
carbohydrates  in  the  diet  is  increased.  From  our  study  of  the  digestion  of 
carbohydrates  (p.  257)  we  have  found  that  most  of  the  carbohydrates  of  our 
food  pass  into  the  blood  as  dextrose  (or  levulose),  and  any  excess  above  a  cer- 
tain percentage  is  converted  temporarily  to  glycogen  in  the  liver,  the  nuiscles, 
etc.,  to  be  again  changed  to  dextrose  before  being  used.  The  sugar  undergoes 
final  oxidation  in  the  tissues  to  COg  and  HgO.  AVhile  it  is  possible  that  this 
oxidation  may  be  direct — that  is,  that  the  sugar  may  be  burnt  directly  to  COg  and 


CHEMISTRY   OF   DIOESTION  AND    NUTRITION.  293 

H  O-it  is  usually  suppose.1  to  be  pveccM  by  a  splitting  of  the  sug-ar  molocule. 
The  stops  in  the  process  arc  not  <lcfinitoly  known  ;  a,«,nl,ng  to  one  hypotb- 
^te  the  n>oloe„lo  H,.t  nn.le,-goc«  elcavagc,  with  the  t  onnat.on  of  la*c  ad 
^  i-T  O  -  2C  1I,0,),  which  is  then  oxidized.  Accoi-dmg  to  another  liypoth- 
Sf  the'sngar  first  breaks  down,  with  the  formation  of  aleohol  an,l  CO,,  a.s  n> 
tbe'veast  fermentation  outside  the  body. 

There  have  been  diseovered  recently  in  connecfon  wul,  the   pancrea.,  a 
number  of  facts  that  are  interesting  not  only  in  thcn.selves,  but  doubly  so 
be".t  thev  pron.ise,  when  n.ore  fully  investigatetl,  to  throw  son.ebght  on 
the  nl  er-o    consn.nption  of  sugar  by  the  tissues.     It  has  been  shown  by 
V  Merin.  and  Minkowski'  and  othe,.  that  if  the  pancreas  of  a  dog  ,s  e,  m- 
pktely  removed,  the  tissues  lose  the  power  of  eonsummg  sugar,  so  that 
am,„  ulates   in  the  blood   and   finally  escapes  in  the  ur.ne,  eausmg  what 
ir     en  llled  "pancreatic  diabetes."     If  a  small  part  of  the  pancreas  ,s 
S  i     the  body,  even  though  it  is  not  connected  by  its  duct  w,th  the  duo- 
dtum    dabetes  does  not  i^eur.     The  inference  usually  made  from  these 
e  pe   me  r    that  the  pancreas  gives  off  something  to  the  blood-an  n.ternal 
s^reton-whieh    is   necessary  to  the    physiological    consun.p  .on   of    sugar. 
rXt  way  the  pancreas  exerts  this  influence  has  yet  to  be  d.scovered ; 
™  Jb  ;  it  is  throuU  the  action  of  a  sp.=ific  enzyme  wh.ch  helps  to  break 
Town  the  sugar;  possibly  it  is  by  some  other  means.     But  the  neces-sUy  of 
thTpancreas  in   ome  wav  for  the  normal  consumption  of  sugar  by  tbe  t.ssu^ 
generally  seen,  to  be  indisputably  established.    It  is  a  d.scovery  of  the  utmos 
fZrtanee  in  its  relations  to  the  normal   nutrition  of  the  body,  and  also 
l^CTf  it,  possible  bearing  on  the  pathological  condition  known  as  *«M.. 
^nZ      In  this  latter  disease  the  tissues,  for  some  reason    are  unable  to 
Tx  d      ■  th     sugar  in  normal  amounts,  and  a  good  part  of  it,  therefore,  escapes 
th  outh  the   urine.     The  facts  and  theories  bearing  upon  d.abetes  are  of 
unu":      1-est  in  connection  with  the  nutritive  history  of  the  carbohydrates, 
toti^r  a  fuller  description  reference  must  be  made  to  moi-e  elabo.-a^e  works. 
'    Anotler  statement' in  connection  with  the  fate  "^ -■^^  '»  *;^^«'^„: 
worthv  of  a  brief  reference:  It  has  been  asserted  by  Lepine  and  Banal  that 
There  is  normally  present  in  blood  an  enzyme  capable  of  destroy.ng  sugar 
Tlb-tlory  rest' upon  the  undoubted  fact  that  sugar  adcW  to  blood  outsue 
I   wTsoou  disappear.    They  call  the  process  "  glycolys.s,"  and  t  e  enzy^^. 
to  which  they  attr  bute  this  disappearance  the  "  glycolytic  enzyme.      Othe.s 
how  V     (Afhus),  have  claimed  that  this  enzyme  is  only  a  post-mortem  resul 
ofTedi  it    grain  of  the  corpuscles  of  the  btel,  and  that  .t  -  -    P-"' 
in  circulating  blood.     We  must  await  further  mvest.gafon  upon  th,s  po.nt, 
and  be  content  here  with  a  mere  trference  ^^^,^^^^ 
Nutritive  Value  of  Water  and  Salts.— Watei  is  losi  (uni.v  i  i 

in  WeCntities  through  the  kidney,  the  skin,  the  lungs,  and  the  fec^,  and 
•       it  is  fepC  by  water  teken  in  the  food  or  separately,  and  partially  also  by 
tl,:"l£  formed  in  the  oxidations  of  the  body.     A  certain  percentage  of 

1  ATchi,  fir  eipermenUUe  Pathologk  u.  PUrmAohgk,  1893,  IJXI.  p.  85. 


294  AN  AMERICAN    TEXT-BOOK'    OE    PHYSIOLOaY. 

water  in  tlie  tissues  and  in  the  li([iii(ls  <»i'  tlie  body  is  naturally  al)solntely 
essential  to  the  normal  play  of  metabolism;  and  eonditions,  snch  as  muscular 
exercise,  which  increase  the  water-loss  brint^  about  also  an  increjtsed  water- 
consumption,  the  regulation  being  effected  through  the  nervous  mechanism 
whicli  mediates  the  sensation  of  thirst.  The  water  taken  into  the  bodv  does 
not,  however,  serve  directly  as  a  source  of  energy,  since  it  is  finally  eliminated 
in  the  form  in  which  it  is  taken  in ;  it  serves  only  to  replace  water  lost  from 
the  tissues  and  licjuids  of  the  body,  and  it  furnishes  also  tlie  menstruum  for  the 
varied  chemical  reactions  which  take  place.  Continued  deprivation  of  water 
leads  to  intolerable  thirst,  the  cause  of  which  is  usually  referred  to  the  altered 
composition  of  the  tissues  generally,  including  the  peripheral  nervous  system. 
Inorganic  Salts. — The  essential  value  of  the  inorganic  salts  to  the  proper 
nutrition  of  the  body  does  not  commonly  force  itself  upon  our  attention,  since, 
as  a  rule,  we  get  our  proper  supply  unconsciously  with  our  food,  without  the 
necessity  of  making  a  deliberate  selection,  NaCl  (common  table-salt)  forms 
an  exception,  however,  to  this  rule.  Speaking  generally,  inorganic  salts  do 
not  serve  as  a  source  of  energy  to  the  body.  Most  of  the  salts  found  in 
the  urine  and  other  excreta  are  eliminated  in  the  same  form  in  which  they 
were  received  into  the  body.  Some  of  them,  however,  notably  the  phosphates 
and  the  sulphates,  are  formed  in  the  course  of  the  metabolism  of  the  tissues, 
and  without  doubt  reactions  of  various  kinds  occur  affecting  the  composition 
of  many  of  the  salts — for  example,  the  decomposition  of  the  chlorides  to  form 
the  HCl  of  gastric  juice.  But  these  reactions  do  not  materially  influence  the 
supply  of  energy  in  the  body :  the  value  of  the  salts  lies  in  the  general  fact 
that  they  are  necessary  to  the  maintenance  of  the  normal  ])hysical  and  chem- 
ical properties  of  the  tissues  and  the  body-fluids.  Experimental  investigation  ' 
has  shown  in  a  surprising  way  how  immediately  important  the  salts  are  in  this 
respect.  Forster  fed  dogs  and  pigeons  on  a  diet  in  which  the  saline  constit- 
uents had  been  much  reduced,  althougli  not  completely  removed.  The  animals 
were  given  proteids,  fats,  and  carbohydrates,  but  they  soon  passed  into  a 
moribund  condition.  It  seemed,  in  fact,  that  the  animals  died  more  quickly 
on  a  diet  poor  in  salts  than  if  they  had  been  entirely  deprived  of  food. 
Similar  experiments  were  made  by  Lunin  upon  mice,  with  corresponding 
results.  He  showed,  moreover,  that  while  mice  live  very  well  upon  cow's  milk 
alone,  yet  if  given  a  diet  almost  free  from  inorganic  salts,  consisting  of  the 
casein  and  fats  of  milk  plus  cane-sugar,  they  soon  died.  INIoreover,  if  all  the 
inorganic  salts  of  milk  were  added  to  this  diet  in  the  exact  proportion  in  which 
they  exist  in  the  ash  of  milk,  the  mixture  still  failed  to  supjwrt  life.  It  would 
seem  from  this  result  that  the  inorganic  salts  cannot  fulfil  completely  their 
proper  functions  in  the  body  unless  they  exist  in  some  special  combination 
with  the  organic  constituents  of  the  food.  In  this  coiniection  it  is  well  to  bear 
in  mind  that  proteids  as  they  occur  in  nature  seem  always  to  be  combined 
with  inorganic  salts,  and  the  jiroperties  of  proteids,  as  we  know  them,  are 
undoubtedly  dependent  in  part  upon  the  presence  of  this  inorganic  constituent. 
'  Bunge:  Physiological  and  Pathological  Chemistry,  translated  by  Wooldridge,  1890. 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  295 

It  has  been  shown,  lor  example,  that  if  egg-albuiniu  is  completely  deprived 
of  its  ash,  it  is  no  longer  soluble  in  water.  We  may  assume  that  the  original 
synthesis  of  the  organic  and  inorganic  constituents  is  made  in  the  plant  king- 
dom, and  that,  in  its  own  way,  the  inorganic  constituent  of  the  molecule  is  as 
necessary  to  the  proper  nutrition  of  the  animal  tissues  as  is  the  organic.  One 
salt  (NaCl)  is  consumed  by  many  animals,  including  man,  in  excess  of  the 
amount  unconsciously  ingested  with  the  food.  Bunge  points  out  that  purely 
carnivorous  animals  are  not  known  to  crave  this  salt,  while  the  herbivora 
with  some  exceptions — for  example,  the  rabbit — take  it  at  times  largely  in  ex- 
cess. The  need  of  salt  on  the  part  of  these  animals  is  well  illustrated  among 
the  wild  forms  by  the  eagerness  with  which  they  visit  salt-licks.  Bunge 
advances  an  ingenious  theory  to  account  for  the  difference  in  regard  to  the  use 
of  salt  between  the  herbivora  and  the  carnivora.  He  points  out  that  in  plant 
food  there  is  a  relatively  large  excess  of  potassium  salts.  When  these  salts 
enter  the  liquids  of  the  body  they  react  with  the  NaCl  present  and  a  mutual 
decomposition  ensues,  with  the  formation  of  KCl  and  the  sodium  salt  of  the 
acid  formerly  combined  with  the  potassium,  and  the  new  salts  thus  formed  are 
eliminated  by  the  kidneys  as  soon  as  they  accumulate  beyond  the  normal  limit. 
In  this  way  the  normal  proportion  of  NaCl  in  the  tissues  and  the  body-fluids 
is  lowered  and  a  craving  for  the  salt  is  produced.  Bunge  states  that  it  has  been 
shown  among  men  that  vegetarians  habitually  consume  more  salt  than  those 
who  are  accustomed  to  eat  meats.  The  salts  of  calcium  and  of  iron  have  also 
a  special  importance  which  needs  a  word  of  reference.  The  particular  import- 
ance of  the  iron  salts  lies  in  their  relation  to  hsemoglobin.  The  continual 
formation  of  new  red  blood-corpuscles  in  the  body  requires  a  supply  of  iron 
salts  for  the  synthesis  of  the  haemoglobin,  and,  although  there  is  a  probability 
(see  p.  263)  that  the  iron  compound  of  the  disintegrating  corpuscles  is  again 
used  in  part  for  this  purpose,  we  must  suppose  that  the  body  requires  addi- 
tional iron  in  the  food  from  time  to  time  to  take  the  place  of  that  which  is 
undoubtedly  lost  in  the  excretions.  It  has  been  shown  that  iron  is  contained 
in  animal  and  vegetable  foods  in  the  form  of  an  organic  compound,  and  the 
evidence  at  hand  goes  to  show  that  only  when  it  is  so  combined  can  the  iron 
be  absorbed  readily  and  utilized  in  the  body,  while  the  efficacy  of  the  inor- 
ganic salts  of  iron  as  furnishing  directly  a  material  for  the  production  of  hserao- 
globin  is,  to  say  the  least,  open  to  doubt.  Bunge  isolated  from  the  yolk  of 
eggs  an  iron-containing  nuclein  which  he  calls  hcematogen,  because  in  the 
developing  hen's  egg  it  is  the  only  source  from  which  the  iron  required 
for  the  production  of  haemoglobin  can  be  obtained.  It  is  possible  that  sim- 
ilar compounds  occur  in  other  articles  of  food.  Most  of  the  iron  taken  with 
food,  however,  including  that  present  in  the  haemoglobin  of  meats,  passes 
out  in  the  feces  unabsorbed.  It  is  probable  that  there  is  an  actual  excre- 
tion of  iron  from  the  body,  and,  so  far  as  known,  this  excretion  is  effected 
in  small  part  through  the  urine,  but  mainly  through  the  walls  of  the  intes- 
tine, the  iron  being  eliminated  finally  in  the  feces.  The  large  proportion  of 
calcium  salts  found  in  the  skeleton  implies  a  special  need  of  these  salts  in 


296  AN  AMERICAN   TEXT- BOOK    OF  PHYSIOLOGY. 

the  food,  particularly  in  that  of"  the  young.  It  has  been  shown  that  if"  young 
dogs  are  fed  upon  a  diet  poor  in  Ca  salts,  the  bones  f"ail  to  develop  properly, 
and  a  condition  similar  to  rieUets  in  children  becomes  a})parent.  In  addition 
to  their  relations  to  bonc-iormation  and  the  fact  that  they  form  a  normal  con- 
stituent of  the  tissues  and  liquids  of  the  body,  calcium  salts  are  necessary  to 
the  coagulation  of  blood  (see  p.  355),  and,  moreover,  they  seem  to  be  connected 
in  some  intimate  way  with  the  rhythmic  contractility  of  heart-muscle,  and, 
indeed,  with  the  normal  activity  of  protoplasm  in  general,  animal  as  well  as 
plant.  Notwithstanding  the  special  importance  of  calcium  in  the  body,  no 
great  amount  of  it  seems  to  be  normally  absorbed  or  excreted.  Voit  has 
shown  that  the  calcium  eliminated  from  the  body  is  excreted  mainly  througli 
the  intestinal  walls,  but  that  most  of  the  Ca  in  the  feces  is  the  unabsorbed  Ca 
of  the  food.  It  is  possible  that  the  Ca  must  be  present  in  some  special  com- 
bination in  order  to  be  absorbed  and  utilized  in  the  body.  A  point  of  special 
interest  in  connection  with  the  nutritive  value  of  the  inorganic  salts  was  brought 
out  by  Bunge  in  some  analyses  of  the  body-ash  of  sucking  animals  in  compar- 
ison with  analyses  of  the  milk  and  the  blood  of  the  mother.  In  the  case  of  the 
dog  he  obtained  the  following  results  (mineral  constituents  in  100  parts  of  ash) : 

Young  Pup.  Dog's  Milk.  Dog's  Serum. 

K,0 8.5  10.7  2.4 

Na.,0 8.2  6.1  52.1 

CaO 35.8  34.4  2.1 

MgO 1.6  1.5  0.5 

FA 0.34  0.14  0.12 

P.,05 39.8  37.5  5.9 

CI 7.3  12.4  47.6 

The  remarkable  quantitative  resemblance  between  the  ash  of  milk  and  the 
ash  of  the  body  of  the  young  indicates  that  the  inorganic  constituents  of  milk 
are  especially  adapted  to  the  needs  of  the  young;  while  the  equally  striking 
difference  between  the  ash  of  milk  and  the  ash  of  the  maternal  blood  seems  to 
show  that  the  inorganic  salts  of  milk  are  formed  from  the  blood-serum  not 
simply  by  osmosis,  but  rather  by  some  selective  secretory  act.  These  facts 
come  out  most  markedly  in  connection  with  the  CaO  and  the  P2O5.  For 
further  details  as  to  the  history  of  calcium  and  iron  in  the  body,  consult  the 
section  on  Chemistry  of  the  Body,  under  calcium  and  iron. 

I.  Accessory  Articles  of  Diet  ;  Variations  of  Body-metabolism 

UNDER  Different  Conditions  ;   Potential  Energy  of  Food  ; 

Dietetics. 

Accessory  Articles  of  Diet. — By  accessory  articles  of  diet  we  mean  those 

substances  which  are  taken  with  foml,  not  for  the  purpo.se  of  replacing  ti.-^sue  or 

yielding  energy,  but  to  add  to  the  enjoyment  of  eating,  to  stinmlate  the  appetite, 

to  aid  in  digestion  and  absorption,  or  for  some  other  subsidiary  purpose.    They 

include  such  things  ils  the  condiments  (mustard,  pepper,  etc.),  the  flavoi-s,  and 

the  stimulants  (alcohol,  coffee,  tea,  chocolate,  beef-extracts).     They  all  possess, 

undoubtedly,  a  positive  nutritive  or  digestive  value  beyond  contributing  to  the 


CHEMISTRY    OF  DIGESTION  AND    NUTRITION  207 

mere  pleasures  ol"  tlie  palate,  but  their  iin})ortauce  is  of  a  subordinate  character. 
They  may  be  omitted  from  the  diet,  as  happens  or  may  happen  in  the  case  of 
animals,  without  affecting  injuriously  the  nutrition  of  the  Ixxly,  although  it  is 
probable  that  neither  man  nor  the  lower  animals  would  voluntarily  eat  Ibod 
entirely  devoid  of  flavor. 

Stiiimlants. — The  well-known  stimulating  effect  of  alcohol,  tea,  coffee,  etc. 
is  probablv  due  to  a  specific  action  on  the  nervous  system  whereby  the  irri- 
tabilitv  of  the  tissue  is  increased.     The  physiological  effect  of  tea,  coffee,  and 
chocolate  is  due  to  the  alkaloids  caffein  (trimethyl-xanthin)  and  theobromin 
(dimethyl-xanthin).      In    small    doses  these   substances  are  oxidized    in   the 
body  and  yield  a  corresponding  amount  of  energy,  but  their  value  from  this 
standpoint  is  altogether  unimj)ortant  compared  with  their  action  as  .stimulants. 
Alcohol  also,  when  not  taken  in  too  large  quantities,  may  be  oxidized  in  the 
bodv  and  furnish  a  not  inconsiderable  amount  of  energy.     It  is,  however,  a 
matter  of  controversy  at  present  whether  alcohol  in  small  doses  can  be  con- 
sidered a  true  food-stuff,  capable  of  serving  as  a  direct  source  of  energy  and  of 
replacing  a  corresponding  amount  of  fats  or  of  carbohydrates  in  the  daily  diet. 
The  evidence  is  parti  v  for  and  partly  against  such  a  use  of  alcohol.    For  examj^le, 
Reichert^  finds  that  moderate  doses  of  alcohol  given  to  a  dog  do  not  affect  the 
heat-production  of  the  body  as  measured  by  a  calorimeter.     Since  the  alcohol 
is  completely  or  nearly  completely  oxidized  in  the  body  and  gives  off  consider- 
able heat  in  the  process,  the  fact  that  the  total  heat-production  remains  unal- 
tered indicates  that  the  oxidation  of  the  alcohol  protects  an  isodynamic  amount 
of  proteid  or  nou-proteid  material  in  the  body  from  consumption,  thus  actiiig 
as  a  food-stuff  capable  of  replacing  other  elements  of  the  food.     On  the  con- 
trary, Miura^  has  arrived  at  exactly  opposite  results  in  a  series  of  experiments 
made  by  another  method.     In  these  experiments  Miura  brought  himself  into 
a  condition  of  nitrogen  equilibrium  upon  a  mixed  diet.     Then  for  a  certain 
period  a  portion  of  the  carbohydrates  was  omitted  from  the  diet  and  its  place 
substituted  by  an  isodynamic  amount  of  alcohol.     The  result  was  a  loss  of 
proteid  from  the  body,  showing  that  the  alcohol  had  not  protected  the  proteid 
tissue  as  it  should  have  done  if  it  acts  as  a  food.     In  a  third  period  the  old 
diet  was  resumed,  and  after  nitrogen  equilil^rium  had  again  been  established  the 
same  proportion  of  carbohydrate  was  omitted  from  the  diet,  but  alcohol  was 
not  substituted.    When  the  diet  was  poor  in  proteid,  it  was  found  that  less  pro- 
teid was  lost  from  the  body  when  the  alcohol  was  omitted  than  when  it  was  used, 
indicating  that,  so  far  from  protecting  the  tissues  of  the  body  by  its  oxidation, 
the  alcohol  exercised  a  directly  injurious   effect   upon  proteid-consumption. 
Numerous  other  researches  might  be  quoted  to  show  that  the  effect  of  moderate 
quantities  of  alcohol  upon  body-metabolism  is  not  yet  satisfactorily  understood. 
Before  making  any  positive  statements  as  to  the  details  of  its  action  it  is  wise, 
therefore,  to  wait  until  reliable  experimental  results  have  accumulated.     The 
specific  action  of  alcohol  on  the  heart,  stomach,  and  other  organs  has  been  inves- 
tigated more  or  less  completely,  but  the  literature  is  too  great  and  the  results  are 
1  Therapeutic  Gazette,  1890.  ^  ZeUschrifl  f.  Min.  Medicin,  1892,  vol.  xx.  p.  137. 


298  .l.V   AMEBIC  AX   TEXT-BOOK   OF  PHYSIOLOGY. 

too  uncertain  to  permit  any  rfeum6  to  be  given  here.  When  alcohol  is  taken 
in  excess  it  produces  the  familiar  svmptoms  of  intoxication,  which  may  pass 
subsequently  into  a  condition  of  stupor  or  even  death,  ])rovided  the  quantity 
taken  is  siitlicieurly  great.  So,  also,  the  long-continued  use  of  alcohol  in  large 
quantities  is  known  to  produce  serious  lesions  of  the  stomach,  liver,  nerves,  blood- 
vessels, and  other  organs.  The  effect  of  alcohol  upon  the  Ixxlv  evidently  varies 
greatly  with  the  quantity  used.  It  may  perhaps  be  said  with  safety  that  in  small 
quantities  it  is  beneficial,  or  at  least  not  injurious,  barring  the  danger  of  acquiring 
an  alcohol  habit,  while  in  large  quantities  it  is  directly  injurious  to  various  ti.ssues. 

Condimotts  and  Flavors. — These  substances  probably  have  a  directly  bene- 
ficial effect  on  the  processes  of  digestion  by  promoting  the  secretion  of  saliva, 
gastric  juice,  etc.,  in  addition  to  the  important  fact  that  they  increase  the  pal- 
atableness  of  foo<l,  and  hence  increase  the  desire  for  food.  With  reference  to 
the  condiments,  Brandl  has  shown,  in  the  paper  referred  to  on  p.  252,  that  mus- 
tard and  pepjjer  also  markedly  increase  the  absorption  of  soluble  products  from 
the  stomaeli. 

Conditions  Influencing-  Body -metabolism. — In  considering  the  influence 
of  the  various  food-stuffs  upon  body-metabolism  we  have  for  the  most  part 
neglected  to  mention  the  effect  of  changes  in  the  condition  of  the  body.  It 
goes  without  saying  that  such  things  as  muscular  work,  sleep,  variations  in 
temperature,  etc.  have  or  might  have  an  important  effect  upon  the  character 
and  amount  of  the  chemical  changes  going  on  in  the  body,  and  in  conse- 
quence a  great  many  elaborate  investigations  have  been  made  to  ascertain  pre- 
cisely the  effect  of  conditions  such  as  those  mentioned  upon  the  amount  of 
the  excretions,  the  production  of  heat  in  the  body,  and  other  similar  points 
which  throw  light  upon  the  nature  of  the  metabolic  processes. 

Effect  of  Muscular  Work. — It  is  a  matter  of  common  knowledge  that  mus- 
cular work  increases  the  amount  of  food  consumed,  and  therefore  the  total 
body-metabolism,  but  it  has  been  a  point  in  controversy  whether  the  increased 
oxidations  affect  the  proteid  or  the  non-proteid  material.  According  to  Liebig, 
the  source  of  the  energy  of  muscular  work  lies  in  the  metabolism  of  the  proteid 
constituents,  and  with  increased  muscular  work  there  should  be  increased  de- 
struction of  proteid  and  an  increase  in  the  nitrogenous  excretions.  That  the 
total  energy  of  muscular  work  is  not  derived  from  the  oxidation  or  metabolism 
of  proteid  alone  was  clearly  demonstrated  by  the  famous  experiment  of  Fick 
and  Wislicenus.  These  physiologists  ascended  the  Faulhorn  to  a  height  of 
1956  meters.  Knowing  the  weight  of  his  body,  each  could  estimate  how  much 
work  was  done  in  ascending  such  a  height.  Fick's  weight,  for  example,  was 
66  kilograms,  therefore  in  climbing  the  mountain  he  performetl  66  X  1956  = 
129,096  kilogrammetei-s  of  work.  In  addition,  the  work  of  the  heart  and  the 
respiratory  muscles,  which  could  not  be  determined  accurately,  was  estimated 
at  30,000  kilogrammeters.  There  was,  moreover,  a  certain  amount  of  muscular 
work  performed  in  the  movements  of  the  arms  and  in  walking  upon  level 
ground  that  was  omitted  entirely  from  their  calculations.  For  seventeen  hours 
before  the  ascent,  during  the  climb  of  eight  hours,  and  for  six  hours  afterward 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  299 

their  food  was  entirely  non-nitrogenous,  so  that  the  urea  eliminated  came 
entirely  from  the  proteid  of  the  body.  Nevertheless,  when  the  urine  was 
collected  and  the  urea  estimated  it  was  found  that  the  potential  energy  c(jntained 
in  the  proteid  destroyed  was  entirely  insufiicient  to  account  for  the  work  done. 
Although  later  estimates  would  modify  somewhat  the  actual  figures  of  their 
calcnlation,  the  margin  was  so  great  that  the  experiment  has  been  accepted  as 
showing  conclusively  that  the  total  energy  of  muscular  work  does  not  come 
from  the  oxidation  of  proteid  alone.  Later  experiments  made  by  Voit  upon 
a  dog  working  in  a  tread-wheel  and  upon  a  man  performing  work  while  in  the 
respiratory  chamber  (p.  283)  gave  the  surprising  result  that  not  only  may  the 
energy  of  nuiscular  work  be  far  greater  than  the  potential  energy  of  the  proteid 
simultaneously  oxidized,  but  that  the  performance  of  muscular  work  within 
certain  limits  does  not  affect  at  all  the  amount  of  proteid  metabolized  in  the 
body,  since  the  output  of  urea  is  the  same  on  working-days  as  during  days  of 
rest.  Careful  experiments  by  an  English  physiologist,  Parkes,  made  upon 
soldiers  while  resting  and  after  performing  long  marches  showed  also  that 
there  is  no  distinct  increase  in  tlie  excretion  of  urea  after  muscular  exercise. 
It  follows  from  these  experiments  that  Liebig's  theory  as  to  the  source  of  the 
energy  of  muscular  work  is  incorrect,  and  that  the  increase  in  the  oxidations 
in  the  body  which  inidoubtedly  occurs  during  nmscular  activity  must  atfect 
only  the  non-proteid  material,  that  is,  the  fats  and  carbohydrates.  Quite 
recently  the  question  has  been  reopened  by  experiments  made  under  Pfliiger 
by  Argutinsky.^  In  these  experiments  the  total  nitrogen  excreted  was  deter- 
mined with  especial  care  in  the  sweat  as  well  as  in  the  urine  and  the  feces. 
The  muscular  work  done  consisted  in  long  walks  and  mountain-climbs. 
Argutinsky  found  that  w^ork  caused  a  marked  increase  in  the  elimination  of 
nitrogen,  the  increase  extending  over  a  period  of  three  days,  and  he  estimated 
that  the  additional  proteid  metabolized  in  consequence  of  the  work  was  suf- 
ficient to  account  for  most  of  the  energy  expended  in  performing  the  walks 
and  climbs.  A  number  of  objections  have  been  made  to  Argutinsky's  work. 
It  has  been  asserted  that  during  his  experiment  he  kept  himself  upon  a 
diet  deficient  in  non-proteid  material ;  that  if  the  supply  of  this  material  had 
been  sufficient,  none  of  the  additional  proteid  would  have  been  oxidized.  It 
must  be  admitted,  however,  that  the  experiments  of  Argutinsky  compel  us  to 
state  the  proposition  above  as  to  the  relation  between  muscular  work  and 
proteid  metabolism  in  a  more  careful  way.  It  is  necessary  to  modify  the 
statement  generally  made  to  the  extent  of  saying  that  muscular  work  causes 
no  increase  in  proteid  metabolism,  provided  the  supply  of  food  is  abundant. 
If  now  we  compare  the  amounts  of  CO2  eliminated  during  work  and  during 
rest,  it  will  be  found  that  there  is  a  very  decided  increase  during  work.  In  the 
experiments  made  by  Pettenkofer  and  Voit  the  CO2  given  off  by  a  man 
during  a  day  of  muscular  work  was  nearly  double  that  eliminated  during  a 
resting-day.  Indeed,  the  same  fact  has  been  observed  repeatedly  upon  isolated 
muscles  made  to  contract  by  artificial  stimuli.     Assuming,  then,  that  muscular 

'  Pfliiger' s  A  rchiv  fixr  die  gesammie  Physiologie,  1890,  vol.  46,  p.  552. 


300  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

work  causes  no  increase  in  the  nitrogen  excreted,  hut  a  marked  increase  in  the 
CO2  eliminated,  we  are  justified  in  saying  that  the  energy  of  muscuhn-  work 
under  normal  conditions  comes  mainly,  if  not  exclusively,  from  tlie  oxidation 
of  non-proteid  material.  The  machine  that  does  the  work,  tiie  muscle,  is 
par  excellence  a  proteid  tissue,  but  the  normal  resting  metabolism  of  its  pro- 
teid  substance  is  not  increased  by  the  chemical  changes  of  contraction.  Or, 
to  j)ut  it  in  another  way,  the  chemical  changes  wdiich  give  rise  to  the  energy 
liberated  in  contraction  involve  only  the  non-proteid  material.  It  is  interest- 
ing to  remember  in  this  connection  that  the  consumption  of  glycogen,  or  of 
the  sugar  derived  from  it,  is  intimately  connected  with  muscular  work.  The 
glycogen  of  the  body  in  an  animal  deprived  of  food  disappears  much  more 
rapidly  if  the  animal  is  made  to  work  his  muscles  than  if  he  remains  at 
rest.  In  an  exi)eriment  by  Kiilz  upon  well-fed  dogs  it  was  found  that  the 
glycogen  was  practically  all  used  up  in  a  single  fasting-day  during  which  the 
animals  did  a  great  deal  of  work.  Morat  and  Dufourt  have  shown  also  that 
a  muscle  after  prolonged  contraction  takes  much  more  sugar  from  the  blood  than 
it  did  previous  to  the  contraction,  and  Ilarley  ^  finds  that  power  to  perform 
muscular  work  may  be  increased  and  susceptibility  to  fatigue  be  diminished 
by  eating  sugar  in  quantities.  It  is,  in  fact,  generally  agreed  that  glycogen  is 
used  up  in  muscle-contractions,  but  the  way  in  w'hich  the  destruction  of  the 
glycogen  is  effected  is  not  definitely  known.  After  the  glycogen  has  been  con- 
sumed it  is  probable  that  the  other  constituents  of  the  body,  the  fats  and  the 
proteids,  are  called  upon  to  furnish  the  necessary  energy.  For  this  reason 
we  should  expect,  in  a  person  performing  excessive  muscular  work,  that  there 
would  be  an  increased  destruction  of  proteid  when  the  supply  of  non-proteid 
food  is  insufficient. 

Metabolism  during  Sleep. — It  has  been  shown  that  during  sleep  there  is  no 
marked  diminution  of  the  nitrogen  excreted,  and  therefore  no  distinct  decrease 
in  the  proteid  metabolism;  on  the  contrary,  the  COg  eliminated  and  the 
oxygen  absorbed  are  unquestionably  diminished.  This  latter  fact  finds  its 
simplest  explanation  in  the  supposition  that  the  muscles  are  less  active  during 
sleep.  The  muscles  do  less  work  in  the  way  of  contractions,  and,  in  addition, 
probably  suffer  a  diminution  in  tonicity  which  also  affects  their  total  metab- 
olism. 

Effect  of  Variations  in  Temperature. — In  w^arm-blooded  animals  variations 
of  outside  temperature  Within  ordinary  limits  do  not  affect  the  body-tem- 
perature. A  full  account  of  the  means  by  which  this  regulation  is  effected 
will  be  found  in  the  section  upon  Animal  Heat.  So  long  as  the  temper- 
ature of  the  body  remains  constant,  it  has  been  found  that  a  fall  of  outside 
temperature  increases  the  oxidation  of  non-proteid  material  in  the  body,  the 
increase  being  in  a  general  way  proportional  to  the  fall  in  temperature.  That 
the  increased  oxidation  affects  the  non-proteid  constituents  is  shown  by  the 
fact  that  the  urea  remains  unchanged  in  quantity,  other  conditions  being  the 
same,  while  the  oxygen-consumption  and  the  COg-elimination  are  increased.  A 
*  Journal  of  Physiology,  1894,  vol.  xvi.  p.  97. 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  301 

rise  of  outside  temperature  has  naturally  tlie  opposite  effect :  oxygen-consump- 
tion and  COa-elimination  are  diminished.  This  effect  of  temperature  upon 
the  body-metabolism  is  due  mainly  to  a  reflex  stimulation  of  the  motor  nerv^es 
to  the  musc^les.  The  temperature-nerves  of  the  skin  are  affected  by  the  rise 
or  fall  in  outside  temperature,  and  bring  about  reflexly  an  increased  or  a  dimin- 
ished innervation  of  the  muscles  of  the  body.  The  fact  that  variations  in 
outside  temperature  affect  only  the  consumption  of  non-proteid  material  falls 
in,  therefore,  with  the  conception  of  the  nature  of  the  metabolism  of  muscle  in 
activity,  given  above.  When  the  means  of  regulating  the  body-temperature 
break  down  from  too  long  an  exposure  to  excessively  low  or  excessively  high 
temperatures,  the  total  body-metabolism,  proteid  as  well  as  non-proteid,  in- 
creases with  a  rise  in  body-temperature  and  decreases  with  a  fall  in  temperature. 
In  fevers  arising  from  pathological  causes  it  has  been  shown  that  there  is  also 
an  increased  production  of  urea  as  well  as  of  COg. 

Effect  of  Starvation. — A  starving  animal  must  live  upon  the  material  pres- 
ent in  its  body.  This  material  consists  of  the  fat  stored  up,  the  circulating 
and  tissue  proteid,  and  the  glycogen.  The  latter,  which  is  present  in  compara- 
tively small  quantities,  is  quickly  used,  disappearing  more  or  less  rapidly 
according  to  the  extent  of  muscular  movements  made,  although  in  any  case  it 
practically  vanishes  in  a  few  days.  Thereafter  the  animal  lives  on  its  own 
proteid  and  fat,  and  if  the  starvation  is  continued  to  a  fatal  termination  the 
body  becomes  correspondingly  emaciated.  Examination  of  the  several  tissues 
in  animals  starved  to  death  has  brought  out  some  interesting  facts.  Voit  took 
two  cats  of  nearly  equal  weight,  fed  them  equally  for  ten  days,  and  then  killed 
one  to  serve  as  a  standard  of  comparison  and  starved  the  other  for  thirteen 
days:  the  latter  animal  lost  1017  grams  in  weight,  and  the  loss  was  divided  as 
follows  among  the  different  organs : 

Actual  loss  Loss  to  each  100  grams 

(in  fresh  organ).  (fresh  organ). 

Bone 55  grams.  14  grams. 

Muscle 429      "  31       " 

Liver 49       "  54      " 

Kidney 7       "  26      " 

Spleen 6       "  .  67       " 

Pancreas 1       "  17       " 

Testis 1       "  40      " 

Lung 3       "  18       " 

Heart 0       "  3       " 

Intestine 21       "  18       " 

Brain  and  cord 1       "  3       " 

Skin  and  hair 89       "  21       " 

Fat 267       '•  97       " 

Blood 37      "  27       " 

According  to  these  results,  the  greatest  absolute  loss  was  in  the  muscles  (429 
grams),  while  the  greatest  percentage  loss  was  in  the  fat  (97  per  cent.),  which 
had  practically  disappeared  from  the  body.  It  is  very  significant  that  the 
central  nervous  system  and  the  heart,  organs  which  we  may  suppose  were  in 
continual  activity,  suffered  no  loss  of  weight:  they  had  lived  at  the  expense  of 


302  A^"  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

the  other  tis^sues.  We  must  suppase  that  in  a  starving  animal  the  fat  and  the 
proteid  material,  particularly  that  of  the  voluntary  muscles,  pass  into  solution 
in  the  blood,  and  are  then  used  to  nourish  the  tissues  generally  and  to  supply 
the  heat  necessary  to  nuiintain  the  body-temperature.  Examination  of  the 
excreta  in  starving  animals  has  shown  that  a  greater  quantity  of  pnjteid  is 
destroyed  during  the  first  day  or  two  than  in  the  subsequent  days.  This  fact 
is  explained  on  the  supposition  that  the  body  is  at  first  richly  supplied  with 
"circulating  proteid"  derived  from  its  previous  food,  and  that  after  this  is 
metabolized  the  animal  lives  entirely,  so  far  as  proteid-consiimption  is  concerned, 
upon  its  ''  tissue  proteid."  The  general  fact  that  the  lo&s  of  proteid  is  great- 
est during  the  first  one  or  two  days  of  starvation  has  been  confirmed  recently 
upon  men,  in  a  number  of  interesting  experiments  made  upon  professional 
fasters.  For  the  numerous  details  as  to  loss  of  weight,  variations  of  tempera- 
ture, etc.,  carefully  recorded  in  these  latter  experiments,  reference  must  be  made 
to  original  sources.^  It  may  be  added,  in  conclusion,  that  the  fatter  the  body  is 
to  begin  with,  the  longer  will  starvation  be  endured,  and  that  if  water  is  con- 
sumed freely  the  evil  effects  of  starvation,  as  well  as  the  disagreeable  sensations 
of  hunger,  are  very  much  reduced. 

Potential  Energy  of  Food. — The  chemical  changes  occurring  in  the  body 
are  accompanied  by  a  liberation  of  energy  in  different  forms — for  example,  as 
heat,  electricity,  and  mechanical  work.  By  far  the  most  of  this  energy  takes 
the  form,  directly  or  indirectly,  of  heat.  Even  when  the  muscles  are  ajiparently 
at  rest  we  know  that  they  are  undergoing  chemical  changes  which  give  rise  to 
heat.  AVhen  a  muscle  contracts,  the  greater  part  (four-fifths)  of  the  energy 
liberated  by  the  chemical  change  takes  the  form  of  heat;  a  much  smaller 
part  (about  one-fifth  as  a  maximum)  may  perform  mechanical  work,  which 
in  turn,  as  in  the  case  of  the  res})iratory  muscles  and  the  heart,  may  be  con- 
verted to  heat  within  the  body.  Roughly  speaking,  an  adult  man  gives  off 
from  his  body  in  the  course  of  twenty-four  hours  about  2,400,000  calories  of 
heat  (1  calorie  =  the  heat  necessary  to  raise  1  cubic  centimeter  of  water  1°  C). 
This  supply  of  heat  is  derived  from  the  metabolism  or  physiological  oxidation 
of  the  j)roteids,  the  fats,  and  the  carbohydrates  which  we  take  into  the  body  in 
our  food.  By  means  of  the  oxygen  absorbed  through  the  lungs  these  substances 
are  burnt,  with  the  formation  of  COg,  HjO,  and  urea  or  some  similar  nitrog- 
enous waste  product.  In  the  long  run,  then,  the  source  of  body-energy  is  found 
in  the  potential  energy  contained  in  our  food.  Our  energy-yielding  foods — 
proteids,  fats,  and  carbohydrates — are  more  or  less  complex  botlies  which  are 
built  up  originally  by  plant  organisms  with  the  consumption  of  solar  energy ; 
when  they  are  burnt  or  otherwise  destroyed,  with  the  formation  of  simpler 
bodies  (such  as  COg  or  H^O),  the  contained  potential  energy  is  liberated  in  the 
form  of  heat,  and  this  is  what  occurs  in  the  body.  From  the  standpoint  of  the 
law  of  conservation  of  energv  it  is  easv  to  understand  that  the  amount  of 
available  energy  in  any  food-stuff  may  be  determined  by  burning  it  outside  the 
body  and  measuring  the  quantity  of  heat  liberatetl.  If  a  gram  of  sugar  is 
'  Virchow's  Archiv,  vol.  131,  supplement,  1893,  and  Luciani,  Das  Hungern,  1890. 


CHEMISTRY   OF  DIGESTION  AND   NUTRITION.  303 

burut,  it  is  converted  to  COj  and  H2O  and  a  certain  quantity  of  heat  is  liber- 
ated; if  the  same  gram  of  sugar  had  been  taken  into  the  body,  it  would  event- 
ually have  been  reduced  to  the  form  of  COj  and  HgO,  and  the  total  quantity 
of  heat  liberated  would  have  been  the  same  as  in  the  combustion  outside  the 
body,  although  the  destruction  of  the  sugar  in  the  body  may  not  be  a  direct, 
but  an  indirect,  oxidation ;  that  is,  the  oxygen  may  first  be  combined  with  sugar 
and  other  food-stuffs  to  form  a  complex  molecule  which  afterward  dissociates 
into  simpler  compounds  similar  to  those  obtained  by  direct  oxidation,  or  there 
may  be  first  a  dissociation  or  cleavage  followed  by  oxidation  of  the  dissociation 
products.  In  determining  the  total  energy  given  to  the  body  we  need  only 
consider  the  form  in  which  a  substance  enters  the  body  and  the  form  in  which 
it  is  finally  eliminated.  In  the  case  of  proteids  the  combustion  in  the  body  is 
not  so  complete  as  it  is  outside ;  the  final  products  are  CO2,  HgO,  and  urea ; 
the  urea,  however,  still  contains  potential  energy  which  may  be  liberated  by 
combustion,  and  in  determining  the  energy  of  proteid  available  to  the  body, 
that  which  is  lost  in  the  urea  must  be  deducted.  As  a  matter  of  fact,  there  is 
some  evidence  (see  origin  of  urea,  p.  276)  to  show  that  proteid  in  the  body  is 
completely  oxidized  to  CO2,  HgO,  and  NH3;  but,  since  the  NH3  in  this  case 
recoml^ines  with  a  part  of  the  CO2  and  the  HgO  to  form  ammonium  carbamate, 
and  this  in  turn  is  converted  into  urea,  the  additional  energy  liberated  in  the 
first  combustion  is  balanced  by  that  absorbed  in  the  synthetic  production  of  the 
urea.  The  potential  energy  of  the  fats,  carbohydrates,  and  proteids  can  be 
determined  by  combustion  outside  the  body  ;  the  energy  liberated  is  measured 
in  terms  of  heat  by  some  form  of  calorimeter,  and  the  quantity  of  heat  so 
obtained,  expressed  in  calories,  is  known  usually  as  the  "  combustion  equiva- 
lent." To  be  perfectly  accurate,  each  particular  form  of  fat,  proteid,  etc. 
should  be  burnt  and  its  energy  be  determined,  but  usually  average  figures  are 
employed,  as  the  amount  of  heat  given  off  by  the  different  varieties  of  any  one 
food-stuff — proteids,  for  example — does  not  vary  greatly.  According  to  Stoh- 
manu,  1  gram  of  beef  deprived  of  fat  =  5641  calories,  while  1  gram  of  veal 
gives  5663  calories.  For  muscle  extracted  with  water,  Rubner  obtained  the 
following  figures:  1  gram  =  5778  calories.  The  combustion  equivalent  of  urea 
(Rubner)  is  2523  calories.  Since  1  gram  of  proteid  yields  about  one-third  of 
a  gram  of  urea,  we  must  deduct  841  calories  from  the  combustion  equivalent 
of  one  gram  of  proteid  to  get  its  available  energy  to  the  body :  5778  —  841  = 
4937  calories.  The  combustion  equivalents  of  fats  and  carbohydrates,  as  given 
by  Stohmann,  are:  1  gram  of  fat  =9312  calories;  1  gram  of  starch  =  4116 
calories.  Weight  for  weight,  fat  contains  the  most  energy,  and,  as  we  know, 
in  cold  weather  and  in  cold  climates  the  proportion  of  fat  in  the  food  is 
increased.  In  dietetics,  however,  the  use  of  fat  is  limited  by  the  difficulty 
attending  its  digestion  and  absorption  as  compared  with  carbohydrates.  Fats 
and  carbohydrates  have  the  same  general  nutritive  value  to  the  body:  they 
serve  to  supply  energy.  Since  the  amount  of  potential  energy  contained  in 
each  of  these  substances  may  be  determined  accurately  by  means  of  its  com- 
bustion  equivalent,   it  would  seem   probable  that  they  might  be   mutually 


304  AN  AMERICAN   TEXT- BOOK   OF  PHYSIOLOGY. 

interchangeable  in  dietetics  in  the  ratio  of  their  eoniljiistion  equivalents. 
Such,  in  fact,  is  the  case.  The  ratio  of  interchange  is  known  as  the  "  iso- 
dynamic  equivalent,"  and  it  is  given  usually  as  1  :  2,4  or  2.2  ;  that  is,  fats 
may  replace  over  twice  their  weight  of  carbohydrate  in  the  diet.  It  Ibllows 
from  the  general  principles  just  stated  that  if  we  wished  to  know  the  amount 
of  heat  ])r()duced  in  the  body  in  a  given  time,  say  twenty-four  hours,  wc  might 
ascertain  it  in  one  of  two  ways :  In  the  first  place,  the  animal  might  be  })laccd 
in  a  calorimeter  and  the  heat  given  oif  in  twenty-four  hours  be  measured 
directly.  This  method,  which  is  that  of  direct  calorimetry,  is  described  more 
completely  in  tiic  section  treating  of  Animal  Heat.  Secondly,  one  might 
feed  the  animal  upon  a  diet  containing  known  quantities  of  proteid,  fats,  and 
carbohydrates,  and  by  collecting  the  total  N  and  C  excreta  determine  how  much 
of  each  of  these  had  been  destroyed  in  the  body.  Knowing  the  combustion 
equivalent  of  each,  the  total  quantity  of  heat  liberated  in  the  body  could  be 
ascertained.  This  latter  method  is  known  as  indirect  calorimetry.  The  two 
methods,  if  applied  simultaneously  to  the  same  animal,  should  give  identical 
results.  It  is  very  interesting  to  know  that  an  experiment  of  this  character 
has  been  successfully  performed  by  Rubner;^  his  experiments  were  made  with 
the  greatest  accuracy  and  with  careful  attention  to  all  the  possible  sources  of 
error,  and  it  was  found  that  the  quantities  of  heat  as  determined  by  the  two 
methods  agreed  to  within  less  than  0.5  per  cent.  These  experiments  are  note- 
worthy because  they  furnish  us  with  the  first  successful  experimental  demon- 
stration of  the  accuracy  of  the  general  principles,  stated  above,  upon  which 
the  available  energy  of  foods  is  calculated. 

Dietetics. — The  subject  of  the  ])roper  nourishment  of  individuals  or  col- 
lections of  individuals — armies,  inmates  of  hospitals,  asylums,  prisons,  etc. — 
is  treated  usually  in  books  upon  hygiene,  to  which  the  reader  is  referred  for 
practical  details.  The  general  principles  of  dieting  have  been  obtained,  how- 
ever, from  experimental  work  upon  the  nutrition  of  animals.  These  princij)les 
have  been  stated  more  or  less  completely  in  the  foregoing  pages,  but  some 
additional  facts  of  importance  may  be  referred  to  conveniently  at  this  point. 
In  a  healthy  adult  who  has  attained  his  maximum  weight  and  size  the  main 
object  of  a  diet  is  to  furnish  sufficient  nitrogenous  and  non-nitrogenous  food- 
stuffs, together  with  salts  and  water,  to  maintain  the  body  in  equilibrium — 
that  is,  to  prevent  loss  of  proteid  tissue,  fat,  etc.  In  si)eaking  of  the  nutritive 
value  of  the  food-stuffs  it  was  shown  that  in  carnivora  (dogs)  this  condition 
of  equilibrium  may  be  maintained  upon  proteid  food  alone,  putting  aside  all 
consideration  of  salts  and  water,  or  upon  proteids  and  fats,  or  ui)on  ])roteids  and 
carbohydrates,  or  upon  proteids,  fats,  and  ciirbohyd rates.  AVhcn  proteids  alone 
are  used,  the  quantity  must  be  increased  far  above  that  necessary  in  the  case  of 
a  mixed  diet,  and  it  is  doubtful  whether,  in  the  case  of  man  or  the  herbivora, 
a  healthy  nutritive  condition  could  be  maintained  long  upon  such  a  diet,  owing 
to  the  largely  increased  demand  upon  the  power  of  the  alimentary  canal  to 
digest  and  absorb  proteids,  to  the  greater  labor  thrown  on  the  kidneys,  etc. 
^  Zeitsckrift  fur  Biologic,  1893,  vol.  xxx.  p.  73. 


CHEMISTRY   OF   DIGESTION  AND    NUTRITION. 


305 


The  experience  of  iiKiiikiiid,  as  well  a.s  the  results  of  experimental  investiga- 
tion, shows  that  the  healthy  diet  is  one  composed  of  proteids,  fats,  and  carbo- 
hydrates. The  pr()])ortion  in  which  the  fats  and  the  carbohydrates  should  be 
taken — and,  to  a  certain  extent,  this  is  true  also  of  the  proteids — may  be 
varied  within  comparatively  wide  limits,  in  accordance  with  the  law  of  "  iso- 
dynamic  equivalents."  This  is  illustrated  by  the  following  "average  diets" 
calculated  by  diifevent  physiologists  to  indicate  the  average  amount  of  food- 
stuffs required  by  an  adult  man  under  normal  conditions  of  life : 

Average  Diets. 


Moleschott. 

Ranke. 

Voit. 

Forster. 

Atwater. 

Proteid 130  grams. 

Fats 40     " 

Carbohydrates    ....      550      " 

100  grams. 
100     " 
240     " 

118  grams. 
56      " 
500     " 

131  grams. 
68      " 
494     " 

125  grams. 
125      " 
400      " 

In  Voit's  diet,  which  is  the  one  usually  taken  to  represent  the  daily  needs 
of  the  body,  it  will  be  noticed  that  the  ratio  of  the  nitrogenous  to  the  non- 
nitrogenous  food-stuffs  is  about  as  1:5.  It  must  be  remembered,  in  regard  to 
these  diets,  that  the  amounts  of  food-stuffs  given  refer  to  the  dry  material :  118 
grams  of  proteid  do  not  mean  118  grams  of  lean  meat,  for  example,  since 
lean  meat  (flesh)  contains  a  large  proportion  of  water.  Tables  of  analyses  of 
food  (one  of  which  is  given  on  page  216)  enable  us  to  determine  for  each  par- 
ticular article  of  food  the  proportion  of  dry  food-stuffs  contained  in  it,  and  in  how 
great  quantities  it  must  be  taken  to  furnish  the  requisite  amount  of  proteid, 
fats,  or  carbohydrates.  There  is.  however,  still  another  practical  consideration 
which  must  be  taken  into  account  in  estimating  the  nutritive  value  of  articles 
of  food  from  the  analyses  of  their  composition,  and  that  is  the  extent  to  which 
each  food-stuff  in  each  article  of  food  is  capable  of  being  digested  and  absorbed. 
Practical  experience  has  shown  that  proteids  in  certain  articles  of  food  can  be 
digested  and  absorbed  nearly  completely  when  not  fed  in  excess,  while  in  other 
foods  only  a  certain  percentage  of  the  proteid  is  absorbed  under  the  most  favor- 
able conditions.  This  difference  in  usableness  of  the  food-stuffs  in  various 
foods  is  most  marked  in  the  case  of  proteids,  but  it  occurs  also  with  the  fats 
and  the  carbohydrates.  Facts  of  this  kind  cannot  be  determined  by  mere 
analysis  of  the  foods;  they  must  be  obtained  from  actual  feeding  experiments 
ujion  man  or  the  lower  animals.  In  general,  it  may  be  said  that  in  meats  from 
2  to  3  per  cent.,  in  milk  from  6  to  12  per  cent.,  and  in  vegetables  from  10  to 
40  per  cent,  of  the  proteid  escapes  absorption.  The  greater  value  of  the  meats, 
then,  as  a  source  of  proteid  supply  consists  not  only  in  the  greater  average  per- 
centage of  proteid  contained  in  them  as  compared  with  the  vegetables,  but  also 
in  the  fact  that  their  proteid  is  more  completely  absorbed  from  the  alimentary 
canal,  less  being  lost  in  the  feces.  Munk  ^  gives  an  interesting  table  showing 
how^  much  of  certain  familiar  articles  of  food  would  be  necessary,  if  taken 
alone,  to  supply  the  requisite  daily  amount  of  proteid  or  non-proteid  food ;  his 
'  Weyl's  Handbuch  der  Hygiene,  1893,  vol.  iii.,  part  i.  p.  69. 
20 


306 


AX  AMERICAN    TEXT-BOOK    OF    PHYSIOLOGY. 


estimates  are  based  upon  the  percentage  composition  of  the  foods  and  upon 
experimental  data  showing  tlie  extent  of  absorption  of  the  food-stiiflfs  in  each 
food.  In  this  table  ho  sup})oses  that  the  (hiily  diet  should  contain  110  grams 
proteid  =  17.5  grams  of  N,  and  non-proteids  sufficient  to  contain  270  grams 
of  C: 


For  110  prams  proteid 
(17..')  grams  N). 

For  270  prams  C. 

Milk 

2900  grams. 

540       " 
18  eggs. 

800  grams. 
1650       " 
1900       " 
1870       " 

990       " 

520       " 
4500       " 

3800  grams. 
2000       " 
37  eggs. 

670  grams. 
1000        " 
1100        " 

750        " 

660 

750       " 
2550       " 

Meat  (lean) 

Hen's  eggs 

Wlieat  flour 

AVlieat  bread 

Kve  bread 

Kice 

Corn 

Peas 

Potatoes 

As  Munk  points  out,  this  table  shows  tliat  any  single  food,  if  taken  in  quantities 
sufficient  to  supply  the  nitrogen,  would  give  too  much  or  too  little  C,  and  the  re- 
verse; those  animal  foods  which,  in  certain  amounts,  supply  the  nitrogen  needed 
furnish  only  from  one-quarter  to  two-thirds  of  the  necessary  amount  of  C.  To 
live  for  a  stated  period  upon  a  single  article  of  food — a  diet  sometimes  recom- 
mended to  reduce  obesity — means,  then,  an  insufficient  quantity  of  cither  N 
or  C  and  a  consequent  loss  of  body-weight.  Such  a  method  of  dieting  amounts 
practically  to  a  partial  starvation.  In  practical  dieting  we  are  accustomed  to 
get  our  supply  of  })roteids,  fats,  and  carbohydrates  from  both  vegetable  and 
animal  foods.  To  illustrate  this  fact  by  an  actual  case,  in  which  the  food  was 
carefully  analyzed,  an  experimenter  (Krummacher)  weighing  67  kilograms 
records  that  he  kept  himself  in  N  equilibrium  upon  a  diet  in  which  the  pro- 
teid was  distributed  as  follows  : 


300  grams  meat 
666.3  c.c.  milk 
100  grams  rice 
100       "       bread 
500  c.c.  wine 


63.08 
18.74 

grams 

proteid 

7.74 

K 

11.. 32 

(( 

1.17 
102.05 

<( 
(( 

9.78   grams  N. 
2.905     " 
1.2         "        " 
1.7.55     " 
0.182     " 


15.868 


For  a  person  in  health  and  leading  an  active  normal  life,  appetite  and  experi- 
ence seem  to  be  .safe  and  sufficient  guides  by  which  to  control  the  diet ;  but  in 
conditions  of  di.sease,  in  regulating  the  diet  of  children  and  of  collections  of 
individuals,  scientific  dieting,  if  one  may  use  the  phrase,  has  accomplished 
much,  and  will  be  of  greater  service  as  our  knowledge  of  the  physiology  of 
nutrition  increases. 


V.  MOVEMENTS  OF  THE  ALIMENTARY  CANAL, 
BLADDER,  AND  URETER. 


Plain  Musclej-tissue. 

The  movements  of  the  alimentary  canal  and  the  organs  concerned  in  mic- 
turition are  effected  for  the  most  part  through  the  agency  of  plain  muscle- 
tissue.  The  general  properties  of  this  tissue  have  been  referred  to  in  the 
section  upon  the  Physiology  of  Muscle  and  Nerve,  but  it  seems  appropriate  in 
this  connection  to  again  call  attention  to  some  points  in  its  general  physiology 
and  histology,  inasmuch  as  the  character  of  the  movements  to  be  described 
depends  so  much  upon  the  fundamental  properties  exhibited  by  this  variety  of 
muscle-tissue.  Plain  muscle  as  it  is  found  in  the  walls  of  the  abdominal  and 
pelvic  viscera  is  composed  of  masses  of  minute  spindle-shaped  cells  whose  size, 
is  said  to  vary  from  22  to  560  fx  in  length  and  from  4  to  22  n  in  width,  the 
average  size,  according  to  Kolliker,  being  100  to  200  jjl  in  length  and  4  to  6  // 
in  width.  Each  cell  has  an  elongated  nucleus,  and  its  cytoplasm  shows  a 
longitudinal  fibrillation.  Cross  striation,  such  as  occurs  in  cardiac  and  striped 
muscle,  is  absent.  These  cells  are  united  into  more  or  less  distinct  bundles  or 
fibres,  which  run  in  a  definite  direction  corresponding  to  the  long  axes  of  the 
cells.  The  bundles  of  cells  are  united  to  form  flat  sheets  of  muscle  of  varying 
thicknesses,  which  constitute  part  of  the  walls  of  the  viscera  and  are  distin- 
guished usually  as  longitudinal  and  circular  muscle-coats  according  as  the  cells 
and  bundles  of  cells  have  a  direction  with  or  at  right  angles  to  the  long  axis 
of  the  viscus.  The  constituent  cells  are  united  to  one  another  by  cement- 
substance,  and  according  to  several  observers^  there  is  a  direct  protoplasmic 
continuity  between  neighboring  cells — an  anatomical  fact  of  interest,  since  it 
makes  possible  the  conduction  of  a  wave  of  contraction  directly  from  one  cell 
to  another.  Plain  muscle-tissue,  in  some  organs  at  least,  e.  g.  the  stomach, 
intestines,  bladder,  and  arteries,  is  under  the  control  of  motor  nerves.  There 
must  be,  therefore,  some  connection  between  the  nerve-fibres  and  the  muscle- 
tissue.  The  nature  of  this  connection  is  not  definitely  established ;  according 
to  Miller  2  the  nerve-fibres  terminate  eventually  in  fine  nerve-fibrils  which  run 
in  the  cement-substance  between  the  cells  and  send  off  small  branches  which 
end  in  a  swelling  applied  directly  to  the  muscle-cell.     Berkley  ^  finds  a  similar 

1  See  Bohenian :  Anatomischer  Anzeifier,  1894,  Bd.  10,  No.  10. 
*  Archiv  fiir  mikroskopische  Anatoviie,  1892,  Bd.  40. 
'  Anatomischer  Anzeiger,  1893,  Bd.  8. 

307 


308 


.l.V   AMERICAN   TEXT- BOOK   OF  PHYSIOLOGY. 


oiuling  of  the  nerves,  and  in  acUlitiun  ckscribes  in  the 
muscuhiris  nuieosaj  of  the  intestine  a  larj^e  globuhir 
end-organ  which  he  considers  as  a  motor  phite. 

Perhaps  the  most  striking  physiological  ])eculiarity 
of  plain  muscle,  as  compared  with  the  more  familiar 
striated   muscle,  is   the   sluggishness  of  its  contrac- 
tions.    Plain  nmscle,  like  striated   muscle,  is  inde- 
j)endently    irritable.       Various    forms    of    artificial 
stimuli,    such    as     electrical    current^,,    mechanical, 
chemical,    and    thermal    stimuli,  may  cause  the  tis- 
sue to  contract  when  directly  applied  to  it,  but  the 
contraction    in    all    cases   is    characterized    by  the 
slowness  with  which  it  develops.     There  is  a  long 
latent  period,  a  gradual  shortening  which  may  per- 
sist for  some  time  after  the  stimulus  ceases  to  act, 
and  a  slow  relaxation.      These  features   are  repre- 
sented in  the  curve  shown  in  Figure  81,  which  it  is 
instructive  to  compare  with  the  typical  curve  of  a 
striated  muscle  (Fig.  34).      The  slowness  of  the  con- 
traction of  plain  muscle  seems  to  depend  upon  the 
absence  of  cross  striation.    Striped  muscle  as  found  in 
various  animals  or  in  different  muscles  of  the  same 
animal — e.  g.  the  pale  and  red  muscles  of  the  rabbit 
— differs  greatly  in  the  rapidity  of  its  contraction, 
and  it  has  been  shown  that  the  more  perfect  the  cross 
striation    the  more  rapid   is   the   contraction.      The 
cross  striation,  in  other  words,  is  the  expression  of  a 
mechanism  or  structure  adapted  to  quick  contractions 
and  relaxations,  and  the  relatively  great  slowness  of 
movement  in  the  plain  muscle  seems  to  result  from 
the  absence  of  this  particular  structure.     It  should  be 
added,  however,  that  plain  muscle  in  different  parts 
of  the  body  exhibits    considerable  variation  in  the 
rapiditv  with  which  it   contracts  under  stimulation, 
the  ciliary  muscle  of  the  eyeball,  for  exami)le,  being 
able  to  react  more  rapidly  than  the  muscles  of  the  in- 
testines.   The  gentle  prolonged  contraction  of  the  plain 
muscle  is  admirably  adapted  to  its  function  in  the 
intestine  of  moving  the  food-contents  along  the  canal 
with  sufficient  slowness  to  permit  normal  digestion 
and  absorption.     Like  the  striated  muscle,  and  un- 
like the  cardiac  muscle,  plain  muscle  is  capable  of 


Fig.  85.— Contraction  of  a  strip  of  plain  muscle  from  the  stomach  of  a  terrapin.  The  bottom  line 
gives  the  time-record  in  seconds ;  the  middle  line  shows  the  time  of  application  of  the  stimulus,  a  tetan- 
izing  current  from  an  induction  coil ;  the  upper  line  is  the  curve  recorded  by  the  contracting  muscle. 


MOVEMI^TS    OF    Till-:   ALTMENTARY   CANAL,    ETC.       309 

giving  subiiuiximal  as  well  as  inaxiinal  contractions;  with  incroased  strength 
of  stimulation  the  amount  of  the  shortening  increases  until  a  raaxinmm  is 
reached.  This  fact  may  be  observed  not  only  upon  isolated  strips  of  muscle 
from  the  stomach,  but  may  be  seen  also  in  the  ditfcreut  degrees  of  contraction 
exhibited  by  the  intestinal  musculature  as  a  whole  when  acted  upon  by  various 
stimuli. 

In  his  researches  upon  the  movements  of  the  ureter  Engelmann '  showed 
that  a  stimulus  ajjplieil  to  the  organ  at  any  point  caused  a  contraction  which 
starting  from  the  [)oint  stinnilated  might  spread  for  some  distance  in  either 
direction.  Engelmann  interprets  this  to  mean  that  the  contraction  wave  in 
the  case  of  the  ureter  is  propagated  directly  from  cell  to  cell,  and  this  possi- 
bility is  suj>ported  by  the  fact,  before  referred  to,  that  there  is  direct  proto- 
plasmic continuity  between  adjoining  cells.  This  passage  of  a  contraction  wave 
from  cell  to  cell  has,  in  fact,  often  been  quoted  as  a  peculiarity  of  plain 
muscle-tissue.  In  the  case  of  the  ureter  the  fact  seems  to  be  established,  but 
in  the  intestines,  where  there  is  a  rich  intrinsic  supply  of  nerve-ganglia,  it 
is  not  possible  to  demonstrate  clearly  that  the  same  property  is  exhibited. 
The  wave  of  contraction  in  the  intestine  following  artificial  stimulation  is, 
according  to  most  observers,  usually  localized  at  the  point  stimulated  or  is 
propagated  in  only  one  direction,  and  these  facts  are  difficult  to  reconcile 
with  the  hypothesis  that  each  cell  may  transmit  its  condition  of  activity 
directly  to  neighboring  cells.  Upon  the  plain  muscle  of  the  ureter  Engel- 
mann was  able  to  show  also  an  interesting  resemblance  to  cardiac  muscle, 
in  the  fact  that  each  contraction  is  followed  by  a  temporary  diminution  in 
irritability  and  conductivity  ;  but  this  important  property,  which  in  the  case  of 
the  heart  has  been  so  useful  in  explaining  the  rhythmic  nature  of  its  contrac- 
tions, has  not  been  demonstrated  for  all  varieties  of  plain  muscle  occurring  in 
the  body. 

A  general  property  of  plain  muscle  which  is  of  great  significance  in  explain- 
ing the  functional  activity  of  this  tissue  is  exhibited  in  the  phenomenon  of 
"  tone."  By  tone  or  tonic  activity  as  applied  to  muscle-tissue  is  meant  a  con- 
dition of  continuous  contraction  or  shortening  which  persists  for  long  periods 
and  may  be  slowly  increased  or  decreased  by  various  conditions  affecting  the 
muscle.  Both  striated  and  cardiac  muscle  exhibit  tone,  and  in  the  latter  at 
least  the  condition  is  independent  of  any  inflow  of  nerve-impulses  from  the 
extrinsic  nerves.  Plain  muscle  exhibits  the  property  in  a  marked  degree.  The 
muscular  coats  of  the  alimentary  canal,  the  blood-vessels,  the  bladder,  etc.,  are 
usually  found  under  normal  circumstances  in  a  condition  of  tone  which  varies 
from  time  to  time  and  differs  from  an  ordinary  visible  contraction  in  the  slow- 
ness with  ^vhich  it  develops  and  in  its  persistence  for  long  jieriods.  Such  con- 
ditions as  the  reaction  of  the  blood,  for  example,  are  known  to  alter  greatly 
the  tone  of  the  blood-vessels,  a  less  alkaline  reaction  than  normal  causing 
relaxation,  while  an  increase  in  alkalinity  favors  the  development  of  tone. 
Tone  may  also  be  increased  or  diminished  by  the  action  of  motor  or  inhibitory 

^  Pfluger's  Archivfiir  die  gesammte  Physiologie,  1869,  Bd.  2,  S.  243. 


310  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

neivo-fibres,  but  the  precise  relationship  between  the  changes  underlying  the 
development  of  tone  and  those  leading  to  the  formation  of  an  ordinary  contrac- 
tion has  not  been  satisfactorily  determined. 

The  mode  of  contraction  of  the  plain  muscle  in  the  walls  of  some  of  the 
viscera,  especially  the  intestine  and  ureter,  is  so  characteristic  as  to  be  given 
the  s})eeial  name  of  pci'istjdsis.  By  peristalsis,  or  vermicular  contra(;tion  as  it 
is  sometimes  called,  is  meant  a  contraction  which,  beginning  at  any  point  in 
the  wall  of  a  tubular  viscus,  is  propagated  along  the  length  of  the  tube  in  the 
form  of  a  wave,  each  part  of  the  tube  as  the  wave  reaches  it  passing  slowly 
into  contraction  until  the  maximum  is  reached,  and  then  gradually  relaxing. 
In  viscera  like  the  intestine,  in  which  two  muscular  coats  are  present,  the 
longitudinal  and  the  circular,  the  })eristalsis  may  involve  both  layers,  either 
simultaneously  or  successively,  but  the  striking  feature  observed  when  M'atching 
the  movement  is  the  contraction  of  the  circular  coat.  The  contraction  of  this 
coat  causes  a  visible  constriction  of  the  tube,  which  may  be  followed  by  the 
eye  as  it  passes  onward. 

Mastication. 

Mastication  is  an  entirely  voluntary  act.  The  articulation  of  the  mandi- 
bles with  the  skull  permits  a  variety  of  movements  ;  the  jaw  may  be  raised 
and  lowered,  may  be  projected  and  retracted,  or  may  be  moved  from  side  to 
side,  or  various  combinations  of  these  diiferent  directions  of  movement  may  be 
effected.  The  muscles  concerned  in  these  movements  and  their  innervation  are 
described  as  follows  :  The  masseter,  temporal  and  internal  pterygoids  raise  the 
jaw ;  these  muscles  are  innervated  through  the  inferior  maxillary  division  of 
the  trigeminal.  The  jaw  is  depressed  mainly  by  the  action  of  the  digastric 
muscle,  assisted  in  some  cases  by  the  mylo-hyoid  and  the  genio-hyoid.  The 
two  former  receive  motor-fibres  from  the  inferior  maxillary  division  of  the 
fifth  cranial,  the  last  from  a  branch  of  the  hypoglossal.  The  lateral  movements 
of  the  jaws  are  produced  by  the  external  pterygoids,  when  acting  separately. 
Simultaneous  contraction  of  these  muscles  on  both  sides  causes  projection  of 
the  lower  jaw.  In  this  latter  case  forcible  retraction  of  the  jaw  is  produced  by 
the  contraction  of  a  part  of  the  temporal  muscle.  The  external  pterygoids 
also  receive  their  motor  fibres  from  the  fifth  cranial  nerve,  through  its  inferior 
maxillary  division.  The  grinding  movements  commonly  used  in  masticating 
the  fot)d  between  i\\Q  molar  teeth  are  produced  by  a  combination  of  the  action 
of  the  external  pterygoids,  the  elevators,  and  perhajxs  the  dci)ressors.  At  the 
same  time  the  movements  of  the  tongue  and  of  the  muscles  of  the  cheeks  and 
lips  serve  to  keep  the  food  properly  placed  for  the  action  of  the  teeth,  and  to 
gather  it  into  position  for  the  act  of  swallowing. 

Deglutition. 

The  act  of  swallowing  is  a  complicated  reflex  movement  w'hich  may  be 
initiated  voluntarily,  but  is  for  the  most  part  completed  quite  independently 


MOVEMENTS   OF   THE  ALIMENTARY  CANAL,   ETC.       311 

of  the  will.     The  classical  dccni.tiou  of  the  act  given  by  Magendie  divides  it 
into  three  sb.ges,  corresponding  to  the  three  anatomical  regions,  the  mouth, 
pharynx  and  oesophagus,  through  which  the  swallowed  n.orsel  pa&ses  on  its 
w-w  to  the  stonuwh.     The  Hrst  stage  consists  i..  the  passage  ol  the  bolus  ot 
food  tlu-ongh  the  istlnnus  of  the  fauces-that  is,  the  opening  lymg  between   he 
ridges  formed  by  the  palato-glossi  mnseles,  the  so-c-allcd  antermr  p.llars  of  the 
fauces    This  part  of  the  act  is  usually  ascribal  to  the  movements  ol  the  tongue 
iiself  '    The  bolus  of  food  lying  "po"  '^  "PI*--  S"''*'"'*  '»  ^'""^  ""™"'  ^^ 
the  elevation  of  the  tongue  against  the  soft  i>alate  from  the  fp  toward  the  ba^ 
This  portion  of  the  movement  n.ay  be  regarded  as  voluntary  to  the  extc.it  at 
least  of  manipulating  the  food  into  its  proper  position  on  the  dorsum  of  the 
tongue,  although  it  is  open  to  doubt  whether  the  entire  movement  is  usually 
effe^tei  bv  a  voluntary  act.     Under  normal  conditions  the  P--->-f' "°  » 
food  upon  the  tongue  seems  essential  to  tlie  complete  execiit.on  of  the  act, 
and  an  attempt  to  make  the  movement  with  very  dry  material  upon   he  tongue 
i      ilr  not  successful  or  is  performed  with  difficulty.     The  second  act  com- 
prises thi  pa.ssage  of  the  bolus  from  the  isthmus  of  the  fauces  to  the  oesophagus 
Hat  is,  its  transit  through  the  pharynx.     The  pharynx  being  a  common 
palge  f  r  the  air  and  the  tbod,  it  is  important  that  this  part  o    the  act  should 
be  consummated  quickly.    According  to  the  usual  description  the  -o tor  po-r 
driving  the  bolus  downward  through  the  pharynx  ,s  derived  from  the  contl ac- 
tion of  the  pharyngeal  muscles,  particularly  the  constrictors,  which  con  ract  from 
Ibove  downward  and  drive  the  food  into  the  oesophagus,      f'""!'--"^^' 
however,  a  number  of  other  muscles  are  brought  into  action  the  general  effee 
of  which  is  to  shut  off  the  nasal  and  laryngeal  openings  and  thus  prevent  the 
entrance  of  food  into  the  corresponding  cavities.    The  whole  reflex  ,s  therefore 
an  excellent  example  of  a  finely  co-ordinated  movement.  _     „  ,     .. 

The  following  events  are  oleseribed:  The  mouth  cavity  is  .shut  off  by  the 
position  of  the  tongue  against  the  .soft  palate  and  by  the  coiitraetion  of  the 
mu  cles  of  the  anterior  pillai-s  of  the  fauces.   The  opening  into  the  nasa  cavity 
"Toil  by  the  elevation  of  the  soft  palate  (action  of  the  evator  palati  and 
tlisor  palad  muscles)  and  the  contraction  of  the  posterior  pdlai.  of  the  fauces 
pa  a  o-pharvngei  muscles)  and  the  elevation  of  the  uvula  (azygos  uvnte  mus- 
Ik       The  soft  palate,  uvula,  and  posterior  pillars  thus  form  a  sloping  surface 
tting Iff  the  Lisal  d.ambe;  and  facilitating  the  passage  of  the  fo<^  b-kwa^_ 
into  the  pharynx  where  the  constrictor  muscles  may  act  upon  it.     The       l«n. 
to  V  opering  into  the  larynx  is  closed  by  the  adduction  ot  the  vocal  cords  (lat- 
en   crico-arvtcnoids  and  constrictors  of  the  glottis)  and  by  the  elevation  of  he 
eiirWni  and  a  depression,  in  part  mechanical,  of  the  ep-g  *.  over    h 
larynx  (action  of  the  thyro-hyoids,  digastrics,  genm-hyoiols,  and  mylo-hyo  ds 
ol  the  muscles  in  the  Lytono-epiglottidean  folds).     The  moyemen^  of  * 
epiglottis  during  this  stage  of  swallowing  liave  been  "'-';; 'J™:;t  IK^of 
usual  view  is  that  it  is  pressed  down  upon  the  '->•"•?-  -f^;^'^;^'^™ 
a  box  and  thus  effectually  protects  the  respiratory  passage.    It  has  b««°  ^''°3' 
however,  that  removal  of  the  epiglottis  does  not  prevent  normal  swallowing, 


312  AN  A3IERICAN  TEXT-BOOK   OF  PHYSIOLOGY. 

and  recently  Stuart  and  McCormick  '  have  reported  the  case  of"  a  man  in  whom 
part  of  the  pharynx  had  been  permanently  removed  by  surgical  o})eration  and 
in  whom  the  epiglottis  could  be  seen  during  the  act  of  swallowing.  In  this 
individual,  according  to  their  observations,  the  epiglottis  was  not  folded  back 
during  swallowing,  but  remained  erect.  Later  observations  by  Kanthack  and 
Anderson,^  made  partly  upon  themselves  and  partly  upon  the  lower  animals, 
tend,  on  the  contrary,  to  support  the  older  view.  They  state  that  in  norma! 
individuals  the  movement  of  the  epiglottis  backward  during  swallowing  ma\ 
be  felt  by  simply  passing  the  finger  back  into  the  pharynx  until  it  comes  into 
contact  with  the  epiglottis.  At  the  beginning  of  the  movement  there  is  also  a 
contraction  of  the  longitudinal  muscles  of  the  pharynx  which  tends  to  pull  the 
})harvngeal  walls  toward  the  bolus  of  food  while,  as  has  been  said,  the  nearly 
simultaneous  contraction  of  the  constrictors  presses  upon  the  food  and  forces 
it  downward.  The  food  is  thus  brought  quickly  into  the  opening  of  the 
oesophagus  and  the  third  stage  commences. 

The  transit  of  the  food  through  the  oesophagus  is  eifected  by  the  action 
of  its  intrinsic  musculature.  The  nniscular  coat  is  arranged  in  two  layers,  an 
external  longitudinal  and  an  internal  circular.  These  are  composed  of  plain 
muscle-tissue  in  the  lower  third  or  two-thirds  of  tiie  oesophagus,  but  in  most 
mammals  tlie  upper  third  or  more  contains  striated  muscular  tissue.  The 
chief  factor  in  the  transportation  of  the  bolus  through  the  oesophagus  has 
been  supposed  to  consist  in  the  contraction  of  the  circular  muscle.  This  con- 
traction begins  at  the  pharyngeal  opening  of  the  oesophagus  and  passes  down- 
ward in  the  form  of  a  wave,  peristaltic  contraction,  which  moves  rapidly  in  the 
upper  segment  where  the  musculature  is  striated,  and  more  slowly  in  the  lower 
segments  in  accordance  with  the  ])hysiological  characteristics  of  plain  muscle. 
The  result  of  this  movement  would  naturally  be  to  force  the  food  onward  to 
the  stomach.  The  longitudinal  muscles  of  the  oesophagus  are  without  doubt 
brought  into  action  at  the  same  time,  but  in  this  as  in  other  cases  of  peristalsis 
in  tubular  viscera  it  is  not  perfectly  clear  how  they  co-operate  in  producing 
the  onward  movement.  It  may  be  that  their  contraction  slightly  ])recedes 
that  of  the  circular  muscle,  and  thus  tends  to  dilate  the  tube  and  to  bring  it 
forward  over  the  bolus.  At  the  opening  of  the  oesophagus  into  the  stomach, 
the  cardiac  orifice,  the  circular  fibres  of  the  oesophagus  function  as  a  sphincter 
which  is  normally  in  a  condition  of  tone,  particularly  when  the  stomach  con- 
tains food,  and  thus  shuts  off  the  cavity  of  the  stomach  from  the  oesophagus. 
In  swallowing,  however,  the  advancing  peristaltic  Avave  has  sufficient  force  to 
overcome  the  tonicity  of  the  sphincter,  and  possibly  there  is  at  this  moment  a 
partial  inhibition  of  the  sphincter.  In  cither  case  the  result  is  that  the  food 
is  forced  through  the  narrow  opening  into  the  stomach  with  sufficient  energy 
to  give  rise  to  a  soinid  which  may  be  heard  by  auscultation  over  this  region.^ 
According  to  measurements  by  Kronecker  and  Meltzer  the  entrance  of  the 

'  Joui-nal  of  Anatomy  and  Physiologi),  1892. 

^Journal  of  Phymolocjy,  1893,  vol.  xiv.  p.  154. 

'  See  Meltzer:  Centralblatt  fur  die  med.  Wisseiwchaften,  1881,  Xo.  1. 


MOVEMENTS   OF   THE  ALIMENTARY  CANAL,    ETC.       313 

food  into  the  stomach  occurs  iu  man  about  six  seconds  after  tlie  beginning  of 
the  act  of  swallowing. 

Kronecker-Meltzer  Theory  of  Deglutition.— The  usual  view  of  the 
mechanism  of  swallowing  has  been  seriously  modified  by  Kronecker  and 
Meltzer.'  The  experiments  of  these  observers  seem  to  be  so  conclusive  that 
we  must  believe  that  in  the  main  their  explanation  of  the  process  is  correct. 
According  to  their  view  the  chief  factor  in  ibrcing  soft  or  liquid  food  through 
the  pharynx  and  oesophagus  is  the  sharp  and  strong  contraction  of  the  mylo- 
liyoid  muscles.  The  bolus  of  food  lies  upon  the  dorsum  of  the  tongue  and 
by  the  pressure  of  the  tip  of  the  tongue  against  the  palate  it  is  shut  off  from 
the  front  part  of  the  mouth-cavity.  The  mylo-hyoids  now  contract,  and  tlie 
bolus  of  food  is  put  under  high  pressure  and  is  shot  in  the  direction  of  least 
resistance — namely,  through  the  pharynx  and  oesophagus.  This  effect  is  aided 
by  the  simultaneous  contractions  of  the  hyoglossi  muscles,  which  tend  to  still 
further  increase  the  pressure  upon  the  food  by  moving  the  tongue  backward 
and  downward.  This  same  movement  of  the  tongue  suffices  also  to  depress 
the  epiglottis  over  the  larynx,  and  thus  protect  the  respiratory  opening.  By 
means  of  small  rubber  bags  connected  with  recording  tambours,  which  were 
placed  in  the  pharynx  and  at  different  levels  iu  the  oesophagus,  they  were  able 
to  demonstrate  the  rapid  spirting  of  the  food  through  the  whole  length  of 
pharynx  and  oesophagus,  the  time  elapsing  between  the  beginning  of  the  swal- 
lowing movement  and  the  arrival  of  the  food  at  the  cardiac  orifice  of  the 
stomach  being  not  more  than  0.1  second.  The  contraction  of  the  constrictors 
of  the  pharynx  and  the  peristaltic  wave  along  the  oesophagus,  according  to 
this  view,  normally  follow  after  the  food  has  been  swallowed,  and  may  be 
regarded  as  a  movement  in  reserve  which  is  useful  in  removing  adherent  frag- 
ments along  the  deglutition  passage,  or  possibly,  in  case  of  the  failure  of  the 
first  swallowing  act  from  any  cause — as  may  result,  for  instance,  in  swallowing 
food  too  dry  or  too  solid — serves  to  actually  push  the  bolus  downward, 
although  at  a  much  slower  rate.  From  auscultation  of  the  deglutition  sound 
which  ensues  when  the  food  enters  the  stomach  through  the  cardia,  Kronecker 
and  Meltzer  believe  that  usually  the  swallowed  food  after  reaching  the  end  of 
the  oesophagus  is  kept  from  entering  the  stomach  by  the  tonic  contraction  of 
the  sphincter  at  that  })oint,  until  the  subsequent  peristaltic  wave  of  the  oesoph- 
agus, which  reaches  the  same  point  in  about  six  seconds  after  the  beginning  of 
the  act  of  swallowing,  forces  it  through.  There  are,  however,  exceptions  to 
this  rule.  In  some  persons,  apparently,  the  food  is  forced  into  the  stomach  by 
the  energy  of  the  first  contraction  of  the  mylo-hyoid  muscles.  The  difference 
would  seem  to  depend  upon  the  condition  of  the  sphincter  at  the  cardiac 
orifice.  Moreover,  these  authors  were  able  to  determine  by  their  method  of 
recording  that  the  human  oesophagus  contracts  apparently  in  three  successive 
segments.  The  first  of  these  comjwises  about  six  centimeters  in  the  neck 
region,  and  its  contraction  begins  about  1  or  1.2  seconds  after  the  beginning  of 
swallowing  and  is  comparatively  short,  lasting  2  seconds,  corresponding  to  the 
*  Du  Bois-Reymond's  Archiv  fiir  Physiologic,  1883,  Suppl.  Bd.,  S.  328. 


314  AN  AMERICAN   TlLXT-JiOOK   OF  PHYSIOLOGY. 

striated  character  of  the  imiscle.  Tlie  second  segment  covers  about  ten  (.'enti- 
raeters  of  the  upper  thoracic  portion  of  the  oesophagus;  its  contraction  begins 
about  1.8  seconds  after  tlie  beginning  of  the  contraction  of  the  first  segment, 
and  is  longer,  lasting  (j  to  7  seconds.  Tlie  third  segment  includes  the 
remainder  of  the  oesophagus;  its  contraction  begins  about  3  seconds  at'tci'  the 
contraction  of  the  second  segment,  and  lasts  a  much  longer  time,  about  i)-10 
se<'onds.  These  figures  apply,  of  course,  to  a  single  act  of  swallowing.  It 
will  be  seen  that  according  to  these  authors  the  swallowing  reflex  consists 
essentially  in  the  successive  contractions  of  five  muscular  segments  or  bands — 
namely,  the  mylo-hyoids,  the  constrictors  of  the  pharynx,  and  the  three  seg- 
ments of  the  oesophagus  described.  The  time  elapsing  between  the  contractions 
of  these  successive  parts  was  determined  as  follows  : 

From  the  beginning  of  the  contraction  of  the  niylo-hyoids  to  tliat  of  the 

constrictors  of  the  larynx 0.3  second. 

From  the  beginning  of  the   contraction  of  the  constrictors  to   that  of 

the  first  (Tsophageal  segment 0.9       " 

Between  the  first  and  second  oesophageal  segments 1.8  seconds. 

"  "    second  and  third         "  "  3.0       " 

The  total  time  before  the  wave  of  contraction  reaches  the  stomach  would 
be  therefore,  as  has  been  stated,  about  six  seconds.  When  a  second  act  of 
swallowing  is  made  within  six  seconds  of  the  first  swallow  it  causes  an  inhibi- 
tion, apparently  by  a  reflex  effect  upon  the  deglutition  centre,  of  the  })art  of 
the  tract  wliich  has  not  yet  entered  into  contraction,  so  that  the  peristaltic 
wave  does  not  reach  the  lower  end  of  the  oesophagus  until  six  seconds  after 
the  second  act  of  swallowing. 

Nervous  Control  of  Deglutition. — The  entire  act  of  swallowing,  as  has 
been  said  before,  is  essentially  a  reflex  act.  Even  the  comparatively  simple 
wave  of  contraction  which  sweeps  over  the  oesophagus  is  apparently  due  to  a 
reflex  nervous  stimulation,  and  is  not  a  simple  conduction  of  contraction  from 
one  portion  of  the  tube  to  atiotlier.  This  fact  was  demonstrated  by  the 
experiments  of  Mosso,^  who  found  that  after  removal  of  an  entire  segment 
from  the  oesophagus  the  peristalti(!  wave  passed  to  the  j>oi-tion  of  the  oesoph- 
agus left  on  the  stomach  side  in  spite  of  the  anatomical  break.  The  same 
experiment  was  performed  successfidly  on  rabbits  by  Kronecker  and  Meltzer. 
Observation  of  the  stomach  end  of  the  oesophagus  in  this  animal  showed  tiiat 
it  w-ent  into  contraction  two  seconds  after  the  beginning  of  a  swallowing  act 
whether  the  oesophagus  was  intact  or  ligated  or  completely  divided  by  a  trans- 
verse incision.  The  afferent  nerves  concerned  in  this  reflex  are  the  sensory 
fibres  to  the  mucous  membrane  of  the  pharynx  and  oesophagus,  including 
branches  of  the  glossopharyngeal,  trigeminal,  vagus,  and  superior  laryngeal 
division  of  the  vagus.  Artificial  stimulation  of  this  last  nerve  in  the  lower 
animals  is  known  to  produce  swallowing  movements.  Wassilieff  ^  records  that 
in  rabbits  he  was  able  to  produce  the  swallowing  reflex  by  artificial  stimula- 
tion of  the  nuicous  membrane  of  the  soft  palate  over  a  definite  area.     The 

1  MoleschoU's  Uniersuchnngen,  1876,  Bd.  xi.        *  Zeitschrift  fiir  Biologie,  1888,  Bd.  24,  P.  29. 


MOVEMENTS    OF    THE   ALIMENTARY  CANAL,    ETC.       315 

sensory  Hbres  to  this  area  arise  from  the  trigeminal  nerve.  The  same  observer, 
in  experiments  upon  himself,  was  unable  to  locate  any  particular  area  of  the 
mucous  nu'Mibrane  of  the  mouth  which  seemed  to  be  especially  comieeted  with 
the  swallowing  reflex.  The  physiological  centre  of  the  reflex  is  supposed  to  lie 
quite  far  forward  in  the  medulla,  but  its  anatomical  boundaries  have  not  been 
satisfactorily  defined.  It  seems  probal)le  that  in  this  as  in  other  cases  the 
physiological  centre  is  not  a  circumscribed  collection  of  nerve-cells,  but  com- 
prises certain  portions,  more  or  less  scattered,  of  the  nuclei  of  origin  of  the 
efferent  fibres  to  the  muscles  of  deglutition.  These  muscles  are  innervated  by 
fibres  from  the  hypoglossal,  facial,  trigeminal,  glossopharyngeal,  and  vagus. 
The  latter  nerve  supplies  through  some  of  its  branches  the  entire  oesophagus 
as  well  as  some  of  the  pharyngeal  muscles,  the  muscles  closing  the  glottis,  and 
the  aryteno-epiglottidean,  M-hich  is  supposed  to  aid  in  depressing  <the  epiglottis. 

Movements  of  the  Stomach. 

The  musculature  of  the  stomach  is  usually  divided  into  three  layers,  a  lon- 
gitudinal, an  oblique,  and  a  circular  coat.  The  longitudinal  coat  is  continuous 
at  the  cardia  with  the  longitudinal  fibres  of  the  oesophagus  ;  it  spreads  out  from 
this  point  along  the  length  of  the  stomach,  forming  a  layer  of  varying  thick- 
ness ;  along  the  curvatures  the  layer  is  stronger  than  on  the  front  and  posterior 
surfaces,  while  at  the  pyloric  end  it  increases  considerably  in  thickness,  and 
passes  over  the  pylorus  to  be  continued  directly  into  the  longitudinal  coat  of 
the  duodenum.  The  layer  of  oblique  fibres  is  quite  incomplete ;  it  seems  to  be 
continuous  with  the  circular  fibres  of  the  oesophagus  and  spreads  out  from  the 
cardia  for  a  certain  distance  over  the  front  and  posterior  surfaces  of  the  fundus 
of  the  stomach,  but  toward  the  pyloric  end  disappears,  seeming  to  pass  into 
the  circular  fibres.  The  circular  coat,  which  is  placed  between  the  two  pre- 
ceding layers,  is  the  thickest  and  most  important  part  of  the  musculature  of 
the  stomach.  At  the  extreme  left  end  of  the  fundus  the  circular  bands  are 
thin  and  somewhat  loosely  placed,  but  toward  the  pyloric  end  they  increase 
much  in  thickness,  forming  a  strong  muscular  mass,  which,  as  we  shall  see, 
plays  the  most  important  part  in  the  movements  of  the  stomach.  At  the  pylo- 
rus itself  a  special  development  of  this  layer  functions  as  a  sphincter  pylori, 
which  with  the  aid  of  a  circular  fold  of  the  mucous  membrane  makes  it 
possible  to  shut  oif  the  duodenum  completely  or  partially  from  the  cavity 
of  the  stomach.  The  portion  of  the  stomach  near  the  pylorus  is  fre- 
quently designated  simply  as  the  *'  pyloric  part,"  but  owing  to  its  distinct 
structure  and  functions  the  more  specific  name  of  "antrum  pylori"  seems 
preferable.  The  line  of  separation  between  the  antrum  pylori  and  the  body 
or  fundus  of  the  stomach  is  made  by  a  special  thickening  of  the  circular  fibres 
which  forms  a  structure  known  as  the  "  transverse  band "  by  the  older 
writers,^  and  described  more  recently^  as  the  "sphincter  antri  pylorici." 
This  so-called  sphincter  lies  at  a  distance  of  seven  to  ten  centimeters  from  the 

'  See  Beaumont:  Physiology  of  Digestion,  2d  ed.,  1847,  p.  104. 

^  Hofmeister  und  Schiitz  :  Archiv  fiir  exper.  Pathologie  und  Pharmakologie,  1886,  Bd.  xx. 


316  AN  AMERICAN   TEXT-BOOK   OF  I'llYSlOLOGY. 

pylorus.  Between  it  and  the  pylorus  is  the  ''antrum  j)ylori,"  of"  which  the 
distinguishing;  features  are  the  comparative  smoothness  and  paleness  oC  the 
raucous  membrane,  the  presence  of  the  pyloric  as  distinguished  from  the  finidic 
glands,  and  the  existence  of  a  relatively  very  strong  musculature. 

The  movements  of  the  stomach  during  digestion  have  been  the  subject  of 
much  study  and  experimentation,  both  in  man  and  the  lower  animals,  but  it 
cannot  be  said  that  the  mechanism  of  the  movements  is  as  yet  completely 
understood.  The  fundamental  facts  to  be  borne  in  mind  are  that  during  a 
period  of  several  hours  after  ordinary  food  is  received  into  the  stomach  the 
musculatin-e  of  this  organ  contracts  in  such  a  way  as  t<j  keej)  the  contents  in 
movement,  while  from  time  to  time  the  thinner  portions  of  the  semi-digested 
food  are  sent  through  the  pylorus  into  the  duodenimi.  There  is  a  certain 
orderliness  in  the  movement,  and  especially  in  the  separation  and  ejection  of 
the  more  liquid  from  the  solid  parts,  which  indicates  that  the  whole  act  is 
well  co-ordinated  to  a  definite  end.  The  older  physiologists  spoke  of  a  selec- 
tive power  of  the  pylorus  in  reference  to  the  recurring  acts  of  ejection  of  the 
more  liquid  portions  into  the  intestine,  but  a  phrase  of  this  kind,  as  applied  to 
a  muscular  apparatus,  is  pertiiissible  only  as  a  figure  of  speech,  and  throws  no 
light  whatever  upon  the  nature  of  the  process.  It  has  been  the  object  of 
recent  investigations  to  discover  the  mecihanical  factors  involved  in  these  acts 
and  their  relations  to  the  musculature  known  to  be  present.  It  has  been  shown 
satisfactorily  that  the  movements  of  the  stomach  are  not  de|>endent  Ufwu  its 
connection  with  the  central  nervous  system.  The  stomach  receives  a  rich  sup- 
ply of  extrinsic  nerve-fibres,  some  of  which  are  distributed  to  its  nniscles  and 
serve  to  regulate  its  movements,  as  will  be  described  later ;  but  when  these 
extrinsic  nerves  are  all  severed,  and  indeed  when  the  stomach  is  completely 
removed  from  the  body,  its  movements  may  still  continue  in  apparently  a 
normal  way  so  long  as  proper  conditions  of  moisture  and  temperature  are 
maintained.  We  must  believe,  therefore,  that  the  stomach  is  an  automatic 
organ,  using  the  word  automatic  in  a  limited  sense  to  imply  essential  independ- 
ence of  the  central  nervous  system.  The  normal  stomach  at  rest  is  usually 
quiet,  and  the  stimulus  to  its  movements  comes  from  the  presence  of  the  solid 
or  liipiid  material  received  into  it  from  the  a-sophagus.  Upon  the  reception 
of  this  material  the  movements  begin,  at  first  feebly  but  gradually  increasing  in 
extent,  and  continue  until  most  or  all  of  the  material  has  been  sent  into  the 
duodentun,  the  length  of  time  recpiired  depending  upon  the  nature  and  amount 
of  the  food.  The  exact  character  of  the  movements  has  been  variously  de- 
scribed by  different  observers.  Upon  man  they  were  care  fid  ly  studied  by 
Beaumont*  in  his  famous  observations  upon  Alexis  St.  Martin  (see  p.  225), 
and  the  essential  points  in  his  description  have  of  late  years  been  confirmed  by 
experiments  upon  dogs,^  whose  stomachs  closely  resemble  that  of  man.     These 

^  The  Physiology  of  Digestion,  1883. 

^  Hofmeister  und  Sohiitz:  Archiv  filr  exper.  Pathologic  und  Phannakologie,  1880,  ]?d.  xx. ; 
Moritz:  Zeitschrift  filr  Biologic,  1895,  Bd.  xxxii. ;  Rossbach :  Deutsches  Archiv  fiir  klinische 
Medicin,  1890,  Bd.  xlvi. 


MOVEMENTS    OF   THE  ALIMENTARY   CANAL,    ETC.       317 

observations  all  tend  to  show  that  the  main  movements  of  the  stomach  are 
effected  by  the  musculature  of  the  antrum  pylori,  whose  contraction  is  not  only 
the  chief  factor  in  ejecting  the  material  into  the  duodenum,  but  also  aids  in 
keeping  the  contents  of  the  stomach  in  motion.  The  extent  to  which  contrac- 
tions occur  in  the  fundic  end  of  the  stomach  does  not  seem  to  be  so  clearly  de- 
termined. According  to  some  observers  rhythmic  movements  are  absent  in  the 
fundus  to  the  left  of  about  the  middle  of  the  stomach,  this  portion  simply  re- 
maining in  a  condition  of  tone;  according  to  others  the  contractions  begin  near 
the  oesophageal  opening  and  pass  thence  toward  the  pylorus.  The  very  careful 
experiments  of  ITofmcister  and  Schlitz  upon  the  isolated  stomach  of  the  dog, 
together  with  the  reliable  observations  made  by  Beaumont  under  such  favora- 
ble conditions  on  the  human  stomach,  give  us  a  basis  for  a  description  of  the 
sequence  and  extent  of  the  movements  during  digestion,  which  is  probably  cor- 
rect in  its  main  features  at  least,  although  some  of  the  details  still  need  investi- 
gation. 

According  to  these  observers  a  normal  movement  begins  near  the  cardia  by 
a  flattening  or  constriction  which  is  feeble  and  is  apparent  only  on  the  side  of 
the  great  curvature.     This  constriction  is  due  to  a  contraction  of  the  circular 
muscle-fibres,  and  the  wave  thus  started  passes  toward  the  pylorus,  increasing 
in  strength  as  it  goes,  while  the  parts  behind  previously  in  contraction  slowly 
relax.     This  peristaltic  wave  comes  to  a  stop  a  short  distance  in  front  of  the 
antrum  pylori  by  a  constriction  involving  the  whole  circumference  of  the 
stomach  to  which  Hofraeister  and  Schutz  gave  the  name  of  the  "  pre-antral " 
constriction ;  it  seems  to  mark  the  climax  of  the  peristaltic  movement.     The 
obvious  effect  of  this  movement  so  far  would  be  to  push  forward  some  of  the 
contents  of  the  fundus  into  the  antrum.     Immediately  upon  the  formation  of 
this  constriction  the  strong  "  sphincter  antri  pylorici "  or  transverse  band  which 
marks  the  beginning  of  the  antrum,  contracts  strongly— so  strongly,  in  fact,  in 
what  may  be  considered  normal  movements,  as  to  cut  off  entirely  the  antrum 
pylori  from  the  fundus.     Following  upon  this  the  musculature  of  the  antrum 
contracts  as  a  whole,  squeezing  upon  its  contents  and  sending  them  through  the 
narrow  opening  of  the  pylorus  into  the  duodenum.     If,  however,  the  contents 
of  the  antrum  are  not  entirely  liquid,  but  contain  some  solid  particles  too  large 
to  escape  through  the  narrow  pylorus,  their  presence  seems  to  stimulate  an. 
"  antiperistaltic"  wave  in  the  musculature  of  the  antrum  pylori— that  is,  a  rnus- 
cular  wave  running  in  the  reverse  direction  to  that  of  a  normal  one,  from  right 
to  left,  the  effect  of  which  is  to  throw  back  these  solid  particles  into  the  fundus, 
which  is  now  in  communication  with  the  antrum,  the  sphincter  antri  pylorici 
having  relaxed.  This  reversed  wave  in  the  antrum  seems  to  have  been  observed 
repeatedly  by  Beaumont  upon  the  human  stomach,  as  well  as  by  Hofraeister 
and  Schutz  'upon  the  dog's  stomach,  and  enables  us  to  understand  how  solid 
particles  thrown  against  the  pylorus  are  again  forced  back  into  the  fundus  to 
undergo  further  digestive   and  mechanical  action.     These  movements,  as  a 
whole,  from  fundus  to  pvlorus  occur  with  a  certain  rapidity  which  varies  with 
the  nature  and  amount  of  the  contents  of  the  stomach  and  the  period  of  diges- 


318  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

tion.  In  Beaumont's  observations  the  movements  of  the  pylorus  are  recorded 
as  follownig  each  other  at  intervals  of  two  to  three  minutes,  while  upon  dogs 
similar  movements  are  recorded  as  occurring  from  three  to  six  times  in  a 
minute. 

It  will  be  seen  tiiat  according  to  this  description  the  movements  occur  in 
two  phases  :  first,  the  feeble  peristaltic  movement  running  over  the  fundus 
chiefly  on  the  side  of  the  great  curvature  and  resulting  in  i)ushing  some  of  the 
fundic  contents  into  the  antrum  ;  second,  the  sharp  contraction  of  the  sphincter 
autri  pyloric!  folloM'ed  by  a  similar  contraction  of  the  entire  musculature  of  the 
antrum,  both  circular  autl  longitudinal,  the  effect  of  which  is  to  squeeze  some 
of  the  contents  into  the  duodenum.  It  is  possible  that  either  of  tliese  phases, 
but  especially  the  first,  might  occur  at  times  without  the  other,  and  in  the  first 
-phase  it  is  probable  that  the  longitudinal  fibres  of  the  stomach  also  contract, 
shortening  the  organ  in  its  long  diameter  and  aiding  in  the  propulsive  move- 
ment, but  actual  observation  of  this  factor  has  not  been  successfully  made.  It 
can  well  be  understood  that  a  series  of  these  movements  occurring  at  short 
intervals  would  result  in  putting  the  entire  semi-liquid  contents  of  tlie  stomach 
into  constant  circulation.  The  precise  direction  of  the  current  set  up  is  not 
agreed  upon,  but  it  is  probable  that  the  graphic  description  given  by  Beaumont 
is  substantially  accurate.  A  portion  of  this  description  may  be  quoted,  as  fol- 
lows:  "The  ordinary  course  and  direction  of  the  revolutions  of  the  food  are, 
first,  after  passing  the  oesophageal  ring,  from  right  to  left,  along  the  small 
arch  ;  thence,  through  the  large  curvature,  from  left  to  right.  The  bolus,  as  it 
entei-s  the  cardia,  turns  to  the  left ;  passes  the  aperture ;  descends  into  the  splenic 
extremity,  and  follows  the  great  curvature  toward  the  pyloric  end.  It  then 
returns  in  the  course  of  the  small  curvature."-  The  average  time  taken  for  one 
of  these  complete  revolutions,  according  to  observations  made  by  Beaumont, 
seems  to  vary  from  one  to  three  minutes. 

It  is  possible,  of  course,  that  this  typical  circuit  taken  by  the  food  may  often 
be  varied  more  or  less  l)y  different  conditions,  but  the  muscular  movements 
observed  from  the  outside  would  seem  to  be  adapted  to  keeping  up  a  general 
revolution  of  the  kind  described.  The  general  result  upon  the  food  may  easily 
be  imagined.  It  becomes  thoroughly  mixed  with  the  gastric  juice  and  any  liquid 
.which  may  have  been  swallowed,  and  is  gradually  disintegrated,  dissolved,  and 
more  or  less  completely  digested  so  far  as  the  proteid  and  albuminoid  constitu- 
ents are  concerned.  The  mixing  action  is  aided,  moreover,  by  the  movements 
of  the  diaphragm  in  respiration,  since  at  each  descent  it  presses  upon  the  stomach. 
The  powerful  muscular  contractions  of  the  antrum  serve  also  to  triturate  the 
softened  solid  particles,  and  finally  the  whole  mass  is  reduced  to  a  liquid  or 
semi-liquid  condition  in  which  it  is  known  as  chyme,  and  in  this  condition  the 
rhythmic  contractions  of  the  muscles  of  the  antrum  eject  it  into  the  duodenum. 
The  rhythmic  spirting  of  the  contents  of  the  stomach  into  the  duodenum  has 
been  noticed  by  a  number  of  observers  by  means  of  duodenal  fistulas  in  dogs, 
established  just  beyond  the  pylorus.  It  has  lieen  shown  also  that  when  the 
food  taken  is  entirely  liquid — water,  for  example — the  stomach  is  emptied  in  a 


MOVEMENTS    OF    THE  ALIMENTARY   CANAL,    ETC.       319 

surprisingly  sliort  time,  witliiu  twenty  to  tliirty  minutes ;  if,  however,  the 
water  is  taken  with  solid  food  tlieii  naturally  the  time  it  will  remain  in  the 
stomach  may  be  much  lengthened. 

A  very  interesting  part  of  the  mechanism  of  the  stomach  the  action  of 
which  is  not  thoroughly  understood  is  the  sphincter  of  the  pylorus.  During 
the  act  of  digestion  this  sphincter  remains  in  a  condition  of  tone;  whether 
its  tonic  contraction  is  sufficient  only  to  narrow  the  pylorus,  or  whether  it 
is  sufficient  to  completely  shut  oflp  the  pylorus  so  that  a  partial  relaxation 
must  occur  with  each  contraction  of  the  musculature  of  the  antrum,  is  not 
sufficiently  well  known.  It  has  been  shown,  however,  that  this  part  of  the 
circular  layer  of  muscle  is  distinctly  under  the  control  of  the  extrinsic 
nerves,  its  tonicity  being  increased  by  impulses  received  through  the  vagi  and 
diminished  or  inhibited  by  impulses  through  the  splanchnics.  It  will  be  seen 
from  the  above  brief  description  that  the  muscles  of  the  antrum  pylori  do 
most  of  the  work  of  the  stomach,  while  in  the  much  larger  fundus  the  food 
is  retained  as  in  a  reservoir  to  be  digested  and  mechanically  prepared  for 
expulsion  into  the  intestine,  the  two  parts  of  the  stomach  fulfilling  therefore 
somewhat  different  functions.  Moritz  ^  has  called  especial  attention  to  this 
fact,  and  points  out  the  great  advantage  which  accrues  to  the  digestive  pro- 
cesses in  the  intestine  in  having  the  stomach  to  retain  the  bulk  of  the  food 
swallowed  during  a  meal,  while  from  time  to  time  small  portions  only  are 
sent  into  the  intestine  for  more  complete  digestion  and  absorption.  In  this 
way  the  intestine  is  protected  from  becoming  congested,  and  its  digestive  and 
absorptive  processes  are  more  perfectly  executed. 

Extrinsic  Nerves  to  the  Muscles  of  the  Stomach. — The  stomach  re- 
ceives extrinsic  nerve-fibres  from  two  sources  ;  from  the  two  va^i  and  from 
the  solar  plexus.  The  fibres  from  the  latter  source  arise  ultimately  in  the 
spinal  cord,  pass  to  some  of  the  thoracic  ganglia  of  the  sympathetic  system, 
and  thence  by  way  of  the  splanchnics  to  the  semilunar  or  solar  plexus  and 
then  to  the  stomach.  These  fibres  probably  reach  the  stomach  as  non-medul- 
lated  or  sympathetic  fibres.  The  vagi  where  they  are  distributed  to  the 
stomach  seem  to  consist  almost  entirely  of  non-medullated  fibres  also,  and 
probably  the  fibres  distributed  to  the  muscular  coat  are  of  this  variety.  The 
results  of  numerous  experiments  seem  to  show  quite  conclusively  that  in  general 
the  fibres  received  along  the  vagus  path  are  motor,  artificial  stimulation  of 
them  causing  more  or  less  well  marked  contractions  of  part  or  all  of  the 
musculature  of  the  stomach.  It  has  been  shown  that  the  sphincter  pylori  as 
well  as  the  rest  of  the  musculature  is  supplied  by  motor  fibres  from  these 
nerves.  The  fibres  coming  through  the  splanchnics,  on  the  contrary,  are 
mainly  inhibitory.  When  stimulated  they  cause  a  dilatation  of  the  contracted 
stomach  and  a  relaxation  of  the  sphincter  pylori.  Some  observers  have 
reported  expei'iments  which  seem  to  show  that  this  anatomical  separation  of 
the  motor  and  inhibitory  fibres  is  not  complete ;  that  some  inhibitory  fibres 
may  be  found  in  the  vagi  and  some  motor  fibres  in  the  splanchnics.  The 
*  Zeitschrift  fiir  Biologic,  1895,  Bd.  xxxii. 


320  AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

anatomical  courses  of  tliese  fibres  are  insufficiently  known,  but  there  seems  to 
be  no  question  as  to  the  existence  of  the  two  physiological  varieties.  Through 
their  activity,  without  doubt,  the  movements  of  the  stomach  may  be  regu- 
lated, favorably  or  unfavorably,  by  conditions  directly  or  indirectly  affect- 
ing the  central  nervous  system.  AVertheimer '  has  shown  expcrimcntaliv  that 
stimulation  of  the  central  end  of  the  sciatic  or  the  vagus  nerve  mav  cause 
reflex  inhibition  of  the  tonus  of  the  stomach,  and  Doyon  ^  has  confirmed  this 
result  in  cases  wliere  the  movements  and  tonicity  of  the  stomach  were  first 
increased  by  the  action  of  pilocarpin  and  strychnin.  It  must  be  borne  in 
mind,  however,  that  the  action  of  these  extrinsic  fibres  under  normal  conditions 
is  probably  only  to  regulate  the  movements  of  the  stomach.  As  we  have 
seen,  even  the  extirpated  stomach  under  proper  conditions  seems  to  execute 
movements  of  the  normal  type.  N^ormally  the  movements  are  provoked  bv  a 
stimulus  of  some  kind,  usually  the  presence  of  food  material  in  the  interior 
of  the  stomach.  How  the  stimulus  acts  in  this  case,  Nvhether  directly  upon  the 
muscle-fibres  or  indirectly  through  the  intrinsic  ganglia  of  the  stomach,  has 
not  been  determined,  and  the  evidence  for  either  view  is  so  insufficient  that  a 
discussion  of  the  matter  at  this  time  would  scarcely  be  profitable.  We  must 
wait  for  more  complete  investigations  upon  the  physiology  as  well  as  the  his- 
tology of  the  muscle-  and  nerve-tissue  in  this  and  in  other  visceral  organs 
constructed  on  the  same  type. 

Movements  of  the  Intestines. 

The  muscles  of  the  small  and  the  large  intestine  are  arranged  in  two  layers, 
an  outer  longitudinal  and  an  inner  circular  coat,  while  between  these  coats  and 
in  the  submucous  coat  there  are  present  the  nerve-plexuses  of  Auerbach  and 
Meissner.  The  general  arrangement  of  muscles  and  nerves  is  similar,  there- 
fore, to  that  prevailing  in  the  stomach,  and  in  accordance  with  this  we  find  that 
the  physiological  activities  exhibited  are  of  much  the  same  character,  only,  per- 
haps, not  quite  so  complex. 

Forms  of  Movement. — Two  main  forms  of  intestinal  movement  have  been 
distinguished,  the  peristaltic  and  the  pendular. 

Peristalsis. — The  peristaltic  movement  consists  in  a  constriction  of  the  walls 
of  the  intestine  which  beginning  at  a  certain  point  passes  downward  away  from 
the  stomach,  from  segment  to  segment,  while  the  parts  behind  the  advancing 
zone  of  constriction  gradually  relax.  The  evident  effect  of  such  a  movement 
would  be  to  push  onward  the  contents  of  the  intestines  in  the  direction  of  the 
movement.  It  is  obvious  that  the  circular  layer  of  muscles  is  chiefly  involved  in 
peristalsis,  since  constriction  can  only  be  produced  by  contraction  of  this  layer. 
To  what  extent  the  longitudinal  muscles  enter  into  the  movement  is  not  definitely 
determined.  The  term  "  anti-peri.stalsis  "  is  used  to  describe  the  same  form  of 
movement  running  in  the  opposite  direction — that  is,  toward  the  stomach. 
Anti-peristalsis  is  usually  said  not  to  occur  under  normal  conditions ;  it  has 
been  observed  sometimes  in  isolated  pieces  of  intestine  or  in  the  exposed  intes- 

*  Archives  de  Physiologic  normale  et  pathologique.  1892,  p.  379.  *  Ibid.,  1895^  p.  374. 


MOVEMENTS    OF    THE    ALIMENTARY    CANAL,    ETC.        321 

tine  of  living  animals  when  stimulated  artificially,  and  Griitzner'  reports  a 
number  of  curious  experiments  which  seem  to  show  that  substances  such  as 
hairs,  animal  charcoal,  etc.,  introduced  into  the  rectum  may  travel  upward  to  the 
stomach  under  certain  conditions.  The  peristaltic  wave  normally  passes  down- 
ward, and  that  this  direction  of  movement  is  dependent  upou  some  definite 
arrangement  in  the  intestinal  walls  is  beautifully  shown  by  the  experiments  of 
Mall  ^  and  others  upon  reversal  of  the  intestines.  In  these  experiments  a  por- 
tion of  the  small  intestine  was  resected,  turned  round  and  sutured  in  place 
again,  so  that  in  this  piece  what  was  the  lower  end  became  the  up[)er  end. 
In  those  animals  that  made  a  good  operative  recovery  the  nutritive  condition 
gradually  became  very  serious,  and  in  the  animals  killed  and  examined  the 
autopsy  showed  accunudatiou  of  material  at  the  upper  end  of  the  reversed 
piece  of  intestine,  and  great  dilatation. 

The  peristaltic  movements  of  the  intestines  may  be  observed  upon  living 
animals  when  the  abdomen  is  opened.     If  the  operation  is  made  in  the  air 
and  the  intestines  are  exposed  to  its  influence,  or  if  the  conditions  of  tempera- 
ture  and  circulation   are   otherwise  disturbed,  the   movements  observed  are 
often  violent   and   irregular.     The   peristalsis  runs    rapidly  along  the   intes- 
tines and  may  pass  over  the  whole  length  in  about  a  minute;  at  the  same  time 
the  contraction  of  the  longitudinal  muscles  gives  the  bowels  a  peculiar  writhing 
movement.     Movements  of  this  kind  are  evidently  abnormal,  and  only  occur 
in  the  body  under  the  strong  stimulation  of  pathological  conditions.     Normal 
peristalsis,  the  object  of  which  is  to  move  the  food  slowly  along  the  alimentary 
tract,  is  quite  a  different  affair.     Observers  all  agree  that  the  wave  of  contraction 
is  gentle  and  progresses  slowly.     It  has  been  studied  very  successfully,  so  far  as 
rate  of  movement  is  concerned,  by  experiments  upon  animals  in  which  a  loop 
of  the  intestines  was  resected,  to  make  a  "  Thiry-Vella  "  fistula  (see  p.  246). 
Cash  ^  finds  that  in  such  isolated  loops  foreign  substances  introduced  are  pro- 
pelled at  different  rates  according  to  the  condition  of  the  animal.     In  the  fast- 
ing animal  it  requires  from  one  and  a  half  to  two  and  a  half  minutes  for  a 
distance  of  one  centimeter.     During   exercise  the   movement  is  more  rapid, 
while  during  the  first  few  hours  of  digestion,  that  is  the  time  during  which 
the  stomach  is  emptying  its  contents  into  the  intestine,  the  velocity  of  the 
movement  is  greatly  increased,  requiring  only  from  twenty  to  fifty  seconds  to 
cover  a  distance  of  one  centimeter.     The  force  of  the  contraction  as  measured 
by  Cash  in  the  dog's  intestine  is  very  small.     A  weight  of  five  to  eight  grams 
was  sufficient  to  check  the  onward  movement  of  the  substance  in  the  intestine 
and  to  set  up  violent  colicky  contractions  which  caused  the  animal  evident 
uneasiness.     We  may  suppose  that  under  normal  conditions  each  contraction 
of  the  antrum  pylori  of  the  stomach,  which  ejects  chyme  into  the  duodenum, 
is  followed  by  a  peristalsis  that   beginning   at  the  duodenum   passes  slowly 
downward   for   a  part   or   all    of  the   small    intestine.     According   to   most 

^  Deutsche  medicinische  Wochenschrift,  1894,  No.  48. 
2  The  Johns  Hopkins  Hospital  ReporL%  vol.  i.  p.  93. 
^  Proceedinrjs  of  the  Boyal  Society,  London,  1887,  vol.  41. 
21 


322  AX   AyfFJUrAX   TEXT-BOOK    OF   PHYSIOLOGY. 

observers  the  movement  is  blocked  at  the  ileo-csecal  valve,  and  the  peristaltic 
movements  of  the  large  intestine  form  an  independent  group  similar  in  all 
their  general  characters  to  those  of  the  small  intestine,  but  weaker  and  slower. 
3Iechanism  of  the  Pei'istallic  Movement. — The  means  by  which  the  peri- 
staltic movement  makes  its  orderly  forward  progression  have  not  been  satis- 
factorily determined.  The  simplest  explanation  woidd  be  to  assume  that  an 
impulse  is  conveyed  directly  from  cell  to  cell  in  the  circular  muscular  coat,  so 
that  a  contraction  started  at  any  point  would  spread  by  direct  conduction  of 
the  contraction  change.  This  theory,  however,  does  not  explain  satisfiictorily 
the  normal  conduction  of  the  wave  of  contraction  always  in  one  direction,  nor 
the  fact  that  a  reversed  piece  of  intestine  continues  to  send  its  waves  in  what 
was  for  it  the  normal  direction.  It  is  possible,  therefore,  that  the  co-ordination 
of  the  movement  may  be  effected  through  the  local  nerve-ganglia,  but  our 
knowledge  of  the  mechanism  and  physiology  of  these  peripheral  nerve-plexuses 
is  as  yet  too  incomplete  to  be  applied  satisfactorily  to  the  explanation  of  the 
movements  in  question. 

Pendular  3Iovements. — In  addition  to  the  peristaltic  wave  a  second  kind 
of  movement  may  lie  observed  in  the  exposed  intestines  of  a  living  animal. 
This  movement  is  characterized  by  a  gentle  swinging  to  and  fro  of  the  different 
loops,  whence  its  name  of  pendular  movement.  The  oscillations  occur  at 
regular  intervals,  and  are  usuallv  ascribed  to  rhvthmic  contractions  of  the 
longitudinal  muscles.  Mall,^  however,  believes  that  the  main  feature  of  this 
movement  is  a  rhythmic  contraction  of  the  circular  muscles,  involving  a  part 
or  all  of  the  intestines.  He  prefers  to  speak  of  the  movements  as  rhythmic 
instead  of  pendular  contractions,  and  points  out  that  owing  to  the  arrangement 
of  the  blood-vessels  in  the  coats  of  the  intestine  the  rhythmic  contractions  should 
act  as  a  pump  to  expel  the  blood  from  the  submucous  venous  plexus  into  the 
radicles  of  the  superior  mesenteric  vein,  and  thus  materially  aid  in  keeping  up 
the  circulation  through  the  intestine  and  in  maintaining  a  good  pressure  in  the 
portal  vein,  in  much  the  same  way  as  happens  in  the  case  of  the  spleen  (see  p. 
272).  How  far  these  rhythmic  or  pendular  contractions  occur  under  perfectly 
normal  conditions  has  not  been  determined. 

Extrinsic  Nerves  of  the  Intestines. — As  in  the  case  of  the  stomach,  the 
small  intestine  and  the  greater  part  of  the  large  intestine  receive  viscero-motor 
nerve-fibres  from  the  vagi  and  the  sympathetic  chain.  The  former,  according 
to  most  observers,  when  artificially  stimulated  cause  movements  of  the  intestine, 
and  are  therefore  regarded  as  the  motor  fibres.  It  seems  probable,  however, 
that  the  vajji  carry  or  mav  carry  in  some  animals  inhibitory  fibres  as  well,  and  that 
the  motor  effects  usually  obtained  upon  stimulation  are  due  to  the  fact  that  in  these 
nerves  the  motor  fibres  predominate.  The  fibres  received  from  the  sympathetic 
chain,  on  the  other  hand,  give  mainly  an  inhibitory  effect  when  stimulated, 
although  some  motor  fibres  apparently  may  take  this  path.  Bechterew  and 
Mislawski^  state  that  the  sympathetic  fibres  for  the  small  intestine  emerge  from 

*  The  Johns  Hopkins  Hospital  Reports,  vol.  i.  p.  37. 

'  Du  Bois-Reymond's  ArchivfUr  Physiologic,  1889,  Suppl.  Bd. 


MOVEMENTS    OF    THE   ALIMENTARY   CANAL,   ETC.       323 

the  spiual  cord  as  niedullated  fibres  iu  the  >i.\th  dor.^al  to  the  first  lumbar 
spinal  nerves,  and  pass  to  the  sympathetic  oliain  in  the  splancimic  nerves  and 
thence  to  the  semilunar  j)lexus,  while  the  sympathetic  fibres  to  the  large  intes- 
tine and  rectum  arise  in  the  four  lower  lumbar  and  the  three  upper  sacral  spinal 
nerves.  According  to  Langley  and  Anderson'  the  descending  colon  and  rec- 
tum receive  a  double  norve-supj^ly — first  from  the  lumbar  spinal  nerves  (second 
to  fifth),  the  fibres  })assing  through  the  sympathetic  ganglia  and  the  inferior 
mesenteric  plexus  and  causing  chiefly  an  inhibition  ;  second,  through  the  sacral 
nerves,  the  fibres  ])assing  through  the  norvus  erigens  and  the  hypogastric  plexus 
and  causing  chiefly  contraction  of  the  circular  muscle. 

These  extrinsic  fibres  undoubtedly  serve  for  the  regulation  of  the  move- 
ments of  the  bowels  from  the  central  nervous  system ;  conditions  which  influ- 
ence the  central  system,  either  directly  or  indirectly,  may  thus  affect  the  intesti- 
nal movements.  The  paths  of  these  fibres  through  the  central  nervous  system 
are  not  known,  but  there  are  evidently  connections  extending  to  the  higher 
brain-centres,  since  psychical  states  are  known  to  influence  the  movements  of  the 
intestine,  and  according  to  some  observers  stimulation  of  portions  of  the  cere- 
bral cortex  may  produce  movements  or  relaxation  of  the  walls  of  the  small  and 
large  intestines.  As  in  the  case  of  the  stomach,  the  extrinsic  fibres  seem  to 
have  only  a  regulatory  influence.  When  they  are  completely  severed  the 
tonicity  of  the  walls  of  the  intestine  is  not  altered,  and  peristaltic  and  rhythmic 
movements  may  still  occur.  The  same  results  may  be  obtained  even  upon 
excised  portions  of  the  intestines  (Salvioli,  Mall).  It  seems  probable,  there- 
fore, that  normal  peristalsis  in  the  living  animal  may  be  effected  independently 
of  the  central  nervous  system,  although  its  character  and  strength  is  subject 
to  regulation  through  the  medium  of  the  viscero-motor  fibres,  in  much  the 
same  May,  and  possibly  to  as  great  an  extent,  as  the  movements  of  the  heart  are 
controlled  through  its  extrinsic  nerves. 

Effect  of  Various  Conditions  upon  the  Intestinal  Movements. — Experi- 
ments have  shown  that  the  movements  of  the  intestines  may  be  evoked  in  many 
ways  beside  direct  stimulation  of  the  extrinsic  nerves.  Chemical  stimuli  may 
be  applied  directly  to  the  intestinal  wall.  The  most  noteworthy  reaction  of 
this  kind  is  the  curious  effect  of  potassium  and  sodium  salts  as  first  described 
by  IS^othnagel.^  Potassium  salts  in  proper  concentration  excite  a  strong  local 
contraction  of  the  circular  fibres,  producing  a  deep  constriction  at  the  point  of 
application  of  the  stimulus.  Sodium  salts,  on  the  contrary,  produce  a  contrac- 
tion above  the  point  of  application  which  subsequently  spreads  for  some  dis- 
tance, apparently  in  the  direction  of  a  normal  persistalsis,  since  its  effect  is  to  force 
the  contents  downward.  Violent  movements  may  be  produced  also  by  shutting 
off  the  blood-supply,  and  again  temporarily  when  the  supply  is  re-established. 
A  condition  of  dyspnoea  may  also  start  movements  in  the  intestines  or  in  some 
cases  inhibit  movements  wdiich  are  already  in  progress,  the  stimulus  in  this  case 
seeming  to  act  upon  the  central  nervous  system  and  to  stimulate  both  the  motor 

1  Journal  of  Physiology,  1895,  vol.  xviii.  p.  67. 

^  Virchov/s  Archil  filr  patfiologische  Anatomie  und  Physiologic,  1882,  Bd.  88,  S.  1. 


324  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

and  the  inhibitory  fibres.  Oxygen  gas  within  tlio  howi-ls  tends  to  suspend  the 
movements  of  the  intestine,  wliile  COj,  CH^,  and  H^S  act  as  stimuli,  increasing 
the  movements.  Organic  acids,  such  as  acetic,  propionic,  formic,  and  capryhc, 
which  may  be  formed  normally  within  the  intestine  as  the  result  of  bacterial 
action,  act  also  as  strong  stimulants.' 

Defecation. — The  undigested  and  indigestible  parts  of  the  food,  together 
with  some  of  the  debris  anil  secretions  from  the  alimentary  tract,  are  carried 
slowly  through  the  large  intestine  by  its  peristaltic  movements  and  eventually 
reach  the  sigmoid  flexure  and  rectum.     Here  the  nearly  solid  material  stimu- 
lates by  its  pressure  the  sensory  nerves  of  the  rectum  and  produces  a  distinct 
sensation  and  desire  to  defecate.    The  fecal  material  is  retained  within  the  rectum 
by  the  action  of  the  two  sphincter  muscles  which  close  the  anal  opening.     One 
of  these  muscles,  the  internal  sphincter,  is  a  strong  band  of  the  circular  layer 
of  involuntary  muscles  which  forms  one  of  the  coats  of  the  rectum.     AVhen 
the   rectum  contains  fecal    material  this   muscle  seems  to   be  thrown  into  a 
condition  of  tonic  contraction  until  the  act  of  defecation  begins,  when  it  is 
relaxed.     The  sphincter  is  composed  of  involuntary  muscle  and  is  innervated 
by  fibres  arising  partly  from  the   sympathetic  system,  and  in  part  through 
the  nervus  erigens,  from  the  sacral  spinal  nerves.     The  external  sphincter  ani 
is  composed  of  striated  muscle-tissue  and  is  under  the  control  of  the  will  to 
a  certain  extent ;  when,  however,  the  stimulus  from  the  rectum  is  sufficiently 
intense,  voluntary  control    is   overcome   and  this   sphincter    is    also  relaxed. 
The  act  of  defecation  is  in  part  voluntary  and  in  part   involuntary.     The 
involuntary  factor  is  found  in  the  contractions  of  the  strongly  developed  mus- 
culature of  the  rectum,  especially  the  circular  layer,  which  serves  to  force  the 
feces  onward,  and  the  relaxation  of  the  internal  sphincter.     It  seems  that  these 
two  acts  are  mainly  caused  by  reflex  stimulation  from  the  lumbar  spinal  cord, 
although  it  is  probable  that  the  rectum,  like  the  rest  of  the  alimentary  tract, 
is  capable  of  automatic  contractions.     The  rectal   muscles  receive  a  double 
nervous  supply,  containing  physiologically  both  motor  and  inhibitory  fibres. 
Some  of  these  fibres  come  from  the  nervus  erigens  by  way  of  the  hypogastric 
plexus,  and  some  arise  from  the  lumbar  cord  and  pass  through  the  correspond- 
ing sympathetic  ganglia,  inferior  mesenteric  ganglion,  and  hypogastric  nerve. 
It  has  been  asserted  that  stimulation  of  the  nervus  erigens   causes  contrac- 
tion of  the  longitudinal  muscles  and  inhibition  of  the  circular  muscles,  while 
stimulation  of  the  hypogastric  nerve  causes  contraction  of  the  circular  muscles 
and   inhibition  of  the  longitudinal   layer.     This  division  of  activity   is  not 
confirmed  by  the  recent  experiments  of  Langley  and   Anderson.^ 

The  voluntarv  factor  in  defecation  consists  in  the  inhibition  of  the  external 
sphincter  and  the  contraction  of  the  abdominal  muscles.  When  these  latter 
muscles  are  contracted  and  at  the  same  time  the  diaphragm  is  prevented  from 
moving  upward  by  the  closure  of  the  glottis,  the  increased  abdominal  jjressure 
is  brought  to  bear  upon  the  abdominal  and  pelvic  viscera,  and  aids  strongly  in 
pres.sing  the  contents  of  the  descending  colon  and  sigmoid  flexure  into  the 

'  Bokai:  ArchivfUr  ezper.  Pathologic  und  Pharmakologie,  1888,  Bd.  24,  S.  ]53.         '  Op.  cit. 


MOVEMENTS    OF    THE   ALIMENTARY   CANAL,    ETC.        325 

rectum.  The  pressure  in  the  abdominal  cavity  is  still  further  increased  if 
a  deep  inspiration  is  first  made  and  then  maintained  dnrini^  the  contraction 
of  the  abdominal  nmscles.  Although  the  act  of  defecation  is  normally  initiated 
by  voluntary  effort,  it  may  also  be  aroused  by  a  purely  involuntary  reflex  when 
the  sensory  stinudus  is  sufficiently  strong.  Goltz  '  has  shown  that  in  dogs 
in  which  the  spinal  cord  had  been  severed  in  the  lower  thoracic  region  defe- 
cation was  performed  normally,  the  external  sphincter  being  relaxed. 

It  would  seem  that  the  whole  act  of  defecation  is  at  bottom  an  involuntary 
reflex.  The  })hysiological  centre  for  the  movement  lies  in  the  lumbar  cord, 
and  has  sensory  and  motor  connections  with  the  rectum  and  the  muscles  of 
defecation,  but  this  centre  is  in  part  at  least  provided  with  connections  with 
the  centres  of  the  cerebrum  through  which  the  act  may  be  controlled  by 
voluntary  impulses  and  by  various  psychical  states,  the  effect  of  emotions 
upon  defecation  being  a  matter  of  common  knowledge.  In  infants  the  essen- 
tially involuntary  character  of  the  act  is  well  seen. 

Vomiting. — The  act  of  vomiting  causes  an  ejection  of  the  contents  of  the 
stomach  through  the  oesophagus  and  mouth  to  the  exterior.  It  was  long 
debated  whether  the  force  producing  this  ejection  comes  from  a  strong  contrac- 
tion of  the  walls  of  the  stomach  itself  or  whether  it  is  due  mainly  to  the 
action  of  the  walls  of  the  abdomen.  A  forcible  spasmodic  contraction  of  the 
abdominal  muscles  takes  place,  as  aiay  easily  be  observed  by  any  one  upon 
himself,  and  it  is  now  believed  that  the  contraction  of  these  muscles  is  the 
principal  factor  in  vomiting.  Magendie  found  that  if  the  stomach  was  extir- 
pated and  a  bladder  containing  water  was  substituted  in  its  place  and  connected 
with  the  oesophagus,  injection  of  an  emetic  caused  a  typical  vomiting  movement 
with  ejection  of  the  contents  of  the  bladder.  Gianuzzi  showed,  on  the  other 
hand,  that  upon  a  curarized  animal  vomiting  could  not  be  produced  by  an  emetic 
— because,  apparently,  the  muscles  of  the  abdomen  were  paralyzed  by  the  curare. 
There  are  on  record,  however,  a  number  of  observations  which  tend  to  show  that 
the  stomach  is  not  entirely  passive  during  the  act.  On  the  contrary,  it  may 
exhibit  contractions,  more  or  less  violent  in  character,  which  while  insufficient 
in  themselves  to  eject  its  contents,  probably  aid  in  a  normal  act  of  vomiting. 
The  act  of  vomiting  is  in  fact  a  complex  reflex  movement  into  wdiich  many 
muscles  enter.  The  following  events  are  described  :  The  vomiting  is  usually 
preceded  by  a  sensation  of  nausea  and  a  reflex  flow  of  saliva  into  the  mouth. 
These  phenomena  are  succeeded  or  accompanied  by  retching  movements,  which 
consist  essentially  in  deep  spasmodic  inspirations  with  a  closed  glottis.  The 
effect  of  these  movements  is  to  compress  the  stomach  by  the  descent  of  the 
diaphragm,  and  at  the  same  time  to  increase  decidedly  the  negative  pressure  in 
the  thorax,  and  therefore  in  the  thoracic  portion  of  the  oesophagus.  During 
one  of  these  retching  movements  the  act  of  vomiting  is  effected  by  a  convulsive 
contraction  of  the  abdominal  wall  which  exerts  a  sudden  additional  strong 
pressure  upon  the  stomach.  At  the  same  time  the  cardiac  orifice  of  the 
stomach  is  dilated,  possibly  by  an  inhibition  of  the  sphincter,  aided  it  is  sup- 
'  Archiv  fur  die  gesammte  Physiologic,  1874,  Bd.  viii.  S.  460. 


326  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

posed  by  tlie  contraction  of  the  longitudinal  muscle-fibres  of  the  (esophagus 
and  the  oblique  fibres  of  the  niuxcular  coat  of  the  stomach.  The  stomach 
contents  are,  therefore,  forced  violently  out  of  the  stomach  through  the  u'soj)h- 
agus,  the  negative  pressure  in  the  latter  probably  assisting  in  the  act.  The 
passage  through  the  (cso})hagus  is  effected  mainly  by  the  force  of  the  contrac- 
tion of  the  abdominal  muscles;  there  is  no  evidence  of  antiperistaltic  move- 
ments on  the  part  of  the  oesophagus  itself.  During  the  ejection  of  the  contents 
of  the  stomach  the  glottis  is  kept  closed  by  the  adductor  muscles,  and  usually 
the  nasal  chamber  is  likewise  shut  off  from  the  pharynx  by  the  contraction  of 
the  posterior  pillars  of  the  fauces  on  the  palate  and  uvula.  In  violent  vomit- 
ing, however,  the  vomited  material  may  break  through  this  latter  barrier  and 
be  ejected  partially  through  the  nose. 

Nervous  Mecluaiimii  of  Vomiting. — That  vomiting  is  a  reflex  act  is  abun- 
dantly shown  by  the  frequency  with  which  it  is  produced  in  consequence  of 
the  stimulation  of  sensory  nerves  or  as  the  result  of  injuries  to  various  parts 
of  the  central  nervous  system.  After  lesions  or  injuries  of  the  brain  vomiting 
of\en  results.  Disagreeable  emotions  and  disturbances  of  the  sense  of  equi- 
librium may  produce  the  same  result.  Irritation  of  the  mucous  membrane 
of  various  parts  of  the  alimentary  canal  (as,  for  example,  tickling  the  back 
of  the  pharynx  with  the  finger),  disturbances  of  the  urogenital  apparatus, 
artificial  stimulation  of  the  trunk  of  the  vagus  and  of  other  sensory  nerves, 
may  all  cause  vomiting.  Under  ordinary  conditions,  however,  irritation  of 
the  sensory  nerves  of  the  gastric  nmcous  membrane  is  the  most  common 
cause  of  vomiting.  This  efifect  may  result  from  the  products  of  fermentation 
in  the  stomach  in  cases  of  indigestion,  or  may  be  produced  intentionally  by 
local  emetics,  such  as  mustard,  taken  into  the  stomach.  The  afferent  path 
in  this  case  is  through  the  sensory  fibres  of  the  vagus.  The  efferent  paths 
of  the  reflex  are  found  in  the  motor  nerves  innervating  the  muscles  con- 
cerned in  the  vomiting,  namely,  the  vagus,  the  phrenics,  and  the  spinal  nerves 
supplying  the  abdominal  muscles.  Whether  or  not  there  is  a  definite  vomit- 
ing centre  in  which  the  afferent  impulses  are  received  and  through  which 
a  co-ordinated  series  of  efferent  impulses  is  sent  out  to  the  various  muscles, 
has  not  been  satisfactorily  determined.  It  has  been  shown  that  the  portion 
of  the  nervous  system  through  which  the  reflex  is  effected  lies  in  the  me- 
dulla. But  it  has  been  pointed  out  that  the  muscles  concerned  in  the  act 
are  respiratory  muscles.  Vomiting  in  fact  consists  essentially  in  a  simul- 
taneous spasmodic  contraction  of  expiratory  (abdominal)  muscles  and  inspi- 
ratory muscles  (diaphragm).  It  has  therefore  been  suggested  that  the  reflex 
takes  place  through  the  respiratory  centre,  or  some  part  of  it.  This  view 
seems  to  be  opposed  by  the  experiments  of  Thumas,^  who  has  shown  that 
when  the  medulla  is  divided  down  the  mid-line  respiratory  movements  con- 
tinue as  usual,  but  vomiting  can  no  longer  be  produced  by  the  use  of  emetics. 
Thumas  claims  to  have  located  a  vomiting  centre  in  the  medulla  in  the  imme- 
diate neighborhood  of  the  calamus  scriptorius.  Further  evidence,  however, 
'  Virckow's  Archiv  fur  patholoyische  Anatomie,  etc.,  1891,  Bd.  123,  S.  44. 


MOVEMENTS    OF    THE  ALIMENTARY   CANAL,   ETC.       327 

is  required  upon  this  point.  The  act  of  vomiting  may  be  produced  not  only 
08  a  reflex  from  various  sensory  nerves,  but  may  also  be  caused  by  direct 
action  upou  the  medullary  centres.  The  action  of  apomorphia  is  most  easily 
explained  by  supposing  that  it  acts  directly  on  the  nerve-centres. 

Micturition. — The  urine  is  secreted  continuously  by  the  kidneys,  is  car- 
ried to' the  bladder  through  the  ureters,  and  is  then  at  intervals  finally  ejected 
from  the  bladder  through  the  urethra  by  the  act  of  micturition. 

Movements  of  the  Ureters. — The  ureters  possess  a  muscular  coat  consisting  of 
an  internal  longitudinal  and  external  circular  layer.  The  contractions  of  this 
muscular  coat  are  the  means  by  which  the  urine  is  driven  from  the  pelvis  of  the 
kidney  into  the  bladder.  The  movements  of  the  ureter  have  been  carefully 
studied  by  Engelmann.^  According  to  his  description  the  musculature  of  the 
ureter  contracts  spontaneously  at  intervals  of  ten  to  twenty  seconds  (rabbit),  the 
contraction  beginning  at  the  kidney  and  progressing  toward  the  bladder  in  the 
form  of  a  peristaltic  wave  and  with  a  velocity  of  about  twenty  to  thirty  milli- 
meters per  second.  The  result  of  this  movement  should  be  the  forcing  of  the 
urine  into  the  bladder  in  a  series  of  gentle  rhythmic  spirts,  and  this  method  of 
filling  the  bladder  has  been  observed  in  the  human  being.  Suter  and  Mayer  ^ 
report  some  observations  upon  a  boy  in  wdiom  there  was  ectopia  of  the  bladder 
with  exposure  of  the  orifices  of  the  ureters.  The  flow  into  the  bladder  was 
intermittent  and  was  about  equal  upou  the  two  sides  for  the  time  the  child 
was  under  observation  (three  and  a  half  days). 

The  causation  of  the  contractions  of  the  ureter  musculature  is  not  easily 
explained.  Engelraann  finds  that  artificial  stimulation  of  the  ureter  or  of  a 
piece  of  the  ureter  may  start  peristaltic  contractions  which  mov'e  in  both  direc- 
tions from  the  point  stimulated.  He  was  not  able  to  find  ganglion-cells  in  the 
upper  two-thirds  of  the  ureter,  and  was  led  to  believe,  therefore,  that  the  con- 
traction originates  in  the  muscular  tissue  independently  of  extrinsic  or  intrinsic 
nerves,  and  that  the  contraction  wave  propagates  itself  directly  from  muscle- 
cell  to  muscle-cell,  the  entire  musculature  behaving  as  though  it  were  a  single, 
colossal  hollow  muscle-fibre.  The  liberation  of  the  stimulus  which  inaugurates 
the  normal  peristalsis  of  the  ureter  seems  to  be  connected  with  the  accumulation 
of  urine  in  its  upper  or  kidney  portion.  It  may  be  supposed  that  the  urine 
that  collects  at  this  point  as  it  flows  from  the  kidney  stimulates  the  muscular 
tissue  to  contraction,  either  by  its  pressure  or  in  some  other  way,  and  thus  leads 
to  an  orderly  sequence  of  contraction  waves.  It  is  possible,  however,  that  the 
muscle  of  the  ureter,  like  that  of  the  heart,  is  spontaneously  contractile  under 
normal  conditions,  and  does  not  depend  upon  the  stimulation  of  the  urine. 
Thus,  according  to  Engelmann,  section  of  the  ureter  near  the  kidney  does  not 
materially  affect  the  nature  of  the  contractions  of  the  stump  attached  to  the 
kidney,  although  in  this  case  the  pressure  of  the  urine  could  scarcely  act  as  a 
stimulus.  Moreover,  in  the  case  of  the  rat,  in  which  the  ureter  is  highly  con- 
tractile, the  tube  may  be  cut  into  several  pieces  and  each  piece  will  continue  to 

^  Pfliiger's  Archivfiir  die  gesammte  Physiologie,  1869,  Bd.  ii.  S.  243;  Bd.  iv.  S.  33, 
*  Archivfiir  exper.  Pathologic  und  Pharmakologie,  1893,  Bd.  32,  S.  241. 


328  AN  AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 

exhibit  periodic  peristaltic  contractions.  It  docs  not  seem  possible  at  present 
to  decide  between  these  two  views  as  to  the  cause  of  the  contractions.  The 
nature  of  the  contractions,  their  mode  of  proj^rcssion,  and  the  way  in  which 
they  force  the  urine  thruugh  the  ureter  seem,  however,  to  be  clearly  established. 
Efforts  to  show  a  regulatory  action  upon  tiiese  movements  through  the  central 
nervous  system  have  so  far  given  only  negative  results. 

Movements  of  the  Bladder. — The  bladder  contains  a  muscular  coat  of  plain 
muscle-tissue,  which,  according  to  the  usual  description,  is  arranged  so  as  to 
make  an  external  longitudinal  coat  and  an  internal  circular  or  oblique  coat. 
A  thin  longitudinal  layer  of  muscle-tissue  lying  to  the  interior  of  the  circular 
coat  is  also  described.  The  separation  between  the  longitudinal  and  circular 
layers  is  not  so  definite  as  in  the  ease  of  the  intestine ;  they  seem,  in  fact,  to  form 
a  continuous  layer,  one  passing  gradually  into  the  other  by  a  change  in  the 
direction  of  the  fibres.  At  the  cervix  the  circular  layer  is  strengthened,  and 
has  been  supposed  to  act  as  a  sphincter  with  regard  to  the  urethral  orifice — the 
so-called  sphincter  vesica  iuternus.  Round  the  urethra  just  outside  the  blad- 
der is  a  circular  layer  of  striated  muscle  which  is  frequently  designated  as  the 
external  sphincter  or  sphincter  urethrEe.  The  urine  brought  into  the  bladder 
accimiulates  within  its  cavity  to  a  certain  limit.  It  is  prevented  from  escape 
through  the  urethra  at  first  by  the  mere  elasticity  of  the  parts  at  the  urethral 
orifice,  aided  perhaps  by  tonic  contraction  of  the  internal  sphincter,  although 
this  function  of  the  circular  layer  at  this  point  is  disputed  by  some  observers. 
When  the  accumulation  becomes  greater  the  external  sphincter  is  brought  into 
action.  If  the  desire  to  urinate  is  strong  the  external  sphincter  seems  undoubt- 
edly to  be  controlled  by  voluntary  effort,  but  whether  or  not,  in  moderate  filling 
of  the  bladder,  it  is  brought  into  play  by  an  involuntary  reflex  is  not  definitely 
determined.  Back-flow  of  urine  from  the  bladder  into  the  ureters  is  effectually 
prevented  bv  the  oblique  course  of  the  ureters  through  the  wall  of  the 
bladder.  Owing  to  this  circumstance  pressure  within  the  bladder  serves  to  close 
the  mouths  of  the  ureters,  and  indeed  the  more  completely  the  higher  the  pres- 
sure. At  some  point  in  the  filling  of  the  bladder  the  pressure  is  sufficient  to 
arouse  a  conscious  sensation  of  fulness  and  a  desire  to  micturate.  Under  nor- 
mal conditions  the  act  of  micturition  follows.  It  consists  essentially  in  a  strong 
contraction  of  the  bladder  with  a  simultaneous  relaxation  of  the  external 
sphincter,  if  this  muscle  is  in  action,  the  effect  of  which  is  to  obliterate  more  or 
less  completely  the  cavity  of  the  bladder  and  drive  the  urine  out  through  the 
urethra. 

The  force  of  this  contraction  is  considerable,  as  is  evidenced  by  the  height 
to  which  the  urine  may  spirt  from  the  end  of  the  urethra.  According  to 
Mosso  the  contraction  may  support,  in  the  dog,  a  column  of  li(|uid  two  meters 
high.  The  contractions  of  the  bladder  may  be  and  usually  are  assisted  by 
contractions  of  the  walls  of  the  abdomen,  especially  toward  the  end  of  the  act. 
As  in  defecation  and  vomiting,  the  contraction  of  the  abdominal  muscles,  when 
the  glottis  is  closed  so  as  to  keep  the  diaphragm  fixed,  serves  to  increase  the 
pressure  in  the  abdominal  and  jielvic  cavities,  and  is  thus  used  to  assist  in  or 


MOVEMENTS    OF    THE   ALIMENTARY    CANAL,    ETC.        329 

complete  the  emptying  ol'tlic  l)la(l(l(M-.  It  is,  however,  ixtt  an  essential  part  of 
the  act  of  micturition.  I'lie  last  portions  of  tli(,'  nrine  escaping  into  tlie  urethra 
are  ejected,  in  the  male,  in  spirts  produced  by  the  rhythmic  contractions  of  the 
l)ull)o-cavernosus  nuiscie. 

Considerable  uncertainty  and  difference  of  opinion  exists  as  to  the  physio- 
logical mechanisiu  by  which  this  series  of  muscular  contractions,  and  especiallv 
the  contractions  of  the  bladder  itself,  is  produced.  According  to  the  frequently 
quoted  description  given  by  Goltz^  the  series  of  events  is  as  follows:  The  dis- 
tention of  the  bladder  by  the  urine  causes  finally  a  stimulation  of  the  sensory 
fibres  of  the  organ  and  produces  a  reflex  contraction  of  the  bladder  musculature 
which  squeezes  some  urine  into  the  urethra.  The  first  drops,  however,  that 
enter  the  urethra  stimulate  the  sensory  nerves  there  and  give  rise  to  a  coascious 
desire  to  urinate.  If  no  obstacle  is  presented  the  bladder  then  empties  itself, 
assisted  perhaps  by  the  contractions  of  the  abdominal  muscles.  Tiie  emptying 
of  the  bladder  may,  however,  be  prevented,  if  desirable,  by  a  voluntary  con- 
traction of  the  sphincter  urethrse,  which  op])oses  the  eiFect  of  the  contraction  of 
the  bladder.  If  the  bladder  is  not  too  full  and  the  sphincter  is  kept  in  action 
for  some  time,  the  contractions  of  the  bladder  may  cease  and  the  desire  to 
micturate  pass  oif.  According  to  this  view  the  voluntary  control  of  the 
process  is  limitetl  to  the  action  of  the  external  sphincter  and  the  abdominal 
muscles ;  the  contraction  of  the  bladder  itself  is  purely  an  unconscious  reflex 
taking  place  through  a  lumbar  centre. 

The  experiments  of  Goltz  and  others,  upon  dogs  in  which  the  spinal  cord 
was  severed  at  the  junction  of  the  lumbar  and  the  thoracic  regions,  prove 
that  micturition  is  essentially  a  reflex  act  with  its  centre  in  the  lumbar  cord, 
but  a  number  of  physiologists  have  concluded  that  the  contractions  of  the 
bladder  itself,  in  spite  of  its  involuntary  musculature,  is  also  under  control  of 
the  will.  Mosso  and  Pellacani "  have  made  experiments  upon  women  which 
seem  to  show  that  this  is  the  case.  In  these  experiments  a  catheter  was  intro- 
duced into  the  bladder  and  connected  with  a  recording  apparatus  to  measure 
the  volume  of  the  bladder.  It  was  found  that,  in  some  cases  at  least,  the 
woman  could  empty  the  bladder  at  will  without  using  the  abdominal  muscles. 
The  same  authors  adduce  experimental  evidence  to  show  that  the  sensation  of 
fulness  and  desire  to  micturate  come  from  sensory  stimulation  in  the  bladder 
itself  caused  by  the  pressure  of  the  urine.  They  point  out  that  the  bladder  is 
very  sensitive  to  reflex  stimulation  ;  that  every  psychical  act  and  every  sensory 
stimulus  is  apt  to  cause  a  contraction  or  increased  tone  of  the  bladder.  The 
bladder  is,  therefore,  subject  to  continual  changes  in  size  from  reflex  stimula- 
tion, and  the  pressure  within  it  will  depend  not  simply  on  the  quantity  of 
urine  but  on  the  condition  of  tone  of  the  bladder.  At  a  certain  pressure 
the  sensory  nerves  are  stimulated  and  under  normal  conditions  micturition 
ensues.  We  may  understand,  from  this  point  of  view,  how  it  happens  that  we 
have  sometimes  a  strong  desire  to  micturate  when  the  bladder  contains  but  little 

^  Pfliiger's  Archivfiir  die  gesammte  Physiologie,  1874,  Bd.  viii.  S.  478. 
^  Archives  italienne  de  Biologic,  1882,  tome  i. 


330  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

urine — for  exaiupk',  uikKt  emotional  excitement.  In  snch  cases  if  the  micturi- 
tion is  prevented,  probably  by  the  action  of  the  external  sphincter,  the  bladder 
may  subsequently  relax  and  the  .sensation  of  fulness  and  desire  to  micturate 
pass  away  until  the  urine  accumulates  in  sufficient  (juantity  or  the  pressure  is 
again  raised  by  some  circumstance  which  causes  a  reflex  contraction  of  the 
bladder. 

Nervous  Mechanism. — According  to  a  recent  paper  by  Langley  and  Anders(jn,' 
the  bladder  in  cats,  dogs,  and  rabbits  receives  motor  fibres  from  two  sources:  (1) 
From  the  lumbar  nerves,  the  fibres  passing  out  iu  the  second  to  the  fifth  lumbar 
nerves  and  reaching  the  bladder  through  the  sympathetic  chain  and  the  infe- 
rior mesenteric  ganglion  and  hypogastric  nerves.  Stimulation  of  these  nerves 
causes  comparatively  feeble  contraction  of  the  bladder.  (2)  From  the  sacral 
spinal  nerves,  the  fibres  originating  in  the  second  and  third  sacral  spinal  nerves, 
or  in  the  rabbit  iu  the  third  and  fourth,  and  being  contained  in  the  so-called 
nervus  erigens.  Stimulation  of  these  nerves,  or  some  of  them,  causes  strong 
contractions  of  the  bladder,  sufficient  to  empty  its  contents.  Little  evidence 
was  obtained  of  the  presence  of  vaso-motor  fibres.  According  to  Xawrocki 
and  Skabitschewsky  ^  the  spinal  sensory  fibres  to  the  bladder  are  found  in  part 
in  the  posterior  roots  of  the  first,  second,  third,  and  fourth  sacral  spinal  nerves, 
particularly  the  second  and  third.  When  these  fibres  are  stimulated  they  excite 
reflexlv  the  motor  fibres  to  the  bladder  found  in  the  anterior  roots  of  the  second 
and  third  sacral  spinal  nerves.  Some  sensory  fibres  to  the  bladder  pass  by  way 
of  the  hypogastric  nerves.  When  these  are  stimulated  they  produce,  according 
to  these  authors^  a  reflex  effect  upon  the  motor  fibres  in  the  other  hypogastric 
nerve,  causing  a  contraction  of  the  bladder,  the  reflex  occurring  through  the 
inferior  mesenteric  ganglion.  This  observation  has  been  confirmed  by  several 
authorities,  and  is  the  best  example  of  a  peripheral  ganglion  serving  as  a  reflex 
centre.  Langley  and  Anderson,^  who  also  obtained  this  effect,  give  it  a  special 
explanation,  contending  that  it  is  not  a  true  reflex. 

The  immediate  spinal  centre  through  which  the  contractions  of  the  bladder 
may  be  reflexly  stimulated  or  inhibited  lies,  according  to  the  experiments  of 
Goltz,  in  the  lumbar  portion  of  the  cord,  probably  between  the  second  and  fifth 
lumbar  spinal  nerves.  In  dogs  in  which  this  portion  of  the  cord  was  isolatal 
by  a  cro&s  section  at  the  junction  of  the  thoracic  and  lumbar  regions,  micturi- 
tion still  ensued  when  the  bladder  was  sufficiently  full,  and  could  be  called 
forth  reflexly  by  sensory  stimuli,  especially  by  slight  irritation  of  the  anal 
region. 

'  Jawmul  of  Physiology,  1895,  vol.  xix.  p.  71. 

*  Pfliiger's  Archivfiir  die  gesammte  Physiologie,  1891,  Bd.  49,  S.  141. 

^Journal  of  Physiology,  1894,  vol.  xvi.  p.  410. 


VI.  BLOOD  AND  LYMPH. 


BLOOD. 

A.  General.  Properties:   Physiology  of  the  Corpuscles. 

The  blood  of  the  body  is  contained  in  a  practically  closed  system  of  tubes, 
the  blood-vessel^,  within  which  it  is  kept  circulating  by  the  force  of  the  heart- 
beat. The  blood  is  usually  spoken  of  as  the  nutritive  liquid  of  the  body,  but 
its  functions  may  be  stated  more  explicitly,  although  still  in  quite  general 
terms,  by  saying  that  it  carries  to  the  tissues  food-stuffs  after  they  have  been 
properly  prepared  by  the  digestive  organs;  that  it  transports  to  the  tissues 
oxygen  absorbed  from  the  air  in  the  lungs ;  that  it  carries  off"  from  the  tissues 
various  waste  products  formed  in  the  processes  of  disassimilation,  such  as 
urea,  uric  acid,  water,  CO2,  etc. ;  and  that  in  warm-blooded  animals  it  aids  in 
equalizing  the  temperature  of  the  body.  It  is  quite  obvious,  from  these 
statements,  that  a  complete  consideration  of  the  physiological  relations  of  the 
blood  would  involve  substantially  a  treatment  of  the  whole  subject  of  physi- 
ology. It  is  proposed,  therefore,  in  this  section  to  treat  the  blood  in  a  re- 
stricted way — to  consider  it,  in  fact,  as  a  tissue  in  itself,  and  to  study  its  com- 
position and  properties  without  especial  reference  to  its  nutritive  relationship 
to  other  parts  of  the  body. 

Histological  Structure. — The  blood  is  composed  of  a  liquid  part,  the 
plasma,  in  which  float  a  vast  number  of  microscopic  bodies,  the  blood-corpius- 
des.  There  are  at  least  three  different  kinds  of  corpuscles,  known  respectively 
as  the  red  corpuscles;  the  white  corpuscles  or  leucocytes,  of  which  in  turn 
there  are  a  number  of  different  kinds ;  and  the  hlood-plates.  As  the  details 
of  structure,  size,  and  number  of  these  corpuscles  belong  properly  to  text- 
books on  histology,  they  will  be  mentioned  only  incidentally  in  this  section 
when  treating  of  the  physiological  properties  of  the  corpuscles.  Blood-plasma, 
when  obtained  free  from  corpuscles,  is  perfectly  colorless  in  thin  layers— for 
example,  in  microscopic  preparations ;  when  seen  in  large  quantities  it  shows  a 
slightly  yellowish  tint,  the  depth  of  color  varying  with  different  animals.  This 
color  is  due  to  the  presence  in  small  quantities  of  a  special  pigment,  the  nature 
of  which  is  not  definitely  known.  The  red  color  of  blood  is  not  due,  there- 
fore, to  coloration  of  the  blood-plasma,  but  is  caused  by  the  mass  of  red  cor- 
puscles held  in  suspension  in  this  liquid.  The  proportion  by  bulk  of  plasma 
to  corpuscles  is  usually  given,  roughly,  as  two  to  one. 

Blood-serum  and  Befibrinated  Blood.— In  connection  with  the  explanation 
of  the  term  "  blood-plasma"  just  given,  it  will  be  convenient  to  define  briefly 

331 


332  ^iV^  AMERICAN    TEXT-BOOK    O/'   PHYSIOLOGY. 

the  terms  "  blood-serum  "  and  "  defibriuated  blood."  Blootl,  after  it  escapes 
from  the  vessels,  usually  clots  or  eoa<;ulates ;  the  nature  of  this  j)roce&s  is 
discussed  in  detail  on  j).  352,  The  clot,  as  it  forms,  gradually  shrinks  and 
squeezes  out  a  clear  liquid  to  which  the  name  bfood-.scnDii  is  given,  Serum 
resembles  the  plasma  of  normal  blood  in  general  aj)pearance,  but  differs  from 
it  in  composition,  as  Avill  be  exj)laincd  later.  At  ])resent  we  may  say,  by  way 
of  a  preliminary  definition,  that  blood-serum  is  the  licpiid  part  of  blood  after 
coagulation  has  taken  })lace,  as  blood-plasma  is  the  liquid  part  of  blood  before 
coagulation  has  taken  place.  If  shed  blood  is  whii)])e(l  vigorously  with  a  rod 
or  some  similar  object  while  it  is  clotting,  the  essential  part  of  the  clot — 
namely,  the  fibrin — forms  differently  from  what  it  does  when  the  blood  is 
allowed  to  coagulate  quietly ;  it  is  deposited  in  shreds  on  the  whipper.  Blood 
that  has  been  treated  in  this  way  is  known  as  defibr'mated  blood.  It  consists 
of  blood-serum  plus  the  red  and  white  corpuscles,  and  as  far  as  aj^pearances 
go  it  resembles  exactly  normal  blood ;  it  has  lost,  however,  the  power  of  clot- 
ting. A  more  complete  definition  of  these  terms  will  be  given  after  the  sub- 
ject of  coagulation  has  been  treated. 

Reaction. — The  reaction  of  blood  is  alkaline,  owing  mainly  to  the  alka- 
line salts,  especially  the  carbonates  of  soda,  dissolved  in  the  plasma.  The 
degree  of  alkalinity  varies  with  different  animals:  reckoned  as  NagCOg,  the 
alkalinity  of  dog's  blood  corresponds  to  0,2  per  cent,  of  this  salt;  of  human 
blood,  0.35  per  cent.  The  alkaline  reaction  of  blood  is  very  easily  demon- 
strated upon  clear  plasma  free  from  corpuscles,  but  with  normal  blood  the  red 
color  prevents  the  direct  application  of  the  litmus  test.  A  number  of  simple 
devices  have  been  suggested  to  overcome  this  difficulty.  For  example,  the 
method  employed  by  Zuntz  is  to  soak  a  strip  of  litmus-paper  in  a  concentrated 
solution  of  NaCl,  to  place  on  this  paj)er  a  drop  of  blood,  and,  after  a  few 
seconds,  to  remove  the  drop  with  a  stream  of  water  or  with  a  piece  of  filter- 
paper.  The  alkaline  reaction  becomes  rapidly  less  marked  after  the  blood  has 
been  shed;  it  varies  also  slightly  under  different  conditions  of  normal  life 
and  in  certain  pathological  conditions.  After  meals,  for  instance,  during  the 
act  of  digestion,  it  is  said  to  be  increased,  while,  on  the  contrary,  exercise 
causes  a  diminution.  In  no  case,  hoM'ever,  does  the  reaction  become  acid. 
For  details  of  the  methods  used  for  quantitative  determinations  of  the  alka- 
linity of  human  blood,  reference  must  be  made  to  original  sources.' 

Specific  Gravity. — The  specific  gravity  of  human  blood  in  the  adult  male 

may  vary  from  1041  to  1067,  the  average  being  about  1055.     Jones  ^  made 

a  careful  study  of  the  variations  in  specific  gravity  of  human  blood  under 

different  conditions  of  health  and  disease,  making  use  of  a  simj)le   method 

which  requires  only  a  few  drops  of  l)lood  for  each  determination.     He  found 

that  the  specific  gravity  varies  with  age  and  sex,  that  it  is  diminished  after 

eating  and  is  increased  by  exercise,  that  it  falls  slowly  during  the  day  and 

rises  gradually  during  the  night,  and  that  it  varies  greatly  in  individuals,  "so 

'  Peiper  :    Virchou^s  Archiv,  vol,  cxvi,,  1889,  p.  337, 
*  Journid  of  Phymdogy,  vol.  xii.,  1891,  p.  299. 


BLOOD. 


333 


iniKh  so  that  a  speciHc  gravity  which  is  normal  for  oue  may  be  a  sigu  ol  dis- 
ease in  another."  The  siiecific  gravity  of  the  corpuscles  is  slightly  greater 
than  that  of  the  plasma.  For  this  reason  the  corpuscles  in  shed  blood,  when 
its  coagulation  is  prevented  or  retarded,  tend  to  settle  to  the  bottom  of  the 
containing  utensil,  leaving  a  more  or  less  clear  layer  of  supernatant  pksma. 
Among  themselves,  also,  the  corpuscles  ditfer  slightly  in  specific  gravity,  the 
red  corpuscles  being  heaviest  and  the  blood-plates  being  lightest. 

Red  Corpuscles.— The  red  corpuscles  in  man  and  in  all  the  mammalia, 
with  the  exception  of  the  camel  and  other  members  of  the  group  Camelidie, 
are  biconcave  circular  disks  without  nuclei;  in  the  Caraelid^  they  have  an 
elliptical  form.     Their  average  diameter  in  man  is  given  at  7.7//  (l/i  =  0.001 
of  a  mm.);  their  number,  which  is  usually  reckoned  as  so  many  in  a  cubic 
millimeter,  varies  greatly  under  diiferent  conditions  of  health  and  disease. 
The  average  number  is  given  as  5,000,000  per  cubic  mm.  for  males  and 
4,500,000  for  females.     The  red  color  of  the  corpuscles  is  due  to  the  presence 
in  them  of  a  pigment  known  as  "hemoglobin."     Owing  to  the  minute  size 
of  the  corpuscles,  their  color  when  seen  singly  under  the  microscope  is  a 
ftiint   yellowish-red,   but  when  seen   in    mass   they  exhibit  the  well-known 
blood-red  color,  which  varies  from  scarlet  in  arterial  blood  to  purplish-red 
in  venous  blood,  this  variation  in  color  being  dependent  upon  the  amount  of 
oxygen  contained  in  the  blood  in  combination  with  the  haemoglobin.    Speaking 
generally,  the  function  of  the  red  corpuscles  is  to  carry  oxygen  from  the  lungs 
to  the  tissues.     This  function  is  entirely  dependent  upon  the  presence^  of 
hemoglobin,  which  has  the  power  of  combining  easily  with  oxygen  gas.     The 
physiology  of  the  red  corpuscles,  therefore,  is  largely  contained  in  a  description 
of  the  properties  of  hsemoglobiu. 

Condition  of  the  Haemoglobin  in  the  Corpuscle.— The  finer  structure 
of  the  red  corpuscle  is  not  completely  known.  It  is  commonly  believed  that 
the  corpuscle  consists  of  two  substances— a  delicate,  extensible,  colorless  pro- 
toplasmic material,  which  gives  to  the  corpuscle  its  shape  and  which  is  known 
as  the  stroma,  and  the  hemoglobin.  The  latter  constitutes  the  bulk  of  the  cor- 
puscle, forming  as  much  as  95  per  cent,  of  the  solid  matter.  It  was  formerly 
thought  that  hemoglobin  is  disseminated  as  such  in  the  interstices  of  the 
porous  spongy  stroma,  but  there  seem  to  be  reasons  now  for  believing  that 
it  is  present  in  the  corpuscles  in  some  combination  the  nature  of  which  is 
not  fully  known.  This  belief  is  based  upon  the  fact  that  Hoppe-Seyler  ^  has 
shown  that  hemoglobin  while  in  the  corpuscles  exhibits  certain  minor  differ- 
ences in  properties  as  compared  with  hemoglobin  outside  the  corpuscles.  In 
various  ways  the  compound  of  hemoglobin  in  the  corpuscles  may  be  destroyed, 
the  hemoglobin  being  set  free  and  passing  into  solution  in  the  plasma.  Blood 
in  which  this  change  has  occurred  is  altered  in  color  and  is  known  as  "  laky 
blood."  In  thin  layers  it  is  transparent,  whereas  normal  blood  with  the 
hemo-lobin  still  in  the  corpuscles  is  quite  opaque  even  in  very  thin  strata. 
Blood'may  be  made  laky  by  the  addition  of  ether,  of  chloroform,  of  bile  or 
1  Zeitschrijt  fur  physwlogiscke  Chemie,  vol.  xiii.,  1889,  p.  477. 


334  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

the  bile  acids,  of  the  .•^eniin  of  other  animals,  by  an  excess  of  water,  by 
alternately  freezing  and  thawintr,  and  by  a  nnmber  of  other  methods.  In 
connection  with  two  of  these  methods  of  discharging  haemoglobin  from  the 
corpuscles  theie  have  come  into  use  in  current  medical  and  physiologicjd 
literature  two  technical  terms  which  it  may  be  well  to  attempt  to  define. 

GlohuUcidal  Action  of  S€)'um. — It  was  shown  first  by  Landois  that  the 
serum  of  one  animal  may  have  the  property  of  destroying  the  red  corpuscles 
in  the  blood  of  another  animal,  thus  making  the  blood  laky.  This  fact,  which 
has  since  been  investigated  more  fully,  is  now  designated  under  the  term  of 
"globulicidal  "  action  of  the  serum.  It  has  been  found  that  different  kinds  of 
serum  show  different  degrees  of  globulicidal  activity,  and  that  white  as  well  as 
red  corj)uscles  may  be  destroyed.  Dog's  serum  or  Inmian  serum  is  strongly 
globulicidal  to  rabbit's  blood.  It  would  seem  that  this  lU'tion  is  not  due  to 
mere  variations  in  the  amounts  of  inorganic  salts  in  the  different  kinds  of 
serum,  since  the  remarkable  fact  has  been  discovered  that  heating  serum  to 
55°  or  60°  C.  for  a  few  minutes  destroys  its  globulicidal  action,  although  such 
treatment  causes  no  coagulation  of  the  proteids  nor  any  visible  change  in  the 
liquid.  This  globulicidal  action  seems  to  be  associated  with  a  similar  destruc- 
tive effect  of  serum  on  bacteria — its  so-called  "  bactericidal  action  " — but  a 
satisfactory  explanation  of  either  phenomenon  has  not  yet  been  given.  The 
subject  is  complicated  by  the  fact  that  the  serum  of  some  animals  fails  to  give 
the  globulicidal  reaction ;  horse's  serum,  for  instance,  does  not  destroy  the  red 
corpuscles  of  rabbit's  blood.  A  discussion  of  the  theories  and  facts  bearing 
upon  the  matter  would  lead  too  far  into  pathological  literature,  to  which  the 
reader  is  referred  for  further  information. 

Isotonic  Solutions. — AVhen  blood  or  defibrinated  blood  is  diluted  with 
water,  a  point  is  soon  reached  at  wliich  haemoglobin  begins  to  pass  out  of  the 
corjMiscles  into  the  plasma  or  the  serum,  and  the  blood  begins  to  become  laky; 
to  obtain  this  effect  different  quantities  of  water  may  be  required  for  the 
blood  of  different  animals,  frog's  blood,  for  example,  requiring  more  water  than 
mammalian  blood.  It  appears  that  the  liquid  surrounding  the  corjniscles  must 
have  a  certain  concentration  as  regards  salts  or  other  soluble  substances,  such 
as  sugar,  in  order  to  prevent  the  entrance  of  water  into  the  substance  of  the 
corpuscle.  There  exists  normally  in  the  red  corpuscle  a  certain  quantity 
of  water,  determined  by  the  nature  of  its  own  substance  and  the  attraction  for 
water  exercised  by  the  soluble  substances  in  the  liquid  surrounding  the  corj)us- 
cle.  If  the  concentration  of  the  outside  liquid  is  diminished,  this  equilibrium 
is  destroyed  and  water  passes  into  the  corpuscle;  if  the  dilution  has  been  suf- 
ficient, enough  water  pass&s  into  the  corpuscle  to  make  it  swell  and  eventually 
to  force  out  the  haemoglobin.  Liquids  containing  inorganic  salts,  or  other  sol- 
uble substances  with  an  attraction  for  water,  in  quantities  sufficient  to  prevent 
the  imbibition  of  water  by  the  corpuscles  are  said  to  be  "  isotonic  to  the  cor- 
puscles." Red  corpuscles  suspended  in  such  liquids  do  not  change  in  shape  nor 
lose  their  haemoglobin.  AVhen  solutions  of  different  substances  are  compared 
from  this  standpoint,  it  is  found  that  the  concentration  necessary  varies  with 


BLOOD.  335 

the  substance  used.  Thus,  a  solution  of  NaCl  of  0.64  per  cent,  is  isotonic  with  a 
sohition  of  sugar  of  5.5  per  cent,  or  a  sohitiou  of  KNO3  of  1 .09  per  cent.  When 
placed  in  any  of  these  three  solutions  red  corpuscles  do  not  take  uj)  water — at 
least  not  in  quantities  sufficient  to  discharge  the  haemoglobin.  For  a  more 
complete  account  of  these  relations  the  reader  is  referred  to  <jriginal  sources 
(Hamburger ').  It  may  be  said  that  the  term  was  introduced  first  in  connec- 
tion with  plant-cells.  In  the  animal  body  it  happens  that  the  isotonic  relations 
of  certain  substances  have  been  worked  out  for  the  red  corpuscles,  but  similar 
relations  must  exist  with  reference  to  tiie  other  cells.  Speaking  generally,  it 
may  be  said  that  tlie  composition  of  normal  blood  and  Iymj)li  is  isotonic  to  the 
tissue-elements,  and  that  it  must  be  kept  so  to  preserve  the  cells  from  injury. 

Nature  and  Amount  of  Haemog-lobin. — Hsemoglobin  is  a  vcrv  com})lex 
substance  belonging  to  the  group  of  combined  proteids.  (For  the  definition 
and  classification  of  proteids,  as  well  as  for  the  purely  chemical  properties  of 
hsemoglobin  and  its  derivatives,  reference  must  be  made  to  the  section  on  "  The 
Ciiemistry  of  the  Body.")  When  decomposed  in  various  ways  haemoglobin 
breaks  up  into  a  proteid  (globulin,  96  per  cent.)  and  a  simpler  pigment  (haema- 
tin,  4  per  cent.).  When  the  decomposition  takes  place  in  the  absence  of  oxygen, 
the  products  formed  are  globulin  and  haemochromogen,  and  the  decomposition 
seems  to  be  of  the  nature  of  a  simple  dissociation.  Haemochromogen  in  the 
presence  of  oxygen  quickly  undergoes  oxidation  to  the  more  stable  haematin. 
Ho}>pe-Seyler  has  shown  that  haemochromogen  possesses  the  chemical  group- 
ing which  gives  to  haemoglobin  its  power  of  combining  readily  with  oxygen 
and  its  distinctive  absorption  spectrum.  On  the  basis  of  facts  such  as  these, 
haemoglobin  may  be  defined  as  a  compound  of  a  proteid  body  with  haemochro- 
mogen. It  seems,  then,  that  although  the  haemochromogen  portion  is  the 
essential  thing,  giving  to  the  molecule  of  haemoglobin  its  valuable  physiological 
properties  as  a  respiratory  pigment,  yet  in  the  blood-corpuscles  this  substance 
is  incorporated  into  a  much  larger  and  more  unstable  molecule,  whose  behavior 
toward  oxygen  is  different  from  that  of  the  haemochromogen  itself,  the  differ- 
ence being  mainly  in  the  fact  that  the  haemoglobin  as  it  exists  in  the  corpus- 
cles forms  w^ith  oxygen  a  comparatively  feeble  combination  which  may  be 
broken  up  readily  with  liberation  of  the  gas. 

Haemoglobin  is  widely  distributed  throughout  the  animal  kingdom,  being 
found  in  the  blood-corpuscles  of  mammalia,  birds,  reptiles,  amphibia,  and 
fishes,  and  in  the  blood  or  blood-corpuscles  of  many  of  the  invertebrates. 
The  composition  of  its  molecule  is  found  to  vary  somewhat  in  different  animals, 
so  that,  strictly  speaking,  there  are  probably  a  number  of  different  forms 
of  haemoglobin — all,  however,  closely  related  in  chemical  and  physiological 
properties.  Elementary  analysis  of  dog's  haemoglobin  shows  the  following 
percentage  composition  (Jaquet) :  C  53.91,  H  6.62,  N  15.98,  S  0.542, 
Fe  0.333,  O  22.62.  Its  molecular  formula  is  given  as  C^^^^^^^-^^YeO^^^, 
which  would  make  the  molecular  weight  16,669.  Other  estimates  are  given  of 
the  molecular  formula,  but  they  agree  at  least  in  showing  that  the  molecule 
*  Du  Bois-Reymond's  Archivfur  Physiologic,  1886,  p.  476;  1887,  p.  31. 


336  AN  AMERICAN    TEXT-BOOK    OF   PITYSIOLOGY. 

is  of  enormous  size.  The  molecular  formula  for  hajmochroraogen  is  iiiiich 
simpler;  it  is  usually  \i\\vn  as  C^JTjgN^FoOj.  The  exact  amount  of  h;em()<i;lol)in 
in  iunuau  blood  varies  naturally  with  the  individual  and  with  ditU'rent  condi- 
tions of  life.  According  to  Preyer,^  the  average  amount  for  the  adult  male  is 
14  grams  of  htemoglobin  to  each  100  grams  of  blood.  It  is  estimated  that  in 
the  blood  of  a  man  weighing  Q^  kilos,  there  are  contained  about  750  grams  of 
haemoglobin,  which  is  distributed  among  some  twenty-five  trillions  of  corpuscles, 
giving  a  total  superficial  area  of  about  3200  square  meters.  Practically  all  of 
this  large  surface  of  haemoglobin  is  available  lor  the  absorption  of  oxygen 
from  the  air  in  the  lungs,  for,  owing  to  the  great  number  and  the  minute 
size  of  the  capillaries,  the  blood,  in  passing  through  a  capillary  area,  becomes 
subdivided  to  such  an  extent  that  the  red  corpuscles  stream  through  the  capil- 
laries, one  may  say,  in  single  file.  In  circulating  through  the  linigs,  therefore, 
each  corpuscle  becomes  exposed  more  or  less  completely  to  the  action  of  the 
air,  and  the  utilization  of  the  entire  quantity  of  haemoglobin  must  be  nearly 
}>erfect.  It  may  be  worth  while  to  call  attention  to  the  fact  that  the  biconcave 
form  of  the  red  corpuscle  increases  the  superficies  of  the  corpuscle  and  tends 
to  make  the  surface  exposure  of  the  haemoglobin  more  complete. 

Compounds  -with  Oxygen  and.  other  Gases. — Haemoglobin  has  the 
property  of  uniting  with  oxygen  gas  in  certain  definite  proportions,  forming  a 
true  chemical  compound.  This  compound  is  known  as  oxi/hcemoglobin ; 
it  is  formed  whenever  blood  or  haemoglobin  solutions  are  exposed  to  air  or 
otherwise  brought  into  contact  with  oxygen.  Each  molecule  of  luemoglobin 
is  supposed  to  combine  with  one  molecule  of  oxygen,  and  it  is  usually  estimated 
that  1  gram  of  dried  haemoglobin  (dog)  can  take  up  1.59  c.c.  of  oxygen 
measured  at  0°  C.  and  760  mm.  of  barometric  pressure.  Oxyhaemoglobin  is 
not  a  very  firm  compound.  If  placed  in  an  atmosphere  containing  no  oxy- 
gen, it  will  be  dissociated,  giving  off  free  oxygen  and  leaving  behind  luemo- 
globin, or,  as  it  is  often  called  by  way  of  distinction,  "  reduced  hcemoglobin." 
This  power  of  combining  with  oxygen  to  form  a  loose  chemical  compound, 
which  in  turn  can  be  dissociated  easily  when  the  oxygen-pressure  is  lowered, 
makes  possible  the  function  of  haemoglobin  in  the  blood  as  the  carrier  of 
oxygen  from  the  lungs  to  the  tissues.  The  details  of  this  process  will  be 
described  in  the  section  on  Respiration.  Haemoglobin  forms  with  carbon- 
monoxide  gas  (CO)  a  compound,  similar  to  oxyhaemoglobin,  which  is 
known  as  carbon-monoxide  hcemoglobin.  In  this  compound  also  the  union 
takes  place  in  the  proportion  of  one  molecule  of  haemoglobin  to  one 
molecule  of  the  gas.  The  compound  formed  differs,  however,  from  oxy- 
haemoglobin in  being  much  more  stable,  and  it  is  for  this  reason  that  the 
breathing  of  carbon  monoxide  gas  is  liable  to  prove  fatal.  The  CO  unites 
with  the  haemoglobin,  forming  a  firm  compound ;  the  tissues  of  the  bo<ly  are 
thereby  prevented  from  obtaining  their  necessary  oxygen,  and  death  results 
from  suffocation  or  asphyxia.  Carbon  monoxide  forms  one  of  the  constituents 
of  coal-gas.     The  w-ell-known  fatal  eliect  of  breathing  coal-gas  for  some  time, 

*  Die  Bluthrystalk,  Jena,  1871. 


BLOOD.  337 

as  in  the  case  of  individuals  sleeping  in  a  room  where  gas  is  escaping,  is  trace- 
able directly  to  the  carbon  monoxide.  Nitric  oxide  (NO)  forms  also  with 
haemoglobin  a  dofinite  compound  which  is  even  more  stable  than  the  CO- 
hiemoglobin ;  if,  therefore,  this  gas  were  brought  into  contact  with  the  blood, 
it  would  cause  death  in  the  same  way  as  the  CO. 

Oxyhtemoglobin,  carbon-monoxide  hccmoglobin,  and  nitric-oxide  haemoglo- 
bin are  similar  compounds.  Each  is  formed,  appai'cntly,  by  a  definite  combina- 
tion of  the  gas  with  the  haeraochromogen  portion  of  the  hjemoglobin  molecule, 
and  a  given  weight  of  hfcmoglobin  unites  presumably  with  an  equal  volume  of 
each  gas.  In  marked  contrast  to  these  facts,  Boiir  ^  has  shown  that  luemoglobin 
forms  a  compound  with  carbon-dioxide  gas,  carbo-hcemoglobin,  in  which  the 
quantitative  relationship  of  the  gas  to  the  haemoglobin  differs  from  that  shown 
by  oxygen.  In  a  mixture  of  O  and  CO^  each  gas  is  absorbed  by  hemoglobin 
solutions  independently  of  the  other,  so  that  a  solution  of  haemoglobin  nearly 
saturated  with  oxygen  can  unite  with  as  much  CO2  as  though  it  held  no  oxygen 
in  combination.  Bohr  suggests,  therefore,  that  the  O  and  the  CO2  must  unite 
with  different  portions  of  the  haemoglobin — the  oxygen  with  the  pigment  portion, 
the  haemochromogen,  and  the  COj  possibly  with  the  proteid  portion.  It  seems 
probable  that  haemoglobin  plays  a  part  in  the  transportion  of  the  carbon 
dioxide  as  well  as  the  oxygen  of  the  blood,  but  its  exact  value  in  this  respect 
as  compared  with  the  blood-plasma,  which  also  acts  as  a  carrier  of  CO2,  has 
not  been  definitely  determined  (see  Respiration). 

Presence  of  Iron  in  the  Molecule. — It  is  probable  that  iron  is  quite 
generally  present  in  the  animal  tissues  in  connection  with  nuclein  compounds, 
but  its  existence  in  haemoglobin  is  noteworthy  because  it  has  long  been  known 
and  because  the  important  property  of  combining  with  oxygen  seems  to  be 
connected  with  the  presence  of  this  element.  According  to  the  analyses 
made,  the  proportion  of  iron  in  haemoglobin  varies  somewhat  in  different 
animals :  the  figures  given  are  from  0.335  to  0.47  per  cent.  The  amount  of 
haemoglobin  in  blood  may  be  determined,  therefore,  by  making  a  quantitative 
determination  of  the  iron.  The  amount  of  oxygen  with  which  haemoglobin 
will  combine  may  be  expressed  by  saying  that  one  molecule  of  oxygen  will 
be  fixed  for  each  atom  of  iron  in  the  haemoglobin  molecule.  In  the  decom- 
position of  haemoglobin  into  globulin  and  haematin  or  globulin  and  haemo- 
chromogen, Avhich  has  been  spoken  of  above,  the  iron  is  retained  in  the 
haematin. 

Crystals. — Haemoglobin  may  be  obtained  readily  in  the  form  of  ciystals 

(Fig.  86).    As  usually  prepared,  these  crystals  are  really  oxyhaemoglobin,  but 

it  has  been  shown  that  reduced  haemoglobin  also  crystallizes,  although  with 

more  difficulty.     Haemoglobin  from  the  blood  of  diflferent  animals  varies  to  a 

marked  degree  in  respect  to  the  power  of  crystallization.     From  the  blood  of 

the  rat,  dog,  cat,  guinea-pig,  and  horse,  crystals  are  readily  obtained,  while 

haemoglobin  from  the  blood  of  man  and  of  most  of  the  vertebrates  crystallizes 

much  less  easily.     Methods  for  preparing  and  purifying  these  crystals  will  be 

^  Skandivavisches  Arckivfur  Physiologie,  1892,  Bd.  3,  S.  47. 
22 


338 


AX   AMFJiTCAN    TEXT-IIOOK    OF    PHYSTOLOGY. 


found  iu  the  .section  on  "  The  Chemistry  of"  tlie  Body."  To  obtain  si^eciniens 
quickly  for  examination  under  the  microscope,  one  of  the  most  certain  methods 
is  to  take  some  blood  from  one  of  the  animals  whose  luemoglobin  crystallizes 

easily,  place  it  in  a  test-tube,  add  to  it  a  few 
drops  of  ether,  shake  the  tube  thorouji^hly 
until  the  blood  becomes  laky — that  is, 
until  the  haemoglobin  is  discharged  into 
the  plasma — and  then  place  the  tube 
on  ice  until  the  crystals  are  deposited. 
Small  portions  of  the  crystalline  sedi- 
ment may  then  be  removed  to  a  glass 
slide  for  examination.  Htemoglobin 
from  different  animals  varies  not  only 
as  to  the  ease  with  which  it  crystal- 
lizes, but  in  some  cases  also  as  to  the 
form  that  the  crystals  take.  In  man 
and  in  most  of  the  mammalia  haemoglo- 
bin is  deposited  in  the  form  of  rhom- 
bic prisms;  in  the  guinea-pig  it  crys- 
tallizes in  tetrahedra  {d,  Fig.  86),  and 
in  the  squirrel  in  hexagonal  plates.  The 
crystals  are  readily  soluble  in  water,  and 
by  repeated  crystallizations  the  haemo- 
globin may  be  obtained  ])erfectly  pure. 
As  in  the  case  of  other  soluble  proteid- 
like  bodies,  solutions  of  haemoglobin  are 
guinea-pig;  e,  from  the  blood  of  a  hamster;/,    (decomposed  bv  alcohol,  by  mineral  acids, 

from  the  blood  of  a  squirrel.  ^       /.     i       i  '    i      i       i     •!• 

bv  salts  of  the  heavy  metals,  by  boihug, 
etc.  Notwithstauding  the  fact  that  haemoglobin  crystallizes  so  readily,  it  is  not 
easily  dialyzable,  behaving  in  this  respect  like  proteids  and  other  colloidal 
bodies.  The  compounds  which  hemoglobin  forms  with  carbon  monoxide 
(CO)  and  nitric  oxide  (NO)  are  also  crystallizable,  the  crystals  being  isomor- 
phous  with  those  of  oxyhaemoglobin. 

Absorption  Spectra. — Solutions  of  haemoglobin  and  its  derivative  com- 
pounds, when  examined  with  a  spectroscope,  give  distinctive  absorption  bands. 
A  brief  account  of  the  principle  and  arrangement  of  the  spectroscoi)e,  although 
unnecessaiy  for  those  familiar  with  the  elements  of  Physics,  is  given  by  way 
of  introduction  to  the  description  of  these  absorption  bands. 

Light,  when  made  to  pass  through  a  glass  prism,  is  broken  up  into  its  constituent 
rays,  giving  the  play  of  rainbow  colors  known  as  the  spectrum.  A  spectroscope  is 
an  apparatus  for  producing  and  observing  a  spectrum.  A  simple  form,  which  illus- 
trates sufficiently  well  the  construction  of  the  apparatus,  is  shown  in  Figure  87,  P 
being  the  glass  prism  giving  the  spectrum.  Light  falls  upon  this  prism  through 
the  tube  (a)  to  the  left,  known  as  the  "  collimator  tube."  A  slit  at  the  end  of  this 
tube  (s)  admits  a  narrow  slice  of  light— lamplight  or  sunlight— which  then,  by 
means  of  a  convex  lens  at  the  other  end  of  the  tube,  is  made  to  fall  upon  the  prism 


Fig.  86.-Cr}-stallized  htemoglobin  (after  Frey) : 
a,  h,  crystals  from  venous  blood  of  man ;  e,  from 
the  blood  of  a  cat;  d,  from  the  blood  of  a 


BLOOD. 


339 


(p)  with  its  rays  parallel.  In  passing  through  the  prism  the  rays  are  dispersed  by 
unequal  refraction,  giving  a  spectrum.  The  spectrum  thus  produced  is  examined  by 
the  observer  with  the  aid  of  the  telescope  («).  When  the  telescope  is  properly  focussed 
for  the  rays  entering  it  from  the  prism  (p),  a  clear  picture  of  the  spectrum  is  seen.  The 
length  of  the  spectrum  will  depend  upon  the  nature  and  the  number  of  prisms  through 
which  the  light  is  made  to  pass.  For  ordinary  purposes  a  short  spectrum  is  preferable 
for  haemoglobin  bands,  and  a  spectroscope  with  one  prism  is  generally  used.  If  the 
source  of  light  is  a  lamp-flame  of  some  kind,  the  spectrum  is  continuous,  the  colors 
gradually  merging  one  into  another  from  red  to  violet.  If  sunlight  is  used,  the  spectrum 
will  be  crossed  by  a  number  of  narrow  dark  lines  known  as  the  "  Fraunhofer  lines" 


Fig. 87. —Spectroscope:  p,  the  glass  prism  ;  a,  the  collimator  tube,  showing  the  slit  (s)  through  which  the 
light  is  admitted  ;  b,  the  telescope  for  observing  the  spectrum. 

(see  PI.  I. ,  Fronthpiece,  for  an  illustration  in  colors  of  the  solar  spectrum).  The  position  of 
these  lines  in  the  solar  spectrum  is  fixed,  and  the  more  distinct  ones  are  designated  by  letters 
of  the  alphabet,  A,  b,  c,  d,  e,  etc.,  as  shown  in  the  charts  below.  If  while  using  solar 
light  or  an  artificial  light  a  solution  of  any  substance  which  gives  absorption  bands  is 
so  placed  in  front  of  the  slit  that  the  light  is  obliged  to  traverse  it,  the  spectrum  as 
observed  through  the  telescope  will  show  one  or  more  narrow  or  broad  black  bands, 
which  are  characteristic  of  the  substance  used  and  which  constitute  its  absorption  spec- 
trum. The  positions  of  these  bands  may  be  designated  by  describing  their  relations  to 
the  Fraunhofer  lines,  or  more  directly  by  stating  the  wave-lengths  of  the  portions  of  the 
spectrum  between  which  absorption  takes  place.  Some  spectroscopes  are  provided  with 
a  scale  of  wave-lengths  superimposed  on  the  spectrum,  and  when  properly  adjusted 
this  scale  enables  one  to  read  off  directly  the  wave-length  of  any  part  of  the  spectrum. 

When  very  dilute  solutions  of  oxyhsemoglobin  are  examined  with  the 
spectroscope,  two  absorption  bands  a})pear,  both  occurring  in  the  portion  of 
the  spectrum  included  between  the  Fraunhofer  lines  d  and  E,  The  band 
nearer  the  red  end  of  the  spectrum  is  known  as  the  "  a-band ;"  it  is  narrower, 
darker,  and  more  clearly  defined  than  the  other,  the  "/9-band"  (Fig.  88,and 
also  PI.  I.  spectrum  4).  With  a  solution  containing  0.09  per  cent,  of  oxy- 
hsemoglobin,  and  examined  in  layers  one  centimeter  thick,  the  a-band  extends 
over  the   part  of  the   spectrum   included   between  the   wave-lengths  X  583 


340 


AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOCY. 


(583  millionths  of  a  millimeter)  and  I  571,  and  the  ^-band  between  X  550  and 
I  532  (Gamgee).  The  width  and  distinctness  of  the  bands  vary  natnrally 
with  the  concentration  of  the  solution  used  (see  PI.  I.  spectra  2,  3,  4,  and  5), 


70      65 


55 


50 


4-5 


B    C 


]) 


p:   6 


G 


FiG.88.— Diaprammatic  representation  of  the  absorption  spectrum  of  oxyha-moglobin  (after  Rollett). 
The  numerals  give  the  wave-lengths  in  hundred-thousandths  of  a  millimeter;  the  letters  show  the 
positions  of  the  more  prominent  Fraunhofer  lines  of  the  solar  spectrum.  The  red  end  of  the  spectrum 
is  to  the  left.    The  o-baud  is  to  the  right  of  d,  the  /3-band  to  the  left  of  e. 

or,  if  the  concentration  remains  the  same,  with  the  width  of  the  stratum  of 
liquid  through  which  the  light  passes.     With  a  certain  minimal  percentage  of 

oxyhaemoglobin  (less  than  0.01  per 
cent.)  the  /3-band  is  lost  and  the  a- 
band  is  very  faint  in  layers  one  cen- 
timeter thick.  With  stronger  solu- 
tions the  bands  become  darker  and 
wider  and  finally  fuse,  while  some 
of  the  extreme  red  end  and  a  great 
deal  of  the  violet  end  of  the  spec- 
trum is  also  absorbed.  The  varia- 
tions in  theabsorption  spectrum  with 
differences  in  concentration  are  clear- 
ly shown  in  the  accompanying  illus- 
tration from  Ptollett'  (Fig.  89);  the 
thickness  of  the  layer  of  licpiid  is 
supposed  to  be  one  centimeter.  The 
numbers  on  the  right  indicate  the 
percentage  strength  of  the  oxy- 
haemoglobin solutions.  It  will  be 
noticed  that  the  absorption  which 
takes  place  as  the  concentration  of 
the  solution  increases  affects  the  red- 
orange  end  of  the  spectrum  last  of  all. 
Solutions  of  reduced  hemo- 
globin examined  with  the  spectro- 
scope show  only  one  absorption 
band,  known  sometimes  as  the 
''y-band."  This  band  lies  also  in 
the  portion  of  the  spectrum  included 
between  the  lines  d  and  E;  its  relations  to  these  lines  and  the  bands  of 
oxyhaemoglobin  are  shown  in  Figure  90  and  in  PI.  I.  spectrum  6.  The 
'  Hermann's  Handbuch  der  Physiologic,  vol.  iv.,  1880. 


aBC 


Fig.  89.— Diagram  to  show  the  variations  in  the  ab- 
sorption spectrum  of  oxyhajmoglobin  with  varying 
concentrations  of  the  solution  (after  Rollett).  The 
numbers  to  the  right  give  the  strength  of  the  oxy- 
hemoglobin solution  in  percentages ;  the  letters  give 
the  positions  of  the  Fraunhofer  lines.  To  ascertain 
the  amount  of  absorption  for  any  given  concentration 
up  to  1  per  cent.,  draw  a  horizontal  line  across  the 
diagram  at  the  level  corresponding  to  the  concentra- 
tion. Where  this  line  passes  through  the  shaded  part 
of  the  diagram  absorption  takes  place,  and  the  width 
of  the  absorption  bands  is  .seen  at  once.  The  diagram 
shows  clearly  that  the  amount  of  absorption  increases 
as  the  solutions  become  more  concentrated,  especially 
the  absorption  of  the  blue  end  of  the  spectrum.  It 
will  be  noticed  that  with  concentrations  between  0.6 
and  0.7  per  cent,  the  two  bands  between  d  and  e  fuse 
into  one. 


BLOOD. 


341 


y-band  is  inucli  more  difTuso  than  the  oxy haemoglobin  bands,  and  its  limits 
theretbre,  esjurially  in  weak  solutions,  are  not  well  defined;  in  solutions 
ot"  blood  diluted  100  times  with  water,  whieh  would  give  a  h;enioglobin 
solution  of  about  0.14  per  cent.,  the  absorption  band  lies  in  the  part  of  the 
spectrum  included  between  the  wave-lengths  X  572  and  X  542.     The  width 


70     65 


60 


55 


45 


B  C 


D 


E    h 


Fig.  90.— Diagrammatic  representation  of  the  absorption  spectrum  of  haemoglobin  (reduced  hemoglo- 
bin) (after  Kollett).  The  inuiierals  give  the  wave-lengths  in  hundred-thousandths  of  a  millimeter  ;  tlie 
letters  show  the  positions  of  the  more  prominent  Fraunhofer  lines  of  the  solar  spectrum.  The  red  end 
of  the  spectrum  is  to  the  left.    The  single  diffuse  absorption  band  lies  between  D  and  e. 

and  distinctness  of  this  band  vary  also  with  the  concentration  of  the 
solution.  This  variation  is  sufficiently  well  shown  in  the  accompanying 
illustration  (Fig.  91),  which  is  a  companion  figure  to  the  one  just  given 
for  oxyhaemoglobin  Fig.  89).  It  will  be  noticed  that  the  last  light  to 
be  absorbed  in  this  case  is  partly  in  the  red  end  and  partly  in  the  blue, 
thus  explaining  the  purplish  color 
of  hsemoo-lobin  solutions  and  of 
venous  blood.  Oxyhsemoglobiu  so- 
lutions can  be  converted  to  hiemo- 
globin  solutions,  with  a  correspond- 
ing change  in  the  spectrum  bands, 
by  placing  the  former  in  a  vacuum 
or,  more  conveniently,  by  adding 
reducing  solutions.  The  solutions 
most  commonly  used  for  this  pur- 
pose are  ammonium  sulphide  and 
Stokes's  reagent.^  If  a  solution  of 
reduced  hemoglobin  is  shaken  with 
air,  it  quickly  changes  to  oxyhsemo- 
globin  and  gives  two  bands  instead 
of  one  when  examined  through  the 
spectroscope.  Any  given  solution 
may  be  changed  in  this  way  from 
oxyhsemoglobin  to  hoemoglobin, 
and  the  reverse,  a  great  number 
of  times,  thus  demonstrating  the 
facility  with  which  haemoglobin 
takes  up  and  surrenders  oxygen. 

^  Stokes's  reagent  is  an  ammoniacal  solution  of  a  ferrous  salt.  It  is  made  by  dissolving  2 
parts  (by  weight)  of  ferrous  sulphate,  adding  3  parts  of  tartaric  acid,  and  then  ammonia  to  dis- 
tinct alkaline  reaction.     A  permanent  precipitate  should  not  be  obtained. 


aBC 


Fig.  91.— Diagram  to  show  the  variations  in  the  ab- 
sorption spectrum  of  reduced  hremoglobin  with  vary- 
ing concentrations  of  the  solution  (after  Rollett).  The 
numbers  to  the  right  give  the  strength  of  the  hsemo- 
globin  solution  in  percentages ;  the  letters  give  the  posi- 
tions of  the  Fraunhofer  lines.  For  further  directions 
as  to  the  use  of  the  diagram,  see  the  description  of 
Figure  89. 


342  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

Solutions  of*  carbon-monoxide  hnemoglobin  also  give  a  .spectrum  willi  two 
absorption  bands  closely  resembling  in  position  and  appearance  those  of  oxy- 
ha^nioglobin  (see  PI.  I.  spectrum  7).  They  are  distinguislicd  from  tiie  oxy- 
ha?moglobin  bauds  by  being  slightly  nearer  the  blue  eud  of  the  spectrum,  as 
may  be  demonstrated  by  observing  the  wave-lengths  or,  more  conveniently, 
by  superimposing  the  two  spectra.  Moreover,  solutions  of  carbou-mouoxide 
haemoglobin  are  uot  reduced  to  lueraoglobin  by  adding  Stokes's  licjuid,  two 
bands  being  still  seen  after  such  treatmeut.  A  solution  of  carbon-monoxide 
haemoglobin  suitable  for  spectroscopic  examination  may  be  prepared  easily  by 
passing  ordinary  coal-gas  through  a  dilute  oxyhtemoglobin  solution  lor  a  few 
minutes  and  then  filtering. 

Derivative  Compounds  of  Haemoglobin. — A  number  of  compounds 
directly  related  to  hiemoglobiu  have  been  described,  some  of  them  being 
found  normally  in  the  body.  Brief  mention  is  made  of  the  best  known  of 
these  substances,  but  for  the  details  of  their  preparation  and  chemical  projier- 
ties  reference  must  be  made  to  the  section  on  "  The  Chemistry  of  the  Body." 

Methcmioc/lobin  is  a  compound  obtained  by  the  action  of  oxidizing  agents 
on  haemoglobin ;  it  is  frequently  found,  therefore,  in  blood  stains  or  patho- 
logical liquids  containing  blood  which  have  been  exposed  to  the  air  for  some 
time.  It  is  now  supposed  to  be  identical  in  composition  with  oxyhaemoglobin, 
with  the  exception  that  the  oxygen  is  held  in  more  stable  combination. 
MetluBmoglobin  crystallizes  in  the  same  form  as  oxyhjemoglobiu,  and  has  a 
characteristic  spectrum  (PI.  I.  spectrum  8). 

Hccmochromogen  (Ca^HggN^FcOs)  is  the  substance  obtained  when  haemo- 
globin is  decomposed  by  acids  or  by  alkalies  in  the  absence  of  oxygen.  It 
crystallizes  and  has  a  characteristic  spectrum. 

Hcemat'm  (CagHgaN^FeOJ  is  obtained  when  oxyhaemoglobin  is  decomposed 
by  acids  or  by  alkalies  in  the  presence  of  oxygen.  It  is  amorphous  and  has  a 
characteristic  spectrum  (PI.  L  spectra  9  and  10). 

Hcemin  (CgaHjoN^FeOgHCl)  is  a  compound  of  htcmatin  and  HCl,  and  is 
readily  obtained  in  crystalline  form.  It  is  much  used  in  the  detection  of 
blood  in  medico-legal  cases,  as  the  crystals  are  very  characteristic  and  are  easily 
obtained  from  blood-clots  or  blood-stains,  no  matter  how  old  these  may  be. 

H(cmatoporj)hyrin  (CgjIIggN^Og)  is  a  compound  characterized  by  the  absence 
of  iron.  It  is  frequently  spoken  of  as  "  iron-free  hoematin."  It  is  obtained 
by  the  action  of  strong  sulphuric  acid  on  hiematin. 

Hicmatoidin  (CigHigNgOg)  is  the  name  given  to  a  crystalline  substance 
found  in  old  blood-clots,  and  formed  undoubtedly  from  the  haemoglobin  of 
the  clotted  blood.  It  has  been  shown  to  be  identical  with  one  of  the  bile- 
pigments,  bilirubin.  Its  occurrence  is  interesting  in  that  it  dcmon.strates  the 
relationship  between  haemoglobin  and  the  bile-pigments. 

Histohcrmatins  are  a  group  of  pigments  .said  to  be  ])resent  in  many  of  the 
tissues — for  example,  the  muscles.  They  are  supposed  to  be  respiratory  pig- 
ments, and  are  related  physiologically,  and  possibly  chemically,  to  haemoglobin. 
They  have  not  been  isolated,  but  their  spectra  have  been  described. 


BLOOD.  343 

Bile-pigments  and  Urinary  Pigments — Haemoglobin  is  regarded  as  the 
parent-substance  of  the  bile-pigments  and  the  urinary  pigments. 

Origin  and  Fate  of  the  Red  Corpuscles. — The  mammalian  rod  corpuscle 
is  a  cell  that  has  lost  its  nucleus.  It  is  not  probable,  therefore,  that  any  given 
corpuscle  lives  for  a  great  while  in  the  circulation.  This  is  made  more  certain 
by  the  fact  that  htemoglobin  is  the  mother-substance  from  which  the  bile- 
pigments  are  made,  and,  as  these  pigments  are  being  excreted  continually,  it  is 
fair  to  suppose  that  red  corpuscles  are  as  steadily  undergoing  disintegration  in 
the  blood-stream.  Just  how  long  is  the  average  life  of  the  corpuscles  has  not 
been  determined,  nor  is  it  certain  where  and  how  they  go  to  pieces.  It  has 
been  suggested  that  their  destruction  takes  place  in  the  spleen,  but  the  observa- 
tions advanced  in  support  of  this  hypothesis  are  not  very  numerous  or  con- 
clusive. Among  the  reasons  given  for  assuming  that  the  spleen  is  especially 
concerned  in  the  destruction  of  red  corpuscles,  the  most  weighty  is  the  histo- 
logical fact  that  one  can  sometimes  find  in  teased  preparations  of  spleen-tissue 
certain  large  cells  which  contain  red  corpuscles  in  their  cell-substance  in  various 
stages  of  disintegration.  It  has  been  supposed  that  the  large  cells  actually 
ingest  the  red  corpuscles,  selecting  those,  presumably,  which  are  in  a  state  of 
physiological  decline.  Against  this  idea  a  number  of  objections  may  be 
raised.  Large  leucocytes  with  red  corpuscles  in  their  interior  are  not  found 
so  frequently  nor  so  constantly  in  the  spleen  as  we  would  expect  should  be 
the  case  if  the  act  of  ingestion  were  constantly  going  on.  There  is  some 
reason  for  believing,  indeed,  that  the  whole  act  of  ingestion  may  be  a  post- 
mortem phenomenon  ;  that  is,  after  the  cessation  of  the  blood-stream  the 
amoeboid  movements  of  the  large  leucocytes  continue,  while  the  red  corpuscles 
lie  at  rest — conditions  which  are  favorable  to  the  act  of  ingestion.  It  may  be 
added  also  that  the  blood  of  the  splenic  vein  contains  no  haemoglobin  in  solu- 
tion, indicating  that  no  considerable  dissolution  of  red  corpuscles  is  taking 
place  in  the  spleen.  Moreover,  complete  extirpation  of  the  spleen  does  not 
seem  to  lessen  materially  the  normal  destruction  of  red  corpuscles,  if  we  may 
measure  the  extent  of  that  normal  destruction  by  the  quantity  of  bile-pigment 
formed  in  the  liver,  remembering  that  haemoglobin  is  the  mother-substance 
from  which  the  bile-pigments  are  derived.  It  is  more  probable  that  there  is 
no  special  organ  or  tissue  charged  with  the  function  of  destroying  red  corpus- 
cles, and  that  they  undergo  disintegration  and  dissolution  while  in  the  blood- 
stream and  in  any  part  of  the  circulation,  the  liberated  haemoglobin  being 
carried  to  the  liver  and  excreted  in  part  as  bile-pigment.  The  continual 
destruction  of  red  corpuscles  implies,  of  course,  a  continual  formation  of  new 
ones.  It  has  been  shown  satisfactorily  that  in  the  adult  the  organ  for  the 
reproduction  of  red  corpuscles  is  the  red  marrow  of  bones.  In  this  tissue 
hcematopoiesis,  as  the  process  of  formation  of  red  corpuscles  is  termed,  goes  on 
continually,  the  process  being  much  increased  after  hemorrhages  and  in  certain 
pathological  conditions.  The  details  of  the  histological  changes  will  be  found 
in  the  text-books  of  histology.  It  is  sufficient  here  to  state  simply  that  a 
group  of  nucleated  colorless  cells,  erj^throblasts,  is  found  in  the  red  marrow. 


344  .l^V  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

These  cells  multiply  bv  karvokinesis,  and  the  daughter-cells  eventually  pro- 
duce haniioglobin  in  their  cytoplasm,  thus  forming  nucleated  red  corpuscles. 
The  nuclei  are  subsequently  lost,  either  by  disintegration  or,  more  likely,  by 
extrusion,  and  the  newly-formed  non-nucleated  red  corpuscles  are  forced  into 
the  blood-stream,  owing  to  a  gradual  change  in  their  position  during  develop- 
ment caused  by  the  growing  htpmatopoietic  tissue.  AVhen  the  process  has 
been  greatly  accelerated,  as  after  severe  hemorrhages  or  in  certain  ])athologicaI 
conditions,  red  corpuscles  still  retaining  their  nuclei  may  be  found  in  the  circu- 
lating blood,  having  been  forced  out  prematurely  as  it  were.  Such  corpuscles 
may  subsequently  lose  their  nuclei  while  in  the  blood-stream.  In  the  em- 
bryo, luBmatopoietic  tissue  is  found  in  parts  of  the  body  other  than  the  mar- 
row, notably  in  the  liver  and  spleen,  which  at  that  time  serve  as  organs  for 
the  production  of  new  red  corpuscles.  In  the  blood  of  the  young  embryo 
nucleated  red  corpuscles  are  at  fii-st  abundant,  but  they  become  less  numerous 
as  the  fetus  grows  older.^ 

Variations  in  the  Number  of  Red  Corpuscles. — The  average  number 
of  red  corpuscles  for  the  adult  male,  as  has  been  stated  already,  is  usually 
given  as  5,000,000  per  cubic  mm.  The  number  is  found  to  vary  greatly, 
however.  Outside  of  pathological  conditions,  in  which  the  diminution  in 
number  may  be  extreme,  differences  have  been  observed  in  human  beings 
under  such  conditions  as  the  following :  The  number  is  less  in  females 
(4,500,000);  it  varies  in  individuals  with  the  constitution,  nutrition,  and 
manner  of  life ;  it  varies  with  age,  being  greatest  in  the  fetus  and  in  the  new- 
born child ;  it  varies  with  the  time  of  the  day,  showing  a  distinct  diminution 
after  meals ;  in  the  female  it  varies  somewhat  in  menstruation  and  in  preg- 
nancy, being  slightly  increased  in  the  former  and  diminished  in  the  latter 
condition.  Perhaps  the  most  interesting  example  of  variation  in  the  number 
of  red  corpuscles  is  that  which  occurs  with  changes  in  altitude.  Residence  in 
high  altitudes  is  quickly  followed  by  a  marked  increase  in  the  number  of  red 
corpuscles.  Viault^  has  recently  shown  that  living  in  the  mountains  two 
weeks  at  an  altitude  of  4392  meters  caused  an  increase  in  the  corpuscles  from 
5,000,000  to  over  7,000,000  per  cubic  mm.,  and  in  the  third  week  the  number 
reached  8,000,000.  From  these  and  similar  observations  it  would  seem  that  a 
diminished  pressure  of  oxygen  in  the  atmosphere  stimulates  the  haematopoietic 
organs  to  greater  activity,  and  it  is  interesting  to  compare  this  result  with  the 
effect  of  an  actual  loss  of  blood.  In  the  latter  case  the  production  of  red 
corpuscles  in  the  red  marrow  is  increased,  because,  ap])arently,  the  ansemic 
condition  causes  a  diminution  in  the  oxygen-supply  to  the  haematopoietic  tis- 
sue, and  thereby  stimulates  the  erythroblastic  cells  to  more  rapid  multiplication. 
In  the  case  of  a  sudden  diminution  in  oxygen-pressure,  as  happens  when  the 
altitude  is  markedly  increased,  we  may  suppose  that  one  result  is  again  a  slight 
diminution  in  the  oxygen-supply  to  the  tissues,  including  the  red  marrow,  and 

'  For  further  details  see  Howell,  "  Life  History  of  the  Blood-corpuscles,"  etc.,  Journal  of 
Morphology,  vol.  iv.,  1890. 

*  La  Semaine  medicale,  1890,  p.  464. 


BLOOD.  345 

in  couseqiience  the  eiythroblasts  are  again  stimulated  to  greater  activity.  This 
variation  iu  hiomoglobin  with  the  altitude  is  an  interesting  adaptation  which 
ensures  always  a  normal  oxygen-capacity  for  the  blood. 

Physiology  of  the  Blood-leucocytes. — The  function  of  the  blood-leuco- 
cytes has  been  the  subject  of  numerous  investigations,  particularly  in  connection 
M'ith  the  pathology  of  blood  diseases.  Although  many  hypotheses  have  been 
matle  as  the  result  of  this  work,  it  cannot  be  said  that  we  possess  any  positive 
information  as  to  the  normal  function  of  these  cells  in  the  body.  It  must  be 
borne  in  mind  in  the  first  place  that  the  blood-leucocytes  are  not  all  the  same 
histologically,  and  it  may  be  that  their  functions  are  as  diverse  as  is  their  mor- 
phology. Various  classifications  have  been  made,  based  upon  one  or  another 
difference  in  microscopic  structure  and  reaction.  Thus,  Ehrlich  groups  the  leuco- 
cytes according  to  the  size  and  the  staining  of  the  granules  contained  in  the  cyto- 
plasm, making  in  the  latter  respect  three  main  groups  :  oxyphiles  or  eosinophiles, 
those  whose  granules  stain  only  with  acid  aniline  dyes — that  is,  with  dyes  in 
wdiich  the  acid  part  of  the  dye  acts  as  the  stain  ;  basophiles,  those  which  stain 
only  with  basic  dyes ;  and  neutrophiles,  those  which  stain  only  with  neutral 
dyes  ^  (Fig.  92).     This  classification  is  frequently  used,  especially  in  patholog- 


FiG. 92.— Blood  stained  with  Ehrlich's  "triple  stain"  of  acid-fuehsin,  methyl-green,  and  orange  G. 
(drawn  with  the  camera  lucida  from  normal  blood)  (after  Osier):  a,  red  corpuscles;  b,  lymphocytes;  c, 
large  mononuclear  leucocytes;  d,  transitional  forms;  e,  nexitrophilic  leucocytes  with  polymorphous 
nuclei  (polynuclear  neutrophiles) ;  /,  eosinophilic  leucocytes. 

ical  literature,  but  it  is  not  altogether  satisfactory,  since  no  definite  functional 
relationship  of  the  granules  has  been  established ;  and,  moreover,  it  is  unde- 
cided whether  or  not  the  specific  granules  are  permanent  or  temporary  struc- 
tures in  the  cells.  A  safer  classification  perhaps  is  the  following:  1.  Lympho- 
cytes, which  are  small  corpuscles  with  a  round  vesicular  nucleus  and  very  scanty 
cytoplasm  :  they  are  not  capable  of  amoeboid  movements.  These  corpuscles  are 
so  called  because  they  resemble  the  leucocytes  found  in  the  lymph-gland,  and 

'  For  a  recent  discussion  and  modification  of  this  classification  see  Kanthack  and  Hardy, 
J(mmal  of  Physiology,  vol.  xvii.,  1894,  p.  81. 


346  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

are  supposed  in  fact  to  be  brought  into  the  blood  through  the  lymph.  2.  Mono- 
nuclear leucocytes,  which  are  large  corpuscles  with  a  vesicular  nucleus  and 
abundant  cytoplasm  :  thoy  have  the  power  of  making  anuel)oid  movements. 
3.  Polymorphous  or  polynucleated  leucocytes,  which  are  large  cori)Usck'.s  with 
the  nucleus  divided  into  lobes  that  are  either  entirely  separated  or  are  connected 
by  fine  protoplasmic  threads.     This  form  shows  active  amoeboid  movements. 

It  is  impossible  to  say  whether  these  varieties  of  blood-leucocytes  are 
distinct  histological  units  which  have  independent  origins  and  more  or  less 
dissimilar  functions,  or  whether,  as  seems  more  probable  to  the  writer,  they 
represent  different  stages  in  the  development  of  a  single  type  of  cell,  the 
lymphocytes  forming  the  youngest  and  the  polymorphic  or  polynucleated 
leucocytes  the  oldest  stage.  Perhaps  the  most  striking  property  of  the  leuco- 
cytes as  a  class  is  their  power  of  making  amoeboid  movements — a  charac- 
teristic which  has  gained  for  them  the  sobriquet  of  "wandering"  cells.  By 
virtue  of  this  property  some  of  them  are  able  to  migrate  through  the  walls 
of  blood-capillaries  into  the  surrounding  tissues.  This  process  of  migration 
takes  place  normally,  but  is  vastly  accelerated  under  pathological  conditions. 
As  to  the  function  or  functions  fulfilled  by  the  leucocytes,  numerous  sugges- 
tions have  been  made,  some  of  which  may  be  stated  in  brief  form  as  follows: 
(1)  They  protect  the  body  from  pathogenic  bacteria.  In  explanation  of  this 
action  it  has  been  suggested  that  they  may  either  ingest  the  bacteria,  and  thus 
destroy  them  directly,  or  they  may  form  certain  substances,  defensive  proteids, 
which  destroy  the  bacteria.  Leucocytes  that  act  by  ingesting  the  bacteria 
are  spoken  of  as  "phagocytes"  {(fdyetu,  to  eat;  xotoc,  cell).  This  theory  of 
their  function  is  usually  designated  as  the  "  phagocytosis  theory  of  Metschni- 
koff ;"  it  is  founded  upon  the  fact  that  the  amoeboid  leucocytes  are  known  to 
ingest  foreign  particles  with  which  they  come  in  contact.  The  theory  of  the 
protective  action  of  leucocytes  has  been  used  largely  in  pathology  to  explain 
immunity  from  infectious  diseases,  and  for  details  of  experiments  in  support 
of  it  reference  must  be  made  to  pathological  text-books.  (2)  They  aid  in 
the  absorption  of  fats  from  the  intestine.  (3)  They  aid  in  the  absorption  of 
peptones  from  the  intestine.  These  latter  two  theories  will  be  spoken  of 
more  in  detail  in  describing  the  process  of  absorption.  (See  the  section  upon 
Digestion.)  It  may  be  noticed  here  that  these  theories  apply  to  the  leucocytes 
found  so  abundantly  in  the  lymphoid  tissue  of  the  alimentary  canal,  rather 
than  to  those  contained  in  the  blood  itself.  (4)  They  take  part  in  the  pro- 
cess of  blood-coagulation.  A  complete  statement  with  reference  to  this 
function  must  be  reserved  until  the  phenomenon  of  coagulation  is  de- 
scribed, (o)  They  help  to  maintain  the  normal  composition  of  the  blood- 
plasma  as  to  proteids.  It  may  be  said  for  this  view  that  there  is  considerable 
evidence  that  the  leucocytes  normally  undergo  disintegration  and  dissolu- 
tion in  the  circulating  blowl,  to  some  extent  at  least.  The  blood-proteids  are 
peculiar,  and  they  are  not  obtained  directly  from  the  digested  food.  It  is 
possible  that  the  leucocytes,  which  are  the  only  typical  cells  in  the  blood,  aid 
in  keeping  up  the  normal  supply  of  proteids.     None  of  the  theories  mentioned 


BLOOD.  .  347 

lias  much  positive  evidence  in  its  favor.  It  remains  possible,  on  the  one 
hand,  that  all  these  as  well  as  other  functions  may  be  performed  by  the 
leucocytes,  and,  on  the  other  hand,  further  discoveries  may  give  an  entirely 
new  explanation  of  the  value  of  these  cells  to  the  body.  As  to  the  origin  of 
the  leucocytes,  it  is  known  that  they  increase  in  number  while  in  the  circu- 
lation, undergoing  multipliaition  by  karyokiuesis ;  but  the  greater  number  are 
probably  produced  in  the  lymph-glands  and  in  the  lymphoid  tissue  of  the 
body,  whence  they  get  into  the  lymph-stream  and  eventually  are  brought  into 
the  blood. 

Physiology  of  the  Blood-plates. — The  blood-plates  are  small  circular 
or  elliptical  bodies,  nearly  homogeneous  in  structure  and  variable  in  size  (0.5  to 
5.5//),  but  they  are  always  smaller  than  the  red  corpuscles  (see  Histology).  Less 
is  known  of  their  origin,  fate,  and  functions  than  in  the  case  of  the  leucocytes. 
It  is  certain  that  they  are  not  independent  cells,  and  it  is  altogether  probable, 
therefore,  that  they  soon  disintegrate  and  dissolve  in  the  plasma.  When 
removed  from  the  circulating  blood  they  are  known  to  disintegrate  very 
rapidly.  This  peculiarity,  in  fact,  prevented  them  from  being  discovered  for 
a  long  time  after  the  blood  had  been  studied  microscopically.  Recent  work 
has  shown  that  they  are  formed  elements,  and  not  simply  precipitates  from  the 
plasma,  as  was  suggested  at  one  time.  The  theory  of  Hayem,  their  real 
discoverer,  that  they  develop  into  red  corpuscles  may  also  be  considered  as 
erroneous.  There  is  considerable  evidence  to  show  that  in  shed  blood  they 
take  part  in  the  process  of  coagulation.  The  nature  of  this  evidence  will  be 
described  later. 

Lilienfeld  ^  recently  demonstrated  that  chemically  the  blood-plates  contain 
a  nucleo-albumin  (see  section  on  Chemistry  of  the  Body)  to  which  he  gives 
the  specific  name  of  "  nucleohiston."  The  same  substance  is  contained  in  the 
nuclei  of  leucocytes.  This  latter  fact  may  be  taken  as  additional  evidence  for 
a  view  which  has  already  been  supported  on  morphological  grounds — that  the 
blood-plates  are  derived  from  the  nuclei  of  the  leucocytes.  According  to  this 
theory,  when  the  multinucleated  leucocytes  go  to  pieces  in  the  blood  the 
fragments  of  nuclei  contained  in  them  persist  for  a  longer  or  shorter  time  as 
blood-plates,  which  in  time  eventually  dissolve  in  the  plasma.  If  this  last 
statement  is  correct,  then  it  follows  that  the  substance  contained  in  the  blood- 
plates  either  goes  to  form  one  of  the  normal  constituents  of  the  plasma,  useful 
in  nutrition  or  otherwise,  or  that  it  forms  a  waste  product  which  is  eliminated 
from  the  body.  The  specific  function,  if  any,  of  the  blood-plates,  beyond 
that  of  aiding  in  coagulation,  remains  to  be  discovered. 

B.  Chemical  Composition  of  the  Blood  ;  Coagulation  ;  Total 
Quantity  of  Blood  ;  Regeneration  after  Hemorrhage. 

Composition  of  the  Plasma  and  Corpuscles. — Blood  (plasma  and  cor- 
puscles) contains  a  great  variety  of  substances,  as  may  be  inferred  from  its 
double  relations  to  the  tissues  as  a  source  of  food-supply  and  as  a  means  of 
^  Du  Bois-Reymond!s  Archiv  fur  Physiologie,  1893,  p.  560. 


348  AN  AMERICAN   TEXT- BOOK   OF  PHYSIOLOGY. 

removing  the  waste  products  of  their  fuuctioual  activity.  The  constituents 
existing  in  quantities  sufficiently  large  for  recognition  by  chemical  means  are 
as  follows:  (1)  Water;  (2)  proteids,  of  which  three  varieties  at  least  are 
known  to  exist  in  the  plasma — namely,  fibrinogen,  paraglobulin  (serum- 
globulin),  and  serum-albumin ;  (3)  combined  proteids  (hajmoglobin,  nudeo- 
albumins) ;  (4)  extractives,  including  such  substances  as  fats,  sugar,  urea, 
lecithin,  cholesterin,  etc. ;  and  (5)  inorganic  salts.  The  proportions  of  these 
substances  found  in  the  blood  of  various  mammals  differ  somewhat,  although 
the  qualitative  composition  is  practically  the  same  in  all. 

The  following  tables,  taken  from  different  sources,  summarize  the  main 
results  of  the  quantitative  analyses  which  have  thus  far  been  made : 


Analysts  of  the  Whole  Blood,  Human  (C.  Schmidt). 


Water 

Solids 

Proteids  and  extractives 

Fibrin  (derived  from  the  fibrinogen) 

Ha^matin  (and  iron) 

Salts        


Man 

Woman 

(25  years). 

(30  years.) 

788.71 

824.55 

211.29 

175.45 

191.78 

157.93 

3.93 

1.91 

7.70 

6.99 

7.88 

8.62 

Inorganic  Salts  of  Human  Blood,  1000  parts  {C.  Schmidt). 


Blood-corpuscles. 

CI 1.75 

KjO 3.091 

Na,0 0.470 

so: 0.061 

PA 1-355 

CaO 

MgO 


Blood-plasma. 

CI 3.536 

KjO 0.314 

Na^O 3.410 

SO3 0.129 

P.A 0.145 

Cad 

MgO  .  . 


These  acids  and  bases  exist,  of  course,  in  the  plasma  and  the  corpuscles  as 
salts.  It  is  not  possible  to  determine  exactly  how  they  are  combined  as  salts, 
but  Schmidt  suggests  the  following  probable  combinations : 


Probable  Salts  in  the  Corpuscles. 


Potassium  sulphate 0.132 

Potassium  chloride 3.679 

Potassium  phosphate 2.343 

Sodium  phosphate 0.633 

Sodium  carbonate 0.341 

Calcium  phosphate 0.094 

Magnesium  phosphate  ....  0.060 


Probable  Salts  in  the  Plasma. 


Potassium  sulphate 0.281 

Potassium  chloride 0.359 

Sodium  chloride 5.546 

Sodium  phosphate 0.271 

Sodium  carbonate 1.532 

Calcium  phosphate 0.298 

Magnesium  phosphate   ....  0.218 


One  interesting  fact  brought  out  in  the  above  table  is  the  peculiarity  in 
distribution  of  the  potassium  and  sodium  salts  between  the  plasma  and  the 
corpuscles.  The  plasma  contains  an  excess  of  the  total  sodium  salts,  and  the 
corpuscles  contain  an  excess  of  the  potassium  salts. 


BLOOD. 


349 


Composition  of  Blood-plasma  (1000  parts).' 


Composition  of  Blood-serum  (1000  parts).* 


Water 

Solids 

Total  proteids 

Fibrin  (derived  from  the  fibrinogen 

Paraglobiilin 

Serum-albumin 

Extractives  and  salts 


Horse. 


Horse. 


917.6 
82.4 
69.5 
6.5 
38.4 
24.6 
12.9 


85.97 
72.57 

45.65 
26.92 
13.40 


Man. 


92.07 
76.20 

31.04 
45.16 

15.88 


Ox. 


89.65 
74.99 

41.69 
33.30 
14.66 


Red  Corpuscles,  Human  Blood  {Hoppe-Seyler). 

I.  II. 

Oxyhaemoglobin 86.8  94.3  per  cent. 

Proteid  (and  nuclein  ?) 12.2  5.1       " 

Lecithin      0.7  0.4       " 

Cbolesterin 0.3  0.3       " 

Leucocytes,  Thymus  of  Calf  (Lilienfeld). 
In  the  total  dry  substance  of  the  corpuscles,  which  was  equal  to  11.49  per  cent.,  there  was  contained— 

Proteid 1.76  per  cent. 

Leuco-nuclein 68.78       " 

Histon 8.67       " 

Lecithin 7.51       " 

Fat 4.02       " 

Cbolesterin 4.40       " 

Glycogen 0.80 

The  extractives  present  in  the  blood  vary  in  amount  under  different  conditions. 

Average  estimates  of  some  of  them,  given  in  percentages  of  the  entire  blood, 

have  been  reported  as  follows : 

Dextrose  (grape-sugar) 0.117  percent. 

Urea 0.016       " 

Lecithin 0.0844     " 

Cbolesterin 0.041       " 

Proteids  of  the  Blood-plasma. — The  properties  and  reactions  of  proteids 
and  the  related  compounds,  as  well  as  a  classification  of  those  occurring  iu  the 
animal  body,  are  described  in  the  section  on  the  Chemistry  of  the  Body. 
This  description  should  be  read  before  attempting  to  study  the  proteids  of 
the  plasma  and  the  part  they  take  in  coagulation.  Three  proteids  are  usually 
described  as  existing  in  the  plasma  of  circulating  blood — namely,  fibrinogen, 
paraglobulin,  or,  as  it  is  sometimes  called,  "  serum-globulin,"  and  serum-albu- 
min. The  first  two  of  these  proteids,  fibrinogen  and  paraglobulin,  belong  to 
the  group  of  globulins,  and  hence  have  many  properties  in  common.  Serum- 
albumin  belongs  to  the  group  of  so-called  "  native  albumins "  of  which  egg- 
albumin  constitutes  another  member. 

Serum-albumin. — This  substance  is  a  typical  proteid.  Its  elementary  com- 
position, according  to  Hammarsten,  is  as  follows  : 

c  H  N  s  o 

53.06  6.85  16.04  1.80  22.26 

These  figures  can  be  regarded  as  approximate  only.    Serum-albumin  shows  the 

'  Hammarsten :  A  Text-book  of  Physiological  Chemistry,  1893  (translated  by  Mandel). 


350  AN   AMERICAX    TEXT-BOOK    OF   PHYSIOLOGY. 

general  reactions  of  the  native  albumins.  One  of  its  most  useful  reactions  is 
its  behavior  toward  magnesium  sulphate.  Serum-all)umin  usually  occurs  in 
liquids  together  with  the  globulins,  as  is  the  case  in  blood.  If  such  a  liquid 
is  thoroughly  saturated  with  solid  MgSO^,  the  globulins  are  precipitated  com- 
pletely, wliile  the  albumin  is  not  affected.  So  far  as  the  blood  and  similar 
liquids  are  concerned,  a  definition  of  serum-albumin  might  be  given  by  saying 
that  it  comprises  all  the  proteids  not  precipitated  by  MgSO^.  ^^'hen  its 
solutions  have  a  neutral  or  an  acid  reaction,  serum-albumin  is  precipitated  in 
an  insoluble  form  by  heating  the  solution  above  a  certain  degree.  Precipi- 
tates produced  in  this  way  by  heating  solutions  of  proteids  are  spoken  of 
as  coagulations — heat  coagulations — and  the  exact  temperature  at  which 
coagulation  occurs  is  to  a  certain  extent  characteristic  for  each  proteid.  Tlu- 
temperature  of  coagulation  of  serum-albumin  is  usually  given  at  from  70° 
to  75°  C,  but  it  varies  greatly  with  the  conditions.  It  has  been  asserted, 
in  fact,  that  careful  heating  under  proper  conditions  gives  separate  coagula- 
tions at  three  different  temperatures — namely,  73°,  77°,  and  84°  C. — indi- 
cating the  possibility  that  what  is  called  "serum-albumin  "  may  be  a  mixture 
of  three  or  more  proteids.  Serum-albumin  occurs  in  blood-plasma  and  blood- 
serum,  in  lymph,  and  in  the  different  normal  and  pathological  exudations 
found  in  the  body,  such  as  pericardial  liquid,  hydrocele  fluid,  etc.  The  amount 
of  serum-albumin  in  the  blood  varies  in  different  animals,  ranging  among 
the  mammalia  from  2.67  per  cent,  in  the  horse  to  4.52  per  cent,  in  man.  In 
some  of  the  cold-blooded  animals  it  occui-s  in  surprisingly  small  quantities — 
0.36  to  0.69  per  cent.  As  to  the  source  or  origin  of  serum-albumin,  it  is 
generally  believed  that  it  comes  from  the  digested  proteids  of  the  food.  It 
is  known  that  proteid  material  in  the  food  is  not  changed  at  once  to  serum- 
albumin  during  the  act  of  digestion  ;  indeed,  it  is  known  that  the  final  product 
of  digestion  is  a  proteid  or  group  of  proteids  of  an  entirely  different  character — 
namely,  peptones  and  proteoses;  but  during  the  act  of  absorption  into  the 
blood  these  latter  bodies  are  supposed  to  undergo  transformation  into  serum- 
albumin.  From  a  physiological  standpoint  serum-albumin  is  considered  to  be 
the  main  source  of  proteid  nourishment  for  the  tissues  generally.  As  will  be 
explained  in  the  section  on  Nutrition,  one  of  the  most  important  requisites  in 
the  nutrition  of  the  cells  of  the  body  is  an  adequate  supply  of  proteid  material 
to  replace  that  used  up  in  the  chemical  changes,  the  metabolism,  of  the  tissues. 
Serum-albumin  is  supposed  to  furnish  a  part,  at  least,  of  this  supply.  As  long 
as  the  serum- albumin  is  in  the  blood-vessels  it  is  of  course  cut  off"  from  the 
tissues.  The  cells,  however,  are  bathed  directly  in  lymph,  and  this  in  turn  is 
formed  from  the  plasma  of  the  blood  which  is  filtered — or,  according  to  some 
physiologists,  secreted — through  the  vessel-walls.  Serum-albumin  may  be 
looked  upon,  then,  as  a  supply  of  proteid  nourishment  which  is  replenished, 
after  every  meal  containing  proteids,  by  absorption  from  the  alimentary  canaL 
Paraglohulin,  ^vhich  belongs  to  the  group  of  globulins,  exhibits  the  gen- 
eral reactions  characteristic  of  the  group.  As  stated  above,  it  is  completely 
precipitated  from  its  solutions  by  saturation  with  MgSO^.     It  is  incompletely 


BLOOD.  351 

precipitated  by  saturation  with  common  salt  (NaCl).  In  neutral  or  feebly  acid 
solutions  it  coagulates  upon  heating  to  75°  C.  Ilammareten  gives  its  element- 
ary composition  as — 

c  H  N  s  o 

52.71  7.01  15.85  1.11  23.24 

These  figures  must  also  be  received  as  approximate,  as  it  is  not  absolutely  cer- 
tain that  the  substance  analyzed  was  chemically  pure.  Paraglobulin  occurs  in 
blood,  in  lymph,  and  in  the  normal  and  pathologicid  exudations.  The  amount 
of  })araglol)ulin  present  in  blood  varies  in  diiferent  animals.  Among  the  mam- 
malia the  amount  ranges  from  1.78  per  cent,  in  rabbits  to  4.56  j)er  cent,  in  the 
horse.  In  human  blood  it  is  given  at  3.10  per  cent.,  being  less  in  amount, 
therefore,  than  the  serum-albumin.  It  will  be  seen,  upon  examining  the 
tables  of  composition  of  the  blood-plasma  and  blood-serum  of  the  hor.se 
(p.  349),  that  more  of  this  proteid  is  found  in  the  serum  than  in  the  plasma. 
This  result,  which  is  usually  considered  as  being  true,  is  explained  by  supposing 
that  during  coagulation  some  of  the  leucocytes  disintegrate  and  part  of  their 
substance  passes  into  solution  as  a  globulin  identical  with  or  closely  resembling 
paraglol)ulin.  The  figures  given  above  show  that  a  considerable  amount  of 
paraglobulin  is  normally  present  in  blood.  It  is  rea.sonable  to  suppose  that, 
like  serum-albumin,  this  proteid  is  valuable  as  a  source  of  nitrogenous  food 
to  the  tissues.  It  is  uncertain,  however,  whether  it  is  used  by  the  tissues 
directly  as  paraglobulin  or  is  first  converted  into  some  other  form  of  proteid. 
It  is  entirely  unknown,  also,  whether  its  value  as  a  proteid  supply  is  in  any 
way  different  from  that  of  serum-albumin.  The  origin  of  paraglobulin 
remains  undetermined.  It  may  arise  from  the  digested  proteids  absorbed 
from  the  alimentary  canal,  but  there  is  no  evidence  to  support  such  a  view. 
Another  suggestion  is  that  it  comes  from  the  disintegration  of  the  leucocytes 
(and  oi\\Q.Y  formed  elements)  of  the  blood.  These  bodies  are  known  to  contain 
a  small  quantity  of  a  globulin  resembling  paraglobulin,  and  it  is  passible  that 
this  globulin  may  be  liberated  after  the  dissolution  of  the  leucocytes  in  the 
plasma,  and  thus  go  to  make  up  the  normal  supply  of  paraglobulin.  This 
suggestion,  however,  is  theoretical.  The  fact  remains  that  at  present  the 
origin  and  the  special  use  of  the  paraglobulin  are  entirely  unknown. 

Fibrinogen  is  a  proteid  belonging  to  the  globulin  class  and  exhibiting  all 
the  general  reactions  of  this  group.  It  is  distinguished  from  paraglobulin  by 
a  number  of  special  reactions ;  for  example,  its  temperature  of  heat  coagula- 
tion is  much  lower  (56°  to  60°  C),  and  it  is  completely  thrown  down  from  its 
solutions  by  saturation  with  NaCl  as  well  as  with  MgSO^.  Its  most  import- 
ant and  distinctive  reaction  is,  however,  that  under  proper  conditions  it  gives 
rise  to  an  insoluble  proteid,  fibrin,  whose  formation  is  the  essential  phenom- 
enon in  the  coagulation  of  blood.  Fibrinogen  has  an  elementary  composition, 
according  to  Hammarsten,  of — 


c 

H 

N 

s 

0 

52.93 

6.90 

16.66 

1.25 

22.26 

Fibrinogen  is  found  in  blood-plasma,  in  lymph,  and  in  some  cases,  though  not 


352  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

always,  in  the  normal  and  pathological  exudations.  It  is  absent  from  blood- 
serum,  beini;  used  uj)  during  the  process  of  clotting.  It  occui-s  in  ver>'  small 
quantities  in  blood,  compared  with  the  other  proteids.  There  is  no  good 
method  of  determining  quantitatively  the  amount  of  fibrinogen,  but  estimates 
of  the  amount  of  fibrin,  which  cannot  differ  very  much  from  the  fibrinogen, 
show  that  in  human  blood  it  varies  from  0.22  to  0.4  per  cent.  In  horse's 
blood  it  may  be  more  abundant — 0.65  per  cent.  As  to  the  origin  and  the 
special  physiological  value  of  this  proteid  we  are,  if  possible,  more  in  the  dark 
than  in  the  case  of  pnraglobulin,  with  the  exception  that  fibrinogen  is  known  to 
be  tiie  source  of  the  fil)riu  of  the  blood.  But  clotting  is  an  f)Ccasional  phe- 
nomenon only.  AVhat  nutritive  function,  if  any,  is  possessed  by  fibrinogen 
under  normal  conditions  is  unknown.  Xo  satisfactory  account  has  been  given 
of  its  origin.  It  has  been  suggested  by  different  investigators  that  it  may 
come  from  the  nuclei  of  disintegrating  leucocytes  (and  blood-plates)  or  from 
the  dissolution  of  the  extruded  nuclei  of  newly-made  red  corpuscles,  but  here 
again  we  have  only  speculations,  which  cannot  be  accepted  until  some  experi- 
mental proof  is  advanced  to  support  them. 

Coagulation  of  Blood. — One  of  the  most  striking  ])roperties  of  bloofl  is 
its  power  of  clotting  or  coagulating  shortly  after  it  escapes  from  the  blood- 
ve&sels.  The  general  changes  in  the  bhxxl  during  this  ])rocess  are  easily  fol- 
lowed. At  first  shed  blood  is  perfectly  fluid,  but  in  a  few  minutes  it  becomes 
viscous  and  then  sets  into  a  soft  jelly  which  quickly  becomes  firmer,  so  that 
the  vessel  containing  it  can  be  inverted  without  spilling  the  blood.  The  clot 
continues  to  grow  more  compact  and  gradually  shrinks  in  volume,  pressing  out 
a  smaller  or  larger  quantity  of  a  clear,  faintly  yellow  liquid  to  which  the  name 
blood-serum  has  been  given.  The  essential  part  of  the  clot  is  the  fibrin.  Fibrin 
is  an  insoluble  proteid  wdiich  is  absent  from  normal  blood.  In  shed  blood, 
and  under  certain  conditions  in  blood  while  still  in  the  l)lood-vessels,  this  fibrin 
is  formed  from  the  soluble  fibrinogen.  The  deposition  of  the  fibrin  is  peculiar. 
It  is  precipitated,  if  the  word  may  be  used,  in  the  form  of  an  exceedingly  fine 
network  of  delicate  threads  which  permeate  the  whole  mass  of  the  blood  and 
give  the  clot  its  jelly-like  character.  The  shrinking  of  the  threads  causes 
the  subsequent  contraction  of  the  clot.  If  the  blootl  has  not  been  shaken 
during  the  act  of  clotting,  almost  all  the  red  corpuscles  are  caught  in  the  fine 
fibrin  meshwork,  and  as  the  clot  shrinks  these  corpuscles  are  held  more  firmly, 
only  the  clear  liquid  of  the  blooil  being  squeezed  out,  so  that  it  is  possible  to 
get  specimens  of  serum  containing  few  or  no  red  corpuscles.  The  leucocytes, 
on  the  contrary,  although  they  are  also  caught  at  first  in  the  forming  mesh- 
work of  fibrin,  may  readily  pass  out  into  the  serum  in  the  later  stages  of  clot- 
ting, on  account  of  their  power  of  making  amoeboid  movements.  If  the  blood 
has  been  agitated  during  the  process  of  clotting,  the  delicate  network  will  be 
broken  in  places  and  the  serum  will  be  more  or  less  bloody — that  is,  it  will 
contain  ninnerous  re<l  corpuscles.  If  during  the  time  of  clotting  the  blood  is 
vigorously  whipped  with  a  bundle  of  fine  rods,  all  the  fibrin  will  be  deposited 
as  a  stringy  mass  upon  the  whip,  and  the  remaining  liquid  part  will  consist  of 


BLOOD.  353 

serum  plus  tlie  blootl-corpusdcs.  Blood  which  has  been  whipped  iu  this  way 
is  luiowu  as  "  delibi-iuatcd  blood."  It  resembles  normal  blood  in  appearance, 
but  is  different  in  its  composition  :  it  cannot  clot  again.  The  way  in  which 
the  fibrin  is  normally  deposited  may  be  demonstrated  most  beautifully  under 
the  microscope  by  placing  a  good-sized  droi)  of  blood  on  a  slide,  covering  it 
with  a  cover-slip,  and  allowing  it  to  stand  ior  several  minutes  until  coagu- 
lation is  completed.  If  the  drop  is  now  examined,  it  is  |)os,sible  by  careful 
focussing  to  discover  in  the  spaces  between  the  masses  of  corpuscles  many 
exaini)]cs  of  the  delicate  librin  network.  The  physiological  value  of  clotting 
is  that  it  stops  hemorrhages  by  closing  the  openings  of  the  wounded  blood- 
vessels. 

Time  of  Clotting. — The  time  neceasary  for  the  clot  to  form  varies  slightly 
in  different  individuals,  or  in  the  blood  of  the  same  individual  varies  with  the 
conditions.  It  may  be  said  in  general  that  under  normal  conditions  the  blood 
passes  into  the  jelly  stage  in  from  three  to  ten  minutes.  The  separation  of 
clot  and  serum  takes  place  gradually,  but  is  usually  completed  in  from  ten  to 
forty-eight  hours.  The  time  of  clotting  shows  marked  variations  in  different 
animals;  the  process  is  especially  slow  in  the  horse  and  the  terrapin,  so  that 
coagulation  of  shed  blood  is  more  easily  prevented  in  these  animals.  In  the 
human  being  also  the  time  of  clotting  may  be  much  prolonged  under  certain 
conditions — in  fevers,  for  example.  This  fact  was  noticed  in  the  days  when 
bloodletting  was  a  common  practice.  The  slow  clotting  of  the  blood  permitted 
the  red  corpuscles  to  sink  somewhat,  so  that  the  upper  part  of  the  clot  in  such 
cases  was  of  a  lighter  color,  forming  what  was  called  the  "bufi'y  coat."  The 
time  of  clotting  may  be  shortened  or  be  j)rolonged,  or  the  clotting  may  be  i)re- 
vented  altogether,  in  various  Avays,  and  much  use  has  been  made  of  this  fact 
in  studying  the  composition  and  the  coagulation  of  blood  as  well  as  in  con- 
trolling hemorrhages.  It  will  be  advantageous  to  postpone  an  account  of  these 
methods  for  hastening  or  retarding  coagulation  until  the  theories  of  coagulation 
have  been  considered. 

Theories  of  Coagulation. — The  clotting  of  blood  is  such  a  prominent  phe- 
nomenon that  it  has  attracted  attention  at  all  times,  and  as  a  result  numerous 
theories  to  account  for  it  have  been  advanced.  Most  of  these  theories  possess 
simply  an  historical  interest,  and  need  not  be  discussed  in  a  work  of  this  charac- 
ter, but  some  reference  to  older  views  is  una\'oidable  for  a  proper  presentation 
of  the  subject.  To  prevent  misunderstanding  it  may  be  stated  explicit! v  in 
the  beginning  that  tliere  is  at  present  no  perfectly  satisfactory  theory.  Indeed, 
the  subject  is  a  dilHcult  one,  as  it  is  intimately  connected  witli  the  chemistrv 
of  the  proteids  of  the  blood,  and  it  may  be  said  that  a  complete  understanding 
of  clotting  waits  upon  a  better  knowledge  of  the  nature  of  these  proteids.  It 
happens  that  at  the  present  time  a  great  deal  of  attention  is  being  paid  to  this 
subject  by  experimenters,  and  it  is  possible  that  at  any  moment  new  facts  may 
be  discovered  which  will  alter  present  ideas  of  the  nature  of  the  process.  In 
considering  the  different  theories  that  have  been  proposed  tliere  are  two  general 
facts  which  should  always  be  kept  iu  mind  :  first,  that  the  main  phenomenon 


354  AN  AMERICAN    TENT- BOOK    OF    PIIYSIOLOCY, 

which  a  tlieory  of  coaguhitiou  has  to  explain  is  the  formation  of  fibrin  ;  second, 
that  all  theories  nnite  in  the  common  belief  that  the  fibrin  is  derived,  in  ])art  at 
least,  from  the  fibrinogen  of  tlie  plasma. 

Schmidt's  Older  Theory  of  Coagulation. — The  first  theory  which  gained 
general  acceptance  in  recent  times  was  that  of  Alexander  Schmidt.  It  was 
projK)scd  in  1801,  and  it  has  served  as  the  l)asi,s  for  all  subseqnent  theories. 
Schmidt  held  that  the  fibrin  of  the  clot  is  formed  by  a  reaction  between  para- 
globnlin  (he  called  it  "  fibrinophistin  ")  and  fibrinogen,  and  that  this  reaction  is 
brought  about  by  a  third  body,  to  which  he  gave  the  name  oi'  fibrin  ferment. 
Fibrin  ferment  was  believed  to  be  absent  from  normal  blood,  but  to  be  formed 
after  the  blood  was  shed.  Further  reference  will  presently  be  made  to  the 
nature  of  this  substance.  Schmidt  was  not  able  to  determine  its  nature — 
whether  it  was  a  proteid  or  not — but  he  discovered  a  method  of  preparing  it 
from  blood-serum,  and  demonstrated  that  it  cannot  be  obtained  from  blood 
immediately  after  it  leaves  the  blood-vessels,  and  that  consequently  it  does  not 
exist  in  circulating  blood,  in  any  appreciable  quantity  at  least.  Finally, 
Schmidt  believed  that  a  certain  quantity  of  soluble  salts  is  necessary  as  a 
fourth  "  fibrin  factor." 

Hammarsten's  Theory  of  Coar/ulation. — Ilammarsten,  who  repeated 
Schmidt's  experiments,  demonstrated  that  paraglobulin  is  unnecessary  for 
the  formation  of  fibrin.  He  showed  that  if  a  solution  of  pure  fibrinogen  is 
prepared,  and  if  there  is  added  to  it  a  solution  of  fibrin  ferment  entirely  free 
from  paraglobulin,  a  typical  clot  is  formed.  This  exi)eriment  has  since  been 
confirmed  by  others,  so  that  at  present  it  is  generally  accepted  that  paraglob- 
ulin takes  no  direct  part  in  the  formation  of  fibrin.  Hammarsten's  theory 
is  that  there  are  two  fibrin  factors,  fibrin  ferment  and  fibrinogen,  and  that 
fibrin  results  from  a  reaction  between  these  two  bodies.  The  nature  of  this 
reaction  could  not  be  determined,  but  Hammarsten  showed  that  the  entire 
fibrinogen  molecule  is  not  changed  to  fibrin.  A  dissociation  or  splitting 
occurs,  so  that  in  place  of  the  fibrinogen  there  is  present  after  clotting,  on  the 
one  hand,  fibrin  representing  most  of  the  weight  of  fibrinogen,  and,  on  the 
other  hand,  a  newly-formed  globulin-like  proteid  retained  in  solution  in  the 
serum,  to  which  proteid  the  name  fibrin-globulin  has  been  given.  Ham- 
marsten supposed  that  although  paraglobulin  took  no  direct  part  in  the  process, 
it  acted  as  a  favoring  condition,  a  greater  quantity  of  fibrin  being  formed 
when  it  was  present.  Some  recent  experiments '  show  that  this  sup])ositiou 
is  incorrect,  and  that  paraglobulin  may  be  eliminated  entirely  from  the  theory. 
The  theory  of  Hammarsten,  which  is  perhaps  generally  accepted  at  the  present 
time,  is  incomplete,  however,  in  that  it  leaves  undetermined  the  nature  of  the 
ferment  and  of  the  reaction  between  it  and  the  fibrinogen.  The  aim  of  the 
newer  theories  has  been  to  supply  this  deficiency. 

Schmidt's  Recent  Theory  of  Coagidation. — In  a  recent  book  ^  containing 
the  results  of  a  lifetime  of  work  devoted  to  the  study  of  blood-coagulation, 

'  Frederikse :  Zeitschrlft  fiir  physiohgische  Chemie,  vol.  19,  1894,  p.  143. 
«  Zur  Blutlehre,  Leipzig,  1893. 


BLOOD.  no  5 

Sehmiclt  has  inodifiod  liis  well-known  theory.  His  present  ideas  of  the  direct 
and  indirect  connection  of  the  proteids  of  the  plasma  with  the  formation  of 
fibrin  are  too  complex  to  be  stated  clearly  in  brief  compass.  He  classifies  the 
conditions  necessary  for  coagulation  as  follows  :  (1)  Certain  soluble  jji-otcids — 
namely,  the  two  globulins  of  the  blood — as  the  material  from  which  fibrin  is 
made.  Schmidt  does  not  believe,  however,  that  paraglobuliu  and  fibrinogen 
react  to  make  fibrin,  but  believes  that  fibrinogen  is  formed  from  paraglobulin, 
and  that  fibrinogen  in  turn  is  changed  to  fibrin.  (2)  A  specific  ferment,  fibrin 
ferment,  to  effect  the  changes  in  the  proteids  just  stated.  He  pix3])oses  for 
fibrin  ferment  the  distinctive  name  of  thrombin.  (3)  A  certain  quantity  of 
neutral  salts  is  necessary  for  the  precipitation  of  the  fibrin  in  an  insoluble  form. 

T/ie  Relation  of  Calcium  Salts  to  Coagulation. — It  has  been  shown  by  a 
number  of  observers  that  calcium  salts  take  an  important  part  in  the  pro- 
cess of  clotting.  This  fact  was  most  clearly  demonstrated  by  Arthus  and 
Pages,  who  found  that  if  oxalate  of  potash  or  soda  is  added  to  freshly-drawn 
blood  in  quantities  sufficient  to  precipitate  the  calcium  salts,  clotting  will  be 
prevented.  If,  however,  a  soluble  calcium  salt  is  again  added,  clotting  occurs 
promptly.  This  fact  has  been  demonstrated  not  only  for  the  blood,  but  also 
for  pure  solutions  of  fibrinogen,  and  we  are  justified  in  saying  that  without 
the  presence  of  calcium  salts  fibrin  cannot  be  formed  from  fibrinogen.  This 
is  one  of  the  most  significant  facts  recently  brought  out  in  connection  with 
coagulation.  We  know  that  fibrinogen  when  acted  upon  by  fibrin  ferment 
produces  fibrin,  but  we  now  know  also  that  calcium  salts  must  be  present. 
What  is  the  relation  of  these  salts  to  the  so-called  "  ferment"?  This  question 
has  been  differently  answered  in  two  recent  theories  of  coagulation. 

Pehelharing^ s  Theory  of  Coagulation. — Pekelharing^  succeeded  in  sepa- 
rating from  blood-plasma  a  proteid  body  which  has  the  properties  of  a  nucleo- 
albumin.  He  finds  that  if  this  substance  is  brought  into  solution  together 
with  fibrinogen  and  calcium  salts,  a  typical  clot  will  form,  while  nucleo- 
albumin  alone,  or  calcium  salts  alone,  added  to  fibrinogen  solutions,  cause 
no  clotting.  His  theory  of  coagulation  is  that  what  has  been  called  "  fibrin 
ferment"  is  a  compound  of  nucleo-albumin  and  calcium,  and  that  when 
this  compound  is  brought  into  contact  with  fibrinogen  a  reaction  occurs,  the 
calcium  passing  over  to  the  fibrinogen  and  forming  an  insoluble  calcium 
compound,  fibrin.  According  to  this  theory,  fibrin  is  a  calcium  compound 
with  fibrinogen  or  with  a  part  of  the  fibrinogen  molecule.  This  idea  is 
strengthened  by  the  unusually  large  percentage  of  calcium  found  in  fibrin 
ash.  The  theory  supposes  also  that  the  fibrin  ferment  is  not  present  in  blood- 
plasma — that  is,  in  sufficient  quantity  to  set  up  coagulation — but  that  it  is  formed 
after  the  blood  is  shed.  The  nucleo-albumin  part  is  derived  from  the  cor- 
puscles of  the  blood  (leucocytes,  blood-plates),  Mhich  break  down  and  go  into 
solution.  This  nucleo-albumin  then  unites  with  the  calcium  salts  present  in 
the  blood  to  form  fibrin  ferment,  an  organic  compound  of  calcium  capable  of 
reacting  with  fibrinogen.     The  theory  is  a  simple  one ;  it  accounts  for  the 

'  Untersuckungen  iiber  das  Fibrivfei-ment,  Amsterdam,  1892. 


35G  AN  AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 

importance  of  calcium  salts  in  coajjjulation,  and  reduces  tiie  iiiler<liaiiL!:e  he- 
tweeu  fibrinotrt'H  and  fibrin  ferment  to  the  nature  of  an  ordinai'v  clieniical 
reaction. 

LUicnfeliVii  T/icori/  of  Coagnhiiion. —  Lilienfeld  '  has  carried  still  further  the 
clieniical  stiidv  of  the  changes  occurrinir  in  coatrulation.  Like  lY'Uelharing: 
he  finds  that  the  three  inipoi'tant  sui)staiices  to  be  considered  in  coa<^ulalioii 
are  tlbrinoj^en,  nuclein  compounds,  and  cal(;iuni  salts.  He  differs  from  Pekel- 
haring,  however,  in  his  description  of  liow  these  substances  react  with  one 
another  in  producing  fibrin.  Lilienfeld  and  others  have  shown  that  a  com- 
pound proteid  to  which  the  name  "  nucleohiston  "  is  given  may  be  extracted 
from  the  nuclei  of  leucocytes  and  other  cells,  and  that  this  ueucleohiston  under 
some  circumstances  favors  the  coagulation  of  liquids  containing  fibrinogen,  but 
under  other  circumstances  prevents  or  retards  coagulation.  Nucleohiston  is 
readily  decomposed  into  its  two  constituents — histon,  a  proteid  body,  and  a 
nueleo-proteid  to  which  the  specific  name  of"  leuconuclein  "  is  given.  Histon 
when  injected  into  the  blood  of  a  living  animal  has  a  remarkable  influence  in 
preventing  coagulation  :  blood  drawn  shortly  after  the  injection  remains  per- 
fectly fluid,  and  its  histological  elements,  red  and  white  corpuscles  and  blood- 
plates,  retain  perfectly  their  normal  shapes.  Leuconuclein,  on  the  contrary, 
although  it  is  not  able  to  produce  fibrin  from  fibrinogen,  does  cause  the  fibrin- 
ogen molecule  to  split,  with  the  formation  of  a  substance,  "  thrombosin," 
which  comes  down  as  a  precipitate.  If  this  thrombosin  is  dissolved  in 
dilute  alkaline  solution  it  clots  readily  when  brought  into  contact  with  cal- 
cium salts.  Thrombosin  may  also  be  formed  from  fibrinogen  by  the  action  of 
dilute  acetic  acid  or  nucleic  acid  (nuclein).  Normal  coagulation,  according  to 
Lilienfeld,  takes  place  as  follows :  After  blood  is  shed  there  occurs  a  disinte- 
gration of  leucocytes  (and  blood-plates)  resulting  in  the  giving  off  of  nuclein 
compounds  to  the  plasma.  These  nuclein  substances,  being  dissolved  in  the 
alkaline  jilasnia,  come  in  contact  with  the  fibrinogen  and  decompose  it,  with 
the  formation  of  thrombosin.  This  latter  substance  then  unites  with  the  cal- 
cium salts  of  the  plasma  to  form  fibrin,  wiiieli,  on  this  theory,  might  be  defined 
as  a  calcium  compound  of  thrombosin.  Lilienfeld's  theory  does  not  give  a 
satisfactory  explanation  of  the  nature  of  fibrin  ferment,  but  is  very  valuable 
in  demonstrating  that  the  essential  act  of  clotting — that  is,  of  the  formation 
of  fibrin — is  the  union  of  calcium  salts  with  a  portion  of  the  fibrinogen  mole- 
cule, and  that  this  portion  of  the  fibrinogen  molecule  may  first  be  s])lit  off  by 
the  action  of  acetic  acid  or  the  acid  nuclein  coiiii)ounds.  LTntil  further  inves- 
tigations are  made  it  is  not  possible  to  decide  between  the  theories  of  Pekel- 
haring  and  Lilienfeld.  It  is  well,  however,  to  emj)liasize  the  fact  that  there 
is  much  in  common  between  the  two  theories.  E;ieh  holds  that  the  fibrin  is  a 
compound  of  calcium  salts  with  a  jiortion  of  the  fii)iinogeii  molecule,  the  latter 
undergoing  splitting  during  the  act  of  clotting.  According  to  I^ilienfeld,  this 
splitting  of  the  fibrinogen  molecule  is  caused  by  nueleo-proteid,  and  the 
thrombosin  thus  formed  then  comI)ii)es  with  the  calcium.     According  to  Pekel- 

'  Du  Bois-Reymond's  Arch ir  fib-  Phyxioloyie,  1893,  p.  560. 


BLOOD.  357 

haring,  the  micleo-proteid  first  combines  with  the  oalciiini,  and  tlien  this  cal- 
cium compound  reacts  with  the  fibrinogen,  transferring  its  calcium  to  a  portion 
of  the  molecule.  We  might  say,  therefore,  that  there  are  three  fibrin  fiictors 
— fibrinogen,  nucleo-proteid,  and  calcium  salts;  the  first  and  last  of"  these  exist 
in  the  circulating  blood,  but  the  nucleo-proteid  is  formed  usually  only  after 
the  blood  is  shed,  and  is  derived  from  the  disintegration  of  the  formed  ele- 
ments, the  leucocytes  and  blood-})l;ites.  ilow  these  three  factors  interact  to 
form  fibrin  cannot  be  stated  i)ositive!y,  but  it  seems  to  be  satisfactorily  deter- 
mined that  the  fibrin  is  a  c()m|)ound  of  calcium  with  a  ])ro(hict  derived  from 
the  splitting  of  the  fibrinogen. 

Nature  and  Orig-in  of  Fibrin  Ferment  (Thrombin). — Recent  views  as 
to  the  nature  of  fibrin  ferment  have  been  referred  to  incidentally  in  the 
description  of  the  theories  of  coagulation  just  given.  The  relation  of  these 
newer  views  to  the  older  ideas  can  be  presented  most  easily  by  giving  a 
brief  description  of  the  development  of  our  knowledge  concerning  this  bodv. 
Schmidt'  prepared  solutions  of  fibrin  ferment  originally  by  adding  a  large 
excess  of  alcohol  to  blood-serum  and  allowing  the  proteids  thus  precipitated 
to  stand  under  strong  alcohol  for  a  long  time  until  they  were  thoroughly  coagu- 
lated and  rendered  nearly  insoluble  in  water.  At  the  end  of  the  proper  period 
the  coagulated  proteids  were  extracted  with  water,  and  there  was  obtained  a 
solution  Avhich  contained  only  small  quantities  of  proteid.  It  was  found  that 
solutions  prepared  in  this  way  had  a  marked  effect  in  inducing  coagulation 
when  added  to  liquids,  such  as  hydrocele  liquid,  which  contained  fibrinogen, 
but  which  did  not  clot  spontaneously  or  else  clotted  very  slowly.  It  was  after- 
ward shown  that  similar  solutions  of  fibrin  ferment  are  capable  of  setting  up 
coagulation  very  readily  in  so-called  salted  plasma — that  is,  in  blood-plasraa 
prevented  from  clotting  by  the  addition  of  a  certain  quantity  of  neutral  salts. 
It  was  not  possible  to  say  whether  the  coagulating  power  of  these  solutions 
was  due  to  the  small  traces  of  proteid  contained  in  them,  or  whether  the  ])ro- 
teid  was  merely  an  impurity.  The  general  belief  for  a  time,  however,  was 
that  the  proteids  present  were  not  the  active  agent,  and  that  there  was  in  solu- 
tion something  of  an  unknown  chemical  nature  which  acted  upon  the  fibrinogen 
after  the  manner  of  unorganized  ferments.  This  belief  was  founded  mainly 
upon  three  facts :  first,  that  the  substance  seemed  to  be  able  to  act  powerfully 
upon  fibrinogen,  although  present  in  such  minute  quantities  that  it  could  not  be 
isolated  satisfactorily  ;  second,  it  was  destroyed  by  heating  its  solutions  for  a  few 
minutes  at  60°  C. ;  and,  third,  it  did  not  seem  to  be  destroyed  in  the  reaction 
of  coagulation  which  it  set  up,  since  it  was  always  present  in  the  serum  squeezed 
out  of  the  clot.  Schmidt  proved  that  fibrin  ferment  could  not  be  obtained 
from  blood  by  the  method  described  above  if  the  blood  was  made  to  flow  im- 
mediately from  the  cut  artery  into  the  alcohol.  On  the  other  hand,  if  the  shed 
blood  was  allowed  to  stand,  the  quantity  of  fibrin  ferment  increased  up  to 
the  time  of  coagulation,  and  was  present  in  quantity  in  the  serum.  Schmidt 
believed  that  the  ferment  was  formed  in  shed  blood  from  the  disintegration 
of  the  leucocytes,  and  this  belief  was  corroborated  by  subsequent  histological 


358  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

work.  It  was  shown  in  microscopic  preparations  of  coagulated  blood  that  the 
fibrin  threads  often  radiated  from  broken-down  leucocytes — an  appearance 
which  seemed  to  indicate  that  the  leucocytes  served  as  p(Mnts  of  orij^in  for  the 
deposition  of  tiic  fibrin.  When  the  blood-plates  were  discovered  a  great  deal 
of  microscopic  work  was  done  tending  to  show  that  these  bodies  also  are  con- 
nected with  coagulation  in  the  same  way  as  the  leucocytes,  and  serve  probably 
as  sources  of  fibrin  ferment.  In  microscopic  preparations  the  fibrin  threads 
were  found  to  radiate  from  masses  of  partially  disintegrated  plates ;  and,  more- 
over, it  was  discovered  that  conditions  which  retard  or  prevent  coagulation  of  • 
blood  often  serve  to  preserve  the  delicate  plates  from  disintegration.  At  the 
present  time  it  is  generally  believed  that  there  is  derived  from  the  disintegra- 
tion of  the  leucocytes  and  blood-plates  something  which  is  necessary  to  the 
coao-ulation  of  blood,  but  there  is  some  difierence  of  opinion  as  to  the  nature 
of  this  substance  and  whether  it  is  identical  with  Schmidt's  fibrin  ferment. 
Pekelharing  thinks  that  the  substance  set  free  from  the  corpuscles  and  plates 
is  a  nuclco-])roteid,  but  that  this  uucleo-proteid  is  not  capable  of  acting  upon 
fibrinoo-en  until  it  has  combined  with  the  calcium  salts  of  the  blood.  According 
to  his  view,  therefore,  fibrin  ferment,  in  Schmidt's  sense,  is  a  compound  of  cal- 
cium and  nucleo-proteid.  Lilienfeld  has  shown  by  chemical  reactions  that 
blood-plates  and  nuclei  of  leucocytes  contain  nucleo-proteid  material  which  in 
all  probability  is  liberated  in  the  blood-plasma  by  the  disintegration  of  these 
elements  after  the  blood  is  shed.  As  he  has  shown  also  that  this  nucleo- 
proteid  material  with  the  aid  of  calcium  salts  acts  upon  the  fibrinogen  to  pro- 
duce fibrin,  it  would  seem  clear  that  the  so-called  fibrin  ferment  is  really  a 
nucleo-proteid  compound.  Lilienfeld  contends,  however,  that  solutions  of 
fibrin  ferment  prepared  by  Schmidt's  method  do  not  contain  any  nucleo-proteid 
material,  and  that,  although  the  liberation  of  the  nucleo-proteid  material  is  what 
starts  normal  coagulation  of  blood,  nevertheless  so-called  fibrin  ferment  is  some- 
thing entirely  different  from  nucleo-proteid.  In  this  point,  however,  his  results 
are  contradicted  by  the  experiments  of  Pekelharing  and  of  Halliburton,  who 
both  find  that  solutions  of  fibrin  ferment  prepared  by  Schmidt's  method  give 
distinct  evidence  of  containing  nucleo-])roteid  material.  We  may  conclude, 
therefore,  that  the  essential  element  of  Schmidt's  fibrin  ferment  is  a  nucleo- 
proteid  compound.  Whether  or  not  this  nucleo-proteid  can  act  upon  fibrinogen 
directly,  as  Lilienfeld  claims,  or  must  first  combine  with  calcium  salts,  as  held 
by  Pekelharing,  is  a  matter  which  must  be  left  to  future  investigation. 

Intravascular  Clotting. — Clotting  may  be  induced  within  the  blood- 
vessels by  the  introduction  of  foreign  particles,  either  solid  or  gaseous — for 
example,  air — or  by  injuring  the  inner  coat  of  the  blood-vessels,  as  in  ligat- 
ing.  In  the  latter  case  the  area  injured  by  the  ligature  acts  as  a  foreign 
surface  and  probably  causes  the  disintegration  of  a  number  of  corpuscles. 
The  clot  in  this  case  is  confined  at  first  to  the  injured  area,  and  is  known 
as  a  "thrombus."  Intravascular  clotting  more  or  less  general  in  occurrence 
may  be  produced  by  injecting  into  the  circulation  such  substances  as  leucocytes 
obtained  by  macerating  lymph-glands,  extracts  of  fibrin  ferment,  solutions  of 


BLOOD.  ;J59 

nucleo-albumius  of  different  kiud.s,  etc.  According  to  tiic;  tlu-ory  of  coagu- 
lation adopted  above,  injections  of  these  latter  substances  ought  to  cause  coagu- 
lation very  readily,  since  the  blood  ahvady  contains  fibrinogen,  and  needs  only 
the  presence  of  ferment  to  set  up  conguiation.  As  a  matter  of  fact,  however, 
intravascular  clotting  is  produced  with  some  difficulty  by  these  methods,  show- 
ing that  the  body  can  protect  itself  within  certain  limits  from  an  excess  of 
ferment  in  the  circulating  blood.  Just  how  this  is  done  is  not  known,  but 
possibly  it  is  due  to  some  defensive  activity  of  the  living  endothelial  cells  lining 
the  interior  of  the  blood-vessels.  Moreover,  injection  of  leucocytes,  nucleo- 
albumins,  etc.  sometimes  diminishes  instead  of  increasing  the  coagulability  of 
blood,  making  the  so-called  "negative  phase"  of  the  injection.  In  the  case 
of  leucocytes  it  is  probable  that  this  result  is  accounted  for  by  the  fact  that 
the  nucleohiston  liberated  by  their  disintegration  may  undergo  decomposition 
in  the  blood  with  the  formation  of  histon,  which  is  known  to  prevent  coagu- 
lation (see  p.  356). 

Why  Blood  does  not  Clot  within  the  Blood-vessels. — The  reasons 
why  blood  remains  fluid  while  in  the  living  blood-vessels,  but  clots  quickly 
after  being  shed  or  after  being  brought  into  contact  with  a  foreign  substance  in 
any  way,  have  already  been  stated  in  describing  the  theories  of  coagulation, 
but  they  will  be  restated  here  in  more  categorical  form.  Briefly,  then,  blood 
does  not  clot  within  the  blood-vessels  because  nucleo-proteids  are  not  present 
in  sufficient  quantities  at  any  one  time.  Leucocytes  and  blood-plates  probably 
disintegrate  here  and  there  within  the  circulation,  but  the  small  amount  of  fer- 
ment thus  formed  is  insufficient  to  act  upon  the  blood,  and  probably  the  ferment 
is  quickly  destroyed  or  changed.  When  blood  is  shed,  however,  the  formed 
elements  break  down  in  mass,  as  it  were,  liberating  a  relatively  large  amount 
of  nucleo-proteids,  which,  in  combination  with  the  calcium  salts,  produce  fibrin 
from  the  fibrinogen.  In  shed  blood  the  restraining  action  of  the  endothelial 
cells  of  the  blood-vessels,  a  more  or  less  unknown  factor,  is  also  eliminated. 

Means  of  Hastening  or  of  Retarding  Coagulation. — Blood  coagulates 
normally  within  a  few  minutes,  but  the  process  may  be  hastened  by  increasing 
the  extent  of  foreign  surface  with  which  it  comes  in  contact.  Thus,  moving 
the  liquid  when  in  quantity,  or  the  application  of  a  sponge  or  a  handkerchief  to 
a  wound,  will  hasten  the  onset  of  clotting.  This  is  easily  understood  when  it  is 
remembered  that  nucleo-proteids  arise  from  the  breaking  down  of  leucocytes 
and  blood-plates,  and  that  these  corpuscles  go  to  pieces  more  rapidly  when  in 
contact  with  a  dead  surface.  It  has  been  proposed  also  to  hasten  clotting  in 
case  of  hemorrhage  by  the  use  of  ferment  solutions.  Hot  sponges  or  cloths 
applied  to  a  wound  will  hasten  clotting,  probably  by  accelerating  the  formation 
of  ferment  and  the  chemical  changes  of  clotting.  Coagulation  may  be  retarded 
or  be  prevented  altogether  by  a  variety  of  means,  of  which  the  following  are 
the  most  important : 

1.  By  Cooling. — This  method  succeeds  well  only  in  blood  which  clots 
slowly — for  example,  the  blood  of  the  horse  or  the  terrapin.  Blood  from 
these  animals  received  into  narrow  vessels  surrounded  by  crushed  ice  may  be 


860  AN  ami:  in  ('AN    TKXr-BOOK    OF   PHYSIOLOGY. 

kept  fluid  for  an  indefinite  time.  Tlie  blo()d-cur])u.scles  .s(Jon  sink,  so  that  this 
method  is  an  exeellent  one  for  obtaining  pure  blood-plasma.  The  cooling 
probably  prevents  clotting  Jbv  keeping  the  corpuscles  intact. 

2.  By  the  Action  of  Neutral  Salts. — Blood  received  at  once  from  the  blood- 
vessels into  a  solution  of  such  neutral  salts  as  sodium  sulphate  or  magnesium 
sulphate,  and  well  mixed,  will  not  clot.  In  this  case  also  the  corpuscles  settle 
sluwiv,  or  thev  may  be  centrifugalizcd,  and  specimens  of  plasma  can  be 
obtained.  For  this  purpose  hoi-si-'s  or  cat's  blood  is  to  be  preferred.  Such 
})lasma  is  known  as  ".salted  plasma;"  it  is  frequently  used  in  experiments  in 
coagulation — for  exam|)le,  in  testing  the  efficacy  of  a  given  ferment  solution. 
The  best  salt  to  use  is  MgSO^  in  solutions  of  27  i)er  cent. :  1  part  by  volume 
of  this  solution  is  usually  mixed  with  4  parts  of  blood  ;  if  cat's  blood  is  used  a 
smaller  amount  may  be  taken — 1  part  of  the  solution  to  9  of  blood.  Salted 
plasma  or  salted  blood  again  clots  when  diluted  sufficiently  with  water  or  when 
ferment  solutions  are  added  to  it.  How  the  salts  prevent  coagulation  is  not 
definitely  known — possibly  by  preventing  the  disintegration  of  corpuscles  and 
the  formation  of  ferment,  possibly  by  altering  the  chemical  properties  of  the 
proteids. 

3.  By  the  Action  of  Albnmose  Solutions. — Certain  of  the  products  of 
protcid  digestion,  pei)tones  and  albumoses,  when  injected  into  the  circulation 
retard  clotting  for  a  long  time.  For  injection  into  dogs  one  uses  0.3  gi-am 
to  each  kilogram  of  animal.  If  the  blood  is  withdrawn  shortly  after  the 
injection,  it  will  remain  fluid  for  a  long  time.  According  to  Pekelharing,  the 
albumoses  act  by  combining  with  the  calcium  salts,  or  at  least  by  preventing 
them  from  reacting  normally. 

4.  By  the  Use  of  Leech  Extracts. — Extract  of  the  heads  of  leeches,  when 
mixed  with  blood,  will  prevent  coagulation.  The  extract  contains  some  sub- 
stance formed  in  the  salivary  glands  of  the  leech.  It  is  probable  that  this 
substance  acts  normally  to  prevent  the  clotting  of  blood  when  sucked  in  by  the 
animal. 

5.  By  the  Action  of  Oxalate  Solutions. — If  blood  as  it  flows  from  the 
vessels  is  mixed  with  solutions  of  j^otassium  or  sodium  oxalate  in  proportiim 
sufficient  to  make  a  total  strength  of  0.1  per  cent,  or  more  of  these  salts, 
coagulation  will  be  prevented  entirely.  Addition  of  an  excess  of  water  will 
not  produce  clotting  in  this  case,  but  solutions  of  some  soluble  calcium  salt 
will  quickly  start  the  process.  The  explanation  of  the  action  of  the  oxalate 
solutions  is  simple:  they  are  supposed  to  precipitate  the  calcium  as  insoluble 
calcium  oxalate. 

Total  Quantity  of  Blood  in  the  Body. — The  total  quantity  of  blood  in 
the  body  has  been  determined  approximately  for  man  and  a  number  of  the 
lower  animals.  The  method  used  in  such  determinations  consists  essentially 
in  first  bleeding  the  animal  as  thoroughly  as  possible  and  weighing  the  quan- 
tity of  blood  thus  obtained,  and  afterward  washing  out  the  blood-vessels  with 
water  and  estimating  the  amount  of  luemoglobin  in  the  washings.  The  results 
are  a.s  follows:    Man,  7.7  per  cent,  (^r^)  of  the  body-weight ;  that  is,  a  man 


BLOOD,  3G1 

weigliin^-  G8  kilos,  has  about  52-jG  grams,  or  49G.5  c.c,  of  blood  in  his  body; 
dog,  7.7  per  cent.;  rabbit  and  cat,  5  percent.;  new-born  human  being,  5.26 
per  cent. ;  and  birds,  10  per  cent.  Moreover,  tiie  distribution  of  this  blood 
in  the  tissues  of  the  body  at  any  one  time  has  been  estimated  by  Kanke,'  from 
experiments  on  freshly-killed  rabbits,  as  follows: 

Spleen 0.'2.'>  i)er  cent. 

Briiin  anil  cord 1.24  "  " 

Kidneys 1.63  "  " 

Skin 2.10  "  " 

Intestines 6.30  "  " 

Bones 8.24  "  " 

Heart,  lungs,  and  great  blood-vessels 22.76  "  " 

Kesting  muscles 29.20  "  " 

Liver 29.30  "  " 

It  will  be  seen  from  inspection  of  this  table  that  in  the  rabbit  the  blood  of 
the  body  i.s  distributed  at  any  one  time  about  as  follows :  one-fourth  to  the 
heart,  lungs,  and  great  blood-vessels;  one-fourth  to  the  liver;  one-fourth  to 
the  resting  muscles;  and  one-fourth  to  the  remaining  organs. 

Regeneration  of  the  Blood  after  Hemorrhage. — A  large  portion  of  the 
entire  quantity  of  blood  in  the  body  may  be  lost  suddenly  by  hemorrhage 
without  producing  a  fatal  result.  The  extent  of  hemorrhage  Avhich  can  be 
recovered  from  safely  has  been  investigated  upon  a  number  of  animals. 
Although  the  results  show  more  or  less  individual  variation,  it  can  be  said 
that  in  dogs  a  hemorrhage  of  from  2  to  3  per  cent,  of  the  body-weight  ^  is 
recovered  from  easily,  while  a  loss  of  4.5  per  cent.,  more  than  half  the  entire 
blood,  will  probably  prove  fatal.  In  cats  a  hemorrhage  of  from  2  to  3  ]>er 
cent,  of  the  body-weight  is  not  usually  followed  by  a  fatal  result.  Just  what 
percentage  of  loss  can  be  borne  by  the  human  being  has  not  been  deter- 
mined, but  it  is  probable  that  a  healthy  individual  may  recover  without 
serious  difficulty  from  the  loss  of  a  quantity  of  blood  amounting  to  as  much 
as  3  per  cent,  of  the  body-weight.  It  is  known  that  if  liquids  which  are  iso- 
tonic to  the  blood,  such  as  a  0.9  per  cent,  .solution  of  NaCl,  are  injected  into 
the  veins  immediately  after  a  severe  hemorrhage,  recovery  will  be  more  certain  ; 
in  fact,  it  is  possible  by  this  means  to  restore  persons  after  a  hemorrhage  which 
would  otherwise  have  been  fatal.  The  phy.siological  reason  for  this  fact  seems 
to  be  that  the  large  access  of  neutral  liquid  puts  into  circulation  all  the  red 
corpuscles.  Ordinarily  the  number  of  red  corpuscles  is  greater  than  that  neces- 
sary for  a  barely  sufficient  supply  of  oxygen,  and  increasing  the  bulk  of  liquid 
in  the  vessels  after  a  severe  hemorrhage  makes  more  effecti\e  as  oxygen-carriers 
the  remaining  red  corpuscles,  inasmuch  as  it  ensures  a  more  rapid  circulation. 
If  a  hemorrhage  has  not  been  fatal,  experiments  on  lower  animals  show  that 
the  plasma  of  the  blood  is  regenerated  with  astonishing  rapidity,  the  blood 
regaining  its  normal  volume  within  a  few  hours  in  slight  hemorrhages,  and 

1  Taken  from  Vierordt's  Anatomische,  physiologisehe  und  physikalische  Daten  und  Tabellen,  Jen&j 
1893. 

'^  Fredericq  :   Travaux  du  Laboratoire  (  Univeii^ite  de  Liege),  vo].  i.,  1885,  p.  189. 


362  AN  AMERICAN   TEXT-BOOK   OF  PJIYSIOLOGY. 

in  from  twenty-four  to  forty-eight  hours  if  the  loss  of  hh)ocl  has  been 
severe ;  but  the  number  of  red  corpuscles  and  the  hsenioglobin  are  regenerated 
more  slowly,  getting  back  to  normal  only  after  a  number  of  days  or  after 
several  weeks. 

Blood-transfusion. — Shortly  after  the  discovery  of  the  circulation  of  the 
blood  (Harvey,  1628),  the  operation  was  introduced  of  transfusing  blood  from 
one  individual  to  another  or  from  some  of  the  lower  animals  to  man.  Ex- 
travagant hopes  were  held  as  to  the  value  of  such  transfusion  not  only  as  a 
means  of  replacing  the  blood  lost  by  hemorrhage,  but  also  as  a  cure  for  various 
infirmities  and  diseases.  Then  and  subsequently,  fatal  as  well  as  successful 
results  followed  the  operation.  It  is  now  known  to  be  a  dangerous  under- 
taking, mainly  for  two  reasons:  first,  the  strange  blood,  whether  transfu.sed 
directly  or  after  defibrination,  is  liable  to  contain  a  quantity  of  fil)rin  ferment 
sufficient  to  cause  intravascular  clotting;  secondly,  the  serum  of  one  animal  is 
known  to  cause  often  a  destruction  of  the  blood-corpuscles  of  another.  Owing 
to  this  globulicidal  action,  which  has  previously  been  referred  to  (p.  334),  the 
injection  of  foreign  blood  is  likely  to  be  directly  injurious  instead  of  beneficial. 
In  cases  of  loss  of  blood  from  severe  hemorrhage,  therefore,  it  is  far  safer  to 
inject  a  neutral  liquid,  such  as  the  so-called  "physiological  salt-solution" — a 
solution  of  NaCl  of  such  a  strength  (0.9  per  cent.)  as  to  be  isotonic  to  the  cor- 
puscles. The  bulk  of  the  circulating  liquid  is  thereby  augmented,  and  all  the 
red  corpuscles  are  made  more  efficient  as  oxygen-carriers,  partly  owing  to  the 
fact  that  the  velocity  of  the  circulation  is  increased,  and  partly  because  the 
corpuscles  are  kept  from  stagnation  in  the  capillary  areas. 


LYMPH. 

Lymph  is  a  colorless  liquid  found  in  the  lymph-vessels  as  well  as  in  the 
extravascular  spaces  of  the  body.  All  the  tissue-elements,  in  fact,  may  be 
regarded  as  being  bathed  in  lymph.  To  understand  its  occurrence  in  the  body 
one  has  only  to  bear  in  mind  its  method  of  origin  from  the  blood.  Throughout 
the  entire  body  there  is  a  rich  supply  of  blood-vessels  penetrating  every  tissue 
with  the  exception  of  the  epidermis  and  some  epidermal  structures,  as  the  nails 
and  the  hair.  The  plasma  of  the  blood  filters  through,  or  is  secreted  through, 
the  thin  walls  of  the  capillaries,  and  is  thus  l)rought  into  immediate  contact 
with  the  tissues,  to  which  it  brings  the  nourishment  and  oxygen  of  the  bloo<l 
and  from  which  it  removes  the  waste  products  of  metabolism.  This  extravas- 
cular Ivmph  is  collected  into  small  capillary  spaces  which  in  turn  open  into 
definite  lymphatic  vessels.  These  vessels  unite  to  larger  and  larger  trunks, 
forming  eventually  one  main  trunk,  the  thoracic  or  left  lymphatic  duct,  and  a 
second  smaller  right  lymphatic  duct,  which  oi)en  into  the  blood-vessels,  each 
on  its  own  side,  at  the  junction  of  the  subclavian  and  internal  jugular  veins. 
The  lymph  movement  is  from  the  tissues  to  the  veins,  and  the  flow  is  main- 
tained chiefly  by  the  difference  in  pressure  between  the  lyrajih  at  its  origin  in 


L  YMPH.  363 


the  tissues  and  in  the  large  lymphatic  vessels.  The  continual  formation  of 
lymph  in  the  tissues  leads  to  the  development  of  a  relatively  high  pressure  in 
the  lymph  capillaries,  and  as  a  result  of  this  the  lymph  is  forced  toward  the 
point  of  lowest  pressure— namely,  the  points  of  junction  of  the  large  lymph- 
ducts  with  the  venous  system.  A  fuller  discussion  of  the  factors  concerned  in 
the  movement  of  lymph  will  be  found  in  the  section  on  Circulation.  As  would 
be  inferred  from  its  origin,  the  composition  of  lymph  is  essentially  the  same  as 
that  of  blood-})lasma.  Lymph  contains  the  three  blood-proteids,  the  extractives 
(urea,  fat,  lecithin,  cholesterin,  sugar),  and  inorganic  salts.  The  salts  are  found 
in  the  same  proportions  as  in  the  plasma ;  the  proteids  are  less  in  amount,  espe- 
cially the  fibrinogen.  Lymph  coagulates,  but  does  so  more  slowly  and  less 
firmly  than  the  blood.  Histologically,  lymph  consists  of  a  colorless  liquid  con- 
taining a  number  of  leucocytes,  and  after  meals  a  number  of  minute  fat-drop- 
lets; red  blood-corpuscles  occur  only  accidentally,  and  blood-plates,  according 
to  most  accounts,  are  likewise  normally  absent. 

Formation  of  Lymph. — The  careful  researches  of  Ludwig  and  his  pupils 
were  formerly  believed  to  prove  that  the  lymph  is  derived  directly  from  the 
plasma  of  the  blood  by  filtration  through  the  capillary  walls.     Various  condi- 
tions which  alter  the  pressure  of  the  blood  were  shown  to  influence  the  amount 
of  lymph  formed  in  accordance  with  the  demands  of  a  theory  of  filtration. 
Moreover,  the  composition  of  lymph  as  usually  given  seems  to  support  such  a 
theory,  inasmuch  as  the  inorganic  salts  contained  in  it  are  in  the  same  concen- 
tration, approximately,  as  in  blood-plasma,  while  the  proteids  are  in  less  con- 
centration, following  the  well-known   law  that  in  the  filtration  of  colloids 
through  animal  membranes  the  filtrate  is  more  dilute  than  the  original  solution. 
This  simple  and  apparently  satisfactory  theory  has  been  subjected  to  critical 
examination  within  recent  years,  and  it  has  been  shown  that  filtration  alone 
does  not  suffice  to  explain  the  composition  of  the  lymph  untl^r  all  circum- 
stances.    At  present  two  divergent  views  are  held  upon  the  subject.     Accord- 
ing to  some  physiologists,  all  the  facts  known  with  regard  to  the  composition 
of  lymph  may  be  satisfactorily  explained  if  we  suppose  that  this  liquid  is 
formed  from  blood-plasma  by  the  combined  action  of  the  two  physical  pro- 
cesses of  filtration  and  diffusion.     According  to  others,  it  is  believed  that,  in 
addition  to  filtration  and  diffusion,  it  is  necessary  to  assume  an  active  secretory 
process  on  the  part  of  the  endothelial  cells  composing  the  capillary  walls.     A 
discussion  upon  these  points  is  in  progress  at  present  in  current  physiological 
literature,  and  it  is  impossible  to  foresee  definitely  what  the  outcome  will  be, 
since  a  final  conclusion  can  be  reached  only  by  repeated  experimental  investi- 
gations.   The  actual  condition  of  our  knowledge  of  the  subject  can  be  presented 
most  easily  bv  briefly  stating  the  objections  which  have  been  raised  by  Heiden- 
hain  ^  to  a  pure  filtration-and-diffusion  theory,  and  indicating  how  these  objec- 
tions have  been  met. 

L  Heidenhain  shows  by  simple  calculations  that  an  impossible  formation 
of  lymph  would  be  required,  upon  the  filtration  theory,  to  supply  the  chemical 
"^  Arehiv  fur  die  gesammte  Physwlogie,  1891,  Bd.  xlix.  S.  209. 


;3(j4  AN  AMERTCAN    TEXT- HOOK    OF    PIl  YSIOLOC  Y. 

needs  of  tlie  organs  in  various  organic  and  inorganic  constituents.  Thus,  to 
take  an  illustration  which  has  Ihcu  nuich  discussed,  one  kilogram  of  cow's 
milk  contains  1.7  grams  CaO,  and  the  entire  milk  of  twcntv-four  iiours  would 
contain  in  round  numbers  42.5  grams  CaO.  Since  the  lym})li  contains  nor- 
mally al)out  0.18  parts  of  CaO  per  tiiousand,  it  would  require  23(>  liters  of 
lymph  per  day  to  supply  the  necessary  CaO  to  the  mammary  glands.  Heiden- 
hain  iiimself  suggests  that  the  difficulty  in  this  case  may  he  met  by  assuming 
active  diffusion  processes  in  connection  with  liltration.  If,  for  instance,  in  the 
case  cited,  we  suppose  that  the  CaO  of  the  lympii  is  quickly  combined  by  the 
tissues  of  the  mammary  gland,  then  the  tension  of  calcium  salts  in  the  lymph 
will  be  kept  at  zero,  and  an  active  ditl'usion  of  calcium  into  the  lymph  will  occur 
so  long  as  the  gland  is  secreting.  In  other  wM)r(ls,  the  gland  will  receive  its 
calcium  by  mnch  the  same  process  as  it  receives  its  oxygen,  and  will  get  its 
daily  supply  from  a  comparatively  small  bulk  of  lymph.  Cohnstein  ^  has 
answered  the  problem  in  another  way.  He  calls  attention  to  the  fact  that 
in  the  body  the  capillaries  contain  blood  under  a  comparatively  liigh  pres- 
sure, while  on  their  exterior  they  are  bathed  with  lymph,  also  under  pres- 
sure, although  less  than  that  of  the  blood.  The  pressure  causing  filtration 
in  this  case  is  the  difference  in  pressure  between  the  inside  and  the  outside 
liquid.  Moreover  these  liquids  differ  in  comj)osition,  so  that  diffusion  must 
also  take  place  in  such  a  manner  that  crystalloids  will  diffuse  out  into  the 
lymph,  and  an  amount  of  water  corresponding  to  the  osmotic  equivalent  will 
pass  into  the  blood.  The  lymph  that  is  actually  formed  will  therefore  be  the 
balance  between  these  tw^o  processes,  and  a  liquid  produced  in  this  way  he 
designates  specifically  as  a  transudation.  From  laboratory  experiments  made 
with  ureters  and  veins  he  shows  that  the  percentage  composition  of  the  transu- 
dation in  crystalloid  substances  will  increase  with  the  pressure  of  the  outside 
liquid.  As  this  pressure  is  raised  the  filtration -stream  is  diminished,  but  the 
diffusion  is  unaffected,  hence  the  transudation  will  be  more  concentrated.  It 
is  possible  in  this  way,  as  he  shows  by  experiment,  to  get  a  transudation  much 
more  concentrated  than  the  original  liquid,  and  he  assumes  that  in  the  body 
the  lymph  formed  in  the  tissues  may  be  more  concentrated  than  the  blood,  and 
thus  a  small  quantity  of  lymph  may  transport  a  large  amount  of  crystalloid 
substance.  What  seems  to  be  a  fatal  objection  to  this  reasoning,  so  far  as  it 
applies  to  the  difficulty  first  suggested  with  regard  to  the  chemical  needs  of  the 
organs,  is  the  time  element.  As  Heidenhain  points  out,  the  more  concentrated 
the  transudation  the  less  its  bulk,  so  that  to  get  the  required  amount  of  CaO, 
for  example,  would  upon  this  hypothesis  require  nuich  more  than  twenty- 
four  hours.  Strictly  speaking,  however,  the  difficulty  we  are  dealing  with 
here  shows  only  the  insufficiency  of  a  pure  filtration  theory.  It  seems  possible 
that  filtration  and  diffusion  together  woidd  suffice  to  supply  the  organs,  so  far 
at  least  as  the  diffusible  substances  are  concerned. 

2.  Heidenhain  found  that  occlusion  of  the  inferior  vena  cava  causes  not 
only  an  increase  in  the  flow  of  lymph — as  might  be  expected,  on  the  filtration 

'  Archiv  fur  die  gesamvite  Plnjifiolofiie,  1894,  Bd.  lix.  S.  350. 


/.  YMI'lI.  365 

theory,  from  the  cousequent  rise  of  pressure  in  the  capiUary  regions — but  also 
an  increased  concentration  in  the  percentage  of  proteiil  in  the  lymph.  This 
latter  fact  has  been  satisfactorily  explained  by  the  experiments  of  Starling.' 
Accordhig  to  this  observer,  the  lymph  Ibrmed  in  the  liver  is  normally  more 
concentrated  than  that  of  the  rest  of  the  body.  The  occlusion  of  the  vena 
cava  causes  a  marked  rise  in  the  capillary  pressure  in  the  liver,  and  most  of 
the  increased  lymph-flow  under  these  circumstances  comes  from  the  liver, 
hence  the  greater  concentration.  The  results  of  this  experiment,  therefore,  do 
not  antagonize  the  filtration-and-diflusion  theory. 

3.  Heidenhein  discovered  that  extracts  of  various  substances  which  he 
designated  as  "  lymphagogues  of  the  first  class"  cause  a  marked  increase  in  the 
flow  of  lymph  from  the  thoracic  duct,  the  lymph  being  more  concentrated  than 
normal,  and  the  increased  flow  continuing  for  a  long  ])eriod.  Nevertheless, 
these  substances  cause  little,  if  any,  increase  in  general  arterial  pressure;  in 
fact,  if  injected  in  sufficient  quantity  they  produce  usually  a  fall  of  arterial 
pressure.  The  substances  belonging  to  this  class  comprise  such  things  as  pep- 
tone, egg-albumin,  extracts  of  liver  and  intestine,  and  especially  extracts  of  the 
muscles  of  crabs,  crayfish,  mussels,  and  leeches.  Heidenhain  sn})poses  that 
these  extracts  contain  an  organic  substance  which  acts  as  a  specific  stimulns  to 
the  endothelial  cells  of  the  capillaries  and  increases  their  secretory  action.  The 
results  of  the  action  of  these  substances  has  been  differently  explained  by  those 
■who  are  unwilling  to  believe  in  the  secretion  theory.  Starling^  finds  experi- 
mentally that  the  increased  flow  of  lymph  in  this  case,  as  after  obstruction  of 
the  vena  cava,  comes  mainly  from  the  liver.  There  is  at  the  same  time  in  the 
portal  area  an  increased  pressure  which  may  account  in  part  for  the  greater  flow 
of  lymph ;  but,  since  this  effect  upon  the  portal  pressure  lasts  but  a  short  time, 
while  the  greater  flow  of  lymph  may  continue  for  one  or  two  hours,  it  is 
obvious  that  this  factor  alone  does  not  suffice  to  explain  the  result  of  the  injec- 
tions. Starling  suggests,  therefore,  that  these  extracts  act  pathologically 
upon  the  blood-capillaries,  particularly  those  of  the  liver,  and  render  them 
more  permeable,  so  that  a  greater  quantity  of  concentrated  lymph  filters 
through  them.  No  experimental  proof  is  given  to  show  that  these  extracts 
do  so  affect  the  capillary  walls.  Starling's  explanation  is  supported  by 
the  experiments  of  Popoff*.^  According  to  this  observer,  if  the  lymyh  is  col- 
lected simultaneously  from  the  lower  portions  of  the  thoracic  duct,  which  con- 
veys the  Ivmph  from  the  abdominal  organs,  and  from  the  upper  part,  which 
contains  the  lymph  from  the  head,  neck,  etc.,  it  will  be  found  that  injection 
of  peptone  increases  the  flow  only  from  the  abdominal  organs.  Popoff"  finds 
also  that  the  peptone  causes  a  dilatation  in  the  intestinal  circulation  and  a 
marked  rise  in  the  portal  pressure.  At  the  same  time  there  is  some  evidence 
of  injury  to  the  walls  of  the  blood-vessels  from  the  occurrence  of  extravasa- 
tion in  the  intestine.     Cohnstein,^  from  experiments  made  with  peptone  solu- 

'  Journal  of  Physiology,  1894,  vol.  xvi.  p.  234.  -  Ibid.,  1894,  vol.  xvii.  p.  30. 

*  Centralhlatt  fiir  Physiologie,  1895,  Bd.  ix.,  No.  2. 

*  Archiv  fiir  die  gesammte  Physiologie,  1894,  Bd.  lix.  S.  3G6. 


'S{}(i  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

tioDS,  suggests  a  different  explanatiou  of  tlie  action  of"  tliesc  lyniphagogues. 
He  believes  that  these  substances  diminish  in  some  way  tlie  osmotic  tension  of 
the  blood.  In  consequence  of  this  diminution  the  diffusion-stream  of  water 
from  lymph  into  the  blood  is  lessened,  and  therefore  the  filtration-stream  in 
the  opposite  direction,  if  it  remains  unchanged,  must  cause  an  increased  volume 
of  lymph.  This,  theory,  although  supported  to  some  extent  by  exj)erimental 
evidence,  does  not  seem  to  explain  the  greater  concentration  of  lymph  obtained 
in  these  cases.  So  far,  however,  as  the  action  of  the  lyniphagogues  of  the  first 
class  is  concerned,  it  may  be  said  that  the  advocates  of  the  filtration-and-diffu- 
sion  theory  have  suggested  a  plausible  explanation  in  accord  with  their  theory. 
The  facts  emphasized  by  Heidenliain  with  regard  to  this  class  of  substances  do 
not  compel  us  to  assume  a  secretory  function  for  the  endothelial  cells. 

4.  Inj(>ction  of  certain  crystalline  substances,  such  as  sugar,  NaCl,  and 
other  neutral  salts,  causes  a  marked  increase  in  the  flow  of  lymph  from  the 
thoracic  duct.  The  lymph  in  these  cases  is  more  dilute  than  normal,  and  the 
blood-plasma  also  becomes  more  watery,  thus  indicating  that  the  increase  in 
water  comes  from  the  tissues  themselves.  Heidenliain  designated  these  bodies 
as  "  lymphagogues  of  the  second  class."  His  explanation  of  their  action  is 
that  the  crystalloid  materials  introduced  into  the  blood  are  eliminated  by  the 
secretorv  activity  of  the  endothelial  cells,  and  that  they  then  attract  water 
from  the  tissue-elements,  thus  augmenting  the  flow  of  lymph.  These  sub- 
stances cause  but  little  change  in  arterial  blood-pressure,  hence  Heidenhain 
thought  that  the  greater  flow  of  lymph  could  not  be  explained  by  an  increased 
flltration.  Starling^  has  shown,  however,  that,  although  these  bodies  may  not 
seriously  alter  general  arterial  pressure,  they  may  greatly  augment  intracapil- 
lary  pressure,  particularly  in  the  abdominal  organs.  His  explanation  of  the 
greater  flow  of  lymph  in  these  cases  is  as  follows  :  ''  On  their  injection  into 
the  blood  the  osmotic  pressure  of  the  circulating  fluid  is  largely  increased.  In 
consequence  of  this  increase  water  is  attracted  from  lymph  and  tissues  into  the 
blood  by  a  process  of  osmosis,  until  the  osmotic  pressure  of  the  circulating 
fluid  is  restored  to  normal.  A  condition  of  hydrremic  j)lethora  is  thereby  pro- 
duced, attended  with  a  rise  of  pressure  in  the  capillaries  generally,  especially 
in  those  of  the  abdominal  viscera.  This  rise  of  ]>ressure  will  be  proportional 
to  the  increase  in  the  volume  of  the  blood,  and  therefore  to  the  osmotic  pres- 
sure of  the  solutions  injected.  The  rise  of  ca])illary  pressure  causes  great 
increase  in  the  transudation  of  fluid  from  the  capillaries,  and  therefore  in  the 
lymph-flow  from  the  thoracic  duct."  This  explanation  is  well  supported  by 
experiments,  and  seems  to  obviate  the  necessity  of  assuming  a  secretory  action 
on  the  part  of  the  capillary  walls. 

5.  One  of  the  most  interesting  facts  developed  by  the  experiments  of  Hei- 
denhain and  his  pupils  is  that  after  the  injection  of  sugar  or  neutral  salts  in 
the  blood  the  percentage  of  these  substances  in  the  lymph  of  the  thoracic  duct 
may  be  greater  than  in  the  blood  itself  It  is  obviously  difficult  to  explain 
how  this  can  occur  by  filtration  or  diffusion,  since  it  seems  to  involve  the  pas- 

'  Op.  ciL 


LYMPH.  307 

sage  of  crystalloid  bodies  from  a  less  concentrated  to  a  more  concentrated  solu- 
tion. Cohnstein  ^  has  endeavored  to  sliow  a  fallacy  in  these  results.  He  con- 
tends that  since  it  requires  some  time  (several  miiiiitcs)  for  the  lymph  to  form 
and  pass  into  the  thoracic  ducrt,  it  is  not  justifialjle  to  compare  the  quantitative 
composition  of  specimens  of  blood  and  lymph  taken  at  the  same  time.  If  one 
compares,  in  any  given  experiment,  the  maximal  percentage  in  the  blood  of 
the  substance  injected  with  its  maximal  percentage  in  tiie  lymph,  the  latter 
will  be  found  to  be  lower.  This,  however,  does  not  seem  to  be  the  case  in  all 
the  experiments  reported.  The  work  of  Mendel  ^  with  sodium  iodide  seems  to 
establish  the  fact  that  when  this  salt  is  injected  slowly  its  maximal  percentage 
in  the  lymph  may  exceed  that  in  the  blood ;  and  in  the  experiments  made  by 
Cohnstein,  as  well  as  those  by  Mendel,  it  is  shown  that  the  percentage  of  the 
substance  in  the  lymph  remains  above  that  in  the  blood  throughout  most  of 
the  experiment.  In  this  point,  therefore,  there  seems  to  be  a  real  difficulty  in 
the  direct  application  of  the  laws  of  filtration  and  difiTusion  to  the  explanation 
of  the  composition  of  lymph.  It  is  possible,  however,  that  a  better  under- 
standing of  the  conditions  prevailing  in  the  capillaries  with  regard  to  osmosis 
and  filtration  may  clear  up  this  difficulty.'  Meanwhile  it  seems  evident  that 
in  spite  of  the  very  valuable  work  of  Heidenhain,  which  has  added  so  much 
to  our  knowledge  of  the  conditions  influencing  the  formation  of  lymph,  the 
existence  of  a  definite  secretory  activity  of  the  pndothelial  cells  of  the  capil- 
laries has  not  been  proved. 

^  Archivfiir  die  gesammte  Physiologie,  1894-95,  Bde.  lix.,  Ix.  und  Ixii. 

^  Journal  of  Physiology,  1896,  vol.  xix.  p.  227. 

^  See  Hamberger:  Du  Bois-Reymnnd' s  Archivfiir  Physiologie,  1896,  S.  36. 


VII.  CIRCULATION. 


PART  I.— THE  MECHANICS  OF  THE  CIRCULATION  OF  THE 
BLOOD  AND  OF  THE  MOVEMENT  OF  THE  LYMPH. 

A.  General  Considerations. 

The  metaphorical  phrase  "  circulation  of  the  blood  "  means  that  every  par- 
ticle of  blood,  so  long  as  it  remains  within  the  vessels,  moves  along  a  path 
which,  no  matter  how  tortuous,  finally  returns  into  itself;  that,  therefore,  the 
particles  wliich  pass  a  given  point  of  that  patli  may  be  the  same  which  have 
passed  it  many  times  already ;  and  that  the  blood  moves  in  its  path  always  in 
a  definite  direction,  and  never  in  the  reverse. 

The  discoverer  of  these  weighty  facts  was  "  William  Harvey,  physician, 
of  London,"  as  he  styled  himself.  In  the  lecture  notes  of  the  year  1616, 
mostly  in  Latin,  which  contain  the  earliest  record  of  his  discovery,  he  declares 
that  a  "perpetual  movement  of  the  blood  in  a  circle  is  caused  by  tiie  beat  of 
the  heart"  ("perpetuum  sanguinis  motum  in  circulo  fieri  pulsu  cordis").* 
For  a  long  time  afterw^ard  the  name  of  the  discoverer  was  coupled  with  the 
expression  which  he  himself  had  introduced,  and  the  true  movement  of  the 
blood  was  known  as  the  "Harveian  circulation." - 

Course  of  the  Blood. — The  metaphorical  circle  of  the  blood-path  may 
be  shown  l)y  such  a  diagram  as  Figure  93. 

If,  in  the  body  of  a  warm-blooded  animal,  we  trace  the  course  of  a  given 
particle,  beginning  at  the  point  where  it  leaves  the  right  ventricle  of  the  heart, 
we  find  that  course  to  be  as  follows  :  From  the  trunk  of  the  pulmonary  artery 
(PA)  through  a  succession  of  arterial  branches  derived  therefrom  into  a  capil- 
lary of  the  lungs  (PC) ;  out  of  that,  through  a  succession  of  pulmonary  veins,  to 
one  of  the  main  pulmonary  veins  (PI'^  and  the  left  auricle  of  the  heart  (LA) ; 
thence  to  the  left  ventricle  (LV);  to  the  trunk  of  the  aorta  (.1);  through  a 
succession  of  arterial  branr-hes  derived  therefrom  into  any  capillary  (C)  not 
supplied  by  the  pulmonary  artery  ;  out  of  that,  through  a  succession  of  veins 
(T'')  to  one  of  the  venre  cavoe  or  to  a  vein  of  the  heart  itself;  thence  to  the 
right  auricle  (RA),  to  the  right  ventricle  (RV),  and  to  the  trunk  of  the  pul- 
monary artery,  where  the  tracing  of  the  circuit  began. 

'William  Harvev  :  Prcledlnnex  Analrnnio'  Univeranlix,  edited,  with  an  antotvpe  reproduction 
of  the  original,  by  a  committee  of  tlie  Royal  College  of  Physicians  of  London,  1886,  p.  80. 

*  Harvey's  discovery  of  the  circulation  was  first  published  in  the  modern  sense  in  his  work 
ExercUalio  nnatomicn  de  motu  cordis  et  san(juinis  in  anim/tlibus,  Francofurti,  lfi'28.     This  great 
classic  c:in  be  read  in  English  in  the  following  :  On  the  Motion  of  the  Heart  and  Blood  in  Animals. 
By  William  Harvey,  M.  D. ;  Willis's  translation,  revised  and  edited  by  Alex.  Bowie,  1889. 
,S6S 


CIRCULATION. 


36U 


It  must  be  noted  here  that  a  particle  of  blood  which  traverses  a  capillary 
of"  the  spleen,  of  the  pancreas,  of  the  stomach,  or  of  the  intestines,  and  enters 
the  portal  vein,  must  next  traverse  a  series  of  venous  branches  of  diminishing 
size,  and  a  caj)illary  of  the  liver,  before  entering  the  succession  of  veins  which 
will  conduct  the  particle  to  the  ascending  vena  cava  (compare  Figs.  93  and  94). 

Most  of  the  blood,  therefore,  whicli 
leaves  the  liver  has  traversed  two  sets 
of  capillaries,  connected  with  one 
another  by  the  portal  vein,  since  quit- 
tiusr   the  arterial    svstem.      This   ar- 


FiG.  93. — General  diagram  of  the  circulation : 
the  arrows  indicate  the  course  of  the  blood :  PA, 
pulmonary  artery  :  P  C,  pulmonary  capillaries ; 
P  y,  pulmonar>'  veins ;  L  A,  left  auricle  ;  L  V,  left 
ventricle  ;  A,  systemic  arteries ;  C,  systemic  capil- 
laries ;  T',  systemic  veins  ;  R  A,  right  auricle  ,  li  V, 
right  ventricle. 


Fig.  94.— Diagram  of  the  portal  system :  the  ar- 
rows indicate  the  course  of  the  blood:  A,  arterial 
system ;  V,  venous  system  :  C,  capillaries  of  the 
spleen,  pancreas,  and  alimentary  canal :  P  V,  portal 
vein ;  C",  capillaries  of  the  liver ;  C,  the  rest  of  the 
systemic  capillaries.  The  hepatic  artery  is  not 
represented. 


rangement  is  of  extreme  importance  for  the  physiology  of  nutrition.  An 
arrangement  of  the  same  order,  though  less  conspicuous,  exists  in  the 
kidney. 

Causes  of  the  Blood-flew. — The  force  by  which  the  blood  is  driven  from 
the  right  to  the  left  side  of  the  heart  through  the  capillaries  which  are  related 
to  the  respiratory  surface  of  the  lungs,  is  nearly  all  derived,  from  the  contrac- 
tion of  the  muscular  wall  of  the  right  ventricle,  which  narrows  the  cavity 
thereof  and  ejects  the  blood  contained  in  it;  the  force  by  Avhich  the  blood  is 
driven  from  the  left  to  the  right  side  of  the  heart  through  all  the  other  capil- 
laries of  the  body,  often  called  the  "systemic"  capillaries,  is  derived  nearly 
all  from  the  contraction  of  the  muscular  wall  of  the  left  ventricle,  which  nar- 
rows its  cavity  and  ejects  its  contents.  The  contractions  of  the  two  ventricles 
are  simultaneous.  The  force  derived, from  each  contraction  is  generated  by 
the  conversion  of  potential  energy,  present  in  the  chemical  constituents  of  the 
muscular  tissue,  into  energy  of  visible  motion  ;  a  part  also  of  the  potential 
energy  at  the  same  time  becoming  manifest  as  heat.  In  the  maintenance  of 
the  circulation  the  force  generated  by  the  heart  is  to  a  very  subordinate  degree 
supplemented  by  the  forces  which  produce  the  aspiration  of  the  chest  and  by 

24 


370  .4^y  AMERICAN    TEXT-BOOK    OF    PIIYSIOLOOY. 

the  force  generated  by  the  contractions  of  the  skeletal  muscles  throughout  the 
body  (sec  p.  ')87). 

Mode  of  Working  of  the  Pumping  Mechanism. — During  eacii  contrac- 
tion or  ''systole"  of  the  ventricles  the  blood  is  ejected  into  tiie  arteries  only, 
because  at  that  time  the  auricuio-vcntricular  openings  arc  each  closed  by  a  valve. 
During  the  innncdiatcly  succeeding  "  diastole  "  of  the  ventricles,  which  con- 
sists in  the  relaxation  of  their  muscular  walls  and  the  dilatation  of  their 
cavities,  blood  enters  the  ventricles  by  way  of  the  auricles  only,  because  at  that 
time  the  arterial  openings  are  closed  each  by  a  valve  which  was  open  during 
the  ventricular  systole  ;  and  because  the  auriculo-ventricular  valves  which 
were  closed  during  the  systole  of  the  ventricles  are  open  during  their  diastole. 
During  the  first  and  longer  part  of  the  diastole  of  the  ventricles  the  auricles, 
too,  are  in  diastole;  the  whole  heart  is  in  repose;  and  blood  is  not  ()nly  enter- 
ing the  auricles,  but  passing  directly  through  them  into  the  ventricles. 
Near  the  end  of  the  ventricular  diastole  a  brief  simultaneous  systole  of  both 
auricles  takes  place,  during  which  they,  too,  narrow  their  cavities  by  the 
muscular  contraction  of  their  walls,  and  eject  into  the  ventricles  blood  which 
had  entered  the  auricles  from  the  "  systemic "  and  pulmonary  veins  respec- 
tively. The  systole  of  the  auricles  ends  immediately  before  that  of  the  ventri- 
cles begins.  The  brief  systole  of  the  auricles  is  succeeded  by  their  long  dias- 
tole, which  corresponds  in  time  with  the  whole  of  the  ventricular  systole  and 
with  the  greater  part  of  the  succeeding  ventricular  diastole.  During  the  dias- 
tole of  the  auricles  blood  is  entering  them  out  of  the  veins.  Thus  it  is  seen 
that  the  direction  in  which  the  blood  is  forced  is  essentially  determined  by  the 
mechanism  of  the  valves  at  the  apertures  of  the  ventricles;  and  that  it  is  due 
to  these  valves  that  the  blood  moves  only  in  the  definite  direction  before 
alluded  to.  In  the  words,  again,  of  Harvey's  note-book,  at  this  point  written 
in  English,  the  blood  is  perpetually  transferred  through  the  lungs  into  the 
aorta  "  as  by  two  clacks  of  a  water  bellows  to  rayse  water."' 

Pulmonary  Blood-path. — In  the  birds  and  mammals  the  entire  breadth  of 
the  blood-path,  at  one  part  of  the  physiological  circle,  consists  in  the  capillaries 
spread  out  beneath  the  respiratory  surface  of  the  lungs.  The  right  side  of  the 
heart  exists  only  to  force  the  blood  into  and  past  this  portion  of  its  circuit, 
where,  as  in  the  systemic  capillaries,  the  friction  due  to  the  fineness  of  the  tubes 
causes  much  resistance  to  the  flow.  This  great  comparative  development  of  the 
pulmonary  portion  of  the  blood-path  in  the  warm-blooded  vertel)rates  is  related 
to  the  activity,  in  them,  of  the  respiration  of  the  tissues,  which  calls  for  a  cor- 
responding activity  of  function  at  the  respiratory  surface  of  the  lungs,  and  for  a 
rapitl  renewal  in  every  systemic  capillary  of  the  internal  respiratory  medium,  the 
blood.  This  raj)id  renewal  implies  a  rapid  circulation  ;  and  that  the  speed  is 
great  with  M-hich  the  circuit  of  the  heart  and  vessels  is  com))leted  has  been 
proven  by  experiment,  the  method  being  too  complicated  for  description  here.^ 

^  PreledioTies,  etc.,  p.  80. 

*  Karl  Vierordt :  Die  Erscheinungen  und  Oesetze  der  Stromgeschwindigkeilen  des  Blutes.  2te 
Ausgabe,  18S2. 


CIRCULATION.  371 

Rapidity  of  the  Circulation. — By  experiment  the  shortest  time  has  been 
measured  whieh  is  taken  by  a  particle  of  blootl  in  passing  from  a  point  in  the 
external  jugular  vein  of  a  dog  to  and  through  the  right  cavities  of  the  heart, 
the  pulmonary  vessels,  the  left  cavities  of  the  heart,  the  commencement  of 
the  aorta,  and  the  arteries,  capillaries,  and  veins  of  the  head,  to  the  starting- 
point,  or  to  the  same  ]X)int  of  the  vein  of  the  other  side.  This  time  has 
been  found  to  be  from  fifteen  to  eighteen  seconds.  Naturally,  the  time  would 
be  different  in  different  kiuds  of  animals  and  in  the  different  circuits  in  the 
same  individual. 

Order  of  Study  of  the  Mechanics  of  the  Circulation. — The  significance 
and  the  fundamental  facts  of  the  circulation  have  now  been  indicated.  Its 
phenomena  must  next  be  studied  in  detail.^  As  the  blood  moves  in  a  circle, 
we  may,  in  order  to  study  the  movement,  strike  into  the  circle  at  any  point. 
It  will,  however  be  found  both  logical  and  instructive  to  study  first  the  move- 
ment of  the  blood  in  the  capillaries,  whether  systemic  or  pulmonary.  It  is 
only  in  passing  through  these  and  the  minute  arteries  and  veins  adjoining  that 
the  blood  fulfils  its  essential  functions ;  elsewhere  it  is  in  transit  merely. 
Moreover,  it  is  only  in  the  minute  vessels  that  the  blood  and  the  nature  of 
its  movement  are  actually  visible. 

After  the  capillary  flow  shall  have  become  familiar,  it  will  be  found  that 
the  other  phenomena  of  the  circulation  will  fall  naturally  into  place  as  indi- 
cating how  that  flow  is  caused,  is  varied,  and  is  regulated. 

B.  The  Movement  of  the  Blood  in  the  Capillaries  and  in  the 
Minute  Arteries  and  Veins. 

Characters  of  the  Capillaries. — Each  of  the  vessels  which  compose  the 
immensely  multiplied  capillary  network  of  the  body  is  a  tube,  commonly  of 
less  than  one  millimeter  in  length,  and  of  a  few  one-thousandths  only  of  a 
millimeter  in  calibre,  the  wall  of  which  is  so  thin  as  to  elude  accurate  measure- 


FiG.  95.— A  capillary  from  the  mesentery  of  the  frog  (Ranvier). 

meut.  The  calibre  of  each  capillary  may  vary  from  time  to  time.  These 
facts  indicate  the  minute  subdivision  of  the  blood-stream  in  the  lungs,  and 
among  the  tissues — that  is,  at  the  two  points  of  its  course  where  the  essential 
functions  of  the  blood  are  fulfilled.     These  facts  also  show  the  shortness  of 

^  The   following  is   a  very  valuable   book  of  reference :   Robert  Tigerstedt :  Lehrbuch  der 
Physiologie  des  Kreislaufes,  1893. 


372  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

the  distance  to  be  traversed  by  tlie  blood  wliile  f'ulfilliug  these  functions; 
aud  explain  the  importance  of  the  comparatively  slow  rate  at  which  it  will  be 
found  to  move  throuj!;h  that  short  distance.  The  histological  study  of  a  typ- 
ical capillary  (see  Fig.  95)  shows  that  its  thin  wall  is  composed  of  a  single 
layer  only  of  living  flat  endothelial  cells  feet  edge  to  edge  in  close  contact ;  and 
that  the  edges  of  the  cells  are  united  by  a  small  quantity  of  the  so-called 
cement-substance.  If  the  capillary  be  traced  in  either  anatomical  direction, 
the  wall  of  the  vessel  is  seen  to  become  less  thin  and  more  comj)lex,  till  it 
merges  into  that  of  a  typical  arteriole  or  venule,  the  walls  of  which  arci  still 
delicate,  though  less  so  than  that  of  a  capillary.  That  the  (capillary  walls  are 
so  thin  and  soft,  and  are  made  of  living  cells,  are  very  important  facts  as 
regards  the  relations  between  blood  aud  tissue.  It  is  of  great  importance 
for  the  variation  of  the  blood-supply  to  a  part  that  they  are  also  distensible, 
elastic,  aud  possibly  contractile. 

Direct  Observation  of  the  Plow  in  the  Small  Vessels. — The  capillary 
flow  is  visible  under  the  compound  microscope,  best  by  transmitted  light,  in 
the  transparent  parts  of  both  warm-blooded  and  cold-blooded  animals.  It  is 
important  that  the  phenomena  observed  in  the  latter  should  be  compared  with 
observations  upon  the  higher  animals;  but  the  fundamental  facts  can  be  most 
fruitfully  studied  in  the  frog,  tadpole,  or  fish,  inasmuch  as  no  special  arrange- 
ments are  needed  to  maintain  the  temperature  of  the  exposed  parts  of  these 
animals.  Moreover,  their  large  oval  and  nucleated  red  blood-corpuscles  are 
well  fitted  to  indicate  the  forces  to  which  they  are  subjected.  The  capillary 
movement,  therefore,  will  be  described  as  seen  in  the  frog;  it  being  nnder- 
stood  that  tiie  ])henomena  are  similar  in  the  other  vertebrates.  In  the 
frog  the  movement  may  be  studied  in  the  lung,  the  mesentery,  the  urinary 
bladder,  the  tongue,  -or  the  web  between  the  toes.  During  such  study  the 
proper  wall  of  the  living  capillary  is  hardly  to  be  seen,  but  only  the  line  on 
each  side  which  marks  the  profile  of  its  cavity.  Even  the  proper  walls  of 
the  transparent  arterioles  aud  venules  are  but  vaguely  indicated.  The  plasma 
of  the  blood,  too,  has  so  nearly  the  same  index  of  refraction  as  the  tissues, 
that  it  remains  invisible.  It  is  only  the  red  corpuscles  and  leucocytes  that 
are  conspicuous  ;  and  when  one  speaks  of  seeing  the  blood  in  motion,  he  means, 
strictly  speaking,  that  he  sees  the  moving  corpuscles,  and  can  make  out  the 
calibre  of  the  vessels  in  which  they  move.  The  observer  uses  as  low  a  power 
of  the  microscope  as  will  suffice,  and  takes  first  a  general  survey  of  the  minute 
arteries,  veins,  and  capillaries  of  the  part  he  is  studying,  noting  their  form, 
size,  and  connections.  In  the  arteries  and  veins  he  sees  that  the  size  of  the 
vessels  is  ample  in  comparison  with  that  of  the  c()r])u.scles  ;  that,  in  the  veins, 
the  movement  of  the  blood  is  steady,  but  in  the  arteries  accelerated  and 
retarded,  with  a  rhythm  corresponding  to  that  of  the  heart's  beat.  In  the 
veins,  moreover,  the  individual  red  corpuscles  can  be  distinguished,  while  in 
the  arteries  they  cannot,  as  at  all  times  they  shoot  past  the  eye  too  swiftly. 
The  fundamental. observation  now  is  verified  that  the  blood  is  incessantly 
moving  out  of  the  arteries,  through  the  capillaries,  into  the  veiu.s. 


CIRCULA  TION. 


37:3 


Behavior  of  the  Red  Corpuscles. — Capillarit-s  will  readily  be  found  iu 
wliicli  the  red  eorpuseles  move  two  or  three  abreast,  or  only  in  single  file. 
They  generally  go  with  their  long  diameters  parallel  to,  or  moderately  oblique 
to,  the  current.  Tn  no  ease  will  any  blockade  of  corpuscles  occur,  so  lono-  as 
the  parts  are  normal.  The  numerous  red  corpuscles  are  seen  to  be  well  fitted 
by  their  softness  and  elasticity,  as  well  as  by  their  form  and  size,  for  moving 
through  the  narrow  channels.  They  bend  easily  ui)()m  themselves  as  they 
turn  sharp  corners,  but  instantly  regain  their  form  when  free  to  do  so  (see 
Fig.  90).  A  very  common  occurrence  is  for  a  corpuscle  to  catch  upon  the 
edge  which  parts  two  capillaries  at  a  bifurcation  of  the  network.  For  some 
time  the  corpuscle  may  remain  doubled  over  the  projection  like  a  sack  thrown 
across  a  horse's  back  ;  but,  after  oscillating  for  a  while,  it  will  be  disengaged, 
at  once  return  to  its  own  shape,  and  disappear  in  one  of  the  two  branches 


Fig.  96. — To  illustrate  the  behavior  of  red  eor- 
puseles in  the  capillaries:  the  arrows  mark  the 
course  of  the  blood:  a,  a  "saddle-bag"  corpus- 
cle ;  h,  a  corpuscle  bending  upon  itself  as  it 
enters  a  side  branch. 


Fig.  97.— To  illustrate  the  deformity  pro- 
duced in  red  corpuscles  in  passing  through 
a  capillary  of  a  less  diameter  than  them- 
selves. 


(see  Fig.  96).  It  is  instructive  to  watch  red  corpuscles  passing  iu  single  file 
through  a  capillary  the  calibre  of  which,  at  the  time,  is  actually  less  than  the 
shorter  diameter  of  the  corpuscles.  Through  such  a  capillary  each  corpuscle 
is  squeezed,  with  lengthening  and  narrowing  of  its  soft  mass,  but  on  emerging 
into  a  larger  ve.ssel  its  elasticity  at  once  corrects  even  this  deformity  ;  it  regains 
its  form,  and  passes  on  (Fig.  97). 

Evidences  of  Friction. — In  the  minute  ves.sels,  capillary  and  other,  cer- 
tain appearances  should  carefully  be  observed  which  are  the  direct  ocular 
evidence  of  that  friction  which  M-e  shall  find  to  be  one  of  the  prime  forces 
concerned  in  the  blood-movement,  to  which  it  constitutes  a  strong  resistance. 
If,  in  a  channel  which  admits  three  red  corpuscles  beside  one  another,  three 
be  observed  when  just  abreast,  it  will  be  found  that  very  soon  the  middle  one 
forges  ahead,  indicating  that  the  stream  is  swiftest  at  its  core.  This  is  because 
the  friction  within  the  vessel  is  least  in  the  middle,  and  progressively  greater 
outward  to  the  wall  (Fig.  98).     In  the  small  veins  the  signs  of  friction   are 


374  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

strikiDgly  seeu,  as  the  outer  layers  among  the  mmierous  corpuscles  lag  con- 
spicuously, lu  liie  arterioles  similar  pheixjmena  are  seen  if  the  normal  swift- 
ness of  movement  become  sutiicieutly  retarded  for  the  individual  corpuscles 
to  be  visible. 


Fig.  98— To  illustrate  the  forging  ahead  of  a  Fig.  99.— The  inert  layer  of  plasma  in  the 

corpuscle  at  the  centre  of  the  blood-stream.  small  vessels. 

The  arrow  marks  the  direction  of  the  blood. 

An  appearance  which  also  tells  of  friction  is  that  of  the  so-called  "  inert 
layer"  of  plasma.^  In  vessels,  of  whatever  kind,  which  are  wide  enough  for 
several  corpuscles  to  pass  abreast,  it  is  seeu  that  all  the  red  corpuscles  are  always 
separated  from  the  profile  of  their  channel  by  a  narrow  clear  and  colorless 
interval — occupied,  of  course,  by  plasma.  This  is  caused  by  the  excess  of  the 
friction  in  the  layers  nearest  to  the  vascular  wall  (see  Fig.  99).  The  friction 
thus  indicated,  other  things  being  equal,  is  less  in  a  dilated  than  in  a  con- 
tracted tube;  and  less  in  a  sluggish  than  in  a  rapid  stream.  It  probably 
varies  also  with  changes  of  an  unknown  kind  in  the  condition  of  the  cells  of 
the  vascular  wall. 

Behavior  of  the  Leucocytes. — If  the  behavior  of  the  leucocytes  be 
watched,  it  will  be  seen  to  differ  markedly  from  that  of  the  red  corpuscles,  at 
least  when  the  blood-stream  is  somewhat  retarded,  as  it  so  commonly  is  under 
the  microscope.  Whereas  the  friction  within  the  vessels  causes  tlie  throng  of 
red  corpuscles  to  occupy  the  core  of  the  stream,  the  scantier  leucocytes  may 
move  mainly  in  contact  with  the  wall,  and  thus  be  present  freely  in  the  inert 
layer  of  plasma.  Naturally  their  progression  is  then  much  slower  and  more 
irregular  than  that  of  tiie  red  disks.  Indeed,  the  leucocytes  often  adhere  to 
the  wall  for  a  while,  in  spite  of  shocks  from  the  red  cells  which  pass  thorn. 
Moreover,  the  spheroidal  leucocyte  rolls  over  and  over  as  it  moves  along  the 
wall  in  a  way  very  different  from  the  progression  of  the  red  disk,  which  only 
occasionally  may  revolve  about  one  of  its  diametei-s.  A  leucocyte  entangled 
among  the  red  cells  near  the  middle  of  the  stream  is  seen  generally  not  only 
to  move  onward  but  also  to  move  outward  toward  the  wall,  and,  before  long, 
to  join  the  other  leucocytes  which  are  bathed  by  the  inert  layer  of  plasma. 
It  is  due  solely  to  the  lighter  specific  gravity  of  the  leucocytes  that,  under 
the  forces  at  work  within  the  smaller  vessels,  they  go  to  the  wall,  while  the 
denser  disks  go  to  the  core  of  the  current.  This  has  been  proved  experimen- 
tally by  driving  through  artificial  capillaries  a  fluid  having  in  suspension  par- 
ticles of  two  kinds.     Those  of  the  lighter  kind  go  to  the  wall,  of  the  heavier 

1  Poiseuille:  "Recherches  siir  les  causes  du  mouvement  du  sang  dans  les  vaisseaux  capil- 
laires,"  Academie  des  Sciences — Savans  itrangeis,  1835. 


CIRCULATION.  375 

kind  to  the  core,  even  wlieii  the  luituie  and  form  of  the  particles  employed 
are  varied.' 

Emigration  of  Leucocytes. — It  lias  been  said  that  a  leucocyte  may  often 
adhere  for  a  time  to  the  wall  of  the  capillary,  or  of  the  arteriole  or  venule, 
in  which  it  is.  Sometimes  the  leucocyte  not  only  adheres  to  the  wall,  but 
passes  throutjh  it  into  the  tissue  without  by  a  process  which  has  received  the 
name  of  ''emigration."^  A  minute  projection  from  the  protoplasm  of  the 
leucocyte  is  thrust  into  the  wall,  usually  where  this  consists  of  the  soft  cement- 
substance  between  the  endothelial  cells.  The  delicate  pseudopod  is  seen  pres- 
ently to  have  pierced  the  wall,  to  have  grown  at  the  expense  of  the  main  body 
of  the  cell,  and  to  have  become  knobbed  at  the  free  end  which  is  in  the  tissue. 
Later,  the  flowing  of  the  protoplasm  will  have  caused  the  leucocyte  to  assume 
something  of  a  dumb-bell  form,  with  one  end  within  the  blood-vessel  and  the 
other  without.  Then,  by  converse  changes,  the  flowing  protoplasm  comes  to 
lie  mainly  within  the  lymph-space,  with  a  small  knob  only  within  the  vessel ; 
and,  lastly,  this  knob  too  flows  out ;  what  had  been  the  neck  of  the  dumb-bell 
shrinks  and  is  withdrawn  into  the  cell-body,  and  the  leucocyte  now  lies  wholly 
without  the  blood-vessel,  while  the  minute  breach  in  the  soft  wall  has  closed 
behind  the  retiring  pseudopod.  This  phenomenon  has  been  seen  in  capillaries, 
venules,  and  arterioles,  but  mainly  in  the  two  former.  It  seems  to  be  due  to 
the  amoeboid  properties  of  the  leucocytes  as  well  as  to  purely  physical 
causes.  Emigration,  although  it  may  probably  occur  in  normal  vessels,  is 
strikingly  seen  in  inflammation,  in  which  there  seems  to  be  an  increased 
adhesiveness  between  the  vascular  wall   and  the  various   corpuscles  of    the 

blood. 

Speed  of  the  Blood  in  the  Mmute  Vessels.— As  a  measure  of  the  speed 
of  tlie  blood  in  a  vessel,  we  may  fairly  take  the  speed  of  the  red  corpuscles. 
It  must,  however,  be  remembered  that  as  the  friction  increases  toward  the  wall, 
the  speed  of  the  red  corpuscles  is  least  in  the  outer  layers  of  blood,  and  in- 
creases rapidly  toward  the  long  axis  of  the  tube.  At  the  core  of  the  stream  the 
speed  may  be  twice  as  great  as  near  the  wall.  As  we  have  seen,  the  stream  of  red 
corpuscles  in  an  arteriole  is  rapid  and  pulsating.  In  the  corresponding  venule, 
which  is  commonly  a  wider  vessel,  the  stream  is  less  swift,  and  its  pulse  has  dis- 
appeared. In  the  capillary  network  between  the  two  vessels  the  speed  of  the  red 
corpuscles  is  evidently  slower  than  in  either  arteriole  or  venule  ;  and  here,  as  in 
the  veins,  no  pulse  is  to  be  seen ;  the  pulse  comes  to  an  end  with  the  artery 
which  exhibits  it.  In  one  capillary  of  the  network  under  observation  the 
movement  may  be  more  active  than  in  another ;  and  even  in  a  given  capillary 
irregular  variations  of  speed  at  different  moments  may  be  observed.  Where 
two^capillaries  in  which  the  pressure  is  nearly  the  same  are  connected  by  a 
cross-branch,  the  red  corpuscles  in  this  last  may  sometimes  even  be  seen  to 

'  A.  Schklarewsky  :  "Ueber  das  Bliit  und  die  Suspensionsflussigkeiten,"  Pfliiger's  Archivfur 
die  qe.fammie  Physioloqie,  1868,  Bd.  i.  p.  603.  „    ,   ,  >  ^  .i 

■^  For  the  literature  of  emigration  see  R.  Thoma  :  Text-book  of  General  Pathology  and  Patho- 
logical Anatomy,  translated  by  A.  Bruce,  1896,  vol.  i.  p.  344. 


'}7G  .l.V  AMERICAN   TEXT-BOOK    OF  PJIY.SIOLOd  Y. 

oscillate,  come  to  u  staiKlstill,  and  then  reverse  the  directiou  of"  their  inove- 
raent,  and  return  to  the  capillary  whence  they  had  started.  Naturally,  no 
such  reversal  will  ever  be  seen  in  a  capillary  which  springs  directly  from  an 
artery  or  which  directly  joins  a  vein.  It  will  he  remembered,  however,  that 
any  apparent  speed  of  a  corpuscle  is  much  magnilied  by  the  microscope,  and 
that  therefore  the  variations  referred  to  are  comparatively  uniniportant.  \\'e 
may,  in  fact,  without  material  error,  treat  the  speed  of  the  blood  in  the  Cnipii- 
laries  which  intervene  between  the  arteries  and  veins  of  a  region  as  a})proxi- 
mately  uniform  lor  an  ordinary  period  of  observation,  as  the  minute  varia- 
tions will  tend  to  comj)ensate  for  one  another.  This  speed  is  sluggish,  as 
already  noted.  In  the  capillaries  of  the  web  of  the  frog's  foot  it  has  been 
found  to  be  about  0.5  millimeter  per  second.  The  causes  of  this  sluggishness 
wmH  be  set  forth  later.  That  the  very  short  distance  between  artery  and  vein 
is  traversed  slowly,  deserves  to  be  insisted  on,  as  thus  time  is  atlfbrded  for  the 
uses  of  the  blood  to  be  lulfilled. 

Capillary  Blood-pressure. — The  pressure  of  the  blood  against  the  capil- 
lary wall  is  low,  though  higher  than  that  of  the  lymph  without.  This  pres- 
sure is  subject  to  changes,  and  is  readily  yielded  to  by  the  elastic  and  deli- 
cate wall.  From  these  changes  of  pressure  chauges  of  calibre  result.  The 
microscope  tells  us  less  about  tiie  capillaiy  blood-pressure  than  about  the  other 
phenomena  of  the  flow;  but  the  microscope  may  sometimes  show  one  striking 
fact.  In  a  capillary  district  under  observation,  a  capillary  not  noted  before 
may  suddenly  start  into  view  as  if  newly  formed  under  tiie  eye.  This  is 
because  its  calibre  has  been  too  small  for  red  corpuscles  and  leucocytes  to  enter, 
until  some  slight  increase  of  pressure  has  dilated  the  transparent  tube,  hitherto 
filled  with  transparent  plasma  only.  This  dilatation  has  admitted  corpuscles, 
and  has  caused  the  vessel  to  appear. 

That  the  caj)illary  pressure  is  low  is  shown,  moreover,  by  the  fact  that  when 
one's  finger  is  pricked  or  slightly  cut,  the  blood  simply  drips  away  ;  that  it 
does  not  spring  in  a  jet,  as  when  an  artery  of  any  size  has  been  divided.  That 
the  capillary  pressure  is  low  may  also  be  shown,  and  more  accurately,  by  the 
careful  scientific  application  of  a  familiar  fact:  If  one  press  with  a  blunt 
lead-pencil  upon  the  skin  between  the  base  of  a  finger-nail  and  the  neigh- 
boring joint,  the  ruddy  surface  becomes  pale,  because  the  blood  is  exj^elled 
from  the  capillaries  and  they  are  flattened.  If  delicate  weights  be  used, 
instead  of  the  pencil,  the  force  can  be  measured  which  just  suffices  to  whiten 
the  surface  somewhat,  that  is,  to  counterbalance  the  pressure  of  the  distend- 
ing blood,  which  pressure  thus  can  be  measured  approximately.  It  has  been 
found  to  be  very  much  lower  than  the  pressure  in  the  large  arteries,  con- 
siderably higher  than  that  in  the  large  veins,  and  thus  intermediate  between 
the  two ;  whereas  the  blood-speed  in  the  capillaries  is  less  than  the  speed 
in  either  the  arteries  or  the  veins.  The  pressure  in  the  capillaries,  meas- 
ured by  the  method  just  described,  has  been  found  to  be  equal  to  that 
required  to  sustain  against  gravity  a  column  of  mercury  from  24  to  54  milli- 


CIRCULA  TION.  377 

meters  higli ;  or,  in  the  parlance  of  the  laboratory,  has  been  found  equal  to 
from  24  to  ')  I  inillinictcrs  of  nierciirv.' 

Summary  of  the  Capillary  Flow. — Whether  in  the  lungs  or  in  the  rest 
of  the  body,  the  general  characters  of  the  capillary  flow,  as  learned  from  direct 
inspection  and  from  experiment,  may  be  summed  up  as  follows:  The  blood 
moves  through  the  capillaries  toward  the  veins  with  much  friction,  contin- 
uously, slowly,  without  pulse,  and  under  low  pressure.  To  account  for  these 
facts  is  to  deal  systematic^ally  with  the  mechanics  of  the  circulation ;  and  to 
that  task  we  must  now  address  ourselves.    • 

0.  The  Pressure  of  the  Blood  in  the  Arteries,  Capillaries,  and 

Veins. 

"Why  does  the  blood  move  continuously  out  of  the  arteries  through  the 
capillaries  into  the  veins?  Because  there  is  continuously  a  high  pressure  of 
blood  in  the  arteries  and  a  low  pressure  in  the  veins,  and  from  the  seat  of  high 
to  that  of  low  pressure  the  blood  must  continuously  flow  through  the  capillaries, 
where  pressure  is  intermediate,  as  already  stated. 

Method  of  Studying  Arterial  and  Venous  Pressure,  and  General 
Results. — Before  stating  quantitatively  the  ditfereuces  of  pressure,  we  nuist 
see  how  they  are  ascertained  for  the  arteries  and  veins.  The  method  of  obtain- 
ing the  capillary  pressure  has  been  referred  to  already.  If,  in  the  neck  of  a 
mammal,  the  left  common  carotid  artery  be  clamped  in  two  places,  it  can, 
without  loss  of  blood,  be  divided  between  the  clamps,  and  a  long  straight  glass 
tube,  open  at  both  ends,  and  of  small  calibre,  can  be  tied  into  that  stump  of 
the  artery  which  is  still  connected  with  the  aorta,  and  which  is  called  the 
"  proximal "  stump.  If  now  the  glass  tube  be  held  upright,  and  the  clamp 
be  taken  oif  which  has  hitherto  closed  the  artery  between  the  tube  and  the 
aorta,  the  blood  will  mount  in  the  tube,  which  is  open  at  the  top,  to  a  consid- 
erable height,  and  will  remain  there.  The  external  jugular  vein  of  the  other 
side  should  have  been  treated  in  the  same  way,  but  its  tube  should  have  been 
inserted  into  tlie  "  distal "  stump — that  is,  the  stump  connected  with  the  veins 
of  the  head,  and  not  with  the  subclavian  veins.  If  the  clamp  between  the  tube 
and  the  head  have  been  removed  at  nearly  the  same  time  with  that  upon  the 
artery,  the  blood  may  have  mounted  in  the  upright  venous  tube  also,  but  only 
to  a  small  distance.  To  cite  an  actual  case  in  illustration,  in  a  small  etherized 
dog  the  arterial  blood-column  has  been  seen  to  stand  at  a  height  of  about  1 55 
centimeters  above  the  level  of  the  aorta,  the  height  of  the  venous  column 
about  18  centimeters  above  the  same  level.  The  heights  of  the  arterial  and 
venous  columns  of  blood  measure  the  pressures  obtaining  within  the  aorta  and 
the  veins  of  the  head  respectively,  while  at  the  same  time  the  circulation  con- 
tinues to  be  free  through  both  the  aorta  and  the  venous  network.  Therefore, 
in  the  dog  above  referred  to,  the  aortic  pressure  was  between  eight  and  nine 

'  N.  V.  Kries :  "  Ueber  den  Druck^ii  den  Blntcapillaren  der  menschlichen  Haut,"  Berichte 
liber  die  Verhandlungender  k.sdclusmhen  Gesellachaft  der  Wissenschaf ten  zu  Leipzig,  nvdih.-phys'ische 
Classe,  1875,  p.  149. 


378  AX  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

times  as  great  a-  that  in  the  smaller  veins  of  the  head.  As,  during  such  an 
experiment,  the  blood  is  free  to  pass  from  the  aorta  through  one  fxirotid  and 
botii  vertebral  arteries  to  the  head,  and  to  return  through  all  the  veins  of 
that  part,  except  one  external  jugular,  to  the  vena  cava,  it  is  demonstrated 
that  there  must  be  a  continuous  flow  from  the  aorta,  through  the  capillaries 
of  the  head,  into  the  veins,  because  the  pressure  in  the  aorta  is  many  times  as 
great  as  the  pressure  in  the  veins.  Obviously,  such  an  experiment,  although 
very  instructive,  gives  only  roughly  qualitative  results. 

Two  things  will  be  noted,  moreover,  in  such  an  experiment.  One  is  that 
the  venous  column  is  steady  ;  the  other  is  that  the  arterial  column  is  perpetu- 
ally fluctuating  in  a  rhythmic  manner.  The  top  of  the  arterial  column  shows 
a  regular  rise  and  fall  of  perhaps  a  few  centimeters,  the  rhythm  of  which  is 
the  same  as  that  of  the  breathing  of  the  animal ;  and,  while  the  surface  is  thus 
rising  and  falling,  it  is  also  the  seat  of  frequent  flickering  fluctuations  of 
smaller  extent,  the  rhythm  of  which  is  regular,  and  agrees  with  that  of  the 
heart's  beat.  At  no  time,  however,  do  the  respiratory  fluctuations  of  the  arte- 
rial column  amount  to  more  than  a  fraction  of  its  mean  height ;  compared  to 
which  last,  again,  the  cardiac  fluctuations  are  still  smaller.  It  is  clear,  then, 
that  the  aortic  pressure  changes  with  the  movements  of  the  chest,  and  with 
the  systoles  and  diastoles  of  the  left  ventricle.  But  stress  is  laid  at  present 
upon  the  fact  that  the  aortic  pressure  at  its  lowest  is  several  times  as  high  as 
the  pressure  in  the  smaller  veins  of  the  head.  Therefore,  the  occurrence  of 
incessant  fluctuations  in  the  aortic  pressure  cannot  prevent  the  continuous 
movement  of  the  blood  out  of  the  arteries,  through  the  capillaries,  into  the 
veins. 

The  upright  tubes  employed  in  the  foregoing  experiment  are  called  "  man- 
ometers." ^  They  were  first  applied  to  the  measurement  of  the  arterial  and 
venous  blood-pressures  by  a  clergyman  of  the  Church  of  England,  Stephen 
Hales,  rector  of  Farriugdon  in  Hampshire,  who  experimented  with  them 
upon  the  horse  first,  and  afterward  upon  other  mammals.  He  published  his 
method  and  residts  in  1733.^  The  height  of  the  manometric  column  is  a 
true  measure  of  the  pressure  which  sustains  it ;  for  the  force  derived  from 
gravity  with  which  the  blood  in  the  tube  presses  downward  at  its  lower  open- 
ing is  exactly  equal  to  the  force  with  which  the  blood  in  the  artery  or  vein  is 
pressed  upward  at  the  same  opening.  The  downward  force  exerted  bv  the 
column  of  blood  varies  directly  with  the  height  of  the  column,  but,  by  the  laws 
of  fluid  pressure,  does  not  vary  with  the  calibre  of  the  manometer,  which  cali- 
bre may  therefore  be  settled  on  other  grounds.  It  follows  also  that  the  arterial 
and  venous  manometers  need  not  be  of  the  same  calibre.  Were,  however, 
another  fluid  than  the  blood  itself  used  in  the  manometer  to  measure  a  given 
intravascular  pressure,  as  is  easily  possible,  the  height  of  the  column  would 
differ  from  that  of  the  column  of  blood.     For  a  given  pressure  the  height 

^  From  /uavoc,  rare.  The  name  was  given  from  such  tjibes  being  used  to  measure  the  tension 
of  gases. 

*  Stephen  Hales  :  Statical  Essays:  containing  Haemaslaticks,  etc.,  London,  1733,  vol.  ii.  p.  1. 


CIRCULATION, 


379 


of  the  column  is  invei'se  to  the 
density  of  tiie  manonietric  fluid. 
For  example,  a  j^ivcu  pressure  will 
sustain  a  far  taller  eoluiun  i)f  blood 
than  of  niereurv. 

The  Mercurial  Manometer. — 
The  method  of  Hales,  in  its  orig- 
inal simplicity,  is  valuable  from 
that  very  simplicity  ibr  demonstra- 
tion, but  not  for  research.  The 
elotting  of  the  blood  soon  ends  the 
experiment,  and,  while  it  continues, 
the  tallness  of  the  tube  required  for 
the  artery,  and  the  height  of  the 
column  of  blood,  are  very  incon- 
venient. It  is  essential  to  under- 
stand next  the  principles  of  the 
more  exact  instruments  employed 
in  the  modern  laboratory. 

In  1828  the  French  physician 
and  physiologist  J.  L.  M.  Poiseuille 
devised  means  both  of  keeping  the 
blood  from  clotting  in  the  tubes, 
and  of  using  as  a  measuring  fluid 
the  heavy  mercury  instead  of  the 
much  lighter  blood.  He  thereby 
secured  a  long  observation,  a  low 
column,  and  a  manageable  man- 
ometer.^ The  "  mercurial  man- 
ometer" of  to-day  is  that  of  Poi- 
seuille, though  modified  (see  Fig. 
100).  In  an  improved  form  it  con- 
sists of  a  glass  tube  open  at  both 
ends,  and  bent  upon  itself  to  the 
shape  of  the  letter  U.  This  is  held 
upright  by  an  iron  frame.  If  mer- 
cury be  poured  into  one  branch  of 
the  U,  it  will  fill  both  branches  to 
an  equal  height.  If  fluid  be  driven 
down  upon  the  mercury  in  one 
branch  or  "  limb  "  of  the  tube,  it 
will  drive  some  of  the  mercury  out 
of  that  limb  into  the  other,  and  the 
rest  at  very  unequal  levels.  The  di 
^  J.  L.  M.  Poiseuille :  Becherches 


Fig.  100.— Diagram  of  the  recording  mercurial  man- 
ometer and  the  liymograph ;  the  mercury  is  indicated  in 
deep  black :  M,  the  manometer,  connected  by  the  leaden 
pipe,  L,  with  a  glass  cannula  tied  into  the  proximal 
stump  of  the  left  common  carotid  artery  of  a  dog  ;  A, 
the  aorta;  C,  the  stop-cock,  by  opening  which  the  man- 
ometer may  be  made  to  communicate  through  JiT.  the 
rubber  tube,  with  a  pressure-bottle  of  solution  of  sodium 
carbonate  ;  F,  the  float  of  ivory  and  hard  rubber ;  R,  the 
light  steel  rod,  kept  perpendicular  by  B,  the  steel  bear- 
ing ;  P,  the  glass  capillary  pen  charged  with  quickly  dry- 
ing ink  ;  T,  a  thread  which  is  caused,  by  the  weight  of  a 
light  ring  of  metal  suspended  from  it,  to  press  the  pen 
obliquely  and  gently  against  the  paper  with  wliicli  is 
covered  D,  the  brass  "drum"  of  the  kymograph,  which 
drum  revolves  in  the  direction  of  the  arrow.  The  sup- 
ports of  the  manometer  and  the  body  and  clock-work 
of  the  kymograph  are  omitted  for  the  sake  of  simplicity. 
The  aorta  and  its  branches  are  drawn  disproportionately 
large  for  the  sake  of  clearness. 

two  surfaces  of  the  mercury  may  come  to 
fference  of  level,  expressed  in  millimeters, 

sur  la  force  du  coeur  aoriique,  Paris,  1 828. 


38U  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

measures  the  height  of  the  manonietric  column  of  mercury  the  downwaril  pres- 
sure of  which  in  one  limb  of  the  tube  is  just  equal  to  the  downward  pressure 
of  the  fluid  in  the  other.  In  order  to  adapt  this  "  U-tube"  to  the  study  of  the 
blood-pressure,  that  limb  of  the  tube  which  is  to  communicate  with  the  artery 
or  vein  is  caj)pcd  with  a  cock  which  can  be  closed.  Into  this  same  limb,  a  little 
way  below  the  cock,  opens  at  right  angles  a  short  straight  glass  tube,  which  is 
to  communicate  with  the  blood-vessel  through  a  long  flexible  tube  of  lead,  sup- 
ported by  the  iron  frame,  and  a  short  glass  cannida  tied  into  the  blood-vessel 
itself.  Two  short  pieces  of  india-rubber  tube  join  the  lead  tube  to  the  manometer 
and  the  cannula.  Before  the  blood-vessel  is  connected  with  the  manometer,  the 
latter  is  filled  with  fluid  between  the  surface  of  the  mercury  next  the  blood- 
vessel and  the  outer  end  of  the  lead  tube,  which  fluid  is  such  that  when  mixed 
with  blood  it  prevents  or  greatly  retards  coagulation.  With  this  same  fluid 
the  glass  cannula  in  the  blood-vessel  is  also  filled,  and  then  this  cannula  and 
the  lead  tube  are  connected.  The  cock  at  the  upper  end  of  the  "  proximal 
limb"  of  the  manometer  is  to  facilitate  this  filling,  being  connected  l)y  a  rub- 
ber tube  with  a  "  pressure  bottle,"  and  is  closed  when  the  filling  has  been 
accomplished.  The  fluid  introduced  by  Poiseuille  and  still  generally  used  is 
a  strong  watery  solution  of  sodium  carbonate.  A  solution  of  magnesium  sul- 
phate is  also  good.  If,  in  injecting  this  fluid,  the  column  of  mercury  in  the 
"distal  limb"  is  brought  to  about  the  height  which  is  expected  to  indicate  the 
blood-pressure,  but  little  blood  will  escape  from  the  blood-vessel  when  the 
clamp  is  taken  from  it,  and  coagulation  may  not  set  in  for  a  long  time. 

The  Recording  Mercurial  Manometer  and  the  Graphic  Method. — 
AVhen  the  arterial  pressure  is  under  observation,  the  combined  respiratory 
and  cardiac  fluctuations  of  tiie  mercurial  column  are  so  complex  and  fre- 
quent that  it  is  very  hard  to  read  off  their  course  accurately  even  with  the 
help  of  a  millimeter-scale  pUiced  beside  the  tube.  In  1847  this  difliculty  led 
the  German  physiologist  Carl  Ludwig  to  convert  the  mercurial  manometer 
into  a  self-registering  instrument.  This  invention  marked  an  epoch  not 
merelv  iu  the  investigation  of  the  circulation,  but  in  the  whole  science  of 
phvsiology,  by  beginning  the  present  "  graphic  method "  of  physiological 
work,  which  has  led  to  an  immense  advance  of  knowledge  in  many  depart- 
ments. Ludwig  devised  the  "  recording  manometer "  by  placing  upon  the 
mercury  in  the  distal  air-containing  limb  of  Poiseuille's  instrument  an  ivory 
float,  bearing  a  light,  stifl',  vertical  rod  (see  Fig.  100).  Any  fluctuation  of  the 
mercurial  column  caused  float  and  rod  to  rise  and  fall  like  a  pistou.  The  rod 
projected  well  above  the  manometer,  at  the  month  of  which  a  delicate  bear- 
ing was  provided  to  keep  the  motion  of  the  rod  vertical.  A  very  delicate 
pen  placed  horizontally  was  fastened  at  right  angles  to  the  upper  end  of  the 
rod.  If  a  firm  vertical  surface,  covered  with  ]iai)ei-,  were  now  placed  lightly 
in  contact  with  the  pen,  a  rise  of  the  mercury  would  cause  a  corresponding 
vertical  line  to  be  marked  upon  tiie  paj^er,  and  a  succeeding  fall  would 
cause  the  descending  pen  to  inscribe  a  second  line  covering  the  first.  If 
now  the  vertical  surface  were  made  to  move  i)ast  the  pen  at  a  uniform  rate, 


CIRCULATION.  381 

the  jjiiccessive  up-aiul-down  movciiuiiits  of  the  mercury  would  uo  lonj^er  be 
marked  over  aii<l  over  again  iu  the  same  place  so  as  to  produce  a  single  ver- 
tical line.  The  space  and  time  taken  up  by  each  fluctuation  would  be  graph- 
ically recordetl  in  the  form  of  a  curve,  itself  a  portion  of  a  continuous  trace 
marked  by  the  successive  fluctuations;  thus  both  the  respiratory  and  cardiac 
fluctuations  could  be  registered  throughout  an  observation  by  a  single  complex 
curving  line.  Ludwig  stretched  his  paper  around  a  vertical  hollow  cylinder 
of  brass,  made  to  revolve  at  a  regular  known  rate  by  means  of  clock-woi'k, 
and  the  conditions  above  indicated  were  satisfied  ^  (see  Fig.  100).  Upon  the 
surface  of  such  a  cylinder  vertical  distance  represents  space,  and  a  vertical  line 
of  measurement  is  called,  by  an  application  of  the  language  of  mathematics, 
an  "ordinate;"  horizontal  distance  represents  time,  and  a  horizontal  line  of 
measurement  is  called  an  "  abscissa."  The  curve  marked  by  the  events  re- 
corded is  always  a  mixed  record  of  space  and  time.  The  instrument  itself, 
the  essential  part  of  which  is  the  regularly  revolving  cylinder,  is  called  the 
"kymograph."^  It  has  undergone  many  chatiges,  and  many  varieties  of  it 
are  in  use.  Any  motor  may  be  used  to  drive  the  cylinder,  provided  that  the 
speed  of  the  latter  be  uniform  and  suitable. 

The  curve  written  by  the  manometer  or  other  recording  instrument  may 
either  be  marked  upon  paper  with  ink,  as  iu  Lud wig's  earliest  work  ;  or  may 
be  marked  with  a  needle  or  some  other  fine  pointed  thing  upon  paper  black- 


FiG.  101.— The  trace  of  arterial  blood-pressure  from  a  dog  anaesthetized  with  morphia  aud  ether.  The 
cannula  -was  in  the  proximal  stump  of  the  common  carotid  artery.  The  curve  is  to  be  read  from  left 
to  right. 

P,  the  pressure-trace  written  by  the  recording  mercurial  manometer  ; 

B  L,  the  base-line  or  abscissa,  representing  the  pressure  of  the  atmosphere.  The  distance  between 
the  base-line  and  the  pressure-curve  varies,  in  the  original  trace,  between  62  and  77  millimeters,  there- 
fore the  pressure  varies  between  124  and  154  millimeters  of  mercury,  less  a  small  correction  for  the 
weight  of  the  sodium-carbonate  solution ; 

T,  the  time-trace,  made  up  of  intervals  of  two  seconds  each,  and  written  by  an  electro-mag- 
netic chronograph. 

eued  with  soot  over  a  flame.  The  trace  written  upon  smoked  pajjcr  is  the 
more  delicate.  After  the  trace  has  been  written,  the  smoked  paper  is  removed 
from  the  kymograph   and   passed   through  a  pan  of  shellac  varnish.     This 

'  C.  Lndwig:  "Beitriige  zur  Kenntniss  des  Einflusses  der  Kespirationsbewegungen  auf 
den  Blutlauf  ini  Aortensysteme,"  MulWs  Archiv  fiir  Anatomie,  Physioloc/ie,  nnd  inssenschaflliche 
Medicin,  etc.,  1847,  p.  242.  '  From  nvfia,  a  wave. 


382  AX  AMERICAN   TEXT- BOOK    OF  PHYSIOLOGY. 

ulicii  dry  fixfs  tlic  trace,  which  tlicreafter  will  not  ix'  spoiled  by  han<lling. 
Ill  Fij^iire  101  liu-  uppermost  line  shows  a  trace  which  fairly  represents  the 
successive  fluctuations  of  the  aortic  pressure  of  the  dog.  The  longer  and 
ampler  fluctuations  are  respiratory,  tiie  briefer  and  slighter  are  cardiac.  lu 
each  res])iratory  curve  the  lowest  jmint  and  the  succeeding  ascent  coincide  with 
inspiration;  the  highest  point  and  the  succeeding  descent  with  expiration. 
The  horizontal  middle  line  is  the  base  line,  rej)resenting  the  pressure  of  the 
atmosphere.  The  base-line  has  been  shifted  upward  in  the  figure  simply  in 
order  to  save  room  on  the  page.  In  the  lowermost  line  the  successive  spaces 
from  left  to  right  of  the  reader  re])resent  successive  intervals  of  time  of  two 
seconds  each,  written  by  an  electro-magnetic  chronograph.  The  pressure-trace 
taken  from  a  vein  may  in  certain  regions  near  the  chest  show  respiratory  fluc- 
tuations, but  nowhere  cardiac  ones,  as  the  pulse  is  not  transmitted  to  the  veins. 
The  venous  pressure  is  so  small,  that  for  the  practical  study  of  it  a  recording 
manometer  must  be  used  in  which  some  lighter  fluid  replaces  the  mercury, 
M'hich  would  give  a  column  of  insuflicient  height  for  working  purposes.  The 
values  obtained  are  then  reduced  by  calculation  to  millimeters  of  mercury,  for 
comparison  with  the  arterial  pressure.  The  intravascular  pressure  at  a  given 
moment  can  be  measurer!  by  measuring  a  vertical  line  or  "  ordinate  "  drawn 
from  the  curve  written  by  the  manometer  to  the  horizontal  base-line.  The 
latter  represents  the  height  of  the  manometric  column  when  just  disconnected 
from  the  blood-vessel ;  that  is,  when  acted  u])on  only  l)y  the  weight  of  the 
atmosj)here  and  of  the  solution  of  sodium  carbonate.  To  ascertain  the  blood- 
pressure,  the  length  of  the  line  thus  measured  must  be  doubled ;  because  the 
mercury  in  the  proximal  limb  of  the  manometer  sinks  under  the  blood-pres- 
sure exactly  as  much  as  the  float  rises  in  the  distal  limb.  A  small  correction 
must  also  be  made  for  the  weight  of  the  solution  of  sodium  carbonate. 

The  Mean  Pressure. — The  "  mean  pressure  "  is  the  average  pressure  dur- 
ing whatever  length  of  time  the  observer  chooses.  The  mean  pressure  for  the 
given  time  is  ascertained  from  the  manometric  trace  by  measurements  too 
complicated  to  be  explained  here.  As  the  weight  and  consequent  inertia  of 
the  mercurv  cause  it  to  fluctuate  accordincj  to  circumstances  more  or  less  than 
the  pressure,  the  mean  pressure  is  much  more  accurately  obtained  from  the 
mercurial  manometer  than  is  the  true  height  of  each  fluctuation,  which  is  very 
commonly  written  too  small.  Therefore,  it  is  especially  the  mean  pressure 
that  is  studied  by  means  of  the  mercurial  manometer.  The  true  extent  and 
finer  characters  of  the  single  fluctuations  caused  by  the  heart's  beat  are  better 
studied  with  other  instruments,  as  we  shall  see  in  dealing  with  the  pulse. 

It  has  been  seen  that  the  blood  flows  continuously  through  the  capillaries 
because  the  pressure  is  continually  high  in  the  arteries  and  low  in  the  veins. 
The  reader  is  now  in  position  to  understand  statements  of  the  blood-pressure 
expressed  in  millimeters  of  mercury.  The  mean  aortic  pressure  in  the  dog  is 
far  from  being  always  the  same  even  in  the  same  animal.  We  have  found  it, 
in  the  case  referred  to  on  page  377,  to  be  equivalent  to  about  121  millimeters 
of  mercury.     It  will  very  commonly  be  found  higher  than  this,  and  may  range 


CIRCULA  TION.  383 

up  to,  or  above,  200  millimeter.  In  man  it  is  pr<)l)al)ly  higher  than  in  the 
(l()<r.  i'lie  pressure  in  tiie  other  arteries  derived  from  the  aorta  which  have 
been  studietl  manometrically  is  not  very  greatly  lower  than  in  that  vessel.  In 
the  pulmouary  arteries  the  pressure  is  probably  much  lower  than  in  the  aortic 
system.  The  pressure  in  the  small  veins  of  the  head  of  the  dog,  the  cannula 
being  in  the  distal  stump  of  the  external  jugular  vein,  we  have  found  already 
in  one  case  to  equal  about  14  millimeters  of  mercury.  In  such  a  case  the 
presence  of  valves  in  the  veins  and  other  elements  of  difficulty  make  the 
mean  pressure  hard  to  obtain  as  opposed  to  the  maximum  pressure  during 
the  period  of  observation. 

If  a  cannula  be  so  inserted  as  to  transmit  the  pressure  obtaining  within 
the  great  veins  of  the  neck  just  at  the  entrance  of  the  chest,  without  interfer- 
ing with  the  movement  of  the  blood  through  them,  and  if  a  manometer  be 
connected  with  this  cannula,  the  fluid  wnll  fall  below  the  zero-point  in  the 
distal  limb,  indicating  a  slight  suction  from  within  the  vein,  and  thus  a 
slightly  "  negative  "  pressure.^  This  negative  pressure  may  sometimes  become 
more  pronounced  during  inspiration  and  regain  its  former  value  during  ex- 
piration. Sometimes,  again,  the  pressure  during  expiration  may  become  posi- 
tive. The  continuous  flow  from  the  great  arteries  through  the  capillaries  to 
the  veins,  and  through  these  to  the  auricle,  is  therefore  shown  by  careful 
quantitative  methods,  no  less  than  by  the  tube  of  Hales,  to  be  simply  a 
case  of  movement  of  a  fluid  from  seats  of  lijgii  to  seats  of  lower  pressure. 

The  Symptoms  of  Bleeding  in  Relation  to  Blood-pressure. — The  dif- 
ferences of  pressure  revealed  scientifically  by  the  manometer  exhibit  them- 
selv^es  in  a  very  important  practical  way  when  blood-vessels  are  wounded  and 
bleeding  occurs.  If  an  artery  be  cleanly  cut,  the  high  pressure  within  drives 
out  the  blood  in  a  long  jet,  the  length  of  which  varies  rhythmically  ^vith  the 
cardiac  pulse,  but  varies  only  to  a  moderate  degree.  From  wounded  capil- 
laries, or  from  a  wounded  vein,  owing  to  the  low  pressure,  the  blood  does  not 
sjjring  in  a  jet,  but  simply  flows  out  over  the  surface  and  drips  away  without 
pulsation.  At  the  root  of  the  neck,  where  the  venous  pressure  may  rhythmi- 
cally fall  below  and  rise  above  the  atmospheric  pressure,  the  bleeding  from 
a  wounded  vein  may  be  intermittent. 

D.  The  Causes  of  the  Pressure  in  the  Arteries,  Capillaries, 

AND  Veins. 

The  causes  of  the  continuous  high  pressure  in  the  arteries  must  first  engage 
our  attention. 

Resistance. — The  great  ramification  of  the  arterial  sy.stem  at  a  distance 
from  the  heart  culminates  in  the  formation  of  the  countless  arterioles  on  the 
confines  of  the  capillary  system.  We  have  already  seen  direct  evidence  of  the 
friction  in  the  minute  vessels  which  results  from  this  enormous  subdivision  of 
the  blood-path.     The  force  resulting  from  this  friction  is  propagated  back- 

'  H.  Jacobson:  "  Ueber  die  Blutbewegung  in  den  Venen,"  Rcicherfs  und  du  Bois-Bey- 
moTuTs  Archil-  fur  Anatomie,  Physiologie,  etc.,  1867,  p.  224. 


384  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

ward  according  to  the  laws  of  Huid  pressure,  and  constitutes  a  strong  resist- 
ance to  the  onward  movement  of"  the  blood  out  of  the  iieart  itself.  Friction 
is  everywhere  present  in  the  vessels,  but  is  greatest  in  the  very  small  ones 
collectively. 

Power. — Where  the  aorta  springs  from  tiie  heart,  the  rhythmic  contrac- 
tions of  the  left  ventricle  force  open  the  arterial  valve,  and  force  intermittent 
charges  of  blood  into  the  arterial  system,  overcoming  thus  the  opposing  force 
derived  from  friction.  The  wall  of  the  arterial  system  is  very  elastic  every- 
where. Thus  the  high  pressure  in  the  arteries  results  from  the  interaction  of 
the  |)ower  derived  from  the  heart's  beat  and  the  resistance  derived  from  fric- 
tion. Tiiat  the  high  pressure  is  continuous  dei)ends  upon  the  capacity  for 
distention  possessed  by  the  elastic  arterial  wall. 

Balance  of  the  Factors  of  the  Arterial  Pressure. — In  order  to 
study  the  causation  of  the  arterial  pressure,  let  us  imagine  that  it  has  for  some 
reason  sunk  very  low ;  but  that,  at  the  moment  of  observation,  a  normally 
beating  heart  is  injecting  a  normal  blood-charge  into  the  aorta.  The  first 
injection  would  find  the  resistance  of  friction  present,  and  the  elastic  arterial 
wall  but  little  distended.  For  this  injection  some  room  would  be  made  by 
the  displacement  of  blood  into  the  capillaries.  But  it  would  be  easier  for  the 
arterial  wall  to  yield  thau  for  the  friction  to  be  overcome,  so  the  injected 
blood  would  largely  be  stored  within  the  arterial  system  and  thus  raise  the 
pressure.  Succeeding  injections  would  have  similar  results ;  it  would  continue 
to  be  easier  for  the  injected  blood  to  distend  the  arteries  than  to  escape  from 
them ;  and  the  arterial  pressure  would  rise  rapidly  toward  its  normal  height. 
Presently,  however,  a  limit  would  be  reached  ;  a  time  would  come  when  the 
elastic  wall,  already  well  stretched,  would  have  become  tenser  and  stifier  anil 
would  yield  less  readily  before  the  entering  blood ;  and  now  a  larger  part 
than  before  of  each  successive  charge  of  blood  would  be  accommodated 
by  the  displacement  of  an  equivalent  quantity  into  the  capillaries,  and  a  smaller 
part  by  the  yielding  of  the  arterial  wall.  Normal  conditions  of  pressure 
would  be  reached  and  maintained  when  the  blood  accommodated,  during  each 
systole  of  the  ventricle,  by  the  yielding  of  the  arterial  wall  should  exactly 
equal  in  amount  the  blood  discharged  from  the  arteries  into  the  capillaries 
during  each  ventricular  diastole ;  for  then  the  quantity  of  blood  parted  with 
by  the  arteries  during  both  the  systole  and  the  diastole  of  the  heart  would 
be  exactly  the  same  as  that  received  during  its  systole  alone. 

We  see  that,  at  each  cardiac  systole,  the  cardiac  muscle  does  work  in  main- 
taining the  capillary  flow  against  friction,  and  also  docs  work  upon  the  arte- 
rial wall  in  expanding  it.  A  portion  of  the  manifest  energy  of  the  heart's 
beat  thus  becomes  potential  in  the  stretched  elastic  fibres  of  the  artery.  The 
moment  that  the  work  of  ex})ansion  ceases,  the  stretched  elastic  fibres  recoil ; 
their  potential  energy,  just  received  from  the  heart,  becomes  manifest,  and 
work  is  done  in  maintaining  the  capillary  flow  against  friction  during  the 
repose  of  the  cardiac  muscle.  At  the  beginning  of  this  repose  the  arterial 
valves  have  been  closed  by  the  arterial  recoil.     When,  at  each  cardiac  systole, 


CIRCULATION.  385 

the  arterial  wall  expands  before  tlie  entering  blood,  the  pressure  rises,  for 
more  blood  is  entering  the  arterial  system  than  is  leaving  it;  when,  at  each 
cardiac  diastole,  the  arterial  wall  recoils,  the  pressure  falls,  for  blood  is  leaving 
the  arterial  system,  and  none  is  entering  it.  But  before  the  fall  has  had  time 
to  become  pronounced,  while  the  arterial  pressure  is  still  high,  the  cardiac  sys- 
tole recurs,  and  tlie  prcs-ui-e  rises  again,  as  at  the  preceding  fluctuation. 

The  Arterial  Pulse. — The  increased  arterial  pressure  and  amplitude  at 
the  cardiac  systole,  followed  by  diminished  pressure  and  amplitude  at  the 
cardiac  diastole,  constitute  the  main  phenomena  of  the  arterial  pulse.  They 
are  marked  in  the  maiiometric  trace  by  those  lesser  rhythmic  fluctuations  of 
the  mercury  which  correspond  with  the  heart-beats.  The  causes  of  the  arte- 
rial pul.se  have  just  been  indicated  in  dealing  with  the  causes  of  the  arterial 
pressure.  The  pulse,  in  some  of  its  details,  Nvill  be  studied  further  for  it.self 
in  a  later  chapter.  For  the  sake  of  simplicity,  the  respiratory  fluctuations  of 
the  arterial  pressure  have  not  been  dealt  with  in  the  discussion  just  con- 
cluded. The  causes  of  these  important  fluctuations  are  very  complex  and  are 
treated  of  under  the  head  of.  Respiration. 

The  arterial  pressure,  then,  results  from  the  volume  and  frequency  of  the 
injections  of  blood  made  by  the  heart's  contraction  ;  from  the  friction  in  the 
vessels ;  and  from  the  elasticity  of  the  arterial  wall. 

The  Capillary  Pressure  and  its  Causes. — When  we  studied  the  move- 
ment of  the  blood  in  the  capillaries,  we  found  the  pressure  in  them  to  be  low 
and  free  from  rhythmic  fluctuations.  In  both  of  the.se  qualities  the  capillary 
pressure  is  in  sharp  contrast  with  the  arterial.  What  is  the  reason  of  the  differ- 
ence ?  The  work  of  driving  the  blood  through  as  well  as  into  the  capillaries  is 
done  during  the  contraction  of  the  heart's  wall  by  its  kinetic  energy.  During 
the  repose  of  the  heart's  wall  and  the  arterial  recoil  this  work  is  continued  by 
kinetic  energy  derived,  as  we  have  seen,  from  the  preceding  cardiac  contraction. 
The  work  of  producing  the  capillary  flow  is  done  in  overcoming  the  resistance 
of  friction.  The  capillary  walls  are  elastic.  The  same  three  factors,  then — 
the  power  of  the  heart,  the  resistance  of  friction,  the  elasticity  of  the  wall — 
which  produce  the  arterial  pressure  produce  the  capillary  pressure  also.  Why 
is  the  capillary  pressure  normally  low  and  pulseless?  The  answer  is  not 
difficult.  The  friction  which  must  be  overcome  in  order  to  propel  the  blood 
out  of  the  capillaries  into  the  wider  venous  branches  is  only  a  part  of  the  total 
friction  which  oppo.ses  the  admission  of  the  blood  to  the  minuter  vessels.  The 
resi.stance  is  therefore  diminished  which  the  blood  has  yet  to  encounter  after 
it  has  actually  entered  the  capillaries.  The  force  which  propels  the  blood 
through  the  capillaries,  althougli  amply  sufficient,  is  greatly  less  than  the 
force  which  propels  it  into  and  through  the  larger  arteries.  In  both 
cases  alike  the  force  is  that  of  the  heart's  beat.  But,  in  overcoming  the 
friction  which  resists  the  entrance  of  the  blood  into  the  capillaries,  a  large 
amount  of  the  kinetic  energy  derived  from  the  heart  has  become  converted 
into  heat.  The  power  is  therefore  diminished.  As,  in  producing  the  high 
arterial  pres.sure,  much  power  is  met  by  much  resistance,  and  the  elastic  wall 

25 


386  AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

is,  therefore,  clisteiicleil  with  act'iiimihitcd  blood  ;  so,  in  producing  the  low  capil- 
larv  pressure,  diminished  power  is  met  by  diminished  resistance,  outflow  is 
relatively  easy,  accumulation  is  slight,  and  the  elasticity  of  the  delicate- wall 
is  but  little  called   upon. 

The  Extinction  of  the  Arterial  Pulse. —  Uiit  why  is  the  capillary  pres- 
sure pulseless,  as  the  microscope  shows?  To  explain  this,  no  new  factors  need 
<liscussion,  but  only  the  adjustment  of  the  arterial  elasticity  to  the  intermittent 
injections  from  the  heart  and  to  the  total  friction  which  opposes  the  admission 
of  blood  to  the  ca))illaries.  This  adjustment  is  such  that  the  recoil  of  the 
arteries  displaces  blood  into  the  capillaries  during  the  ventricular  diastole  at 
exactly  the  same  rate  as  that  })roduced  by  the  ventricular  contraction  during 
the  ventricular  systole.  Thus,  through  the  elasticity  of  the  arteries,  the  car- 
diac pulse  undergoes  extinction  ;  and  this  becomes  complete  at  the  confines 
of  the  capillaries.  The  respiratory  fluctuations  become  extinguished  also,  and 
the  movement  of  the  blood  in  the  capillaries  exhibits  no  rhythmic  changes. 
This  conversion  of  an  intermittent  flow  into  one  not  merely  continuous  but 
approximately  constant  affords  a  constant  blood-supply  to  the  tissues,  at  the 
same  time  that  the  cardiac  muscle  can  have  its  diastolic  repose,  and  the  ven- 
tricular cavities  the  necessary  opportunities  to  receive  from  the  veins  the 
blood   which  is  to  be  transferred  to  the  arteries. 

A  simple  experiment  will  illustrate  the  foregoing.  Let  a  long  india-rubber 
tube  be  taken,  the  wall  of  which  is  thin  and  very  elastic.  Tie  into  one  end 
of  the  tube  a  short  bit  of  glass  tubing  ending  in  a  fine  nozzle,  the  friction  at 
which  will  cause  great  resistance  to  any  outflow  through  it.  Tie  into  the 
other  end  of  the  rubber  tube  an  ordinary  syringe-bulb  of  india-rubber,  with 
valves.  Expel  the  air,  and  inject  water  into  the  tube  from  the  valved  bulb 
by  alternately  squeezing  the  latter  and  allowing  it  to  expand  and  be  filled 
from  a  basin.  The  rubber  tube  will  swell  and  pulsate,  but  if  its  elasticity 
have  the  right  relation  to  the  size  of  the  fine  glass  nozzle  and  to  the  amplitude 
and  frequency  of  the  strokes  of  the  syringe,  a  continuous  and  uniform  jet  will 
be  delivered  from  the  nozzle,  while  the  injections  of  water  will,  of  course,  be 
intermittent. 

The  Venous  Pressure  and  its  Causes. — The  pressure  in  the  peripheral 
veins  is  less  than  in  the  capillaries  and  declines  as  the  blood  reaches  the  larger 
veins.  Very  close  to  the  chest  the  pressure  is  below  the  pressure  of  the 
atmosphere,  and  may  sometimes  vary  from  negative  to  positive,  following  the 
rhythm  of  the  breathing.  These  respiratory  fluctuations  will  be  considered  later. 
The  low  and  declining  pressures  under  which  the  blood  moves  through  the 
venules  and  the  larger  veins  are  due  to  the  same  causes  as  those  which  account 
for  the  capillary  pressure.  It  is  still  the  force  generated  by  the  heart's  con- 
tractions, and  made  uniform  by  the  elastic  arteries,  which  drives  the  blood 
into  and  through  the  veins  back  to  the  very  heart  itself.  As  the  blood  moves 
through  the  veins,  what  resistance  it  encounters  is  still  that  of  the  friction 
ahead.  But  the  friction  ahe^d  is  progressively  less ;  the  conversion  of  kinetic 
energy  into  heat  is  progressively  greater.     The  venous  wall  possesses  elas- 


CIRCULA  TION.  387 

ticity,  but  this  is  even  less  called  upon  than  that  of  the  capillaries ;  and,  pres- 
ently, in  the  larger  veins,  the  niovinti;  blood  is  found  to  press  no  harder  from 
within  than  the  atniosphere  fi'oni  witiiout. 

Subsidiary  Forces  which  Assist  the  Flow  in  the  Veins. — There  are 
certain  forces  \vhi(!h,  occasionally  or  regularly,  assist  the  heart  to  return  the 
venous  blood  into  itself.  Too  much  stress  is  often  laid  upon  these ;  for  it  is 
easy  to  see  by  experiment  that  the  heart  can  maintain  the  circulation  wholly 
without  help.  The  origins  of  these  subsidiary  forces  are,  first,  the  contraction 
of  the  skeletal  muscles  in  general ;  second,  the  continuous  traction  of  the 
lungs;  third,  the  contraction  of  the  muscles  of  inspiration. 

The  Skeletal  Muscles  and  the  Venous  Valves. — A  vein  may  lie  in 
such  relation  to  a  muscle  that  when  the  latter  contracts  the  vein  is  pressed 
upon,  its  feeble  blood-pressure  is  overborne,  the  vein  is  narrowed,  and  blood 
is  squeezed  out  of  it.  The  veins  in  many  parts  are  rich  in  valves,  competent 
to  prevent  regurgitation  of  the  blood  while  permitting  its  flow  in  the  physio- 
logical direction.  The  pressure  of  a  contracting  muscle,  therefore,  can  only 
squeeze  blood  out  of  a  vein  toward  the  heart,  never  in  the  reverse  direction. 
Muscular  contraction,  then,  may,  and  often  does,  assist  in  the  return  of  the 
venous  blood  with  a  force  not  even  indirectly  derived  from  the  heart.  But 
such  assistance,  although  it  may  be  vigorous  and  at  times  important,  is  tran- 
sient and  irregular.  Indeed,  were  a  given  muscle  to  remain  long  in  contrac- 
tion, the  continued  squeezing  of  the  vein  would  be  an  obstruction  to  the  flow 
through  it. 

The  Continuous  Pull  of  the  Elastic  Lungs. — The  influence  of  thoracic 
aspiration  upon  the  movement  of  the  blood  in  the  veins  deserves  a  fuller  dis- 
cussion. The  root  of  the  neck  is  the  region  where  this  influence  shows  itself 
most  clearly,  but  it  may  also  be  verified  in  the  ascending  vena  cava  of  an 
animal  in  which  the  abdomen  has  been  opened.  The  physiology  of  respira- 
tion shows  that  not  only  in  inspiration,  but  also  in  expiration,  the  elastic  fibres 
of  the  lungs  are  upon  the  stretch,  and  are  pulling  upon  the  ribs  and  intercostal 
spaces,  upon  the  diaphragm,  and  upon  the  heart  and  the  great  vessels.  This 
dilating  force  at  all  times  exerted  upon  the  heart  by  the  lungs  is  of  assistance, 
as  we  shall  see,  in  the  diastolic  expansion  of  its  ventricles.  In  the  same  way 
the  elastic  pull  of  the  lungs  acts  upon  the  venae  cavae  within  the  chest,  and 
generates  within  them,  as  well  as  within  the  right  auricle,  a  force  of  suction. 
The  effects  upon  the  venous  flow  of  this  continuous  aspiration  are  best  known 
in  the  system  of  the  ascending  vena  cava.  This  suction  from  within  the 
chest  extends  to  the  great  veins  just  without  it  in  the  neck.  In  these,  close  to 
the  chest,  as  we  have  seen,  manometric  observation  reveals  a  continuous  slightly 
negative  pressure.  A  little  farther  from  the  chest,  however,  but  still  within 
the  lower  portions  of  the  neck,  the  intravenous  pressure  is  slightly  positive. 
The  elastic  pull  of  the  lung,  therefore,  continuously  assists  in  unloading  the 
terminal  part  of  the  venous  system,  and  thus  differs  markedly  from  the  irreg- 
ular contractions  of  the  skeletal  muscles. 

The  Contraction  of  the  Muscles  of  Inspiration. — But  some  skeletal 


388  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

muscles,  those  of  inspiration,  re<rularly  add  tlieir  rhytluuie  contractions  to  tlie 
contiuuoiiri  pull  <)t"  tlu'  lun>;s,  to  reinforce  the  latter.  P^ach  time  that  the  chest 
expands  there  is  an  increased  tendency  for  blood  to  be  sucked  into  it  through 
the  veins.  At  the  beginninj^  of  eaeii  expiration  this  increase  of  suction 
abruptly  ceases. 

The  Respiratory  Pulse  in  the  Veins  near  the  Chest,  and  its  Limita- 
tion.—  In  quiet  breathinu-  the  niovenients  of  the  eliest-wall  j)ro(liic(;  no  very 
conspicuous  effect.  If,  however,  deep  and  infrequent  breaths  be  taken,  the 
pressure  within  the  veins  close  to  the  chest  becomes  at  each  inspiration  nnich 
more  negative  than  before ;  and  at  each  inspiration  tiie  area  of  negative 
pressure  mav  extend  to  a  greater  distance  from  the  chest  along  the  veins  of 
the  neck,  and  perhaps  of  the  axilla.  As  the  venous  pressure  in  these  parts 
now  falls  as  the  chest  rises,  and  rises  as  the  chest  falls,  a  visible  venous  pulse 
presents  itself,  coinciding,  not  with  the  heart-beats,  but  with  the  breathing. 
At  each  inspiration  the  veins  diminish  in  size,  as  their  contents  are  sucked 
into  the  chest  faster  than  they  are  renewed.  At  each  expiration  the  veins  may 
be  seen  to  swell  under  the  pressure  of  the  blood  coming  from  the  periphery. 
If  the  movements  of  the  air  in  the  windpipe  be  mechanically  imj)eded, 
these  changes  in  the  veins  reach  their  highest  pitch  ;  for  then  the  muscles  of 
expiration  may  actually  compress  the  air  within  the  lungs,  and  produce  a 
positive  pressure  within  the  vena  cava  and  its  branches,  with  resistance  to  the 
return  of  venous  blood  during  expiration,  shown  by  the  exaggerated  swelling 
of  the  veins.  These  phenomena  are  suddenly  succeeded  by  suction,  and  by 
collapse  and  disappearance  of  the  veins  from  view,  as  inspiration  suddenly  re- 
curs. The  respiratory  venous  pulse,  when  it  occurs,  diminishes  progressively 
and  rapidlv  as  the  veins  are  observed  ftirther  and  farther  from  the  root  of  the 
neck, — a  fact  which  results  from  the  Haceidity  of  the  venous  wall.  Were  the 
walls  of  the  veins  rigid,  like  glass,  the  successive  inspirations  would  produce 
rhythmic  accelerations  of  the  flow  throughout  the  whole  venous  system,  and 
the  contractions  of  the  muscles  of  inspiration  would  rank  higher  than  they  do 
among  the  causes  of  the  circulation.  In  flict,  the  walls  of  the  veins  are  very 
soft  and  thin.  If,  therefore,  near  the  chest,  the  pressure  of  the  blood  within 
the  veins  sink  below  that  of  the  atmosphere  without,  the  ])lace  of  the  blood 
sucked  into  the  chest  is  filled  only  partly  by  a  heightened  flow  of  blood  from 
the  periphery,  but  partly  also  by  the  soft  venous  wall,  which  promptly  sinks 
under  the  atmospheric  pressure.  This  is  shown  by  the  visible  flattening, 
perhaps  disappearance  from  view,  of  the  vein.  This  process  reduces  the 
venous  pulse,  where  it  occurs,  to  a  local  phenomenon  ;  for,  at  each  inspira- 
tion, the  ]>romptly  resulting  shrinkage  of  all  the  affected  veins  together  is  just 
equivalent  to  the  loss  of  volume  due  to  the  sucking  of  blood  into  the  chest. 
Therefore  the  flow  in  the  more  peripheral  veins  remains  unaffected,  and  the 
pressure  within  them  continues  to  be  pulseless  and  positive.  During  expira- 
tion the  swelling  of  the  veins  near  the  chest,  the  return  of  positive  pressure 
within  them,  may  be  simply  from  the  return  of  the  ordinary  balance  of  forces 
after  the  effects  of  a  deep  inspiration  have  disappeared.     But,  if  expiration  be 


CIBCULA  riON.  389 

violent  and  much  inipoded,  the  positive  pressure  may  rise  much  above  the 
normal.  Here  again,  however,  rej^ui-gitation  will  meet  with  opposition 
from  the  venous  valves,  though  the  flow  from  the  periphery  may  be  much 
impeded. 

The  "  Dangerous  Region,"  and  the  Entrance  of  Air  into  a  Wounded 
Vein. — Quite  close  to  the  chest,  then,  the  normal  venous  pressure  is  always 
slightly  negative;  and  in  deep  inspiration  it  may  become  more  so,  and  this 
condition  may  extend  farther  from  the  chest  along  the  neck  and  axilla,  through- 
out a  region  known  to  surgeons  as  "the  dangerous  region."  It  is  important 
to  understand  tlie  reason  for  this  expression.  It  has  already  been  mentioned 
that  the  wounding  of  a  vein  in  this  region  may  cause  intermittent  bleeding. 
It  now  will  easily  be  understood  that  such  bleeding  will  occur  only  when  the 
pressure  is  positive — that  is,  during  expiration.  During  deep  and  difficult 
breathing,  indeed,  the  venous  blood  may  spring  iu  a  jet  during  expiration 
instead  of  merely  flowing  out,  and  may  wholly  cease  to  flow  during  inspira- 
tion. The  cessation  is  due,  of  course,  to  the  blood  being  sucked  into  the 
chest  past  the  wound  rather  than  pressed  out  of  it. 

It  is  not,  however,  the  risks  of  hemorrhage  that  have  earned  the  name  of 
"dangerous"  for  the  region  where  intermittent  bleeding  may  occur.  The 
danger  referred  to  is  of  the  entrance  of  air  into  the  wounded  vein  and  into  the 
heart, — an  accident  which  is  commonly  followed  by  immediate  death,  for 
reasons  not  here  to  be  discussed.  Very  close  to  the  chest,  where  the  venous 
pressure  is  continuously  negative  and  the  veins  are  so  bound  to  the  fasciae  that 
they  may  not  collapse,  this  danger  is  always  present.  Throughout  the  rest 
of  the  dangerous  region,  the  entrance  of  air  into  a  wounded  vein  will  take 
place  only  exceptionally.  In  quiet  breathing  the  venous  pressure  is  continu- 
ously positive  throughout  most  of  this  region;  and  then  a  wounded  vein  will 
merely  bleed.  It  is  only  in  deep  breathing  that  a  venous  pulse  becomes  vis- 
ible here,  and  that  the  venous  pressure  becomes  negative  in  inspiration.  But 
even  in  forced  breathino-  it  is  I'are  for  a  wounded  vein  of  the  dauoerous  reg-ion 
to  do  more  than  bleed.  The  cause  of  this  lies  iu  the  flaccidity  of  the  venous 
wall.  At  each  expiration  the  blood  may  jet  from  the  wound  ;  but  at  the  fol- 
lowing deep  inspiration  the  weight  of  the  atmosphere  flattens  the  vein  so 
promptly  that  the  blood  is  followed  down  by  the  wounded  wall  and  no  air 
enters  at  the  opening.  It  is  only  when,  during  deep  breathing,  the  wounded 
wall  for  some  reason  cannot  collapse,  that  the  main  part  of  the  "dangerous 
region "  justifies  its  name.  Should  the  tissues  through  which  the  vein  runs 
have  been  stiffened  by  disease,  or  should  the  wall  of  the  vein  adhere  to  a 
tumor  which  a  surgeon  is  lifting  as  he  cuts  beneath  it,  in  either  case  the  vein 
will  have  become  practically  a  rigid  tube.  Should  it  be  wounded  during  a 
deep  inspiration,  blood  will  be  sucked  past  the  wound,  but  the  atmospheric 
pressure  will  fail  to  make  the  wall  collapse ;  air  will  be  drawn  into  the  cut, 
and  blood  and  air  will  enter  the  heart  together,  probably  with  deadly  effect. 

Summary. — It  appears  from  what  has  gone  before  that  the  elasticity  of 
the  lungs  and  the  contractions  of  the  muscles  of  inspiration  regularly  assist  Id 


390  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

uuloading  the  veins  in  the  immediate  neighborhood  of"  the  heart,  and  so  remove 
some  part  of  the  resistance  to  be  overcome  by  the  contractions  of  tiie  cardiac 
muscle.  Wlion  we  come  to  the  detaik'd  study  of  the  heart  it  will  appear  also 
that  a  slight  force  of  suction  is  generated  i)y  the  heart  itself,  which  force  adds 
its  effects  upon  the  flow  of  venous  blood  to  those  of  the  elasticity  of  the  lungs 
and  of  the  contraction  of  the  muscles  of  inspiration. 

Tt  must  here  be  repeated,  however,  that  the  heart  is  quite  competent  to 
maintain  the  circulation  unaided.  This  is  proven  as  follows :  If  in  an  anaes- 
thetized mammal  a  cannula  be  placed  in  the  windpipe,  the  chest  be  widely 
opened,  and  artificial  respiration  be  established,  the  circulation,  though  modi- 
fied, continues  to  be  etfective.  By  the  opening  of  the  chest  its  aspiration  has 
been  ended,  and  can  no  longer  assist  in  the  venous  return.  If,  further,  the 
animal  be  drugged  in  such  a  manner  as  completely  to  paralyze  the  skeletal 
muscles  throughout  the  body,  their  contractions  can  exert  no  influence  upon 
the  venous  return ;  yet  the  circulation  is  still  kept  up  by  the  heart,  unaided 
either  by  the  elasticity  of  the  lungs,  by  the  contractions  of  the  muscles  which 
produce  inspiration,  or  by  those  of  any  other  skeletal  muscles. 

E.  The  Speed  of  the  Blood  in  the  Arteries,  Capillaries, 

AND  Veins. 

If  we  keep  as  our  text,  in  discussing  the  circulation,  the  character  of  the 
capillary  flow,  it  will  be  seen  that  we  have  now  accounted  for  the  facts  that 
the  capillary  flow  is  toward  the  veins ;  that  it  shows  much  friction ;  that  it  is 
continuous,  pulseless,  and  under  low  pressure.  We  have  not  yet  accounted 
for  the  fact  that  it  is  slow.  We  must  now  do  so,  but  must  first  state  and 
account  for  the  speed  of  the  blood  in  tiie  arteries  and  veins. 

The  Measurement  of  the  Blood-speed  in  Large  Vessels ;  the  "  Strom- 
uhr." — The  speed  of  the  blood  in  the  larger  veins  and  arteries  must  be  meas- 
ured indirectly.  We  can  picture  to  ourselves  the  volume  of  blood  which  moves 
past  a  given  point  in  a  given  blood-vessel  in  one  second,  as  a  cylinder  of 
blood  havina:  the  same  diameter  as  the  interior  of  the  blood-vessel.  The 
length  of  this  cylinder  will  then  be  expressed  by  the  same  number  which  will 
express  the  velocity  with  which  a  particle  of  the  blood  would  pass  the  given 
point  in  one  second,  provided  that  this  velocity  be  uniform  and  be  the  same 
for  all  the  particles.  In  order,  then,  to  learn  the  average  speed  of  the  blood 
at  a  given  point  of  an  artery  or  vein  during  a  certain  number  of  seconds,  we 
have  only  to  measure  the  calibre  of  the  blood-vessel  and  the  quantity  of 
blood  which  passes  the  selected  point  during  the  period  of  observation. 
From  these  two  measurements  the  speed  can  be  obtained  by  calculation.  But 
these  two  measurements  are  not  quite  easy.  The  physical  properties  of  the 
blood-vessels,  especially  of  the  veins,  make  their  calibres  variable  and  hard 
to  estimate  justly  as  affected  by  the  conditions  present  during  an  experiment. 
The  means  adopted  for  measuring  the  quantity  of  blood  passing  a  point  in  a 
given  time  necessarily  alters  the  resistance  encountered  by  the  flow,  and  so  of 
itself  affects   both  the  rate  of  flow  and  the  blood-pressure;  and,  with  the 


CIRCULA  TION. 


391 


Fig.  102.— Diagram  of  longitudinal  sec- 
tion of  Ludwig's  "Stroniuhr."  The  ar- 
rows mark  the  direction  of  the  blood- 
stream. For  further  description  see  the 
text. 


latter,  the  calibre  of  the  vessel.  For  tiie.se  reasons  any  measuretneut  of 
the  average  speed  of  tiie  blood  l)y  tlie  above  method  is  only  a])proxiniately 
correct.  The  be.st  instrunu'nt  for  nieasurinu; 
the  quantity  of  blood  driven  past  a  point 
during  an  experiment  is  the  so-called  "stroni- 
uhr" or  "rheouR'ter"  of  Ludwig,  a  longitu- 
dinal section  of  wiiich  is  given  diagrammati- 
cally  in  Figure  102.'  This  is  essentially  a 
curved  tube  shaped  like  the  Greek  capital 
letter  S2.  Each  end  of  the  tube  is  tied  into 
one  of  the  two  stumps  (a  and  b)  of  the  divided 
vessel.  These  ends  of  the  tube  are  as  nearly 
as  possible  of  the  same  calibre  as  the  vessel 
selected.  Each  limb  of  the  tube  is  dilated 
into  a  bulb,  and  the  upper  part  of  the  tube, 
including  the  two  bulbs,  is  of  glass;  the  lower 
part  of  each  limb  is  of  metal.  At  the  top, 
between  the  bulbs,  is  an  opening  for  filling 
the  tubes,  which  can  easily  be  closed  when  not 
in  use.  Each  end  of  the  tube  is  filled  with 
defibrinated  blood  before  being  tied  into  the 
blood-vessel.  In  the  limb  of  the  tube  {B, 
Fig.  102)  which  is  the  farther  from  the  heart  if  an  artery  be  used,  or  the 
nearer  to  the  heart  if  a  vein,  the  defibrinated  blood  is  made  to  fill  the  cavity 
up  to  the  top  of  the  bulb.  In  the  other  limb  (.4,  Fig.  102)  the  blood  fills  the 
tube  only  up  to  a  mark  (e.  Fig.  102)  near  the  bottom  of  the  bulb.  Through 
the  opening  between  the  bulbs  the  still  vacant  space,  which  includes  the  whole 
of  the  bulb  A,  is  filled  with  oil,  all  air  being  excluded.  The  opening  is  then 
closed.  If  now  the  clamps  be  removed  from  the  blood-vessel,  the  blood  of  the 
animal  will  enter  the  tube  at  a  and  drive  before  it  the  contents  of  the  tube. 
Thus  defibrinated  blood  from  B  will  be  driven  into  the  distal  stump  of  the 
vessel  at  6,  and  will  enter  the  circulation  of  the  animal.  Oil  will  at  the  same 
time  be  driven  over  from  A  to  B.  The  bulb  A  has  upon  it  two  marks,  d  and 
e,  one  near  the  top  of  it,  the  other  near  the  bottom.  The  instant  when  the 
line  between  the  oil  and  the  advancing  blood  reaches  the  mark  near  the  top 
of  A  is  the  instant  when  a  volume  of  blood  equal  to  that  of  the  displaced  oil 
has  entered  A,  past  the  mark  near  the  bottom  of  it.  The  capacity  of  the  tube 
between  the  two  marks  is  accurately  known.  The  time  required  for  this 
space  to  be  filled  with  the  entering  blood  is  measured  by  the  observer.  The 
calibre  of  the  metal  tube  at  a  is  accurately  known,  and  is  assumed  to  be  equal 
to  the  calibre  of  the  blood-vessel.  From  these  measurements  the  average 
speed  of  the  blood-stream  at  a  is  calculated. 

^  .J.  Dogiel  :  "Die  Aiismessung  der  stromenden  Bliitvolumina,"  Berichle  Uber  die  Verhand- 
lungen  der  k.  sdchsischen  Gesellschaft  der  Wissenschaften  zu  Leipzig,  Math.-physische  Classe,  1867, 
p.  200. 


392  AN  AMERICAN    TEXT- HOOK    OE  PHYSIOLOGY. 

Tlie  metallic  lower  part  of  tlie  instrument,  wliicii  includes  both  limbs  of 
the  tube,  is  com|)letely  divided  li()rizt)ntally  at  c.  The  two  parts  are  so  built, 
however,  as  to  be  maintained  in  water-tight  apposition.  This  arrangement 
permits  the  whole  upper  part  of  tlie  instrument,  induding  the  glass  bulbs,  to 
be  rotated  suddenly  upon  the  lower,  so  that  the  bulb  B  may  corresjioiid  with 
the  entrance  for  the  blood  at  a,  antl  the  bulb  A  with  the  exit  for  the  l)lood  at 
h.  If  this  rotation  be  effected  at  the  instant  when  the  space  between  the  two 
marks  on  .1  has  been  filled  with  blood,  the  bulb  B,  now  charged  with  oil, 
will  be  filled  bv  the  blood  which  eutei's  next,  and  the  first  charge  of  the  ani- 
mal's own  blood  will  make  its  exit  at  b.  Oil  will  now  pass  over  from  B  to 
A;  when  the  line  between  it  and  the  blood  whieh  is  leaving  A  has  just 
reached  the  lower  mark  on  yl,the  bulbs  are  turned  back  to  their  original 
position.  Thus,  by  repeated  rotations,  each  of  which  can  be  made  to  record 
upon  the  kymograpii  the  instant  of  its  occurrence,  a  number  of  charges  of 
blood  can  be  received  and  transmitted  in  succession  ;  it  is  always  the  same 
space,  between  the  marks  on  A,  which  is  used  for  measuring  the  charge ;  and 
the  time  of  the  experiment  can  be  much  prolonged.  By  this  procedure  the 
errors  due  to  a  single  brief  observation  can  be  greatly  reduced.  Indeed,  the 
time  of  entrance  of  a  single  charge  of  blood  would  be  quite  too  short  to  give 
a  satisfactory  result. 

The  use  of  the  stromuhr  not  only  affords  necessary  data  for  the  calcu- 
lation of  tlie  average  speed  of  the  blood,  but  seeks  directly  to  measure  the 
volume  of  blood  delivered  in  a  given  time  by  an  artery  to  its  capillary  dis- 
trict. It  is  evident  that  this  volume  is  a  quantity  of  fundamental  importance 
in  the  physiology  of  the  circulation.  Could  we  ascertain  it,  by  direct  meas- 
urement or  by  calculation,  for  the  aorta  or  pulmonary  artery,  we  should  know 
at  once  the  volume  of  blood  delivered  to  the"  capillaries  in  one  second,  and 
thus  the  time  taken  for  the  entire  blood  to  enter  either  those  of  the  lungs  or 
of  the  system  at  large.  By  this  knowledge,  many  important  problems  would 
be  advanced  toward  solution. 

The  Measurement  of  Rapid  Fluctuations  of  Speed. — The  stromidir 
can  give  only  the  average  speed  of  the  blood  during  the  experiment.  To 
study  rapid  fluctuations  of  speed,  another  method  is  needed.  If,  in  a  large 
animal,  a  vessel,  best  an  artery,  be  laid  bare,  a  needle  may  be  thrust  into  it  at 
right  angles.  If  the  needle  be  left  to  itself,  the  end  which  projects  from  the 
artery  will  be  deflected  toward  the  heart,  because  the  point  will  have  been 
deflected  toward  the  capillaries  by  the  blood-stream.  The  angle  of  deflection 
might  be  read  off,  could  a  graduated  semicircle  be  adjusted  to  the  needle.  If 
the  stream  be  arrested,  the  needle  returns  to  its  position  at  right  angles  to  the 
artery.  The  greater  the  velocity  of  the  stream,  the  greater  is  the  deflectiou  of 
the  needle.  If,  later,  the  same  needle  be  thrust  into  a  tube  of  rubber  through 
which  water  flows  at  known  rates  of  speed,  the  speed  corresponding  to  each 
angle  of  deflection  of  the  needle  may  be  determined.  If  the  needle  were 
made  to  mark  upon  a  kymograph,  variations  of  the  speed  would  be  recorded 
as  a  curve. 


CinCULA  TION.  393 

An  instrument  based  on  (lie  principles  just  described  is  valuable  for  the 
Study  of  rapid  clianjrcs  of  velocitv.'  In  an  artery,  its  needle  oscillates  rlivth- 
niically,  showing  tliat  there  tiie  speed  of  the  blood  varies  during  each  beat  of 
the  heart,  being  greatly  accelerated  by  the  systole  of  the  ventricle,  and  retarded 
by  the  cessation  of  the  systole.  It  will  be  remembered  that  the  microscope 
directly  shows  faint  rhythmic  accelerations  in  the  minute  arteries  of  the  frog. 
lu  the  veins  rhythmic  changes  of  speed  do  not  occur  except  near  the  heart 
from    respiratory  causes. 

The  Speed  of  the  Blood  in  the  Arteries. — The  stromuhr  shows  that  the 
speed  of  the  blood  is  liable  to  great  variations.  This  flict,  and  the  range  of 
speed  in  the  arteries,  are  fairly  exhibited  by  the  results  obtained  by  Dogiel 
from  the  common  carotid  artery  of  a  dog,  the  experiment  upon  which  lasted 
127  seconds.  During  this  time  six  observations  were  made  which  varied  in 
length  from  14  to  30  seconds  each.  For  one  of  these  periods  the  average 
speed  was  243  millimeters  in  one  second  ;  for  another  ])eriod,  520  millimeters. 
These  were  the  extremes  of  speed  noted  in  tliis  case.'^  The  speed  in  the 
arteries  diminishes  toward  the  capillaries. 

The  Speed  of  the  Blood  in  the  Veins. — The  speed  in  a  vein  tends  to  be 
slower  than  that  in  an  artery  of  about  the  same  importance,  but  is  not  neces- 
sarily so.^     It  increases  from  the  capillaries  toward  the  heart. 

The  Speed  of  the  Blood  in  the  Capillaries. — The  rate  of  the  capillary 
flow  may  be  measured  directly  under  the  microscope.  Certain  physiologists 
have  also  observed  the  movement  of  the  blood  in  the  retinal  capillaries  of 
their  own  eyes,  and  have  measured. its  rate  there.*  Both  methods  show  that 
in  the  capillaries  the  speed  is  very  much  less  than  in  the  large  arteries  or  large 
veins.  In  the  capillaries  of  the  web  of  the  frog's  foot  it  is  only  about  0.5 
millimeter  in  one  second.  In  those  of  the  mesentery  of  a  young  dog  it  has 
been  found  to  be  0.8  millimeter;  in  those  of  the  human  retina,  from  0.6  to 
0.9  millimeter. 

Speed  and  Pressure  of  the  Blood  Compared. — If  now  we  compare  the 
speed  with  the  pressure  of  the  blood  in  the  arteries,  in  the  capillaries,  and  in 
the  veins,  we  shall  be  struck  by  both  similarities  and  differences.  In  the 
arteries  both  pressure  and  speed  rhythmically  rise  and  fall  together;  and  both 
the  mean  pressure  and  the  mean  speed  decline  from  the  heart  to  the  capillaries. 
In  the  ca])illaries  both  pressure  and  speed  are  pulseless  and  low, — very  low 
compared  with  the  great  arteries.  In  the  veins,  however,  the  pressure  is 
everywhere  lower  than  in  the  capillaries  and  falls  from  the  capillaries  to  the 
heart ;  the  speed  is  everywhere  higher  than  in  the  capillaries  and  rises  from 

*  M.  L.  Lortet :  Recherche-s^  sur  la  vitesse  du  cours  du  sang  dans  les  art^res  du  cheval  au  moyen 
d^un  nouvel  hemodromographe,  Paris,  1867. 

■■^  J.  Dogiel  :  loc.  cit. 

^  E.  Cyon  und  F.  Steinmann  :  "  Die  Geschwindigkeit  des  Blutstroms  in  den  Venen,"  Bulletin 
de  V Academie  Imperiale  des  Sciences  de  St.  Petershourg,  1871 ;  also  in  E.  Cyon  :  Gesammelte  physio- 
log^ie  Arbeiten,  1888,  p.  110. 

*  K.  Vierordt :  Die  Erscheinungen  und  Gesetze  der  Stromgeschwindigkeiten  des  Blutes,  etc.,  1862, 

pp.  4i,iri. 


394  AN  AMEEICAX   TEXT-BOOK   OF  PHYSIOLOGY. 

the  capillaries  to  the  heart.  It  is  apparent,  therefore,  that  there  is  no  direct 
couueetiou  between  the  pressure  and  the  speed  of  the  blood  at  a  given  jwint; 
inasmuch  as  they  change  together  along  tlie  arteries  and  change  inversely 
along  the  veins.  How  varied  the  combinations  may  be  of  pressure  and  speed 
will  be  seen  in  studying  the  regulation  of  the  circulation. 

In  the  great  veins,  as  in  the  arteries,  the  speed  is  very  high  compared  with 
the  capillaries.  In  the  capillaries  the  speed  of  the  blood  is  least,  while  in 
the  tubes  which  supply  and  which  drain  them  the  speed  is  great.  The  physi- 
ological value  of  these  facts  is  clear.  It  has  already  been  pointed  out  that  the 
blood  moves  slowly  through  the  short  and  narrow  tubes,  where  its  exchanges 
with  tissue  and  with  air  are  effected,  and  swiftly  through  the  long  tubes  of 
communication.  What  are  the  physical  conditions  wiiicii  underlie  these 
physiological  facts  ? 

The  speed  of  the  blood  varies  inversely  as  the  collective  sectional 
area  of  its  path.  If  the  circulation  in  an  animal  continue  uniform  for  a  time 
— during  several  breaths  and  heart-beats — it  is  evident  that  the  forces  con- 
cerned must  be  so  balanced  that,  during  that  time,  equal  quantities  of  blood 
will  have  entered  and  left  the  heart,  the  arteries,  the  capillaries,  and  the  veins, 
respectively.  If  the  arteries,  for  instance,  lose  more  blood  than  the  heart 
transmits  to  them,  this  blood  must  accumulate  in  the  veins  till  the  arteries 
become  drained  and  the  supply  to  the  capillaries  fails.  The  very  maintenance 
of  a  circulation,  then,  implies  that  equal  quantities  of  blood  must  pass  any 
two  points  of  the  collective  blood-path  in  equal  times,  except  when  a  general 
readjustment  of  the  rate  of  flow  may  lead  to  a  temporary  disturbance  of  it. 
It  will  be  seen  at  once  that  this  principle  is  consistent  with  the  widest  differ- 
ences of  rate  between  individual  arteries  of  the  same  importance,  or  between 
individual  veins  or  capillaries.  If  in  one  artery  the  flow  be  increased  by  one- 
half,  and  in  another  be  diminished  by  one-half,  the  total  flow  in  the  two 
arteries  collectively  will  be  the  same  as  before. 

If  the  principle  just  stated  be  considered  in  connection  with  tlie  anatomy 
of  the  blood-path,  the  differences  of  speed  in  the  arterial,  capillary,  and  venous 
systems  will  at  once  be  understood.  The  wider  arteries  and  veins  are  few. 
Dissection  shows  that  when  an  artery  or  vein  divides,  the  calibre,  and,  with 
the  calibre,  the  "sectional  area"  of  the  branches  taken  together,  is  commonly 
larger  than  that  of  the  parent  trunk.  In  general  it  is  a  law  of  the  arterial 
and  venous  anatomy  that  the  collective  sectional  area  of  the  vessels  of  either 
system  increases  from  the  heart  to  the  capillaries.  The  smaller  the  individual 
vessels  are,  the  wider  is  the  blood-path  which  they  make  up  collectively. 
Widest  of  all  is  the  blood-path  where  the  individual  vessels  are  smallest — that 
is,  in  the  capillary  system.  The  collective  sectional  area  of  the  capillaries  is 
several  hundred  times  that  of  the  root  of  the  aorta.  The  collective  sectional 
area  of  the  veins  which  enter  the  right  auricle  is  greater,  perhaps  twice  as 
great,  as  that  of  the  root  of  the  aorta.  The  venous  system,  regarded  as  a 
single  tube,  is  of  much  greater  calibre  than  the  arterial.  It  is  perhaps  better 
to  make  these  general  statements  than  to  compare  the  different  figures  given 


CIRCULATION.  395 

by  different  observers.  The  arterial  and  venous  systems,  treated  as  eacli  a 
single  tube,  may  be  compared  roughly  to  two  funnels,  each  having  its  nar- 
row end  at  the  heart.  The  very  wiile  and  very  short  single  tube  of"  the  ca})il- 
lary  system  may  be  imagined  to  connect  the  wide  ends  of  the  two  funnels. 
Equal  quantities  of  blood  pass  in  equal  times  any  two  points  of  the  collec- 
tive blood-path  between  the  left  ventricle  and  the  right  auricle.  Therefore 
where  the  blood-path  is  wide,  these  quantities  must  move  slowly,  and  swiftly 
where  the  blood-path  is  narrow.  It  is  owing,  then,  to  the  rapid  widening  of 
the  arterial  path  that  the  speed  declines,  like  the  pressure,  toward  the  capilla- 
ries. It  is  owing  to  the  huge  relative  calibre  of  the  path  at  the  capillaries 
that  in  them  the  speed  is  by  far  the  least  while  the  same  volume  is  passing 
that  passes  a  point  in  the  narrow  aorta  in  the  same  time  ;  it  is  owing  to  the 
steady  narrowing  of  the  venous  path  toward  the  heart  that  the  venous  blood 
is  constantly  quickening  its  speed  while  its  pressure  is  falling.  As  the  calibre 
of  the  venous  system  is  greater  than  that  of  the  arterial,  the  average  speed  in 
the  veins  is  probably  less  than  in  the  arteries.  As  the  collective  calibre  of 
the  veins  which  enter  the  right  auricle  is  greater  than  that  of  the  aorta,  the 
blood  probably  moves  into  the  heart  less  swiftly  than  out  of  it ;  though  of 
course  equal  quantities  enter  and  leave  it  in  equal  times  provided  those  times 
are  not  mere  fractions  of  a  beat.  In  connection  with  this  it  is  significant 
that  the  entrance  of  blood  into  the  heart  takes  place  during  the  long  auric- 
ular diastole,  while  its  exit  is  limited  to  the  shorter  ventricular  systole. 

Time  Spent  by  the  Blood  in  a  Systemic  Capillary. — The  width  of  the 
path,  then,  determines  the  slow  movement  of  the  blood  in  the  areas  where  it  is 
fidfilling  its  functions ;  the  narrowness  of  the  path,  the  swiftness  of  move- 
ment of  the  blood  in  leaving  and  returning  to  the  heart.  We  have  seen  (p. 
371)  that  a  particle  of  blood  may  make  the  entire  round  of  a  dog's  circulation 
in  from  fifteen  to  eighteen  seconds.  If  we  assume  the  systemic  capillary  flow 
to  be  at  the  rate  of  0.8  millimeter  in  one  second,  the  blood  would  remain  about 
0.6  of  a  second  in  a  systemic  capillary  half  a  millimeter  long.  Slow  as  is  the 
capillary  flow,  it  thus  appears  that  it  is  none  too  slow  to  give  time  for  the  usos 
of  the  blood  to  be  fulfilled. 

P.  The  Flow  op  Blood  through  the  Lungs. 
The  blood  moves  from  the  right  ventricle  to  the  left  auricle  under  the 
same  general  laws  as  from  the  left  ventricle  to  the  right  auricle.  Certain  dif- 
ferences, however,  are  apparent,  and  must  be  noted.  One  difference  is  that 
the  collective  friction  is  less  in  the  pulmonary  than  in  the  systemic  vessels, 
and  that  therefore  the  resistance  to  be  overcome  by  each  contraction  of  the 
right  ventricle  is  less  than  that  opposed  to  the  left  ventricle.  Accordingly  it 
appears  from  dissection  that  the  muscular  wall  of  the  right  ventricle  is  much 
thinner  than  that  of  the  left.  No  accurate  measurements  can  be  made  of  the 
normal  pressure  and  speed  of  the  blood  in  the  arteries,  capillaries,  and  veins 
of  the  lungs,  because  they  can  be  reached  only  by  opening  the  chest  and 
destroying  the  mechanism  of  respiration,  and  thereby  disturbing  the  normal 


396  .l.V  AMERICAN    TEXT-BOOK    OF   PHYHIOLOdY. 

conditions  of  the  pulmonary  hlood-stiram.  In  the  opened  chest  these  cannot 
be  entirely  restored  by  artificial  respiration.  The  thinness  of  the  wall  of  the 
pnlinonarv  artery,  however,  indicates  that  it  has  much  less  pressure  to  support 
than  that  of  the  aorta,  whicli  tact  als<j  is  indicated  by  such  roughly  approxi- 
mate results  as  have  been  obtained  witli  the  manometer  after  opening  the 
chest. 

As  the  pulmonary  artery  and  veins  lie  wholly  within  the  chest,  but  outside 
tiie  lungs,  their  trunks  and  larger  branches  all  tend  to  be  dilated  continuously 
by  the  elastic  pull  of  the  lungs — a  pull  which  increases  at  each  inspiration. 
On  the  other  hand,  the  pulmonary  capillaries  lie  so  close  to  the  surface  of  each 
lung  that  they  are  exposed  to  the  same  pressure,  practically,  as  that  surface, 
and  the  full  weight  of  the  atmosphere  may  act  upon  them.  These  conditions 
all  tend  to  unload  the  capillaries  and  the  pulmonary  veins,  but  to  weaken  the 
unloading  of  the  pulmonary  artery.  The  two  effects  can  hardly  balance  one 
another,  however.  The  wall  of  the  pulmonary  artery  is  so  much  stiffer  than 
that  of  ihe  vein,  that  the  actual  results  should  be  favorable  to  the  flow.  The 
elastieitv  of  the  lungs  and  the  contractions  of  the  muscles  of  inspiration  thus 
lighten,  probably,  the  work  of  the  right  ventricle  as  well  as  of  the  left.  The 
right  ventricle,  however,  like  the  left,  can  accomplish  its  work  without  assist- 
ance ;  for  the  entire  circulation,  including,  of  course,  the  flow  through  the 
lungs,  continues  after  the  chest  has  been  opened,  if  artificial  respiration  be 
maintained. 

G.  The  Pulse-volume  and  the  Work  done  by  the  Ventricles 

OF  the  Heart. 

The  Cardiac  Cycle. — It  is  assumed  that  the  anatomy  of  the  heart  is  known 
to  the  reader. 

The  general  nature  and  effects  of  the  heart's  beat  have  been  sketched 
already.  Each  beat  has  been  seen  to  comprise  a  number  of  ])lienomena,  which 
occur  in  regular  order,  and  which  recur  in  the  same  order  during  each  of  the 
succeeding  beats.  Each  beat  is  therefore  a  cycle;  and  the  phrase  "  cardiac 
cvcle"  has  become  a  technical  expression  for  "  beat,"  as  it  conveys,  in  a  word, 
the  idea  of  a  regular  order  of  events.  As  each  of  the  four  chambers  of  the 
heart  has  its  own  systole  and  diastole,  there  are  eight  events  to  be  studied  in 
connection  with  each  cycle.  The  systoles  of  the  two  auricles,  however,  are 
exactly  simultaneous,  as  are  their  diastoles;  and  the  same  is  true  of  the  sys- 
toles and  of  the  diastoles  of  the  two  ventricles.  We  may,  therefore,  without 
confusion,  speak  of  the  auricular  systole  and  diastole,  and  of  the  ventric- 
ular systole  and  diastole,  as  of  four  events,  each  involving  the  narrowing  or 
widening  of  two  chambers,  a  right  and  a  left.  The  heart  of  the  mammal 
or  bird  consists  essentially  of  a  pair  of  pumps,  the  ventricles,  each  of  which 
acts  alternatelv  as  ^  ]>owerful  force-pump  and  as  a  very  feeble  suction- 
pump.  To  each  ventricle  is  superadded  a  contractile  apjiendage,  the  auricle, 
through  which,  and  to  some  extent  by  the  agency  of  which,  blood  enters  the 
ventricle. 


CIRCULA  TION.  397 

The  Pulse-volume. — The  central  fact  of  the  circulation  of  the  blood  is  the 
injoctioii,  at  intervals,  by  each  ventricle,  against  a  strong  resistance,  of  a  charge 
of  blood  into  its  artery,  which  charge  the  ventricle  has  just  received  out  of  its 
veins  through  its  auricle.  This  (juantity  nuist  be  exactly  the  same  for  the 
two  ventricles  under  normal  conditions,  or  the  circulation  would  soon  come  to 
an  end  by  the  accumidation  of  the  blood  in  either  the  j)ulmonary  or  the  sys- 
temic vessels.  The  blood  ejected  from  each  ventricle  during  the  systole 
nuist  also  be  equal  in  volume  to  tiie  blood  which  enters  each  set  of  capillaries, 
the  pulmonary  or  systemic,  during  that  systole  and  the  succeeding  diastole  of 
the  ventricles,  provided  the  circulation  be  proceeding  uniformly.  The  quantity 
just  referred  to  is  called  the  "contraction  volume"  or  "pulse-volume"  of  the 
heart.  Were  it  always  the  same,  and  could  we  measure  it,  we  should  possess 
the  key  to  the  quantitative  study  of  the  circulation. 

The  pulse-volume  may  vary  in  the  same  heart  at  different  times,  as  is  easily 
shown  by  opening  the  chest,  causing  the  conditions  of  the  circulation  to  change, 
and  noting  that  under  certain  conditions  the  heart  during  each  beat  varies 
in  size  more  than  before.  This  variation  of  volume  is  easily  possible  because 
the  walls  of  the  heart  are  of  muscle,  soft  and  distensible  when  relaxed.  It  is 
probable  that  at  no  systole  is  the  ventricle  quite  emptied  ;  that  most  of  its 
cavity  may  become  obliterated  by  the  coming  together  of  its  walls,  but  that  a 
spa(!e  remains,  just  below  the  valves  and  above  the  papillary  muscles,  which  is 
not  cleared  of  blood.  It  is  also  probable  that  not  only  the  blood  which  is 
ejected  at  the  systole  may  vary  in  amount,  but  also  the  residual  blood  which 
remains  in  the  ventricle  at  the  end  of  the  systole.^  It  is  therefore  clear  that 
it  is  useless  to  attempt  the  measurement  of  the  pulse-volume  by  measuring 
the  fluid  needed  to  fill  the  ventricle,  even  if  the  heart  be  freshly  excised  from 
the  living  body  and  injected  under  the  normal  blood-pressure.  Rough  approx- 
imations to  this  measurement  may,  however,  be  attempted  in  at  least  two 
ways : 

In  the  first  place,  a  modification  of  the  stromuhr  has  been  applied  suc- 
cessfully to  the  aorta  of  the  rabbit,  between  the  origins  of  the  corondry  arteries 
and  of  the  innominate.  This  operation  requires  that  the  auricles  be  clamped 
temporarily  so  as  to  stop  the  flow  of  blood  into  the  venti'icles,  and  to  permit 
the  aorta  in  its  turn  to  be  clamped  and  divided  between  the  clamp  and  the 
ventricle,  without  serious  bleeding.  After  the  circulation  has  been  re-estab- 
lished, the  volume  of  the  blood  which  passes  through  the  instrument  during 
the  ex])eriment,  divided  by  the  number  of  the  heart-beats  during  the  same 
period,  gives  the  pulse-volume.     The  average  result  obtained,  for  the  rabbit, 

1  F.  Hesse:  "  Beitrage  zur  Mechanik  der  Herzbewegung,"  Arckw/iir  Anatomie  und  Physiolo- 
gie  (anatomische  Abtheilung),  1880,  p.  328.  C.  Sandborg  und  W.  Miiller  :  "Studien  uberden 
jMeclianismus  des  Herzens,"  Pflih/er's  Archiv  fur  die  gesammte  Physioloc/ie,  1880,  xxii.  p.  408.  C.  S. 
Roy  and  .1.  G.  Adami:  "Contributions  to  the  Physiology  and  Pathology  of  the  Mammalian 
Heart,"  Proceedings  of  the  Boyal  Society  of  London,  1891-92,  i.  p.  435.  J.  E.  Johansson  und  R. 
Tigerstedt :  "  Ueber  die  gegenseitigen  Beziehungen  des  Herzens  und  der  Geftisse  ;"  "  Ueber  die 
Herzthiitigkeit  bei  verschieden  grossem  Wiederstand  in  den  Gefiissen,"  Skandinamsches  Archiv 
fiir  Physioloyie,  1891,  ii.  p.  409. 


398  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

is  a  volume  of  blood  the  weight  of  which  is  0.00027  of  the  weight  of  the 
animal.' 

A  second  way  of  attempting  to  ascertain  the  pulse-volume  is  to  measure  the 
swelling  and  thesiirinkageof  the  heart.  This  is  called  the"plethysmographic"  ^ 
method.  One  application  of  it  is  as  follows  :  The  chest  and  pericardium  of  an 
animal  are  opened,  and  the  heart  is  inserted  into  a  brass  case  full  of  oil.  The 
opening  through  which  the  great  vessels  pass  is  made  water-tight  by  mechanical 
means  which  do  not  impede  the  movement  of  the  blood  into  and  out  of  the 
heart.  The  top  of  the  brass  case  is  prolonged  into  a  tube,  the  oil  in  which 
rises  as  the  heart  swells  and  falls  as  it  shrinks.  Upon  the  oil  a  light  piston 
moves  up  and  down,  and  records  its  movements  upon  the  kymograph.  The 
instrument  is  called  a  "  cardiometer,"  ^ 

The  average  pulse-volume  of  the  human  ventricle  has  been  very  variously 
estimated  upon  the  basis  of  observations  of  various  kinds  made  upon  mam- 
mals of  various  species.  The  figures  offered  range,  in  round  numbers,  from 
50  to  190  cubic  centimeters.  If  we  assume  the  human  pulse- volume  to 
weigh  100  grams,  and  the  blood  of  a  man  who  weighs  69  kilograms  to  weigh 
5.308  kilograms,  or  ^  of  his  body-weight,  the  pulse-volume  will  be  about  -^ 
of  the  entire  blood,  and  the  entire  blood  will  pass  through  the  heart,  from 
the  veins  to  the  arteries,  in  only  fifty-three  beats — that  is,  in  less  than  one 
minute.  The  speed  with  which  a  man  may  bleed  to  death  if  a  great  artery- 
be  severed  is  therefore  not  surprising. 

The  "Work  done  by  the  Contracting  Ventricles. — Uncertain  as  is  this 
important  quantity  of  the  pulse-volume,  the  estimation  of  the  work  done  by  the 
heart  in  maintaining  the  circulation  must  be  based  upon  it,  and  upon  the  force 
with  which  each  ventricle  ejects  the  pulse-volume.  A  small  fraction  of  this 
force  is  expended  in  im})arting  a  certain  velocity  to  the  ejected  blood  ;  all  the 
rest  serves  to  overcome  a  number  of  opposing  forces.  The  force  exerted  by 
the  muscular  contraction  is  opposed  by  the  weight  of  the  volume  ejected,  and 
by  the  strong  arterial  pressure,  which  resists  the  opening  of  the  semilunar 
valve  and  the  ejection  of  the  pulse-volume.  Moreover,  the  elasticity  of  the 
lungs  tends  at  all  times  to  dilate  the  ventricles,  with  a  force  which  is  increased 
at  each  recurring  contraction  of  the  muscles  of  inspiration.  Probably  there  is 
also  in  the  wall  of  the  ventricle  itself  a  slight  elasticity  which  must  be  over- 
come by  the  ventricle's  own  contraction  in  order  that  its  cavity  may  be  effaced. 
The  strong  arterial  pressure,  with  which  the  reader  is  already  familiar,  is  by 
far  the  greatest  of  these  resisting  forces — in  fact,  is  the  only  one  of  them 
which  is  not  of  small  importance  in  the  present  connection. 

Are  we  obliged  to  measure  the  force  of  the  systole  indirectly  ?  Cau  we  not 
ascertain  it  by  direct  experiment?  Manometers  of  various  kinds  have  been 
placed  in  direct  communication  with  the  cavities  of  the  ventricles.     The  fol- 

*  R.  Tigerstedt:  "  Studien  iiber  die  Blutvertheilung  im  Korper."  Erste  Abhandlung. 
"Bestimmuug  der  von  dem  linken  Herzen  herausgetriebenen  Blutmenge,"  Skandinavisches 
Archiv  fiir  Physiologic,  1891,  iii.  p.  145. 

■•  From  Tvl^vofidc,  enlargement.  '  C  S.  Roy  and  J.  G.  Adarai,  op.  cit. 


CIRCULATION.  399 

lowiug  method,  anioug  others,  has  been  employed  :  A  tube  open  at  both  ends 
is  introduced  througli  tlie  external  jugular  vein  of  an  animal  into  the  right 
ventricle,  or,  with  greater  difficulty,  through  the  carotid  artery  into  the  left 
ventricle.  In  neither  case  is  the  valve,  whether  tricuspid  or  aortic,  rendered 
incompetent  duriug  this  proceeding,  nor  need  the  general  mechanism  of  the 
heart  and  vessels  be  gravely  disturbed.  If  the  outer  end  of  the  tube  be 
connected  with  a  recording  mercurial  manometer,  a  tracing  of  the  pressure 
within  the  right  or  left  ventricle  may  be  written  upon  the  kymograph.  It 
is  found,  however,  that  the  pressure  within  the  heart  varies  so  much  and  so 
rapidly  that  the  inert  mercurial  column  will  not  follow  the  fluctuations,  and 
that  the  attempt  to  learn  the  mean  pressure  by  this  method  fails.  A  valve, 
however,  may  be  intercalated  in  the  tube  between  the  ventricle  and  the  man- 
ometer— a  valve  so  made  as  to  admit  fluid  freely  to  the  manometer,  but  to  let 
none  out.  The  manometer  will  then  record,  and  record  not  too  incorrectly,  the 
maximum  pressure  within  the  right  or  left  ventricle  during  the  experiment ;  in 
other  words,  it  will  record  the  greatest  force  exerted  during  that  time  by  the  ven- 
tricle in  order  to  do  its  work.^  In  this  way  the  maximum  pressure  within 
the  left  ventricle  of  the  dog  has  been  found  to  present  such  values  as  176  and 
234  millimeters  of  mercury,  the  corresponding  maximum  pressure  in  the  aorta 
being  158  and  21 2  millimeters  respectively.^  The  maximum  pressures  obtained 
from  simultaneous  observations  upon  the  right  and  left  ventricle  of  a  dog  are 
variously  reported.  It  M'ould  perhaps  be  not  far  wrong  to  say  that  in  this 
animal  the  pressure  in  the  right  ventricle  is  to  that  in  the  left  as  1  to  2.6.^ 

The  work  done  by  each  ventricle  during  its  systole  is  found  by  multiplying 
the  weight  of  the  pulse-volume  ejected  into  the  force  put  forth  in  ejecting  it. 
That  force  is  equal  to  the  pressure  under  which  the  pulse  volume  is  expelled. 
If  we  use  as  a  basis  of  calculation  the  pressures  observed  in  the  dog's  heart  with 
the  maximum  manometer,  we  may  assume  as  the  measure  of  a  given  pressure 
within  the  contracting  human  left  ventricle  200  millimeters  of  mercury,  and  for 
the  human  right  ventricle  77  millimeters.  If  for  each  column  of  mercury  there 
be  substituted  the  corresponding  column  of  blood,  the  heights  will  be  2.567 
meters  and  0.988  meter  respectively.  The  force  exerted  by  the  right  or  left 
ventricle  upon  the  pulse-volume  might  therefore  just  equal  that  put  forth  in 
lifting  it  to  a  height  of  0.988  or  2.567  meters.  If  we  assume  100  grams  as 
the  weight  of  a  possible  pulse-volume  ejected  by  a  human  ventricle,  the  work 
done  at  each  systole  of  the  left  ventricle  would  be  100  X  2.567  =  256.7  gram- 
meters,  and  at  each  systole  of  the  right  ventricle  100X0.988  =  98.8  gram- 
meters;  a  grammeter  being  the  work  done  in  raising  one  gram  to  the  height 
of  one  meter.  The  work  of  both  ventricles  together  would  be  256.7  -f-  98.8 
=  355.5  grammeters.  The  foregoing  estimates  are  offered  not  as  statements 
of  what  does  occur,  but  as  very  rough  indications  of  what  may  occur.     Even 

'  F.  Goltz  und  J.  Gaule:  "Ueber  die  Druckverhaltnisse  im  Innern  des  Herzens,"  Archiv 
fiir  die  gesammte  Physiologie,  1878,  xvii.  p.  100. 

*  S.  de  Jager:  "Ueber  die  Saugkraft  des  Herzens,"  Pfliiger's  Archiv  fiir  die  gesammte  Physi- 
ologic, 1883,  pp.  504,  505.  ^  Goltz  und  Gaule,  op.  ciL,  p.  106. 


400  -.l.V   AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

thus,  liovvever,  they  are  of  inoiiu'iit.  When  we  think  of  the  vast  miinber  of 
beats  executed  by  the  heart  every  (hiy,  the  j^reat  aiuoiint  of  energy  rendered 
manifest  in  maintainini;  the  ('ircukitit)n  beeomes  apparent,  and  our  interest  is 
heigiitened  in  tiie  faet  tiiat  all  of  this  laro;e  sum  of  energy  is  liberated  in  the 
muscular  tissue  of  the  heart  itself.  Thus,  too,  the  physiological  significance 
of  the  diastole  is  accentuated  as  a  time  of  rest  for  the  cardiac  muscle,  as  well 
as  a  necessary  pause  for  the  admission  of  blood  into  the  ventricle.  To  disre- 
gard minor  considerations,  the  work  done  at  a  systole  will  evidently  dej)end 
u]ion  the  amount  of  the  pulse-volume,  of  tlie  arterial  jiressure  overcome,  and 
of  the  velocity  imparted  to  the  ejected  blood.  All  these  are  variable.  The 
work  of  the  ventricles  therefore  is  eminently  variable. 

The  Heart's  Contraction  as  a  Source  of  Heat. — In  dealing  with  the 
movement  of  the  blood  in  the  vessels  we  have  seen  that  the  energy  of  visible 
motion  liberated  by  the  cardiac  contractions  is  progressively  changed  into  heat 
by  the  friction  encountered  by  the  blood  ;  and  that  this  change  is  nearly  com- 
plete by  the  time  the  blood  has  returned  to  the  heart,  the  kinetic  energy  of 
each  systole  sufficing  to  drive  the  blood  from  the  heart  back  to  the  heart  again, 
but  probably  not  being  much  more  than  is  required  for  this  purpose.  Practi- 
cidlv,  therefore,  all  the  energy  of  the  heart's  contraction  becomes  heat  within 
the  body  itself,  and  leaves  the  body  under  this  form.  As  the  heart  liberates 
during  every  day  an  amount  of  energy  which  is  always  large  but  very  variable, 
its  contractions  evidently  make  no  mean  contribution  to  the  heat  produced  in 
the  body  and  parted  with  at  its  surface. 

H.  The  Mechanism  of  the  Valves  of  the  Heart. 
■  Use  and  Importance  of  the  Valves. — The  discussion  just  concluded 
shows  the  work  of  the  heart  to  be  the  forcible  pumping  of  a  variable  pulse- 
volume  out  of  veins  where  the  pressure  is  low  into  arteries  where  the  pressure 
is  high.  It  is  owing  to  the  valves  that  this  is  possible,  and  so  dependent  is 
the  normal  movement  of  the  blood  upon  the  valves  at  the  four  ventricular 
apertures  that  the  crippling  of  a  single  valve  by  disease  may  suffice  to  destroy 
life  after  a  longer  or  shorter  period  of  imjiaired  circulation. 

The  Auriculo-ventricular  Valves. — The  working  of  the  aurieulo- ven- 
tricular valves  (see  Fig.  103)  is  not  hard  to  grasp.  When  the  pressure  within 
the  ventricle  in  its  diastole  is  low,  the  curtains  hang  free  in  the  ventricle, 
although  probably  never  in  close  contact  with  its  wall.  As  the  blood  pours 
into  the  ventricle,  the  pressure  within  it  rises,  currents  flow  into  the  space  be- 
tween the  wall  and  th.e  valve,  and  probably  bring  near  together  the  edges  of 
the  curtains  and  also  their  surfaces  for  some  distance  from  the  edges.  Thus, 
upon  the  cessation  of  the  auricular  systole,  the  sujiervening  of  a  superior  pres- 
sure within  the  ventricle  probably  applies  the  already  approximated  edges 
and  surfaces  of  the  curtains  to  one  another  so  ])romi)tly  that  the  commencing 
contraction  of  the  ventricle  is  not  attended  by  regurgitation  into  the  auricle. 
The  principle  of  closure  is  the  same  for  the  tricuspid  valve  as  for  the  mi- 
tral.    As  the  forces  are  exactly  equal  and  <»p[)osite  which  press  together  the 


(Jl UVULA  TION. 


401 


opposed  parts  of  tlie  surfaces  of  the  curtains,  those  parts  undergo  no  strain, 
and  hence  are  enabled  to  be  excpiisitely  delicate  and  flexible  and  therefore 
easily  fitted  to  one  another.  On  the  other  hand,  the  parts  of  the  valve  which 
intervene  between  ti>e  surfaces  of  coutact  and  the  auriculo-ventricular  ring  are 
tough  and  nuich  thicker,  as  they  have  to  bear  the  brunt  of  the  pressure  within 
the  contracting  ventricle.  As  the  systole  of  the  ventricle  increases,  the  aiiric- 
lUo-ventricular  ring  probably  becomes  smaller,  and  the  curtains  of  the  valve 
probably  become  somewhat  fluted  from  base  to  apex,  so  that  their  line  of  con- 
tact is  a  zig-zag.  At  the  same  time  their  surfaces  of  contact  may  increase  in 
extent. 

Tendinous  Cords  and  their  Uses. — The  structure  so  far  described  is 
wonderfully  elfective  because  it  is  combined  with  an  arrangement  to  prevent  a 
reversal  of  the  valve  into  the  auricle,  which  otherwise  would  occur  at  once. 
This  arrangement  consists  in  the  disposition  of  the  tendinous  cords,  which  act 


Fig.  103.— The  left  ventricle  and  aorta  laid  open,  to  show  the  mitral  and  aortic  semilunar  valves  (Henle). 


as  guy-ropes  stretched  between  the  mu.scular  wall  of  the  ventricle  and  the 
valve,  whether  mitral  or  tricuspid.  These  cords  are  tough  and  inela.stic,  and, 
like  the  valve,  are  coated  with  the  slippery  lining  of  the  heart.  They  are 
stout  where  they  spring  from  the  muscle,  but  divide  and  subdivide  into 
branches,  strong  but  sometimes  very  fine,  which  proceed  fan-wise  from  their 

2G 


402  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

stem  to  their  insertions  (.see  Fig.  lO-'j).  Tiiese  insertions  are  both  into  the  free 
margin  of  the  valve  and  into  the  whole  extent  of  that  sni-faee  of  it  whieh 
looks  toAvard  the  wall  of  the  veutriele,  quite  up  to  the  ring.  J^y  means  of  this 
arrangement  of  the  eords  each  curtain  is  held  taut  from  base  to  apex  thiough- 
out  the  systole  of  the  ventricles,  the  opposed  surfaces  being  kept  in  apj)osition, 
and  the  parts  of  the  curtains  between  these  surfaces  and  the  ring  In-ing  kept 
from  bellying  unduly  toward  the  auricle.  Each  curtain  is  held  sufficiently 
taut  from  side  to  side  as  well,  because  the  tendinous  cords  inserted  into  one 
lateral  half  of  the  curtain  spring  from  a  widely  different  part  of  the  wall  of 
the  heart  from  those  of  the  other  lateral  half  of  it  (see  Fig.  103).  At  all  times, 
therefore,  even  when  the  walls  of  the  ventricle  are  most  closely  approximated 
during  systole,  the  cords  may  pull  in  slightly  divergent  directions  upon  the 
two  lateral  halves  of  each  curtain.  This  arrangement  of  the  cords  may  also 
cause  them,  when  taut,  to  pull  in  slightly  convergent  directions  upon  the 
contiguous  lateral  halves  of  two  neighboring  curtains  and  thus  to  favor  the 
pressing  of  them  together  (see  Fig.  103). 

Papillary  Muscles  and.  their  Uses. — In  the  left  ventricle  the  tendinous 
cords  arise  in  two  groups,  like  bouquets,  from  two  teat-like  muscular  projec- 
tions which  s])ring  from  opposite  points  of  the  wall  of  the  heart,  and  which 
are  called  the  "  papillary  muscles  "  (.see  Fig.  103).  One  of  these  gives  origin 
to  the  cords  for  the  right  half  of  the  anterior  and  for  the  right  half  of  the 
posterior  curtain  ;  the  other  papillary  muscle  gives  rise  to  the  cords  for  the 
left  halves  of  the  two  curtains.  Each  papillary  muscle  is  commonly  more  or 
less  subdivided  (see  Fig.  103).  The  same  principles  are  carried  out,  but  less 
regularly,  for  the  origins  of  the  tendinous  cords  of  the  more  complex  tricuspid 
valve.  Various  opinions  have  been  held  as  to  the  use  of  the  papillary  mu.scles. 
It  seems  probable  that  during  the  change  of  size  and  form  wrought  in  the 
ventricle  by  its  systole,  the  origins  of  the  tendinous  cords  and  the  auriculo- 
ventricular  ring  tend  to  be  approximated  and  the  cords  to  be  slackened  in 
consequence.  Perhaps  this  is  checked  by  a  compensatory  shortening  of  the 
papillary  muscles,  due  to  their  sharing  in  the  systolic  contraction  of  the  mus- 
cular ma.ss  of  which  they  form  a  part.  Observations  have  recently  been  made 
which  have  been  interpreted  to  mean  that  the  papillary  nui.'^cles  begin  their 
contraction  slightly  later  and  end  it  slightly  earlier  than  the  mass  of  the 
ventricle.^ 

Semilunar  Valves. — The  anatomy  and  the  working  of  the  semilunar 
valves  are  the  same  in  the  aorta  as  in  the  pulmonary  artery,  and  one  account 
will  answer  for  both  valves.  Each  valve  is  composed  of  three  entirely  sepa- 
rate segments,  set  end  to  end  within  and  around  the  artery  just  at  its  origin 
from  the  ventricle.  The  attachments  of  the  segments  occupy  the  entire  cir- 
cumference of  the  vessel  (Fig.  103).  Like  the  tricu.«pid  and  mitral  valves, 
each  semilunar  segment  is  composed  of  a  sheet  of  tis-sue  which  is  tough,  thin, 
supple,  and  slippery  ;  but  the  semilunar  valves  differ  from  the  tricuspid  and 

^C.  S.  Roy  and  J.  G.  Adami :  "Heart-beat  and  Pulse-wave,"  The  Practitioner,  1890,  i. 
p.  88. 


CIRCULA  TION.  403 

mitral,  not  only  in  the  complete  distinctness  of  their  segments,  but  also  in 
their  mechanism.  The  tendinous  cords  are  wholly  luckinus  and  each  segment 
depends  upon  its  direct  connection  with  the  arterial  wall  to  prevent  reversal 
into  the  ventricle  during  the  diastole  of  the  latter.  If  the  artery  he  carefully 
laid  open  by  cutting  exactly  between  two  of  the  segments,  each  of  the  three  is 
seen  to  have  the  form  of  a  pocket  with  its  opening  turned  away  from  the  heart 
(see  Fig.  103).  Behind  each  segment,  the  artery  is  dilated  into  one  of  the  hol- 
lows or  ''sinuses"  of  Valsalva.^  As  the  valve  lies  immediately  above  the 
base  of  the  ventricle  the  segments  rest  upon  the  top  of  the  thick  muscular 
wall  of  the  latter,  which  atfords  them  a  powerful  support  (see  Fig.  104). 
Each  segment  is  attached  by  the  whole  length  of  its  longer  edge  to  the  artery, 
while  the  free  margin  is  formed  by  the  shorter  edge.  It  is  this  arrangement 
which  renders  reversal  of  a  segment  impossible  (see  Fig.  103). 


Fig  104  -Diagram  to  illustrate  the  mechanism  of  Fig.  105.-Diagram  to  illustrate  the  mechanism  of 

■       ■  the  semilunar  valve.  the  semilunar  valve  and  corpora  Arantn. 

While  the  blood  is  streaming  from  the  ventricle  into  the  artery,  the  three 
segments  are  pressed  away  by  the  stream  from  the  centre  of  the  vessel,  but 
never  nearly  so  far  as  to  touch  its  wall.  At  all  times,  therefore,  a  pouch  ex- 
ists behind  each  segment,  which  pouch  freely  communicates  with  the  general 
cavity  of  the  artery.  As  the  ventricular  systole  nears  its  end,  the  ventricular 
cavity  doubtless  becomes  narrowed  just  below  the  root  of  the  artery,  and  with 
it  the  arterial  aperture  itself,  while  currents  enter  the  sinuses  of  Valsalva. 
Thus  for  a  double  reason  the  three  segments  of  the  valve  are  approximated, 
and  probably  the  last  blood  pressed  out  of  the  ventricle  issues  through  a  nar- 
row chink  between  them.  The  instant  that  the  pressure  in  the  ventricle  falls 
below  the  arterial  pressure,  the  three  segments  must  be  brought  together  by 
the  superior  pressure  within  the  artery,  and  tightly  closed  by  its  forcible  recoil, 
without  regurgitation  having  occurred  in  the  process  (see  Figs.  104,  lOS)." 

Lunuli  and  their  Uses.— Each  segment  of  a  semilunar  valve,  when 
closed,  is  in  firm  contact  with  its  fellows  not  only  at  its  free  margin  but  also 
over  a  considerable  surface,  marked  in  the  anatomy  of  the  segment  by  the 
two  "lunula"  or  little  crescents,  each  of  which  occupies  the  surface  of  the 
seo-ment  from  one  of  its  ends  to  the  middle  of  its  free  margin,  the  shorter  edge 

1  Named  from  the  Italian  physician  and  anatomist  Valsalva  of  Bologna,  born  in  1666 

^L  Krehl-  "  Beitra-e  zur  Kenntniss  der  Fullung  und  Entleerung  des  Herzens,    Abhand- 

lungen'der  matk.-physisehln  Classe  der  k.  sdchsischen  Gesellsehaft  der  Wissemchaflm,  1891,  Bd.  xvu. 

No.  5,  p.  360. 


404  AiX  AMERICAX   TEXT-BOOK    OF  PHYSIOLOGY. 

of  tlie  lunula  being  one-half  of  the  free  margin  of  the  segment  (see  Fig.  103). 
Over  the  surface  of  each  hiniilu  each  segment  is  in  contact  with  a  different 
one  of  its  two  fellows  (see  Fig.  105).  The  firmness  of  closure  tlius  secured  is 
shown  by  Figure  104,  wiiich  represents  a  longitudinal  section  of  the  artery, 
passing  through  two  of  the  closed  segments.  The  forces  which  press  together 
the  opposed  surfaces  are  equal  and  opj)osite,  and  the  j)arts  of  the  segments 
■which  correspond  to  these  surfaces  undergo  no  strain.  The  lunulae,  therefore, 
like  the  mutually  opposed  portions  of  the  mitral  or  tricuspid  valve,  are  very 
delicate  and  flexible,  while  the  rest  of  each  semilunar  segment  is  strongly 
made,  to  resist  of  itself  the  arterial  pressure. 

Corpora  Arantii  and  their  Uses. — At  the  centre  of  the  free  margin  of 
each  semilunar  segment,  just  between  the  ends  of  the  two  lunuhe,  there  is  a 
small  thickening,  more  pronounced  in  the  aorta  than  in  the  pulmonary  artery, 
called  the  "  body  of  Aranzi  "  ^  (corpus  Arantii).  This  thickening  both  rises 
above  the  edge  and  projects  from  the  surface  between  tlie  lunulas.  When  the 
valve  is  closed,  the  three  corpora  Arantii  come  together  and  exactly  fill  a  small 
triangular  chink,  which  otherwise  might  be  left  open  just  in  the  centre  of  the 
cross  section  of  the  artery  (see  Figs.  103,  105). 

The  foregoing  shows  that  the  meclianism  of  the  semilunar  valves  is  no  less 
effective,  though  far  simpler,  than  that  of  the  mitral  and  tricuspid.  That  the 
latter  two  should  be  more  complex  is  natural ;  for  each  of  them  must  give 
free  entrance  to  and  prevent  regurgitation  from  a  chamber  which  nearly 
empties  itself,  and  hence  undergoes  a  very  great  relative  change  of  volume; 
while  the  arterial  system  is  at  all  times  distended  and  undergoes  a  change  of 
capacity  which  is  relatively  small  while  receiving  a  pulse-volume  and  trans- 
mitting it  to  the  capillaries. 

I.  The  Changes  in  Form  and  Position  of  the  Beating  Heart,  and 

THE  Cardiac  Impulse. 

General  Changes  in  the  Heart  and  Arteries. — During  the  brief  systole 
of  the  auricles  these  diminish  in  size  while  the  swelling  of  the  ventricles  is 
completed.  During  the  more  protracted  systole  of  the  v^entricles,  which  imme- 
diately follows,  these  diminish  in  size  while  the  auricles  are  swelling  and  the 
injected  arteries  expand  and  lengthen.  During  the  greater  part  of  the  suc- 
ceeding diastole  of  the  ventricles  both  these  and  the  auricles  are  swelling,  and 
all  the  muscular  fibres  of  the  heart  are  flaccid,  up  to  the  moment  when  a  new 
auricular  systole  completes  the  diastolic  distention  of  the  ventricles,  as  above 
stated.  During  the  ventricular  diastole,  as  the  great  arteries  recoil  they 
shrink  and  shorten.  The  changes  of  size  in  the  beating  heart  depend  entirely 
upon  the  changes  in  the  volume  of  blood  contained  in  it,  and  not  upon  changes 
in  the  volume  of  the  muscular  walls.  Tiie  muscular  fibres  of  the  heart  agree 
with  those  found  elsewhere  in  not  changing  their  volume  appreciably  during 
contraction,  but  their  form  only.     The  cardiac  cycle  thus  runs  its  course  with 

'  Named  from  Julius  Caesar  Aranzi  of  Bologna,  an  Italian  physician  and  anatomist,  born 
in  1530.  * 


CIRCULA  TION.  405 

regularly  recurring  changes  of  .size  in  the  auricles,  the  ventricles,  and  the 
arteries.  These  changes  of  size  are  accompanied  by  corresponding  changes 
in  the  form  a"d  ])ositiou  of  tlie  iieart,  which  are  l)oth  interesting  iu  them- 
selves and  important  in  relation  to  the  diagnosis  of  disease.  The  basis 
of  their  study  consists  in  opening  the  chest  and  pericardium  of  an  animal, 
and  seeing,  touching,  and  otherwise  investigating  the  beating  heart.  The 
changes  in  the  beating  heart,  moreover,  underlie  the  production  of  the 
so-called  cardiac  impulse,  or  apex-beat,  which  is  of  interest  iu  physical 
diagnosis. 

Observation  of  the  Heart  and  Vessels  in  the  Open  Chest. — The  beat- 
ing heart  may  be  exposed  for  observation  in  a  mammal  by  laying  it  upon  its 
back,  performing  tracheotomy,  and  completely  dividing  the  sternum  in  the 
median  line,  beginning  at  the  ensiform  cartilage.  Artificial  respiration  is  next 
established,  a  tube  having  been  tied  into  the  trachea  before  the  chest  was 
opened.  The  two  sides  of  the  chest  are  now  drawn  asunder  and  the  pericar- 
dium is  laid  open  to  expose  the  heart. 

If,  in  any  mammal,  the  ventricles  be  lightly  taken  between  the  thumb  and 
forefinger,  the  moment  of  their  systole  is  revealed  by  the  sudden  hardening  of 
the  heart  produced  by  it,  as  the  muscular  fibres  contract  and  press  with  force 
upon  the  liquid  within.  On  the  other  hand,  the  ventricular  diastole  is  marked 
by  such  flaccidity  of  the  muscular  fibres  that  very  light  pressure  indents  the 
surface,  and  causes  the  finger  to  sink  into  it,  in  spite  of  care  being  taken  to 
prevent  this.  Commonly,  therefore,  at  the  systole  the  thumb  and  finger  are 
palpably  and  visibly  forced  apart,  no  matter  where  applied,  in  spite  of  the  fact 
that  the  volume  of  the  ventricles  is  diminishing.  This  sinking  of  the  finger 
or  of  an  instrument  into  the  relaxed  wall  of  the  heart  has  given  rise  to  many 
errors  of  observation  regarding  changes  during  the  beat.  The  time  when  the 
ventricles  are  hardened  beneath  the  finger  coincides  with  the  up-stroke  of  the 
arterial  pulse  near  the  heart,  and,  as  shown  by  Harvey,^  with  the  time  when 
an  intermittent  jet  of  blood  springs  from  a  wound  of  either  ventricle.  The 
hardening  is  proven  thus  to  mark  the  systole  of  the  ventricles.  Those  changes 
of  size,  form,  and  position  of  the  exposed  heart  which  accompany  the  harden- 
ing of  the  ventricles  beneath  the  finger  are  therefore  the  chnnges  of  the  ven- 
tricular systole ;  and  the  converse  changes  are  those  of  the  ventricular  diastole. 
To  interpret  all  the  changes  correctly  by  the  eye  alone,  without  the  aid  of  the 
finger  or  of  the  jet  of  blood,  is  a  task  of  surpassing  difficulty  in  a  rapidly  beat- 
ing heart,  as  was  eloquently  set  forth  by  Harvey.^ 

Changes  of  Size  and  Form  in  the  Beating  Ventricles. — In  a  mam- 
mal, lying  upon  its  back,  with  the  heart  exposed,  the  ventricles  evidently 
become  smaller  during  their  systole.  Their  girth  is  everywhere  diminished 
and  their  length  also,  the  latter  much  less  than  the  former ;  indeed  the  dimi- 
nution in  length   is  a  disputed  point.     Not  merely  a  change  of  size,   but  a 

'  Ezerciiaiio  Anatomiea  de  Motu  Cordis  et  Sanguinis  in.  Animnlibus,  1628,  p.  23;  Willis'  trans- 
lation, Bowie's  edition,  1889,  p.  23. 

'  Op.  ciL,  1628,  p.  20;  Willis'  translation,  Bowie's  edition,  p.  20. 


406  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

change  of  form  is  thus  produced  ;  the  heart  becomes  a  smaller  and  shorter, 
but  a  more  pointed,  cone.  The  systolic  narrowing  from  side  to  side  is  very 
conspicuous.  In  a  mammal  lying  on  its  back,  this  narrowing  is  accompanied 
by  some  increase  in  the  diameter  of  the  heart  from  breast  to  back  so  that  the 
surface  of  the  ventricles  toward  the  observer  becomes  more  convex.  Tims  the 
base  of  the  ventricles,  which  tendeil  to  be  roughly  elliptical  during  their 
relaxation,  tends  to  become  circular  during  their  contraction  ;  and  tiie  diameter 
of  the  circle  is  greater  than  the  shortest  diameter  of  the  ellipse,  which  latter 
diameter  extends  from  breast  to  back.  At  the  same  time,  the  area  of  the  base 
when  circular  and  contracted  is  much  less  thau  when  elliptical  and  relaxed.* 
Naturally,  none  of  these  comparisons  to  mathematical  figures  makes  any  pre- 
tence to  exactness.  At  the  same  time  that  the  contracting  heart  undergoes 
these  changes,  the  direction  of  its  long  axis  becomes  altered.  In  animals  in 
which  the  heart  is  oblique  within  the  chest,  the  line  from  the  centre  of  the 
base  to  the  apex,  that  is,  the  long  axis,  while  it  points  in  general  from  head 
to  tail,  points  also  toward  the  breast  and  to  the  left.  In  an  animal  lying  ou 
its  back,  the  ventricles  when  relaxed  in  diastole  tend  to  form  an  oblique  cone, 
the  apex  having  subsided  obliquely  to  the  left  and  toward  the  tail.  As  the 
ventricles  harden  in  their  systole,  they  tend  to  change  from  an  oblique  cone  to 
a  right  cone  ;  the  long  axis  tends  to  lie  more  nearly  at  right  angles  to  the  base ; 
and  consequently  the  apex,  unfettered  by  pericardium  or  chest-wall,  makes  a 
slight  sweep  obliquely  toward  the  head  and  to  the  right,  and  thus  rises  up 
bodily  for  a  little  way  toward  the  observer.  This  movement  was  graphicallv 
called  by  Harvey  the  erection  of  the  heart.^  It  is  accompanied  by  a  slight 
twisting  of  the  ventricles  about  their  long  axis,  in  such  fashion  that  the  left 
ventricle  turns  a  little  toward  the  breast,  the  right  ventricle  toward  the  back. 
This  twisting  movement  is  probably  due  simply  to  the  course  of  the  cardiac 
muscular  fibres. 

Chang-es  of  Position  in  the  Beating  Ventricles. — The  changes  in  form 
imply  changes  in  position.  The  oblique  movement  of  the  long  axis  inq)lies 
that  in  systole  the  mass  of  the  ventricles  sweeps  over  a  little  toward  the 
median  line  and  also  a  little  toward  the  head.  The  shortening  of  the  long 
axis  implies  that  either  the  apex  recedes  from  the  breast,  or  the  base  of  the 
ventricles  recedes  from  the  back,  or  both.  Of  these  last  three  possible  cases, 
the  second  is  the  one  that  occurs.  The  oblique  movement  of  the  apex  is 
accompanied  by  no  recession  of  it;  but  the  auriculo-ventricular  furrow  and 
the  roots  of  the  aorta  and  pulmonary  artery  move  away  from  the  s})inal 
column  as  the  injected  arteries  lengthen  and  expand,  and,  as  the  auricles  swell, 
during  the  contraction  of  the  ventricles.  During  their  diastole  the  ventricles 
are  soft;  they  swell;  and  changes  of  form  and  position  occur  which  need  not 
be  detailed  now,  as  they  are  simply  converse  to  those  of  the  systole  and  have 
been  indicated  already  in  dealing  with  the  latter. 

^  C.  Ludwjg:  "  Ueber  den  Bau  und  die  Bewegiingen  der  Herzventrikel,"  Zeitachrifl  fiir 
rationeUe  Medizin,  1849,  vii.  p.  1S9. 

^  Op.  cit.,  1628,  p.  22.     Translation,  1889,  p.  22. 


CTRCT^LA  TTOX.  407 

Changes  in  the  Beating  Auricles. —  Kxccjit  in  small  uiiiinals,  the  walls 
of  both  the  ventricles  are  so  thiek  that  the  eolor  of  the  two  is  the  same  and 
is  unchanging,  namely,  that  of  their  muscular  mass;  but  the  walls  of  the 
auricles  are  so  thin  that  their  color  is  ail'ected  In-  that  of  the  blood  within,  so 
that  the  right  auricle  looks  bluish  and  dark  and  the  left  auricle  red  and 
bright.  During  the  brief  systole  of  the  auricles  they  are  seen  to  become 
smaller  and  paler  as  blood  is  expelled  from  them,  wdiile  their  serrated  edges 
and  auricular  appendages  shrink  raj)idly  away  from  the  observer.  The 
changes  of  the  auricular  systole  are  seen  to  ])re(;ede  immediately  the  changes 
of  the  systole  of  the  ventricles  and  to  succeed  the  repose  of  the  whole  heart. 
During  the  relatively  long  diastole  of  the  auricles  these  are  seen  to  swell, 
whether  the  ventricles  are  shrinking  in  systole  or  are  swelling  during  the 
first  and  greater  part  of  their  diastole. 

Changes  in  the  Great  Veins. — In  the  vense  cavse  and  pulmonary  veins  a 
pulse  is  visible,  more  plainly  in  the  former  than  in  the  latter,  which  pulse  has 
the  same  rhythm  as  that  of  the  heart's  beat.  The  causes  of  this  pulse  are 
complex  and  imperfectly  understood.  It  depends  in  part  upon  the  rhythmic 
contraction  of  muscular  fibres  iu  the  w^alls  of  the  veins  near  the  auricles,  which 
must  heighten  the  flow^  into  the  latter,  and  which  contraction  the  auricular 
systole  immediately  follows.^  This  venous  pulse  w^ill  be  mentioned  again  in 
discussing  the  details  of  the  events  of  the  cycle  (see  p.  430). 

Changes  in  the  Great  Arteries, — It  is  interesting  to  note  that  even  in 
so  large  an  animal  as  the  calf  the  pulse  of  the  aorta  or  of  the  pulmonary 
artery  can  hardly  be  appreciated  by  the  eye,  so  far  as  the  increase  in  girth  of 
either  vessel  is  concerned.  The  expansion  of  the  artery  affects  equally  all 
points  iu  its  circumference,  and  being  thus  distributed,  is  so  slight  in  propor- 
tion to  the  girth  of  the  vessel  that  the  profile  of  the  latter  scarcely  seems  to 
change  its  place.  The  lengthening  of  the  expanding  artery  can  be  more 
readily  seen. 

Effects  of  Opening  the  Chest. — Such  are  the  changes  observed  in  the 
heart  and  vessels  when  exposed  in  the  opened  chest  of  a  mammal  lying  on 
its  back.  The  question  at  once  arises.  Can  these  changes  be  accepted  as  iden- 
tical with  those  which  occur  in  the  unopened  chest  of  a  quadruped  standing 
upon  its  feet,  or  of  a  man  standing  erect  ?  It  will  be  most  profitable  to  deal 
at  once  with  the  case  of  the  hunian  subject.  What  are  the  possible,  indeed 
probable,  diiFereuces  between  the  changes  in  the  heart  in  the  unopened  upright 
chest  and  in  the  same  when  opened  and  supine  ? 

When  air  is  freely  admitted  to  both  pleural  sacs,  all  those  complex  efiPects 
upon  the  circulation  are  at  once  abolished  which  we  have  seen  to  be  caused 
by  the  elasticity  of  the  lungs  and  the  movements  of  respiration.  The  arti- 
ficial respiration  will  have  an  effect  upon  the  pulmonary  transit  of  the  blood 
and  so  upon  the  circulation  ;  but  the  details  of  this  effect  are  not  the  same  as 
those  of  natural  respiration,  and,  for  our  present  purpose,  may  be  disregarded. 

^  T.  Lauder  Brunton  and  F.  Fayrer  :  "Note  on  Independent  Pulsation  of  the  Pulmonary 
Veins  and  Vena  Cava,"  Proceedincjs  of  the  Royal  Society,  1876,  vol.  xxv.  p.  174. 


408  AN  AMERICAN    TEXT- HOOK    OF    lUFYSIOLOGY. 

"What  has  been  abolished  i.s  tin-  coiitimial  suction,  riiythniically  increased  in 
inspiration,  exerted  by  the  hings  njion  the  heait  and  all  the  vessels  within  the 
chest,  which  snction  at  all  times  favors  the  expansion  and  resists  the  con- 
traction of  the  cavities  of  the  heart  and  of  the  vessels.  On  the  opening  of 
both  pleural  sacs  the  heart  and  vessels  are  exposed  to  the  undiminished  and 
unvarying  pressure  of  the  atmosphere.  Moreover,  the  heart  has  ceased  to  be 
packed,  as  it  were,  between  the  j)leura!  and  lungs  to  right  and  left,  the  spine, 
the  front  of  the  chest-wall,  and  the  tliaphragni.  From  these  considerations  it 
follows  that  the  heart  must  be  freer  to  (;hange  its  form  and  position  in  the 
opened  than  in  the  unopened  chest ;  and  that  these  changes  must  be  more 
modified  by  simple  gravity  in  the  former  case  than  in  the  latter.  Even  in 
the  open  chest  we  have  studied  these  changes  only  in  an  animal  lying  on  its 
back.  But  if  we  turn  the  creature  to  either  side,  or  place  it  upright  in  imi- 
tation of  the  natural  human  posture,  the  ventricles  of  the  exj)()sed  heart  in 
any  case  tend  to  assume,  in  systole,  the  same  form,  which  has  been  com- 
pared roughly  to  a  right  cone  with  a  circular  base.  This  is  the  form  proper 
to  the  hardened  structure  of  branching  and  connected  fibres  of  which  the 
contracting  ventricles  consist.  But  if  the  exposed  ventricles  be  noted  in  dias- 
tole, it  will  appear  that  their  form  depends  very  largely  upon  the  effects  of 
gravity  upon  the  exceedingly  soft  and  yielding  mass  formed  by  their  relaxed 
fibres.  We  have  seen  them,  in  diastole,  to  flatten  from  breast  to  back,  to 
spread  out  from  side  to  side,  to  gravitate  toward  the  tail  and  to  the  left.  If 
the  animal  is  laid  on  its  side,  they  flatten  from  side  to  side,  they  spread 
out  from  breast  to  back,  and  gravitate  to  the  right  or  left,  as  the  case 
may  be.^ 

Probable  Changes  in  the  Heart's  Form  and  Position  in  the  Unopened 
Chest. — It  is  fair  to  conjecture  that  the  increase  of  the  relaxed  ventricles  in 
girth  and  in  length  which  is  seen  in  the  open  chest  would  not  be  greatly  differ- 
ent in  the  closed  chest  of  a  man  in  the  upright  posture.  But  it  is  ])robable 
that  the  flattening  of  the  exposed  heart  from  breast  to  back,  which  is  seen  in 
diastole,  would  not  occur  if  the  chest  were  closed.  It  is  precisely  in  this  direc- 
tion that  the  flaccid  heart  exposed  in  the  supine  chest  would  be  flattened  un- 
duly by  its  own  weight,  when  deprived  of  many  of  its  anatomical  supports 
and  of  the  dilating  influence  of  the  lungs.  The  flattening  from  breast  to  back 
must  cause  an  exaggerated  spreading  out  from  side  to  side  and  hence  an  unduly 
elliptical  form  of  the  base,  inasmuch  as,  at  the  same  time,  the  girth  of  the  ven- 
tricles is  increasing  as  they  enlarge  in  their  diastole.  Conversely,  it  is  prob- 
able, both  a  priori  and  from  experimental  evidence,  that  in  the  chest,  when 
closed  and  upright,  the  diminution  in  size  of  the  contracting  ventricles  pro- 
ceeds more  symmetrically  ;  that  their  girth  everywhere  diminishes  through  a 
diminution  of  the  diameter  from  breast  to  back  as  well  as  of  that  from  side  to 

'  J.  B.  Haycraft:  "Tlie  Movements  of  the  Heart  within  tlie  Chest-cavity,  and  the  Cardio- 
gram," The  Joumnl  nf  I'liyxinl<u/ij,  vol.  xii.,  Nos.  5  and  6,  December,  1891,  p.  44S ;  ,J.  B.  Hay- 
craft  and  T).  R.  Patcrson  :  ''The  Changes  in  Shape  and  in  Position  of  the  Heart  during  the 
Cardiac  Cycle,"  The  Journal  of  Physiology,  vol.  xix.,  Nos.  5  and  (!,  May,  1896.  p.  496. 


CIRCULA  TION.  409 

side,  and  not  through  an  exaggerated  lessening  of  the  latter  and  an  actual 
increase  of  the  former.  In  this  case,  too,  the  base  would  tend  to  become 
more  circular  during  the  systole  by  means  of  a  less  marked  change  from  the 
diastolic  form.^ 

It  has  been  said  that  in  systole  the  ventricles  are  somewhat  shortened 
in  the  exposed  heart,  and  probably  also  in  the  unopened  human  chest.  In 
the  open  chest  the  apex  does  not  recede  at  all  in  virtue  of  this  shorten- 
ing ;  on  the  contrary,  the  base  of  the  ventricles  is  seen  to  move  toward 
the  apex,  and  away,  therefore,  from  the  spine.  Experiment  has  proven  that 
the  foregoing  is  true  also  of  the  unopened  chest.^  It  has  been  noted  already 
that  this  movement  of  the  base,  which  in  the  upright  chest  would  be  a  descent, 
is  accompanied  by  a  lengthening  of  the  aorta  and  pulmonary  artery  as  their 
distention  takes  place.  Very  probably  it  is  the  thrust  of  the  lengthened  arte- 
ries which  largely  causes  the  descent  of  the  base  of  the  contracting  ventricles, 
which  descent  compensates  for  the  shortening  of  the  ventricles  and  retains  the 
apex  in  contact  Avith  the  chest- wall. 

The  Impulse  or  Apex-beat. — It  must  always  have  been  a  matter  of  com- 
mon knowledge  that,  in  man,  a  portion  of  the  heart  lies  so  close  to  the  chest- 
wall  that,  at  each  beat,  the  soft  parts  of  that  wall  may  be  seen  and  felt  to  pul- 
sate over  a  limited  area.  This  is  commonly  in  the  fourth  or  fifth  intercostal 
space,  midway  between  the  left  margin  of  the  sternum  and  a  vertical  line  let 
fall  from  the  left  nipple.  A  similar  pulsation  may  be  observed  in  other  mam- 
mals. The  protrusion  of  the  chest-wall  at  the  site  of  this  "  impulse  "  or  "  apex- 
beat  "  occurs  when  the  arteries  expand,  and  the  up-stroke  of  their  pulse  is  felt ; 
and  the  recession  of  the  chest  coincides  with  the  shrinking  of  the  arteries  away 
from  the  finger.  The  impulse  proper,  that  is  the  protrusion  of  the  chest-wall, 
occurs,  therefore,  at  the  time  of  the  systole  of  the  ventricles.  By  far  the  most 
important  factor  of  the  apex-beat  is  probably  the  effort  of  the  hardening  ven- 
tricles to  change  the  direction  of  their  long  axis  against  the  resistance  of  the 
chest-wall.  A  heart  severed  from  the  body  and  bloodless,  if  laid  upon  a 
table,  lifts  its  apex  as  it  hardens  in  systole  and  assumes  its  proper  form.  If  a 
finger  be  placed  near  enough  to  the  rising  apex  to  be  struck  by  it,  the  same 
sensation  is  received  as  from  the  impulse. 

It  is  interesting  to  note  that  around  the  point  where  the  soft  parts  of  the 
chest  are  protruded  by  the  impulse,  they  are  found  to  be  very  slightly  drawn 
in  at  the  time  of  its  occurrence.  This  drawing-in  is  called  the  ''negative 
impulse,"  and  must  be  caused  by  the  diminution  in  size  of  the  contracting 
ventricles.  These  are  air-tig-ht  within  the  chest,  and  so  their  forciblv  lessened 
surface  must  be  followed  down,  in  varying  degrees,  under  the  pressure  of 
the  atmosphere,  by  the  elastic  and  yielding  lungs  and  by  the  far  less  yield- 
ing soft  parts  of  the  chest-wall. 

The  apex-beat  can  be  brought  to  bear  in  various  ways  upon  a  recording 
lever,  and  thus  be  made  to  inscribe  upon  the  kymograph  a  rhythmically  fluc- 
tuating trace,  which  is  called  a  cardiogram.     Considerable  attention  has  been 

*  J.  B.  Haycraft :  loc.  cit.  "  Haycraft :  loc.  cit. 


410  Ay  AMERICAN  TEXT-BOOK   OF  PHYSIOLOGY. 

given  to  the  oliu'idation  of  the  curve  thus  recorded;  but,  so  far,  too  little 
agreement  has  been   reached  for  the  subject  to  be  entered  u])on  here.' 

J.  The  Sounds  of  the  Heart. 

If  the  ear  be  applied  to  the  human  chest,  at  or  near  the  [)la('e  of  the  apex- 
beat,  the  heart's  pulsation  will  be  heard  as  well  as  felt.  This  lact  was  known 
to  Harvey.^  About  two  hundred  years  later  than  Harvey,  iu  1819,  the 
French  physician  Laennec,  the  inventor  of  auscultation,  made  known  the  fact 
that  each  beat  of  the  heart  is  accompanied  not  by  one  but  by  two  separate 
sounds.  He  also  called  attention  to  their  great  importance  in  the  diagnosis  of 
the  diseases  of  the  heart.* 

Relations  of  the  Sounds — The  first  sound  is  heard  during  the  time  when 
the  apex-beat  is  felt ;  it  theretbre  coincides  with  the  systole  of  the  ventricles. 
The  second  sound  is  nuieh  shorter,  and  follows  the  first  immediately,  or,  to 
speak  more  strictly,  after  a  scarcely  appreciable  interval.  The  second  sound, 
therefore,  coincides  with  the  earlier  part  of  the  diastole  of  the  ventricles. 
The  second  sound  is  followed  in  its  turn  by  a  period  of  silence,  commonly 
longer  considerably  than  the  second  sound,  which  silence  lasts  till  the  begin- 
ning of  the  first  sound  of  the  next  ventricular  beat.  The  period  of  silence, 
therefore,  coincides  with  the  later,  and  usually  longer,  portion  of  the  diastole 
of  the  ventricles,  and  with  the  systole  of  the  auricles.  It  is  interesting  that 
the  great  auscultator,  Laennec,  offered  no  explanation  of  the  cause  of  either 
sound,  while  he  made  and  reiterated  the  incorrect  and  misleading  statement 
that  the  second  sound  coincides  with  the  systole  of  the  auricles.  When  the 
heart  beats  oftener  than  usual,  each  beat  must  be  accomplished  in  a  shorter 
time ;  and  it  is  found  that,  during  a  briefer  beat,  the  period  of  silence  is 
shortened  much  more  than  the  period  during  which  the  two  sounds  are  audi- 
ble ;  which  latter  period  may  not  be  altered  appreciably. 

Characters  of  the  Sounds. — The  first  sound  is  not  only  comparatively 
long,  but  is  low-pitched  and  muffled.  The  second  sound  is  comj)aratively 
short,  and  is  high  and  clear.  The  two  sounds,  therefore,  are  sharply  con- 
trasted in  duration,  pitch,  and  quality.  A  rough  notion  of  the  contrasted 
characters  of  the  sounds  may  be  obtained  by  pronouncing  the  meaningless 
syllables  "lubb  dup."  In  other  mammals  the  sounds  have  substantially  the 
same  characters  as  in  man. 

Cause  of  the  Second  Sound. — Since  Laennec's  time,  the  cause  of  the 
second  sound  has  been  demonstrated  by  experiment.  The  second  sound  is  due 
to  the  vibrations  caused  by  the  sinniltancous  closure  of  the  semilunar  valves 
of  the  pidmonary  artery  and  of  the  aorta,  when  the  diastole  of  the  ventricles 
has  just  begun.      This  cause  was  first  suggested  by   the  French  physician 

1  M.  von  Frey:  Die  Untermchung  des.  Pulses,  etc.,  1892,  p.  lOli;  K.  Tigerstedt:  Lchrbuch  der 
Physiologie  des  Kreislaufes,  Leipzig,  1893,  p.  112. 

^  ExercUniio  Anntomica  dc  Main  Cordis  et  Sanguinis  in  Animalibus,  1628,  p.  30 ;  Willis's  trans- 
lation, Bowie's  edition,  1889,  p.  34. 

*  R.  T.  II.  Laennec:  iJe  rauscullalion  mediak;  etc.,  Paris,  1819. 


CIRCULA  riON.  411 

Rouauet  in  1832  ;'  not  long  afterward  it  was  conclusively  proven  by  experi- 
ment l)y  the  Enolisli  physician  C.  J.  B.  Williams.^ 

Dr.  \\'illianis'.s  experiment  was  as  follows:  In  a  yonn^  ass  the  chest  was 
opened  and  the  heart  was  exposed.  It  was  ascertained  tliat  the  second  sound 
was  audible  throuirh  a  stethoscope  applied  to  the  heart  itself.  A  sharp  hook 
was  then  passed  throui^h  the  wall  of  the  pulmonary  artery,  and  was  so  directed 
as  to  make  the  semilunar  valve  incompetent  temporarily.  By  means  of  a 
second  hook,  the  aortic  semilunar  valve  \vas  likewise  made  incompetent. 
When  both  hooks  were  in  position,  the  heart  was  auscultated  afresh,  and  tha 
second  sound  was  found  to  have  disappeared,  and  to  be  replaced  by  a  hissing 
murmur.  The  hooks  were  withdrawn  during  auscultation,  and  at  the  moment 
of  withdrawal  the  murmur  disappeared  and  the  normal  second  sound  recurred. 
Subsequent  clinical  and  post-mortem  observations  have  shown  that  the  second 
sound  may  be  altered  by  disease  which  cripples  the  aortic  valves. 

Causes  of  the  First  Sound. — The  causes  of  the  first  sound  have  not 
been  proven  so  clearly  by  the  available  evidence,  which  is  partly  experimental 
and  partly  derived  from  physical  diagnosis  followed  by  post-mortem  verifica- 
tion. The  first  sound,  like  the  second,  was  ascribed  by  Rouauet^  to  vibrations 
depending  upon  valvular  closure, — the  simultaneous  closure  of  the  tricuspid 
and  mitral  valves ;  but  the  persistence  of  the  sound  throughout  the  whole 
ventricular  systole  made  this  cause  less  probable  than  in  the  case  of  the  second 
sound.  Williams,^  on  the  other  hand,  ascribed  the  first  sound  to  the  con- 
traction of  the  muscular  tissue  of  the  ventricles, — an  explanation  consistent 
with  the  muffled  quality  of  the  first  sound,  and  with  its  persistence  through- 
out the  systole  of  the  ventricles.  It  is  now  believed  by  many  that  both  of 
the  foregoing  explanations  are  correct,  and  that  the  first  sound  is  composite  in 
its  origin,  and  due  both  to  closure  of  the  valves  and  to  muscular  contraction. 
The  evidence  in  favor  of  these  causes  is,  briefly,  as  follows : 

In  favor  of  a  valvular  element  in  the  first  sound,  it  may  be  urged  :  That 
if  the  ventricles  of  a  dead  heart  be  suddenly  distended  with  liquid,  the  mitral 
and  tricuspid  valves  produce  a  sound  in  closing ;  and  that  clinical  and  post- 
mortem observations  show  that  the  first  sound  may  be  altered  by  disease 
which  cripples  the  auriculo-ventricular  valves. 

In  favor  of  an  element  in  the  first  sound  caused  by  muscular  contraction 
it  may  be  urged  :  That  in  a  still  living  but  excised  heart,  the  first  sound  con- 
tinues to  be  heard  under  circumstances  which  preclude  the  closure  and  vibra- 
tion of  the  valves,  and  leave  in  operation  no  conceivable  cause  for  the  first 
sound  except  muscular  contraction.  Experiments  upon  the  first  sound  of 
the  excised  heart  were  reported  in   1868  by  Ludwig  and  Dogiel,^  and  were 

^  J.  Eouanet :  Analyse  des  bruits  du  cceur,  Paris,  1832. 

^  C.  J.  B.  Williams  :  Die.  Pathologie  und  Diagnose  der  Krankheiten  der  Brust,  etc.  Nach  der 
dritten,  sehr  vermchrten  Aiiflage  aiis  dem  Englischen  iibersetzt,  Bonn,  1838.  (The  writer  has 
not  seen  an  English  edition.)  *  Loc.  cit.  *  Loc.  cit. 

=  J.  Dogiel  and  C.  Liidwig:  "  Ein  neiier  Versuch  iiber  den  ersten  Herzton,"  Berichte  iiber 
die  Verhandlungen  der  k.  sdchsischen  Gesellsckaft  der  Wissenschaften  zu  Leipzig,  math.-physische 
Classe,  1868,  p.  89. 


412  ^^V  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

performed  upon  the  dog  as  follows:  The  heart  was  exi)osed  during  arti- 
ficial respiration,  and  loose  ligatures  were  placed  upon  the  venae  cavse,  the 
pulmonary  artery,  the  pulmonary  veins,  and  the  aorta.  Next,  the  loose 
ligatures  were  tightened  in  the  order  above  written,  during  which  process 
the  beating  heart  necessarily  pumped  itself  as  free  as  possible  of  blood. 
The  vessels  were  then  divided  distally  to  the  ligatures,  and  the  heart  was 
excised  and  suspended  in  a  conical  glass  vessel  containing  freshly  drawn  defi- 
brinated  blood,  in  which  the  heart  was  fully  immersed  without  touching  the 
glass  at  any  point.  Under  these  conditions  the  excised  heart  might  execute 
as  many  as  thirty  beats.  The  conical  glass  vessel  was  supported  in  a  "  ring- 
stand."  The  narrow  bottom  of  the  vessel  consisted  of  a  thin  sheet  of  india- 
rubber,  with  which  last  was  connected  the  flexible  tube  and  ear-piece  of  a 
stethoscope.  By  means  of  the  latter  any  sound  produced  by  the  beating 
heart  could  be  heard  through  the  blood  and  the  sheet  of  rubber.  The  second 
sound  was  not  heard  ;  but  at  each  contraction  of  the  ventricles  the  first  sound 
was  heard,  not  of  the  same  length  or  loudness  as  normally,  but  otherwise  unal- 
tered. The  conditions  of  experiment  precluded  error  resulting  from  adventi- 
tious sounds ;  moreover,  the  heart  before  excision  had  pumped  itself  free  of 
all  but  a  fraction  of  the  amount  of  blood  required  to  close  the  valves,  and 
had  been  so  treated  that  no  more  could  enter.  It  was  therefore  practically 
impossible  that  the  sound  heard  could  have  its  origin  at  the  valves ;  and  no 
origin  remained  conceivable  other  than  in  the  muscular  contraction  of  the  ven- 
tricular systole.  Later  experiments,  in  which  the  auriculo-ventricular  valves 
have  been  rendered  incompetent  by  mechanical  means,  have  seemed  to  confirm 
the  importance  of  muscular  contraction  as  a  cause  of  the  first  sound.^ 

Acoustic  Analysis  of  the  First  Sound. — By  the  use  of  a  stethoscope 
coml)ine(l  with  a  jwculiar  resonatoi-,  the  German  physician  Wintrich  of  Erlan- 
gen^  satisfied  himself  that  he  could  analyze  the  first  sound  uj)()n  auscultation, 
so  as  to  detect  in  it  two  com])onents,  one  higher  pitched,  which  he  attributed 
to  the  vibration  of  the  auriculo-ventricular  valves,  and  a  component  of  lower 
pitch,  attributed  to  the  muscular  contraction  of  the  heart.  The  other  experi- 
ments above  referred  to,  however,  which  sustain  muscular  contraction  as  a  cause 
of  the  first  sound,  did  not  reveal  a  change  of  pitch  following  incompetence 
of  the  valves,  but  only  a  diminution  in  loudness  and  duration. 

K.   The  Frequency  of  the  Cardiac  Cycles.^ 

In  a  healthy  full-grown  man,  resting  quietly  in  the  sitting  posture,  the 
heart   beats  on  the  average  about  72    times  a  minute.     In  the  full-grown 

'  L.  Krehl :  '' Ueber  den  Plerzmuskelton,"  Archiv  fur  Anntnmie  und  Physiologic,  Physiolo- 
gische  Abtheilung,  1889,  p.  253 ;  A.  Kasem-Bek  :  "  Ueber  die  Entstehung  des  ersten  Herztones," 
Pflilger's  Archiv  fiir  die  gesammte  Physiologic,  1890,  Bd.  xlvii.  p.  53. 

*  Wintrich  :  "  Experimentalstudien  iiber  Resonanzbewegungen  der  Membranen,"  <SVr2?m7.s- 
berichle  der  phys.-med.  ^ocieldt  zu  Eriangen,  1873;  Wintrich:  "Ueber  Causation  und  Analyse 
der  Herztone,"  Ibid.,  1875. 

■' Tigerstedt :  Lehrbuch  der  Physiologic  des  Kreislaufes,  Leipzig,  1893,  pp.  25-35;  Vierordt: 
Daten  und  TabeUen  zum  Oebrauchefiir  Mediciner,  1888,  pp.  105-109,  259. 


CIRCULA  TION.  413 

woman  the  average  is  slightly  higher,  perimps  80  to  the  minute.  The  heart 
beats  less  frequently  iu  tall  people  than  in  short  ones.  The  difference  between 
men  and  women  largely  depeuds  upon  this,  but  careful  observation  shows  that 
in  the  case  of  men  and  women  of  the  same  stature  the  heart-beats  are  slightlv 
more  frequent  in  the  women.  There  is,  therefore,  a  real  difference  as  to  the 
pulse  between  the  sexes.  Shortly  before  and  after  birth  the  heart-beats  are 
very  frequent,  from  120  to  140  to  the  minute.  During  childhood  and  youth, 
the  frequency  diminishes  gradually,  the  average  falling  below  100  to  the  min- 
ute at  about  the  sixth  year,  and  below  80  to  the  minute  at  about  the  eighteenth 
year.  In  extreme  old  age  the  pulse  becomes  slightly  increased  in  frequency. 
It  must,  however,  be  borne  in  mind  that  there  are  very  wide  differences 
between  individuals  as  to  the  average  frequency  of  the  heart-beats.  Pulses 
of  40  and  even  fewer  strokes  to  the  minute,  or,  on  the  other  hand,  of  more 
than  100  to  the  minute,  are  natural  to  some  healthy  people. 

In  every  individual  the  frequency  of  the  pulse  varies  decidedly,  and  may 
vary  very  greatly,  during  each  twenty-four  hours.  It  is  least  during  sleep, 
and  less  in  the  lying  than  in  the  sitting  posture.  Standing  makes  the  heart 
beat  oftener,  the  difference  being  greater  between  standing  and  sitting  than 
between  sitting  and  lying.  During  muscular  exercise  the  pulse-rate  is  much 
increased,  violent  exercise  carrying  it  possibly  to  150  or  even  more.  Thermal 
influences  have  a  marked  effect,  a  hot  bath,  for  instance,  heightening  the  fre- 
quency of  the  pulse  and  a  cold  bath  diminishing  it.  The  taking  of  a  meal 
also  commonly  puts  up  the  frequency.  The  influence  of  emotion  upon  the 
heart's  contractions  is  well  known.  It  may  act  either  to  heighten  the  rate  or 
to  lower  it.  Finally,  the  practising  physician  soon  learns  that  the  heart's 
rate  is  more  easily  affected  by  comparatively  slight  causes,  emotional  or  other- 
wise, in  women,  and  especially  in  children,  than  in  men — a  fact  of  some 
importance  in  diagnosis. 

The  causes  of  the  differences  referred  to  in  this  section  are  partly  unkuoM-n, 
and  partly  belong  to  the  subject  of  the  regulation  of  the  circulation. 

L.   The  Relations  in  Time  op  the  Main  Events  of  the  Cardiac 

Cycle. 

We  have  now  considered  the  effects  produced  by  the  cardiac  pump ;  its 
general  mode  of  working ;  and  the  actual  frequency  of  its  strokes.  We  must 
next  study  certain  important  details  relating  to  the  individual  strokes  or  beats 
of  the  ventricles  and  of  the  auricles.  For  this  study  the  basis  has  already 
been  laid  in  the  sections  headed  "  Causes  of  the  Blood-flow  "  (p.  369),  "  Mode 
of  Working  of  the  Pumping  Mechanism"  (p.  370),  ''The  Cardiac  Cycle" 
(p.  396),  and  "Use  and  Importance  of  the  Valves"  (p.  400).  These  sections 
should  now  be  read  again  in  the  order  just  given.  Details  can  best  be  dealt 
with  if  we  use,  instead  of  the  more  familiar  word  "  beat,"  the  more  technical 
one  "  cycle." 

The  Auricular  Cycle ;  the  Ventricular  Cycle ;  the  Cardiac  Cycle. — 
Each   systole  and  succeeding  diastole  of  the  auricles  constitute  a  regularly 


414  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

recurring  pair  of  events  wliicli  may  truly  be  sjiokcn  of  as  an  ''auricular 
cycle;"  and  so  also  it  is  exaet  to  say  that  the  ventricles  have  theii-  evele,  eon- 
sisting  of  systole  and  sneeeeding  diastole.  As  soon,  however,  as  we  strive  for 
clearness,  we  iind  that  the  useful  j)hrase  "cardiac  cycle"  is  necessarilv  arl)i- 
trary  and  imperfect.  A  perusal  of  the  account  given  on  p.  370  of  the  "  INIode 
of  Working  of  the  Pumping  INIeehanism  "  shows  at  once  that  each  auricular 
cycle,  consisting  of  systole  followed  by  diastole,  must  begin  shortly  before 
the  corresponding  ventricular  cycle  begins,  and  must  end  shortly  before  the 
corresponding  ventricular  cycle  ends.  The  pumping  mechanism  is  such  that 
the  auricular  systole  is  completed  just  before  the  ventricular  systole  begins. 
The  phrase  "  cardiac  cycle  "  implies  a  reference  to  both  auricular  and  ven- 
tricular events ;  if  now  we  assume  that  the  beginning  of  the  auricular  sys- 
tole marks  the  beginning  of  the  cardiac  cycle,  this  must  end  either  with  the 
end  of  the  auricular  diastole  or  with  the  end  of  the  ventricular  diastole.  In 
the  former  case  the  cardiac  cycle  would  coincide  with  the  auricular  cycle,  but 
would  begin  before  the  end  of  one  ventricular  diastole  and  would  end  before 
the  end  of  another,  thus  containing  no  one  complete  ventricular  diastole.  In 
the  second  case,  the  cardiac  cycle  would  contain  one  complete  ventricular  dias- 
tole and  a  fraction  of  another,  and  would  also  contain  two  auricular  sys- 
toles. The  second  case  is  clearly  even  more  objectionable  than  the  first.  The 
cardiac  cycle  had  best  be  defined  as  consisting  of  all  the  events  both  auricular 
and  ventricular  which  occur  during  one  complete  auricular  cycle.  The  above 
discussion  deals  with  a  phrase  which  is  a  constant  stumbling-block  to  stu- 
dents ;  and  the  question  may  well  be  asked.  Why  should  the  expression 
"cardiac  cycle"  not  be  abolished?  The  answer  is,  that  this  phrase  is  indis- 
pensable in  order  to  accentuate  certain  important  relations  of  the  auricular 
cycle  to  the  ventricular.  During  a  heart-beat  there  is  a  period  when  the 
auricles  and  ventricles  are  in  diastole  at  the  same  time.  During  this  period, 
as  we  have  seen,  blood  is  passing  from  the  veins  directly  through  the  auricles 
into  the  ventricles,  and  all  the  muscular  fibres  of  the  heart  are  resting.  This 
period  is  therefore  called  that  of  "  the  repose  of  the  whole  heart,"  or  the 
"  pause."  Whenever  the  heart  is  not  wholly  at  rest,  either  auricles  or  ven- 
tricles must  be  in  systole.  We  see,  therefore,  that  each  cardiac  cycle  must 
coincide  with  an  auricular  systole,  the  instantly  succeeding  ventricular  systole, 
and  a  period  of  repose  of  the  whole  heart ;  and  it  is  precisely  these  two 
systoles  and  the  succeeding  universal  rest  which  most  engage  the  attention 
when  the  beating  heart  is  looked  at  in  the  opened  chest.  These  three 
phenomena,  it  will  be  noted,  exactly  coincide  with  one  complete  auricular 
cycle,  and  so  do  not  confuse  the  definition  of  the  cardiac  cycle  which  has  been 
given  already.  We  see,  therefore,  that  the  phrase  which  seemed  at  first  so 
misleading  has  a  real  value,  and  will  cease  to  confuse  if  its  limitations  be  care- 
fully noted. 

The  Brevity  and  Variability  of  Each  Cycle. — From  the  frequency  with 
which  the  cycles  recur,  it  follows  at  once  that  each  one,  with  its  complex 
changes  in  the  walls,  chambers,  and  valves,  is  very  rapidly  performed.    If,  for 


CIRCULATIOX.  415 

instance,  the  heart  beat  72  times  in  one  niniute,  each  cycle  occupies  only  a 
little  more  than  0.83  of  a  second.  The  brevity  of  each  cycle  is  both  an  im- 
portant physiological  fact  and  a  cause  of  difficulty  in  studying  details,  P^ach 
cycle,  however,  necessarily  is  capable  of  completion  in  much  less  time  if  the 
pulse-rate  rise;  for  instance,  during  exercise.  If  repeated  144  times  a  minute 
instead  of  72  times,  each  cycle  would  occupy  only  one-half  of  its  previous 
time  of  completion.  With  a  pulse  of  les?  than  60,  again,  each  cycle  would 
occuj)y   over  one  second. 

Relative  Lengths  of  the  Ventricular  Systole  and  Diastole, — An  im- 
portant question  is  whether  or  no  there  is  any  fixed  relation  between  the  time 
required  for  a  systole  of  the  ventricles  and  the  time  required  for  a  diastole. 
When  the  length  of  the  cycle  changes  from  one  second  to  one-half  a  second, 
will  the  length  of  the  systole  be  diminished  by  one-half,  and  that  of  the  dias- 
tole also  by  one-half?  Or  is  a  nearly  invariable  time  required  for  the  ventri- 
cles to  do  their  work  of  ejection,  while  the  period  of  rest  and  of  receiving  blood 
can  be  greatly  shortened,  for  a  while  at  least?  The  answer  is  that,  while  both 
systole  and  diastole  may  vary  in  length,  the  length  of  the  systole  is  nnich  the 
less  variable,  while  the  diastole  is  greatly  shortened  or  lengthened  according  as 
the  heart  beats  often  or  seldom. 

These  facts  have  been  ascertained  as  follows:  A  trained  observer^  auscul- 
tated the  sounds  of  the  human  heart  during  a  number  of  cycles,  and,  at  the 
instant  when  he  heard  the  beginning  either  of  the  first  or  of  the  second  sound, 
made  a  mark  upon  the  revolving  drum  of  a  kymograph  by  means  of  a  sig- 
nalling apparatus.  Of  course,  careful  account  was  taken  of  the  time  lost 
between  the  occurrence  of  a  sound  and  the  recording  of  it.  It  was  found 
that  the  time  between  the  beginning  of  the  first  and  that  of  the  second 
sound  did  not  vary  to  the  same  degree  as  the  frequency  of  the  beats. 
Although  the  interval  in  question  may  not  be  an  exact  measure  of  the 
period  of  ventricular  systole,  it  is  sufficiently  near  it  for  the  purposes  of  this 
observation. 

A  second  method  ^  depended  upon  the  interpretation  of  the  curve  inscribed 
by  a  lever  pressed  upon  the  skin  over  a  pulsating  human  artery.  Such  a  curve 
exhibits  two  sudden  changes  of  direction,  which  were  taken  to  indicate  approxi- 
mately the  beginning  and  end  of  the  injection  of  blood  by  the  ventricle,  and, 
therefore,  to  affi3rd  a  rough  measure  of  the  duration  of  its  systole.  While  the 
interpretation  of  the  curve  in  question  is  not  wholly  settled,  it  seems,  neverthe- 
less, to  give  a  fair  basis  for  conclusions  as  to  the  present  question.  The  figures 
resulting  from  the  second  method  are  especially  instructive.  It  was  found  that, 
with  a  pulse  of  47  to  the  minute,  the  approximate  length  of  the  ventricular 
systole  was  0.347  of  a  second  ;  of  the  diastole,  0.930  of  a  second.  With  a 
pulse  of  128  to  the  minute,  while  the  systole  was  only  moderately  diminished, 

*  F.  C.  Bonders :  "  De  Rhytlimus  der  Hartstoonen,"  Nederlandsch  Archief  roor  Getiees-  en 
Naiuurkunde,  1865,  p.  141. 

2  E.  Thurston  :  "  The  Length  of  the  Systole  of  the  Heart  as  Estimated  from  Sphygmographic 
Tracings,"  Journal  of  Anatomy  and  Physiology,  1876,  vol.  x.  p.  494. 


416  AN  AMERICAN   TEXT-BOOK    OF    PHYSIOLOGY. 

viz.  to  0.256  of  a  second,  the  diastole  was  reduced  to  0.213  of  a  second — an 
enormous  decline. 

These  results  upon  the  human  subject  have  been  confirmed  upon  animals 
by  experiments  in  which  were  registered  the  movements  of  a  lever  laid  across 
the  exposed  heart; '  or  the  fluctuations  of  the  pressures  within  the  ventricles.* 

By  whatever  means  investigated,  the  ventricular  systole  is  found  to  be 
shortened  with  the  cycle,  and  to  be  lengthened  with  it;  the  diastole  is  short- 
ened or  lengthened  much  more,  however.  In  fact,  if  the  pulse  become  very 
frequent,  the  diastole  may  be  so  shortened  that  the  "pause"  nearly  disap- 
pears, and  the  systole  of  the  auricles  follows  speedily  after  the  opening  of 
the  cuspid  valves.  This  signifies  that,  for  a  time,  the  cardiac  muscle  can  do 
with  very  little  rest,  and  that  effective  means  exist  for  a  very  rapid  "charg- 
ing "  of  the  ventricular  cavity  when  necessary.  For  the  working  period  of 
the  ventricle,  however,  a  more  uniform  time  is  required.  For  the  average 
human  pulse-rate  this  time  of  work  is  decidedly  shorter  than  the  time  of 
rest — viz.  about  0.3  of  a  second  for  the  former  as  against  about  0.5  for  the 
latter. 

Lengths  of  Auricular  Events  and  of  the  Pause. — The  systole  of  the 
auricles  is  very  brief,  being  commonly  reckoned  at  about  0.1  of  a  second,  as 
the  result  of  various  observations.^  At  the  average  pulse-rate,  therefore,  the 
auricular  systole  is  only  about  one-third  as  long  as  the  ventricular,  and  the 
length  of  the  auricular  diastole  is  to  that  of  the  ventricular  as  seven  to  five. 
Consequently,  a  cardiac  cycle  of  0.8  of  a  second  would  comprise  an  auricular 
systole  of  0.1  of  a  second ;  a  ventricular  systole  of  0.3  of  a  second ;  and  a 
pause,  or  repose  of  the  whole  heart,  of  0.4  of  a  second — one-half  of  the  cycle. 

Practical  Application. — The  observations  above  described  upon  the  inter- 
val between  the  beginnings  of  the  sounds  have  a  practical  bearing  upon  physical 
diagnosis ;  for  they  show  how  faulty  are  the  statements  often  made  which 
assign  regular  proportions  to  the  lengths  of  the  sounds  and  the  silences  of  the 
heart.  The  length  of  the  "  second  silence "  must  be  very  fluctuating,  as  it 
comprises  the  longer  part  of  the  fluctuating  ventricular  diastole.  The  length 
of  the  first  sound  and  of  the  very  brief  first  silence  together  nmst  be  very  con- 
stant, as  they  nearly  coincide  with  the  ventricular  systole. 

M.    The  Pressures  within  the  Ventricles.^ 

We  nmst  now  approach  the  study  of  further  details  of  the  working  of  the 
ventricular  pumps,  which  details  depend  for  their  elucidation  upon  the  measur- 
ing and  recording  of  the  pressures  within  the  ventricles. 

^  N.  Baxt:  "Die  Verkiirzung  der  Systolenzeit  durch  den  Nervns  accelerans  cordis,"  Archiv 
fur  Anntomie  und  Phijs^iolof/ie,  Physiologisclie  Abtlieilung,  1878,  p.  122. 

*  M.  von  Frey  und  L.  Krelil:  "  Untersuchungen  iiber  den  Puis,"  ^4)t/i!'i'  fiir  Anatomie  und 
Physwlogie,  Physiologisclie  Abtheilung,  1890,  p.  31.  W.  T.  Porter:  "  Researches  on  the  Filling 
of  the  Heart,"  Journal  of  Physiology,  1892,  vol.  xiii.  p.  531. 

^  H.  Vierordt :  Daten  und  Tabellen  zum  Gebranche  fiir  Mediciner,  1888,  p.  10.5. 

*  The  matters  connected  with  the  ventricular  pressure-curve  may  best  be  studied  in  the  fol- 
lowing writings,  in   which  citations  of  other  papers  may  be  found :   K.  Hiirthle,  in  Pfliiger'a 


CIRCULA  TION.  4 1 7 

Absolute  Range  of  Pressure  within  the  Ventricles  and  its  Signifi- 
cance.— In  dealing;  with  tlic  work  done  by  the  t'ontractiiii^  ventricles  (p.  398) 
we  have  .seen  that  tlie  mereiuial  inanonietcr,  as  used  fur  studying  the  pressure 
within  the  arteries,  is  quite  unable  to  follow  the  changes  of  tlie  intra-ventric- 
ular  pressure;  but  that,  by  the  intercalation  of  a  valve,  this  instrununt  can  be 
converted  into  a  useful  "  niaxinuini  luanoineter"  for  tlie  nieasurino-  and  record- 
ing  of  the  hi^•llcst  pressure  occurring  witiiin  the  ventricle  during  a  given  time 
— that  is,  during  a  certain  number  of  cycles.  It  must  now  be  added  that  by  a 
simple  change  of  valves  this  same  instrument  can  at  any  moment  be  changed 
into  a  '*  minimum  manometer."'  We  can  thus,  by  means  of  the  modified  mer- 
curial manometer,  learn  with  fair  correctness  tlie  extreme  range  of  jircssure 
within  the  ventricles.  As  instances  of  the  extent  of  this  range,  two  observa- 
tions may  be  cited  upon  the  left  ventricle  of  the  dog,  the  chest  not  having  been 
opened.  In  one  animal  the  maximum  was  found  to  be  234  millimeters  of  mer- 
cury, the  maximum  pressure  in  the  aorta  being  212  millimeters;  and  the  min- 
imum in  the  left  ventricle  was  —38  millimeters — that  is  to  say,  38  millimeters 
less  than  the  pressure  of  the  atmosphere,  the  minimum  pressure  in  the  aorta 
being  120  millimeters.  In  a  second  doo;  the  fiofures  were  176  and  —30  milli- 
meters  for  the  ventricle,  the  aortic  range  being  from  158  to  112  millimeters.^ 
In  the  right  ventricle  of  the  dog  such  ranges  as  from  26  to  —8  millimeters, 
from  72  to  —25,  and  various  intermediate  values,  have  been  noted,  both  in 
the  unopened  and  the  opened  cbest.^  For  reasons  already  stated  (p.  395)  no 
trustworthy  figures  can  be  given  for  the  pressures  in  the  pulmonary  artery ; 
but  they  can  never  fail  to  be  less  than  the  highest  pressures  Avithin  the  right 
ventricle. 

The  range  of  pressure,  therefore,  within  either  ventricle  is  in  sharp  contrast 

Archiv  fur  die  gesammte  Physiologic,  as  follows :  "  Zur  Technik  der  Untersuchung  des  Blut- 
druckes,"  1888,  vol.  43,  p.  399.  "Technische  Miuheilungen,"  1890,  vol.  47,  p.  1.  '^Ueber 
den  Ursprungsort  der  sekundiiren  Wellen  der  Pulscnrve,"  vol.  47,  p.  17.  "  Technische  Mit- 
theilungen,"  1891,  vol.  49,  p.  29.  "  Ueber  den  Zusammenhang  zwischen  Herzthutigkeit  und 
Pulsforni,"  vol.  49,  p.  51.  "  Kritik  des  Lufttransmissionsverfahrens,"  1892,  vol.  53,  p.  281. 
"  Vergleichende  Prufiing  der  Tonographen  von  Frey's  und  Hiirthle's,"  1893,  vol.  55,  p.  319. 
K.  Hiirthle:  "Orientirungsversuche  iiber  die  Wirkung  des  Oxyspartein  auf  das  Herz,"  Archiv 
fib- experimentelle  Palholngie  unci  Phannakologie,  1892,  vol.  xxx.  p.  141.  W.  T.  Porter :  "  Researches 
on  the  Filling  of  the  Heart,"  The  Journal  of  Physiology,  1892,  vol.  xiii.  p.  513.  "  A  Kew  Method 
for  the  Study  of  the  Intracardiac  Pressure  Curve,"  Journal  of  Experimental  Medicine,  vol.  i., 
No.  2,  1896.  M.  von  Frey  und  L.  Krehl :  "  Untersuchungen  iiber  den  Puis,"  Archiv  fUr 
Anatomic  und  Physiologic,  Physiologisehe  Abtheilung,  1890,  p.  31.  M.  von  Frey:  "Die  Unter- 
suchung des  Pulses,"  Berlin,  1892.  "Das  Plateau  des  Kammerpulses,"  ^Irc^iV /«»•  Jnatornie 
und  Physiologic,  Physiologisehe  Abtheilung,  1893,  p.  1.  "  Die  Ermittlung  absoluter  Werthe  fiir 
die  Leistung  von  Piilsschreibern,"  Archiv  filr  Anaiomie  und  Physiologie,  Physiologisehe  Abtheil- 
ung, 1893,  p.  17.  "Zur  Theorie  der  Lufttonographen,"  Archiv  fiir  Anatomic  und  Physiologie, 
Physiologisehe  Abtheilung,  1893,  p.  204.  "Die  Erwarmung  der  Luft  in  Tonographen,"  Uen- 
tralblatt  fiir  Physiologie  vom  30  Juni  1894,  Heft  7. 

1  F.  Goltz  und  J.  Gaule :  "Ueber  die  Druckverhiiltnisse  im  Innern  des  Herzens,"  Pjliigei-'s 
Archiv  fiir  die  gesammte  Physiologie,  1878,  xvii.  p.  100. 

■^  S.  de  Jager :  "  Ueber  die  Saugkraft  des  Herzens,"  Pfliiger's  Archiv  fiir  die  gesammte  Physi- 
ologie, 1883,  Bd.  xxxi.  p.  491. 

'  S.  de  Jager:  Loc.  cit.,  pp.  506,  507  ;  Goltz  und  Gaule:  Loc.  cit.,  p.  106. 
27 


418 


AN  AMERICAN    TEXT- BOOK   OE   PHYSIOLOGY. 


to  that  within  tlie  artery  which  it  .suj)plios  witli  blood  ;  for  the  arterial  ])rossiire, 
although  it  fluctuates,  is  at  all  times  far  above  tiiat  of  the  atmosphere,  and  is 
able,  as  we  have  seen,  to  maintain  the  circulation  while  tlie  semilunar  valve  is 
closed  and  the  ventricular  muscle  is  at  rest.  On  the  otlier  hand,  the  pressure 
within  the  ventricle,  when  at  its  highest,  rises  decidedly  above  the  highest 
arterial  pressure,  and  thus  the  ventricle  can  overcome  this  and  other  opposing 
forces,  open  the  valve,  and  expel  the  blood.  These  facts  have  been  stated 
already.  In  falling,  however,  the  pressure  within  the  ventricle  not  only  sinks 
below  that  in  the  artery,  and  so  permits  the  semilunar  valve  to  close,  but 
sweeps  downward  to  a  point,  it  may  be,  below  the  pressure  of  the  atmos})here, 
and,  in  so  doing,  falls  below  the  pressure  in  the  auricle,  and  permits  the  open- 
ing of  the  auriculo-ventricular  valve  and  the  entrance  of  blood  out  of  the 
auricle  and  the  veins.  As  such  a  great  range  of  pressure  occurs  in  either 
ventricle  of  a  heart  which  is  repeating  its  cycles  with  entire  regularity,  it  is 
presumable  that  at  every  cycle  the  pressure  not  only  rises  above  that  in  the 
arteries  but  may  sink  below  that  of  the  atmosphere. 

Methods  of  Recording'  the  Course  of  the  Ventricular  Pressure. — It 
now  becomes  of  interest  to  ascertain,  if  possible,  not  only  the  range,  but  the 
exact  course,  of  these  swift  variations  of  pressure ;  the  causes  of  them,  and  the 
effects  which  accompany  them.  It  is  hard  to  obtain,  by  the  graphic  method,  a 
correct  curve  of  the  pressure  within  either  ventricle.  We  have  seen  that  the 
mercurial  manometer  is  useless  for  this  purpose;  and  it  is  very  difficult  to 
devise  any  self-registering  manometer  which  shall  truly  keep  pace  with  fluctu- 
ations at  once  so  great  and  so  rapid.     The  true  form  of  this  pressure-curve, 


Fir..  106.— Diapram  of  the  elastic  manometer:  A,  auricle;  V,  ventricle  ;  D,  drum  of  the  kjTnograph, 
revolving  in  the  direction  of  the  arrow,  and  covered  with  smoked  paper;  L,  recording  lever  in  contact 
with  the  revolving  drum.  (The  working  details  of  the  instrument  are  suppressed  for  the  sake  of  clear- 
ness.) 

therefore,  still  is  partially  in  doubt,  and  is  the  subject  of  controversies  which 
largely  resolve  themselves  into  contests  between  rival  instruments.  We  may 
pass  by  without  mention  methods  which  are  either  antiquated  or  little  used. 
The  following  characters  are  common  to  the  manometers  with  which  the  most 
serious  attempts  have  lately  been  made  to  obtain  a  true  and  minute  record  of 
the  fluctuations  of  pressure,  even  if  great  and  rapid,  within  the  heart  or  the 
vessels  (see  Fig.  106).     As  in  the  case  of  the  mercurial  manometer,  a  cannula, 


CIBCULA  TION.  419 

open  at  the  end  and  charged  with  a  Hiiid  which  checks  the  coagulatiou  of  the 
hlood,  is  tied  into  a  vessel,  or,  if  the  heart  is  under  observation,  is  passed  down 
into  it  through  an  opening  in  a  jugular  vein  or  a  carotid  artery.     If  the  chest 
have  been  opened,  the  cannula  may  also  be  passed  into  the  heart  through  a  small 
wound  in  an  auricle  or  even  through  the  walls  of  the  ventricle  itself     The  end 
of  the  cannula  which  remains  without  the  animal's  body  is  connected,  air-tight, 
with  a  rigid  tube  of  small,  carefully  chosen  calibre,  and  as  short  as  the  condi- 
tions of  the  experiment  permit.     The  other  end  of  this  tube  is  not,  as  in  the 
mercurial  manometer,  left  as  an  open  mouth,  but  is  connected,  air-tight,  with 
a  very  small  metallic  chamber,  which  constitutes,  practically,  a  dilated  blind 
extremity  of  the  system  formed  by  the  tube  and  the  cannula  together.     The 
roof  of  this  small  metallic  chamber  is  a  highly  elastic  disk  either  of  thin  metal 
or  of  india-rubber.     Except  for  this  small  disk,  all  parts  of  the  chamber,  tube, 
and  cannula  are  rigid.     In  the  instruments  of  some  observers,  the  entire  cavity 
of  the  system  formed  by  the  chamber,  tube,  and  cannula  is  filled  with  liquid, 
viz.  the  solution  which  checks  coagulation.     Other  observers  introduce  this 
liquid  only  into  the  portion  of  the  system  nearest  the  blood ;  the.  terminal 
chamber,  and  most  of  the  rest  of  the  system,  containing  only  air.     In  every 
case  the  blood  in  the  vessel  or  in  the  heart  is  in  free  communication,  through 
the  mouth  of  the  tied-in  cannula,  with  the  cavity  common  to  the  tubes  and 
to  the  terminal  chamber.     At  every  rise  of  blood-pressure  a  little  blood  enters 
this  cavity,  room  being  made  for  it  by  a  displacement  of  liquid  or  of  air, 
which  in  turn  causes  a  slight  bulging  of  tlie  elastic  disk.     At  every  fall  of 
blood-pressure  a  little  blood  mixed  with  liquid  leaves  the  tubes  as  the  elastic 
disk  recoils.     If  the  disk  is  of  the  right  elasticity,  its  rise  and  fall  are  directly 
proportional  to  the  rise  and  fall  of  the  blood-pressure,  and  can  be  used  to 
measure  it.     Upon  the  centre  of  the  disk  rests  a  delicate  lever  of  the  "  third 
order,"  which  rises  and  falls  with  the  disk.     The  point  of  this  lever  traces 
upon  the  revolving  drum  of  the  kymograph  a  curve  which  records  the  fluctua- 
tions of  the  disk  and  therefore  those  of  the  blood-pressure.     The  elastic  disk 
and  the  contents,  together,  of  such  an  apparatus  possess  less  inertia  than  mer- 
cury, and  therefore  follow  far  more  closely  rapid  fluctuations  of  pressure. 
Such  instruments  may  be  called  "  elastic  manometers,"  and  are  often  called 
"  tonographs,"  i.  e.  "  tension-writers."     They  are  of  several  forms. 

It  lias  been  indicated  already  that  the  pressure  of  the  blood  may  be 
communicated  to  the  disk  of  an  elastic  manometer  either  by  means  ^  of 
liquid  or  of  air.  A  given  series  of  fluctuations  of  blood-pressure  may  yield 
decidedly  different  curves  according  to  the  method  of  "  transmission  "  emploj^ed 
to  obtain  them ;  and  the  controversies  as  to  the  true  form  of  the  endocardiac 
pressure-trace  turn  upon  the  question  whether  such  "  transmission  by  air  "  or 
"  transmission  by  liquid  "  yield  the  truer  curve.  The  objections  to  the  former 
method  depend  upon  the  readier  compressibility  of  air ;  the  objections  to  trans- 
mission by  liquid  depend  upon  its  greater  inertia. 

The  General  Characters  of  the  Ventricular  Pressure-curve.— What- 
ever  kind   of  elastic    manometer  and   of  transmission   be   used,   the   curve 


420  AN  AMERICAN    TEXT-IiOOK    OF   I'll  YSJOIJJIJ  V. 

obtiiined  shows  certain  characters  which  arc  rccoirnizetl  by  all  as  properly 
belonging  to  the  changes  of  pressure  within  the  ventricle,  whether  right  or 
left.  These  general  characters,  moreover,  pei-sist  after  the  opening  of  the 
chest.     They  are  as  follows  (see  Figs.  107,  108,  109):   The  muscular  con- 

Millimeters  of 
mercury. 

Line  of  atmoHpheric 
pressure. 

Seconds. 

Fig.  107  — Matriiifii-d  curve  of  the  course  of  pressure  within  the  linht  ventricle  of  the  dog,  the  chest 
being  open  ;  to  be  read  from  left  to  right.  Recorded  by  the  elastic  manometer,  with  transmission  by  air 
(von  Frey). 

traction  of  the  systole  begins  quite  suddenly,  and  produces  a  swift  and  ex- 
tensive rise  of  pressure,  marked  in  the  curve  by  a  line  but  slightly  inclined 
from  the  vertical.  In  the  same  way  the  fall  of  pressure  is  nearly  as  sudden 
and  as  swift  as  the  rise,  and  perhaps  even  more  extensive.  The  systolic  ri.se 
begins  at  a  pressure  a  little  above  that  of  the  atmosphere ;  the  diastolic  fall 
continues,  toward  its  end,  perhaps,  with  diminishing  rapidity,  till  a  point  is 
reached  often  below  the  pressure  of  the  atmo.'^phere.  The  pressure  then 
rises,  perhaps  continuing  negative  for  a  longer  or  shorter  time,  but  presently 
becoming  equal  to  that  of  the  atmosphere.  Near  this  it  continues,  perhaps 
with  a  gentle  upward  tendency,  until,  near  the  end  of  the  ventricular  diastole, 
the  rise  becomes  more  rai)id  to  the  point  at  which  the  succeeding  ventricular 
systole  is  to  begin. 

It  is  the  course  of  the  pressure  between  its  rapid  ri.se  and  its  rapid  fall  which 
has  been  the  most  disputed.    The  ob-servers  who  employ  manometers  with  liquid 


lAne  of  atmonpheric 
pressure. 


Fig.  108.— Magnified  curve  of  the  course  of  pressure  within  the  left  ventricle  and  the  aorta  of  the 
dog,  the  chest  being  open  ;  to  be  read  from  left  to  right.  Recorded  simultaneously  by  two  elastic  man- 
ometers with  transmission  by  liquid.  In  both  curves  the  ordinates  having  the  same  numbers  have  the 
following  meaning:  1,  the  instant  preceding  the  closing  of  the  mitral  valve  ;  2,  the  opening  of  the  semi- 
lunar valve;  3,  the  beginning  of  the  "dicrotic  wave,"  regarded  as  marking  the  instant  of  closure  of  the 
semilunar  valve ;  4,  the  instant  preceding  the  opening  of  the  mitral  valve  (Porter). 

transmiasion,  have  so  far  found  that  the  high  swift  rise  at  the  outset  of  the 
systole  is  soon  succeeded  by  a  sudden  change.  According  to  them  the  pressure 
within  the  manometer  now  exhibits  fluctuations  of  greater  or  less  extent  which 


CIRCULA  TION. 


421 


arc  due,  partly  at  least,  to  tlie  inertia  of  the  trau.smitting  liquid  ;  but,  with  due 
allowaiife  made  tor  the.se,  the  cardiac  pressure  is  seeu  to  niaiutain  itself  at  a 
high  point  iliri»tigliont  most  of  the  systole  until  the  rapid  fall  Ix'gius.  During 
this  period  of  high  preasure,  the  height  about  which  the  fiuctuatious  occur  may 
remain  nearly  the  same ;  or  this  height  may  gradually  increase,  or  gradually 
decrease,  up  to  the  beginning  of  the  rapid  fall.  As  is  shown  by  Figure  108, 
this  course  of  the  systolic  pressure  causes  its  curve  to  bend  alternately  down- 
ward and  upward  between  the  end  of  its  greatest  rise  and  the  beginning  of  its 
greatest  fall  ;  but  between  these  two  points  the  general  direction  of  the  curve 
approaches  the  horizontal,  and  therefore  entitles  this  portion  of  it  to  the  name 
of  the  "systolic  plateau."  The  best  of  the  manometers  with  air-transmis- 
sion yields  a  curve  of  the  pressure  within  the  ventricle  which  presents  a 
ditfereut  picture  (Figs.  107  and  109).     The  steeply  rising  line  may  diminish 


Millimeters  of 
mercury. 


ine  of  atmospheric 
pressure. 


Tenthn  of  a  second. 


Fig.  109.— Magnified  curve  of  the  course  of  pressure  -within  the  left  ventricle  of  the  dog,  the  chest 
being  open :  to  be  read  from  left  to  right.  Recorded  by  the  elastic  manometer  with  transmission  by  air. 
The  ordinates  have  the  following  meaning:  1,  the  closure  of  the  mitral  valve ;  2,  the  opening  of  the  semi- 
lunar valve  ;  3,  the  closure  of  the  semilunar  valve ;  4,  the  opening  of  the  mitral  valve  (von  Frey). 

its  steepness  somewhat  as  it  aiscends,  but  its  rapid  turn  at  the  highest  point  of 
the  curve  is  succeeded  by  no  plateau.  The  line  simply  describes  a  single  peak, 
and  begins  the  descent  which  marks  the  rapid  fall  of  pressure  recognized  by 
all  observers.  In  these  peaked  curves  this  descent  is  often  steepest  in  its 
middle  part.  Such  a  peaked  curve  would  indicate,  of  coui-se,  that  there  is  no 
such  thing  as  the  maintenance,  during  any  large  part  of  the  systole  of  the 
ventricles,  of  a  varying  but  high  pressure.  The  experienced  observer  who  is 
the  chief  defender  of  the  peaked  curve  holds  the  plateau  to  be  a  product  either 
of  too  much  friction  within  the  manometer  tubes,  or  of  a  faulty  position  of  the 
cannula  within  the  heart,  whereby  communication  with  the  manometer  is,  for 
a  time,  cut  off.  The  able  and  more  numerous  adherents  of  the  plateau,  on  the 
other  hand,  attribute  the  failure  to  obtain  it  to  the  sluggishness  of  the  instru- 
ment employed.  Recent  comparative  tests  of  elastic  manometers,  and  other 
studies,  would  seem  to  .show  that  the  curves  obtained  by  liquid  transmission, 
and  which  exhibit  the  plateau,  afford  a  truer  picture  of  the  general  course  of  the 
pressure  within  the  ventricles  than  the  peaked  curves  written  by  means  of  air. 


422 


^.V  AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 


The  Ventricular  Pressure-curve  and  the  Auricular  Systole. — It  is 
striking  tcstimouy  to  the  siiu)othiie.<s  of  working  of  tiio  cardiac  mechanism, 
that  the  curve  of  intra-ventricular  pressure  rarely  gives  any  clear  indication  of 
the  beginning  or  end  of  the  auricular  systole.  This  event  may  be  expected  to 
increase  the  pressure  within  the  ventricles;  and,  in  the  curve,  the  verv  gentle 
rise  which  coincides  with  the  latter  and  longer  part  of  the  ventricular  diastole 
passes  into  the  .steep  ascent  of  the  commencing  ventricidar  systole  bv  a 
rounded  sweep,  which  indicates  a  more  rai)idl\-  heightened  pressure  within 
the  ventricle  during  the  auricular  systole.  ^Vs  a  rule,  no  angle  reveals  an 
instantaneous  change  of  rate  to  show  the  beginning  or  end  of  the  injection  of 
blood  by  the  contracting  auricle  (see  Figs.  107,  108,  109).  Occasionallv,  how- 
ever, a  slight  "  presystolic "  fluctuation  of  the  curve  may  seem  to  n)ark  the 
auricular  systole.' 

The  Ventricular  Pressure-curve  and  the  Valve-play. — It  is  also 
exceedingly  striking  that  no  curve,  whether  it  be  pointed  or  show  the  sys- 
tolic plateau,  gives  a  clear  indication  of  tlie  instant  of  the  closing  or  open- 
ing of  either  valve,  auriculo-ventricular  or  arterial  (see  Figs.  107,  108,  109). 
These  instants,  so  important  for  the  significance  of  the  curve,  can,  however, 
be  marked  upon  it  after  they  have  been  ascertained  indirectly.  A  method 
of  general  application  would  be  as  follows :  Two  elastic  manometers  are 
"absolutely  graduated  "  by  causing  each  of  them  to  record  a  series  of  pressures 
already  measured  by  a  mercurial  manometer.  The  two  elastic  manometers  can 
then  be  made  to  mark  upon  the  same  revolving  drum  the  simultaneous  changes 
of  pressure  in  a  ventricle  and  in  its  auricle,  or  in  a  ventricle  and  its  artery. 


Fig.  no.— Diagram  of  the  differential  manometer:  A,  artery:  T',  ventricle;  /),  drum  of  kymopraph, 
revolving  in  the  direction  of  the  arrow,  and  covered  with  smoked  paper;  /.,  recording  lever  in  contact 
with  the  revolving  drum  ;  S,  a  spring  by  which  the  movement  of  the  lever  worked  by  the  disks  is  trans- 
mitted to  the  recording  lever.  (The  working  details  of  the  instrument  are  suppressed  or  altered  for  the 
sake  of  clearness.) 

The  pressure  indicated  by  any  point  of  either  curve  can  then  be  calculated 
in  terms  of  millimeters  of  mercury.  That  point  upon  the  intra-ventricular 
curve  which  marks  a  rising  pressure  just  higher  than  the  simultaneons  pre.'^sure 
in  the  auricle  or  artery,  may  be  taken  to  mark  the  closing  of  the  cuspid  valve 
^  von  Frey  and  Krelil :   Op.  cit.,  p.  61. 


CIRCULA  TION.  42;] 

or  the  opening  of  the  seniihmar  valve,  as  the  case  may  be.  By  a  converse 
proce&s,  the  moment  of  opening  of  the  cuspid  valve,  or  of  closing  of  the  semi- 
lunar, may  also  be  ascertained.  The  practical  difficulties  in  the  way  of 
applying  this  method  to  the  ventricle  and  auricle  are  much  greater  than  to  the 
ventricle  and  artery.  By  another  application  of  the  principle  just  described,  a 
"differential  manometer"  has  been  devised  for  the  })urpose  of  registering  as  a 
single  curve  the  successive  differences,  from  moment  to  moment,  between  the 
ventricular  and  auricular  pressures,  or  the  ventricular  and  arterial  pressures 
(see  Fig.  110).  To  this  end,  two  elastic  manometers  are  fastened  immovably 
together,  and  their  two  elastic  disks,  instead  of  bearing  upon  separate  levers, 
are  made  to  bear  upon  a  single  one,  which  has  its  fulcrum  between  the  disks, 
and  is  a  lever  not  of  the  third  order,  but  of  the  first,  like  a  common  balance. 
As  the  lever  or  beam  of  the  balance  turns  from  the  horizontal  as  soon  as  the 
scales  are  pressed  upon  by  unequal  weights,  so  the  lever  of  the  differential 
manometer  turns  as  soon  as  the  disks  are  unequally  affected  by  the  pressures 
within  the  ventricle  and  the  auricle,  or  the  ventricle  and  the  artery.  As,  how- 
ever, the  pressures  upon  the  scales  are  from  above,  while  those  upon  the  disks 
are  from  below,  the  disk  which  tends  to  "  kick  the  beam  "  is  the  one  acted 
upon  by  the  greater  pressure,  instead  of  by  the  less,  as  in  the  case  of  the  scales. 
The  manometric  lever  marks  its  oscillations  as  a  curve  upon  the  kymograph 
by  the  help  of  a  second  or  "  writing  lever  "  connected  with  it.  The  persistence 
of  exactly  equal  pressures,  no  matter  what  their  absolute  value,  in  the  two 
manometers  would  cause  a  horizontal  line  to  be  drawn  by  the  writing  lever. 
This  would  serve  as  a  base-line.  The  differential  manometer  is  a  valuable 
instrument,  although  it  is  evident  that  where  such  minute  differences  of  space 
and  time  are  recorded  as  a  curve  by  such  complicated  mechanisms,  the  sources 
of  error  must  be  numerous  and  difficult  to  avoid.^ 

The  methods  which  proceed  by  the  measurement  of  differences  of  pressure 
may  sometimes  be  controlled,  or  even  replaced,  by  an  easier  method,  as  follows: 
If  two  manometers  simultaneously  record  on  the  same  kymograph  the  pressure- 
curves  of  the  ventricle  and  the  auricle,  or  of  the  ventricle  and  the  artery,  any 
very  sudden  change  of  pressure,  produced  in  auricle  or  artery  at  the  opening  or 
shutting  of  a  cardiac  valve,  wnll  produce  a  peak  or  angle  in  the  curve  of  pres- 
sure of  the  auricle  or  artery.  By  the  rules  of  the  graphic  method  the  point  in 
the  pressure-curve  of  the  ventricle  can  easily  be  found  which  was  written  at 
the  same  instant  with  the  peak  or  angle  in  the  auricular  or  arterial  curve. 
That  point  upon  the  ventricular  curve,  when  marked,  will  indicate  the  instant 
of  opening  or  shutting  of  the  valve  in  question.  In  the  pressure-curve  ob- 
tained from  the  aorta  close  to  the  heart,  there  is  a  sudden  angle  which  clearly 
marks  the  instant  when  the  opening  of  the  semilunar  valve  leads  to  the  sudden 
rise  of  pressure  which  causes  the  up-stroke  of  the  pulse  (see  Fig.  108).  Again, 
the  fluctuation  of  aortic  pressure  which  we  shall  learn  to  know  as  the  "dicrotic 
wave"  begins  at  a  moment  which  many  believe  to  follow  closely  upon  the  clos- 
ure of  the  semilunar  valve.     That  moment  may  be  indicated  by  a  notch  in  the 

'  K.  Hiirthle:  Pfluger's  Archivfiir  die  gesammte  PhysioJofjie,  1891,  vol.  49,  p.  45. 


424  A^'^  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

aortic  curve.  So,  too,  the  rise  ot"  pressure  witiiin  the  auricle  produced  by  its 
systole  may  suddenly  be  succetded  by  a  fall,  the  beginning  ot"  which  must  mark 
the  closure  of  the  cuspid  valve,  which  closure  thus  may  correspond  with  the 
apex  of  the  auricular  curve. 

In  Figure  108,  ordinate  1  indicates  the  closing,  and  ordinate  4  the  o])cn- 
iug,  of  the  mitral  valve.  These  two  points  were  found  by  help  of  the  dif- 
ferential manometer.  Ordinate  2  indicates  the  opening,  and  ordinate  3  the 
closing,  of  the  aortic  valve.  These  two  points  were  marked  with  the  help 
of  the  curve  of  aortic  pressure,  also  shown  in  Figure  108,  each  ordinate  of 
wOiich  has  the  same  number  as  the  corresponding  ordinate  of  the  ventricular 
curve.  In  the  arterial  curve,  2  marks  the  beginning  of  the  systolic  rise, 
and  3  the  beginning  oi'  the  dicrotic  wave,  which  latter  point  is  treated  by 
the  observer  as  closely  corresponding  to  the  closure  of  the  aortic  valve.  In 
Figure  109  each  ordinate  has  the  same  number,  and,  as  regards  the  valve- 
play,  the  same  significance,  as  in  Figure  108.  Ordinate  1  corresponds  to  the 
apex  of  a  peak  in  the  auricular  curve  (not  here  given)  which  represents  the 
end  of  the  auricular  systole.  Ordinate  2  corresponds  to  the  beginning  of  the 
systolic  ascent  in  the  aortic  curve  (not  here  given).  Ordinate  3  was  found 
by  comj)aring,  by  means  of  two  elastic  manometers,  the  simultaneous  pressures 
in  the  ventricle  and  the  aorta.  Ordinate  4  corresponds,  on  the  auricular 
pressure-curve,  to  a  j)oint  which  marks  the  beginning  of  a  decline  of  pres- 
sure believed  by  the  observer  to  succeed  the  opening  of  the  cuspid  valve. 
In  both  the  figures  given  of  the  ventricular  curve,  and  in  such  curves 
in  general,  the  ]K)ints  which  mark  the  valve-play  occur  as  follows:  The 
closure  of  the  cuspid  valve  corresponds  to  a  point,  not  far  above  the  line 
of  atmospheric  jiressure,  where  the  moderate  upward  sweep  of  the  ventric- 
ular curve  takes  on  the  steepness  of  the  systolic  ascent.  The  systole  of  the 
auricle  is  of  little  force,  and  the  blood  injected  by  it  into  the  distensible  ven- 
tricle raises  the  pressure  there  but  little;  that  little,  however,  is  more  than 
the  relaxing  auricle  presents,  and  the  cuspid  valve  is  closed.  Somewhere  on 
the  steep  systolic  ascent  occurs  the  point  corresponding  to  the  rise  of  the  ven- 
tricular above  the  arterial  pressure,  and  therefore  to  the  opening  of  the  semi- 
lunar valve.  But  other  forces  beside  the  arterial  ])ressure  must  be  overcome 
by  the  contracting  muscle ;  and  the  ventricular  pressure  mounts  higher  yet, 
and  either  stays  high  for  a  while,  producing  the  plateau,  or,  in  a  peaked  curve, 
at  once  descends.  In  either  case,  not  long  after  the  beginning  of  the  sharp 
descent,  the  point  occurs  at  which  the  ventricular  pressure  falls  below  the  arte- 
rial, and  the  semilunar  valve  is  closed.  Beyond  this  point  the  curve  continues 
steeply  downward,  but  it  is  not  till  a  point  is  reached  not  far  above,  or  possibly 
even  below,  the  atmospheric  pressure  that  the  pressure  in  the  ventricle  falls 
below  that  in  the  auricle,  and  the  cuspid  valve  is  o])ened. 

The  Period  of  Reception,  the  Period  of  Ejection,  and  the  Two  Periods 
of  Complete  Closure  of  the  Ventricle. — During  the  whole  of  the  jwriod 
when  the  cuspid  valve  is  open,  the  pressure  is  lower  in  the  ventricle  than  in 
the  artery;  the  arterial   valve  is  shut;    and   blood  is  entering  the  ventricle. 


CTRCULA  TION.  425 

This  may  be  o^iUed  the  ''period  of  reeeption  of  blood."  Diiiiiij;  the  greater 
part  of  tiie  ])eri<)d  when  tlie  cuspid  valve  is  sliiit,  tlie  arterial  valve  is  open  ; 
the  pressure  is  hii>:lier  in  the  ventricle  than  in  tlie  artery;  and  the  ejection 
of  blood  iVoin  the  Ibrnier  is  takint^  j)lace.  This  may  be  called  the  "period 
of  ejection,"  and  lies  in  Fi<^ures  108  and  109  between  the  ordinates  2  and 
3.  The  careful  work  which  jjas  enabled  us  to  mark  the  valve-play  upon 
the  ventricular  curve  has  demonstrated  the  interesting  fact  that  there  occur 
two  brief  j)eriods  during  each  of  which  both  valves  are  shut,  and  the  ven- 
tricle is  a  closed  cavity.  Of  these  two  periods,  one  immediately  precedes  the 
period  of  ejection,  and  the  other  immediately  follows  it.  The  first  lies,  in 
Figures  108  and  109,  between  the  ordinates  1  and  2 ;  the  second,  between  3 
and  4.  The  ex})lanation  of  these  two  periods  is  simple.  It  takes  a  brief  but 
measurable  time  for  the  cardiac  muscle,  forcibly  contracting  upon  the  impris- 
oned liquid  contents  of  the  closed  ventricle,  to  raise  the  pressure  to  the  high 
point  required  to  overcome  the  opposing  pressure  within  the  artery  and  to  open 
the  semilunar  valve.  Again,  it  takes  a  measurable  time,  probably  seldom 
quite  so  brief  as  the  period  just  discussed,  for  the  cardiac  muscle  to  relax  suffi- 
ciently to  permit  the  pressure  in  the  closed  ventricle  to  fall  to  the  low  point 
required  for  the  opening  of  the  cuspid  valve.  The  ventricular  cycle,  thus 
studied,  falls  into  four  periods:  the  first  is  a  brief  period  of  complete  closure 
with  swiftly  rising  pressure;  the  second  is  the  period  of  ejection,  relatively 
long,  and  but  little  variable ;  the  third  is  a  period  of  complete  closure,  with 
swiftly  falling  pressure;  the  fourth  is  the  period  when  the  pressure  is  low  and 
blood  is  entering  the  ventricle.  This  last  period  is  very  variable  in  length, 
but  at  the  average  pulse-rate  it  is  the  longest  period  of  all. 

Phenomena  of  the  Period  of  Reception  of  Blood. — We  have  already 
followed  the  course  of  the  pressure  within  the  ventricle  from  the  moment  of 
oj)ening  of  the  auriculo-ventricular  valve  to  that  of  its  closing  (p.  416). 
During  this  time  the  ventricle  is  receiving  its  charge  of  blood,  the  flaccidity  of 
the  wall  rendering  expansion  easy  and  keeping  the  pressure  low.  The  blood 
which  enters  first  has  been  accumulating  in  the  auricle  since  the  closing  of  the 
cuspid  valve,  and  now,  upon  the  opening  of  this,  it  both  flows  and  is  to  some 
slight  degree  drawn  into  the  ventricle.  This  blood  is  followed  by  that  which, 
during  the  remainder  of  the  "  repose  of  the  whole  heart,"  moves  through  the  veins 
and  the  aiu'icle  into  the  ventricle  under  the  influence  of  the  arterial  recoil  and 
the  other  forces  which  cause  the  venous  flow  (p.  397) ;  and  the  charge  of  the 
ventricle  is  completed  by  the  blood  wdiich  is  injected  at  the  auricular  systole. 

The  Neg-ative  Pressure  within  the  Ventricles. — That  the  heart,  in  its 
diastole,  draws  something  from  without  into  itself  is  a  very  ancient  belief,  and 
this  mode  of  its  working  played  a  great  part  in  the  doctrines  of  Galen  and  of 
the  Middle  Ages.  In  1543,  Vesalius,  who,  on  anatomical  grounds,  questioned 
some  of  Galen's  views  as  to  the  cardiac  physiology,  fully  accepted  this  one.' 

*  AndreoR  Vesalii  Bruxellensis,  Scholce  medicorum  Patavince  professoris,  de  Humani  corporis 
fabrica  Libri  steptem.  Basilese,  ex  officina  loannis  Oporini,  Anno  Salutis  reparatae  MDXLIII. 
Page  587. 


426  AiY  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

On  tlie  other  hand,  in  1628,  Harvey  rejected  it.  "It  is  manifest,"  he  says, 
"  that  the  blood  enters  the  ventricles  not  by  any  attraction  or  dilatation  of  the 
heart,  but  by  being  thrown  into  thcni  by  the  pulses  of  the  auricles." '  In  this 
particular,  modern  research  in  some  degree  confirms  the  opinion  of  the  ancients, 
while  denying  to  suction  within  the  ventricles  any  such  great  effect  as  was 
once  believed  in.  As  a  rule,  the  cuspid  valve  is  not  opened  till  the  pressure  in 
the  ventricle  has  fallen  to  a  point  not  far  from  the  pressure  of  the  atmcjsphere ; 
it  may  be  even  below  it.  In  any  case  the  ventricular  pressure  usually  becomes 
negative  very  soon  after  the  o|)ening  of  the  cuspid  valve.  This  negative  pres- 
sure is  of  variable  extent  and  continues  for  a  variable  time.  It  is  always 
small  as  compared  with  the  positive  pressure  of  the  systole.  Under 
some  circumstances  negative  pressure  may  be  absent,  but  it  is  so  very  com- 
monly present  as  certainly  to  be  a  normal  phenomenon  (see  Figs.  107, 
108,  and  109).  This  negative  pressure  is  revealed  by  the  elastic  as  well 
as  by  the  minimum  mercurial  manometer;  it  is  present  in  both  ventri- 
cles ;  and  it  is  present,  to  a  less  degree,  even  after  the  chest  has  been 
opened,  and  its  aspiration  destroyed.  It  is  in  virtue  of  the  forces  which 
produce  the  negative  pressure  in  the  manometer  that  blood  is  drawn  into 
the  heart. 

Passing  by  disproven  or  improbable  theories  as  to  the  causes  of  this  suction, 
we  shall  find  the  following  statements  justified :  As  the  heart  lies  between  the 
lungs  and  the  chest-wall  (including  in  this  term  the  diaphragm),  it  is  subject, 
like  the  chest-wall  and  the  great  vessels,  to  the  continuous  aspiration  produced 
by  the  stretched  fibres  of  the  elastic  lungs.  At  every  inspiration  this  aspiration 
is  increased  by  the  contraction  of  the  inspiratory  muscles.  We  see,  therefore, 
that  the  ventricle  must  overcome  this  aspiration  as  part  of  the  resistance  to  its 
contraction ;  and  that,  as  soon  as  that  contraction  has  ceased,  the  walls  of  the 
ventricle  must  tend  to  be  drawn  asunder  by  those  same  forces  of  elastic  recoil 
in  the  pulmonary  fibres,  and  of  contraction  of  the  muscles  of  inspiration,  which 
we  have  seen  (p.  387)  to  produce  a  slight  suction  within  the  great  veins  in  and 
very  near  the  chest.  These  same  forces  produce  a  slight  suction  within  the 
ventricles,  relaxed  in  their  diastole.  But  a  very  slight  suction  occurs  at  each 
ventricular  diastole  even  after  the  chest  has  been  opened.  The  causes  of  this 
are  still  obscure ;  but  it  is  to  be  borne  in  mind  that  the  relaxing  wall  of  the 
ventricle,  flabby  as  it  is,  possesses  some  little  elasticity,  especially  at  the  am-iculo- 
ventricular  ring,  and  therefore  may  tend  to  resume  a  somewhat  different  form 
from  that  due  to  its  contraction.  As  the  result  of  this  slight  elastic  recoil,  a 
feeble  suction  may  occur. 

N.  The  Functions  of  the  Auricles. 

Connections  of  the  Auricle. — Into  the  right  and  left  auricles  open  the 
systemic  and  pulmonary  veins  respectively,  and  each  auricle  may  justly  be  re- 
garded as  the  enlarged  termination  of  that  venous  system  with  which  it  is  con- 
nected.    Until  modern  times  the  terms  of  anatomy  reflected  this  view,  and 
'  Op.  ciL,  1628,  p.  26:  Willis's  translation,  Bowie's  edition,  1889,  p.  28. 


CIRCULATION.  427 

from  the  ancient  Greeks  to  a  time  later  tlian  Harvey,  the  word  "  heart "  com- 
monly meant  the  ventricles  only,  as  it  still  does  in  the  language  of  the 
slaughter-house.  This  termination  of  the  venous  system,  the  auricle,  com- 
municates directly  with  the  ventricle,  at  the  auriculo-ventricular  ring,  by  an 
aperture  so  wide  that,  when  the  cuspid  valve  is  freely  open,  auricle  and  ven- 
tricle together  seem  to  form  but  a  single  chamber. 

The  Auricle  a  Feeble  Force-pump  ;  the  Pressure  of  its  Systole. — The 
wall  of  the  auricle  is  thin  and  distensible;  it  is  also  muscular  and  contractile. 
But  the  slightest  inspection  of  the  dead  heart  shows  how  little  force  can  be 
exerted  by  the  contraction  of  so  thin  a  sheet  of  muscle.  In  the  wall  of  the 
appendix,  however,  the  muscular  structure  is  more  vigorously  developed  than 
over  the  rest  of  the  auricle.  The  auricle,  then,  should  be  a  very  feeble  force- 
pump  ;  and  such  in  fact,  it  is ;  for  the  highest  pressure  scarcely  rises  above  20 
millimeters  of  mercury  in  the  right  auricle  of  the  dog,'  and  an  auricular  sys- 
tole often  produces  a  pressure  of  only  5  or  10  millimeters.^  This  would  be 
but  a  small  fraction  of  the  maximum  ventricular  pressure  of  the  same  heart. 
The  auricle,  however,  is  equal  to  its  work  of  completing  the  filling  of  the 
ventricle;  and  the  feebleness  of  the  auricle  will  not  surprise  us  when  we 
consider  that,  at  the  beginning  of  its  systole,  the  pressure  exerted  by  the 
contents  of  the  relaxed  ventricle  is  but  little  above  that  of  the  atmosphere, 
and  offers  small  resistance  to  the  injection  of  an  additional  quantitv  of 
blood. 

The  systole  of  the  auricles  is  so  conspicuous  a  part  of  the  cardiac  cycle  when 
the  beating  heart  is  looked  at,  that  its  necessity  is  easily  overrated.  Even  Har- 
vey, in  attacking  the  errors  of  his  day,  was  led  by  imperfect  methods  to  estimate 
too  highly  the  work  of  the  auricular  systole  (see  p.  426).  The  error,  although 
a  gross  one,  is  not  rare,  of  considering  the  systole  of  the  auricles  to  be  as  im- 
portant for  the  charging  of  the  ventricles  as  the  systole  of  the  ventricles  is  for 
the  charging  of  the  arteries.  On  page  390  the  proof  has  already  been  given 
that  the  work  of  the  heart  may  entirely  suffice  to  maintain  the  circulation  with- 
out aid  from  any  subsidiary  source  of  energy.  It  must  now  be  added  that  the 
ventricles  can,  for  a  time,  maintain  the  circulation  without  the  aid  of  the  auric- 
ular systole — a  clear  proof  that  this  systole  is  not  a  sine  qua  non  for  the 
working  of  the  cardiac  pump. 

If  in  an  animal,  not  only  anaesthetized  but  so  drugged  that  all  its  skeletal 
muscles  are  paralyzed,  artificial  respiration  be  established  and  the  chest  be 
opened,  the  circulation  continues.  If  the  artificial  respiration  be  suspended 
for  a  time,  the  lungs  collapse,  asphyxia  begins,  and  the  blood  accumulates 
conspicuously  in  the  veins  and  in  the  heart.  Presently  the  muscular  walls 
of  the  auricles  may  become  paralyzed  by  overdistention,  and  their  systoles 
may  cease,  while  the  ventricles  continue  at  work  and  may  maintain  a  circu- 
lation, although  of  course  an  abnormal  one.  After  the  renewal  of  artificial 
respiration,  it  may  not  be  till  several  beats  of  the  ventricles  have  succeeded, 

^  Goltz  und  Gaule :  op.  cif.,  p.  106. 

*  W.  T.  Porter  :  op.  cit.,  p.  533.     S.  de  Jager :  op.  cit.,  p.  506. 


428  AN  AMERICAX   TEXT-BOOK   OF   PTTYSIOLOGY. 

without  help  iroin  the  auricles,  in  iinlctadiiijjj  the  latter  and  the  \-eiiis,  that  the 
auricles  recouHueiice  their  beats.' 

On  the  other  hand,  it  is  clear  that  the  auricle  is  not  without  importance  as 
a  t()rce-j)ump  for  conipletini;  the  tilling-  of  the  ventricle,  even  if  it  can  be  dis- 
pensetl  with  for  a  time.  In  curves  of  the  blood-pressure  during  as])hy.\ia  taken 
sinndtaneously  from  the  auricle  and  the  ventricle,  there  may  be  noted  the  influ- 
ence exerted  upon  the  ventricular  curve  by  ineffectiveness  of  the  auricular  sys- 
tole. It  is  found  that,  in  this  case,  that  slight  but  accelerated  rise  of  pressure 
may  fail  which  normally  just  precedes,  and  merges  itself  in,  the  large  swift  rise 
of  the  ventricular  systole.  It  is  found,  too,  that,  under  these  circumstances, 
the  total  height  of  this  systolic  rise  may  be  diminished.^  We  shall  see  pres- 
ently how,  when  the  pulse  becomes  very  frequent,  the  importance  of  the  auric- 
ular systole  may  be  increased.  We  have  seen  already  (p.  424)  that  normally  it 
may  probably  effect  the  closure  of  the  cuspid  valves. 

Time-relations  of  the  Auricular  Systole  and  Diastole. — The  auricular 
systole  is  not  only  weak,  but  brief,  being  commonly  reckoned  at  about  U.l  of  a 
second  (see  p.  416).  If  this  be  correct  for  man,  at  the  average  pulse-rate  of 
72  the  auricular  systole  would  comprise  only  about  one-eighth  of  the  cycle; 
would  be  only  one-seventh  as  long  as  the  auricular  diastole ;  and  only  about 
one-third  as  long  as  the  ventricular  systole  which  immediately  follows  that  of 
the  auricle. 

The  Auricle  a  Mechanism  for  Facilitating  the  Venous  Flow  and 
for  the  "  Quick-charging  "  of  the  Ventricle. — Further  points  in  regard  to 
the  systole  of  the  auricles  can  best  be  treated  of  incidentally  to  the  general 
question,  AVhat  is  the  princi])al  use  of  this  portion  of  the  heart?  The  answer 
is  not  so  obvious  as  in  the  ease  of  the  ventricles.  It  may,  however,  be  stated 
as  follows :  The  auricle  is  a  reservoir,  lying  at  the  very  door  of  the  ventricle. 
That  door,  the  cuspid  valve,  remains  shut  during  the  relatively  long  and  un- 
varying period  of  the  ventricular  systole  and  the  brief  succeeding  period  of  fall- 
ing pressure  within  the  ventricle.  These  periods  coincide  with  the  earlier  part 
of  the  auricular  diastole.  During  all  this  time  the  forces  which  cause  the 
venous  flow  are  delivering  blood  into  the  flaccid  and  distensible  reservoir  of 
the  auricle,  and  can  thus  maintain  a  continuous  flow.  But  the  blood  of  which 
the  veins  are  thus  relieved  during  the  period  of  closure  of  the  cuspid  valve, 
accumulates  just  above  that  valve  to  await  its  opening.  When  it  is  opened 
by  the  superior  auricular  pressure,  the  stored-up  blood  both  flows  and  is  drawn 
into  the  ventricle  promptly  from  the  adjoining  reservoir.  From  this  time 
on,  auricle  and  ventricle  together  are  converted  into  a  common  storehouse  for 
the  returning  blood  during  the  remainder  of  the  repose  of  the  whole  heart, 
which  coincides  with  the  later  portion  of  the  long  auricular  diastole.  The 
next  auricular  systole  completes  the  charging  of  the  ventricle  ;  and  a  second 
use  of  this  systole  now  becomes  apparent,  for  the  sudden  transfer  by  it  of 
blood  from  auricle  to  ventricle  not  only  completes  the  filling  of  the  latter,  but 

'  von  Frey  iind  Krehl :  op.  cit.,  pp.  49,  59.  G.  Colin:  Traile  de  physiologie  comparee  den  ani- 
maux,  Paris.  1S88,  vol.  ii.  p.  424.  *  von  Frey  und  Krehl :  op.  ci(.,  p.  59. 


CIRCULA  TION.  429 

lessens  the  contents  of  the  anriele,  jukI  so  jjicpjires  it  to  act  as  a  storehouse 
duriii«:^  tlie  coniinir  systole  of  the  ventricle.  The  auricle,  then,  is  an  apparatus 
for  the  niuinteiiance  of  as  even  a  flow  as  possible  in  the  veins  and  for  the  ra})id 
and  thorough  charging  of  the  ventricle.  It  is  clear  that,  for  both  uses,  the 
auricle's  fiuiction  as  a  reservoir  is  certainly  no  less  important  than  its  function 
as  a  force-pump. 

The  value  of  a  mechanism  for  the  rapid  filling  of  the  ventricle  increases 
with  the  pulse-rate,  and  with  a  very  frequent  pulse  must  be  of  great  imj)ort- 
ance,  because  now  time  must  be  saved  at  the  exj)ense  of  the  pause,  with  its 
quiet  flow  of  blood  through  the  auricle  into  the  ventricle ;  and  the  auricular 
systole  nmst  follow  more  promptly  than  before  upon  the  opening  of  the  cus- 
pid valve.  If  the  pulse  double  in  frequency,  each  cardiac  cycle  must  be  com- 
pleted in  one-half  the  former  time;  but  we  have  seen  that  the  ventricle 
requires  for  its  systole  a  time  which  cannot  be  shortened  with  the  cycle  to  the 
same  degree  as  can  its  diastole.  Of  heightened  value  now  to  the  ventricle 
will  be  the  adjoining  reservoir,  which  is  filling  while  the  cuspid  valve  remains 
closed,  and  from  which,  as  soon  as  that  valve  is  opened,  the  necessary  supply 
not  only  flows,  but  is  sucked  and  pumped  into  the  ventricle,  for,  when  increased 
demands  are  made  upon  the  heart,  the  usefulness  of  an  increased  frequency  of 
beat  disappears  if  the  volume  transferred  at  each  beat  from  veins  to  arteries 
diminish  in  the  same  proportion  as  the  frequency  increases.  No  increase  of 
the  capillary  stream  can  then  follow  the  more  frequent  strokes  of  the  pump.^ 

Negative  Pressure  •within  the  Auricle  ;  its  Probable  Usefulness. — The 
course  of  the  pressure-curve  of  the  auricle,  as  shown  by  the  elastic  manome- 
ter, is  too  complex  and  variable,  and  its  details  are  too  much  disputed,  for  it 
to  be  given  here.  But  certain  facts  regarding  the  auricular  pressure  are  of 
much  interest  in  connection  with  the  use  of  the  auricle  which  has  just  been 
discussed.  Once,  and  perhaps  oftener,  in  each  cycle,  the  pressure  in  the  auricle 
may  become  negative,  perhaps  to  the  degree  of  from  —2  to  —10  millimeters  of 
mercury  even  in  the  open  chest,^  and  of  course  becomes  still  more  so  when 
the  latter  is  intact,  sinking  in  this  case  to  perhaps— 11.2  millimeters.^  What 
is  striking  in  connection  with  the  "  quick-charging  "  of  the  ventricle  is  that 
the  greatest  and  longest  negative  pressure  in  the  aiu-icle  coincides,  as  we  should 
expect,  with  the  earlier  part  of  its  diastole,  and  therefore  with  the  systole  of 
the  ventricle,  when  the  auricle  is  cut  off  from  it  by  the  shut  valve.*  By 
this  suction  within  the  auricle  the  flow  from  the  veins  into  it  probably  is 
heightened,  and  the  store  of  blood  increased  which  accumulates  in  the  reservoir 
to  await  the  opening  of  the  valve.  The  quick-charging  mechanism  itself'  is 
quickly  charged.  Nor  should  it  be  forgotten  that  the  work  of  the  ventricle 
contributes  in  some  degree  to  this  suction  within  the  auricle.  The  heart  is 
air-tight  in  the  chest,  which  is  a  more  or  less  rigid  case.     At  each  ventricular 

*  von  Frey  un<l  Krehl :  op.  cit.,  p.  61. 

^  de  Jager  :  op.  cit.,  p.  507.     W.  T.  Porter :  op.  cit.,  p.  533. 

*  Goltz  und  Gaiile:  op.  cit.,  p.  109. 

*  von  Frey  und  Krehl,  op.  cit.,  p.  53.     Porter,  op.  cit.,  p.  523. 


430  ^liV  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

systole  the  heart  pumps  some  blood  out  of  tiiis  case,  and  shrinks  as  it  does  so, 
thus  tending  to  produce  a  vacuum;  in  other  words,  to  increase  tiie  amount  of 
negative  pressure  within  the  chest,  and  thus  help  to  expand  the  swelling  auri- 
cles. Therefore  for  the  suction  which  helps  to  charge  the  auricles  during  the 
systole  of  the  ventricles,  that  systole  itself  is  partly  resj)ousible.' 

Is  the  Auricle  Emptied  by  its  Systole  ? — Authorities  differ  still  as  to  the 
extent  to  which  the  auricle  is  emptied  by  its  systole;  some  holding  the  scarcely 
probable  view  that,  during  this  time,  its  contents  are  all,  or  nearly  all,  trans- 
ferred to  the  ventricle ;  ^  and  others  taking  tlie  widely  different  view  that  the 
auricle  actually  continues  to  receive  blood  during  its  systole,  which  latter  simply 
increases  the  discharge  into  the  ventricle.  According  to  this  latter  opinion  the 
flow  from  the  great  veins  into  the  auricle  is  absolutely  unbroken.^  All  are 
agreed  however,  that  the  auricular  appendix  is  the  raost  completely  emptied 
portion  of  the  chamber. 

Are  the  Venous  Openings  into  the  Auricle  closed  during  its  Systole  ? 
If  not,  does  Blood  then  regurgitate,  or  enter  ? — As  to  these  questions  dif- 
ferences of  opinion  are  possible,  because  at  the  openings  of  the  veins  into  the 
auricle  no  valves  exist  which  are  effective  in  the  adult,  except  at  the  mouth  of 
the  coronary  sinus.  It  Ls  therefore  a  question,  what  happens  at  the  mouths  of 
the  veins  during  the  auricular  systole.  These  mouths  are  surrounded  by  rings 
composed  of  the  muscular  fibres  of  the  auricular  wall ;  and  for  some  distance 
from  the  heart  the  walls  of  some  of  the  great  veins  are  rich  in  circular  fibres 
of  muscle.  We  have  seen  already  (p.  407)  that  a  rhythmic  contraction  of  the 
vense  cavae  and  pulmonary  veins  occurs  just  before  the  systole  of  the  auricles 
and  must  accelerate  the  flow  into  the  latter.  Their  swiftly  following  systole  is 
known  to  begin  at  the  mouths  of  the  great  veins  and  from  these  to  spread  over 
the  rest  of  each  auricle.  It  is  evident  at  once  that  the  circular  fibres  must 
either  narrow  or  obliterate,  like  sphincters,  the  mouths  of  the  veins  at  the  out- 
set of  the  systole,  and  that  these  fibres  thus  take  the  place  of  valves.  If  the 
closure  be  complete,  all  the  blood  ejected  by  the  systole  must  enter  the  ventricle, 
and  a  momentary  standstill  of  blood  and  rise  of  pressure  in  the  veins  just  with- 
out the  auricle  must  accompany  its  brief  systole.  A  recent  observer  believes 
the  flow  into  the  auricle  to  be  interrupte<l  even  more  than  once  during  its  cycle.* 
If  the  venous  openings  be  not  closed  but  only  narrowed  during  the  systole 
of  the  auricles,  the  transfer  of  all  or  most  of  the  ejected  blood  to  the  ventricle 
must  depend  upon  the  pressure  being  lower  therein  than  at  the  venous  openings. 
A  slight  regurgitation  into  the  veins  would,  like  the  complete  closing  of  their 
mouths,  cause  a  momentary  checking  of  their  blood-flow  just  without  the  auri- 
cle, and  a  slight  rise  of  pressure.     Such  a  checking  of  the  flow  has  in  some 

'  A.  Mosso:  Die  Diar/nostik  des  Pulses,  etc.  Zweiter  Theil  :  Ueber  den  negativen  Puis, 
p.  42. 

"^  M.  Foster:  A  Text-book  of  PhysloJorpj,  New  York,  1895,  p.  182. 

'  Skoda :  "  Ueber  die  Function  der  Vorkammern  des  Herzens,"  Sitzungsben'chte  der  mnthem.- 
natw-w.  Classe  der  kais.  Akademie  der  Wissenschaften  in  Wien,  1852,  vol.  ix.  p.  788.  L.  Her- 
mann :  Lehrbuch  der  Physiologic,  1892,  p.  66.  *  W.  T.  Porter:  Op.  cit.,  p.  534. 


CIRCULATION.  431 

cases  been  observed  and  ascribed  to  regurgitation.'  A  systolic  narrowing  with- 
out closure  of  the  venous  mouths  would  leave  room  also  for  the  view  already 
given,  that  so  far  is  regurgitation  from  taking  place,  that  even  during  the  sys- 
tole of  the  auricles  blood  enters  them  incessantly,  and  the  venous  flow  is  never 
checked.  In  this  case  the  systole  of  the  auricle  would  still  empty  it  partially 
into  the  ventricle,  owing  to  the  lowness  of  the  pressure  there. 

The  time  has  not  arrived  for  a  decision  as  to  all  these  questions,  which  are 
surrounded  by  practical  difficulties ;  but  fortunately  they  do  not  throw  doubt 
upon  the  functions  of  the  auricle  as  a  reservoir  and  pump  which  may  be 
swiftly  filled,  and  may  swiftly  complete  the  filling  of  the  ventricle  which  it 
adjoins. 

O.  The  Arterial  Pulse. 

Nature  and  Importance. — The  expression  "  arterial  pulse  "  is  restricted 
commonly  to  those  incessant  fluctuations  of  the  arterial  pressure  which  corre- 
spond with  the  incessant  beatings  of  the  ventricles  of  the  heart.  These  rhyth- 
mic fluctuations  of  the  arterial  pressure  have  been  explained  already  (p.  385) 
to  depend  upon  the  rhythmic  intermittent  injections  of  blood  from  the  ven- 
tricles ;  upon  the  resistance  to  these  injections  produced  by  the  friction  within 
the  blood-vessels ;  and  upon  the  elasticity  of  the  arterial  walls.  It  has  also 
been  explained  that  the  interaction  of  these  three  factors  is  such  that  the  blood, 
in  traversing  the  capillaries,  comes  to  exert  a  continuous  pressure,  free  from 
rhythmic  fluctuations ;  in  other  words,  that  the  pulse  undergoes  extinction  at 
the  confines  of  the  arterial  system.  It  is  at  once  a])parent  that  the  pulse  may 
be  affected  by  an  abnormal  change,  either  in  the  heart's  beat,  in  the  elas- 
ticity of  the  arteries,  or  in  the  peripheral  resistance,  or  by  a  combination 
of  such  changes ;  and  that,  therefore,  the  characters  of  the  pulse  possess 
an  importance  in  medical  diagnosis  which  justifies  a  brief  further  discus- 
sion of  them. 

A  pulsating-  artery  not  only  expands,  but  is  lengthened.  The  sudden 
increase  in  the  contents  of  an  artery  which  causes  the  pulse  therein,  is  accom- 
modated not  merely  by  the  increase  of  calibre  which  produces  the  "  up-stroke  " 
of  the  arterial  wall  against  the  finger,  but  also  by  an  increase  in  the  length 
of  the  elastic  vessel.  If  the  artery  be  sinuous  in  its  course,  this  increase  in 
length  suddenly  exaggerates  the  curves  of  the  vessel,  and  thus  produces  a 
slight  wriggling  movement.  This  is  sometimes  very  clearly  visible  in  the 
temporal  arteries  of  emaciated  persons.  On  the  other  hand,  the  increase  in 
the  calibre  of  the  artery  is  relatively  so  slight  that  it  is  invisible  at  the  profile 
even  of  a  large  artery,  dissected  clean  for  a  short  distance  for  the  purpose  of 
tying  it.  Such  a  vessel  appears  pulseless  to  the  eye,  although  its  pulse  is 
easily  felt  by  the  finger,  which  slightly  flattens  the  artery  and  thus  gains  a 
larger  surface  of  contact. 

Transmission  of  the  Pulse. — If  an  observer  feel  his  own  pulse,  placing 

'  Franfois-Franck :  "  Variations  de  la  vitesse  du  sang  dans  les  veines  sous  I'influence 
de  la  systole  de  I'oreillette  droite,"  Archives  de  physiologie  normale  et  pathologique,  1890,  p.  347. 


432  AN  AMERICAN    TEXT- BOOK'    OF   PIIYSIOLOaV. 

the  Hnger  ot"  one  hand  iijxni  the  (•(Uiiiiiuii  carotid  aftci'v,  and  that  oi"  the  other 
upon  tlie  dorsal  artery  of'tlie  ibot  at  \\\v  instep,  he  will  pei-ccivc  that  the  pulse 
corresponding  to  a  given  heart-heat  ocrurs  later  in  the  loot  than  in  the  neck. 
This  phenomenon  is  readily  comprehended  by  considering  that  room  for  the 
"  pidse-vohime  "  injected  by  the  heart  is  made  in  the  root  of  the  arterial  system 
both  by  local  expansion  and  by  a  more  rapid  displacement  of  blood  into  the 
Dext  arterial  segment.  This  next  segment,  in  turn,  acc(.)mmo(lates  its  increased 
charge  by  local  ex})ansion  and  by  a  more  rapid  disj)lacement  ;  and  this  same 
process  involves  segment  after  segment  in  succession,  onward  toward  the 
capillaries.  The  expansion  of  the  arterial  system,  then,  is  a  progressive  one, 
and,  as  the  phrase  is,  spreads  as  a  wave  from  the  aorta  onward  to  the  arteri- 
oles. The  rate  of  transmission  of  the  "  pulse- wave "  from  a  point  near  the 
heart  to  one  remote  from  it,  may  be  calculated.  This  is  done  by  comparing 
the  time  which  elapses  between  the  occurrence  of  the  up-stroke  of  the  pulse 
in  the  Dearer  and  in  the  farther  artery  with  the  distance  along  the  arterial 
system  which  separates  the  two  points  of  observation.  In  one  case,  for  exam- 
ple, that  of  an  adult,  the  absolute  amount  (if  the  postponement  of  the  pulse — 
that  is,  the  time  required  for  the  transmission  of  the  pulse-wave  from  the 
heart  itself  to  the  arteria  dorsalis  pedis,  w^as  0.193  second.^  The  time  of 
transmission  of  the  pulse-wave  from  the  heart  to  the  dorsa/is  pedis  is  often 
longer  than  in  this  case,  amounting  to  0.2  second  or  a  little  more.  If  we 
reckon  the  duration  of  the  ventricular  systole  at  about  0.3  second,  it  is  evi- 
dent that  the  fact  of  the  postponement  of  the  pulse  in  the  arteries  distant  from 
the  heart  does  not  invalidate  the  general  statement  that  the  arterial  pulse  is 
synchronous  with  the  systole  of  the  ventricles. 

The  general  estimates  of  the  rate,  as  opposed  to  the  absolute  time,  of  trans- 
mission of  the  pulse-wave  vary,  in  different  cases,  from  more  than  3  meters 
to  more  than  9  meters  per  second.  As  the  blood  in  the  arteries  does  not  pass 
onward  at  a  swifter  rate  than  about  0.5  meter  per  second,  it  is  clear  that  the 
wave  of  expansion  moves  along  the  artery  many  times  faster  than- the  l)h>od 
does ;  and  that  to  confound  the  travelling  of  the  wave  with  the  travelling  of 
the  blood  would  be  a  very  serious  error,  easily  avoided  by  bearing  in  mind 
the  causes  of  the  pulse-wave  as  already  given. 

Investigation  by  the  Finger. — The  feeling  of  tiie  pulse  has  been  a  valu- 
able and  constantly  used  means  of  diagnosis  since  ancient  times.  Indeed,  the 
ancient  medicine  attached  to  it  more  importance  than  does  the  practice  of 
to-day.  But  it  is  still  advisable  to  warn  the  beginner  that  he  may  not  look 
to  the  pulse  for  "pathognomonic"  information  ;  that  is  to  say,  he  may  not 
expect  to  diagnosticate  a  disease  solely  by  touching  an  artery  of  the  patient 
under  examination.  The  ])ulse  is  most  commonly  felt  in  the  radial  artery, 
which  is  convenient,  superficial,  and  well  supported  against  an  examining 
finger  by  the  underlying  bone.  Many  other  arteries,  however,  may  be  util- 
ized. 

Frequency  and.  Regularity. — The  most  conspicuous  qualities  of  the  pulse 
'  J.  X.  Czermak  :  Gesammelte  Schriften,  1879,  Bd.  i.  Abth.  2,  p.  711. 


CIRCULA  TION.  433 

are  frequency  and  rea;ularity.  Usually  these  can  he  appreciated  not  merely  hy 
a  physician  hut  hy  any  intellii^ent  person.  'J'he  j)liysi()logical  variations  in 
tiie  frequency  of  the  heart's  heats  liave  heeu  referred  to  already  (p.  412).  In 
an  intermittent  pulse  the  rhythm  is  usually  ret^ular,  hut,  at  longer  or  shorter 
intervals,  the  ventricle  omits  a  systole,  and  therefore,  the  pulse  omits  an  up- 
stroke. Either  intermittence  or  irregularity  of  the  cartliac  IJeats  may  he 
caused  hy  transient  disorder  as  well  as  hy  serious  disease. 

Tension. — When  unusual  force  is  required  in  order  to  extinguish  the  ])ulse 
hy  compressing  the  artery  against  the  hone,  the  arterial  Avail,  and  hence  the 
pulse,  is  said  to  possess  high  tension,  or  the  pulse  is  called  incompressible,  or 
hard.  Conversely,  the  pulse  is  said  to  he  of  low  tension,  compressible,  or  soft, 
when  its  obliteration  is  unusually  easy.  A  very  hard  pulse  is  sometimes  called 
"wiry;"  a  very  soft  one,  "gaseous."  High  tension,  hardness,  incompressibil- 
ity,  obviously  are  directly  indicative  of  a  high  blood-pressure  in  the  artery ; 
and  the  converse  qualities  of  a  low  pressure.  It  follows  from  what  has  gone 
before  that  the  causes  of  changes  in  the  arterial  pressure,  and  hence  in  the 
tension,  may  be  found  in  changes  either  in  the  heart's  action,  or  in  the  periph- 
eral resistance,  or,  as  is  very  common,  in  both.  An  instrument  called  the 
sphygmomanometer^  is  sometimes  ap])lied  to  the  skin  over  an  artery,  in  order 
to  obtain  a  better  measurement  of  its  hardness  or  softness  than  the  finger  can 
make.     This  instrument  is  not  free  from  sources  of  error. 

Size. — When  the  artery  is  unusually  increased  in  calibre  at  each  up-stroke 
of  the  pulse,  the  pulse  is  said  to  be  large.  When,  at  the  up-stroke,  the  calibre 
changes  but  little,  the  pulse  is  said  to  be  small.  A  very  large  pulse  is  some- 
times called  "bounding;"  a  very  small  one,  "  thready."  Largeness  of  the 
pulse  must  be  distinguished  carefully  from  largeness  of  the  artery.  The  for- 
mer phrase  means  that  the  fluctuating  part  of  the  arterial  pressure  is  large 
in  pro])ortion  to  the  mean  pressure.  But  if  the  mean  pressure  be  great 
while  the  fluctuating  part  of  the  pressure  is  relatively  small,  the  artery,  even 
at  the  end  of  the  down-stroke,  will  be  of  large  calibre,  while  the  pulse  will 
be  small. 

It  has  been  seen  that  the  increased  charge  of  blood  which  an  artery  receives 
at  the  ventricular  systole  is  accommodated  partly  by  increased  displacement  of 
blood  toward  the  capillaries,  and  partly  by  that  increase  in  the  capacity  of  the 
artery  which  is  accompanied  by  the  up-stroke  of  the  pulse.  The  less  the  con- 
tents of  the  artery  the  less  is  the  arterial  pressure,  the  less  the  tension  of  the 
wall,  and  the  more  yielding  is  that  wall.  The  more  yielding  the  wall,  the  more 
of  the  increased  charge  of  blood  does  the  artery  accommodate  by  an  increase  of 
capacity  and  the  less  by  an  increase  of  displacement.  Therefore,  a  large  pulse 
often  accompanies  a  low  mean  pressure  in  the  arteries,  and  hence  may  appear 
as  a  symptom  after  large  losses  of  blood.  In  former  days,  when  bloodletting 
was  practised  as  a  remedial  measure,  imperfect  knowledge  of  the  mechanics 
of  the  circulation  sometimes  caused  life  to  be  endangered  ;  for  a  "throbbing" 
pulse  in  a  patient  who  had  been  bled  already  was  liable  to  be  taken  as  an  "  in- 

'  From  (7(pvy/u6c,  pulse. 
28 


434  AX  AMERICAN    TEXT-BOOK   OE  PHYSIOLOGY. 

dicatioii  "  lor  the  letting  of  more  blood,  i'i  this  were  done,  an  eflot-t  was 
combated   l>y  repeatiniT  its  cause.' 

Celerity  of  Stroke. — When  each  iip-stroke  of  the  pulse  appears  to  be 
slowly  accomplished,  requiring  a  relatively  long  interval  of  tinif,  the  pulse 
is  called  slow,  or  long.  When  each  up-stroke  ap|)ears  to  be  (piickly  accom- 
plished, requiring  a  relatively  short  time,  the  pulse  is  called  (juiek  or  short. 
These  contrasted  qualities  are  among  the  mo.st  obscure  of  those  which  the 
skilled  touch  is  called  upon  to  appreciate. 

The  Pulse-trace. — The  rise  and  fall  of  a  j)ulsating  human  artery,  if  near 
enough  to  the  skin,  may  be  made  to  raise  and  lower  the  recording  lever  of  a 
somewhat  complicated  instrument  called  a  sphygmograph.-  Of  this  instru- 
ment a  number  of  varieties  are  in  use.  If  the  fine  point  of  the  lever  be  kept 
in  contact  with  a  piece  of  smoked  paper  which  is  in  uniform  motion,  a  "pulse- 
trace  "  or  "  i)ulse-curve "  is  inscribed,  which  shows  successive  fluctuations, 
larger  and  smaller,  which  tend  to  be  rhythmically  repeated,  and  Nvhich  depend 
upon  tlie  movements  of  the  arterial  wall  produced  by  the  fluctuations  of  blood- 
pressure.  In  an  animal,  a  manometer  may  be  connected  with  the  interi(jr  of 
an  artery,  and  thus  the  fluctuations  of  the  blood-pressure  may  be  observed 
more  directly.  It  has  been  explained  (p.  382)  that  the  mercurial  manometer 
is  of  no  value  for  the  study  of  the  finer  characters  of  the  pulse,  owing  to 
the  inertia  of  the  mercury.  On  the  other  hand,  the  best  forms  of  elastic 
manometer  give  pulse-traces  which  are  more  reliable  than  those  of  the  sphyg- 
mograph. This  is  because  the  sphygmographic  trace  is  subject  to  unavoid- 
able errors  dependent  upon  the  physical  (jualities  of  the  skin  and  other 
parts  which  intervene  between  the  instrument  and  the  cavity  of  the  artery. 
Nevertheless,  the  sphygmographic  pulse-trace,  or  "  sphygmogram,"  is  the 
only  pulse-trace  which  can  be  obtained  from  the  human  subject;  and,  when 
obtained  from  an  animal,  it  has  so  much  in  common  with  the  trace  recorded 
by  the  elastic  manometer,  that  the  sphygmograph  has  been  much  used  for  the 
study  of  the  human  pulse,  in  health  and  disease,  both  by  physiologists  and  by 
medical  practitioners.  As  a  means  of  diagnosis,  however,  the  sphygmogram 
still  leaves  much  to  be  desired.  The  same  instrument,  applied  in  immediate 
succession  to  different  arteries  of  the  same  person,  gives,  as  might  be  expected, 
pulse-traces  of  somewhat  different  forms.  The  same  artery  of  the  same  per- 
son yields  to  the  same  instrument  at  different  times  different  forms  of  trace, 
depending  upon  different  physiological  states  of  the  circulation.  But  the  same 
artery  yields  traces  of  different  form  to  sphygmographs  of  different  varieties 
applied  to  it  in  immediate  succession  ;  and  even  moderate  changes  in  adjust- 
ment cause  differences  in  the  form  of  the  successive  traces  which  the  same 
instrument  obtains  from  the  same  artery.  It  is  no  wonder,  therefore,  that 
great  care  must  be  exercised  in  comparing  sphygmogra)>hic  observations,  and 
in  drawing  general  conclusions  from  the  information  which  they  impart. 

The  Details  of  the  Sphygmo^am. — Figure  111   is  a  fair  example  of 

'  Marshall  Hall :  Researches  principally  relative  to  the  Morbid  and  Curative  EffecU^  of  Loss  of 
Blood,  London,  1830.  *  From  afvjfidr,  pulse,  and  ypa<p£tv,  to  record. 


CIRCLLA  TION.  435 

the  sphygniograms  commonly  obtained  from  the  healtliy  human  radial  pulse. 
"When  this  traee  was  taken,  the  sul.jc-t's  heart  was  iKatin;^-  from  58  to  GU  times 


Fig.  111.— Sphygmograiii  frmn  a  normal  huiuau  radial  pulse  beatiii),'  from  5»  to  CO  liines  a  minute.    To  be 
read  from  left  to  right  (Burdon-Sanderson). 

a  minute.  The  trace  records  the  effects  upou  the  lever  of  five  successive  com- 
plete pulsations  of  the  artery,  which  all  agree  in  the  general  character  of  their 
details,  while  differing  in  minor  respects.  By  the  tracing  of  each  pulsation 
the  up-stroke  is  shown  to  be  sudden,  brief,  and  steady,  wdiile  the  down-stroke 
is  gradual,  protracted,  and  oscillating.  The  commencing  recoil  of  the  arterial 
wall  succeeds  its  expansion  with  some  suddenness.  In  many  sphygniograms 
this  is  exaggerated  by  the  inertia  of  the  instrument.  As  shown  by  the  trace  rep- 
resented in  the  figure,  and  by  most  such  traces,  the  recoil  soon  changes  from 
rapid  to  gradual,  and,  in  the  trace,  its  protracted  line  becomes  wavy,  indicating 
that  the  slow  diminution  of  calibre  varies  its  rate,  or  even  is  interrupted  by  one 
or  more  slight  expansions,  before  it  reaches  its  lowest,  and  is  succeeded  by  the 
up-stroke  of  the  next  pulsation.  In  each  of  the  five  successive  pulsations  the 
traces  of  which  are  shown  in  Figure  111,  the  line  which  represents  the  more 
gradual  portion  of  the  down-stroke  of  the  pulse  is  made  up  of  three  waves, 
of  which  the  first  is  the  shortest,  the  last  the  longest  and  lowest,  and  the  mid- 
dle one  intermediate  in  length,  but  by  far  the  highest.  This  middle  wave  is, 
in  fact,  the  only  one  of  the  three  to  produce  which  an  actual  rise  of  pressure 
occurs  ;  in  each  of  the  other  two,  no  rise,  but  only  a  diminished  rate  of  decline, 
is  exhibited.  The  changes  of  pressure  which  produce  the  first  and  third  of 
the  waves  just  spoken  of,  in  the  pulse-trace  under  consideratioH,  are  very 
obscure  in  their  origin,  and  are  inconstant  in  their  occurrence,  sometimes  being 
more  numerous  than  in  the  trace  shown  in  Figure  111,  and  sometimes  failing 
altogether  to  appear. 

The  Dicrotic  Wave. — The  oscillation  of  pressure,  however,  which  i)ro- 
duces  the  middle  wave  of  each  of  the  pulsations  of  Figure  111,  is  so  constant 
in  its  occurrence  that  it  is  undoubtedly  a  normal  and  important  phenomenon, 
although,  in  different  sphygniograms,  the  height,  and  position  in  the  trace,  of 
the  wave  inscribed  by  this  oscillation  may  vary.  Occasionally  this  oscillation 
is  morbidly  exaggerated,  so  that  it  may  be  not  only  recorded  by  the  sphygmo- 
graph,  but  even  felt  by  the  finger,  as  a  second  usually  smaller  up-stroke  of 
the  pulse.  In  such  a  case  the  artery  is  felt  to  beat  twice  at  each  single  beat 
of  the  ventricle,  and  is  said,  technically,  to  show  a  "  dicrotic  "  ^  pulse.  Where 
a  dicrotic  pul.se  can  be  detected  by  the  finger,  it  is  apt  to  accompany  a  mark- 
edly low  mean  tension  of  the  arterial  wall.  The  dicrotic  pulse  was  known, 
and  named,  long  before  the  sphygmograph  revealed  the  fact  that  the  pulse  is 
always  dicrotic,  although  to  a  degree  normally  too  slight  for  the  finger  to 

^  From  ^(KpoTOf,  double-beating. 


430  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

appreciate,  Tlie  yphygmograplii(!  wave  wliieli  records  the  slight  "diorotisin" 
of  the  normal  pulse  is  called  the  "dicrotic  wave."  Wliere  dicrotism  can  be 
felt  by  the  finger,  the  sphygniograin  naturally  exhii)its  a  very  conspicuous 
dicrotic  wave. 

The  origin  of  the  dicrotic  oscillation  has  been  much  discussed,  and  is  not 
yet  thoroughly  settled,  important  as  a  complete  settlement  of  it  would  be  to 
the  true  interpretation  and  clinical  usefulness  of  the  sphygmogram.  It  is 
believed  by  some  that  this  fluctuation  of  pressure  is  produced  at  the  smaller 
arterial  bi-aiiehes,  as  a  reflection  of  the  main  pulse-wave,  and  that  the  dicrotic 
wave,  tiius  reflected,  travels  toward  the  heart,  and,  naturally,  reaches  a  given 
artery  after  the  main  wave  of  the  pulse  has  passed  over  it,  travelling  in  the 
opposite  direction.  The  weight  of  opinion  and  of  probability,  however,  is  in 
favor  of  the  view  that  the  dicrotic  wave  essentially  depends  upon  a  slight  rise  of 
the  arterial  pressure,  or  slackening  of  its  decline,  due  to  the  closing  of  the  semi- 
lunar valve ;  and  that,  therefore,  this  wave  follows  the  main  wave  of  arterial 
expansion  outward  from  the  heart,  instead  of  being  reflected  inward  from  the 
periphery.  If  the  dicrotic  wave  be  caused  solely  by  reflection  from  the 
periphery,  it  ought,  in  a  sphygmogram  from  a  peripheral  arteiy,  to  begin  at 
a  point  nearer  to  the  highest  point  of  each  pulsation  than  in  the  case  of  an 
artery  near  the  heart,  in  which  latter  vessel,  naturally,  a  reflected  wave  would 
undergo  postponement.  On  the  other  hand,  if  the  dicrotic  wave  be  trans- 
mitted toward  the  periphery,  and  caused  solely  by  the  closure  of  the  aortic 
valve,  it  ought,  in  a  sphygmogram  from  a  peripheral  artery,  to  occupy  very 
nearly  the  same  relative  position  as  in  a  sphygmogram  taken  from  an  artery 
near  the  heart.  But  a  wave  running  toward  the  perijihery  may  be  modified 
by  a  reflected  wave  in  the  same  vessel,  and  a  reflected  wave  may  undergo  a 
second  reflection  at  the  closed  aortic  valve,  or  even  elsewhere,  and  thus  give 
rise  to  an  oscillation  which  will  be  transmitted  toward  the  periphery.  These 
statements  show  with  what  technical  diflfieulties  the  subject  is  beset,  whether 
the  sphygmograph  be  employed,  or,  in  the  case  of  animals,  the  elastic  man- 
ometer, the  traces  recorded  by  which  also  exhibit  the  dicrotic  wave.  As 
already  stated,  however,  the  probabilities  are  in  favor  of  the  valvular  origin 
of  the  dicrotic  wave. 

If  it  be  true  that  the  closure  of  the  aortic  valve  causes  the  dicrotic  wave, 
the  instant  marked  by  the  commencement  of  this  wave,  in  the  manometric 
trace  inscribed  by  the  pressure  within  the  first  part  of  tiie  arch  of  the  aorta 
itself,  practically  marks  the  instant  of  closure  of  the  aortic  valve.  We  have 
seen  (p.  422)  that  this  doctrine  has  been  made  use  of  in  the  elucidation  of  the 
curve  of  the  ])ressnrc  within  the  ventricle. 

The  Diagnostic  Limitations  of  the  Sphygmogram. — The  feeling  of 
the  pulse,  imperfect  as  is  the  most  skilled  touch,  cannot  be  replaced  by  the 
use  of  the  sphygmograph.  The  presence,  between  the  cavity  of  the  artery 
and  the  surface  of  the  body,  of  a  quantity  of  tissue  the  amount  and  elasticity 
of  which  differ  in  different  people,  and  even  differ  over  neighboring  points  of 
the  same  artery,  renders  it  impossible  so  to  adjust  the  spring  of  the  sphygrao- 


CIRCULATION.  437 

graph  as  to  be  able  to  obtain  a  reliable  base-line  corresponding  to  the  abscissa, 
or  line  of  atmospheric  pressure,  in  the  case  of  the  inanonietric  curve  of  blood- 
pressuro.  The  effects  produced  by  slight  differences  in  the  placing  of  the 
instrument  tend  to  the  same  result.  \\y  the  absence  of  such  a  base-line  the 
sphygmographic  curve  is  shorn  of  quantitative  value  as  a  curve  of  blood- 
pressure,  and  cannot  give  information  as  to  whether,  in  clinical  language,  the 
pulse  be  hard  or  soft,  large  or  small.  Nor  can  a  long  or  short  pulse  be  iden- 
tified from  the  appearance  of  the  sphygmogram.'  The  pulse-trace  still 
requires  much  elucidation  ;  but  when  further  study  shall  have  rendered 
clearer  the  true  extent,  the  normal  variations,  and  the  causes  of  the  complex 
and  incessant  oscillations  of  the  walls  of  the  arteries,  it  may  well  be  believed 
that  both  physiology  and  ])ractical  medicine  will  have  gained  an  important 
insight  into  the  laws  of  the  circulation  of  the  blood. 

P.  The  Movement  of  the  Lymph. 

The  Lymphatic  System. — The  lymph  is  contained  within  the  so-called 
lymphatic  system,  the  nature  of  which  may  be  summarized  as  follows  : 

The  lym])h  appears  first  in  innumerable  minute  irregular  ga])s  in  the  tis- 
sues, which  gaps  con>municate  in  various  ways  with  one  another,  and  with 
minute  lymphatic  vessels,  which  latter,  when  traced  onward  from  their  begin- 
nings, presently  assume  a  structure  comparable  to  that  of  narrow  veins  with 
very  delicate  walls  and  extremely  numerous  valves.  These  valves  open  away 
from  the  gaps  of  the  tissues,  as  the  valves  of  the  veins  open  away  from  the 
capillaries.  The  lymphatic  vessels  unite  to  form  somewhat  larger  ones,  each 
of  which,  however,  is  of  small  calibre  as 'compared  with  a  vein  of  medium 
size,  until  at  length  the  entire  system  of  vessels  ends,  by  numerous  openings, 
in  two  main  trunks  of  very  unequal  importance,  the  thoracic  duct  and  the 
right  lymphatic  duct.  The  latter  is  exceedingly  short,  and  receives  the  ter- 
minations of  the  lymphatics  of  a  very  limited  portion  of  the  body  ;  the  termi- 
nations of  all  the  rest,  including  the  lymphatics  of  the  alimentary  canal,  are 
received  by  the  thoracic  duct,  which  runs  the  whole  length  of  the  chest. 
Both  of  the  main  ducts  have  walls  which,  relatively,  are  very  thin;  and,  like 
the  smaller  lymphatics,  the  ducts  are  abundantly  provided  with  valves  so 
disposed  as  to  prevent  any  regurgitation  of  lymph  from  either  duct  into  its 
branches.  Each  duct  terminates  on  one  side  of  the  root  of  the  neck,  where, 
in  man,  the  cavity  of  the  duct  joins  by  an  open  mouth  the  confluence  of  the 
internal  jugular  and  subclavian  veins  where  they  form  the  innominate  vein. 
At  the  opening  of  each  duct  into  the  vein  a  valve  exists,  which  permits  the 
free  entrance  of  lymph  into  the  vein,  but  forbids  the  entrance  of  blood  into 
the  duct. 

It  is  a  peculiarity  of  the  lymphatic  system  that  some  of  its  vessels  end  and 
begin  by  open  mouths  in  the  so-called  serous  cavities  of  the  body — those  vast 
irregular  interstices  between  organs  the  membranous  walls  of  which  interstices 
are  known  as  the  peritoneum,  the  pleurae,  and  the  like.     For  present  purposes, 

'  M.  von  Frey  :  Die  ZJntersncJmng  dea  PuJsrf,  l.'^92,  p.  So. 


438  AX  AMERICAN   TEX2-B00K   OF  PHYSIOLOGY. 

therefore,  these  serou.s  cavities  may  be  regarded  as  vast  local  exj)ausioiis  of 
portions  of  the  lyinph-])ath.  Another  j)eeuliarity  of  the  lyinpiiatie  system  de- 
pends upon  the  presence  of  the  lym])hatic  glands  or  ganglia,  which  also  are 
intercalated  here  and  there  between  the  mouths  of  lymj)hatic  vessels  which 
enter  and  leave  them.  The  nature  and  importance  of  these  bodies  have  been 
dealt  with  in  dealing  with  the  origin  of  the  leucocytes  and  the  nature  of  the 
lymph  (p.  345).  For  the  present  purposes  the  ganglia  are  of  interest  in  this, 
that  the  lymph  which  traverses  their  texture  meets,  in  so  doing,  with  much 
resistance  from  friction.  Physiologically,  therefore,  the  lymph-path  as  a  whole, 
extending  from  the  tissue-gaps  to  the  veins  at  the  root  of  the  neck,  both  differs 
from,  and  in  some  respects  resembles,  the  blood-path  from  the  capillaries  to  the 
same  point. 

The  origin  of  the  lymph  has  been  discussed  already  (p.  362),  and  has  been 
found  to  be  partly  from  the  i:)lood  in  the  capillaries,  and  partly  from  the  tis- 
sues, to  say  nothing  of  the  products  directly  absorbed  from  the  alimentary 
canal  during  digestion.  The  quantity  of  material  which  leaves  the  lymph-jiath 
and  enters  the  blood  during  twenty-four  hours  is  undoubtedly  large,  amount- 
ing, in  the  dog,  to  about  sixty  cubic  centimeters  for  each  kilogram  of  body- 
weight.  The  movement  of  the  lymph  is,  therefore,  of  physiological  import- 
ance ;  and  the  causes  of  this  movement  must  now  be  considered. 

Absence  of  Lymph-hearts. — It  is  a  striking  fact  that,  in  man  and  the 
other  mammals,  there  exist  no  "lymph-hearts"  for  the  maintenance  of  the 
lymphatic  flow.  Unstriped  muscular  fibres,  indeed,  exist  in  the  walls  of  the 
lymphatics;  and  rhythmical  variations  in  the  calibre  of  some  of  these  hav^e 
been  described.  It  remains  doubtful,  however,  whether  these  variations,  when 
present,  are  produced  by  muscular  contractions  in  the  walls  of  the  lymphatics, 
or  whether  the  muscular  fibres  exist  in  these,  as  in  the  blood-vessels,  rather 
for  the  regulation  of  their  calibre  than  for  the  propulsion  of  their  contents. 
It  is  not  improbable  that  the  muscular  fibres  of  the  walls  of  the  lymphatics 
further  resemble  those  of  the  blood-vessels  in  being  under  the  control  of  the 
nervous  system;  and  it  has  been  shown  that,  in  the  splanchnic  nerve  of  the 
dog,  there  exist  centrifugal  fibres,  stimulation  of  which  produces  dilatation  of 
the  receptaculum  chi/li? 

Differences  of  Pressure. — The  fundamental  causes  of  the  movement  of  the 
lymph  are,  that  at  the  beginning  of  its  path  in  the  gaps  of  the  tissues  it  is 
under  considerable  pressure ;  that  at  the  end  of  its  path  at  the  veins  of  the 
neck  it  is  under  very  low  pressure,  which  often,  if  not  usually,  is  negative; 
and  that,  throughout  the  lymph-path,  the  valves  are  so  numerous  as  to  work 
effectively  against  regurgitation.  The  pressure  of  the  lymph  in  the  gaps  of 
the  tissues  has  been  estimated  at  one  half,  or  more,  of  the  capillary  blood- 
pressure,*  which  latter  has  been  stated  (p.  376)  to  be  from  24  to  54  millimeters 

'  L.  Camus  et  E.  (ilev:  "  Recherches  .exp^rimentales  sur  les  nerfs  des  vaisseaux  lymph- 
atiques,"  Archives  de  physiologie  normale  et  pathologique,  1894,  p.  454. 

'  A.  Landerer :  Die  Gewebsspannung  in  ihrem  Einfluss  auj  die  ortliche  Blui-  und  Lymphbeuegung, 
Leipzig,  1884,  p.  103. 


VIRVVLATION.  439 

of  niercurv.  Tlic  {lifrerenee  between  one  half  of  either  of  these  pressures  and 
the  prcssni-e  in  the  veins  of  the  neck,  which  pressure  is  not  far  from  zero,  is 
quite  enough  to  produce  a  How  from  the  one  point  to  the  other.  To  this  flow 
a  resistance  is  caused  by  tiie  friction  ah)ug  the  lymph-path,  which  resistance 
causes  the  lymph  to  accumulate  in  the  gaps  of  the  tissues,  and  the  pressure 
there  to  rise,  until  the  tension  of  the  tissues  resists  further  accumulatiou  more 
forcibly  than  friction  resists  the  onward  movement  of  the  lymph.  The  little- 
known  forces  which  continually  produce  fresh  lymph,  and  ])our  it  into  the 
tissue-gaps  against  resistance,  cannot  be  discussed  here  further  than  has  been 
done  in  treating  of  the  origin  of  the  lymph  (p.  362). 

Thoracic  Aspiration. — The  causes  have  already  been  stated  fully  of  that 
low,  perhaps  negative,  pressure  in  the  veins  at  the  root  of  the  neck  which  ren- 
ders possible  the  continuous  discharge  of  the  lymph  into  the  blood  (p.  387). 
It  need  only  be  noted  here  that  when  inspiration  rhythmically  produces,  or 
heightens,  the  suction  of  blood  into  the  chest,  it  must  also  produce,  or  heighten, 
the  suction  of  lymph  out  of  the  mouths  of  the  thoracic  and  right  lymphatic 
ducts.  Moreover,  as  the  thoracic  duct  lies  with  most  of  its  length  within  the 
chest,  each  expansion  of  the  chest  must  tend  to  expand  the  main  part  of  the 
duct,  and  thus  to  suck  into  it  lymph  from  the  numerous  lymphatics  which 
join  the  duct  from  without  the  chest ;  while  the  numerous  valves  in  the  duct 
must  promptly  check  any  tendency  to  regurgitation  from  the  neck. 

The  Bodily  Movements  and  the  Valves. — Like  the  flow  of  the  blood  in 
the  veins,  the  flow  of  the  lymph  in  its  vessels  is  powerfully  assisted  by  the 
pressure  exerted  upon  the  thin-walled  lymphatics  by  the  contractions  of  the 
skeletal  muscles ;  for  the  very  numerous  valves  of  the  lymphatics  render  it 
impossible  for  the  lymph  to  be  pressed  along  them  by  this  means  in  any  other 
than  the  physiological  direction  toward  the  venous  system.  Experiment  shows 
that  even  passive  bending  and  straightening  of  a  limb  in  which  the  mus- 
cles remain  relaxed,  increases  to  a  very  great  extent  the  discharge  of  lymph 
from  a  divided  lymphatic  vessel  of  that  limb.  It  is  probable,  therefore, 
that  movement  in  any  external  or  internal  part  of  the  body,  however  pro- 
duced, tends  to  relieve  the  tension  in  the  tissues  by  pressing  the  lymph  along 
its  path. 

Conclusion. — The  movement  of  the  lymph  produced  in  these  various  ways 
is  doubtless  irregular ;  but  a  substance  in  solution,  injected  into  the  blood,  can 
be  identified  in  the  lymph  collected  from  an  opening  in  the  thoracic  duct  at 
the  neck  in  from  four  to  seven  minutes  after  the  injection.^  The  physiological 
importance  of  the  lymph-movement  is  shown  not  only  by  the  large  amount 
of  matter  which  daily  leaves  the  lymphatic  system  to  join  the  blood,  but  also 
by  the  evil  effects  which  result  from  an  undue  accumulation  of  lymph,  more 
or  less  changed  in  character,  in  the  gaps  of  the  tissues.  Such  an  accumulation 
constitutes  dropsy.  It  may  occur  in  a  serous  cavity  or  in  the  subcutaneous 
tissue;  in  the  latter  case  giving  rise  to  a  peculiar  swelling  which  "pits  on 

*  S.  Tschirwinsky  :  "  Zur  Frage  uber  die  Schnelligkeit  des  Lymphstromes  und  der  Lymph- 
filtration,"  Centrcdblatt  fiir  Physiologic,  1895,  Band  ix.  p.  49. 


440  .i.V  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

pressure."     Auy  tissue  the  meshes  of  which  are  thus  engorged  with  lymph  is 
said  to  be  "  a'dematous."  ' 


PART  II.— THE  INNERVATION  OF  THE  HEART. 

It  has  long  been  known  that  tlie  frog^s  heart  can  be  kept  beating  for  many 
hours  after  it;?  removal  from  the  body.  In  1881,  Martin^  succeeded  in  main- 
taining the  beat  of  the  dog's  iieart  after  its  complete  isolation  from  the  central 
nervous  system  and  the  systemic  blood-vessels.  Ludwig  and  his  pupils^  have 
attained  the  same  result  in  a  different  way.  In  1895,  Langendorff^  was  able 
by  circulating  warmed  oxygenated,  defibriuated  blood  through  the  coronary 
vessels  to  maintain  the  hearts  of  rabbits,  cats,  and  dogs  in  activity  after  their 
total  extirpation  from  the  body.  It  is  evident,  thr-refore,  that  the  cause  of  the 
riiythmic  beat  of  the  heart  lies  within  the  heart  itself,  and  not  within  the  cen- 
tral nervous  system. 

Cause  of  Rhythmic  Beat. — It  has  been  nmch  disjjuted  whether  the  car- 
diac muscle  possesses  the  power  of  rhythmical  contraction  or  whether  the 
rhythmic  beat  is  due  to  the  periodic  stimulation  of  the  muscle  by  the  discharge 
of  nerve-impulses  from  the  ganglion-cells  of  the  heart.  The  arrangement  of 
the  ganglion-cells  and  nerves  suggests  the  latter  view. 

The  Intracardiac  GangUon-cells  and  Nerves. — In  the  frog  the  cardiac  nerves 
arise  by  a  single  branch  from  each  vagus  trunk  and  run  along  the  great  veins 
through  the  wall  of  the  sinus  venosus,  wiiere  many  ganglion-cells  are  found,^ 
to  the  auricular  septum.  Here  they  unite  in  a  strong  plexus  richly  provided 
with  ganglion-cells.®  Two  nerves  of  unequal  length  and  thickness  leave  this 
plexus  and  pass  along  the  borders  of  the  septum  to  the  auriculo-ventricular 
junction,  where  each  enters  a  conspicuous  mass  of  cells  known  as  Bidder's 
ganglion.^  Ventricular  nerves  spring  from  these  ganglia  and  can  be  followed 
with  the  unaided  eye  some  distance  on  the  ventricle.  With  the  chloride-of- 
gold  method,  the  methylene-blue  stain,  and  especially  the  nitrate-of-silver  im- 
pregnation, the  ventricular  nerves  can  be  traced  to  their  termination.  Some 
difference  of  opinion  exists  regarding  the  manner  of  their  distribution  and  the 
precise  nature  of  their  terminal  organs.  The  following  fiicts,  however,  may  be 
considered  established  both  for  the  batrachian  and  the  mammalian  heart.^ 

The  ventricular  nerves  form  a  rich  plexus  beneath  the  pericardium  and 
endocardium.  Branches  from  these  plexuses  form  a  third  plexus  in  the  myo- 
cardium or  heart  nuiscle,  from  which  arise  a  vast  number  of  non-medullated 

'  From  ohiijiia,  a  swelling.  *  Martin,  1S81,  p.  119. 

»  Stolnikow,  18S6,  p.  2;  Pawlow,  1887,  p.  452. 

*  Langendortt;  1895,  p.  293:  also  >rartin  and  Applegarth,  1890,  p.  275;  Aniaiid,  1S91,  p. 
396;  H^on  and  Gilis,  1892,  p.  760;  Porter,  1896,  p.  39.  *  Remak,  1844,  p.  463. 

6  Ludwig,  1848,  p.  140.  '  Bidder,  1852,  p.  169. 

*  The  literature  of  this  subject  has  been  collected  by  Jacques  (1894,  p.  622;  and  1896, 
p.  517)  and  by  Heymans  and  Demoor  (1895,  p.  619).  For  the  development  of  the  cardiac 
nervous  system  in  different  classes  of  vertebrates,  see  His,  Jr.,  1891,  pp.  1-64  ;  compare  His 
and  Romberg,  1890,  pp.  374  and  416. 


CIRCULATION.  441 

terminal  nerves,  enveloping  the  muscle-fibres  and  ending  in  small  enlargements 
or  nodosities  of  various  forms.  Similar  "  varicose"  enlargements  are  observed 
along  the  course  of  the  nerves.  The  nerve-endings  are  in  contact  with  the 
naked  muscle-substance,  the  mode  of  termination  resembling  in  general  that 
observed  in  non-striated  muscle.  Ganglion-cells  are  found  chiefly  in  the 
auricular  septum  and  the  auriculo-vcntricular  furrow,  but  are  present  also 
beneath  the  pericardium  of  the  upper  half  of  the  ventricle.  Xo  ganglia  have 
as  yet  been  satisfactorily  demonstrated  within  the  apical  hall"  of  the  ventricle, 
and  most  observers  do  not  admit  their  presence  within  the  ventricular  nmscle 
itself.*     The  nerve-cells  are  unipolar,  bipolar,  or  multipolar. 

Certain  unipolar  cells  in  the  frog  are  distinguished  by  a  spherical  form,  a 
pericellular  network,  and  two  processes — namely,  the  axis-cylinder  or  straight 
process,  and  the  spiral  {)rocess.  The  latter  is  wound  in  sj)iral  fashion  ab(jut 
the  axis-cylinder,  ending  in  the  pericellular  net.  According  to  Retzius  and 
others,  the  spiral  is  not  really  a  process  of  the  cell,  but  arises  in  a  distant  extra- 
cardiac  cell  and  carries  to  the  heart-cell  a  nervous  impulse  which  is  transmitted 
from  the  spiral  })rocess  to  the  cell  by  means  of  the  contact  between  the  peri- 
cellular net  and  the  cell-body.  Section  of  the  cardiac  fibres  of  the  vagus 
causes  the  spiral  "  process "  and  pericellular  net  to  degenerate,  the  cell-body 
and  axis-cylinder  process  remaining  untouched,  showing  that  the  spiral  process 
is  the  terminal  of  a  nerve-fibre  running  in  the  vagus  trunk.^ 

Xerve-theory  of  Heart-beat. — The  theory  of  the  nervous  origin  of  the 
heart-beat  rests  in  part  on  the  correspondence  between  the  degree  of  contrac- 
tility of  the  various  parts  of  the  heart  and  the  number  of  nerve-cells  present 
in  them.  Thus  the  power  of  rhythmical  contraction  is  greater  in  the  auricle, 
in  which  there  are  many  cells,  than  in  the  ventricle,  in  which  there  are  fewer. 
The  properties  of  the  apical  half,  or  "  apex,"  of  the  ventricle  are  considered 
to  be  of  especial  importance  in  the  study  of  this  problem,  because  the  apex,  as 
has  been  said,  is  believed  to  contain  no  ganglion-cells.  This  part  of  the  ven- 
tricle stops  beating  when  separated  from  the  heart,  while  the  auricles  and  the 
ventricular  stump  continue  to  beat.  The  apex  need  not  be  cut  away  in  order 
to  isolate  it.  By  ligating^  or  squeezing  the  frog's  ventricle  across  the  middle 
with  a  pair  of  forceps  the  tissues  at  the  junction  of  the  upper  and  the  lower 
half  of  the  ventricle  can  be  crushed  to  the  point  at  which  physiological  con- 
nection is  destroyed  but  physical  continuity  still  preserved.*  Such  frogs  have 
been  kept  alive  as  long  as  six  weeks.  The  apex  does  not  as  a  rule  beat  again.^ 
The  exceptions  can  be  exj)lained  as  the  consequence  of  accidental  stimulation. 
The  conclusion  draw'n  is  that  the  apex,  in  which  ganglion-cells  have  not  been 
satisfactorily  demonstrated,  has  not  the  power  of  spontaneous  pulsation  which 

^  For  contrary  opinion  see  Tnniiinzew  and  Dogiel,  1890,  p.  494,  and  Berkeley,  1894,  p.  90; 
also  the  very  beautiful  plates  of  Lee,  1849,  p.  43,  showing  subpericardial  nerves  and  ganglia  (?) 
in  the  calf's  heart. 

^  Nikolajew,  1893,  p.  73.  ^  Heidenhain,  1854,  p.  47. 

*  Bernstein,  1876,  p.  386;  Bowditch,  1879,  p.  105. 

5  Bowditch,  1871,  p.  169  ;  Merunowicz,  1875,  p.  132;  Bernstein,  1876,  pp.  386,  435;  Bowditch, 
1879,  p.  104 ;  Aubert,  1881,  p.  362 ;  Ludwig  and  Luchsinger,  1881,  p.  231 ;  Langeudorff,  1884,  p.  6. 


442  AjV  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

distinguislies  the  remainder  of  the  lieart.  This  view  is  further  .supported  by 
the  observation  that  a  slight  stimulus  applied  to  the  base  of  a  resting  ventricle 
M'ill  often  provoke  a  series  of  contractions,  wliilc  the  same  stinndus  applied  to 
the  apex  will  cause  but  a  single  contraction.' 

The  action  of  muscariu  on  the  heart  is  often  luld  to  indicate  the  nervous 
origin  of  the  heart-beat.  Mu.scarin  arrests  the  heart  of  the  frog  and  other 
vertebrates,  but  has  no  similar  action  on  any  other  muscle  either  .striped  or 
smooth,  nor  does  it  arrest  the  heart  of  insects  and  mollusks.  It  follows  that 
rauscarin  does  not  cause  arrest  by  acting  directly  upon  the  contractile  material 
of  the  heart.  The  contractile  material  being  excluded,  the  a.ssumption  of  a 
nervous  mechanism  on  the  integrity  of  which  the  heart-beat  depends  seems 
necessary  to  explain  the  effect  of  the  poison.^ 

Further  arguments  are  based  on  uncertain  analogies  between  the  heart  and 
othei'  rhythmically  contracting  organs. 

Muscular  Theory  of  Heart-beat. — The  evidence  just  stated  cannot  be  re- 
garded as  proof  of  the  nervous  origin  of  the  heart-beat.  The  most  that  can 
be  claimed  is  that  it  makes  such  a  conception  plausible.  Even  this  claim  has 
been  denied  by  not  a  few  investigators  who  believe  that  the  heart-beat  is  a 
purely  muscular  phenomenon.  Here  again  the  properties  of  the  apex  are  con- 
sidered to  be  of  the  first  importance.  It  has  been  shown  that  a  strip  of  muscle 
cut  from  the  apex  of  the  tortoise  ventricle  and  suspended  in  a  moist  chamber 
begins  in  a  few  hours  to  beat  apparently  of  its  own  accord  with  a  regular  but 
slow  rhythm,  which  has  been  seen  to  continue  as  long  as  thirty  hours.  If  the 
strip  is  cut  into  pieces  and  placed  on  moistened  glass  slides  each  piece  will  con- 
tract rhythmically.^    Yet  in  the  apex  of  the  heart  no  nerve-cells  have  been  found. 

The  apex  of  the  batrachian  heart  will  beat  rhythmically  in  response  to  a 
constant  stimulus.  Thus  if  the  apex  is  suspended  in  normal  saline  solution 
and  a  constant  electrical  current  kept  passing  through  it,  beats  will  appear 
after  a  time,  the  frequency  of  pulsation  increasing  with  the  strength  of  the 
current.^  Very  strong  currents  cau.se  tonic  contraction.  An  apex  made  inac- 
tive by  Bernstein's  crushing  can  be  made  to  beat  again  by  clamping  the  aorta 
and  thus  raising  the  endocardiac  pressure,*  Chemical  stimulation  is  also  effect- 
ive. Delphinin,*  quinine,^  mu.scarin  with  atropin,^  atropin  alone,'  morphin 
and  various  other  alkaloids,  dilute  mineral  acids,  dilute  alkalies,  bile,  .sodium 
chloride,  alcohol,  and  other  bodies,'"  when  painted  on  the  resting  ventricle,  call 
forth  a  longer  or  shorter  series  of  beats.  Stimulation  with  induction  shocks 
gives  a  similar  result." 

•  Scherhey,  1880,  p.  260.  ^  Ciishny,  1893,  p.  451.  »  Gaskell,  1883,  p.  54. 

*  Bernstein,  1871,  p.  230  ;  Foster  and  Dewsmitli,  1876,  p.  737  ;  von  Basch,  1879,  p.  71 ;  Scher- 
hey, 1880,  p.  259;  Langendorff.  1895,  p.  336;  Kaiser,  1895,  p.  464. 

^  Gaskell,  1880,  p.  51 ;  Aubcrt,  1881,  p.  366;  Liidwig  and  Luchsinger,  1881,  p.  231 ;  Dastre, 
1882,  p.  458:  Biedermann,  1884,  p.  24;  Langendorff,  1884,  p.  6. 

«  Bowditch,  1871,  p.  169.  '  Schtschepotjew,  1879,  p.  56.  «  v.  Basch,  1879,  p.  73. 

9  Lowit,  1881,  p.  447.  >»  Langendorff,  1884,  p.  21 ;  1895.  p.  333;  Kaiser,  1895,  p.  6. 

"  Bowditch,  1871,  p.  149;  Kronecker,  1875,  p.  178;  1879,  p.  381;  1880,  p.  285;  v.  Basch, 
1879,  p.  71  ;  Ranvier,  1880,  p.  46;  Dastre,  1882,  p.  433;  Gaskell,  1883,  p.  52. 


CIBCULA  TION.  443 

Other  muscles  iu  wliicli  no  nerve-cells  have  heeu  discovered  can  contract 
rhythmically.  Tiius  the  hulbus  aortaj  of  the  frog  beats  regularly  after  its 
removal  from  the  body,  even  the  smallest  pieces  showing  under  the  microscope 
rhvthmical  contractions.  Engelmann,  who  observed  this  fact,  declares  that 
the  entire  bulbus  is  lacking  in  nerve-cells.  This  is  contradicted  by  Dogiel ; 
yet  it  seems  hardly  reasonable  that  these  "smallest  pieces"  which  Engelmann 
mentions  were  each  provided  with  ganglion-cells.  It  is  more  probable  that  the 
contractions  were  the  result  of  a  constant  artificial  stimulus.^  Curarized  stri- 
ated muscles  placed  in  certain  saline  solutions  may  contract  from  time  to  time.^ 
The  hearts  of  many  invertebrates  in  which  ganglion-cells  are  apparently  absent 
beat  rhythmically.^ 

Much  has  been  made  of  the  fact  that  the  ganglion-cells  grow  into  the  heart 
long  after  the  cardiac  rhythm  is  established/  showing  that  the  embryonic  heart 
muscle  has  rhythmic  contractile  powers.  The  adult  heart  muscle,  it  is  alleged, 
retains  certain  embryonic  peculiarities  of  structure,  and  as  structure  and  func- 
tion are  correlated,  should  also  retain  the  embryonic  power  of  contraction 
■without  nerve-cells.^ 

It  cannot  be  denied  that  these  facts  prove  that  the  embryo  heart  muscle 
possesses  rhythmic  contractility,  that  the  apical  half  of  the  heart  of  the  adult 
frog  and  tortoise  may  be  made  to  contract  rhythmically,  and  that  even  fully 
striated  muscle  will  under  some  conditions  show  more  or  less  periodic  contrac- 
tions. They  can,  however,  hardly  be  said  to  prove  that  the  beat  of  the  mam- 
malian or  even  the  batrachian  adult  heart  is  not  dependent  on  discharges  from 
the  cardiac  nerve-cells.  Even  the  freedom  of  the  apex  from  ganglion-cells, 
which  is  the  very  foundation  of  the  doctrine  of  muscular  origin,  has  recently 
been  questioned.^      This  problem  is  still  unsolved. 

The  Excitation-wave. — The  change  in  form  which  constitutes  what  com- 
monly is  called  the  cardiac  contraction  is  preceded  by  a  change  in  electrical 
potential,  supposed  to  be  a  manifestation  of  the  unknown  process  by  which  the 
heart-muscle  is  excited  to  contract.  Both  the  contraction  and  the  electrical 
change  sweep  over  the  heart  in  the  form  of  waves,  and  it  has  become  the  cus- 
tom to  speak  of  the  electrical  change  as  the  excitation-wave.  It  should  not  be 
forgotten,  however,  that  this  usage  rests  merely  on  an  assumption,  for  the  real 
nature  of  the  excitation  is  still  a  mystery.  The  contraction-wave  begins  nor- 
mally at  the  great  veins,  travels  rapidly  through  the  auricle,  and,  after  a  dis- 
tinct interval,  spreads  through  the  ventricle.  The  excitation-wave,  which  pre- 
cedes and  is  the  cause  of  the  contraction,  probably  takes  the  same  course,^  and 
in  fact  it  is  possible  to  show  that  the  change  in  electrical  potential  actually 
begins  under  normal  conditions  at  the  great  veins  and  passes  thence  over  the 
entire  heart.    But  this  sequence  is  not  invariable.    The  ventricle  under  abnor- 

1  Engelmann,  1882,  p.  446;  Dogiel,  1894,  p.  225.  ^   Biedermann,  1880,  p.  2-59. 

^  Concerning  the  cardiac  apex  in  fishes,  see  Ludwig  and  Luchsinger,  1881,  p.  247;  Kazem- 
Beck  and  Dogiel,  1882,  p.  259  ;  McWilliam,  1885,  p.  197  ;  Mills,  1886,  p.  91. 

*  Wagner,  1854,  p.  227 ;  Schenck,  1867,  p.  Ill ;  His,  Jr.,  1893,  p.  25;  Pickering,  1893,  p.  391. 

*  Gaskell,  1883,  p.  77.  «  Berkeley,  1894,  p.  90.  '  Compare  Kaiser,  1895,  p.  447. 


444  AlV  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

mal  couditions  has  been  seen  to  contract  before  the  auricle,  the  normal  sequence 
of  great  veins,  auricle,  and  ventricle  being  reversed.'  The  energy  of  the  ven- 
tricular muscle-cell  may,  therefore,  be  discharged  by  an  excitation  arising 
within  the  ventricle  itself.  Evidence  of  this  is  afforded  also  by  the  experi- 
ment of  Wooldridge,^  who  isolated  the  ventricles  by  drawing  a  silk  ligature 
tightly  about  the  auricles  at  their  junction  with  the  ventricles,  completely 
crushing  the  muscle  and  nerves  of  the  auricle  in  the  track  of  the  ligature  with- 
out tearing  through  the  more  resistant  pericardium.  This  experiment  was 
rejwated  the  following  year  by  Tigerstedt,'  wiio  devised  a  special  clamp  for 
crushing  the  auricular  tissues.  Both  observers  found  that  the  auricles  and 
ventricles  continued  to  beat.  The  rhythm,  however,  was  no  longer  the 
same.  The  ventricular  beat  was  slower  than  before  *  and  was  independent  of 
the  beat  of  the  auricle.  Thus  the  ventricle,  no  longer  connected  physiologically 
with  the  auricle,  develops  a  rhythm  of  its  own,  an  idio-ventricular  rhythm.  It 
seems  improbable  that  tlie  very  small  part  of  the  auricular  tissue  which  cannot 
be  included  in  Wooldridge's  ligature  for  fear  of  closing  the  coronary  arteries 
should  be  able  to  maintain  the  ventricular  contractions. 

Independent  contraction  is  said  to  be  secured  by  properly  regulated  excita- 
tion of  the  cardiac  end  of  the  cut  vagus  nerve.  Stimuli  of  one  second  duration 
applied  to  the  vagus  at  intervals  of  six  to  seven  seconds  arrest  the  auricles 
completely,  but  do  not  stop  the  ventricles,  except  during  the  second  of  stimu- 
lation. The  ventricles,  now  dissociated  from  the  auricles,  beat  with  a  rhythm 
diiferent  from  that  which  characterized  the  normal  heart,^  The  force  of  this 
demonstration  is  somewhat  weakened  by  the  possibility  that  the  auricles, 
although  not  beating  themselves,  might  still  excite  the  ventricles  to  contraction. 

Conduction  of  the  Excitation. — If  the  points  of  non-polarizable  electrodes 
are  placed  on  the  surface  of  the  ventricle  and  connected  with  a  delicate  galvan- 
ometer, a  variation  of  the  galvanometer  needle  will  be  seen  with  each  ventric- 
ular beat.  If  one  electrode  is  placed  near  the  Irase  of  the  heart  and  the  other 
near  the  apex  it  is  seen  that  the  former  electrode  becomes  negative  before  the 
latter,  indicating  that  the  part  of  the  heart  muscle  on  which  the  basal  electrode 
rests  is  stimulated  before  the  apical  portion,  and  that  the  ditferenee  in  electrical 
potential,  or  excitation-wave,  according  to  the  prevailing  hypothesis,  travels  as 
a  wave  over  the  ventricle  from  the  base  to  the  apex  (see  Fig.  112).  Burdon- 
Sanderson  and  Page^  have  found  that  the  duration  of  the  ditferenee  of  poten- 
tial is  about  two  seconds  in  the  frog's  heart  at  ordinary  temperatures.  Cooling 
lengthens  the  period  of  negativity,  warming  diminishes  it.     Some  observers 

'  Recently  studied  by  Engelmann,  1895,  p.  275;  see  also  Knoll,  1894,  p.  306,  who  observed 
fibrillary  contraction  of  the  auricle  coincident  with  strong  co-ordinated  contractions  of  the  ven- 
tricles. 

*  Wooldridge,  1883,  p.  527. 

'  Tigerstedt,  1884,  p.  500;  see  also  Krehl  and  Romberg,  1892,  p.  54. 

*  The  isolated  ventricle  may,  however,  beat  as  rapidly  as  the  auricle,  although  independ- 
ently of  it  (Bayliss  and  Starling,  1892,  p.  408). 

*  Roy  and  Adami,  1892,  p.  236;  see  also  Knoll,  1884,  p.  312. 

*  Burdon-Sanderson  and  Page,  1884,  p.  338. 


CIRCULA  TION. 


445 


believe  that  the  excitation-wave  under  certain  conditions  returns  toward  the 
base  after  havinj^  reached  the  apex.'  The  sjieed  of  the  excitation-wave  has  been 
measuretl  by  the  interval  between  the  appearance  of  nei^ative  variation  in  the 
ventricle  when  the  auricle  is  stimulated  first  near  and  then  as  far  as  possible 


Fig.  112.— The  electrical  variation  in  the  spontaneou.sly  contracting  heart  of  the  frog,  recorded  by  a 
capillary  electrometer,  the  apex  being  connected  with  the  sulphuric  acid  and  the  base  with  the  mercury 
of  the  electrometer.  The  changes  in  electrical  potential  are  shown  by  the  line  e,  e,  which  is  obtained  by 
throwing  the  shadow  .of  the  mercury  in  the  capillary  on  a  travelling  sheet  of  sensitized  paper.  The  con- 
traction of  the  heart  is  recorded  by  the  line  h,  h  ;  time,  in  j'j  second,  by  t,  t.  The  curves  read  from  left 
to  right.  The  electrical  variation  is  diphasic ;  in  the  first  phase  the  base  is  negative  to  the  apex  ;  in  the 
second,  the  apex  is  negative  to  the  base ;  the  negative  variation  passes  as  a  wave  from  base  to  apex 
(Waller,  1887,  p.  231). 

from  the  non-polarizable  electrodes.  The  interval  is  the  time  which  the  excita- 
tion-wave requires  to  pass  the  distance  between  the  two  points  stimulated.  The 
average  rate  is  at  least  50  millimeters  per  second.^  The  negative  variation 
begins  apparently  instantly  after  the  application  of  the  stimulus.  Its  phases 
and  their  characteristics  have  been  described  by  Engelmann.^ 
The  latent  period  of  a  frog's  heart  muscle  is  about  0.08  .second.* 
Although  the  normal  course  of  the  excitation-wave  is  from  base  to  apex,  it 
can  be  made  to  travel  in  any  direction.  If  the  frog's  ventricle  is  cut  with  fine 
scissors  into  a  number  of  pieces  in  such  a  way  as  to  leave  small  bridges  of 
heart-tissue  between  each  piece,  and  any  one  of  the  pieces  is  stimulated,  the 
contraction  will  begin  in  the  stimulated  piece  and  then  run  from  piece  to  piece 
over  the  connectino-  bridg-es  until  all  have  successively  contracted.  The  direc- 
tion  in  which  the  excitation-wave  travels  can  thus  be  altered  at  the  pleasure 
of  the  operator.^ 

Whether  the  excitation  is  propagated  from  muscle-cell  to  muscle-cell  or  by 
means  of  nerve-fibres  has  given  rise  to  much  discu.ssion.  Anatomical  evidence 
can  be  adduced  on  both  sides.  On  the  one  hand  the  rich  plexus  of  nerve- 
fibres  everywhere  present  in  the  heart-muscle  suggests  conduction  through 
nerves  ;  on  the  other  is  the  intimate  contact  of  neighboring  mu.scle-cells  over 

'  Bayliss  and  Starling,  1892,  pp.  260,  380. 

2  Engelmann,  1878,  p.  91  ;  Burdon-Sanderson  and  Page,  1880,  p.  426,  give  150  millimeters 
per  second. 

^  Engelmann,  1878,  p.  74.  *  Ibid.,  1874,  p.  6. 

*  Ibid.,  p.  3;  compare  Bayliss  and  Starling,  1892,  p.  262. 


446  AN  AMERICAN    Ti: XT- HOOK    OF   PIIVSIOLOGY. 

a  part  at  least  of  their  surfaee,  thus  hriiiging  one  mass  of  irritable  protoplasm 
against  another  ant.!  ofTering  a  ])ath  by  whieh  the  excitation  might  travel  from 
cell  to  cell.* 

If  the  excitation-wave  were  conducted  by  means  of  nerves,  the  difi'ereuce 
between  the  moment  of  contraction  of  the  ventricle  when  the  auricle  is  stimu- 
lated near  the  ventricle,  and  again  as  far  as  possible  from  the  ventricle,  should 
be  very  slight,  because  of  the  gt-eat  speed  at  which  the  nervous  impulse  travels 
(about  33  raetei*s  per  second).  If,  on  the  contrary,  the  conduction  were  by 
means  of  muscle,  the  difference  would  be  relatively  much  greater,  correspond- 
ing to  the  much  slower  conductivity  of  muscular  tissue.  It  has  been  found  by 
Engfelmann  that  the  ventricle  contracts  later  when  the  auricle  is  stimulated  far 
from  the  ventricle  than  when  it  is  stimulated  near  the  ventricle.  The  rate  of 
propagation  being  calculated  from  the  dilference  in  the  time  of  ventricular  con- 
traction was  found  to  be  90  millimeters  per  second,  which  is  about  300  times 
less  than  the  rate  which  would  have  been  obtained  had  conduction  over  the 
measured  distance  taken  place  through  nerves.^  Hence  the  stimulus  that  trav- 
els through  the  auricle  to  the  ventricle  and  causes  its  contraction  should  be 
propagated  in  the  auricle  by  muscle-fibres  and  not  by  nerves. 

Passage  of  Excitation-wave  from  Auricle  to  Ventricle. — The  normal  con- 
traction of  the  heart  begins,  as  has  been  said,  at  the  junction  of  the  great 
veins  and  the  auricle,  spreads  rapidly  over  the  auricle  and,  after  a  distinct 
pause,  reaches  the  ventricle.  The  normal  excitation-wave  preceding  the  con- 
traction passes  likewise  from  the  auricle  to  the  ventricle  and  is  delayed  at  or 
near  the  auriculo- ventricular  junction.  The  controversy  over  the  nerv^ous  or 
muscular  conduction  of  the  excitation  within  the  auricle  and  ventricle  has 
been  extended  to  its  passage  from  auricle  to  ventricle.  A  path  for  conduction 
by  nerves  is  presented  by  the  numerous  nerves  which  go  from  the  auricle  to 
the  ventricle.  It  has  been  shown  recently  that  nuiscular  connections  also 
exist.^  In  the  frog,  muscle-bundles  pass  from  the  auricle  to  the  ventricle 
where  the  auricular  septum  adjoins  the  base  of  the  ventricle.  Muscular 
bridges  pass  also  from  the  sinus  venosus  to  the  auricles  and  from  the  ventricle 
to  the  bulbus  arteriosus.^  These  muscle-fibres  appear  to  be  in  intimate  con- 
tact with  the  muscle-cells  of  the  divisions  of  the  heart  which  they  unite.  Gas- 
kell  ^  believes  that  the  connecting  fibres  are  morphologically  and  physiologically 
related  to  embryonic  muscle,  and  therefore  possess  the  power  of  contracting 
rhythmically. 

The  delay  experienced  by  the  excitation  in  its  passage  from  the  auricle  to 
the  ventricle — in  other  words,  the  normal  interval  between  the  contrac^tion  of 
the  auricle  and  the  contraction  of  the  ventricle — is  explained  by  those  favoring 

^  Engelmann,  1874,  p.  7. 

'  Ibid.,  1894,  p.  188;  1890,  p.  549;  the  measurements  of  Bayliss  and  Starling',  1892.  p.  271, 
on  the  mammalian  heart  are  probably  of  little  value  because  of  the  variation  due  to  tempera- 
ture (p.  272).     See  also  Kaiser,  1895,  p.  2,  and  Enselmann's  reply,  1890,  p.  547. 

^Paladino,  1876;  Gaskell,  1880,  p.  70;  Krehl  and  Komberg,  1892,  p.  71 ;  Kent,  1893,  p. 
240;  Engelmann,  1894,  p.  158. 

*  Engelmann,  1894,  p.  158.  »  Gaskell,  1883,  p.  77. 


CIBCULA  TION.  447 

the  nervous  conduction  as  the  delay  wliidi  the  excitation  experiences  in  dis- 
charging the  ganglion-cells  of  the  ventricle,  in  accordance  with  the  well-known 
hypotheses  of"  the  retardation  of  the  nerve-impulse  in  sympathetic  ganglia 
and  the  slow  passage  of  the  nervous  impulse  through  spinal  cells. 

The  explanation  given  by  those  who  believe  in  muscular  conduction  is  that 
the  small  number  of  nuiscular  fibres  composing  the  bridge  between  auricle 
and  ventricle  acts  as  a  "  block  "  to  the  excitation-wave.  If  the  auricle  of  the 
tortoise  heart  is  cut  into  two  pieces  connected  by  a  small  bridge  of  auricular 
tissue,  the  stimulation  of  one  piece  will  be  followed  immediately  by  the  con- 
traction of  that  piece,  and  after  an  interval  by  the  contraction  of  the  other. 
The  smaller  the  bridge,  the  longer  the  interval ;  that  is  the  longer  the  excita- 
tion-wave will  be  in  passing  from  one  piece  to  another.^ 

The  duration  of  the  pause  or  "  block  "  in  the  frog  has  been  found  to  be  from 
0.15  to  0.30  second.  The  length  of  the  muscle-fibres  connecting  auricle  and 
ventricle  is  about  one  millimeter.  The  speed  of  the  excitation-wave  in  em- 
bryonic heart  muscle  is  from  3.6  to  11.5  millimeters  per  second.  The  duration 
of  the  pause  agrees,  therefore,  with  the  time  which  would  be  required  for 
muscular  conduction.^ 

The  extensive  extirpations  of  the  auricular  nerves  which  have  been  made 
without  stopping  conduction  from  auricle  to  ventricle  ^ — for  example,  the  ex- 
tirpation of  the  entire  auricular  septum  of  the  frog's  heart — are  of  little 
importance  to  this  question,  since  the  great  number  of  nerve-cells  revealed  by 
recent  methods  make  it  improbable  that  any  extirpation  short  of  total  removal 
of  both  auricles  could  cut  off  all  the  nerve-cells  of  the  auricle. 

Refractory  Period  and  Compensatory  Pause. — SchiflF*  found  in  1850 
that  the  heart  which  contracted  to  each  stimulus  of  a  series  of  slowly  repeated 
mechanical  stimuli  would  not  contract  to  the  same  stimuli  if  they  followed  each 
other  in  too  rapid  succession.  Kronecker'  got  a  similar  result  with  induction 
shocks.  The  heart  contracted  to  every  stimulus  only  when  the  interval  between 
them  was  not  too  brief.  The  following  year  Marey^  published  a  systematic 
study  of  the  phenomenon.  He  observed  that  the  irritability  of  the  heart  sank 
during  a  part  of  the  systole,  but  returned  during  the  remainder  of  the  systole 
and  the  following  diastole.'^  The  stimulus  which  fell  between  the  beginning  of 
the  systole  and  its  maximum  produced  no  extra  contraction,  whilst  that  which 
fell  between  the  maximum  of  one  systole  and  the  beginning  of  the  next 
called  forth  an  extra  contraction.  During  a  part  of  the  cardiac  cycle  therefore 
the  heart  is  "  refractory "  toward  stimuli.  The  irritability  of  the  heart  is 
removed  for  a  time  by  an  adequate  stimulus. 

Kronecker  and  Marey  noticed  further  that  stimulation  with  the  induction 
shock  during  the  non-refractory  period  did  not  influence  the  total  number  of 
systoles.  The  extra  systole  called  forth  by  the  artificial  stimulus  was  followed 
by  a  pause  the  length  of  which  was  that  of  the  normal  pause  plus  the  interval 

1  Gaskell,  1883,  p.  64.  ''  Engelmann,  1894,  p.  159. 

^  Gaskell,  1883,  p.  75;  HoflFmann,  1895,  p.  169.  *  Schiff,  1850,  p.  50. 

*  Kronecker,  1875,  p.  181.  «  Marey,  1876,  p.  73.  '  Cf.  Engelmann,  1895,  p.  313. 


448  A!^  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

between  the  appearance  of  the  extra  systole  and  what  would  have  been  the  end 
of  the  cardiac  cycle  in  which  the  extra  systole  fell.  The  extra  length  of  this 
pause  restored  the  normal  frequency  or  rhythm.  It  was  called  the  conij)ensa- 
tory  pause  (see  Fiij.  1 13). 


Fig.  113.— The  refractory  period  aiul  compensatory  pause.  The  curves  are  rccorrtefi  by  a  writinfr  lever 
resting  on  the  ventricle  of  the  frog's  heart.  They  read  from  left  to  right.  A  break  in  the  horizontal  line 
below  each  curve  indicates  the  moment  at  which  an  induction  shock  was  sent  through  the  ventricle.  In 
curves  1,  2,  and  .3  the  ventricle  proved  refractory  to  this  stimulus ;  in  the  remaining  curves,  the  stimulus 
having  fallen  outside  ihe  refractory  period,  an  extra  contraction  and  compensatory  pause  are  seen. 
Many  of  the  phenomena  mentioned  in  the  text  are  illustrated  by  this  figure  (Marey,  1876,  p.  72). 

If  the  heart,  or  the  i.solated  apex,  is  beating  at  a  rate  so  slow  that  an  extra 
contraction  falling  in  the  interval  between  two  normal  contractions  has  time  to 
complete  its  entire  phase  before  the  next  normal  contraction  is  due,  there  will 
be  no  compeu.satory  pause.' 

The  refractory  pha.se  di.sapj>ears  with  sufficiently  strong  .stimuli,  e.-jpecially 
if  the  heart  is  warmed.'"^  In  such  a  case  an  artificial  stimulus  falling  in  the 
beginning  of  a  spontaneous  contraction  produces  an  extra  contraction.  This 
extra  contraction,  however,  comes  first  after  the  end  of  the  .systole  during  which 
the  artificial  .stimulation  is  made,^  occurring  in   fact  tt)ward  the  end  of  the 

'  Kaiser,  1895,  p.  449. 

*  Engelmann,  1882,  p.  453;  compare  Bnrdon-Sanderson  and  Page,  1880,  p.  401. 
'  This  is  apparently  true  only  of    the  whole  heart,  and  not  of  the  isolated  apex  (Engel- 
mann,  1>^95,  p.  .317). 


CIRCULA  TION.  449 

followiiif;  diastole.  The  latent  period  of"  such  a  contraction  lengthens  with 
the  length  of  the  interval  between  the  artificial  stimulation  and  the  end  of  the 
systole. 

A  refractory  period  has  been  demonstrated  in  the  auricle  of  the  frog '  and 
dog;-  in  the  ventricle  of  the  cat,''  rabbit  and  dog/  and  in  the  sinus  venosus' 
and  bulbu.s  arteriosus  "  of  the  frog. 

In  some  cases,  the  extra  stimulus  provokes  not  merely  one,  but  two  or  three 
extra  contractions.^ 

The  amplitude  of  the  extra  contraction  increases  with  the  length  of  the 
interval  between  the  maximum  of  contraction  and  the  extra  stimulus.  If  the 
extra  stimulus  is  given  at  the  beginning  of  relaxation,  the  extra  contraction  is 
exceedingly  small ;  on  the  other  hand,  the  exti^a  contraction  may  be  greater 
than  the  primary  one,  when  the  stimulus  falls  in  the  pause  between  two  normal 
beats.* 

The  supplementary  systole  of  the  auricle  is  sometimes  followed  by  a  sup- 
plementary systole  and  compensatory  pause  of  the  ventricle,  sometimes  by  the 
compensatory  pause  alone,  probably  because  the  excitation  wave  reaches  the 
ventricle  during  its  refractory  period,'  Multiple  extra  contractions  of  the 
auricle  are  often  followed  by  the  same  number  of  extra  contractions  of  the 
ventricle.^"  If  the  frog's  heart  is  made  to  beat  in  reversed  order,  ventricle 
first,  auricle  second,  extra  contractions  of  the  ventricle  may  be  produced,  and 
will  cause  extra  contractions  of  the  auricle  with  compensatory  pause.  If  the 
reversed  excitation  wave  travelling  from  the  ventricle  to  the  auricle  reaches 
the  latter  during  auricular  systole,  the  extra  auricular  contraction  is  omitted, 
but  a  distinct  though  shortened  compensatory  pause  is  still  observed.  The 
phenomena  with  reversed  contraction  are  therefore  similar  to  those  seen  under 
the  usual  conditions." 

Kaiser '-  finds  in  frogs  poisoned  with  muscarin  that  stimulation  of  the  ven- 
tricle during  the  refractory  period  causes  the  contraction  in  which  the  stimulus 
falls  to  be  more  complete,  as  shown  by  the  contraction  curve  rising  above  its 
former  level.  He  concludes  that  the  ventricle  is  not  wholly  inexcitable  even 
during  the  refractory  period. 

The  question  whether  the  refractory  state  and  compensatory  pause  are 
properties  of  the  muscle-substance  or  of  the  nervous  system  of  the  heart  has 
excited  considerable  attention.  If  the  ganglion-free  apex'  of  the  frog's  ven- 
tricle is  stimulated  by  rapidly  repeated  induction  shocks  it  can  be  made  to  con- 
tract periodically  for  a  time.  By  momentarily  increasing  the  strength  of  any 
one  induction  shock  an  extra  stimulus  can  be  given  from  time  to  time.     When 

1  Hiklebrand,  1877,  quoted  by  Lov^n,  1886,  p.  5 ;  Brnnton  and  Cash,  1883,  p.  461 ;  Kaiser, 
1895,  p.  15;  Engelmann,  1895,  p.  322.  '^  Meyer,  1893,  p.  185. 

3  McWilliam,  1888,  p.  169.  *  Gley,  1889,  p.  501  ;  1890,  p.  437. 

5  Stromberg  and  Tigerstedt,  1888,  p.  26 ;  Brunton  and  Cash,  1883,  p.  463. 
«  Engelmann,  1882,  p.  453. 

'  Hildebrand,  1877;  Stromberg  and  Tigerstedt,  1888,  p.  33;  Meyer,  1893,  p.  187. 
»  Stromberg  and  Tigerstedt,  1888,  p.  36.  '  Kaiser,  1895,  p.  16. 

»»  Mever,  1893,  p.  188.  "  Kaiser,  1895,  p.  19.  '*  Ihid.,  1892,  p.  219. 


4o0  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

the  extra  stimulus  falls  after  the  cuutraetion  luaxiiuuui  or  during  diastole  an 
extra  contraction  results,  otherwise  not.  The  refractory  period  exists,  there- 
fore, indei)endent]y  of  the  cardiac  ganglia/ 

The  con)])ensatory  pause  can  also,  though  not  always,  be  secured  with  the 
ganglion-free  apex.'^ 

The  refractory  period  has  been  used  to  show  how  a  contijuious  stinuilus 
might  produce  a  rhythmic  heart-beat.  The  continuous  stimulus  cannot  affect 
the  heart  during  tlie  refractory  period  from  the  beginning  to  near  the  maxi- 
mum of  systole.  At  the  close  of  the  refractory  period  the  constant  stimulus 
becomes  effective,  causing  an  extra  contraction  with  long  latent  period.  This 
latent  period  is,  according  to  this  theory,  the  interval  between  the  first  and  the 
second  contraction.^ 

A  tonic  contraction  of  the  heart  muscle  is  sometimes  produced  by  strong, 
rapidly  repeated  induction  shocks*  and  by  various  other  means,  such  as  filling 
the  ventricle  with  old  blood,^  by  weak  sodium  hydrate  solution,*  and  by  certain 
poisons,  such  as  digitalin  and  voratrin,^ 

A.  The   Cardiac  Nerves. 

The  cardiac  nerves  are  branches  of  the  vagus  and  the  sympathetic  nerves. 

In  the  dog  the  vagus  arises  by  about  a  dozen  fine  roots  from  the  ventro- 
lateral aspect  of  the  medulla  and  passes  outward  to  the  jugular  foramen  in 
company  with  the  spinal  accessory  nerve.  In  the  jugular  canal  the  vagus 
bears  a  ganglion  called  the  jugular  ganglion.  The  spinal  accessory  nerve 
joins  the  vagus  here,  the  spinal  portion  almost  immediately  leaving  the  vagus 
to  be  distributed  to  certain  muscles  in  the  neck,  while  the  medullary  portion 
passes  to  the  heart  through  the  trunk  ganglion  and  thereafter  in  the  substance 
of  the  vagus.  Directly  after  emerging  from  the  skull,  the  vagus  presents  a 
second  ganglion,  fusiform  in  shape  and  in  a  fairly  large  dog  about  one  centi- 
meter in  length.  From  the  caudal  end  or  middle  of  this  "  ganglion  of  the 
trunk "  is  given  off"  the  superior  laryngeal  nerve,  slightly  behind  which  a 
large  nerve  is  seen  passing  from  the  sympathetic  chain  to  the  trunk  of  the 
vagus.  This  nerve  is  in  reality  the  main  cord  of  the  sympathetic  chain,  the 
sympathetic  nerve  being  bound  up  with  the  vagus  from  the  "  inferior"  cervical 
ganglion  to  the  point  just  mentioned.  Posterior  to  the  trunk  ganglion  of  the 
vagus,  the  vago-sympathetic  runs  caudalward  as  a  large  nerv^e  dorsal  to  the 
common  carotid  artery  as  far  as  the  first  rib  or  near  it,  where  it  enters  the 
so-called  inferior  cervical  ganglion.  This  ganglion  belongs  to  the  sympathetic 
system  and  not  to  the  vagus ;  from  a  morphological  point  of  view  it  is  the 
middle  cervical  sympathetic  ganglion.     The  true  inferior  cervical  sympathetic 

'  Dastre,  1882,  p.  447  ;  Kaiser,  1895,  p.  449  ;  Engelmann,  1895,  p.  326 ;  compare  Kronecker, 
1875,  p.  181. 

=*  Kaiser,  1895,  pp.  449,  457 ;  Engelmann,  1895,  p.  311 ;  Dastre  dissents,  1882,  p.  464. 
»  Tigerstedt,  1893,  p.  169.  *  Engelmann,  1882,  p.  453. 

*  Aubert,  1881,  p.  381 ;  compare  Rossbach,  1874,  p.  97. 
6  Gaskell,  1880,  p.  53.  '  Roy,  1879,  p.  477. 


CIRCULA  TION. 


451 


ganglion  is  fused  with  tlio  first  ono  or  two  thoracic  ganglia  to  form  the  gan- 
glion stellatiini,  situated  opposite  the  first  intercostal  space.  At  the  "  inferior 
cervical  "  ganglion  the  vagus  and  the  sympathetic  part  company,  the  vagus 
passing  cjiudalward  behind  the  root  of  the  lung  and  the  sympathetic  passing 
to  the  stellate  ganglion,  dividing  on  its  way  into  two  portions  (the  annulus  of 
Vieussens),  which  embrace  the  subclavian  artery.  In  many  cases  the  lower  loop 
of  the  annulus  of  Vieussens  joins  the  trunk  of  the  vagus  caudal  to  the  ganglion.' 
The  cardiac  nerves  spring  from  the  vagus  and  the  sympathetic  nerve  in 
the  region  of  the  inferior  cervical  ganglion.  They  n.ay  be  divided  into  an 
inner  and  an  outer  group. 

The  inner  group  is  composed  of  one  medium,  one  ^hick,  and  from  two  to 
three  slender  nerves.  The  nerve  of  medium  thickness  springs  from  the  gan- 
glion itself.  The  thick  branch  rises  from  the  trunk  of  the  vagus  near  the 
origin  of  the  inferior  laryngeal  nerve  about  1.25  centimeters  caudal  to  the 

inferior  cervical  ganglion.     It  can  be 

easily  followed  to  its  final  distribution.  ^""" 

It  passes  behind  the  vena  cava  superior, 

perforates  the  pericardium,  and   runs 

parallel  with  the  ascending  aorta  across 

the  pulmonary  artery,  on  which  it  lies 

in  the  connective  tissue  already  divided 

into  two  or  three  tolerably  thick  twigs 

or  spread  in  a  fan  of  smaller  branches. 

These  now  bend  beneath  the  artery, 

pass  round  its  base  on  the  inner  side, 

and  reach  the  anterior  inter- ventricular 

groove.      Here  they  spread  over  the 

surface  of  the  ventricle.     The  slender 

branches  leave  the  vagus  trunk  caudal 

to  the  branch  just  described.  ^^^  I14.-Cardiac  plexus  and  stellate  ganglion 

The  outer  group  comprises  two  thick     of  the  cat,  drawn  from  nature  after  the  removal  of 

,  the  arteries  and  veins;  about  one  and  one-half  times 

branches — namely,   an    upper    nerve,    natural  size  (Boehm.isTS,  p.  258): 

springing    from    the   ganglion   or    from  R,  right;  i.left:  1,1,  vagus  nerve;  2    cervical 

i^       o     t?  &      t>  _  sympathetic ;  2',  annulus  of  Vieussens ;  2",  thoracic 

the    trunk  of  the  vagus   near  it,  and  a     sympathetic;  3,  recurrent  laryngeal  nerve;  4,  de- 

InwPr    nerve    from    the    lower   loon   of     P'"e^«o'"  "^^^^'  entering  the  vagus  on  the  right,  on 
lOWei    nerve,  irom    tne    JOWei     luup    ui      ^^^  ^^^^  running  a  separate  course  to  the  heart; 

the    annulus,  or   from   the   vagus    1—1^     5,  middle  (often  called  "inferior")  cervical  gan- 

.        ,         ,  J  TT^^l,  ^^  ^U^^^     glion ;  5',  communicating  branch  between  middle 

centimeters  lower  down.     Each  of  these     S^^^. -^^  '^^^^uon  and  vagus  nerve ;  6,  stellate  gan- 

thick    branches    may  be    replaced    by  a     glion  ;  6',  6"  &",  spinal  roots  of  stellate  ganglion ; 

,,         p„  I'l  i-^A?,  communication  between   stellate  ganglion  and 

bundle  of  finer  branches,  and  in  tact    ^agus ;  8',  8",  8'",  cardiac  nerves. 

the  description  of  the  cardiac  nerves 

here  given  can  be  regarded  as  a  close  approximation  only,  so  frequent  are  the 

individual  variations.^ 

1  Schmiedeberg,  1871,  p.  34. 

2  Details  concerning  the  composition  of  the  cardiac  plexuses  in  the  dog  are  given  by  Lira 
Boon  Keng,  1893,  p.  467. 


452  AjV  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

Ill  the  rabbit  the  cervical  sympathetic  and  the  vaj^iis  trunk  are  not  joined, 
as  ill  the  dog,  but  run  a  separate  course.  Cardiac  fibres  from  the  spinal  cord 
reach  the  lower  cervical  and  first  thoracic  ganglion  (ganglion  stellatum)  along 
their  rami  couiinunicantcs '  and  pass  to  the  heart  by  two  sympathetic  cardiac 
nerves,  one  from  the  inferior  cervical  ganglion  and  one  from  the  ganglion 
stellatum.^ 

The  arrangement  of  the  cardiac  nerves  in  the  cat  is  shown  in  Figure  114. 

In  the  frog  the  cardiac  nerves,  both  vagal  and  sympathetic,  reach  the  heart 
through  the  splanchnic  branch  of  the  vagus.  The  sympathetic  fibres  pass  out 
of  the  spinal  cord  with  the  third  spinal  nerve,  through  the  ramus  comraunicaus 
of  this  nerve  into  the  third  sympathetic  ganglion,^  up  the  sympathetic  chain 
to  the  ganglion  of  the  vagus,  and  down  the  vagus  trunk  to  the  heart.^ 

The  Inhibitory  Nerves. 

In  1845,  Ernst  Heinrich  and  Eduard  Weber '^  ann(Miiiced  that  stimulation 
of  the  vagus  nerves  or  the  parts  of  the  brain  where  they  arise  slows  the  heart 
even  to  arrest.  When  one  pole  of  an  induction  apparatus  was  placed  in  the 
nasal  cavity  of  a  frog  and  the  other  on  the  spinal  cord  at  the  fourth  or  fifth 
vertebra,  the  heart  was  completely  arrested  after  one  or  tM'o  pulsations  and 
remained  motionless  several  seconds  after  the  interruption  of  the  current. 
During  the  arrest,  the  heart  was  relaxed  and  filled  gradually  with  blood. 
When  the  stimulus  was  continued  many  seconds,  the  heart  began  to  beat  again, 
at  first  weakly  and  with  long  intervals,  then  more  strongly  and  frequently, 
until  at  length  the  beats  were  as  vigorous  and  as  frequent  as  before,  though  all 
this  time  the  stimulation  was  uninterrupted. 

In  order  to  determine  from  what  part  of  the  brain  this  influence  proceeds, 
the  electrodes  were  brought  very  near  together  and  placed  upon  the  cerebral 
hemispheres.  The  movements  of  the  heart  were  not  affected.  Negative  results 
followed  also  the  stimulation  of  the  spinal  cord.  Not  until  the  medulla  oblon- 
gata between  the  corpora  quadrigemina  and  the  lower  end  of  the  calamus  scrip- 
torius  was  stimulated  did  the  arrest  take  place.  Cutting  away  the  spinal  cord 
and  the  remainder  of  the  brain  did  not  alter  the  result. 

Having  determined  that  the  inhibitory  power  had  its  seat  in  the  medulla 
oblongata,  the  question  arose  through  what  nerve  the  inhibitory  influence  is 
transmitted  to  the  heart.  In  a  frog  in  which  the  stimulation  of  the  medulla 
had  stopped  the  heart,  the  vagus  nerves  were  cut  and  the  ends  in  connection 
with  the  heart  stimulated.     The  heart  was  arrested  as  before. 

Thus  the  fundamental  fact  of  the  inhibition  of  a  peripheral  motor  mechan- 
ism by  the  central  nervous  system  through  the  agency  of  si)ecial  inhibitory 

1  Bever  and  von  Bezold,  1867,  pp.  236,  247. 

"  Ludwig  and  Thiry,  1864,  p.  429;  Bever,  1867,  p.  249. 

^  It  is  probable  tliat  the  fibres  of  spinal  origin  end  in  the  sympathetic  ganglia,  making  con- 
tacts there  with  sympathetic  ganglion-cells,  the  axis-cylinder  processes  of  which  pass  up  the 
cervical  chain  and  descend  to  the  heart  in  company  with  the  vagus. 

*  Gaskell  and  Gadow,  1884,  p.  369.  *  E.  Weber,  1846,  p.  42. 


CIRCULATION. 


453 


nerves  was  firmly  established.  A  great  imniher  of  investigations  have  demon- 
strated that  this  inhibitory  power  is  found  in  many  if  not  all  vertebrates  and 
not  a  few  invertebrates.' 

The  effect  of  vagus  stinmlation  on  the  heart  is  not  immediate;  a.  latent 
period  is  seen  extending  over  one  beat  and  sometimes  two,  according  to  the 
moment  of  stimulation'-  (see  Fig.  115). 


Fig.  115.— Pulsations  of  frog's  heart,  inhibited  by  the  excitation  of  the  left  vagus  nerve  (TarchanoflF. 
1876,  p.  296) :  C,  pulsations  of  heart ;  S,  electric  signal  which  vibrated  during  the  passage  of  the  stimu- 
lating current,  one  vibration  for  each  induction  shock. 


Changes  in  the  Ventricle. — The  periodicity  of  the  ventricular  contraction 
is  altered  by  vagus  excitation,  a  weak  excitation  lengthening  the  duration  of  dias- 
tole, while  leaving  the  duration  of  systole  unchanged  (see  Fig.  116).  A 
stronger  excitation,  capably  of  modifying  largely  the  force  of  the  contraction, 
lengthens  both  systole  and  diastole.^  The  difficulty  of  producing  a  continued 
arrest  in  diastole  is  much  greater  in  some  animals  than  in  others.  Even  when 
easily  produced,  the  arrest  soon  gives  away  in  the  manner  described  by  E.  H. 
and  E.  Weber,  the  heart  beginning  to  beat  in  spite  of  the  vagus  excitation.* 


Fig.  116.— Showing  the  lengthened  diastole  and  diminished  force  of  ventricular  contraction  during 
weak  stimulation  of  the  peripheral  end  of  the  cut  vagus  nerve.  The  heart  (cat)  was  isolated  from  both 
systemic  and  pulmonary  vessels,  and  was  kept  beating  by  circulating  defibrinated  blood  through  the 
coronary  arteries  :  A,  Pressure  in  left  ventricle,  which  was  filled  with  normal  saline  solution,  and  com- 
municated with  a  Iliirthle  membrane  manometer  by  means  of  a  cannula  which  was  passed  through  the 
auricular  appendix  and  the  mitral  orifice  ;  B,  line  drawn  by  the  armature  of  an  electro-magnet  in  the 
primary  circuit;  the  heavy  line  indicates  the  duration  of  stimulation  ;  C,  time  in  seconds. 

The  force  of  the  contraction,  measured  by  the  height  of  the  up-stroke  of  the 
intra-ventricular  pressure  curve,  or  by  placing  a  recording  lever  on  the  heart, 

^  P'or  literature  see  Tigerstedt,  Physiologie  des  Kreislaufes,  1893. 

^Schiff,  1849,  p.  192;  Pliiiser,  1865,  p.  30;  Czermak,  1868,  p.  644;  1868,  p.  32;  Donders, 
1868,  p.  339;  1872,  p.  6;  Tarchanoff  1876,  p.  300;  Pruszynski,  1889,  p.  569. 

'  Arloing,  1894,  p.  88 ;   Meyer,  1894,  p.  698. 

*  Hough,  1895,  p.  161.  The  terrapin  heart  is  said  not  to  escape,  as  a  rule,  from  vagus  inhibi- 
tion.     Compare  Mills,  1885,  p.  255  ;  see  also  Laulanie,  1889,  p.  409. 


454  AN  AMERICAN   TEXT-BOOK'   OF  PHYSIOLOGY. 

is  lessened/  this  diiuiiiution   in   force  appearing  often  before  any   notiw-able 
change  in  periodicity. 

The  d'uistolic  pressure  increases,  as  is  shown  by  the  lower  level  of  the  cnrve 
gradually  rising  farther  and  farther  above  the  atmospheric  pressure  line.*- 

The  volume  of  blood  in  the  ventricle  at  the  close  of  diastole  is  increased.  So 
also  is  the  volume  at  the  close  of  systole  (residual  blood) — sometimes  to  such 
a  degree  that  the  volume  of  the  heart  at  the  end  of  systole  may  be  greater  than 
the  volume  of  the  organ  at  the  end  of  diastole  before  the  vagus  was  excited.^ 

The  oufjmf  and  the  input  of  the  ventricle,  that  is,  the  quantity  of  blood  dis- 
charged and  received,  are  both  diminished  by  vagus  excitation.^ 

The  ventricular  tonus,  or  state  of  constant  slight  contraction  on  whic-h  the 
systolic  contractions  are  superimposed,  is  also  diminished,  as  is  well  shown  by 
an  experiment  of  Stefani.^  In  this  experiment  the  pericardial  sac  is  filled  with 
normal  saline  solution  under  a  pressure  just  sufficient  to  prevent  the  expansion 
of  the  heart  in  diastole.  On  stimulation  of  the  vagus,  the  heart  dilates  fur- 
ther. A  considerably  higher  pressure  is  necessary  to  overcome  this  dilatation. 
Stefani  finds  also  that  the  pressure  necessary  to  prevent  diastolic  expansion  is 
much  greater  with  intact  than  with  cut  vagi.  Furthermore,  the  heart  is  much 
more  easily  distended  by  the  rise  of  arterial  pressure  through  compression  of 
the  aorta  when  the  vagi  are  severed  than  when  they  are  intact.  Franck  has 
noticed  that  the  walls  of  the  empty  ventricle  become  softer  when  the  vagus  is 
stimulated.* 

The  propagation  of  the  cardiac  excitation  is  more  difficult  during  vagus 
excitation.^  Bayliss  and  Starling^  demonstrate  this  on  mammalian  hearts 
made  to  contract  by  exciting  the  auricle  three  or  four  times  per  second  ;  the  ven- 
tricle as  a  rule  responds  regularly  to  every  auricular  beat.  If,  then,  the  vagus 
is  stimulated  with  a  weak  induced  current,  the  ventricle  may  drop  every  other 
beat,  or  may  for  a  short  time  cease  to  respond  at  all  to  the  auricular  contrac- 
tions. The  defective  propagation  is  not  due  to  changes  in  the  auricular  con- 
traction, for  even  an  almost  inappreciable  beat  of  the  auricle  can  cause  the 
ventricle  to  contract.  Nor  is  it  due  to  lowered  excitability  of  the  ventricle, 
for  the  effi?ct  described  is  seen  with  currents  too  weak  to  depress  the  irrita- 
bility of  the  ventricle  to  an  appreciable  extent. 

The  action  of  the  vagus  is  accompanied  by  an  electrical  variation.  This 
has  been  shown  in  the  muscular  tissue  of  the  resting  auricle  of  the  tortoise' 
(see  Fig.  117).  The  auricle  is  cut  away  from  the  sinus  without  injuring  the 
coronary  nerve,  which  in  the  tortoise  passes  from  the  sinus  to  the  auricle  and 
contains  the  cardiac  fibres  of  the  vagus.  After  this  operation  the  auricle  and 
ventricle  remain  motionless  for  a  time, -and  this  quiescent  period  is  utilized  for 

1  Coats,  1869,  p.  1S7  ;  Niiel,  1874,  p.  87  ;  Gaskell,  1882,  p.  1011 ;  Heidenhain,  1882,  p.  388; 
Mills,  1885,  p.  283.     Roy  and  Adami,  1892,  p.  224,  are  of  contrary  opinion. 

2  Roy  and  Adami,  1892,  p.  227. 

"  Roy  and  Adami,  1892,  p.  218;  compare  Stefani,  1893,  p.  136;  1895,  p.  175. 

♦  Roy  and  Adami,  1892,  pp.  217,  228.  *  Stefani,  1891,  p.  182. 

6  Franck,  1891,  p.  486.  '  Gaskell,  1883,  p.  100 ;  McWilliam,  1888,  p.  367. 

»  Bayliss  and  Starling,  1892,  p.  412.  «  Gaskell,  1887,  p.  116  ;  1887,  p.  404. 


CIRCULA  TION. 


455 


the  experiment.  The  tip  of  tlic  aurich^  is  injured  by  immersion  in  hot  water, 
and  the  demareation  current  (the  injured  tissue  bein<^-  negative  toward  tlie  unin- 
jured) is  led  oir  to  a  galvanometer.  On  exciting  the  vagus  in  the  neck,  the 
demarcation  current  is  markedly  increased.  No  visible  change  of  form  is  seen 
in  the  auricular  strip. 


Fig  117  -The  tortoise  heart  prepared  for  the  demonstration  of  the  electrical  change  in  the  cardiac 
muscle'accompanyingthe  excitation  of  the  vagus  nerve:  r,  vagus  nerve;  ^'' ''^'^;^^'J^l''^l'l:^^2 
and  part  of  auricle  in  connection  with  it ;  G,  galvanometer,  in  the  circuvt  fo^ned  by  Uv  o  non-polanzable 
electrodes  and  the  part  of  the  auricle  between  them ;  E,  induction  coil  (Gaskell.  1887). 

Changes  in  the  Auricle.— There  is  little  probability  that  the  action  of 
the  vao-us  on  the  auricle^  differs  essentially  from  the  action  on  the  ventricle. 
The  force  of  the  auricular  contraction  is  diminished.  The  diastole  is  length- 
ened The  change  in  force  appears  earlier  than  in  the  change  in  periodicity 
and  sometimes  without  it.  On  the  whole,  the  auricle  is  more  easily  affected 
by  vagus  excitation  than  the  ventricle.  ^   i      /•      j 

Action  on  Bulbus  Arteriosus.— If  the  bulbus  arteriosus  of  the  Irog  s 
heart  is  extirpated  in  such  a  way  as  to  leave  untouched  the  nerve-fibres  that 
connect  it  with  the  auricular  septum,  the  contractions  of  the  isolated  bulbus 
will  be  arrested  when  the  peripheral  end  of  the  vagus  is  excited.^ 

Diminished  Irritability  of  Heart.-During  vagus  excitation  with  cur- 
rents of  moderate  strength,  the  arrested  heart  will  respond  to  direct  stimula- 
tion by  a  single  contraction.  With  strong  vagus  excitation,  however,  the 
directlv  stimulated  heart  contracts  not  at  all  or  less  readily  than  before 

Effects  of  Varying  the  Stimulus.-A  single  excitation  of  the  vagus  does 
not  stop  the  heart.^  IMorat  has  investigated  the  effect  of  excitations  of  varied 
I  Eckhard,  1860,  p.  140;  Nnel,  1874,  p.  86;  Gaskell,  1882,  p.  1010;  1883  p.  89;  Mills, 
1885  p  250;  886,  p.  550 ;  McWillian.,  1885,  p.  225;  1887,  p.  309;  1888  p.  348;  Johansson 
and  Tigerst;dt,  1889;  Franck,  1891,  p.  581;  Bayliss  and  ^^-1"^^^^^- J" /g^*^;  ^^^j;.^"' 
^^";85o!p.'64;  1877,p.494;  Einbrodt,  1859.  p.  353 ;   Eckhard.T^  p.  25  ;    McWil- 

Uam,  1885,  p.  222;  1888,  p.  351 ;  Mills,  1888,  p.  3.  „,o     rr  • ,     u  •  ,   1889  n  ^ 

*  Donders,  1868,  p.  344;  1872,  p.  5  ;  Tarchanofi;  1876,  p.  303;  Heidenhain,  1882,  p.  386. 


456  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

duration,  uuinber,  and  frequency  on  the  tortoise  lieart.'  With  excitations  of 
the  same  duration,  the  effect  was  minimal  at  2  per  second,  maximal  at  7 
per  second,  diminishing  theroaftor  as  tiie  frequency  increased.  The  longer  the 
stinuilation,  the  longer  (within  limits)  was  the  inhibition.  An  excitation  that 
is  too  feeble  or  too  slow,  or,  on  the  contrary,  is  over-strong  or  over-frequent, 
has  no  effect.  Within  limits,  however,  the  degree  of  inhibition  increases  with 
the  strength  of  the  stinudus." 

Weak  stimuli  affect  primarily  the  auricles,  diminishing  frequency  and  force 
of  contraction,  and  secondarily  lower  the  frequency  of  the  ventricle.  Stronger 
stimuli  arrest  the  aiu'icle,  the  ventricles  continuing  to  beat  with  almost  undi- 
minished force  but  with  altered  rhythm.  Still  stronger  stimuli  inhibit  the 
ventricles  also.^ 

The  frequencv  can  be  kept  comparatively  small  by  continued  moderate 
stimulation.'' 

Arrest  in  Systole. — The  excitation  of  the  tortoise  vagus  in  the  upper  or 
middle  cervical  region  is  sometimes  followed,  according  to  Rouget,^  by  a  state 
of  continued,  prolonged  contraction — in  short,  an  arrest  in  systole.  The  same 
effect  is  observed  in  rabbits  strongly  curarized  and  in  curarized  frogs.  Arloing  * 
noticed  that  the  mechanical  irritation  produced  by  raising  on  a  thread  the  left 
vagus  nerve  of  a  horse  caused  the  right  ventricle  to  remain  contracted  during 
seven  seconds.  The  ventricular  curve  during  this  time  presented  the  characters 
of  the  tetanus  curve  of  a  striated  muscle.' 

Comparative  Inhibitory  Power. — One  vagus  often  possesses  more  inhibi- 
tory power  than  the  other.^ 

Septal  Nerves  in  Frog. — The  electrical  stimulation  of  the  peripheral 
stump  of  either  of  two  large  nerves  of  the  inter-auricular  septum  in  the  frog 
alters  the  tonus  and  the  force  of  contraction  of  the  ventricle,  but  not  the  fre- 
quency. After  section  of  these  nerves,  the  excitation  of  the  vagus  has  very 
little  effect  on  the  tonus,  and  almost  none  on  the  force  of  the  ventricular  beat, 
while  the  frequency  is  diminished  in  the  characteristic  manner.  Evidently, 
therefore,  the  two  large  septal  nerves  take  no  part  in  the  regulation  of  fre- 
quency, but  leave  this  to  the  nerves  diffusely  distributed  through  the  auricles. 
There  is  then  au  anatomical  division  of  the  septal  branches  of  the  frog's  vagus, 
the  fibres  affecting  periodicity  running  outside  the  septal  nerves,  while  those 
modifying  the  force  of  contraction  and  the  tonusof  the  ventricle  run  within  them.^ 

*  Morat,  1894,  p.  10;  Legros  and  Onimus,  1872,  p.  565. 

2  V.  Bezold,  1868,  p.  50;  Ptluger,  1859,  p.  19;  Bonders,  1868,  p.  356. 

'Johansson  and  Tigerstedt,  1889;  Rov  and  Adami,  1892,  p.  237  ;  Bayliss  and  Starling, 
1892,  p.  411.  '  Laulani^,  1889,  p.  408. 

*  Rouget,  1894,  p.  398.  *  Arloing,  1893,  p.  112. 

"  For  other  unusual  alterations  in  the  heart-beat  in  consequence  of  vagus  excitation  see 
Arloing,  1893,  p.  163. 

«  Cold-blooded  Anivmlx:  Meyer,  1869,  p.  61  ;  Tarchanoff,  1876,  p.  293;  Gaskell,  1882,  p.  82; 
McWilliam,  1885,  xvi. ;  Mills,"  188.5,  p.  259;  18S7,  p.  11 ;  1888,  p.  2. 

Mammals:  Miusoin,  1S72,  p.  410;  Legros  and  Onimus,  1872,  p.  575;  Arloing  and  Tripier, 
1872,  p.  420;  Langendortt",  1878,  p.  68;  compare  Brown-S^quard,  1880,  p.  211. 

»  Hofniann,  1895,  p.  169;  examine  Pxkhard,  1876,  p.  192;  and  Dogiel,  1890,  p.  258. 


CIRCULA  TION.  457 

Nature  of  Vagus  Influence  on  Heart.— The  nature  of  the  terminal 
apparatus  by  which  the  vagus  inhibits  the  heart  is  unknown.  It  is  probable 
that  the  same  iutracaidiac  apparatus  serves  for  both  nerves,  for  Hiiflcr  finds 
that  when  the  heart  escapes  from  the  inhibition  caused  by  continued  stimula- 
tion of  one  vagus,  the  prolonged  diastole  growing  shortca-  again,  the  immediate 
stinmlation  of'' the  second  vagus  has  no  effect  upon  the  heart.^  Dogiel  and 
Grahe  have  recently  observed  that  the  lengthening  of  diastole  which  follows 
stimulation  of  the  peripheral  stump  of  the  vagus,  the  other  vagus  l)eing  intact, 
is  less  marked  than  when  both  vagi  are  cut.^ 

The  question  whether  the  vagus  acts  on  the  heart  muscle  directly  or  through 
the  medium  of  some  nervous  mechanism  has  not  yet  been  answered.  The  only 
fact  bearing  immediately  on  this  problem  is  the  diminution  in  the  irritability  of 
the  ventricle  during  vagus  excitation,  and  this  does  not  exclude  an  action  upon 
a  nervous  mechanism.^ 

The  earlier  attempts  to  form  a  satisfactory  theory  for  the  inhibitory  power 
of  the  vagus  met  with  little  success.  The  statement  of  the  Webers'  that  the  vagus 
inhibits  the  movements  of  the  heart  gave  to  nerves  a  new  attribute,  but  is 
hardlv  an  explanation.  The  view  of  Budge  ^  and  Schiff,^  that  the  vagus  is  the 
motor  nerve  of  the  heart  and  that  inhibition  is  the  expression  of  its  exhaustion, 
is  now  of  only  historical  interest.  Nor  has  a  better  fate  overtaken  the  theory 
of  Brown-Sequard,«  who  saw  in  the  vagus  the  vaso-motor  nerve  of  the  heart, 
the  stimulation  of  which,  by  narrowing  the  coronary  arteries,  deprived  the 
heart  of  the  blood  that,  according  to  Brown-Sequard,  is  the  exciting  cause  of  the 

contraction.  ... 

Of  recent  years,  the  explanation  that  has  commanded  most  attention  is  the 
one  advanced  by  Stefani^  and  Gaskell,  namely,  that  the  vagus  is  the  trophic  nerve 
of  the  heart,  producing  a  dis-assirailation  or  katabolism  in  systole  and  an 
assimilation  or  anabolism  in  diastole.  Gaskell  supports  this  theory  by  the 
observation  that  the  after-effect  of  vagus  excitation  is  to  strengthen  the  force 
of  the  cardiac  contraction  and  to  increase  the  speed  with  which  the  excitation 
wave  passes  over  the  heart,  while  the  contrary  effects  are  witnessed  after  the 
excitation  of  the  augraentor  nerves.^ 

Various  attempts  have  been  made  to  prove  a  trophic  action  of  the  vagus  on 

the  heart  by  cutting  the  nerve  in  animals  kept  alive  until  degenerative  changes 

t  Hiifler,  1889,  p.  307  ;  Hough,  1895,  p.  198.     Earlier  experimenters  obtained  conflicting 

results  •  see  Tarchanoff  and  Puelma,  1875,  p,  757  ;  Tarchanoff,  1876,  p  296  ;  Eckhard   18-9  p. 

r8T;  Gamgee  and  Priestley,  1878,  p.  39  ;  Tscherepin,  1881  ;  MoWilham,  188o,  p.  217  ;  Mills, 

1885,  p.  257  ;  Laulanie,  1889,  p.  377. 

2  Dogiel  and  Grahe,  1895,  p.  393.  ^  ^    ,,  „.•,,•        iqqq  „  i~'=. 

3  Chlnges  in  the  peripheral  efficiency  of  the  vagi  are  discussed  by^M<^^^^ll--^1^93,^p.  4.5. 

*  Budge,  1846,  p.  418.  '  '^ "  '  '  P' 

;  S:^^^^:'l^  M#;  Eichhorst,  I879,  p.  I8  ;  GasUell,  1886,  p.  49 ;  Fantino,  1^8, 
p.  243 ;  Timofeew,  1889  ;  Tigerstedt,  1893,  p.  259.  Gaskell  gives  a  resume  of  his  work  on  the 
heart  in  Archives  de  Physiolog^e,  1888,  pp.  56-68.  ,  .^  ,„„„        ,«    ^  «x^„.r^   1880 

«  Gaskell,  1883,  pp.  81,  94 ;  also  Gianuzzi,  1871 ;  Schiff,  1878,  p.  16;  Brown-Sequard,  1880, 
p.  211 ;  Laffont,  1887,  p.  1095;  Konow  and  Stenbeck,  1889,  p.  414. 


458  yl.V  AMERICAN   TEXT-BOOK    OF   PHYSTOLOGY. 

in  the  heait-niiLscle  should  have  had  time  to  appear.  The  important  distril)u- 
tion  of  the  vagus  nerve  to  many  organs,  and  tlie  consequently  wide  extent  of 
the  loss  of  function  following  its  section,  makes  it  difficult  to  decide  whether  the 
changes  produced  in  the  heart  are  not  secondary  to  the  alterations  in  other  tis- 
sues. The  work  of  Fautino  ^  will  serve  for  an  example  of  these  investigations. 
Fantino  cut  a  single  vagus  to  avoid  the  paralysis  of  deglutition  aud  the  inani- 
tion and  occasional  broncho-pueumouia  that  follow  section  of  both  nerves. 
Young  and  perfectly  healthy  rabbits  and  guinea-pigs  were  selected.  The  opera- 
tion was  strictly  ase])tic,  and  all  cases  in  which  the  wound  suppurated  were 
excluded.  A  piece  of  the  nerve  about  one  centimeter  long  was  cut  out,  so  that 
no  reunion  could  be  possible.  After  the  operation  the  animals  were  as  a  rule 
lively,  ate  well,  and  gained  weight.  Post-mortem  examination  of  animals 
killed  two  days  or  more  after  section  of  the  vagus  nerve  disclosed  no  patho- 
logical changes  in  the  lungs,  spleen,  liver,  and  stomach.  In  the  heart,  areas 
were  found  in  which  the  nuclei  and  the  striation  of  the  muscle-cells  had  disap- 
peared. Eighteen  days  after  section  the  atrophy  of  the  cardiac  muscle  in  these 
areas  was  observed  to  be  extreme.  The  degenerations  following  section  of  the 
right  vagus  were  situated  in  a  different  part  of  the  ventricular  wall  from  those 
following:  section  of  the  left  nerve. 

The  effects  of  stimulation  of  the  vagus  nerve  in  the  new-boi'n  do  not  differ 
essentially  from  those  seen  in  the  adult.^ 

The  relation  between  the  action  of  the  vagus  and  the  intracardiac  jwessure 
has  been  recently  studied  by  Stewart.^  He  finds  that  an  increase  in  the  pressure 
in  the  sinus  or  auricle  makes  it  difficult  to  inhibit  the  heart  through  the  vagus. 

The  inhibitory  action  of  the  vagus  diminishes  as  the  temperature*^  of  the 
heart  falls.  At  a  low  limit  the  inhibitory  power  is  lost,  but  may  return  when 
the  heart  is  warmed  again.  Even  when  the  stimulation  of  the  trunk  of  the 
nerve  has  failed  to  affect  the  cooled  heart,  the  direct  stimulation  of  the  sinus 
can  still  cause  distinct  inhibition.  The  power  of  inhibiting  the  ventricle  is 
first  lost.  Loss  of  inhibitory  power  do&s  not  follow  the  raising  of  the  heart 
to  high  temperatures.  The  vagus  remains  active  to  the  verge  of  heat  rigor, 
and  resumes  its  power  as  soon  as  the  rigor  passes  away. 

The  Augmentor  Nerves. 
V.  Bezold'  observed  in  1862  that  stimulation  of  the  cervical  spinal  cord 
caused  an  increased  frequency  of  heart-beat.  This  seemed  to  him  to  prove 
the  existence  of  special  accelerating  nerves.  Ludwig  and  Thiry,*  however, 
soon  pointed  out  that  stimulation  of  the  s]Mnal  cord  in  the  cervical  region 
excited  many  vaso-constrictor  fibres,  leading  to  the  narrowing  of  many  vessels 
and  a  corresponding  rise  of  blood-pressure.     The  acceleration  of  the  heart-beat 

'  Fantino,  1888,  p.  239;  see  also  Bidder,  1868,  p.  41  ;  Eichhorst,  1879,  p.  18;  Wa&silLeff, 
1881,  p.  317  ;  King,  1881,  p.  946. 

"  Compare  Soltmann,  1877,  p.  106;  Bochefontaine,  1877,  p.  226;  Tarchanoff,  1878,  p.  217; 
Langendorfl;  1879,  p.  247  ;  von  Anrep,  1880,  p.  78;  Meyer,  1893,  p.  477. 

3  Stewart,  1892,  p.  138.  *  Stewart,  1892,  p.  SO. 

*  von  Bezold,  1863,  p.  191.  «  Ludwig  and  Thiry,  1804,  p.  421. 


CIRCULATION.  459 

accompanying  this  rise  in  blood-pre&sure  would  alone  explain  the  observation 
of  vou  J>ezokl.  Three  years  later  Bever  and  von  Bezold '  were  more  suc- 
cessful. The  intluence  of  the  vaso-motor  nerves  was  excluded  by  section  of 
the  spinal  cord  between  the  first  and  second  thoracic  vertebrae.  Stimulation 
of  the  cervical  cord  now  caused  an  increase  \\\  the  frequency  of  the  heart-beat 
without  a  sinmltaneous  increase  of  blood-pressure.  The  fibres  carrying  the 
accelerating  impulse  were  traced  from  the  spinal  cord  to  the  last  cervical  gan- 
glion and  from  there  toward  the  heart. 

In  the  dof)  the  ''  augmenting "  or  "  accelerating "  nerves  thus  discovered 
leave  the  spinal  cord  mainly  by  the  roots  of  the  second  dorsal  nerves,  and  enter 
the  ganglion  stellatum,  whence  they  pass  through  the  anterior  and  posterior 
loops  of  the  annulus  of  Vieussens  into  the  inferior  cervical  ganglion,  from 
which  they  go,  in  tiie  cardiac  branches  of  the  latter,  to  the  heart.'  Some  of 
the  cardiac  fibres  in  the  annulus  pass  directly  thence  to  the  cardiac  plexus  and 
do  not  enter  the  inferior  cervical  ganglion. 

In  the  rabbit^  the  course  of  the  augmentor  fibres  is  probably  closely  similar 
to  that  in  the  dog. 

In  the  cat,*  the  augmentor  nerves  spring  from  the  ganglion  stellatum,  and 
very  rarely  from  the  inferior  cervical  ganglion  as  well.  The  right  cardiac 
sympathetic  nerve  communicates  with  the  vagus. 

The  stimulation  of  the  sympathetic  chain  in  the  frog,  "  between  ganglion  1 
and  the  vagus  ganglion,  and  also  stimulation  of  the  chain  between  ganglia  2 
and  3,  causes  marked  acceleration  and 
augmentation  of  the  auricular  and  ven- 
tricular contractions.  Stimulation  be- 
tween ganglia  3  and  4  produces  no  effect  y^y 
whatever  upon  the  heart."  ^  This  ex- 
periment of  Gaskell  and  Gadow's  shows 
that  augmentor  fibres  enter  the  sympa- 
thetic from  the  spinal  cord  along  the 
ramus  communicans  of  the  third  spinal 
nerve  and  pass  upward  in  the  sympa- 
thetic chain.  In  this  animal  the  sym- 
pathetic chain,  after  dividing  between 

the  first  and  second  ganglia  to  form  the  Fig.  llS— The  cardiac  sympathetic  nerves  in 

1  n  -i^- ^^^.     r^:„-,    +U^    t,..i.-,l-       Rana    temporaria    (twice    natural    size):    V-Sy, 

annulus    of    \  leUSSens,  joms    the    tlUUk       ^.^^^.^^^^^.^.^^^^ ,  ^.,,  arteria  vertebralis;  II, 

of  the  vagus  between- the  united  vagus       ir,  second  and  fourth  spinal  nerves  (Gaskell 
1      ,  ,  1  T  1    ,1  and  Gadow,  1884). 

and  glosso-pharyngeal  ganglia  and  tne 

vertebral  column  (see  Fig.  118).    Here  the  sympathetic  again  divides,  some  of 

1  von  Bezold,  1866,  p.  834;  Bever  and  von  Bezold,  1867,  p.  227. 

-  Eoy  and  Adanii,  1892,  p.  238  ;  compare  Schmiedeberg,  1871,  p.  38,  and  Langley,  1893,  p. 
108  ;  the  latter  states  on  p.  108  the  results  of  Bever  and  von  Bezold,  1867,  Schmiedeberg,  1871, 
Boehm  and  Nussbaum,  1875,  Strieker  and  Wagner,  1878,  Bradford,  1889,  and  Bradford  and 
Dean,  1889. 

3  Bever  and  von  Bezold,  1867,  p.  247 ;  see  remarks  of  Gaskell  and  Gadow,  1884,  p.  370. 
*  Boehm,  1875,  p.  260.  °  Gaskell  and  Gadow,  1884,  p.  369. 


460 


AN  AMERICAN   TEXT- BOOK   OF  PHYSIOLOGY. 


the  fibres  passing  alongside  the  vagus  into  the  cranial  cavity,  the  rest  accompany- 
ing the  vagus  nerve  perii)herally.  The  augmentor  nerves  for  the  heart  are 
anionff  the  latter,  for  the  slinuilation  of  the  intracranial  vagus  results  in  pure 
inhibition,'  while  the  stimulation  of  the  vagus  trunk  after  it  is  joined  by  the 
sympathetic  may  give  either  inhibition  or  augmentation.  We  may  say,  there- 
fore, that  the  augmentor  nerves  of  the  frog  pass  out  of  the  spinal  cord  by  the 
third  spinal  nerve,  through  the  ramus  comnmnicans  of  this  nerve,  into  the 
third  sympathetic  ganglion,  up  the  sympathetic  chain  to  the  ganglion  of  the 
vagus,  and  down  the  vagus  trunk  to  the  heart. 

Stimulation  of  Augmentor  Nerves. — The  most  obvious  effect  of  the  stim- 
ulation of  the  augmentor  nerves  is  an  increase  of  from  7  to  70  per  cent,  in  the 
frequency  of  the  heart-beat  (see  Fig.  119).  The  quicker  the  heart  is  beating 
before  thn  stimulation,  the  less  marked  is  the  acceleration.     The  absolute  maxi- 


Fig.  119.— Curve  of  blood-pressure  in  the  cat,  recorded  by  a  mercury  manometer,  showing  the 
increase  in  frequency  of  heart-beat  from  excitation  of  the  augmentor  nerves.  The  curve  reads  from 
right  to  left.  The  augmentor  nerves  were  excited  during  thirty  seconds,  between  the  two  stars.  The 
number  of  beats  per  ten  seconds  rose  from  24  to  33  (Boehm,  1875,  p.  258). 

mum  of  frequency  is,  however,  independent  of  the  frequency  before  stimulation.^ 
The  maximum  of  acceleration  is  largely  independent  of  the  duration  of  stimula- 
tion. The  duration  of  stimulation  and  the  duration  of  acceleration  are  not 
related,  a  long  stimulation  causing  no  greater  acceleration  than  a  short  one.^ 

The /o>-ce  of  the  ventricular  beat  is  increased.*  The  ventricle  is  filled  more 
completely  by  the  auricles,  the  volume  of  the  ventricle  being  increased.     The 


^rr  /  'yV  /i'-c    r/ 


Fig.  120.— Increase  in  the  force  of  the  ventricular  contraction  (curve  of  pressure  in  right  ventricle)  from 
stimulation  of  angmentor  fibres.    There  is  little  or  no  change  in  frequency  (Franck,  1890,  p.  819). 

output  of  the  heart  is  rai.sed.'  There  is  no  definite  relation  between  the  in- 
crease of  contraction  volume  or  force  of  contraction  and  the  increase  in  fre- 
quency (see  Fig.  120).     Either  may  appear  without  the  other,  though  this  is 

'  Gaskell,  1884,  p.  48.  "  Boehm,  1875,  p.  277.  ^  Baxt,  1877,  p.  523. 

*  Heidenhain,  1882,  p.  396;  Ga-skell,  1884,  p.  47;  1886,  p.  42;  Mills,  1886,  p.  554;  Franck, 
1890,  p.  814;  Roy  and  Adami,  1892,  p.  242;  Baylies  and  Starling,  1892,  p.  413. 
5  Roy  and  Adami,  1892,  p.  240. 


CIRCULATION.  461 

rare.*  The  simultaneous  stimulation  of  the  nerves'of  Ijoth  sides  does  not 
give  a  greater  maximum  frequcncv  than  the  stimulation  of  one  nerve  alone.^ 

The  strength  and  the  volume  of  the  auricular  contractions  are  also  in- 
creased. The  increase  in  volume  is  not  due  to  a  rise  of  pressure  in  the  veins 
— in  fact,  the  pressure  falls  in  the  veins — but  to  a  change  in  the  elasticitv  of 
tiie  relaxed  auricle,  a  lowering  of  its  tonus.  This  change  is  not  related  to  the 
increase  in  the  force  of  the  auricular  contractions  that  stimulation  of  the  auo^- 
mentor  nerves  also  causes.  It  varies  much  in  amount  and  is  less  constantly 
met  with  than  the  change  in  force.^  The  changes  in  the  ventricle  and  auricle 
probably  account  for  the  rise  of  blood-pressure  in  the  systemic  arteries  and  the 
fall  in  both  systemic  and  pulmonary  veins  observed  by  Roy  and  Adami.* 

The  speed  of  the  cardiac  excitation  icave  is  increased.  Its  passage  across 
the  auriculo- ventricular  groove  is  also  quickened,  as  is  shown  in  the  following 
experiment  of  Bayliss  and  Starling.'^  In  the  dog,  the  artificial  excitation  of 
the  ventricle  may  cause  the  excitation  wave  to  travel  in  a  reverse  direction, 
namely,  from  ventricle  to  auricle.  If  the  ventricles  are  excited  rhythmically 
and  the  rate  of  excitation  is  gradually  increased,  a  limit  will  be  reached  beyond 
which  the  auricle  no  longer  beats  in  response  to  every  ventricular  contraction. 
With  intact  vagi,  a  rate  of  3  per  second  is  generally  the  limit.  If  now  the 
augmentor  nerve  is  stimulated,  the  "block"  is  partially  removed,  and  the 
auricle  beats  during  and  for  a  short  time  after  the  stimulation  at  the  same 
rapid  rate  as  the  ventricle. 

The  latent  periocjAf  the  excitation  is  long.  In  the  dog,  about  two  seconds 
pass  between  the  beginning  of  stimulation  and  the  beginning  of  acceleration, 
and  ten  seconds  may  pass  before  the  maximum  acceleration  is  reached.^  The 
after-effect  mav  continue  two  minutes  or  more."  It  consists  of  a  weakenino;  of 
the  contractions  and  an  increase  in  the  difficulty  with  M'hich  the  excitation 
wave  passes  from  the  auricle  to  the  ventricle.  The  return  to  the  former  fre- 
quency is  more  rapid  after  short  than  after  long  stimulations.^ 

The  simultaneous  stimulation  of  the  inhibitory  and  the  augmenting  nerves 
of  the  heart,  either  in  the  vagus  or  separately,  causes,  in  warm-blooded  ani- 
mals, inhibition  and  not  auo-nientation.  The  inhibition  overcomes  the  auo[- 
mentation,^  but  the  vagus  effect  is  diminished  nevertheless.  The  acceleration 
that  is  seen  after  the  stimulation  of  the  vagus  is  due  to  the  after-effect  of  the 
stimulation  of  accelerating  filires  in  the  vagus. 

The  simultaneous  stimulation  of  the  auo:;mentors  and  the  vagi,  the  strength 
of  the  current  being  sufficient  to  stop  the  auricular  contractions,  causes  accel- 
eration of  the  ventricular  contractions.*'' 

1  Franck,  1S90,  p.  819 ;  Roy  and  Adami,  1892,  p.  240.  ^  Franck,  1880,  p.  85. 

^  Rov  and  Adami,  1892.  p.  240.  *  Ibid. 

»  Bavliss  and  Starling,  1892,  p.  415.  «  Baxt,  1877,  p.  529. 

'  von  Bezold  and  Bever,  1867,  p.  245;  Schraiedeberg,  1870,  p.  136;  1871,  p.  43;  Boehm, 
1875,  p.  273.  ^  Baxt,  1877,  p.  536. 

»  Bowditch,  1873.  p.  273;  Bast,  1875,  p.  204:  Boehm,  1875,  p.  278. 

^°  Bayliss  and  Starling,  1892,  p.  414.  For  further  discussion  of  the  effects  of  simultaneous 
stimulation,  see  Meltzer,  1892,  p.  376. 


402 


^iV^  AMERICAN  TEXT-BOOK   OF  PHYSIOLOGY. 


Other  Centrifugal  Heart-nerves. 

Ill  the  vago-sympathetic  trunk  and  tlic  annulus  of  Vieussens  fibres  pass  to 
the  heart  tliat  cannot  be  chissed  either  with  the  vatj^us  or  the  augmentor  nerves. 
Tlie  evidence  for  their  existence  is  furnished  bv  Roy  and  Adami's  observation 
that  when  the  intracardiac  vagus  mechanism  is  acting  strongly,  so  that  the 
auricles  are  more  or  less  completely  arrested,  the  stimulation  of  the  vago- 
sympathetic trunk  sometimes  causes  a  decided  increase  in  the  force  both  of 
the  ventricles  and  the  auricles,  usually  accompanied  by  an  acceleration  of  the 
rhythm  of  the  heart.  These  changes  are  too  rapidly  produced  to  be  aiig- 
mentor  effects.' 

Centrifugal  inhibitory  nerves  have  been  found  as  an  anomaly  in  the  right 
depressor  nerve  of  a  rabbit.^ 

Pawlow^  dividers  the  inhibitory  and  augmentor  nerves  into  four  classes — 
(1)  nerves  inhibiting  the  frequency  of  the  beat,  (2)  nerves  inhibiting  the  force  of 

the  contraction,  (3)  nerves  augmenting 
frequency,  and  (4)  nerves  augmenting 
force.  The  origin  of  this  subdivision 
of  the  two  groups  generally  recog- 
nized was  the  observation  that,  in  cer- 
tain stages  of  convallaria  poisoning,  the 
excitation  of  the  vagus  in  the  neck — all 
the  branches  of  the  nerve  except  those 
going  to  heart  ancrlungs  being  cut — re- 
duced the  blood-pressure  without  alter- 
ing the  frequency  of  the  beat.  Further 
researches  showed  that  the  stimulation 
of  branch  3  (Fig.  121)  even  in  unpoi- 
soned  animals  reduced  the  blood-pres- 
sure independently  of  the  variable  al- 
teration simultaneously  produced  in  the 
pulse-rate.  Stimulation  of  branch  5 
produced  an  acceleration  of  the  heart- 
beat without  increase  of  blood-pressure. 
Other  branches  brought  about  rise  of 
pressure  without  acceleration,  and  in- 
creased discharge  by  the  left  ventricle  without  alteration  in  the  }>ulse-rate. 
These  results  are  supported  further  by  Wooldridge's  observation  that  exci- 
tation of  the  peripheral  ends  of  certain  nerves  on  the  posterior  surface  of  the 
ventricle  raised  the  blood-pressure  without  modifying  the  frequency  of  contrac- 
tion,^ and  by  Roy  and  Adami's  demonstration  that  certain  branches  of  the  first 
thoracic  ganglion  lessen  the  force  of  the  cardiac  contraction  without  influencing 
its  rhythm.^      But  the  matter  is  as  yet  far  from  certain. 

>  Roy  and  Adami,  1892,  p.  249.  *  Herins;,  1894,  p.  78. 

»  Pawlow,  1887,  p.  510.  *  Wooldridge,  1883,  p.  537. 

*  Rot  and  Adami,  1892,  p.  246. 


Fig.  121. — Scheme  of  the  centrifugal  nerves  of 
the  heart  according  to  Pawlow  :  1,  vago-sympa- 
thetic  nerve ;  2,  upper  inner  branch ;  3,  strong 
inner  branch;  4,  lower  inner  branch:  5,  upper 
and  lower  outer  branches ;  6,  ganglion  stellatum  ; 
7,  annulus  of  Vieussens ;  8,  middle  (inferior)  cer- 
vical ganglion ;  9,  recurrent  laryngeal  nerve. 


CIRCiJLA  TIOX.  463 

The  Centripetal  Nerves  of  the  Heart. 

The  Ventricular  Nerves. — When  the  nuiininalian  heiirt  is  freed  from 
blood  by  wa.sliiii^-  it  out  with  normal  saline  solution  and  the  ventricle  is  painted 
with  pure  carbolic  acid,  liquefied  by  \varmiu<^,  numerous  nerves  appear  as 
white  threads  on  a  i)rown  back<2:;round.  They  are  non-medullated,  form  many 
plexuses,  and  run  beneath  the  pericardium  obliquely  downward  from  the  base 
to  the  apex  of  the  ventricle.  They  may  be  traced  to  the  cardiac  plexus. 
These  fibres  are  not  centrifugal  branches  of  the  vagus  or  the  augmentor  nerves, 
for  the  characteristic  eifects  of  vagus  and  augmentoi'  stimulation  are  seen  after 
section  of  the  nerves  in  question.  The  stimulation  of  their  peripheral  ends, 
moreover,  the  fibre  being  carefully  dissected  out  from  the  subpericardial  tissue, 
cut  across,  and  the  cut  end  raised  on  a  thread  in  the  air,  is  without  effect  on 
the  blood-})ressure  and  pulse-rate.  The  stimulation  of  the  central  stumps  of 
these  nerves,  on  the  contrary,  is  followed  by  changes  both  in  the  blood-pressure 
and  the  pulse,  showing  that  they  carry  impulses  from  the  heart  to  the  cardiac 
centres  in  the  central  nervous  system,  or  perhaps,  according  to  the  views  of 
some  recent  investigators,  to  peripheral  ganglia,  thus  modifying  the  action  of 
the  heart  reflexly.^ 

Sensory  Nerves  of  the  Heart. — The  stimulation  of  intracardiac  nerves 
by  the  application  of  acids  and  other  chemical  agents  to  the  surface  of  the 
heart  causes  various  reflex  actions,  such  as  movements  of  the  limbs.  The 
afferent  nerves  in  these  reflexes  are  the  vagi,  for  the  reflex  movements  dis- 
appear when  the  vagi  are  cut.^  On  the  strength  of  these  experiments  the 
vagus  has  been  believed  to  carry  sensory  impressions  from  the  heart  to  the 
brain.  Direct  stimulation  of  the  human  heart,  in  cases  in  which  a  defect  in 
the  chest-wall  has  made  the  organ  accessible,  give  evidence  of  a  dim  and  very 
limited  recognition  of  cardiac  events — for  example,  the  compression  of  the 
heart.^ 

Vagus. — The  stimulation  of  the  central  end  of  the  cut  vagus  nerve,  the 
other  vagus  being  intact,  causes  a  slowing  of  the  pulse-rate.  The  section  of 
the  second  vagus  causes  this  retardation  of  the  pulse  to  disappear,  indicating 
that  the  stimulation  of  the  central  end  of  the  one  affects  the  heart  reflexly 
through  the  agency  of  the  other  vagus.  The  blood-pressure  is  simultaneously 
affected,  being  sometimes  lowered  and  sometimes  raised,  the  difference  seeming 
to  depend  largely  on  the  varying  composition  of  the  vagus  in  different  ani- 
mals and  in  different  individuals  of  the  same  species.*  The  stimulation  of  the 
pulmonary  branches,  by  gently  forcing  air  into  the  lungs,  loud  speaking,  singing, 
etc.,  is  said  to  increase  the  frequency  of  the  heart-beat.^  Yet  the  chemical 
stimulation  of.  the  raucous  membrane  of  the  lungs  is  alleged  to  slow  the  pulse- 

1  Wooldridge,  ia83,  pp.  523,  529,  539 ;  see  also  Lee,  1849,  p.  43. 

^  Budge,  1846,  p.  588 ;  Goltz,  1863,  p.  5 ;  Giirboki,  1872,  p.  289;  Franck,  1880,  p.  382. 

3  V.  Ziemssen,  1882,  p.  297 ;  Nothnagel,  1891,  p.  209. 

*  See  Franck,  1880,  p.  281 ;  v.  Bezold,  1863,  p.  281  ;  Dreschfeld,  1867,  p.  326 ;  Aubert  and 
Eoever,  1868,  p.  211 ;  Kowalewsky  and  Adamiik,  1868,  p.  546;  Cybulski  and  Wartanow,  1883; 
Eey  and  Aducco,  1887,  p.  188;   Arendt,  1890,  p.  11 ;   Koy  and  Adami,  1892,  p.  251. 

5  Hering,  1871  ;  Sommerbrodt,  1881,  p.  602. 


464  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

rate  and  lower  the  blood-pressure.'  Observers  differ  as  to  the  results  of  stim- 
ulation of  the  central  end  of  the  laryngeal  branches  of  the  vagus  on  the  pulse- 
rate  and  blodd-prcssure.* 

Depressor  Nerve. — The  earlier  stiiiuilatii)iis  of  the  nerves  that  pass 
between  the  central  nervous  system  and  the  iieart,  with  the  exception  of  the 
vao-us,  altered  neither  the  blood-pressiu'e  nor  the  pulse-rate.  Ludwig  and  (  yon  ^ 
suspected  that  the  negative  results  were  owing  to  the  fact  that  the  stiMuilations 
were  confined  to  the  end  of  the  cut  nerve  in  connection  with  the  heart.  Some 
of  the  nerves,  they  thousrht,  should  carry  impulses  from  the  heart  to  the  brain, 
and  such  nerves  could  be  found  only  by  stimulation  of  the  brain  end  of  the 
cut  nerve.  Thev  began  their  research  for  these  aflereut  nerves  with  the  branch 
which  springs  from  the  rabbit's  vagus  high  in  the  neck  and  passes  downward 
to  the  ganglion  stoUatum.  Their  suspicion  was  at  once  confirmed.  The  stimu- 
lation of  the  central  end  of  this  nerve,  called  by  Ludwig  and  Cyon  the  depres- 
sor, caused  a  considerable  fall  of  the  blood-pressure. 

The  depressor  nerve  arises  in  the  rabbit  by  two  roots,  one  of  which  comes 
from  the  trunk  of  the  vagus  itself,  the  other  from  a  branch  of  the  vagus,  the 
superior  laryngeal  nerve.  Frequently  the  origin  is  single  ;  in  that  case  it  is 
usuallv  from  the  nervus  laryngeus.*  The  nervus  depressor  runs  in  company 
with  the  svmpathetic  nerve  to  the  chest,  where  commuuicatious  are  made  with 
the  branches  of  the  ganglion  stellatum. 

The  stimulation  of  the  peripheral  end  of  the  depressor  nerve  is  without 
effect  on  |he  blood-pressure  and  heart-beat.  The  stimulation  of  the  central 
end,  on  the  contrary,  causes  a  gradual  fall  of  the  general  blood-pressure  to  the 
half  or  the  third  of  its  former  height.  After  the  stimulation  is  stopped,  the 
blood-pressure  returns  gradually  to  its  previous  level. 

Simultaneously  with  the  fall  in  blood-pressure  a  lessening  of  the  pulse-rate 
sets  in.  The  slowing  is  most  marked  at  the  beginning  of  stimulation,  and  after 
rapidlv  reaching  its  maximum  gives  way  gradually  until  the  rate  is  almost 
what  it  was  before  the  stimulation  began.  After  stimulation  the  frequency  is 
commonly  greater  than  previous  to  stimulation. 

After  section  of  both  vagi,  the  stimulation  of  the  depressor  causes  no  change 
in  the  pulse-rate,  but  the  blood-pressure  falls  as  usual.  The  alteration  in  fre- 
quencv  is  therefore  brought  about  through  stimulation  of  the  cardiac  inhibitory 
centre,  acting  on  the  heart  through  the  vagi.  The  experiment  teaches,  further, 
that  the  alteraticm  in  pressure  is  not  dependent  on  the  integrity  of  the  vagi. 

Poisoning  with  curare  paralyzes  all  motor  mechanisms  except  the  heart  and 
the  muscles  of  the  blood-vessels.  Yet  curare-poisoning  does  not  affect  the 
result  of  depressor  stimulation.  The  cause  of  the  fall  in  blood-jiressure  must 
be  sought  then  either  in  the  heart  or  the  reflex  dilatation  of  the  blood-vessels. 
It  cannot  be  in  the  heart,  for  depressor  stimulation  lowers  the  blood-pressure 
after  all  the  nerves  going  to  the  heart  have  been  .severed.     It  must  therefore 

>  Franck,  1880,  p.  378.  *  Aubert  and  Roever,  1868,  p.  241  ;  Franck,  1880,  p.  357. 

'  Ludwig  and  Cyon,  1866,  p.  128. 

*  Tschirwinsky,  1896,  p.  778,  gives  a  somewhat  different  account. 


CIRCULATION.  465 

lie  in  the  blood-vessels.  Liulwig  and  Cyou  knew  that  the  dilatation  of 
the  intestinal  vessels  could  produce  a  great  fall  in  the  blood-pressure  and 
turned  at  once  to  them.  Section  of  the  splanchnic  nerve -caused  a  dilata- 
tion of  the  abdominal  vessels  and  a  fall  in  the  blood-pressure.  Stimula- 
tion of  the  peripheral  end  of  the  cut  splanchnic  caused  the  blood-pressure  to 
rise  even  beyond  its  former  height.  If  now  the  depressor  lowers  the  blood- 
pressure  chiefly  by  affecting  the  splanchnic  nerve  reflexly,  the  stimulation  of 
the  central  end  of  the  depressor  after  section  of  the  splanchnic  nerves  ought  to 
have  little  effect  on  the  blood-pressure.  This  proved  to  be  the  case.  The 
depressor,  therefore,  reduces  the  blood-pressure  chiefly  by  lessening  the  tonus 
of  the  vessels  governed  by  the  splanchnic  nerve,  thus  allowing  their  dilatation 
and  in  consequence  lessening  the  peripheral  resistance. 

It  has  already  been  said  that  .the  depressor  fibres  pass  from  the  heart  to  the 
vaso-motor  mechanism  in  the  central  nervous  system.  The  cardiac  fibres  are 
probably  stimulated  when  the  heart  is  overfilled  through  lack  of  expulsive 
force  or  through  excessive  venous  inflow,  and,  by  reducing  the  peripheral  resist- 
ance, assist  the  engorged  organ  to  empty  itself. 

The  depressor  nerve  is  not  in  continual  action  ;  it  has  no  tonus ;  for  the  sec- 
tion of  both  depressor  nerves  causes  no  alteration  in  the  blood-pressure. 

The  many  successors  of  Cyon  and  Ludwig  have  added  relatively  few  im- 
portant facts  to  their  extraordinary  investigation. 

Sewall  and  Steiuer  ^  have  obtained  in  some  cases  a  permanent  rise  in  blood- 
pressure  following  section  of  both  depressors,  yet  they  hesitate  to  say  that  the 
depressor  exercises  a  tonic  action. 

Spallita  and  Consiglio  ^  have  stimulated  the  depressor  before  and  after  the 


rao 


\ 

v^ 

^v^ 

'A.A 

A  A 

,A 

N 

'■\ 

A 

/V 

Fig.  122.— Showing  the  fall  in  blood-pressure  and  the  dilatation  of  peripheral  vessels  from  stimula- 
tion of  the  central  end  of  the  depressor  nerve  (Bayliss) :  A,  curve  of  blood-pressure  in  the  carotid  artery ; 
B,  volume  of  hind  limb,  recorded  by  a  plethysmograph ;  C,  electro-magnet  line,  in  which  the  elevation 
shows  the  time  of  stimulation  of  the  nerve ;  D,  atmospheric  pressure-line ;  E,  time  in  seconds. 

section  of  the  spinal  accessory  nerve  near  its  junction  with  the  vagus.     They 
find  that  after  section  of  the  spinal  accessory,  the  stimulation  of  the  depressor 
'  Sewall  and  Steiner,  1885,  p.  168.  "^  Spallita  and  Consiglio,  1892,  p.  42. 

30 


46G  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

docs  not  arteot  the  pulse,  whence  they  conclude  that  the  depressor  fibres  that 
affect  the  blood-pressure  are  separate  from  those  that  affect  the  rate  of  beat,  the 
latter  being  derived  from  the  spinal  accessory  nerve. 

A  recent  study  by  JJayliss '  brings  out  several  new  facts.  II'  a  limb  is  i)la(cd 
in  Mosso's  plethysmogra])li  and  the  central  end  of  the  depressor  stinudated, 
the  volume  of  the  lind)  increases,  showing  an  active  dilatation  of  tiie  vessels 
that  supply  it.  The  latent  period  of  this  dilatation  varies  greatly,  'i'he  vessels 
of  the  skin  play  a  large  part  in  its  production.  A  similar  local  action  is  seen 
on  the  vessels  of  the  head  and  neck  (see  Fig.  122). 

The  depressor  fibres  vary  much  in  size  in  different  animals.  When  the 
nerve  is  small,  a  greater  depressor  effect  can  be  obtained  by  stimulating  the 
central  end  of  the  vagus  than  from  the  depressor  itself  But  the  course  of  the 
fall  is  different  in  the  two  cases.  With  the  depressor,  the  fall  is  maintained  at 
a  constant  level  during  the  whole  excitation,  however  long  it  lasts,  whereas 
in  the  case  of  the  vagus  the  pressure  very  soon  returns  to  its  original 
hei^dit  although  the  excitation  still  continues.  Bayliss  believes,  therefore, 
that  there  is  a  considerable  difference  between  the  central  connections  of 
the  depressor  nerve  itself  and  the  depressor  fibres  sometimes  found  in  other 
nerves. 

The  left  depressor  nerve  usually  produces  a  greater  fall  of  pressure  than  the 
right.  The  excitation  of  the  second  nerve  during  the  excitation  of  the  first 
produces  a  greater  fall  than  the  excitation  of  one  alone. 

The  fibres  of  the  depressor,  in  part  at  least,  end  in  the  wall  of  the  ventricle.^ 
A  similar  nerve  has  been  demonstrated  in  the  cat,^  horse,*  dog,*  sheep,^  swine/ 
and  in  raan.^ 

Sensory  Nerves. — The  first  and  usually  the  only  effect  of  the  stimulation 
of  the  central  end  of  a  mixed  nerve  like  the  sciatic,  according  to  Roy  and 
Adami,^  is  an  increase  in  the  force  and  the  frequency  of  the  heart-beat.  Other 
observers  ^"^  have  sometimes  found  quickening  and  sometimes  slowing  of  the  pulse- 
rate,  so  that  sensory  nerves,  as  Tigerstedt"  suggests,  appear  to  affect  both  the 
inhibitory  and  the  augmenting  heart-nerves.  When  a  sensory  nerve  is  weakly 
excited  the  augmentor  effect  predominates,  when  strongly  excited  the  inhibi- 
tory. A  well-known  demonstration  of  the  reflex  action  of  the  sensory  nerves 
on  the  heart  is  seen  in  the  slowing  of  the  rabbit's  heart  when  the  animal 

1  Bayliss,  1893,  p.  304.  '  Kazem-Beck,  1888,  p.  329. 

'  Bernhardt,  1868,  p.  5;  Auhert  and  Roever,  1868,  p.  214;  Kowalewsky  and  Adamiik,  1868, 
p.  545;  Roever,  1869,  p.  68;  Kazem-Beck,  1888,  p.  331. 

*  Bernliardt,  1868,  p.  5  ;  Cyon,  1870,  p.  262;  Finkelstein,  1880,  p.  350. 

*  Roever,  1869,  p.  71 ;  Langenbacher,  1877  ;  Kreidniann,  1878,  p.  411 ;  Finkelstein,  1880,  p. 
248  ;  Kazem-Beck,  1888,  p.  332. 

«  Kriedmann,  1878,  p.  407.  ^ 

'  Langenbacher,  1877;  Kazem-Beck,  1888,  p.  335;  the  latter  describes  also  (p.  .338)  a  de- 
pressor nerve  in  cold-blooded  animals;  compare  Ga.skell  and  Gadow,  1885,  p.  362. 

8  Bernhardt,  1868,  p.  5;  Kreidmann,  1878,  p.  408;  Finkelstein,  1880,  p.  249;  B^k^sy,  1888. 

9  Roy  and  Adami,  1892.  p.  254. 

>•>  Lov^n,  1866,  p.  5  ;  Bernard,  1858,  p.  291 ;  Asp,  1867,  p.  173  ;  Tranck,  1876,  p.  246 ;  Siman- 
owskv,  1881.  "  Figerstedt,  1893,  p.  287. 


CIRCULA  TION.  467 

is  mado  to  inhale  oliloroform.  Tlie  superior  laryngeal  and  the  trigeminus 
nerves,  especially  the  latter,  convey  the  stimulus  to  the  nerve-centres.* 

The  stiiiuilation  of  the  nenrs  of  special  sense,  optic,  auditory,  olfactory  and 
glosso-pharyngeal  nerves,  also  sometimes  slows  and  sometitues  quickens  the 
heart.^ 

Sympathetic. — The  reflex  action  of"  the  sympathetic  nerve  upon  the  heart 
is  well  shown  by  the  celebrated  experiment  of  F.  Goltz.^  In  a  medium-sized 
frog,  the  [)ericardium  was  exposed  by  carefully  cutting  a  small  window  in  the 
chest-wall.  The  pulsations  of  the  heart  could  be  seen  through  the  thin  peri- 
cardial membrane.  Goltz  now  began  to  beat  upon  the  abdomen  about  140 
times  a  minute  M'ith  the  handle  of  a  scalpel.  The  heart  gradually  slowed,  and 
at  length  stood  still  in  diastole.  Goltz  now  ceased  the  rain  of  little  blows. 
The  heart  remained  quiet  for  a  time  and  then  began  to  beat  again,  at  first  slowly 
and  then  more  rapidly.  Some  time  after  the  experiment,  the  heart  beat  about 
five  strokes  in  the  minute  faster  than  before  the  experiment  was  begun.  The 
effect  cannot  be  obtained  after  section  of  the  vagi. 

Bernstein  *  found  that  the  afferent  nerves  in  Goltz's  experiment  were  branches 
of  the  abdominal  sym])athetic,  and  discovered  that  the  stimulation  of  the  cen- 
tral end  of  the  abdominal  sympathetic  in  the  rabbit  was  followed  also  by  reflex 
inhibition  of  the  heart. 

The  stimulation  of  the  central  end  of  the  splanchnic  produces  a  reflex  rise 
of  blood-pressure  and,  perhaps  secondarily,  a  slowing  of  the  heart.^  In  some 
cases  acceleration  has  been  observed.^  According  to  Roy  and  Adami  splanch- 
nic stimulation  sometimes  produces  a  combination  of  augmentor  and  vagus 
effects,  the  augmentation  appearing  during  stimulation  and  giving  place 
abruptly  to  well-marked  inhibitory  slowing  at  the  close  of  stimulation,'' 

The  results  of  stimulating  various  abdominal  viscera  have  been  studied  by 
Mayer  and  Pribram.  One  of  the  most  interesting  of  the  reflexes  observed  by 
them  was  the  inhibition  of  the  heart  called  forth  by  dilating  the  stomach.^ 

The  stimulation  of  the  cervical  sympathetic  does  not  give  any  very  constant 
results  on  the  action  of  the  heart,^ 

B.  The  Centres  op  the  Heart-nerves. 

Inhibitory  Centre. — It  has  been  already  mentioned  that  the  brothers 
Weber  *"  localized  the  cardiac  inhibitory  centre  in  the  medulla  oblongata.  The 
efforts  to  fix  the  exact  location  of  the  centre  by  stimulation  of  various  parts, 
either  mechanically,  by  thrusting  fine  needles  into  the  medulla,*'  or  electrically, 

1  Dogiel,  1866,  p.  236;  Kratschmer,  1870,  p.  159;  Franck,  1876,  p.  227;  Simanowsky,  1881. 

2  Couty  and  Charpentier,  1877,  p.  563.  *  Goltz,  1863,  p.  11. 

*  Bernstein,  1863,  p.  818 ;  1864,  pp.  617,  642.  *  Asp,  1867,  p.  150. 
6  V.  Bezold,  1863,  p.  252;  Asp,  1867,  p.  172;  Sabbatini,  1891,  p.  219. 

'  Roy  and  Adami,  1892,  p.  258. 

*  Mayer  and  Pribram,  1872,  p.  107  ;  Simanowsky,  1881. 

8  Bernstein,  1864,  p.  630;  Aubert  and  Roever,  1868,  p.  240  ;  1869,  p.  95;  Bernstein,  1868, 
p.  601.  '"  Weber,  1846,  p.  45. 

"  Eckhard,  1878,  p.  187 ;  Klug,  1880,  p.  516 ;  Laborde,  1888,  p.  400. 


4GS  AX  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

cannot  inspire  great  confidence  becau.se  of  the  difficulty  of  distinguishing 
between  rhe  resuhs  that  follow  the  excitation  of  a  nerve-path  from  or  to  the 
centre  and  those  following  the  excitation  of  the  centre  itself.  According  to 
Laborde,  who  also  used  this  method,  the  cardiac  inhibitory  centre  is  situated  at 
the  level  of  the  mass  of  cells  known  as  the  accessory  nucleus  of  the  hypoglossus 
and  the  mixed  nerves  (vagus,  spinal  accessory,  glosso-pharj'ngeal).^ 

Tiie  localization  of  the  centre  by  the  method  of  successive  sections  is  per- 
haps more  trustworthy.  Frauck  -  has  found  that  the  separation  of  the  bulb 
from  the  spinal  cord  cuts  off  the  reflexes  c-alled  forth  by  nerves  that  enter  the 
spinal  cord,  while  leaving  undisturbed  the  reflex  produced  by  stimulation  of 
the  trigeminus  nerve. 

On  the  whole,  there  seems  to  be  no  doubt  that  the  cardiac  inhibitory  centre 
is  situated  in  the  bulb. 

Tonus  of  Cardiac  Inhibitory  Centre. — The  cardiac  inhibitory  centre  is  prob- 
ably always  in  action,  for  when  the  vagus  nerves  are  cut,  the  heart-beat 
becomes  more  frequent.  The  source  of  this  continued  or  "tonic"  activity 
may  lie  in  the  continuous  discharge  of  inhibitory  impulses  created  by  the 
liberation  of  energy  in  the  cell  independeut  of  direct  external  influences,  or 
the  cells  may  be  disciiarged  by  the  continuous  stream  of  afferent  impulses 
that  must  constantly  play  upon  them  from  the  multitude  of  afferent  nerves. 
This  latter  theory,  the  conception  of  a  reflex  tonus,  is  made  probable  by  the 
observations  that  section  of  the  vagi  does  not  increase  the  rate  of  beat  after 
the  greater  part  of  the  afferent  impulses  have  been  cut  off"  by  division  of  the 
spinal  cord  near  its  junction  with  the  bulb,^  and  that  the  sudden  decrease  in 
the  number  of  afferent  impulses  caused  by  section  of  the  splanchnic  nerve 
quickens  the  pulse-rate,^ 

Irradiation. — The  slowing  of  the  rate  of  beat  observed  chiefly  during  the 
expiratory  i)ortion  of  respiration  disappears  after  the  section  of  both  vagus 
nerves.  The  slowing  may  perhaps  be  due  to  the  stimulation  of  the  cardiac 
inhibitory  centre  by  irradiation  from  the  respiratory  centre.'^ 

Origin  of  Cardiac  Inhibitory  Fibres. — Since  the  researches  of  "Waller^  and 
others,  it  has  been  generally  believed  that  the  cardiac  inhibitory  fibres  enter 
the  vagus  from  the  spinal  accessory  nerve,  for  the  reason  that  cardiac  inhibi- 
tion was  not  secured  in  animals  in  which  the  fibres  in  the  vagus  derived  from 
the  spinal  accessory  nerve  were  made  to  degenerate  by  tearing  out  the  latter 
before  its  junction  with  the  vagus.  These  results  have  lately  been  called  in 
question  by  Grossmann.^  The  method  employed  by  his  predecessors,  according 
to  him,  probably  involved  the  destruction  of  vagus  roots  as  well  as  those  of 
the  spinal  accessory.  Grossmann  finds  that  the  stimulation  of  the  spinal 
accessory  nerve  before  its  junction  with  the  vagus  does  not  inhibit  the  heart. 
Nor  does  inhibition  follow  the  stimulation  of  the  bulbar  roots  supposed  to  be 
contributed  to  the  mixed  nerve  by  the  spinal  accessory. 

^  Laborde,  1888,  p.  415.  '  Franck,  1876,  p.  255.  '  Bernstein,  1864,  p.  654. 

♦  Asp.  1867.  p.  136.  ^  Laulanie.  1S93.  p.  72.S. 

•Waller,  1856,  p.  420;  Schiff,  1858;  Heidenhain,  1865.  p.  109;  Gianuzzi.  1872;  Franck, 
1876,  p.  264.  '  Grossmann,  1895,  p.  6. 


CIRCULATION.  469 

Augmentor  Centre.— The  situation  (.f  the  centre  for  the  augmentor 
nerves  of  tlie  heart  is  not  definitely  known,  aUhough  from  analogy  it  seems 
probable  that  it  will  be  found  in  the  bulb.  That  this  centre  is  constantly  in 
action  is  indicated  by  the  lowering  of  the  pulse-rate  after  section  of  the  vagi 
followed  bv  the  bilateral  extirpation  of  the  inferior  cervical  and  first  thoracic 
gano:lia.  The  division  of  the  spinal  cord  in  the  upper  cervical  region  after  the 
section  of  the  vagi  has  the  same  etfect.^  Vagus  inhibition,  moreover,  is  .said 
to  be  moi-e  readily  i)roduced  after  section  of  the  augmentor  nerves.^ 

:McWilliam  ^  has  remarked  that  the  latent  period  and  the  character  of  the 
acceleration  often  accompanying  the  excitation  of  afferent  nerves  may  differ 
entirely  from  the  characteristic  effects  of  the  excitation  of  augmentor  nerves. 
The  stimulation  of  the  latter  is  followed  by  a  long  latent  period,  after  M-hich 
the  rate  of  beat  gradually  increases  to  its  maximum  and,  after  excitation  is 
over,  as  gradually  declines.  The  excitation  of  an  afferent  nerve,  on  the  con- 
trary, causes  often,  with  almost  no  latent  jieriod,  a  remarkably  sudden  accel- 
eration, that  reaches  at  once  a  high  value  and  often  suddenly  gives  way  to  a 
slow  heart-beat.  These  facts  seem  to  show  that  reflex  acceleration  of  the  heart- 
beat is  due  to  changes  in  the  cardiac  inhibitory  centre,  and  not  to  augmentor 
excitation.  This  view  is  strengthened  by  the  fact  that  if  the  augmentor  nerves 
are  cut,  the  vagi  remaining  intact,  the  stimulation  of  afferent  fibres,  fi)r  exam- 
ple in  the  brachial  nerves,  can  still  cause  a  marked  quickening  of  the  pulse- 
rate.  In  short,  the  action  of  afferent  nerves  upon  the  rate  of  beat  is  essentially 
the  same,  according  to  this  observer,  whether  the  augmentor  nerves  are  divided 

or  intact. 

Roy  and  Adami '  believe  that  the  stimulation  of  afferent  nerves,  such  as  the 
sciatic  or  the  splanchnic,  excites  both  augmentor  and  vagus  centres.  The 
augmentor  centre  is  almost  always  the  more  strongly  excited  of  the  two,  so 
that  augmentor  effects  alone  are  usually  obtained. 

Action  of  Higher  Parts  of  the  Brain  on  Cardiac  Centres.— Repeated 
efforts  have  been  made  to  find  areas  in  the  cortex  of  the  brain  especially 
related  to  the  inhibition  or  augmentation  of  the  heart,  but  with  results  so  con- 
tradictory as  to  warrant  the  conclusion  that  the  influence  on  the  heart-beat 
of  the  parts  of  the  brain  lying  above  the  cardiac  centres  does  not  differ  essen- 
tially from  that  of  other  organs  peripheral  to  those  centres.* 

Yoluntarv  control  of  the  heart,  by  which  is  meant  the  power  to  alter  the 
rate  of  beat  bv  the  exercise  of  the  will,  is  impossible  except  as  a  rare  indi- 
vidual peculiaritv,  commonlv  accompanied  by  an  unusual  control  over  muscles, 
such  as  the  platvsma,  not  usually  subject  to  the  will.  Cases  are  described  by 
Tarchanoff^  and  Pease,^  in  which  acceleration  of  the  beat  up  to  twenty-seven 

1  Tschirjew,  1877,  p.  164 ;  Strieker  and  Wagner,  1878,  p.  370. 

^  Sustschinsky,  1868,  p.  164.  '  Mc^\  ilham,  1893,  p.  472. 

*  Rov  and  Adami,  1892,  p.  260. 

5  See  Danilew.kv,  1875,  p.  130;  Bochefontaine,  1876,  p.  140;  1883,  p.  33;  Balogh,76; 
Eckhard.  1878,  p.  185;  Bechterew  and  Mislawsky,  1886,  p[..  193,  416;  Franck,  1887,  p.  162. 

6  Tarchanoff,  1884,  p.  113. 

7  Pease,  1889,  p.  525. 


470  AN  A3IERICAN  TEXT-BOOK   OF  PHYSIOLOGY. 

in  the  minute  was  produced,  together  with  increase  of  blood-pressure,  from 
vaso-constrictor  action.     The  experiments  are  dangerous. 

Peripheral  Reflex  Centres. — It  is  now  much  discussed  wliethcr  the  periph- 
eral ganglia  can  act  as  centres  of  rcHcx  action.  According  to  Franck '  the  excita- 
tion of  the  central  stump  of  the  divided  left  anterior  limb  of  the  annulus  of 
Vieussens  is  transformed  within  the  first  thoracic  ganglion,  isolated  from  the 
spinal  cord  by  section  of  its  ramus  communicans,  into  a  motor  impulse  trans- 
mitted by  the  posterior  limb  of  the  annulus.  This  motor  impulse  causes,  inde- 
pendently of  the  bulbo-spinal  centres,  a  reflex  augmtmtation  in  the  action  of  the 
heart,  and  a  reflex  constriction  of  the  vessels  in  the  external  ear,  the  sul)maxil- 
lary  gland,  and  the  nasal  mucous  membrane.  This  experiment,  in  conjunction 
with  the  facts  in  favor  of  other  .sympathetic  ganglia  acting  as  reflex  centres,^ 
seems  to  demonstrate  that  some  afferent  impulses  are  transformed  in  the  sym- 
pathetic cardiac  ganglia  into  efferent  impulses  modifying  the  action  of  the 
heart.  If  this  conclusion  is  confirmed  by  future  investigations  it  will  pro- 
foundly modify  the  views  now  entertained  regarding  the  innervation  of  the 
heart. 

Intra- ventricular  Centre. — Kronecker  and  Schmey,^  finding  that  puncture 
of  the  inter-ventricular  septum  at  the  junction  of  the  upper  and  middle  thirds 
often  caused  arrest  of  the  heart  with  fibrillary  contractions,  have  set  up  the 
hypothesis  of  a  co-ordinating  centre  at  that  point,  essential  to  the  co-ordinated 
contractions  of  the  ventricle.  Their  results  are  possibly  due  to  inhibition  ;■*  cer- 
tainly they  are  not  to  be  explained  by  the  destruction  of  a  co-ordinating  centre. 
The  anatomical  basis  for  such  a  conception  is  wanting,  careful  search  having 
failed  to  reveal  any  ganglion-cells  in  the  locality  in  question,^  and  the  heart  has 
been  observed  to  beat  for  hours  and  even  days  after  the  cardiac  tissue  of  this 
part  of  the  septum  liad  been  destroyed  by  infarction,  caused  by  the  ligation  of 
its  nutrient  arteries.^ 

The  expenments  of  Stannius,  published  in  1852,  have  been  the  starting- 
point  of  a  very  great  number  of  researches  on  the  innervation  of  the  frog's 
heart.  Stannius  observed,  among  other  facts,  that  the  heart  remained  for  a 
time  arrested  in  diastole  when  a  ligature  was  tied  about  the  heart  precisely  at 
the  junction  of  the  sinus  venosus  with  the  right  auricle.  No  sufficient 
explanation  of  this  result  has  yet  been  giyen,  nor  is  one  likely  to  be  found 
until  the  innervation  of  the   heart  is  better    understood.     Stannius^  further 

1  Franck,  1894,  p.  721. 

''See  Wertheimer,  1890,  p.  519;  Skabitschewsky,  1891,  p.  15G ;  Langley  and  Anderson, 
1893,  p.  435. 

^  Kronecker  and  Schmey,  1884,  p.  89;  S^e  and  Gley,  1887,  p.  827  ;  the  latter  could  not  get 
arrest  in  11  out  of  14  dogs. 

*  Knoll,  1894,  p.  312,  observed  fibrillation  of  the  auricles  in  consequence  of  vagus  stimula- 
tion ;  escape  of  current  into  tlie  heart  was  guarded  against. 

*  Krehl  and  Romberg,  1892,  p.  54. 

*  Porter,  1893,  p.  366;  for  the  effect  of  wounds  of  the  heart  upon  its  rhythm,  see  Rodet 
and  Nicolas,  1896,  p.  167. 

'  A  review  of  the  Stannius  literature  is  given  by  Tigerstedt,  Physiobgie  des  Kreidaiifes, 
1893,  p.  196. 


CIR  CULA  TION.  4  7 1 

observed  that  after  the  ligature  just  described  had  been  drawn  tight,  thus 
arresting  the  heart,  the  placing  of  a  second  ligature  around  the  heart  at  the 
junction  of  the  aui-icle  and  ventricle  caused  the  latter  to  begin  to  beat  again, 
while  the  auricle  remained  at  rest.  This  second  ligature,  it  is  generally 
admitted,  stimulates  the  ganglion  of  Bidder,  and  the  ventricle  responds  by 
rhythmic  contractions  to  the  constant  excitation  thus  produced.  Loosening  the 
ligature  and  so  interrupting  the  excitation  stops  the  ventricular  beat.^ 


PART  III.— THE  NUTRITION  OF  THE  HEART. 

The  cells  of  which  the  heart-wall  are  composed  are  nourished  by  contact 
with  a  nutrient  fluid.  In  hearts  consisting  of  relatively  few  cells  no  special 
means  of  bringing  the  nutrient  fluid  to  the  cells  is  required.  The  walls  of  the 
minute  globular  heart  of  the  small  crustacean  Daphnia,  for  example,  are  com- 
posed of  a  single  layer  of  cells,  each  of  which  is  bathed  by  the  fluid  which  the 
heart  pumps.  In  larger  hearts  with  thicker  w-alls  only  the  innermost  cells 
could  be  fed  in  this  way.  Special  means  of  distributing  the  blood  throughout 
the  substance  of  the  organ  are  necessary  here. 

Passages  in  the  Prog's  Heart. — In  the  frog  this  distribution  is  accom- 
plished chiefly  through  the  irregular  passages  which  go  out  from  the  cavities 
of  the  heart  between  the  muscle-bundles  to  within  even  the  fraction  of  a  milli- 
meter of  the  external  surface.^  These  passages  vary  greatly  in  size.  Many  are 
mere  capillaries.  They  are  lined  by  a  prolongation  of  the  endothelium  of  the 
heart.  Filled  by  every  diastole  and  emptied  by  every  systole,  they  do  the 
work  of  blood-vessels  and  carry  the  blood  to  every  part  of  the  cardiac  muscle. 
Henri  Martin^  describes  a  coronary  artery  in  the  frog,  analogous  to  the 
coronary  arteries  of  higher  vertebrates.  This  artery  supplies  a  part  of  the 
auricles  and  the  upper  fourth  of  the  ventricle. 

In  the  rabbit,  cat  and  dog,  and  in  man  a  well-developed  system  of  cardiac 
vessels  exists,  the  coronary  arteries  and  veins.  Their  distribution  in  the  dog 
deserves  especial  notice,  because  the  physiological  problems  connected  with  these 
vessels  have  been  studied  chiefly  in  this  animal. 

Coronary  Arteries  in  the  Dog. — In  the  dog  the  coronary  arteries  and 
their  larger  branches  lie  upon  the  surface  of  the  heart,  covered  as  a  rule  only 
by  the  pericardium  and  a  varying  quantity  of  connective  tissue  and  fat.  The 
left  coronary  artery  is  extraordinarily  short.  A  few  millimeters  after  its  origin 
from  the  aorta  it  divides  into  the  large  ramus  circumflex  and  the  descen- 
dens,  nearly  as  large.  The  former  runs  in  the  auriculo-ventricular  furrow 
around  the  left  side  of  the  heart  to  the  posterior  surface,  ending  in  the  pos- 
terior inter-ventricular  furrow.  The  left  auricle  and  the  upper  anterior  and  the 
posterior  portion  of  the  left  ventricle  are  supplied  by  this  artery.  The  descen- 
dens  runs  downward  in  the  anterior  inter- ventricular  furrow  to  the  apex.  Close 
to  its  origin  the  descendens  gives  off  the  arteria  septi,  which  at  once  enters  the 

1  Goltz,  1861,  p.  201.       2  Engelmann,  1874,  p.  11.       »  Martin,  1893,  p.  754  ;  1894,  p.  46. 


472  AN  AMERICAN    TEXT- BOOK    OF   PHYSIOLOGY. 

inter-veiitriciilar  sei)tiiin  and  passes,  sparsely  covered  with  iiiiisele-buiidlcs, 
obliquely  downward  and  backward  on  the  right  side  of  the  septum.  The 
descendens  in  its  farther  course  gives  off  numerous  branches  to  the  left  ventricle 
and  the  anterior  ])art  of  the  septum.  Only  a  few  small  branches  go  to  tlie 
right  ventricle.  Thus  the  descendens  supplies  the  septum  and  the  inferior 
anterif)r  part  of  the  left  ventricle.  The  right  coronary  artery,  imbetlded  in 
fat,  runs  in  the  right  auriculo-ventricular  groove  around  tiie  right  side  of  the 
heart,  supplying  the  right  auricle  and  ventricle.  It  is  a  much  smaller  artery 
than  either  the  circumflex  or  descendens.  Each  coronary  artery  kee|)S  to  its 
own  boundaries  and  does  not,  in  the  dog,  pass  into  the  field  of  another  artery, 
as  sometimes  happens  in  man.^ 

Terminal  Nature  of  Coronary  Arteries. — The  coronary  arteries  in  the 
dog,  as  in  man,  are  terminal  arteries,  that  is,  the  anastomoses  which  their  branches 
have  with  neighboring  vessels  do  not  permit  the  making  of  a  collateral  circula- 
tion. Their  terminal  nature  in  the  human  heart  is  shown  by  the  formation  of 
infarcts  in  the  areas  supplied  by  arteries  which  have  been  plugged  by  embo- 
lism or  thrombosis.  That  part  of  the  heart- wall  supplied  by  the  stopped  arteiy 
speedily  decays.  The  bloodless  area  is  of  a  dull  white  color,  often  faintly 
tinged  with  yellow  ;  rarely  it  is  red,  being  stained  by  luemoglobin  from  the 
veins  of  neighboring  capillaries.  The  cross  section  is  coarsely  gramdar.  The 
nuclei  of  the  muscle-cells  have  lost  their  power  of  staining.  The  muscle-cells 
are  dead  and  connective  tissue  soon  replaces  them.^  This  loss  of  function  and 
rapid  decay  of  cardiac  tissue  would  not  take  place  did  anastomoses  permit  the 
establishment  of  collateral  circulation  between  the  artery  going  to  the  part  and 
neighboring  arteries.  The  terminal  nature  of  the  coronary  arteries  in  the  dog 
has  been  placed  beyond  doubt  by  direct  experiment.  It  is  possible  to  tie  them 
and  keep  the  animal  alive  until  a  distinct  infarct  has  formed.^ 

The  objection  that  one  of  the  coronary  arteries  can  be  injected  from 
another,*  and  that  therefore  they  are  not  terminal,  is  based  on  the  incorrect 
premise  that  terminal  arteries  cannot  l)e  thus  injected,  and  has  no  weight  against 
the  positive  evidence  of  the  complete  failure  of  nutrition  following  closure. 
The  |)assage  of  a  fine  injection-mass  from  one  vascular  area  to  another  proves 
nothing  concerning  the  possibility  of  the  one  area  receiving  its  blood-supply 
from  the  other.  Such  supply  is  impossible  if  the  resistance  in  the  communi- 
cating vessels  is  greater  than  the  blood-pressure  in  the  smallest  branches  of  the 
artery  through  which  the  supply  nnist  come.  It  is  the  fact  of  this  high  resist- 
ance, due  to  the  small  size  of  the  communicating  branches,  w'hich  makes  the 
artery  "terminal."  This  condition  of  high  resistance  is  really  j>resent  during 
life,  or  infarction  could  not  take  j^lace. 

The  terminal  nature  of  the  coronary  arteries  is  of  great  importance  w^ith 
regard  to  the  part  taken  by  them   in   the  nutrition  of  the  heart.      Being  ter- 

*  Cohnheim  and  v.  Schiilthess-Rechberg,  1881,  p.  511. 

*  See  also  the  description  by  Kolster,  1893,  p.  14,  of  the  infarctions  produced  experiment- 
ally in  the  dog's  heart. 

»  Kolster,  1893,  p.  14;  Porter,  1893,  p.  366.  *  Miciiaelis,  1894,  p.  289. 


CIRCULA  TION.  473 

miual,  their  experimental  closure  enables  us  to  study  the  effects  of  the  sudden 
stoppin*^  of  tiie  blood-supply  (isfluLMuiu)  of  the  heart  muscle  upon  the  action 
of  the  heart. 

Results  of  Closure  of  the  Coronary  Arteries. — The  sudden  closure  of  one 
of  the  large  coronary  branches  in  the  dog  has  as  a  rule  cither  no  effect  upon 
the  action  of  the  heart  beyond  occasional  and  transient  irregularity/  or  is  fol- 
lowed af\er  the  lapse  of  seconds,  or  of  minutes,  by  the  arrest  of  the  ventricu- 
lar stroke,  the   ventricle  falling  a   moment   later  into   the   rapid,  fluttering, 


Fig.  123.— J,  curve  of  iiUra-vcntricular  pressure,  written  by  a  manometer  connected  with  the  interior 
of  the  left  ventricle;  5,  atmospheric  pressure;  C,  time  in  two-second  intervals.  At  the  iirst  arrow  the 
ramus  circumflexus  of  the  left  coronary  artery  was  ligated  ;  at  the  second  arrow  the  heart  fell  into  fibril- 
lary contractions.  The  lessening  height  of  the  curve  shows  the  gradual  diminution  of  the  force  of  con- 
traction after  ligation.  The  rise  of  the  lower  line  of  the  curve  above  the  atmospheric  pressure  indicates 
a  rise  of  intra-ventricular  pressure  during  diastole.  The  small  elevations  in  the  pressure-curve  after  the 
second  arrow  are  caused  by  the  left  auricle,  which  continued  to  beat  after  the  arrest  of  the  ventricle 
(Porter,  1893). 

undulatory  movements  known  as  fibrillary  contractions  and  produced  by  the 
inco-ordinated,  confused  shortenings  of  individual  muscle-cells,  or  groups  of 
cells.  The  auricles  continue  to  beat  for  a  time,  but  the  power  of  the  ventricles 
to  execute  co-ordinated  contractions  is  lost. 

The  Frequency  of  Arrest. — The  frequency  with  which  closure  is  fol- 
lowed by  ventricular  arrest  depends  on  at  least  two  factors — namely,  the  size 
of  the  artery  ligated  and  the  irritability  of  the  heart.  That  the  size  of  the 
artery  is  of  influence  appears  from  a  series  of  ligations  performed  on  dogs, 
arrest  being  never  observed  after  ligation  of  the  arteria  septi  alone,  rarely 
observed  (14  per  cent.)  with  the  right  coronary  artery,  more  frequently  (28 
per  cent.)  with  the  descendens,  and  still  more  frequently  (64  per  cent.)  with  the 
arteria  circumflexa.^  The  irritability  of  the  heart  is  an  important  factor.  In 
animals  cooled  by  long  artificial  respiration,  or  by  section  of  the  spinal  cord  at 
its  junction  with  the  bulb,  the  ligation  of  the  descendens  arrests  the  heart  less 
frequently  than  in  vigorous  animals  which  have  been  operated  upon  quickly. 
The  frequency  of  arrest  is  increased  by  the  use  of  morphia  and  curare.^ 

Changes  in  the  Heart-beat. — Ligation  destined  to  arrest  the  heart  is  fol- 
lowed almost  immediately  by  a  continuous  fall  in  the  intra-ventricular  pressure 
during  systole  and  a  gradual  rise  in  the  pressure  during  diastole  (see  Fig.  123). 
The  contraction  and  relaxation  of  the  ventricle  are  often  slowed.  The  force 
of  the  ventricular  stroke  is  diminished.  As  arrest  draws  near,  irregularities  in 
the  force  of  the  ventricular  beat  are  seldom  absent.*  The  frequency  of  beat  is 
sometimes  unchanged  throughout,  but  is  usually  diminished  toward  the  end ; 

*  The  changes  produced  by  subsequent  degeneration  are  not  considered  here. 

"''  Porter,  1893,  p.  131.  ^  Ibid.,  1896,  p.  49.  *  Ibid.,  1893,  p.  133. 


474 


^^V  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 


Fig.  12-1.— Showing  fall  in  arte- 
rial pressure  and  diminished  out- 
put of  left  ventricle  in  conse(iuenee 
of  the  ligation  of  the  circumflex 
artery.  The  curve  reads  from  left 
to  right.  It  is  one-half  the  original 
size.  The  upper  curve  is  the  pres- 
sure in  the  carotid  artery.  The 
unbroken  line  is  atmospheric  pres- 
sure. The  next  curve  is  the  meas- 
urement of  the  outflow  from  the 
left  ventricle,  each  rise  and  each 
fall  indicating  the  passage  of  50 
c.cm.  of  blood  into  the  aorta.  The 
lower  line  is  a  time-curve  in  sec- 
onds. At  *  the  circumflex  artery 
•was  Ugated  (Porter,  1896,  p.  51). 


occasionally  the  frequency  is  increased.  iJoth  ven- 
tricles as  a  rule  cease  to  beat  at  the  same  instant. 
The  work  done  by  the  heart,  measured  by  the 
blood  thrown  into  the  aorta  in  a  unit  of  time,  is 
les.sened  by  ligation  when  followed  by  arre.st'  (see 
IV  124). 

The  Exciting  Cause  of  Arrest. — There  are 
two  opinions  concerning  the  exciting  cause  of  the 
changes  following  closure  of  a  coronary  artery, 
some  investigators  holding  for  anaemia  and  others 
for  mechanical  injury  of  the  cardiac  muscle  or  its 
nerves  in  the  operation  of  ligation.  The  latter 
ba.se  their  claim  on  the  frequent  failure  of  ligation 
of  even  a  main  branch  to  stop  the  heart ;  on  the 
fact  that  the  heart  of  the  dog  has  been  seen  to 
beat  from  115  to  150  seconds  after  the  blood-pres- 
sure in  the  aorta  was  so  far  reduced,  by  clamping 
the  auricle  and  opening  the  carotid  artery,  as  to 
make  a  continuance  of  the  coronary  circulation 
very  improbable;^  on  the  revival  of  the  arrested 
heart  by  the  injection  of  defibrinated  blood  into 
the  coronary  arteries  from  the  aorta,  by  which 
means  the  dog's  heart  and  even  the  human  heart 
has  been  made  to  beat  again  many  minutes  after 
the  total  arrest  of  the  circulation,^ — it  being  as- 
sumed, incorrectly,  that  the  dog's  heart  cannot  be 
made  to  beat  after  arrest  with  fibrillary  contrac- 
tions; and,  finally,  on  the  arrest  with  fibrillary 
contractions  which  some  experimenters  have  caused 
by  mechanical  injury  to  the  heart.* 

To  sum  up,  the  argument  in  favor  of  explain- 
ing arrest  with  fibrillary  contractions  simply  by 
the  mechanical  injury  done  the  heart  in  the  jiro- 
cess  of  ligation  consists  of  two  propositions :  first, 
that  anaemia  without  mechanical  injury  does  not 
cause  arrest  with  fibrillary  contractions;  and  .sec- 
ond, that  mechanical  injury  without  anaemia  does 
cause  arrest. 

Against  the  .second  of  these  propositions  must 
be  placed  the  extreme  in  frequency  of  arrest  from 
mechaniad  injuries.     In  more  than  one  hundred 

'  Porter,  1896,  p.  52. 

2  Tigerstedt,  1895,  p.  87 ;  Michaelis,  1894. 
'  Langendorff,    1895,    p.   320;    H^don    and    Gilis,  1892, 
p.  760.  *  Martin  and  Sedgwick,  1882,  p.  168. 


CIRCULA  TION.  475 

ligations  Porter*  observed  not  a  single  arrest  in  consequence  of  laying  the 
artery  bare  and  placing  the  ligature  ready  to  be  drawn,  the  only  effect  of  the 
nieolianical  })ro(_'c<lure  being  an  ocaisional  si igiit  irregularity  in  force.  Ligation 
of  the  periarterial  tissues  in  ten  dogs,  the  artery  itself  being  excluded  from  the 
ligature,  directly  injured  both  muscular  and  nervous  substance,  but  was  only 
once  followed  by  arrest."  Nor  does  arrest  follow  the  ligation  of  a  vein,  although 
the  mechanical  injury  is  possibly  as  great  as  in  tying  an  artery.  The  direct 
stimulation  of  the  superficial  ventricular  nerves  exposed  to  injury  in  the  opera- 
tion of  ligation  does  not  produce  the  effects  that  appear  after  the  ligation  of 
coronary  arteries.^ 

Against  the  remaining  proposition  stated  above — namely,  that  anaemia  with- 
out mechanical  injury  does  not  cause  arrest  with  fibrillary  contractions — it 
should  be  said  that  the  frequency  of  arrest  after  ligation  is  in  proportion  to 
the  size  of  the  artery  ligated,  and  hence  to  the  size  of  the  area  made  anaemic, 
and  is  not  in  proportion  to  the  injury  done  iu  the  preparation  of  the  artery. 
The  circumflex  and  descendens  may  be  prepared  w'ithout  injuring  a  single 
muscle-fibre,  yet  their  ligation  frequently  arrests  the  heart,  while  the  ligation 
of  the  arteria  septi,  which  cannot  be  prepared  without  injuring  the  muscle- 
substance,  does  not  arrest  the  heart.  It  is,  moreover,  possible  to  close  a  coro- 
nary artery  without  mechanical  injury.  Lycopodium  spores  mixed  with  de- 
fibrinated  blood  are  injected  into  the  arch  of  the  aorta  during  the  momentary 
closure  of  that  vessel  and  are  carried  into  the  coronary  arteries,  the  only  way 
left  open  for  the  blood.  The  lycopodium  spores  plug  up  the  finer  branches 
of  the  coronary  vessels.  The  coronary  arteries  are  thus  closed  without  the 
operator  having  touched  the  heart.  Prompt  arrest  with  tumultuous  fibrillary 
contractions  follows.^  There  seems,  then,  to  be  no  doubt  that  fibrillary  contrac- 
tions can  be  brought  on  by  sudden  anaemia  of  the  heart  muscle. 

The  gradual  interruption  of  the  circulation  in  the  coronary  vessels — by 
bleeding  from  the  carotid  artery,  for  example — is  followed  by  feeble  inco- 
ordinated  contractions  not  essentially  different  in  kind  from  those  commonly 
termed  fibrillary  contractions.^  The  manner  of  interruption  probably  explains 
the  difference  in  result.  In  the  former  case,  namely,  ligation  or  other  sudden 
closure,  the  supply  of  blood  to  the  heart  muscle  is  suddenly  stopped  while  the 
heart  continues  to  work  against  a  high  peripheral  resistance ;  in  the  latter,  the 
anaemia  is  gradual  and  the  heart  works  against  little  or  no  peripheral  resistance. 

Recovery  from  Fibrillary  Contractions. — Fibrillary  contractions  brought 
on  by  clamping  the  left  coronary  artery  in  the  rabbit's  heart  are  often  gradually 
replaced  by  normal  contractions  when  the  clamp  is  removed.^  The  isolated 
cat's  heart  after  showing  marked  fibrillary  contractions  during  forty-five 
minutes  has  given  strong  regular  beats  for  more  than  an  hour.''     The  recovery 

^  Porter,  1896,  p.  58 ;  see  also  Fenoglio  and  Drogoul,  1888,  p.  49. 

2  Porter,  1896,  p.  57 ;  see  also  Rodet  and  Nicolas,  1896,  p.  167. 

5  McWilliam,  1887,  p.  298;  Wooldridge,  1883,  p.  532;  compare  Michaelis,  1894,  p.  285. 

*  Porter,  1896,  p.  65.  *  Porter,  1895,  p.  482. 

8  V.  Bezold,  1867,  pp.  263,  285.  '  Magrath  and  Kennedy  (about  to  be  published). 


47() 


AN  AMERICAN    TENT-HOOK    OF    I'll  YSK )L< X ;  Y. 


of"  tho  (loii's  heart  lias  hccii  supposed  iin])ossil)le.^  MeA\'illiaiii,  however,  has 
seen  a  number  ot"  regnhir  heats  after  the  termination  ol'  fihriHarv  conlractioii.^ 
Recent  rcsnhs  suggest  that  llhrilhirv  contractions  even  in  the  high(;st  verte- 
brates niav  be  removed  by  estabbshing  an  artitieial  cireiihition  of  defibrinated 
bhi()d  through  the  coronary  arteries. 

Closure  of  the  Coronary  Veins. — Closure  of  all  the  coronary  veins  in 
the  rabbit  jiroduced  tibrillary  contractions  after  from  fifteen  to  twenty  minutes 
had  passed.^  Their  closure  in  the  dog  is  said  to  be  without  effect ■* — a  negative 
result  perhaps  to  be  explained  by  the  fact  that  a  portion  of  the  coronary  blood 
finds  its  wav  to  the  cavities  of  the  heart  through  the  venae  Thebesii.* 

Volume  of  Coronary  Circulation. — Bohr  and  Heuriques,^  taking  the 
average  of  six  experiments  on  dogs,  found  that  16  cubic  centimeters  of  blood 
passed  through  the  coronary  arteries  per  minute  for  each  100  grams  of  heart 
muscle.  The  (juantity  passing  through  both  coronary  arteries  varied  in  dif- 
ferent animals  from  20  to  64  cubic  centimeters  per  minute ;  the  quantity 
passing  t broil <;h   the  left  coronary  artery  varied  from   22.5  to  60  cubic  centi- 


lliffiilllill^^ 


iMjijif^mmmmmmHH^ 


^lnnilnininninuMiiiiiiiiiiiimi\inniHHiuiuinMiiiiiuin 


iii/flf^<|«tfjJ/Ui^/(//^^  .  •■■  "  "  L" 


Fig.  125.— Diminution  of  the  force  of  contraction  of  the  ventricle  of  the  isohitcd  cat's  lieart  in  con- 
sequence of  dimini.shiug  the  supply  of  blood  to  the  cardiac  muscle  :  A,  hlood-pressure  at  the  root  of  the 
aorta,  recorded  by  a  mercury  manometer;  5,  intra-ventricular  pressure-curve,  left  ventricle:  the  indi- 
vidual beats  do  not  appear,  because  of  the  slow  speed  of  the  smoked  surface ;  C,  time  in  seconds ;  D,  the 
number  of  drops  of  blood  passing  through  the  coronary  arteries,  each  vertical  mark  recording  one  drop. 
As  the  number  of  drops  of  blood  passing  tlirough  the  coronary  arteries  diminishes,  the  contractions  of 
the  left  ventricle  become  weaker,  but  recover  again  when  the  former  volume  of  the  coronary  circula- 
tion is  restored. 

meters  per  minute.  The  hearts  weighed  from  51  to  350  grams.  The  method 
which  Bohr  and  Henriques  found  it  neces.sary  to  employ  placed  the  heart 
under  such  abnormal  conditions  that  their  results  can   be  regarded  as  only 

1  Ck)hnheim  and  v.  Schulthess-Rechberg,  1881,  p.  519;  Tisenstedt,  1895,  p.  546;  and  others. 

'  It  is  not  quite  clear  wlietlier  McWilliam  refers  to  fil)rillary  contraotions  produced  by 
closing  a  coronary  artery  or  to  those  which  follow  strong  faradic  stimulation  of  the  ventricle 
(1887,  p.  299). 

3  V.  Bezold  and  Breymann,  1807,  p.  299.  '  Michaelis,  1894,  p.  291. 

*  Gad,  1886,  p.  382.  *  Bohr  and  Henriques,  1895,  pp.  233-236. 


CIRCULA  TION. 


477 


approximate.  Porter '  supplied  llic  left  coronary  artery  of  the  clog  with  blood 
(lihitcd  one-half  with  sodiinn  cliloridc  sohition  (0.6  per  cent.)  by  means  of  a 
tube  (lumen  2.75  millimeters)  inserted  into  the  aortic  opening  of  the  left  coro- 
nary artery  and  connected  with  a  reservoir  placed  150  centimeters  above  the 
heart.  In  one  dog,  weighing  11,500  grams,  318  cubic  centimeters  flowed 
through  in  eight  minutes.  In  a  second  dog,  weighing  9500  grams,  114  cubic 
centimeters  passed  through  in  four  minutes.  In  the  isolated  heart  of  the  cat 
strong  and  regular  contractions  are  made  on  a  circulation  of  about  4  cubic 
centimeters  per  minute,  or  even  less,  through  the  coronary  systeni.  The 
quantity  passing  through  the  veins  of  Thebesius  into  the  left  auricle  and 
ventricle  is  ,very  slight. 

Blood-supply  and  Heart-beat.— Tlie  relation  between  the  volume  of 
blood  passing  through  the  coronary  arteries  and  the  rate  and  force  of  the 
ventricular  contraction  has  been  studied  by  Magrath  and  Kennedy  (1896). 
Variations  in  the  volume  of  the  coronary  circulation  in  the  isolated  heart 
of  the  cat,  unless  very  considerable,  are  not  accompanied  by  changes  in  the 
rate  of  beat.  The  force  of  contraction,  on  the  contrary,  appears  to  be  closely 
dependent  on  the  volume  of  the  coronary  circulation  (Fig.  125). 

Lymphatics  of  the  Heart.— A  rich  plexus  of  lym])hatic  vessels  has  been 
demonstrated  in  the  heart.  Valuable  information  concerning  the  nutrition  of 
the  heart  could  probably  be  gained  by  the  systematic  study  of  these  vessels. 

0.  Solutions  which  Maintain  the  Beat  of  the  Heart. 
The  beat  of  the  heart  is  maintained  during  life  by  a  constant  supply  of 
oxygenated  blood.  The  blood,  however,  is  a  very  complex  fluid,  and  it  can 
hardly  be  supposed  that  all  of  its  constituents  are  of  equal  value  to  the  heart. 
The  systematic  search  for  those  constituents  of  the  blood  which  are  of  import- 
ance to  the  nutrition  of  the  heart  was  begun  in  Ludwig's  laboratory  in  1875 
by  Merunowicz.2  The  first  step  toward  the  method  used  by  Merunowicz  and 
his  successors  was  taken  by  Cyon.^  Cyon  tied  cannulas  in  the  vena  cava 
inferior  and  in  one  of  the  aort«  of  the  extirpated  heart  of  the  frog,  and 
joined  them  by  a  bowed  tube  filled  with  serum.  The  ventricle  pumped 
the  serum  through  the  aortic  cannula  and  the  bowed  tube  into  the  vena 
cava,  whence  it  reached  the  ventricle  again.  The  force  of  the  contraction 
was  measured  by  a  mercury  manometer  which  was  joined  by  a  side  branch 
to  one  limb  of  the  bowed  tube. 

The  frog  heart  manometer  method  thus  introduced  by  Ludwig  and  Cyon 
has  undergone  various  modifications  at  the  hands  of  Blasius  and  Fick,"  Bow- 
ditch,^  Luciani,«  Kronecker,^  and  others.  Blasius  and  Fick  were  the  first  to 
register  changes  in  the  volume  of  the  heart  by  the  plethysmographic  method, 
the  organ  being  enclosed  in  a  vessel  filled  with   normal  saline  solution  and 

1  Porter,  1896,  p.  64.  '  Merunowicz,  1876,  p.  132. 

3  Cyon,  1867,  p.  80.  *  Blasius,  1872,  p.  9. 

5  Bowditch,  1872,  p.  139.  '  Luciani,  18-3,  p.  113. 

'  Kronecker,  1874,  p.  174. 


478 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


connected  with  a  manometer.     This  idea  reappears  in  the  Strassburg  apparatus 
described  below. 

A  valuable  improvement  was  made  by  Kronecker,  who  invented  a  double 
cannula,  through  one  side  of  which  the  "  nutrient  "  fluid  enters  the  ventricle 

while  it  passes  out  through  the  other  (Fig.  126). 
The  contents  of  the  ventricle  are  thus  contin- 
ually renewed.  In  1878,  Koy  ^  constructed  the  • 
instrument  shown  in  Figure  127,  by  means  of 
which  the  changes  in  the  volume  of  the  heart  at 
each  contraction  are  recorded  on  a  moving  cylin- 
der. A  great  advance  was  made  by  Williams,^ 
in  the  invention  known  as  "  Williams's  valve," 
which  is  the  essential  feature  of  the  apparatus 
devised  by  this  investigator  and  others  in 
Schmiedeberg's  laboratory  at  Strassburg.  The 
present  form  of  this  apparatus  is  illustrated  in 
Figure  128.  A  perfusion  cannula  is  introduced 
into  the  ventricle  through  the  aorta.  Through 
one  tube  of  the  cannula  the  heart  is  fed  from  a 
reservoir  placed  above  it.  Through  the  other 
the  heart  pumps  its  contents  into  a  higher  reser- 
voir or  into  the  same  reservoir.  Thus  the  heart  is  "  loaded  "  with  a  column 
of  liquid  of  known  height  and  pumps  against  a  measurable  resistance.     A 


Fig.  126.— The  perfusion  cannula 
of  Kronecker.  The  ventricle  is  tied 
on  the  cannula  at  d,  a  ring  being 
placed  here  to  prevent  the  ligature 
from  slipping.  The  double  tube, 
shown  in  cross-section  at  e,  divides 
into  the  large  branch  a  and  the 
small  branch  b.  The  nutrient  solu- 
tion enters  the  heart  through  b  and 
escapes  through  a.  The  silver  wire 
c  can  be  connected  with  one  pole  of 
a  battery,  the  cannula  serving  as  one 
electrode,  and  the  fluid  surrounding 
the  heart  as  the  other. 


Fio.  127.— Roy's  apparatus:  the  heart  is  tied  on  a 
perfusion  cannula  and  enclosed  in  a  bell  glass  rest- 
ing on  a  brass  plate,  6,  the  centre  of  which  presents 
an  opening  covered  by  a  rubber  membrane.  Vari- 
ations in  the  volume  of  the  heart  cause  the  mem- 
brane to  rise  and  fall.  The  movements  of  the 
membrane  are  recorded  by  a  lever. 


Fig.  128.— Williams's  apparatus:  H,  frog's  heart; 
V,  V,  Williams's  valves ;  MS,  millimeterscale.  The 
apparatus  is  arranged  to  feed  the  heart  from  the 
reservoir  into  which  the  heart  is  pumping. 


Williams's  valve  in  the  inflow  tube  prevents  any  flow  except  in  the  direction 

of  the  heart.     A  similar  valve  reversed  in  the  outflow  tube  prevents  any  flow 

»  Roy,  1879,  p.  453.  »  Williams,  1881,  p.  3. 


CIRCULA  TION.  479 

except  away  from  the  heart.  The  ventricle  is  filled  and  emptied  alternately  as 
is  the  normal  heart,  the  artificial  valves  rei)laciiig  the  heart-valves,  which  are 
often  necessarily  rendered  useless  by  the  introduction  of  the  cannula  and  are  at 
best  less  certain  in  their  action  than  the  artificial  valve.  The  changes  in  the 
volume  of  the  heart  are  shown  by  the  movements  of  a  liquid  column  in  a 
horizontal  tube  which  communicates  with  the  bottle  filled  with  "nutrient" 
fluid  in  which  the  heart  is  enclosed. 

In  the  original  method  of  Cyon  the  ventricle  is  left  in  connection  with  the 
auricle,  the  ganglion-cells  of  the  ventricle  and  the  neighboring  portions  of  the 
auricle  being  kept  intact.  This  *'  whole  heart "  preparation  is  to  be  distin- 
guished from  the  "  apex  "  preparation  of  Bowditch,  which  has  also  been  used 
in  studies  of  the  effects  of  nutrient  solutions  on  the  heart.  In  Bowditch's 
"  apex  "  preparation,^  the  ventricle  is  bound  to  the  cannula  by  a  thread  tied  at 
the  junction  of  the  upper  and  middle  thirds  of  the  ventricle.  By  this  means 
the  lower  two-thirds  of  the  ventricle,  which  contains  no  ganglion-cells,  is  cut 
off  from  any  physiological  connection  with  the  base  of  the  ventricle  and  a 
"  ganglion-free  apex  "  secured.  The  isolated  "  apex  "  at  first  stands  still,  but 
after  from  ten  to  sixty  minutes  ^  commences  to  beat  again  and  can  then  be  kept 
beating  for  several  hours. 

In  the  use  of  these  various  methods  certain  general  precautions  should  be 
kept  in  mind.  Special  attention  should  be  directed  to  the  difficulty  of  remov- 
ing the  blood  from  the  capillary  fissures  in  the  wall  of  the  frog's  heart.^  A 
small  amount  of  blood  remaining  in  these  passages  is  frequently  a  source  of 
error.  It  should  be  remembered  that,  as  Cyon  *  pointed  out,  a  change  in  the 
nutrient  solution  is  of  itself  a  stimulus  to  the  heart,  increasing  or  diminishing 
the  frequency  of  contraction  and  obliging  the  investigator  to  wait  until  the  heart 
has  become  accustomed  to  the  new  solution  before  making  an  observation.  The 
heart  should,  as  a  rule,  be  constantly  supplied  with  fresh  fluid,  as  in  the  natural 
state.  The  resistance  against  which  the  heart  works  is  also  a  factor  of  import- 
ance. The  water  with  which  the  solutions  are  made  should  be  distilled  in  glass, 
as  the  minutest  trace  of  the  compounds  of  heavy  metals  in  non-colloidal  solu- 
tions affects  the  heart.' 

Nutrient  Solutions. — Cyon  ^  found  that  the  beat  of  the  extirpated  frog's 
heart  is  very  dependent  on  the  nature  of  the  solution  with  which  the  heart  is 
fed.  Hearts  supplied  with  normal  saline  solution  (NaCl,  0.6  per  cent.)  ceased 
to  beat  much  sooner  than  those  left  empty.  The  serum  of  dog's  blood  seemed 
almost  poisonous.  Rabbit's  serum,  on  the  contrary,  postponed  the  exhaustion 
of  the  heart  for  many  hours,  provided  the  limited  quantity  contained  in  the 
apparatus  was  renewed  from  time  to  time.  Serum  used  over  and  over  again 
caused  the  beats  to  lose  force  after  an  hour  or  two.  The  renewal  of  the  serum 
seemed  a  stimulus  to  the  heart,  causing  it  to  contract  very  strongly  during  a 
half  minute  or  more,  after  which  the  contractions  became  less  energetic. 

1  Bowditch,  1872,  p.  139.  ^  Merunowicz,  1876,  p.  135. 

3  Martius  and  Kronecker,  1882,  p.  547.  *  Cyon,  1867,  p.  89. 

5  Locke,  1895,  p.  331 ;  Naegeli,  1893,  p.  12.  «  Cyon,  1867,  p.  89. 


480  ^l.V   AMERICAN    TKXT-UOOK    OF   PHYSIOLOGY. 

Cvon's  immediate  successors,  Bowditch,  Liuiiuii,  and  Rossbacli/  confirmed 
his  observations.  None  of  these  investigators,  however,  was  concerned  pri- 
marily with  the  nutrition  of"  the  heart.  The  first  systematic  work  on  tiiis  sub- 
ject was  done,  as  has  been  said,  l)y  Merunowiez,  who  attenij»ted  to  maintain 
the  beat  ot"  the  iieart  with  nornuil  saline  solution  containing;  various  (quantities 
t)t'  blood,  with  normal  saline  alone,  with  a  watery  solution  ot  the  ash  of  an 
alcholic  extract  of  serum,  and  with  a  normal  saline  solutitju  containing  a 
minute  amount  of  sodium  carbonate.  The  direction  taken  by  him  has  been 
pursued  to  the  present  day,  the  chief  objects  of  stuily  behig  tin;  importance  to 
the  heart  of  sodium  carbonate  or  other  alkali,  sodium  and  potassium  chloride, 
the  salts  of  calcium,  oxygen,  proteids  and  some  other  organic  bodies  such  as 
dextrose,  and,  finally,  of  fluids  possessing  the  physical  characteristics  of  the 
blood.     The  outcome  of  this  work  we  must  now  consider. 

The  value  of  an  alkaline  reaction  has  been  generally  recognized.  Sodium 
carbonate  is  the  alkali  commonly  preferred.  The  favorable  influence  of  this 
salt  probably  does  not  depend  on  any  specific  action,  but  simply  upon  its 
alkalinity.^  The  alkali  promotes  the  beat  of  the  heart  by  neutralizing  the 
carbon  dioxide  and  other  acids  formed  in  the  metabolism  of  the  contracting 
muscle;  this,  however,  may  not  be  its  only  use. 

Certain  of  the  salts  normally  present  in  the  blood  are  necessary  to  main- 
tain the  beat  of  the  heart.  Sodium  chloride  is  one  of  these.  The  solution 
employed  should  contain  a  "physiological  quantity."  Such  a  solution  is  said 
to  be  "  isotonic."  The  amount  required  to  make  a  sodium  chloride  solution 
**  normal"  or  "isotonic"  for  the  frog  is  0.6  per  cent.,  for  the  mammal  nearly 
1  per  cent.  Enough  of  a  calcium  salt  to  prevent  the  washing  out  of  lime 
from  the  tissues  is  also  essential  for  prolonged  maintenance  of  the  contractions.^ 
A  heart  fed  with  normal  saline  solution  is  before  long  brought  to  a  stand  ;  the 
addition  of  a  calcium  salt  to  the  solution  postpones  the  arrest.  The  character 
of  the  contraction,  however,  is  altered  by  the  calcium,  the  relaxation  of  the 
ventricle  being  sometimes  so  much  delayed  that  the  next  contraction  takes 
place  before  the  relaxation  from  the  previous  contraction  has  commenced,  the 
ventricle  falling  thereby  into  a  state  of  persistent  or  "  tonic  "  contraction.  The 
addition  of  a  potassium  salt  restores  the  normal  character  of  the  contraction,* 
calcium  and  potassium  having  an  antagonistic  action  on  the  heart.  The 
importance  of  calciimi  to  the  heart  is  said  to  be  demonstrated  by  the  disap- 
pearance of  the  spontaneous  contractions  of  the  heart  which  follows  the  pre- 
cipitation of  the  calcium  in  the  circulating  fluid  by  the  addition  to  it  of  an 
equivalent  quantity  of  a  soluble  oxalate,  and  by  the  return  of  spontaneous 
contractions  which  is  seen  when  the  calcium  is  restored  to  the  solution.^ 

The  antagonistic  action  of  calcium  and  the  oxalates  was  first  pointed  out 
by  Cyon." 

1  Bowditch,  1872,  p.  139;  Luciani.  1873,  p.  113;  Rossbach,  1875,  p.  90. 

2  Gaiile,  1878,  p.  294.  '  Ringer,  1885,  p.  252. 

*  Ringer,  1885,  p.  247.  *  Ringer,  1885,  p.  85;  compare  Howell,  1894,  p.  478. 

6  Cyon,  1807,  p.  203;  see  also  Sokoloff,  1881,  p.  8;  Ringer,  1885,  p.  86;  Howell  and  Cooke, 
1893,  p.  220 ;  Howell,  1894,  p.  478. 


CIRCULA  TION.  481 

According  to  Riui!;er/  the  substances  thus  far  mentioned  are  effective  in  the 
followinij;  order:  normal  saline  is  the  least  effective;  next  is  saline  contaiuinir 
sodium  bicarbonate;  then  saline  containing  tricalcinm  pho8})hate;  and  best  of 
all,  saline  containing  tri(;alcinm  phosphate  together  with  potassium  chloride. 
He  recommends  the  following  mixture :  Sodiutu  chloride  solution  0.6  per 
cent.,  saturated  with  tribasic  calcium  phosphate,  100  cubic  centimeters;  solu- 
tion potassium  chloride  1  per  cent.,  or  acid  potassium  phosphate  (HKgPOJ 
1  per  cent.,  2  cubic  centimeters.^ 

There  has  been  considerable  dispute  over  the  part  played  by  oxygen  in 
the  beat  of  the  frog's  heart.  McGuire^  and  King*  were  of  opinion  that 
the  beat  is  largely  independent  of  the  amount  of  oxygen  in  the  circulating 
fluid.  Yeo^  concluded  that  the  contracting  heart  uses  more  oxygen  than 
the  resting  heart,  and  that  the  consumption  of  oxygen  increases  with  the  work 
done.  Kronecker  and  Handler,^  on  the  contrary,  believe  that  the  oxygen  con- 
sumption is  increased  by  an  increase  in  the  rate  of  beat,  but  is  independent  of 
the  work  done.^  More  recent  observers  are  united  on  the  necessity  of  oxygen 
to  the  working  heart.  Oehrwall's  studies  in  this  field  are  especially  interesting. 
He  finds  that  a  volume  of  blood  sufficient  to  fill  the  frog's  ventricle  will  main- 
tain contractions  for  hours  provided  the  heart  is  surrounded  by  an  atmosphere  of 
oxygen.  The  heart  is  brought  to  a  stand  by  lack  of  oxygen  and  may  be  made 
to  beat  again,  even  after  an  arrest  of  twenty  minutes,  by  giving  it  a  fresh  sup- 
ply. The  heart  fails  in  oxygen-hunger  probably  because  the  chemical  process 
by  which  the  stimulus  to  contraction  is  called  forth  no  longer  takes  place,  and 
not  because  of  a  failure  in  contractility,  for  even  after  long  inaction  a  gentle 
touch  on  the  pericardium  will  cause  a  vigorous  contraction. 

Carbon  dioxide^  is  injurious  to  the  heart  when  present  in  the  circulating 
fluid  in  considerable  quantities.  The  force  of  the  contraction  is  reduced  before 
the  rate  of  beat.  The  heart  poisoned  with  carbon  dioxide  often  falls  into 
irregular  contractions,  exhibiting  at  times  '"grouping"  and  the  "staircase" 
phenomenon,  a  series  of  beats  regularly  increasing  in  strength. 

Organic  Substances. — An  unsuccessful  effort  has  been  made  to  prove  that 
only  solutions  containing  proteids,  for  example  blood-serum,  chyle,  and  milk, 
can  keep  the  heart  active.^  Recent  observers  have  shown  the  incorrectness  of 
this  claim.  The  inorganic  salts  of  serum  alone  suffice.''^  Locke"  found  that  the 
addition  of  0.1  percent,  of  dextrose  to  a  suitable  inorganic  solution  kept  a  frog's 

'    Ringer,  1886,  p.  294. 

-  Ringer,  1893,  p.  128;  for  the  action  of  rubidium,  strontium,  and  caesium  on  the  heart  see 
Ringer,  1884,  p.  370. 

3   McCluire,  1878,  p.  321.  *  Klug,  1879,  p.  478. 

5   Yeo,  1886,  p.  119.  «  Handler,  1890,  p.  253. 

'   Heffter,  1892,  p.  52 ;  Albanese,  1893,  p.  311  ;  Oehrwall,  1893,  pp.  42,  44. 

8  See  Kronecker  and  Stirling,  1874,  p.  200 ;  McGuire,  1878,  p.  322;  Klug,  1879.  p.  478 ; 
Saltet,  1882,  p.  567  ;  Kronecker  and  Mays,  1883,  p.  263 ;  Langendorff,  1893,  p.  417  ;  Ide,  1893, 
p.  492;  Ringer,  1893,  p.  129. 

9  Martius  and  Kronecker,  1882,  p.  562;  v.  Ott,  1883,  p.  26;  Popoff,  1889,  p.  438  ;  Brinck, 
1889,  p.  472;  White,  1896,  p.  344  ;  compare  Stienon,  1878,  p.  277,  and  Ringer,  1886,  p.  363. 

10  Merunowicz,  1876,  p.  166;  Howell  and  Cooke,  1893,  p.  204.         '^  Locke,  1895,  p.  333. 
.".1 


482  .l.V   AML'Ji'/CAy^    TEXT- HOOK    OF    PlIYSIOLOOY. 

heart  workinjj;  iiiuler  a  load  of  3.5  centigrams,  and  under  aii  "after-load  "  of  3 
centiijranis  iu  spontaneous  activity  for  more  than  twenty-four  iiour.s.  The 
sustainin<»;  action  which  dextrose  appears  to  exercise  is  shared,  according  to  him, 
by  various  other  organic  substances. 

Physical  Characteristics. — Heflter'  and  Albanese,^  having  observed  that 
the  addition  of  gum-arabic  to  the  circulating  fluid  was  of  advantage,  declared 
that  the  nutrient  solutions  should  possess  the  viscosity  of  the  blood.  The 
favorable  action  of  giun-arabic  may,  however,  more  probably  be  ascribed  to  the 
conijiounds  w  hich  it  contains  rather  than  to  its  physical  properties.^ 

Mammalian  Heart. — The  success  attained  within  the  past  two  years  in  the 
isolation  of  the  mammalian  heart  opens  up  an  hitherto  unexplored  region  in 
which  svstematic  investigation  will  surely  bring  to  light  facts  of  wide  interest 
and  value.  At  present,  however,  little  is  known  as  to  the  constituents  of  the 
blood  which  are  essential  to  the  life  of  the  mammalian  heart.  An  abundant 
supply  of  oxygen  is  certainly  highly  important.* 

Blood  of  Various  Animials. — Roy ''  gives  some  data  as  to  the  effect  on  the 
frotr's  ventricle  of  the  blood  of  various  animals.  The  blood  of  the  various  her- 
bivora  (rabbit,  guinea-pig,  horse,  cow,  calf,  sheep),  as  well  as  that  of  the  pigeon, 
were  found  to  have  nearly  the  same  nutritive  value  in  each  case.  That  of  the 
dog,  of  the  cat,  and  more  especially  of  the  pig,  while  in  some  instances  equal  in 
effect  to  that  from  the  hoi-se  or  rabbit,  were  in  other  examples  (from  the  newly 
killed  animals)  apparently  almost  poisonous.  Cyon's  early  observation  of  the  in- 
jurious action  of  dog's  blood  on  the  frog's  ventricle  has  already  been  mentioned. 

Regarding  the  mammalian  heart,  experience  has  shown  that  it  is  best  to 
supply  the  heart  with  blood  from  the  same  species  of  animal.'  The  difficulties 
attending  the  use  of  blood  from  a  different  species  are  seen  in  the  case  of  the 
dog's  heart  supplied  with  calf's  blood.  The  heart  dies  sooner;  ojdema  of  the 
lungs  takes  place,  impeding  the  pulmonary  circulation  and  leading  to  engorge- 
ment of  the  right  heart  and  paralysis  of  the  right  auricle  ;  exudation  into  the 
pericardium  often  seriously  interferes  with  the  beat  of  the  heart;  and,  finally, 
the  elastic  modulus  of  the  cardiac  muscle  is  apparently  altered,  permitting  the 
heart  to  swell  until  it  tightly  fills  the  pericardium,  when  the  jn'opcr  filling  of 
the  heart  is  no  longer  possible  through  lack  of  room  for  diastolic  expansion. 


PART   IV.— THE   INNERVATION   OF  THE   BLOOD-VESSELS. 

About  the  middle  of  the  eighteenth  century  more  or  less  sagacious  hypotheses 
concerning  the  contractility  of  the  blood-vessels  began  to  appear  in  medical 

1  Hefiler,  1892,  p.  52.  "  Albanese,  1S93,  p.  311. 

»  Howell  and  Cooke,  1893,  p.  216;  Locke,  1895,  p.  333. 

*  Experiments  on  the  artificial  circulation  of  defibrinated  blood  through  the  coronary  .irter- 
ies  have  been  performed  by  Martin  and  Applegarth,  1890,  p.  275;  Arnaud,  1891,  p.  396; 
H^don  and  Gilis,  1892,  p.  760;  Langendorff;  1895,  p.  291;  Porter,  1896,  p.  46;  Magrath  and 
Kennedy,  1896.  *  Roy,  1879,  p.  460;  compare  Hefller,  1892,  p.  44. 

6  Cyon,  1867,  p.  89.  '  Martin,  1883,  p.  676 ;  see  also  Langendorfl',  1895,  p.  293. 


aiRCULA  TION.  483 

literature,  but  it  was  not  until  Honlo  demonstrated  the  existence  of  muscular 
elements  in  the  middle  coats  of  the  arteries  in  1840  that  a  secure  foundation 
was  laid  for  the  present  knowledge  of  the  mechanism  by  which  that  contractility 
is  made  to  control  the  distribution  of  the  blood.  More  than  a  hundred  years 
before,  indeed,  Pourfonr  du  Petit  had  shown  that  redness  of  the  conjunctiva 
was  one  of  the  consc(|uenccs  of  the  section  of  the  cervical  sympathetic,  but  iiad 
called  the  ])rocess  an  inflammation,  in  which  false  idea  he  was  supported  by 
C'ruikshank  and  others;  and  Dupuy  of  Alfort  had  noted  redness  of  the  con- 
junctiva, increased  warmth  of  the  forehead,  and  sweat-drops  on  ears,  forehead, 
and  neck  following  his  extirpation  of  the  superior  cervical  ganglia  in  the 
horse;  Brachet,  also,  cutting  the  cervical  sympathetic  in  the  dog,  had  gone  so 
far  as  to  attribute  the  resulting  congestion  to  a  paralysis  of  the  blood-vessels. 
But  these  were  merely  clever  speculations,  for  the  anatomical  basis  necessary 
for  a  real  knowledge  of  this  subject  was  wanting  as  yet.  Henle  furnished  this 
basis,  and  at  the  same  time  reached  the  modern  point  of  view.  "  The  part 
taken  by  the  contractility  of  the  heart  and  the  blood-vessels  in  the  circulation," 
said  Henle,  "  can  be  expressed  in  two  words  :  the  movement  of  the  blood  depends 
on  the  heart,  but  its  distribution  depends  on  the  vessels."  Nor  did  Henle  stop 
here.  It  was  now  known  that  the  vessels  possessed  contractile  walls ;  it  was 
known  further  that  these  walls  contracted  when  mechanically  stimulated ;  for 
example,  by  scraping  them  with  the  point  of  a  scalpel ;  and  various  observers 
had  traced  sympathetic  nerves  from  the  greater  vessels  to  the  lesser  until  lost  in 
their  finest  ramifications.  It  was  therefore  easy  to  construct  a  reasonable 
hypothesis  of  the  control  of  the  blood-vessels  by  the  nerves.  Henle  declared 
that  the  vessels  contract  because  their  nerves  are  stimulated,  either  directly, 
or  reflexly  through  the  agency  of  a  sensory  a})paratus.  The  ground  was 
thus  prepared  for  the  physiological  demonstration  of  the  existence  of  "  vaso- 
motor" nerves,  as  Stilling  began  to  call  them.  Four  names  are  associated 
with  this  great  achievement — Schiff,  Bernard,  Brown-Sequard,  and  Waller,^ 
each  of  whom  worked  independently  of  the  others.  Foremost  among  them 
is  Claude  Bernard,  though  not  the  first  in  point  of  time,  for  it  was  he  who 
put  the  new  doctrine  on  a  firm  basis.  In  his  first  publication  Bernard  ^  stated 
that  section  of  the  cervical  sympathetic,  or  removal  of  the  superior  cervical 
ganglion,  in  the  rabbit,  causes  a  more  active  circulation  on  the  correspond- 
ing side  of  the  face  together  with  an  increase  in  its  temperature.  The  greater 
blood-supply  manifests  itself  in  the  increased  redness  of  the  skin,  particularly 
noticeable  in  the  skin  of  the  ear.  The  elevation  of  temperature  may  be  easily 
felt  by  the  hand.  A  thermometer  placed  in  the  nostril  or  in  the  ear  of  the 
operated  side  shows  a  rise  of  from  4°  to  6°  0.  The  elevation  of  temperature 
may  persist  for  several  months.  Similar  results  are  obtained  in  the  horse  and 
the  dog. 

The  following  year  Brown-S^quard'  announced  that "  if  galvanism  is  applied 

'  Waller,  1853,  p.  378.     The  literature  of  vaso-motor  nerves  is  so  large  that  only  works  of 
the  past  fifteen  years  can  be  cited,  except  in  a  few  important  instances. 

■'Bernard,  1851,  p.  163.  =■  Brown-S^quard,  1852,  p.  490. 


484  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

to  the  superior  portion  of  the  sympathetic  after  it  has  been  cut  in  the  neck,  the 
dihited  vessels  of  the  face  and  of  the  ear  after  a  certain  time  begin  to  contract; 
their  contraction  increases  slowly,  but  at  last  it  is  evident  that  they  resume 
tlieir  normal  condition,  if  they  are  not  even  smaller.  Then  the  temperature 
diminishes  in  the  face  and  the  ear,  and  becomes  in  the  palsied  side  the  same  as 
in  the  sound  side.  AVhen  the  galvanic  current  ceases  to  act,  the  vessels  begin 
to  dilate  again,  and  all  the  phenomena  discovered  by  Dr.  Jiernard  reapj)ear." 
Brovvn-Sequard  concludes  that  "  the  only  direct  efiect  of  tiie  section  of  the 
cervical  part  of  the  sympathetic  is  the  paralysis,  and  consequently  the  dilata- 
tion, of  the  blood-vessels.  Another  evident  conclusion  is  that  the  cervical 
sympathetic  sends  motor  fibres  to  many  of  the  blood-vessels  of  the  head." 

While  Brown-S6quard  was  making  these  important  investigations  in 
America,  Bernard,  in  Paris,  quite  unaware  of  Brown-Sequard's  labors,  was 
reaching  the  same  result.  The  existence  of  nerve-fibres  the  stinmlation  of 
Avhich  causes  constriction  of  the  blood-vessels  to  which  they  are  distributed  was 
thus  established. 

A  considerable  addition  to  this  knowledge  was  presently  made  by  Schiff,^ 
who  pointed  out  in  1856  that  certain  vaso-motor  nerves  take  origin  from  the 
spinal  cord.     The  destruction  of  certain  parts  of  the  spinal  cord  causes  the 
same  vascular  dilatation  and  rise  of  temperature  that  follows  the  section  of  the 
vaso-motor  nerves  outside  the  spinal  cord. 

At  this  time  Schiff  also  offered  evidence  of  vaso-dilator  nerves.  When 
the  left  cervical  sympathetic  is  cut  in  a  dog,  and  the  animal  is  kept  in  his 
kennel,  the  left  ear  will  always  be  found  to  be  5°  to  9°  warmer  than  the 
right.  If  the  dog  is  now  taken  out  for  a  run  in  the  warm  sunshine,  and 
allowed  to  heat  himself  until  he  begins  to  pant  with  outstretched  tongue,  the 
temperature  of  both  ears  will  be  found  to  have  increased.  The  right  ear  is 
now,  however,  the  warmer  of  the  two,  being  from  1°  to  5°  warmer  than  the 
left.  The  blood-vessels  of  the  right  ear  are,  moreover,  now  fuller  than  those 
of  the  left.  When  the  animal  is  quiet  again  the  former  condition  returns,  the 
redness  and  warmth  in  the  right  becoming  again  less  than  in  the  left  ear.  The 
increase  of  the  redness  and  warmth  of  the  right  ear  over  the  left,  in  which  the 
vaso-constrictor  nerves  were  paralyzed,  must  be  the  result  of  a  dilatation  of 
the  vessels  of  the  right  ear  by  some  nervous  mechanism.  For  if  the  dilatation 
of  the  vessels  was  merely  passive,  the  vessels  in  the  right  ear  could  not  dilate  to 
a  greater  degree  than  those  in  the  left  ear  which  had  been  left  in  a  passive  state 
by  the  section  of  their  nerves.  This  experiment,  however,  is  by  no  means  con- 
clusive. 

The  existence  of  vaso-dilator  fibres  was  placed  beyond  doubt  by  the  follow- 
ing experiment  of  Bernard  ^  on  the  chorda  tympani  nerve,  new  facts  regarding 
the  vaso-constrictor  nerves  being  also  secured.  Bernard  exposed  the  submax- 
illary gland  of  a  digesting  dog,  removed  the  digastric  muscle,  isolated  the 
nerves  going  to  the  gland,  introduced  a  tube  into  the  duct,  and,  finally,  sought 

'    Schiff,  1856,  p.  69  ;  1859,  p.  153. 

"^  Bernard,  1858,  p.  '241 ;  see  also  pp.  649  to  658. 


CIRCULATION.  485 

oat  and  opened  the  submaxillary  vein.  The  blood  contained  in  the  vein  was 
dark.  The  nerve-braiieh  coming  to  the  gland  from  the  sympathetic  was  now 
ligated,  whereupon  the  venous  blo(Kl  from  the  gland  grew  red  and  flowed  more 
abundantly  ;  no  saliva  was  excreted.  The  sympathetic  nerve  was  now  stimu- 
lated between  the  ligature  and  the  gland.  At  this  the  blootl  in  the  vein  became 
dark  again,  flowed  in  less  abundance  and  Anally  stopped  entirely.  On  allow- 
ing the  animal  to  rest  the  venous  blood'  grew  red  once  more.  The  chorda 
tympani  nerve,  coming  from  the  lingual  nerve,  was  now  ligated,  and  the  end 
in  connection  with  the  gland  stimulated.  Then  almost  at  once  saliva  streamed 
into  the  duct,  and  large  quantities  of  bright  scarlet  blood  flowe<l  from  the  vein 
in  jets,  synchronous  with  the  pulse. 

This  experiment  may  be  said  to  close  the  earlier  history  of  the  vaso-motor 
nerves.'  It  was  now  established  beyond  question  that  tlie  size  of  the  blood- 
vessels, and  thus  the  quantity  of  blood  carried  by  them  to  diiferent  parts  of  the 
body,  is  controlled  by  nerves  which  when  stimulated  either  narrow  the  blood 
vessels  (vaso-constrictor  nerves)  and  thus  diminish  the  quantity  of  blood  that 
flows  through  them,  or  dilate  the  vessels  (vaso-dilator  nerves)  and  increase  the 
flow.  The  section  of  vaso-constrictor  nerves,  for  example  those  found  in  the 
cervical  sympathetic,  causes  the  vessels  previously  constricted  by  them  to  dilate. 
The  section  of  a  vaso-dilator  nerve,  for  example  the  chorda  tympani,  running 
from  the  lingual  nerve  to  the  submaxillary  gland,  does  not,  however,  cause  the 
constriction  of  the  vessels  to  which  it  is  distributed.  And  finally,  it  was  now 
determined  that  vaso-motor  fibres  are  found  in  the  sympathetic  system  as 
well  as  in  the  spinal  cord  and  the  cerebro-spinal  nerves. 

It  remained  for  a  later  day  to  show  that  vaso-motor  nerves  are  present  in 
the  veins  as  well  as  in  the  arteries.  Mall  ^  has  found  that  when  the  aorta  is 
compressed  below  the  left  subclavian  artery,  the  portal  vein  receives  no  more 
blood  from  the  arteries  of  the  intestine,  yet  remains  for  a  time  moderately  full, 
because  it  cannot  immediately  empty  its  contents  through  the  portal  capil- 
laries of  the  liver  against  the  resistance  which  they  offer.  If  the  peripheral 
end  of  the  cut  splanchnic  nerve  is  now  stimulated,  the  portal  vein  contracts 
visibly  and  may  be  almost  wholly  emptied.  Thompson^  has  extended  the 
discovery  of  Mall  to  the  superficial  veins  of  the  extremities.  He  finds  that 
the  stimulation  of  the  peripheral  end  of  the  cut  sciatic  nerve,  the  crural  artery 
being  tied,  causes  the  constriction  of  the  superficial  veins  of  the  hind  limb. 
The  contraction  begins  soon  after  the  commencement  of  the  stimulation,  and 
usually  goes  so  far  as  to  obliterate  the  lumen  of  the  vein.  Often  the  contrac- 
tion begins  nearer  the  proximal  portion  of  the  vein  and  advances  toward  the 
periphery.  More  commonly,  however,  it  is  limited  to  band-like  constrictions 
between  which  the  vein  is  filled  with  blood.  After  stimulation  ceases  the 
constrictions  gradually  disappear.     A  second  and  third  stimulation  produce 

^  Further  information  regarding  the  history  of  this  subject  is  given  by  Vulpian,  Lemons  sur 
I'appareil  vaso-moieur,  Paris,  1875;  Longet,  Trails  de  physiologic,  Paris,  1869,  t.  ii.  p.  199;  and 
Schiff,  Untersuchungen  zur  Physiologie  des  Nenensy stems,  P'rankfort-am-Main,  1855,  Bd.  i.  p.  124. 

2  Mall,  1890,  p.  57  ;  1892,  p.  409.  '"  Thompson,  1893,  p.  104. 


486  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

much  less  constriction.  The  superficial  veins  of"  the  rabbit's  abdotncii  are 
constricted  by  the  stinuihition  of  tlie  cervical  spinal  cord  at  the  second  ver- 
tebra. 

The  observations  oi"  liernard  and  his  contemporaries  led  to  a  very  great 
number  of  researches  on  the  general  properties  and  the  distribution  of  the 
vaso-motor  nerves,  in  the  course  of  which  a  variety  of  ingenious  methods  of 
observation  liave  been  devised. 

Methods  of  Observation. — One  fruitful  method  of  research  has  been 
already  incidentally  mentioned,  namely,  the  direct  inspection  of  the  vessel,  or 
region,  the  vaso-motor  nerves  of  which  are  being  studied. 

A  second  method  consists  in  accurately  measuring  the  outflow  from  the 
vein.  If  the  blood-vessels  of  the  area  drained  by  the  vein  are  constricted  by 
the  stimulation  of  a  vaso-motor  nerve,  the  quantity  escaping  from  the  vein  in 
a  given  period  previous  to  constriction  will  be  greater  than  that  escaping  in  an 
equal  period  during  constriction.  This  well-known  method  is  especially  avail- 
able where  an  artificial  circulation  is  kept  up  through  the  organ  studied,  as 
the  blood  drained  from  the  vein  does  not  then  weaken  the  animal  and  thus 
disturb  the  accuracy  of  the  observations.' 

A  third  method  is  founded  on  the  principle  in  hydraulics  that  the  lateral 
pressure  at  any  point  in  a  tube  through  which  a  liquid  flows  depends,  other 
things  being  equal,  on  the  resistance  to  be  overcome  below  the  point  at  which 
the  pressure  is  measured.  In  the  animal  body  the  resistance  to  be  overcome 
by  the  blood-stream  varies  with  the  state  of  contraction  of  the  smaller  vessels, 
and  thus  the  variations  in  the  lateral  pressure  of  a  given  artery  may,  under 
certain  restrictions,  be  used  to  determine  variations  in  the  size  of  the  smaller 
vessels  distal  to  the  artery.  The  restrictions  are,  that  the  variations  in  the 
lateral  pressure  in  the  artery  are  indicative  of  changes  in  the  size  of  the  distal 
vessels  only  when  the  general  blood-pressure  remains  unaltered,  or  alters  in  a 
direction  opposite  to  the  change  in  the  artery  investigated.^  An  example  will 
make  this  plain.  Dastre  and  Morat,^  in  order  to  demonstrate  the  presence  of 
vaso-motor  fibres  for  the  hind  limb  in  the  sciatic  nerve,  connected  a  manometer 
with  the  central  end  of  the  left  femoral  artery,  and  a  second  manometer  with 
the  peripheral  end  of  the  right  femoral  artery,  distal  to  the  origin  of  the  pro- 
funda femoris.  The  anastomoses  between  the  principal  branches  of  the  fem- 
oral artery  are  so  numerous  and  so  large  that  the  circulation  in  the  limb  can 
be  maintained  by  the  profunda  femoris  alone.  Dastre  and  Morat  could  there- 
fore compare  the  general  blood-pressure  with  the  blood-pressure  in  the  right 
hind  limb.  On  stimulating  the  peripheral  end  of  the  right  sciatic  nerve,  the 
blood-pressure  rose  in  the  arteries  of  the  limb,  but  remained  stationary  in  the 
arteries  of  the  trunk,  connected  with  the  first  manometer  through  the  central 
end  of  the  left  femoral  artery.  The  rise  of  blood-pressure  in  the  operated 
limb,  while  the  blood-pressure  in  the  rest  of  the  body  remained  unchanged, 
proved  that  the  vessels  in  the  operated  limb  were  constricted. 

*  Cavazzani  and  Manca,  1895,  p.  33.  '  llurthle,  188&,  p.  563. 

'  Dastre  and  Morat,  1883,  p.  556. 


CIRCULATION.  487 

Many  investigators  liave  studied  vaso- motor  phenomena  by  means  of  the 
plethysmograph,  an  apparatus  invented  by  Mosso  for  recording  the  changes  in 
the  volume  of  {\\v  extremities.  The  member,  the  vaso-motor  nerves  of  which 
are  to  be  studied,  is  placed  within  a  cylinder  filled  with  water,  from  which  a 
tube  leads  to  a  recording  tambour.'  An  increase  in  the  volume  of  the  member, 
such  as  would  be  brctught  about  by  the  expansion  of  its  vessels,  causes  a  corre- 
sponding vt)lume  of  water  to  enter  the  tambour  tube,  thus  raising  the  pressure 
in  the  tambour  and  forcing  its  lever  to  rise.  A  constriction  of  the  vessels,  on 
the  contrary,  causes  the  recording  lever  to  fall. 

In  addition  to  these  general  methods,  special  devices  have  been  employed 
in  the  researches  into  the  vaso-motor  nerves  of  the  brain. 

In  considerino-  the  observations  made  Avith  these  various  methods  it  will 
be  advisable  to  beo-in  with  the  differences  between  the  two  kinds  of  vaso-motor 
nerves. 

Differences  bet^ween  Vaso-constrictor  and  Vaso-dilator  Nerves. — The 
differences  between  vaso-constrictor  and  vaso-dilator  nerves  are  particularly 
interesting  for  the  reason  that  both  vaso-constrictor  and  vaso-dilator  fibres  are 
often  found  in  one  and  the  same  anatomical  nerve.  The  sciatic  nerve  is  a 
good  example  of  this.  By  taking  advantage  of  these  differences  the  investi- 
gator may  determine  whether  one  or  both  kinds  of  fibres  are  present  in  any 
anatomical  nerve;  whereas,  without  this  knowledge,  the  effects  produced  by 
the  stimulation  of  the  one  might  be  wholly  masked  by  the  effects  produced  by 
the  stimulation  of  the  other. 

The  vaso-constrictors  are  less  easily  excited  than  the  vaso-dilators.  The 
simultaneous  and  equal  stimulation  of  the  dilator  and  constrictor  nerves  going 
to  the  submaxillary  gland  causes  vaso-constrictiou,  dilatation  appearing  after 
the  stimulation  ceases,  for  the  after-effect  of  excitation  is  of  shorter  duration 
with  the  constrictors  than  with  the  dilators.^  ^yarming  increases  and  cooling 
diminishes  the  excitability  of  the  vaso-constrictors  to  a  greater  degree  than  is 
the  case  with  the  vaso-dilators.  Thus  if  the  hind  limb  of  an  animal  be 
warmed,  the  stimulation  of  the  sciatic  nerve  will  cause  vaso-constriction ; 
while  if  it  be  cooled  the  same  stimulation  will  cause  vaso-dilatation.^  Vaso- 
constrictors are  more  sensitive  to  rapidly  repeated  induction  shocks  (tetaniza- 
tion)  and  less  sensitive  to  single  induction  shocks  than  are  vaso-dilators.  Thus 
if  the  sciatic  nerve  is  stimulated  with  induction  shocks  of  the  same  strength,  it 
will  be  found  that  a  rapid  repetition  of  the  stimuli  will  give  vaso-constriction, 
while  with  single  shocks  at  intervals  of  five  seconds  vaso-dilatation  is  the  result.'* 
Vaso-constrictors  degenerate  more  rapidly  than  vaso-dilators  after  separation 
from  their  cells  of  origin.  The  stimulation  of  the  peripheral  end  of  the  frog's 
sciatic  nerve  immediately  afler  section  causes  constriction.  Several  days  later 
the  same  stimulation  causes  vaso-dilatation,  the  oonstrictor  nerves  having  already 

'  An. improved  inetliod  of  recording  is  given  by  Bowditch  and  Warren,  18S6,  p.  420. 

^  Anrep  and  Cybulski,  1884. 

'■"  Lepine,  1876,  p.  26;  Howell,  Budgett,  and  Leonard,  1894,  p.  306. 

♦  Ostroumoff,  1876,  p.  232;  Bowditch  and  Warren,  1886,  p.  436;  Bradford,  1889,  p.  390. 


488  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

degenerated'  (sec  Fig.  129,  H).  The  maxiinuni  effect  of  stimulation  is  more 
quickly  reached  with  the  vaso-constrictor  than  with  the  vaso-dilator  nerves. 
Tiiere  is  also  a  difference  in  the  latent  period,  or  interval  between  stinudatiim 


.1  It 

Kiii.  12'.t.— Curvi-s  olitaiiKMl  by  enclosiiifj  llie  hiiifl  limb  of  a  cut  in  the  plethysni()t,'ra|)li  and  stimu- 
lating the  peripheral  end  of  the  cut  sciatic  nerve  (Bowditch  and  Warren,  18)5t;,  p.  4-17).  The  curves  read 
from  right  to  left.  In  each  case  the  vertical  lines  show  the  duration  of  the  stimulus— namely,  fifteen 
induction  shocks  per  second  during  twenty  seconds.  Curve  A  shows  the  contraction  of  the  vessels  pro- 
duced by  the  excitation  of  the  freshly-divided  nerve ;  curve  B,  the  dilatation  produced  by  an  equal 
excitation  of  the  nerve  of  the  opposite  side  four  days  after  section,  the  vaso-constrictor  nerves  having 
degenerated  more  rapidly  than  the  vaso-dilators. 

and  response.  Bowditch  and  Warren^  have  found  the  latent  period  of  the 
vaso-constrictor  fibres  in  the  sciatic  to  be  about  1.5  seconds,  while  that  of  the 
vaso-dilators  is  3.5  seconds.  Finally,  the  two  sorts  of  nerves  have  been  said 
to  differ  in  the  manner  in  which  they  are  distributed.  The  vaso-constrictor 
nerves  leave  the  cord  as  medullated  fibres,  enter  the  sympathetic  chain  of  gan- 
glia and  end  in  terminal  branches  probably  in  contact  with  a  sympathetic 
ganglion-cell.  The  constrictor  impulse  is  forwarded  to  the  vessel  by  a 
process  of  this  cell,  either  directly  or  by  means  of  still  other  sympathetic 
ganglion-cells.  The  vaso-dilator  fibre,  on  the  contrary,  was  thought  to  run 
directly  from  the  cord  to  the  blood-ves.sel ;  ^  but  the  latest  investigations  make 
it  probable  that  all  spinal  vaso-motor  fibres  end  in  sympathetic  ganglia.* 

Origin  and  Course. — The  vaso-motor  nerves  the  general  i)roperties  of 
which  have  just  been  .studied  are  axis-cylinder  processes  of  .sympathetic  gan- 
glion-cells. They  follow,  for  a  time  at  least,  the  course  of  the  corresponding 
spinal  nerve.  According  to  Langley,®  they  do  not  differ  from  the  pilo-motor 
and  secretory  nerves  except  in  the  nature  of  the  structure  in  which  they  termi- 
nate. They  are  not  interrupted  by  other  nerve-cells  on  their  coui^e.  The 
action  of  the  sympathetic  vaso-motor  cells  is  influenced  by  the  vaso-motor 
cells  of  the  spinal  cord  and  bulb.  These  arc  probably  small  cells  situated  at 
various  levels  in  the  anterior  horn  and  lateral  gray  substance.^  Their  axi.s- 
cylinder   processes   leave  the   cerebro-spinal  axis  by  the   anterior  roots ^  of 

'  Ostroiimoff,  1876,  p.  228;  Bowditch  and  A\'arren,  1886,  p.  444. 

2  Bowditch  and  Warren,  1886,  p.  440.  ^  Kolliker,  1894,  p.  2. 

*  Lansley,  1895,  p.  314.         *  I^angley,  1895,  p.  314.  «  Kolliker,  1894,  p.  6  (reprint). 

'  Biuljje,  1853,  p.  378  Some  investifiators  hold  that  va-so-niotor  nerves  leave  the  cord  in  the 
posterior  as  well  as  tlie  anterior  roots.  Strieker'  observed  that  excitation  of  the  peripheral  end 
of  the  posterior  roots  of  the  sciatic  nerve  is  followed  by  a  rise  of  temperature  in  ilie  Iiind  limb. 
This  was  denied  bv  Kiihlwetter.*    Bonuzzi^  and  Gartner*  agreed  with  Strieker.    Moral*  found 


»  Strieker,  1877,  p.  279.       2  Kiihlwettcr,  ]HS.\  p.  in.       3  Bonuzzi,  1885,  p.  473.       <  Giirtner.  lb»9,  p.  980. 
6  Morat,  189-2,  pp.  1499,  694;  see  also  Bradford,  1889,  p.  363,  and  Moral,  1890,  p.  473. 


CIRCULATION.  489 

certain  spinal  and  by  certain  cranial  nerves,  and  enter  sympathetic  ganglia, 
wiiere  they  end  in  terminal  twigs  probably  in  contact  with  the  sympathetic 
vaso-motor  cells.  The  vaso-motor  cells  lying  at  various  levels  in  the  cerebro- 
spinal axis  are  in  turn  largely  controlled  by  an  association  of  cells  situated  in 
the  bulb  and  termed  the  vaso-motor  centre.  The  neuraxons  (axis-cylinder 
processes)  of  the  cells  composing  this  "  centre  "  pass  in  part  to  the  nuclei  of 
certain  cranial  nerves  and  in  part  down  the  lateral  columns'  of  the  cord,  to 
end  in  contact  with  the  spinal  vaso-motor  cells.  The  vaso-motor  apparatus 
consists,  then,  of  three  classes  of  nerve-cells.^  The  cell-bodies  of  the  first  class 
lie  in  sympathetic  ganglia,  their  neuraxons  passing  directly  to  the  smooth  mus- 
cles in  the  walls  of  the  vessels ;  the  second  are  situated  at  different  levels  in 
the  cerebro-spinal  axis,  their  neuraxons  passing  thence  to  the  sympathetic  gan- 
glia by  way  of  the  spinal  and  cranial  nerves ;  and  the  third  are  placed  in  the 
bulb  and  control  the  second  through  intraspinal  and  intracranial  paths.  The 
nerve-cell  of  the  first  class  lies  wholly  without  the  cerebro-spinal  axis,  the  third 
wholly  witliin  it,  while  the  second  is  partly  within  and  partly  without,  and 
binds  together  the  refmaining  two. 

The  evidence  for  the  existence  of  these  vaso-motor  nerve-cells  must  now 
be  considered.  We  shall  begin  with  those  of  the  third  class,  constituting  the 
so-called  bulbar  vaso-motor  centre. 

Bulbar  Vaso-motor  Centre. — The  section  of  the  spinal  cord  near  its 
junction  with  the  bulb  is  followed  by  the  general  dilatation  of  the  blood- 
vessels of  the  trunk  and  limbs.^  The  dilated  vessels  are  again  constricted 
when  the  severed  fibres  in  the  spinal  cord  are  artificially  stimulated.  Hence 
the  section  caused  the  dilatation  by  interrupting  the  vaso-constrictor  impulses 
passing  from  the  bulb  to  parts  below.  The  position  of  the  bulbar  vaso- 
constrictor centre  has  been  determined  by  Owsjannikow  and  Dittmar.  The 
former  observer  *  divided  the  bulb  transversely  at  various  levels.  When  the 
section  fell  immediately  caudal  to  the  corpora  quadrigemina,  only  a  slight 
temporary  rise  in  blood-pressure  was  observed.  When,  however,  the  section 
fell  a  millimeter  or  two  nearer  the  cord,  a  considerable  and  permanent  fall  in 
the  blood-pressure  was  noted.  Further  lowering  was  seen  as  the  sections 
were  carried  still  farther  toward  the  spinal  cord,  until  at  length,  about  four 
millimeters  from  the  corpora  quadrigemina,  no  further  fall  took  place.  The 
area  from  which  the  vaso-constrictor  nerves  receive  a  constant  excitation 
extends,  therefore,  in  the  rabbit,  over  about  three  millimeters  of  the  bulb  not 
far  from  the  corpora  quadrigemina.  Two  yeajs  after  this  investigation  Ditt- 
mar added  to  the  observations  of  Owsjannikow  the  fact  that  the  vaso-con- 

in  a  ciirarized  dog  that  excitation  of  the  peripherai  end  of  certain  lumbo-sacral  posterior  roots 
causes  primary  vascular  dilatation  in  the  pulp  of  the  hind  paw  corresponding  to  the  nerves 
stimulated.  The  fibres  in  question,  do  not  degenerate  after  section  of  the  root  containing  them, 
and  are  therefore  not  of  spinal  origin. 

'  Compare  Nicolaides,  1882,  p.  28;  Helweg,  1886,  quoted  by  Tigerstedt,  1893,  p.  536. 

^  By  "nerve-cells"  is  meant  the  cell-body  with  all  its  processes,  namely,  the  neuraxon,  or 
axis-cylinder  process,  and  the  dendrites,  or  protoplasma  processes. 

^  Waller,  1853,  p.  381.  ♦  Owsjannikow,  1871,  p.  25. 


490  AN   AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

strictor  centre  is  bilateral,  lyint!;  in  tlio  aiitoiior  pari  of  tlu-  lateral  eoliiniiis  on 
both  sides  of  the  median  line.'  At  this  site  is  i'oiind  a  t!:n»u})  of  nantrjion-celle 
known  as  the  antero-lateral  nneleus  of  Clarke.  It  is  possible,  tlionj:;h  far 
from  certain,  that  these  are  tlic  cells  of  the  vaso-eonstrictor  centre. 

The  vaso-constrictor  centre  in  the  bulb  is  always  in  a  state  of  action,  or 
"tonic"  excitation,  as  is  shown  by  the  dilatation  of  the  vessels  when  deprived 
of  their  constrictor  impulses  through  the  section  of  the  spinal  cord. 

It  is  not  definitely  known  whether  a  vaso-dilator  centre  is  present  in  the 
bulb. 

Spinal  Centres. — A  complete  demonstration  of  the  existence  of  vaso-raotor 
centres  in  the  spinal  coi'd,  first  suggested  by  Marshall  Hall,  was  made  by  Goltz 
and  Freusberg-  in  their  experiments  on  dogs  which  had  been  kept  alive  after 
the  division  of  the  spinal  cord  at  the  junction  of  the  dorsal  and  the  lumbar 
regions.  This  operation  cuts  off  both  sensory  and  motor  communication 
between  the  parts  lying  above  and  below  the  plane  of  section,  and  divides  the 
animal  ]>hysiologically  into  a  fore  dog  and  a  hind  dog,  to  use  the  author's 
expression.  The  investigator  can  now  explore  the  lumbar  cord  unvexed  by 
cerebral  impulses.  A  great  number  of  motor  reflexes  formerly  thought  to  have 
their  centres  exclusively  in  ^he  brain  are  by  this  means  found  to  take  place 
in  the  absence  of  the  brain. '^  That  vaso-motor  reflexes  were  among  them  was 
discovered  by  accident.  It  was  noticed  that  the  mechanical  stimulation  of  the 
skin  of  the  abdomen  and  penis  while  the  animal  was  being  washed  provoked 
erection,  M'hich,  as  Eckhard^  had  discovered  some  years  before,  is  a  reflex  action 
due  to  the  dilatation  of  the  arteries  of  the  penis  through  impulses  conveyed  by 
the  nervi  erigentes.  Pressure  on  the  bladder,  or  the  walls  of  the  rectum,  also 
had  this  effect.  After  the  destruction  of  the  lumbar  cord  this  reflex  was  no 
longer  possible.  The  vessels  of  the  hind  limb  are  also  connected  with  vaso- 
motor cells  in  the  lumbar  cord.  Soon  after  the  section  of  the  cord  in  the  dorsal 
region  the  hind  paws  are  observed  to  be  warmer  than  the  fore  paws,  and  the 
arteries  of  the  hind  limb  are  seen  to  beat  more  strongly.  This  is  the  result  of 
cutting  off*  the  vaso-constrictor  impulses  from  the  bulbar  centre  to  the  vessels 
in  question.  If  the  animal  survives  a  considerable  time  the  hind  paws  will 
be  observed  to  grow  cooler  from  day  to  day  until  they  are  again  no  warmer 
than  the  fore  paws.  Destruction  of  the  lumbar  cord  now  causes  the  tempera- 
ture of  the  hind  limbs  to  rise  again. 

The  conclusion  drawn  from  these  observations  is  that  vaso-motor  cells  are 
present  in  the  spinal  cord.  It  is  probable  that  they  are  normally  subordinated 
to  the  bulbar  nerve-cells  and  require  a  certain  time  after  separation  from  the 
bulb  in  order  to  develop  their  previously  rudimentary  powers.     Hence  the 

^  Dittmar,  1873,  pp.  110,  114.  Otiier  literature  :  Sohitf,  1855,  p.  198  ;  Heidenhain.  1870, 
510;  Latschenberger  and  Dealma,  1876,  p.  183;  Strieker,  1886,  p.  13. 

'Goltz  and  Freusberg,  1874,  p.  463.  Other  literature:  Smirnow,  1886,  p.  145;  Ustimo- 
witsch,  1887,  p.  187 ;  Thayer  and  Pal,  1888,  p.  29 ;  Konow  and  Stenbeck,  1889,  p.  409. 

'  Later  experiments  by  Goltz  and  Ewald,  showing  the  decree  of  independence  of  the  spinal 
cord  possessed  by  sympathetic  vaso-motor  neurons  will  presently  be  cited. 

*  Eckhard,  1863,  p.  144. 


CIRCULA  TION.  491 

interval  of  many  days  between  the  section  and  the  return  of  arterial  tone  in  areas 
distal  to  tiie  section.  It  has  been  suggested  tliat  during  this  period  the  power 
of  tiie  spinal  nerve-cell  is  inhibited  by  impulses  proceeding  from  the  cut  sur- 
face of  the  cord/  but  this  long  inhibition  is  questionable  in  view  of  the  fact 
that  transverse  section  of  the  cord  in  ral)bits  and  dogs  does  not  inhil)it  the 
phrenic  nuclei.^ 

The  spinal  nerve-cell  takes  part  in  vaso-motor  reflexes.  Thus  the  stimu- 
lation of  the  central  end  of  the  brachial  nerves  after  section  of  the  spinal  cord 
at  the  third  vertebra  causes  a  dilatation  of  the  vessels  of  the  fore  limb.^  The 
stimulation  of  the  central  end  of  the  sciatic  nerve  after  the  division  of  the 
spinal  cord  causes  a  general  rise  of  blood-pressure  indicating  the  constriction 
of  many  vessels.  The  sensory  stimulation  of  one  hind  limb  may  cause  reflexly 
a  narrowing  of  the  vessels  in  the  other,  after  the  spinal  cord  is  severed  in  the 
mid-thoracic  region.^  In  asphyxia,  after  the  separation  of  the  cord  from  the 
brain,  vascular  constriction  is  produced  reflexly  through  the  spinal  centres.^ 
This  constriction  is  not  observed  if  the  cord  is  previously  destroyed.^  Goltz 
and  Ewald  ^  find  that  the  tonic  constriction  of  the  vessels  of  the  hind  limbs 
returns  after  the  extirpation  of  the  lower  part  of  the  spinal  cord. 

Sympathetic  Vaso-motor  Centres. — Gley  ^  finds  that  after  the  destruc- 
tion of  both  bulbar  and  spinal  centres  some  degree  of  vascular  tone  is  still 
maintained.  The  extraordinary  experiments  of  Goltz  and  Ewald '  place  this 
fact  beyond  question.  These  physiologists  remove  the  lower  part  of  the  spinal 
cord  completely,  taking  away  80  millimeters  or  more.  For  a  few  days  after 
the  operation  the  hind  limbs  are  hot  and  red,  from  dilatation  of  their  blood- 
vessels. Soon,  however,  the  hind  limbs  become  as  cool,  and  sometimes  even 
cooler,  than  the  fore  limbs,  their  arterial  tonus  being  re-established  and  main- 
tained without  the  help  of  the  spinal  cord. 

The  sympathetic  ganglia  are  probably  also  centres  of  reflex  vaso-motor 
action.  The  fact  that  these  ganglia  act  as  centres  for  other  motor  reflexes 
would  itself  suggest  this  possibility.  A  direct  proof  of  the  vaso-motor  reflex '" 
function  of  the  first  thoracic  ganglion  has  been  given  recently  by  Fran9ois 
Franck."  The  two  branches  composing  the  annulus  of  Vieussens  contain  both 
afierent  and  efferent  fibres.  If  one  of  the  branches  is  cut,  and  the  end  in  con- 
nection with  the  first  thoracic  ganglion  is  stimulated,  the  ganglion  having  been 
separated  from  the  spinal  cord  by  the  section  of  the  communicating  branches, 
a  constriction  of  the  vessels  of  the  ear,  the  submaxillary  gland,  and  the  nasal 
mucous  membrane  may  be  observed. 

1  Goltz  and  Ewald,  1896,  p.  397.  =  Porter,  1895,  p.  459. 

3  Smirnow,  1886,  p.  147;  compare  Thayer  and  Pal,  1888,  p.  29. 
*  Vulpian,  1875,  p.  290.  '  Knwalewsky  and  Adamiik,  1868,  p.  582. 

«  Konow  and  Stenbeck,  1889,  p.  409.  '  Goltz  and  Ewald.  1891,  p.  496  ;  1896,  p.  388. 

8  Gley,  1894,  p.  704.  »  Goltz  and  Ewald,  1896,  p.  389. 

*•'  See  Wertheimer,  1890,  p.  519 ;  Navrocki  and  Skabitschewsky,  1891,  p.  156  ;  Langley  and 
Anderson,  1893,  p.  417  ;  Franck,  1894,  p.  717  ;  compare  Mosso  and  Pellacani,  1882,  p.  300;  also 
Goltz  and  Ewald,  1896,  p.  391. 

"  Franck,  1894,  p.  721 ;  see  also  Roschansky,  1889,  p.  162. 


492  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

Tliis  evidence,  together  with  the  j)robability  that  tlie  neiiraxons  of  all  the 
spinal  vaso-motor  cells  end  in  sympathetic  ganglia/  makes  it  fairly  credible 
that  the  syni})athetie  vaso-motor  nerve-coll  possesses  central  functions. 

There  has  been  much  discussion  over  the  meaning  of  the  rhythmic  con- 
tractions observed  in  certain  blood-vessels  apparently  independent  of  the  cen- 
tral nervous  system.^  The  median  artery  of  the  rabbit's  ear,  the  arteria 
saphena  in  the  same  animal,  and  the  vessels  in  the  frog's  web  and  frog's  mes- 
entery, slowly  contract  and  relax.  This  rhythmic  contraction  is  easily  seen  in 
the  car  of  a  white  rabbit.  The  movements  are  possibly  of  purely  muscular 
origin,  but  are  more  probably  the  result  of  periodical  discharges  by  vaso-motor 
nerve-cells. 

Rhythmical  variations  in  the  tonus  of  the  vaso-constridor  centres  are  often 
held  to  explain  the  oscillations  seen  in  the  blood-pressure  curve  after  the 
influence  of  thoracic  aspiration  has  been  eliminated  by  opening  the  chest  and 
cutting  the  vagus  nerves.  These  oscillations  are  of  two  sorts.  In  the  one, 
the  blood-pressure  sinks  with  every  inspiration  and  rises  with  every  expiration, 
though  the  rise  and  fall  are  not  precisely  synchronous  with  the  respiratory 
movements ;  in  the  other,  the  so-called  Traube-Hering  waves,  the  oscillations 
embrace  several  resj)i  rations.  It  has  also  been  suggested  that  these  phenomena 
are  due  to  periodical  changes  in  the  respiratory  centre  affecting  the  vaso-con- 
strictor  centre  by  "irradiation."^ 

Vaso-motor  Reflexes. — The  vaso-motor  nerves  can  be  excited  reflexly  by 
afferent  impulses  conveyed  either  from  the  blood-vessels  themselves  or  from 
the  end-organs  of  sensory  nerves  in  general.  The  existence  of  reflexes  from 
the  blood-vessels  may  be  shown  by  Heger's  experiment.  Heger*  observed  a 
rise  of  general  blood-pressure  with  a  subsequent  fall,  and  at  times  a  primary 
fall,  after  the  injection  of  nitrate  of  silver  into  the  peripheral  end  of  the  crural 
artery  of  a  rabbit.  The  limb,  with  the  exception  of  the  sciatic  nerve,  was 
severed  from  the  trunk.  The  quantity  injected  was  so  small  that  it  probably 
was  decomposed  before  passing  the  capillaries  or  escaping  from  the  blood- 
vessels. Thus  the  eflfect  exerted  by  the  nitrate  of  silver  on  the  general  blood- 
pressure  was  probably  caused  by  afferent  impulses  set  up  in  the  blood-vessels 
themselves  and  transmitted  through  the  sciatic  nerve  to  the  vaso-motor  cen- 
tres. Vaso-motor  reflexes  are,  however,  much  more  commonly  produced 
by  the  stimulation  of  sensory  nerves  other  than  those  present  in  the  blood- 
vessels. 

The  reflex  constriction  or  dilatation '  appears  usually  in  the  vascular  area 

*  See  the  statement  of  Langley's  results  with  the  nicotin  method  on  pape  500. 

^  Literature:  Schiff,  1854,  p.  508;  Mosso,  1880,  p.  66;  Pye-Sinitli,  1887,  p.  48;  Fredericq, 
1887,  p.  351;  Konow  and  Stenbeck,  1889,  p.  406.  Discussion  of  the  active  dilatation  of  the 
blood-vessels  has  been  recently  revived  by  Piotrowski,  1892.  p.  701 ;  (iriinhagen,  1892,  p.  829; 
Franck,  1893,  p.  729;  Biedl,  1894;  Stefani,  1894,  pp.  237,  245;  Lui,  1894,  p.  410;  Goltz  and 
Ewald,  1896,  p.  396. 

'  Compare  Fredericq,  1882,  p.  71;  Knoll,  1885,  p.  439.  *  Heger,  1887,  p.  197. 

^  For  a  study  of  reflex  constriction  and  dilatation  produced  by  stimulating  the  skin  see 
Maragliano  and  Lusona,  1889,  p.  246 ;  compare  Hegglin,  1894,  p.  25. 


CIRCULA  TION.  493 

from  wliich  the  afferent  impulses  arise.  For  example,  the  stimulation  of  the 
central  end  of  the  posterior  auricular  nerve  in  the  ral)bit  causes  a  ])assing  con- 
striction followed  by  dilatation,  or  a  primary  dilatation  often  followed  by 
constriction  of  the  vessels  in  the  ear.  The  stimulation  of  the  nervi  erigentes 
causes  dilatation  of  the  vessels  of  the  penis.'  Gaskell  ^  found  that  the  vessels 
of  the  mylo-hyoid  muscle  widened  on  stimulating  the  mucous  membrane  at 
the  entrance  of  the  glottis. 

The  vascular  reflex  ^  may  appear  in  a  part  associated  in  function  with  the 
sensory  surface  stimulated.  Thus  the  stimulation  of  the  tongue  causes  dilata- 
tion of  the  blood-vessels  in  the  submaxillary  gland.*  Frequently  the  vascular 
reflex  is  seen  on  both  sides  of  the  body.  The  stimulation  of  the  mucous 
membrane  on  one  side  of  the  nose  may  cause  vascular  dilatation  in  the  whole 
head;*  the  effect  in  this  case  is  usually  more  marked  on  the  side  stimulated. 
The  vessels  of  one  hand  contract  when  the  other  hand  is  put  in  cold  water.® 
Sometimes  distant  and  apparently  unrelated  parts  are  affected.  Vulpian^ 
noticed  that  the  stimulation  of  the  central  end  of  the  sciatic  caused  the  vessels 
of  the  tongue  to  contract. 

The  vascular  changes  produced  reflexly  in  the  splanchnic  area  are  of 
especial  importance  because  of  the  great  number  of  vessels  innervated  through 
these  nerves  and  the  great  changes  in  the  blood-pressure  that  can  follow  dilata- 
tion or  constriction  on  so  large  a  scale. 

There  is  in  some  degree  an  inverse  relaiion  between  the  vessels  of  the  skin 
and  deeper  parts  on  reflex  stimulation  of  the  vaso-raotor  centres.  The  super- 
ficial vessels  are  often  dilated  while  those  of  deeper  parts  are  constricted.* 
Thus  the  stimulation  of  the  central  end  of  the  sciatic  nerve  may  cause  a  dilata- 
tion of  the  vessels  of  the  lips,  hand  in  hand  with  a  rise  in  general  blood-pres- 
sure.' Exposing  a  loop  of  intestine  dilates  the  intestinal  vessels  in  the  rabbit, 
but  constricts  those  of  the  ear.'"  In  asphyxia,  the  superficial  vessels  of  the  ear, 
face,  and  extremities  dilate,  while  the  vessels  of  the  intestine,  spleen,  kidneys 
and  uterus  are  constricted." 

Relation  of  Cerebruin  to  Vaso-motor  Centres. — A  rise  of  general  blood- 
pressure  has  been  produced  by  the  stimulation  of  different  regions  of  the  cortex 
and  of  various  other  parts  of  the  brain ;  for  example,  the  crura  cerebri  and 
corpora  quadrigemina.  Vaso-dilatation  has  also  been  observed.  The  motor 
area  of  the  cortex  especially  seems  closely  connected  w' ith  the  bulbar  vaso- 
motor centres.     There  is,  however,  no  conclusive  evidence  that  special  vaso- 

»  Eckhard,  1863,  p.  144.  ^  Qaskell,  1877,  p.  742. 

'  The  general  arrangement  of  the  matter  in  this  paragraph  is  that  given  by  Tigerstedt, 
1893,  p.  519.  *  Bernard,  1858,  p.  656.  *  Franck,  1889,  p.  555. 

*  Brown-S^quard  and  Tholozan,  1858,  p.  500;  compare  Teissier  and  Kaufmann,  1881,  p. 
1302;  and  Ranvier,  1892,  p.  629. 

''  Vulpian,  1875,  p.  238;  compare  Sergejew,  1894,  p.  162. 

*  Griitzner  and  Heidenhain,  1878,  p.  20 ;  Dastre  and  Morat,  1884,  p.  329 ;  "Wertheimer, 
1893,  p.  595;  1894,  p.  724;  Franck,  1896,  p.  502;  compare  Bayliss  and  Bradford,  1894,  p.  17. 

*  Wertheimer,  1891,  p.  548 ;  compare  Isergin,  1894,  p.  448. 

1°  Pawlow,  1878,  p.  268.  "  Heidenhain,  1872,  p.  100. 


494  AN  AMERICAN   TEXT-BOOK   OF  PIIYSTOLOGY. 

motor  centres  exist  in  the  brain  aside  I'loni  llie  bulbar  centres  already  described. 
At  present  the  safer  view  is  that  the  changes  iu  blood-pressure  called  forth  by 
the  stimulation  of  various  jiarts  of  the  brain  are  reflex  actions,  the  afferent  im- 
pulse starting  in  the  brain  as  it  might  in  any  other  tissue  peripheral  to  the 
vaso-motor  centres.' 

Pressor  and  Depressor  Fibres. — The  stimulation  of  the  same  aflerent 
nerve  sometimes  causes  reflex  dilation  of  the  vessels  of  a  part,  instead  of  the 
more  usual  reflex  constriction.  Two  explanations  of  this  fact  have  been  sug- 
gested. The  first  assumes  that  the  condition  of  the  vaso-motor  centre  varies  in 
such  a  way  that  the  same  stimuli  might  produce  contrary  effects,  depending 
on  the  relation  between  the  time  of  stimulation  and  tlie  condition  of  the  centre. 
The  second  assumes  the  existence  of  special  reflex  constrictor  or  "  pressor  " 
fibres,  and  reflex  dilator  or  "depressor"  fibres.  The  existence  of  at  least  one 
depressor  nerve  is  beyond  question,  namely  the  cardiac  depressor  nerve,  which 
it  will  be  remembered  runs  from  the  heart  to  the  bulb  and  when  stimulated 
causes  a  dilatation  of  the  splanchnic  and  other  vessels  reflexly  through  the 
bulbar  vaso-motor  centre.  Evidence  of  other  reflex  vaso-dilator  nerves  and  of 
reflex  vaso-constrictor  fibres  as  well  has  been  offered  by  Latschenberger  and 
Deahna,^  Howell,^  and  others.  Howell,  for  example,  has  found  that  if  u  part  of 
the  sciatic  nerve  is  cooled  to  near  0°  C.  and  the  central  end  stimulated  periph- 
erally to  this  part,  the  blood-pressure  falls,  instead  of  rising,  as  it  does  when 
the  nerve  is  stimulated  without  previous  cooling.  Howell's  experiments  have 
been  recently  extended  by  Hunt,*  who  finds  that  the  stimulation  of  the  sciatic 
during  its  regeneration  after  section  gives  at  first  vaso-dilatation  only,  but  when 
regeneration  has  progressed  still  further,  vaso-constriction  is  secured.  These 
results  point  to  the  existence  of  both  pressor  and  depressor  fibres,  the  latter 
being  the  first  to  regenerate  after  section.  A  reflex  fall  in  blood-pressure  is 
also  produced  by  stimulating  various  mixed  nerves  with  weak  currents'  and 
by  the  mechanical  stimulation  of  the  nerve-endings  in  muscle.  The  fiill  is 
more  readily  obtained  when  the  animal  is  under  ether,  cliloroform,  or  chloral, 
less  readily  under  curare. 

Topography. — "We  pass  now  to  the  vaso-motor  nerves  of  various  regions. 

Brain.^ — The  study  of  the  innervation  of  the  intracranial  vessels  is  ren- 
dered exceptionally  difficult  by  the  fact  that  the  brain  and  its  blood-vessels  are 
placed  in  a  closed  cavity  surrounded  by  walls  of  unyielding  bone.  The  funda- 
mental difference  created  by  this  arrangement  between  the  vascular  phenomena 

1  Literature:  Dogiel,  1880,  p.  420;  Strieker,  1886,  p.  9;  Bechterew  and  Mislawsky,  1886, 
p.  193;   Franck,  1887,  p.  1G2. 

*  Latschenberger  and  Dealina.  ISTfi,  p.  165. 

»  Howell,  Budgett,  and  Leonard,  1894,  p.  310.  Other  literature :  Belfield,  1882,  p.  298  ;  Knoll, 
1885,  p.  447,  1889,  p.  249 :  Kleen,  1887,  p.  247 ;  Bayliss,  1893,  p.  317 ;  Bradford  and  Dean, 
1894,  p.  67  ;  Hunt,  1895,  p.  381. 

♦  Hunt,  1895,  p.  381. 

5  See  also  Knoll,  1885,  p.  451. 

6  Literature:  Mosso,  1880,  p.  1-127  ;  Franck,  1887,  p.  199  ;  Gaertner  and  Wagner,  1887,  p.  602; 
Corin,  1888,  p.  185;  Hiirthle,  1889,  p.  561 ;  Eoy  and  Sherrington,  1890,  p.  85;  Cavazzani,  1891, 
p.  23;  1893,  pp.  54,  214;  Bayliss  and  Hill,  1895,  p.  334;  Gulland,  1895,  p.  361. 


CIRCULA  TION.  495 

of  the  brain  and  those  of  otlier  organs  was  recoj^iiized  in  part  at  least  by 
the  yonngor  INIonro  as  long  ago  as  1783.  Monro  declared  that  tiie  quantity 
of  blood  within  the  cranium  is  almost  invariable,  "  for,  being  enclosed  in  a 
case  of  bone,  the  blood  must  be  continually  flowing  out  of  the  veins  that  room 
may  be  given  to  the  blood  which  is  entering  l)y  the  arteries, — as  the  substance 
of  the  brain,  like  that  of  the  other  solids  of  our  body,  is  nearly  incompress- 
ible." Further  differences  between  the  circulation  in  the  brain  and  in  other 
organs  are  introduced  by  the  presence  of  the  cerebro-spinal  fluid  in  the  ventri- 
cles and  in  the  arachnoidal  spaces  at  the  base  of  the  brain.  This  fluid  may  pass 
out  into  tiie  spinal  canal  and  thus  leave  room  for  an  increase  in  the  amount 
of  blood  in  the  cranium.  Finally,  a  rise  of  pressure  in  the  arteries  too  great 
to  be  compensated  by  the  outflow  of  cerebro-spinal  fluid  may  lead  to  com- 
pression of  the  venous  sinuses  and  a  decided  change  in  the  relative  distri- 
bution of  the  blood  in  the  arteries,  capillaries  and  veins — conditions  which  are 
not  present  in  extracranial  tissues.  It  is  evident,  therefore,  that  the  methods 
emj)loyed  in  the  search  for  vaso-motor  nerves  within  the  cranium  must  take 
into  account  many  sources  of  error  that  are  absent  in  vaso-motor  studies  of 
other  regions.  It  is,  indeed,  probable  that  incompleteness  of  method  will  go 
far  toward  explaining  the  disagreement  of  authors  as  to  the  presence  of  vaso- 
motor nerves  in  the  brain.  According  to  Bayliss  and  Hill,^  the  most  recent 
investigators  of  this  subject,  it  is  necessary  to  record  simultaneously  the  arterial 
pressure,  the  general  venous  pressure,  the  intracranial  pressure  and  the  cerebral 
venous  pressure,  the  cranium  as  in  the  normal  condition  being  kept  a  closed 
cavity.  In  their  experiments,  "  a  cannula  was  placed  in  the  central  end  of  the 
carotid  artery.  A  second  long  cannula  was  passed  down  the  external  jugular 
vein,  and  on  the  same  side,  into  the  right  auricle.  The  torcular  Herophili  was 
trephined,  and  a  third  cannula,  this  time  of  brass,  was  screwed  into  the  hole 
thus  made."  The  intracranial  pressure  was  recorded  by  a  cannula  connected 
through  another  trephine-hole  with  the  subdural  space. 

Bayliss  and  Hill  could  find  no  evidence  of  the  existence  of  cerebral  vaso- 
motor nerves.  The  cerebral  circulation,  according  to  them,  passively  follows 
the  changes  in  the  general  arterial  and  venous  pressure.  Gulland  ^  has  examined 
the  cerebral  vessels  by  the  Golgi,  Ehrlich,  and  other  methods,  to  determine 
whether  nerve-fibres  could  be  demonstrated  in  them.  None  were  found.  It 
is  probable  that  the  blood-supply  to  the  brain  is  regulated  through  the  bulbar 
vaso-constrictor  centre.'  Anaemia  or  asphyxia  of  the  brain  stinmlates  the  cells 
composing  this  centre,  vascular  constriction  of  many  vessels  follows,  and  more 
blood  enters  the  cranial  cavity.  The  vessels  of  the  splanchnic  area  play  a 
chief  part  in  this  regulative  process.*  Their  importance  to  the  circulation  in 
the  brain  is  shown  by  the  fatal  effect  of  the  section  of  the  splanchnic  nerves 
in  the  rabbit.  On  placing  the  animal  on  its  feet,  so  much  blood  flows 
into  the  relaxed  abdominal  vessels  that  death  may  follow  from  anaemia  of  the 
brain. 

'  Bayliss  and  Hill,  1895,  p.  S37.  ^  Gulland,  1895,  p.  36L 

»  Bayliss  and  Hill,  1895,  p.  358.  *  Wertheimer,  1893,  p.  297. 


496  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

Vaso-rnotor  Nerves  of  Head. — Tlie  cervical  .sympathetic  contains  vaso-con- 
strictor  fibres  for  the  corresponding  side  of  the  face,  the  eye,  ear,  salivary 
glands'  and  tongne,  and  possibly  the  brain.  The  spinal  vaso-constrictor 
fibres  for  the  vessels  of  the  lioad  in  the  cat  and  dog  leave  the  cord  in  the 
first  five  thoracic  nerves;^  in  the  rabbit,  in  the  second  to  eighth  thoracic,  seven 
in  all.^ 

Vaso-dilator  fibres  for  the  face  and  month  have  been  found  in  the  cervical 
sympathetic  by  Dastre  and  jNIorat,"*  leaving  the  cord  in  the  second  to  fifth 
dorsal  nerves,  and  uniting  (at  least  for  the  most  part)  \vith  the  trigeminus  by 
passing,  according  to  Morat,^  from  the  superior  cervical  sympathetic  ganglion 
to  the  ganglion  of  Gasser.  Other  dilator  fibres  for  the  skin  and  mucous 
membrane  of  the  face  and  mouth  arise  apparently  in  the  trigeminus,  for  the 
stimulation  of  this  nerve  between  the  brain  and  Gasser's  ganglion  causes  dila- 
tation of  the  vessels  of  the  face,^  and  in  the  nerve  of  Wrisberg/ 

The  vaso-motor  nerves  of  the  tongue  have  been  recently  studied  by  Isergin.* 
The  lingual  and  the  glosso-pharyngeal  nerves  are  recognized  by  all  authors  as 
dilators  of  the  lingual  vessels.  The  sympathetic  and  the  hypoglossus  contain 
constrictor  fibres  for  the  tongue.  It  is  possible  that  the  lingual  contains  also 
a  small  number  of  constrictor  fibres.  Most  if  not  all  these  vaso-motor  fibres 
arise  in  the  sympathetic  and  reach  the  above-mentioned  nerves  by  Avay  of  the 
superior  cervical  ganglion.®  They  degenerate  in  from  three  to  five  weeks  after 
the  extirpation  of  the  ganglion. 

Morat  and  Doyon  '"  cut  the  cervical  sympathetic  in  a  curarized  rabbit  and 
examined  the  retinal  arteries  with  the  ophthalmoscope.  They  were  found 
dilated.  The  excitation  of  the  cervical  sympathetic  caused  constriction,  the 
excitation  of  the  thoracic  sympathetic  dilatation  of  these  vessels.  The  retinal 
fibres  leave  the  sympathetic  at  the  superior  cervical  ganglion  and  pass  along 
the  communicating  ramus  to  the  ganglion  of  Gasser,  whence  they  reach  the 
eye  through  the  ophthalmic  branch  of  the  fifth  nerve,  the  gray  root  of  the 
ophthalmic  ganglion,  and  the  ciliary  nerves.  Most,  or  all,  of"  the  fibres  for 
the  anterior  part  of  the  eye  are  found  in  the  fifth  nerve. 

Lungs. — The  methods  ordinarily  employed  for  the  demonstration  of  vaso- 
motor nerves  cannot  without  danger  be  used  in  the  study  of  the  innervation 

1  Compare  Vulpian,  1885,  p.  853.  '  Langley,  1892,  p.  102. 

2  Langley,  1892,  p.  104. 

*  Da,stre  and  Morat,  1884,  pp.  116,  129;  see  also  Pye-Smith,  1887.  p.  25;  Langley,  1890,  p. 
146;  Langley  and  Dickinson,  1890,  p.  380;  Morat,  1891,  p.  87;  Piotrowski,  1892,  p.  464; 
Langley,  1892,  p.  97. 

*  Morat,  1889,  p.  201. 

6  Vulpian,  1885,  p.  982;  compare  Dastre  and  Morat,  1884,  p.  118;  Langley,  1893,  iv.;  Pio- 
trowski, 1894,  p.  278. 

'  Vulpian,  1885,  p.  1038. 

^  Isergin,  1894,  p.  441 ;  other  literature:  Anrep  and  Cybulski,  1884;  Vulpian,  1885,  pp.  854, 
1038;  Piotrowski,  1887,  p.  454;  1894,  p.  246. 

®  For  evidence  that  probably  all  vaso-constrictor  fibres  to  the  head  (nerve-cells  of  the  second 
class)  end  in  thfi  superior  cervical  ganglion,  see  Langley  and  Dickinson,  1889,  p.  425. 

'»  Morat  and  Doyon,  1892,  p.  60  ;  see  also  Langley,  1893,  iv. ;  Doyon,  1890,  p.  774 ;  1891,  p.  154. 


CIRCULA  TION. 


497 


of  tlic  pulmonary  vessels.'  A  fall  in  the  blood-pressure  in  the  pulmonary 
artery,  lor  example,  procluecd  by  stimulating  any  nerve  cannot  be  taken  as 
final  evidence  that  the  stimulation  caused  the  constriction  of  the  pulmonary 
vessels.  The  lesser  circulation  is  so  connected  that  changes  in  the  calibre  of 
the  vessels  of  a  distant  part,  the  liver  for  cxam])le,  may  alter  the  quantity  of 
blood  in  the  Inngs.^  The  method  of  Cava/zani''  avoids  these  dilhculties. 
Cavazzani  establishes  an  artificial  circulation  through  one  lobe  of  a  lung  in 
a  living  animal,  and  measures  the  outflow  per  unit  of  time.  An  increase  in 
the  outflow  means  a  dilatation  of  the  vessels,  diminution  means  constriction. 
He  finds  that  the  outflow  diminishes  in  the  rabbit  when  the  vagus  is  stimulated 
in  the  neck,  and  increases  when  the  cervical  sympathetic  is  stimulated.  Franck 
measures  the  pressure  simultaneously  in  the  pulmonary  artery  and  left  auricle, 
a  method  apparently  also  trustworthy.  The  stimulation  of  the  inner  surface 
of  the  aorta  causes  a  rise  of  pressure  in  the  pulmonary  artery  and  a  simul- 
taneous fall  in  the  left  auricle,  indicating,  according  to  Franck,*  the  vaso-con- 
strictor  power  of  the  sympathetic  nerve  over  the  pulmonary  vessels.  A  reflex 
constriction  is  also  produced  by  the  stimulation  of  the  central  end  of  a  branch 


■•'■^—'> 


if  \^- 


PrA.F.H 


LujLLimi.JLliJ,?i^'[ff. 


Fig.  130.— The  excitation  of  the  central  end  of  the  inguinal  branch  of  the  crural  (sciatic)  nerve  causes 
a  rise  in  the  aortic  pressure  {Pr.A.F.),  a  rise  in  the  pressure  in  the  pulmonary  artery  (Pr.A.P.)  of  10  to  16 
mm.  Hg,  accompanied  by  a  falling  pressure  in  the  left  auricle  (Pr.O.O.)  (Franck,  1896,  p.  184).  The  rise 
of  pressure  in  the  pulmonary  artery,  together  with  the  fall  in  the  left  auricle,  demonstrate,  according 
to  Franck,  a  constriction  of  the  pulmonary  vessels. 

of  the  sciatic,  intercostal,  abdominal  pneumogastric,  and  abdominal  sympa- 
thetic nerves^  (see  Fig.  130). 

Heart — Vaso-motor  fibres  for  the  coronary  arteries  of  the  heart  have  been 
described  in  the  vagus  of  the  dog  ^  and  cat,'' 


1  Literature:  Openchowski,  1882,  p.  233;  Franck,  1889,  p.  555;  Bradford  and  Dean,  1889, 
i.-iv. ;  1889,  p.  369;  Couvreur,  1889,  p.  731  ;  Franck,  1890,  p.  550;  Arthaud  and  Butte,  1890, 
p.  12;  Knoll,  1890,  p.  13;  Cavazzani,  1891,  p.  32;  Doyon,  1893,  p.  101  ;  Henriques,  1893,  p. 
229;  Bradford  and  Dean,  1894,  p.  34;  Franck,  1895,  pp.  744,  816,  1896,  p.  178. 

2  Tigerstedt,  1893,  p.  493.  '  "^  Cavazzani,  1891,  p.  35. 
*  Franck,  1896,  p.  178.  »  Franck,'  1896,  p.  184. 

6  Martin,  1891,  p.  291.  '  Porter,  1896,  p.  39. 

32 


498  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

Intestines} — The  mesenteric  vessels  receive  vaso-constrictor  fibres  from  tlie 
sympathetic  chiefly  tliroiigh  the  s|>l:iii(linic  nerve. ^  The  vaso-constrictoi-.s  of" 
the  jejunum,  as  a  rule,  begin  to  be  lound  in  tiic  rami  of  the  fiftii  dorsal  nerves; 
a  little  lower  down,  those  for  the  ileum  come  off;  and  still  lower  down,  those 
for  the  colon  ;  none  arise  below  the  second  lumbar  pair.^  A(;cor(ling  to  Ilal- 
lion  and  Franek,  vaso-dilator  fibres  are  present  in  the  same  sympathetic  nerves 
that  contain  vaso-constrictors.  The  dilator  fibres  are  most  abundant  or  most 
powerful  in  the  rami  of  the  last  three  dorsal  and  first  two  lumbar  nerves. 
There  is  some  evidence  of  the  presence  of  vaso-dilator  fibres  in  the  vagus. 
The  excitation  of  the  vaso-constrictor  centres  by  the  blood  in  asphyxia  pro- 
duces constriction  of  the  abdominal  vessels/  The  vaso-dilator  as  well  as  the 
vaso-constrictor  fibres  of  the  splanchnic  probably  end  in  the  solar  and  renal 
plexuses/ 

Liver. — Cavazzani  and  Manca  ®  have  recently  attempted  to  show  the  pres- 
ence of  vaso-motor  fibres  in  the  liver.  Their  method  consists  in  passing  warm 
normal  saline  solution  from  a  Mariotte's  flask  at  a  pressure  of  8  to  10  milli- 
meters Hg  through  the  hepatic  branches  of  the  portal  vein  and  measuring 
the  outflow  in  a  unit  of  time  from  the  ascending  vena  cava.  On  stimulating 
the  splanchnic  nerve  they  observed  that  the  outflow  was  usually  diminished 
though  sometimes  increased,  indicating  perhaps  that  the  splanchnics  contain 
both  vaso-constrictor  and  vaso-dilator  fibres  for  the  hepatic  branches  of  the 
portal  vein.  The  vagus  appeared  to  contain  vaso-dilator  fibres.  Further 
studies  are  necessary,  however,  before  pronouncing  definitely  upon  these 
questions. 

Kidney? — The  vaso-motor  nerves  of  the  kidney  leave  the  cord  from  the 
sixth  dorsal  to  the  second  lumbar  nerve.^  In  the  dog,  most  of  the  renal  vaso- 
motor fibres  are  found  in  the  eleventh,  twelfth,  and  thirteenth  dorsal  nerves.' 
The  stimulation  of  the  nerves  entering  the  hilus  of  the  kidney  between  the 
artery  and  vein  causes  a  marked  and  sudden  renal  contraction,  but  the  organ 
soon  regains  its  former  volume.'"  Constriction  follows  also  the  stimulation  of 
the  peripheral  end  of  the  cut  splanchnic  nerve."  Bradfi)rd  has  demonstrated 
renal  vaso-dilator  fibres  for  certain  nerves  by  stimulating  at  the  rate  of  one 
induction  shock  per  second.  For  example,  the  excitation  of  the  thirteenth 
dorsal  nerve  with  50  to  5  induction  shocks  per  second  gave  always  a  constric- 

•  Literature:  Cyon  and  Ludwig,  1866,  p.  136;  Cohnlieim  and  Roy,  1883,  p.  440:  Dastre 
and  Morat,  1884,  p.  294;  Waters,  1885,  p.  460;  Bradford,  1889,  p.  390;  Hallion  and  Franek, 
1896,  p.  478.  ^  Cyon  and  Ludwig,  1866,  p.  136. 

»  Hallion  and  Franek,  1896,  p.  496. 

*  Dastre  and  Morat,  1884,  p.  294;  Hallion  and  Franek,  1896,  p.  506. 
'  *  Langley  and  Dickinson,  1889,  p.  429. 

«  Cavazzani  and  Manca,  1895,  p.  33:  see  also  Pal,  1888,  p.  73. 

^Literature:  Nicolaides,  1S82,  p.  28;  Cohnlieim  and  Roy,  1883,  p.  345;  Klemensiewicz. 
1886,  p.  84;  Masius,  1888,  p.  539;  Bradford,  1889,  p.  404;  Arthaud  and  Butte,  1890,  p.  379; 
Preobrascbensky,  1892;  Wertlieimer,  1893,  p.  1024;  1894,  p.  308;  Bayliss  and  Bradford,  1894, 
p.  17.  '      «  Bayliss  and  Bradford,  1894,  p.  I7.  «  Bradford,  1889,  p.  404. 

»»  Cobnbeini  and  Roy,  1883,  p.  345;  and  Bradford,  1889,  p.  364. 

"  Cohnheim  and  Roy,  1883,  p.  440. 


CIRCULATION.  499 

tiou  of  the  kidney,  but  when  a  single  shock  per  second  was  employed,  the 
kidney  diluted.'  If  the  cells  connected  with  the  renal  vaso-niotor  fibres  are 
stimulated  directly  by  venous  blood  as  in  asphyxia,  the  animal  being  curarized, 
a  decided  constriction  of  the  kidney  results.^  The  reflex  excitation  of  these 
cells  is  of  especial  importance.  The  stimulation  of  the  central  end  of  the 
sciatic  or  the  splanchnic  nerves  causes  renal  constriction.^  The  same  effect  is 
easily  produced  by  stimulating  the  skin,  for  example,  by  the  application  of 
cold.'*  The  stinuilation  of  the  sole  of  the  foot  in  a  curarized  dog  caused 
contraction  of  the  renal  vessels.*  There  is  some  evidence  that  the 
splanchnic  vaso-motor  fibres  for  the  kidney  end  in  the  cells  of  the  renal 
plexus.*" 

Spleen. — The  stimulation  of  the  peripheral  end  of  the  splanchnic  nerves 
causes  a  sudden  and  large  diminution  in  the  volume  of  the  spleen.''  It 
is,  however,  not  certain  Avhether  the  constriction  of  the  spleen  is  to  be 
referred  primarily  to  a  constriction  of  its  blood-vessels  or  to  the  contraction 
of  the  intrinsic  muscular  fibres  which  play  so  large  a  part  in  the  changes  of 
volume  of  this  organ.  The  doubt  is  strengthened  by  the  fact  that  section  of 
the  splanchnic  nerves  does  not  alter  the  volume  of  the  spleen  ;  dilatation 
would  be  expected  were  these  nerves  the  pathway  of  vaso-constrictor  fibres 
for  the  spleen. 

External  Generative  Organs.^ — The  recent  history  of  the  vaso-motor  nerves 
of  the  external  generative  organs — namely,  those  developed  from  the  urogenital 
sinus  and  the  skin  surrounding  the  urogenital  opening^ — begins  with  Eck- 
hard,'"  who  showed  that  the  stimulation  of  certain  branches  of  the  first  and 
second,  and  occasionally  the  third,  sacral  nerves  (dog)  caused  a  dilatation  of  the 
blood-vessels  of  the  penis  and  erection  of  that  organ,  and  with  Goltz,"  who 
found  an  erection  centre  in  the  lumbo-sacral  cord.  Numerous  researches  in 
recent  years,  among  which  the  reader  is  referred  especially  to  the  work  of 
Langley  and  Langley  and  Anderson,'^  have  shown  that  the  vaso-motor  nerves 
of  the  external  generative  organs  of  both  sexes  may  be  divided  into  a  lumbar 
and  a  sacral  group. 

The  lumbar  fibres  pass  out  of  the  cord  in  the  anterior  roots  of  the  second, 
third,  fourth,  and  fifth  lumbar  nerves,  and  run  in  the  white  rami  communi- 
cantes  to  the  sympathetic  chain,  from  which  they  reach  the  periphery  either  by 
way  of  the  pudic  nerves  or  by  the  pelvic  plexus.     The  greater  number  take 

^Bradford,  1889,  p.  387.  *  Coljnheim  and  Roy,  1883,  p.  437. 

3  Cohnheim  and  Roy,  1883,  p.  439. 

*  Preobraschensky,  1892;  Wertheimer,  1894,  p.  308.  ^  Wertheimer,  1893,  p.  1024. 
«  Langley  and  Dickinson,  1889,  p.  429. 

'  Roy,  1882,  p.  225 ;  Schiifer  and  Moore,  1896,  pp.  229,  287. 

*  Literature:  Goltz  and  Freusberg,  1874,  p.  460;  Kaes,  1883,  p.  1;  Anrep  and  Cybulski, 
1884;  Gaskell,  1887,  iv. ;  Morat,  1890,  p.  480;  Piotrowski,  1892,  p.  464;  Sherrington,  1892,  p. 
686;  Franck,  1894,  p.  740;  Piotrowski,  1894,  p.  284;  Franck,  1895,  p.  122;  Langley  and 
Anderson,  1895,  p.  5;  1895,  p.  76. 

*  Langley  and  Anderson,  1895,  p.  76;  1895,  p.  85.  i"  Eckhard,  1863,  p.  145. 
*'  Goltz  and  Freusberg,  1874,  p.  460.                   ^^  Langley  and  Anderson,  1895,  p.  120. 


500  AN  AMEBIC  AN   TEXT-BOOK   OF  PHYSIOLOGY. 

the  former  course,  runniug  down  the  sympathetic  chain  to  the  sacral  ganglia, 
and  passing  from  these  ganglia  through  the  gray  rami  communicantes  to  the 
sacral  nerves.  None  of  the  fibres  thus  derived  enter  the  nervi  erigentes  of 
Eckhard.  Of  the  various  branches  of  the  pudic  nerves  (rabbit),  the  nervus 
dorsalis  causes  constriction  of  the  blood-vessels  of  the  penis  and  the  peri- 
neal nerve  contraction  of  the  blood-vessels  of  the  scrotum.  The  course  by 
way  of  the  pelvic  plexus  is  taken  by  relatively  few  fibres.  They  run  for 
the  most  part  in  the  hypogastric  nerves,  a  few  sometimes  joining  the  plexus 
from  the  lower  lumbar  or  upper  sacral  sym])atlietic  chain,  or  from  the 
aortic  plexus.  The  presence  of  vaso-dilator  fibres  in  the  lumbar  group  is 
disputed.^ 

The  sacral  group  of  nerves  leave  the  spinal  cord  in  the  sacral  nerve  roots. 
Their  stimulation  causes  dilatation  of  the  vessels  of  the  penis  and  vulva. 

Internal  Generative  Organs  (those  developed  from  the  Miillerian,  or  the 
Wolffian,  ducts). — Langley  and  Anderson  ^  find  vaso-constrictor  fibres  for  the 
Fallopian  tubes,  uterus,  and  vagina  in  the  female,  and  the  vasa  deferentia  and 
seminal  vesicles  in  the  male,  in  the  second,  third,  fourth,  and  fifth  lumbar 
nerves.  The  internal  generative  organs  receive  no  afferent,  and  probably  no 
efferent,  fibres  from  the  sacral  nerves.^ 

The  position  of  the  sympathetic  ganglion-cells,  the  processes  of  which  carry 
to  their  peripheral  distribution  the  efferent  impulses  brought  to  them  by  the 
efferent  vaso-motor  fibres  of  the  spinal  cord,  may  be  determined  by  the  nicotin 
method  of  Langley.  About  10  milligrams  of  nicotin  injected  into  a  vein  of  a 
cat  prevent  for  a  time,  according  to  Langley,^  any  passage  of  nerve-impulses 
through  a  sympathetic  cell.  Painting  the  ganglion  with  a  brush  dipped  in 
nicotin  solution  has  a  similar  effect.  The  fibres  peripheral  to  the  cell,  on  the 
contrary,  are  not  paralyzed  by  nicotin.  Now,  after  the  injection  of  nicotin  the 
stimulation  of  the  lumbar  nerves  in  the  spinal  canal  has  no  effect  on  the  vessels 
of  the  generative  organs.*  Hence  all  the  vaso-motor  fibres  of  the  lumbar 
nerves  must  be  connected  with  nerve-cells  somewhere  on  their  course.  The 
lumbar  fibres  which  run  outward  to  the  inferior  mesenteric  ganglia  are  for  the 
most  part  connected  with  the  cells  of  these  ganglia.  A  lesser  number  is  con- 
nected with  small  ganglia  lyitig  as  a  rule  near  the  organs  to  which  the  nerves 
are  distributed.  The  remaining  division  of  lumbar  fibres  running  downward 
in  the  sympathetic  chain,  and  including  the  majority  of  the  nerve-fibres  to  the 
external  generative  organs  are  connected  with  nerve-cells  in  the  sacral  gan- 
glia of  the  sympathetic. 

The  sacral  group  of  nerves  enter  ganglion-cells  scattered  on  their  course, 
most  of  the  nerve-cells  for  any  one  organ  being  in  ganglia  near  that  organ. 

Bladder. — Neither  lumbar  nor  sacral  nerves  send  vaso-motor  fibres  to  the 
vessels  of  the  bladder.® 

1  Franck,  1895,  p.  143 ;  Langley  and  Anderson,  1895,  p.  93. 

*  Langley  and  Anderson,  1895,  p.  129.  ^  Langley  and  Anderson,  1896,  p.  372. 

*  Langley,  1894,  p.  420,  also  Langley  and  Dickinson,  1889,  p.  423. 

6  Langley  and  Anderson,  1895,  p-  131.  ®  Langley  and  Anderson,  1895,  P-  84. 


CIRCULATION.  501 

Portal  System. — It  has  already  been  said  that  vaso-constrictor  fibres  for  the 
portal  vein  were  discovered  by  Mall  ^  in  the  splanchnic  nerve.  Constrictor  fibres 
have  been  Ibund  by  Bayliss  and  Starling^  in  the  nerve-roots  from  the  third  to 
the  eleventh  dorsal  inclusive.  Most  of  the  constrictor  nerves  pass  out  from 
the  fifth  to  the  ninth  dorsal. 

Back. — The  dorsal  branches  of  the  lumbar  and  intercostal  arteries,  issuing 
from  the  dorsal  nmscles  to  supply  the  skin  of  the  back,^  can  be  seen  to  con- 
tract when  the  gray  ramus  of  the  corresponding  sympathetic  ganglia  are 
stimulated. 

Limbs.* — The  vaso-motor  nerves  of  the  limbs  in  the  dog  leave  the  spinal 
cord  from  the  second  dorsal  to  the  third  lumbar  nerves.^  The  area  for  the  hind 
limb,  according  to  Bayliss  and  Bradford,"  is  less  extensive  than  that  for  the 
fore  limb,  the  former  receiving  constrictor  fibres  from  nine  roots,  namely  the 
third  to  the  eleventh  dorsal,  the  latter  from  six  roots,  the  eleventh  dorsal  to 
third  lumbar.  Langley^  finds  that  the  sympathetic  constrictor  and  dilator 
fibres  for  the  fore  foot  are  connected  with  nerve-cells  in  the  ganglion  stella- 
tum  ;  while  those  for  the  hind  foot  are  connected  with  nerve-cells  in  the  sixth 
and  seventh  lumbar,  and  the  first,  and  possibly  the  second,  sacral  ganglia. 

Tail.^  — Stimulation  of  any  part  of  the  sympathetic  from  about  the  third 
lumbar  ganglion  downward  almost  completely  stops  the  flow  of  blood  from 
w^ounds  in  the  tail.  The  vaso-motor  fibres  for  the  tail  leave  the  cord  chiefly 
in  the  third  and  fourth  lumbar  nerves.  Their  stimulation  may  cause  primary 
dilatation  followed  by  constriction. 

Muscles.^  — According  to  Gaskell,^"  the  section  of  the  nerve  belonging  to 
any  particular  muscle  or  group  of  muscles  causes  a  temporary  increase  in  the 
amount  of  blood  which  flows  from  the  muscle  vein.  The  stimulation  of  the 
peripheral  end  of  the  nerve  also  increases  the  rate  of  flow  through  the  muscle. 
The  same  increase  is  seen  on  stimulation  of  the  nerve  when  the  muscle  is  kept 
from  contracting  by  curare,  provided  the  drug  is  not  used  in  amounts  sufiicient 
to  paralyze  the  vaso-dilator  nerves."  Mechanical  stimulation  by  crimping  the 
peripheral  end  of  the  nerve  gives  also  an  increase.^^  The  existence  of  vaso- 
dilator nerves  to  muscles  must  therefore  be  conceded.  The  presence  of  vaso-con- 
strictor fibres  is  shown  by  the  diminution  in  outflow  from  the  left  femoral  vein 
which  followed  Gaskell's  stimulation  of  the  peripheral  end  of  the  abdominal 
sympathetic  in  a  thoroughly  curarized  dog,^^  but  the  supply  of  constrictor  fibres 

1  Mall,  1890,  p.  57  ;  1892,  p.  409.  '  Bayliss  and  Starling,  1895,  p.  125. 

3  Langley,  1895,  p.  314. 

*  Literature  :  Lewaschew,  1882,  p.  389  ;  1884 ;  Laffont,  1882,  p.  864 ;  Bowditch  and  Warren, 
1886,  p.  416;  Humilewski,  1886,  p.  126;  Langley,  1891,  p.  375;  Jegorow,  1892,  p.  69;  Pio- 
trowski,  1892,  p.  464 ;  Thompson,  1893,  p.  104 ;  Langley,  1893,  p.  227 ;  Piotrowski,  1894,  p. 
258 ;  Wertheimer,  1894,  p.  724 ;  Bayliss  and  Bradford,  1894,  p.  16  ;  Langley,  1895,  p.  307. 

*  Bayliss  and  Bradford,  1894,  p.  22. 

*  Bayliss  and  Bradford,  1894,  pp.  16,  17  ;  compare  Langley,  1895,  p.  307. 

^  Langley,  1891,  p.  375.  ^  Langley,  1895,  p.  311. 

9  Literature :  Sadler,  1869,  p.  77  ;  Gaskell,  1876,  p.  45 ;  1877,  pp.  360,  720 ;  Griitzner  and 
Heidenhain,  1878,  p.  1  ;  Gaskell,  1878,  p.  262. 

>»  Gaskell,  1878,  p.  262.  "  Ibid.,  p.  274.  >^  Ibid.,  p.  275.  ^^  Ibid.,  p.  277. 


502  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

is  comparatively  small.  In  tiirarizetl  auimalt^  reflex  dilatation  ai)parently  follows 
the  stimulation  of  the  nerves  tlie  excitation  of  which  would  have  caused  the 
contraction  of  the  muscles  observed,  had  not  the  occurrence  of  actual  contrac- 
tion been  prevented  by  the  curare.  The  stimulation  of  the  central  end  of 
nerves  not  capable  of  calling  forth  reflex  contractions  in  the  muscles  observed 
— for  example,  the  vagus — seems  to  cause  constriction  of  the  muscle- vessels.' 

'  Gaskell,  1878,  p.  289. 


VIII.  RESPIRATION. 


A  STUDY  of  the  plienomena  of  animal  life  teaches  us  that  a  supply  of 
oxygen  and  an  elimination  of  carbon  dioxide  are  essential  to  existence.  Oxy- 
gen is  indispensable  to  life;  carbon  dioxide  is  inimical  to  life.  One  serves  for 
the  disintegration  of  complex  molecules  whereby  energy  is  evolved,  while  the 
other  is  one  of  the  main  effete  products  of  this  dissociation.  We  therefore  find 
an  intimate  relationship  between  the  ingress  of  the  one  and  the  egress  of  the 
other.  During  the  entire  life  of  the  individual  there  is  this  continual  inter- 
change, which  we  term  respiration.  This  term  embraces  two  acts  which,  while 
different,  are  nevertheless  co-operative — first,  the  interchange  of  O  and  COgj 
second,  the  movements  of  certain  parts  of  the  body,  having  for  their  object  the 
inflow  and  outflow  of  air  to  and  from  the  lungs.  The  former,  properly  speak- 
ing, is  respiration  ;  the  latter,  movements  of  respiration. 

Respiration  is  spoken  of  as  internal  and  as  external  respiration.  In  the 
very  lowest  forms  of  life  the  interchange  of  gases  takes  place  directly  between 
the  various  parts  of  the  organism  and  the  air  or  the  water  in  which  the  organ- 
ism lives;  but  in  higher  beings  a  circulating  fluid' becomes  a  means  of 
exchange  between  the  bodily  structures  and  the  surrounding  medium,  so  that 
in  these  beings  there  is  first  an  interchange  between  the  air  or  the  water  in 
which  the  animal  lives  and  the  circulating  medium,  and  subsequently  an  inter- 
change between  the  circulating  medium  and  the  tissues.  Therefore  in  the  most 
primitive  forms  of  life  respiration  is  a  single  process,  while  in  higher  organ- 
isms it  is  a  dual  process,  or  one  consisting  of  two  stages,  the  first  being  the 
interchange  between  the  atmosphere  or  the  water  surrounding  the  body  and 
the  circulating  medium,  and  the  second  between  the  circulating  medium  and 
the  bodily  structures.  In  man,  external  respiration  is  the  interchange  taking 
place  between  the  blood  and  the  gases  in  the  lungs  and  between  the  blood  and 
the  air  through  the  skin  ;  while  internal  respiration  is  the  interchange  between 
the  blood  and  the  tissues.  In  external  respiration  O  is  absorbed  and  COj  is 
given  off  by  the  blood  ;  in  internal  respiration  the  blood  absorbs  CO2  and 
gives  off  O. 

A.  The  Respiratory  Mechanism  in  Man. 

The  respiratory  apparatus  in  man  consists  (1)  of  the  lungs  and  the  air- 
passages  leading  to  them,  the  thorax  and  the  muscular  mechanisms  by  means 
of  which  the  lungs  are  inflated  and  emptied,  and  the  nervous  mechanisms  con- 
nected therewith  ;  and  (2)  the  skin,  whicli,  however,  plays  a  subsidiary  part  in 
man,  and  need  not  here  be  considered. 

503 


604  AJV  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

Tlio  lungs  limy  lie  regarded  as  two  large  bags  broken  up  into  saccular 
divisions  and  subdivisions  which  ultimately  consist  of  a  vast  number  of  little 
pouches,  or  infundibuli,  each  of  which  is,  as  the  name  implies,  funnel-shaped, 
the  walls  being  hollowed  out  into  alveoli,  or  air-vesicles.  These  alveoli  vary 
in  size  from  120//  to  380//,  the  average  diameter  being  about  250//  (y^  inch). 
Each  infundibulum  communicates  by  means  of  a  small  air-passage  with  a 
bronchiole,  which  in  turn  communicates  with  a  smaller  air-tube  or  bronchus, 
and  filially,  through  successive  unions,  with  the  common  air-duct  or  trachea. 
It  is  estimated  that  tiie  alveoli  numl)er  about  725,000,000,  and  that  the  total 
superficies  exposed  by  them  to  the  gases  iu  the  lungs  is  about  200  square 
meters,  or  from  one  hundred  to  one  hundred  and  thirty  times  greater  than 
the  surface  of  the  body  (1.5  to  2  square  meters).  The  wall  of  each  alveolus 
forms  a  delicate  partition  between  the  air  in  the  lungs  and  an  intricate  net- 
work of  blood-vessels ;  this  netw'ork  is  so  dense  that  the  spaces  between  the 
capillaries  are,  as  a  rule,  smaller  than  the  diameters  of  the  vessels.  The 
lungs,  therefore,  are  exceedingly  vascular,  and  it  is  estimated  that  the  vessels 
contain  on  an  average  about  1.5  kilograms  of  blood.  Owing  to  the  minute- 
ness of  the  capillaries  and  the  density  of  the  network,  the  air-cells  may  be 
said  to  be  surrounded  by  a  film  of  l)lood  which  is  about  10/^  in  thickness  and 
has  an  area  of  about  150  square  meters. 

The  lungs  are  highly  elastic,  and  their  elasticity  is  perfect,  as  is  shown  by 
the  fact  that  they  immediately  regain  their  passive  condition  as  soon  as  the 
dilating  or  distending  force  has  been  removed.  Before  birth  the  lungs  are  air- 
less (atelectatic)  and  the  walls  of  the  bronchioles  and  the  infundibuli  are  in 
contact,  yet  in  the  child  before  birth,  as  iu  the  adult,  the  lungs  are  in  apposi- 
tion with  the  thoracic  walls,  being  separated  only  by  two  layers  of  the  pleurae. 
As  soon  as  the  child  is  born  a  few  respiratory  movements  are  sufficient  to 
inflate  them,  and  thereafter  they  never  regain  their  atelectatic  condition,  since 
after  the  most  complete  colla])se,  such  as  occurs  when  the  thorax  is  opened, 
some  air  remains  in  the  alveoli,  owing  to  the  fact  that  the  walls  of  the  bron- 
chioles come  together  before  all  of  the  air  can  escape.  As  the  child  grows  the 
thorax  increases  in  size  more  rapidly  than  the  lungs,  and  becomes  too  large,  as 
it  were,  for  the  lungs,  which,  as  a  consequence,  become  permanently  distended 
because  of  their  being  in  an  air-tight  cavity.  If  the  chest  of  a  cadaver  be 
punctured,  the  lungs  immediately  shrink  so  that  a  considerable  air-sj)ace  will 
be  formed  between  them  and  the  walls  of  the  thorax.  This  collapse  is  due  to 
the  condition  of  elastic  tension  which  exists  from  the  moment  air  is  introduced 
into  the  alveoli,  and  which  increases  with  the  degree  of  ex])ansion.  Therefore, 
after  the  lungs  are  inflated  they  exhibit  a  persistent  tendency  to  collapse;  con- 
sequently they  must  exercise  upon  the  thoracic  walls  and  diaj)hragm  a  constant 
traction  or  "  pull "  which  is  in  proportion  to  the  amount  of  tension.  It  is 
therefore  obvious  that  there  must  exist  within  the  thorax,  under  ordinary 
circumstances,  a  state  of  negative  pressure  (pressure  below  tliat  of  the  atmo- 
sphere). This  can  be  proven  by  connecting  a  trocar  with  a  manometer  and 
then  forcing  the  trocar  into  one  of  the  pleural  sacs. 


BESPIRA  TION.  505 

Doiiders  found  that  the  pressure  at  the  end  of  quiet  expiration  was  —6  mil- 
limeters of  Hg,  and  at  the  end  of  quiet  inspiration  —9  millimeters.  Accord- 
ing to  these  figures,  the  pressure  on  the  heart,  great  i)lood-vessels,  and  other 
thoracic  structures  lying  between  the  lungs  and  the  thoracic  walls  would  be 
754  millimeters  of  Hg  (one  atmosphere,  760  millimeters,  —6  millimeters)  at 
the  end  of  quiet  expiration,  and  751  millimeters  of  Hg  at  the  end  of  quiet 
inspiration.  Corresponding  values  by  Hutchinson  are  —3  millimeters  and 
—4.5  millimeters.  Arron '  found  in  a  case  of  a  woman  with  emphysema  that 
the  ])ressure  at  the  end  of  expiration  ranged  from  —1.9  to  —3.9  millimeters, 
and  at  the  end  of  inspiration  from  —4  to  —6.85  millimeters,  according  to  the 
position  of  the  body,  the  pressure  being  lowest  in  the  lying  posture,  higher 
when  sitting  in  bed,  still  higher  when  sitting  on  a  chair,  and  highest  when  sit- 
ting and  when  inspiration  on  the  well  side  was  hindered,  thus  throwing  a  larger 
portion  of  the  work  on  tiie  diseased  side,  on  which  the  measurements  were 
made.  During  inspiration  negative  pressure  increases  in  proportion  to  the 
depth  of  inspiration — or,  in  other  words,  in  relation  to  the  amount  of  expan- 
sion of  the  lungs — while  during  expiration  it  gradually  falls  to  the  standard  at 
the  beginning  of  inspiration.  During  forced  inspiration  it  may  reach  —30  to 
—40  millimeters  or  more.  The  pressure  thus  observed  within  the  thorax  {out- 
side of  the  lungs)  is  known  as  intratlwracic  pressure,  and  must  not  be  con- 
founded with  intrapulmonary  or  respiratory  pressure,  which  exists  within  the 
lungs  and  the  respiratory  passages  (see  p.  516). 

The  thorax  is  capable  of  enlargement  in  all  directions.  It  is  cone-shaped, 
the  top  of  the  cone  being  closed  in  by  the  structures  of  the  neck ;  the  sides, 
by  the  vertebral  column,  ribs,  costal  cartilages,  sternum,  and  intercostal  sheets 
of  muscular  and  other  tissues ;  and  the  bottom,  by  the  arched  diaphragm.  It 
is  obvious  that,  since  the  thorax  is  an  air-tight  cavity  and  completely  filled 
by  various  structures,  enlargement  in  any  direction  must  cause  a  diminution  of 
pressure  within  the  lungs,  while  a  shrinkage  would  operate  to  bring  about  an 
opposite  condition  of  increased  pressure.  Since  the  trachea  is  the  only  means  of 
communication  between  the  lungs  and  the  atmosphere,  it  is  evident  that  such 
alterations  in  pressure  must  encourage  either  the  inflow  or  the  outflow  of  air,  as 
the  case  may  be ;  consequently,  when  the  thoracic  cavity  is  expanded  the  pres- 
sui-e  within  the  lungs  is  less  than  that  of  the  atmosphere,  and  air  is  forced  into 
the  lungs;  and  when  the  thorax  is  decreased  in  size  the  reverse  of  the  above 
pressure  relation  exists,  and  the  air  is  expelled.  In  fact,  the  thorax  and  the 
lungs  behave  as  a  pair  of  bellows — just  as  air  is  drawn  into  the  expanding 
bellows,  so  is  air  drawn  into  the  lungs  by  the  enlargement  of  the  thorax ; 
similarly,  as  the  air  is  forced  from  the  bellows  by  compression,  so  is  air 
forced  from  the  lungs  bv  the  shrinkage  of  the  lung's  and  the  thorax. 

During  the  expansion  of  the  thorax  the  lungs  are  entirely  passive,  and  by 
virtue  of  their  perfect  elasticity  merely  follow  the  thoracic  walls,  from  which 
they  are  separated  only  by  the  two  layers  of  the  pleurae,  which,  being  moist- 
ened with  lymph,  slide  over  each  other  without  appreciable  friction.  That 
^  Virchow's  Arckiv,  1891,  vol.  126,  p.  523. 


506  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

the  lungs  arc  entirelv  passive  is  shown  by  the  fact  that  when  the  thorax  is 
punctured,  so  as  to  allow  a  free  communication  with  the  atmosphere,  expan- 
sion of  the  chest  is  no  longer  followed  by  dilatation  of  the  lungs.  During  the 
shrinkage  of  the  thorax  the  elastic  reaction  of  the  lungs  plays  an  active  part. 

Respiration,  Inspiration,  and  Expiration. — Each  respiration  or  respiratory 
act  consists  of  an  inspiration  (enlargement  of  the  thorax  and  inflation  of  the 
lungs)  and  an  expiration  (shrinkage  of  the  thorax  and  the  lungs).  Accord- 
ing to  some  observers,  a  pause  exists  after  expiration  {expiratory  pause),  but 
during  quiet  breathing  no  such  interval  can  be  detected.  A  pause  may  be 
present  when  the  respirations  are  deep  and  infrequent.  Under  certain  abnor- 
mal circumstances  a  pause  may  exist  between  inspiration  and  cx])i  ration 
(inspiratory  pause). 

Inspiration  is  accomplished  by  the  contraction  of  certain  muscles  which  are 
designated  inspiratory  muscles.  Expiration  during  quiet  breathing  is  essen- 
tially a  passive  act,  but  during  forced  breathing  various  muscles  are  active; 
these  muscles  are  distinguished  as  expiratory  muscles. 

During  inspiration  the  thorax  is  enlarged  in  the  vertical,  transverse,  and 
antero-posterior  diameters.  During  quiet  breathing  the  vertical  diameter  is 
increased  by  the  descent  of  the  diaphragm,  and  during  deep  inspiration  it  is 
further  increased  by  the  backward  and  slightly  downward  movement  of  the 
floating  ribs,  and  by  the  extension  of  the  vertebral  column,  which  raises  the 
sternum  with  its  costal  cartilages  and  ribs.  The  transverse  diameter  is  in- 
creased by  the  elevation  and  eversion  (rotation  outward  and  upward)  of  the 
ribs.  The  antero-posterior  diameter  is  increased  by  the  uj)ward  and  outward 
movement  of  the  sternum,  costal  cartilages,  and  ribs.  During  quiet  inspiration 
in  men  the  sternum  is  not  raised  to  a  higher  level,  but  the  lower  end  is  rotated 
forward  and  upward.  It  is  only  during  deep  inspiration  in  the  male  and  in 
quiet  or  deep  inspiration  in  women  that  the  sternum  as  a  whole  is  elevated. 

The  movements  of  the  anterior  and  lateral  walls  constitute  costal  respira- 
tion, and  those  of  the  diaphragm  diaphragmatic  or,  as  it  is  sometimes  called, 
abdominal  respiration,  since  the  descent  of  the  diapiiragm  causes  protrusion 
of  the  abdominal  walls.  Both  types  coexist  during  ordinary  resjiiratory  move- 
ments, but  one  may  be  more  prominent  than  the  other.  The  costal  type  is  well 
marked  in  women,  and  the  diaphragmatic  type  in  men.  These  peculiarities 
are  not,  however,  due  to  inherent  sexual  differences,  but  to  dress  and  heredity. 
Young  children  of  both  sexes  exhibit,  as  a  rule,  the  diaphragmatic  type,  and 
it  is  only  near  or  at  puberty  that  the  costal  type  is  developed  in  the  female. 

The  chief  muscles  of  inspiration  are  the  diaphragm,  the  quadrati  Imnborum, 
the  serrati  postici  infer iores,  the  scaleni,  the  serrati  postici  super iores,  the  leva- 
tores  costarum  longi  et  brevea,  and  the  intercostales  externi  et  intercartilaginei. 

Movements  of  the  Diaphragm. — The  diaphragm  is  attached  by  its  two 
crura  to  the  first  three  or  four  lumbar  vertebrte,  to  the  lower  six  or  seven  cos- 
tal cartilages  and  adjoining  parts  of  the  corresponding  ribs,  and  to  the  poste- 
rior surface  of  the  ensiform  appendix.  It  projects  into  the  thoracic  cavity  in 
the  form  of  a  flattened  dome,  the  highest  part  being  formed  by  the  central 


RESPIRATION.  507 

tendon.  Tlie  tendon  consists  of  three  lobes  which  are  partially  separated  by 
deprcs^sions.  The  right  lobe,  or  largest,  is  the  highest  portion  and  lies  over 
tiie  liver;  the  leit  lobe,  which  is  the  smallest,  lies  over  the  stomach  and  the 
spleen ;  while  the  central  lobe  is  situated  anteriorly,  the  upper  surface  blending 
with  the  pericardium.  The  central  tendon  is  a  common  point  of  insertion 
of  all  the  muscular  fibres  of  the  diaphragm.  In  the  passive  condition  the 
lower  portions  of  the  diaphragm  are  in  apposition  to  the  thoracic  walls. 
During  contraction  the  whole  dome  is  drawn  downward,  while  the  parts  of 
the  muscle  in  contact  with  the  chest  are  pulled  inward.  According  to  Hult- 
krauz,  the  cardiac  part  of  the  diaphragm  descends  from  5.5  to  11.5  millimeters 
during  quiet  inspiration,  and  as  much  as  42  millimeters  during  deep  inspira- 
tion. Not  only  is  the  height  of  the  arch  lessened,  but  there  is  also  a  tendency, 
owing  to  the  points  of  attachment  of  the  diaphragm,  toward  the  pulling  of  the 
lower  ribs  with  their  costal  cju'tilages  and  the  lower  end  of  the  sternum  inward 
and  upward ;  this  traction,  however,  is  counterbalanced  by  the  pressure  of  the 
abdominal  viscera,  the  latter  being  forced  downward  and  outward  against  the 
thoracic  and  abdominal  walls.  If  this  counterbalancing  pressure  be  removed 
by  freely  opening  the  abdominal  cavity,  especially  after  removing  the  viscera, 
the  lower  lateral  portions  of  the  thorax  will  be  seen  during  each  inspiration  to 
be  drawn  inward.  It  is  during  labored  inspiration  only  that  this  movement 
occui'S  in  the  intact  individual. 

AVhen  the  diaphragm  ceases  to  contract,  the  negative  intrathoracic  pressure 
is  sufficient  to  draw  the  sunken  dome  upward  into  the  passive  position.  This 
upward  movement  of  the  diaphragm  is  aided  by  the  positive  intra-abdominal 
pressure  exerted  by  the  elastic  tension  of  the  abdominal  walls  through  the 
medium  of  the  abdominal  viscera.  In  forced  expiration  the  contraction  of 
the  abdominal   muscles  (p.  515)  adds  additional  force. 

The  quadrati  lumborum  are  believed  to  assist  the  diaphragm  by  fixing 
the  twelfth  ribs,  or  even  lowering  them  during  deep  inspiration.  Each  of 
these  muscles  arises  from  the  ilio-lumbar  ligament  and  the  iliac  crest,  and 
is  inserted  into  the  transverse  processes  of  the  first,  second,  third,  and 
fourth  lumbar  vertebrae  and  the  lower  border  of  one-half  of  the  length 
of  the  last  rib.  These  muscles  are  regarded  by  some  physiologists  as 
expiratory  agents. 

The  serrati  postici  inferiores  similarly  assist  the  diaphragm  by  drawing  the 
lower  four  ribs  backward,  and  in  deep  inspiration  also  downward.  They  not 
only  thus  oppose  the  tendency  of  the  diaphragm  to  pull  the  lower  ribs 
upward,  which  would  lessen  its  effectiveness  in  enlarging  the  vertical  diam- 
eter of  the  thorax,  but  they  contribute  to  this  enlargement  by  their  down- 
ward and  backward  traction  upon  the  ribs  and  the  attached  portions  of  the 
diaphragm.  These  muscles  pass  from  the  spines  of  the  eleventh  and  twelfth 
dorsal  and  first  two  or  three  lumbar  vertebra  and  the  supraspinous  ligament 
to  the  lower  borders  of  the  ninth,  tenth,  eleventh,  and  twelfth  ribs,  beyond 
their  angles. 

Simultaneously  with  the  contraction  of  the  diaphragm  the  thoracic  walls 


508 


AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 


are  drawn  upward  and  outward  Ity  tlie  contractions  of  other  inspiratory  mus- 
cles, thus  enlarging  the  thorax  in  the  antero-posterior  and  lateral  diameters. 

Movements  of  the  Ribs. — Tiie  movements  of  the  rii)>  during  inspiration 
are,  as  a  whole,  essentially  rotations  upward  and  outward  ujwn  axes  which  are 
directed  obliquely  outward  and  backward,  each  axis  being  directed  through 
the  costo-vertebral  articulation  and  a  little  anterior  to  the  costo-transverse 
articulation.  The  vertebral  ends  of  the  ribs  lie  higher  than  their  sternal 
extremities,  so  that  when  the  ribs  are  elevated  the  anterior  ends  are  advanced 
forward  and  upward.  The  arches  of  the  ribs  are  inclined  downward  and 
outward,  and,  owing  to  the  obliquity  of  the  axes  of  rotation,  the  convexities 
are  rotated  upward  and  outward,  or  everted.  Thus  both  the  antero-posterior 
and  lateral  diameters  are  increased. 

The  degree  of  obliquity  of  the  axes  of  rotation  of  the  different  ribs  varies. 
The  axis  of  the  first  rib  is  almost  transverse  (Fig.  1.31),  while  that  of  each 
succeeding  rib  to  the  ninth,  inclusive,  becomes  more  oblique  (Fig.  132).    The 


Fig.  131.— First  dorsal  vertebra  and  rib. 


Fig.  132.— Sixth  dorsal  vertebra  and  rib. 


more  oblique  the  axis,  the  greater  the  degree  of  eversion ;  consequently  the 
first  rib  is  capable  of  but  slight  eversion,  while  the  lower  ribs  may  be  everted 
to  a  relatively  marked  extent.  iSIoreover,  the  peculiarities  or  the  absence  of 
the  costo-transverse  articulations  materially  affect  the  character  of  the  move- 
ments of  the  different  ribs.  Thus,  the  facets  on  the  transverse  processes  of  the 
first  and  second  dor.sal  vertebrre  are  cup-shaped,  and  into  them  are  inserted 
the  conical  tuberosities  of  the  ribs,  thus  materially  limiting  the  rotation  of  the 
ribs ;  wliile  the  facets  for  the  articulations  of  the  third  to  the  tenth  ribs,  inclu- 
sive, assume  a  plane  character  which  admits  of  larger  movement.  The  facets 
for  the  third  to  the  fifth  ribs  are  almost  vertical,  thus  allowing  a  free  move- 
ment upon  the  oblique  axis ;  while  the  facets  for  the  sixth  to  the  ninth  ribs, 
inclusive,  are  directed  obliquely  upward  and  backward,  and  admit  of  a  move- 


RESPIRATION.  509 

inent  upward  aud  backward  as  well  as  a  rotation  upon  the  oblique  axis. 
Finally,  the  eleventh  and  twelfth  ribs  (and  generally  the  tenth)  have  no  costo- 
transverse articulations,  allowing  a  movement  backward  aud  ibrward  as  well 
as  rotation  upon  their  oblique  axes.  While,  therefore,  the  movements  of  the 
ribs  are  essentially  rotations  upward,  forward,  and  outward  upon  oblique  axes 
directed  through  the  costo- vertebral  articulations  and  a  little  anterior  to  the 
costo-transverse  articulation,  they  are  more  or  less  modified  by  reason  of  the 
motion  permitted  by  the  nature  or  the  absence  of  the  costo-transverse  articu- 
lations. Thus,  the  essential  character  of  the  movement  of  the  first  to  the 
fifth  ribs  is  a  rotation  upward,  forward,  and  outward  ;  that  of  the  sixth  to 
the  ninth  ribs,  a  rotation  upward,  forward,  and  outward  combined  with  a 
movement  u])ward  and  backward ;  that  of  the  tenth  and  eleventh  ribs,  a 
rotation  upward,  forward,  aud  outward  with  a  rotation  backward;  that  of 
the  twelfth  rib,  chiefly  a  rotation  backward  and  rather  downward.  The 
character  of  the  movement  of  each  rib  differs  somewhat  as  we  pass  from 
the  first  to  the  twelfth  ribs. 

During  forced  inspiration  the  sternum  and  its  attached  costal  cartilages 
with  their  ribs  are  pulled  upward  and  outward,  while  the  ninth,  tenth, 
eleventh,  and  twelfth  ribs  are  drawn  backward  and  downward.  During 
expiration  these  movements  are  of  course  reversed. 

The  intercostal  spaces  during  inspiration,  except  the  first  two,  are  widened.^ 
The  reason  for  this  opening  out  must  be  apparent  when  we  remember  that 
the  ribs  are  arranged  in  the  form  of  a  series  of  parallel  curved  bars  directed 
obliquely  downward,  and  the  fact  may  be  demonstrated  by  means  of  a  very  sim- 
ple model  (Fig.  133)  consisting  of  a  vertical  support  and  two  parallel  bars,  a,  b, 
placed  obliquely.  If,  after  measuring  the  distance  c,  d,  w^e 
raise  the  bars  to  a  horizontal  position,  the  distance  e,f  will 
be  found  to  be  greater  than  c,  rf,  since  the  bars  rotate  around 
fixed  points  placed  in  the  same  vertical  line.  This  widening 
of  the  intercostal  spaces  is  readily  accomplished  because  of 
the  elasticity  of  the  costal  cartilages. 

The  muscles  involved  in  the  movements  of  the  ribs 
during  quiet  inspiration  include  the  scaleni,  the  serrafi 
postid  superior es,  the  levator es  costarum  longi  et  breves,  and 
the  intei'costales  extcrni  et  iniercartUaginei. 

The  scaleni  are  active  in  fixing  the  first  and  second  ribs,  lustrate  the  widening 
thus  establishing,  as  it  were,  a  firm  basis  from  which  the  during?nspi"rluon.*^^^ 
external  intercostal  muscles  may  act.  The  scalenus  anticus 
passes  between  the  tubercles  of  the  transverse  processes  of  the  third,  fourth, 
fifth,  and  sixth  cervical  vertebrae  to  the  scalene  tubercle  on  the  first  rib. 
The  scalenus  medius  passes  from  the  posterior  tubercles  of  the  transverse 
l)rocesses  of  the  lower  six  cervical  vertebrae  to  the  upper  surface  of  the 
first  rib,  extending  from  the  tubercle  to  just  behind  the  groove  for  the 
subclavian  artery.  The  scalenus  posticus  passes  from  the  transverse  pro- 
'  Ebner :  Archivfiir  Anatomie  und  Physiologic,  Anatomische  Abtheilung,  1886,  p.  199. 


Fig.  133— Model  to  il- 


510  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

cesses  of  the  two  or  three  lower  cervical  vertebrte  to  the  outer  surface  of  the 
second  rib. 

The  scrrati  postici  supcriores  aid  iu  fixing  the  second  ribs  and  raise  the  third, 
fourth,  and  fifth  ribs.  The  muscles  })ass  from  the  ligamentum  nuchie  and  the 
spines  of  the  seventh  cervical  and  first  two  or  three  dorsal  vertebrae  to  the  upper 
borders  of  the  second,  third,  fourth,  and  fifth  ribs,  beyond  their  angles. 

The  levatores  costarum  breves  con.sist  of  twelve  pairs  which  pass  from  the 
tips  of  the  transvei-se  processes  of  the  seventh  cervical  and  first  to  the  eleventh 
dorsal  vertebrae  downward  and  outward,  each  being  inserted  between  the 
tubercle  and  the  angle  of  the  next  rib  below.  Those  ari.<iug  from  the  lower 
ribs  send  fibres  to  the  second  rib  below  {levatores  costarum  longiores).  They 
assist  iu  the  elevation  and  evei'sion  of  the  first  to  the  tenth  ribs,  inclusive,  and 
co-operate  with  the  quadrati  lumborum  and  the  serrati  postici  inferiores  to 
draw  the  lower  ribs  backward. 

The  functions  of  the  intercostale.9  have  been  a  matter  of  dispute  for  centu- 
ries, and  the  problem  is  still  unsettled.  For  instance,  Galen  looked  upon  the 
external  iutercostals  as  being  expiratory.  Vesalius  asserted  that  both  the 
external  and  the  internal  iutercostals  are  expiratory,  while  Haller  expr&ssed 
the  opposite  belief.  Hamberger  and  Hutchinson  regarded  the  external  iuter- 
costals and  the  interchoudrals  as  being  inspiratory,  and  the  interosseous  portion 
of  the  internal  iutercostals  as  being  expiratory.  Finally,  Landois  believes  that 
while  the  external  iutercostals  and  the  interchondrals  are  active  during  inspira- 
tion, and  the  interosseous  portion  of  the  internal  iutercostals  during  expiration, 
their  chief  actions  are  not  to  enlarge  nor  to  diminish  the  volume  of  the  thoracic 
cavitv,  but  to  maintain  a  pro]>er  degree  of  tension  of  the  intercostal  spaces. 
Each  view  still  has  its  adherents. 

The  actions  of  the  intercostal  muscles  are  generally  demonstrated  by  means 
of  rods  and  elastic  bands  arranged  in  imitation  of  the  ribs  and  the  origins  and 
insertions  of  the  muscles,  or  by  geometric  diagrams.  The  well-known  model 
of  Bernouilli  consists  of  a  vertical  bar  representing  the  vertebral  column,  upon 
which  bar  move  two  parallel  straight  rods  in  imitation  of  the  ribs  (Fig.  134). 
Tf  the  rods  be  placed  at  an  oblique  angle  and  a  tense  rublier  band  (a,  h)  be 
affixed  to  represent  the  relations  of  the  external  iutercostals,  the  rods  M-ill  be 
pulled  upward  and  the  space  between  them  will  be  widened.  The  interchon- 
dral  portion  of  the  internal  iutercostals  bears  the  same  ol)lique  relation  to  the 
costal  cartilages,  and  theoretically  should  have  the  same  action.  The  action 
of  the  interosseous  portion  of  the  internal  iutercostals  is  demonstrated  in  this 
wav:  If  the  rubber  baud  be  placed  at  right  angles  to  the  rods  (Fig.  130,  a,  6) 
and  the  rods  be  raised  to  a  horizontal  position,  the  rubber  is  put  on  the  stretch 
(c,  d),  so  that  when  the  rods  are  released  they  will  be  pulled  downward  by  the 
elastic  reaction  of  the  rubber.  This  last  demonstration  has  been  held  to  indi- 
cate that  during  inspiration  the  interosseous  portion  of  the  internal  intercostals 
is  put  on  the  stretch  and  in  an  oblique  position,  and  therefore  in  a  relation 
favorable  for  effective  action  during  contraction.  The  ribs,  however,  differ 
essentially  from  such  a  model  in  the  fiict  that  they  are  curved  bai-s,  that  their 


RESPIRA  TIOX. 


511 


ends  are  not  free,  and  that  the  movement  of  rotation  is  materially  different. 
In  fact,  the  meolianii'ul  conditions  are  so  complex  that  deductions  from  phe- 
nomena observed  in  .such  gross  demonstrations  or  by  means  of  geometric  figures 
such  as  suggested  by  Rosenthal  and  others  must  be  accepted  with  caution. 

There  is  no  doubt  that  stimulation  of  any  of  the  intercostal  fibres  causes 
au  elevation  of  the  rib  below  if  the  rib  above  be  fixed,  and  that  if  the  excita- 
tion i)e  sufficiently  strong  and  the  area  be  large,  the  effect  may  extend  from  rib 
to  rib,  and  thus  a  large  part  of  the  thoracic  cage  will  be  elevated.  Conse- 
quently, it  has  been  assumed  that,  should  the  upper  ribs  be  fixed,  the  contrac- 
tions of  both  sets  of  intercostals  would  elevate  the  system  of  ribs  below.  But 
the  experiments  of  Martin  and  Hartwcll '  show  that  during  forced  inspiration 
the  ijiternal  intercostals  contract  alternately  with  the  diaphragm  and  the  exter- 
nal intercostals,  and  therefore  are  expiratory.  Moreover,  Ebuer^  has  found, 
as  a  result  of  elaborate  measurements,  that  the  intercostal  spaces,  excepting  the 
first  two,  are,  instead  of  being  narrowed,  actually  widened  during  inspiration. 


Fig.  134.— Model  to  illustrate  the  action  of  the 
external  intercostals  and  interchondrals. 


Fig.  135.— Model  to  illustrate  the  action  of  the  inter- 
osseous portion  of  the  internal  intercostals. 


An  examination  of  the  origins  and  insertions  of  the  external  intercostals  and 
the  interos.seous  portion  of  the  internal  intercostals,  and  of  their  actions  during 
contraction,  renders  it  apparent  that  it  is  possible  for  the  externi  to  elevate  the 
ribs  and  to  widen  the  intercostal  spaces,  but  that  such  effects  are  impossible  in 
the  case  of  the  interosseous  portion  of  the  internal  intercostals.  Thus,  if  we 
take  the  model  described  above  (Fig.  134),  project  a  line  «,  b  in  imitation  of 
the  relation  of  the  external  intercostals  to  the  ribs,  and  raise  the  parallel  bars 
to  a  horizontal  position,  the  distance  between  e,  d  is  shorter  than  that  between 
a,  b.  It  is  but  a  logical  step  from  this  demonstration  to  assume  that,  .should  a 
strip  of  muscle  be  placed  between  a,  b,  the  muscle  in  shortening  would  pull  the 
bars  upward,  at  the  same  time  widening  the  intercostal  spaces.  If  now  the 
upper  ribs  be  fixed,  it  is  obvious  that  the  external  intercostals  must  raise  the 
ribs  and  open  up  the  intercostal  spaces  during  contraction.  This  same  reason- 
ing applies  to  the  interchondrals,  and  the  experiments  of  Hough  ^  show  that 
they  contract  synchronously  with  the  diaphragm,  and  therefore  with  the  exter- 
nal intercostals. 

'  Journal  of  Physiology,  1879-80,  vol.  2,  p.  24.  *  Loc.  eit. 

'  Studies  from  (he  Biological  Laboratory,  Johns  Hopkins  University,  March,  1894. 


512  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

In  considering::  the  interosseous  portion  of  the  internal  intercostals  we  find 
that  (lininir  the  ])as.sive  condition  they  are  placed  nearly  at  rijjjht  angles  to  the 
ribs.  If  contraction  takes  place,  it  is  obvious  that  the  mechanical  response 
must  be  an  ap|)roxiniati()n  of  the  ribs  and  a  lessening  of  the  width  of  the  inter- 
costal spaces.  It  must  also  be  ai)parent  that  during  the  movement  of  inspira- 
tion these  fibres  are  put  on  the  stretch,  which  can  be  demonstrated  in  the  above 
model.  Thus,  if  we  put  a  rubber  band  at  right  angles  to  the  parallel  rods. 
(Fig.  135),  we  will  find  that  when  the  rods  are  in  the  horizontal  position,  in 
imitation  of  the  position  of  the  ril)s  at  the  beginning  of  expiration,  the  distance 
between  c,  d  is  greater  than  that  between  «,  b  ;  therefore  if  we  lessen  the  dis- 
tance between  c,  d,  as  when  the  muscle-fibres  contract,  the  mechanical  result  of 
contraction  must  be  approximation,  the  opposite  to  that  which  occurs  during 
ins])iration. 

While  the  whole  subject  of  the  actions  of  the  intercostal  muscles  must  still 
be  regarded  as  in  an  unsettled  condition,  yet  there  is  no  reasonable  doubt  that 
the  externi  and  the  intercartilaginei  contract  during  inspiration,  and  the  inter- 
osseous portion  of  the  internal  intercostals  during  expiration.  Admitting  this 
to  be  true,  it  is,  however,  by  no  means  clear  whether  or  not  these  muscles  are 
for  the  purpose  of  altering  the  volume  of  the  thorax.  It  is  probable,  as  sug- 
gested by  Landois,  that  their  chief  function  is  to  maintain,  during  all  phases 
of  the  respiratory  movements,  a  proper  degree  of  tension  of  the  intercostal 
tissues.  If  this  view  be  correct,  the  external  intercostals  and  interchondrals  con- 
tract during  inspiration  chiefly  for  the  purpose  of  causing  greater  tension  of 
the  intercostal  tissues,  so  as  to  counteract  the  influence  of  the  increase  of 
negative  intrathoracic  pressure ;  while  during  expiration,  when  their  relax- 
ation occurs,  a  substitution  for  this  relaxation  is  jirovided  by  the  contraction 
of  the  interosseous  portion  of  the  internal  intercostals,  so  that  the  tension  of 
the  intercostal  tissues  is  maintained.  The  internal  intercostals  must  prove 
most  effective  during  forced  expiratory  efforts — for  example,  in  coughing, 
when  the  intercostal  tissues  arc  subjected  to  high  positive  intrathoracic  pres- 
sure, and  there  is  a  consequent  tendency  to  outward  displacement,  which  is 
met  and  counteracted  by  the   internal  intercostals. 

During  forced  inspiration  the  scalcni  and  the  serratl  posticl  siiperiores  con- 
tract vigorously,  so  that  the  sternum  and  the  first  five  ribs  are  elevated,  thus 
raising  the  thoracic  cage  as  a  whole.  At  the  same  time  the  serratl  poslici 
inferiores,  the  quadrati  lumborum,  and  the  sacro-lnmbales  are  active  in  pulling 
the  lower  ribs  downward  and  backward.  Besides  these  muscles  there  are  a 
number  of  others  which  directly  or  indirectly  affect  the  size  of  the  thorax  and 
which  may  be  brought  into  activity  ;  chief  among  these  are  the  sferno-cfeido- 
mastoidci,  the  irapezei,  the  pectorales  minores,  the  jjectorales  majores  (costal 
portion),  the  rhomboidei,  and  the  erectores  spinoe. 

The  .stcrno-cJeldo-mafttoid  passes  from  the  mastoid  process  and  the  superior 
curved  line  of  the  occipital  bone  to  the  upper  front  surface  of  the  manubrium 
and  the  upper  border  of  the  inner  third  of  the  clavicle.  These  muscles  ele- 
vate the  upper  jiart  of  the  chest  when  the  head  and   neck  are  fixed.     The 


RESPIRATION.  .  513 

trapezius  passes  from  the  occipital  bone,  the  liganientum  nucha,  the  spines  of 
the  seventh  cervical  and  of  all  the  dorsal  vcrtci>ne,  and  the  supraspinous  liga- 
ment to  the  posterior  border  of  the  outer  third  of  the  clavicle,  the  inner  border 
of  the  acromion  process,  the  crest  of  the  spine  of  the  scapula,  and  to  the 
tubei-cle  near  the  root.    The  trapezei  help  to  fix  the  shoulders.    The  rfiomboid- 
eus  minor  passes  from  the  ligamentum  nucha?  and  the  spines  of  the  seventh 
cervical  and  first  dorsal  vertebne  to  the  root  of  the  spine  of  the  scapula.    The 
rhomboideus  major  passes  from  the  spines  of  the  first  four  or  five  dorsal  vertebrae 
and  the  supraspinous  ligament  to  the  inferior  angle  of  the  scapula.    The  trapezei 
and  rhomboidei  fix  the  shoulders,  affording  ii  base  of  action  from  which  the 
pectorales  act.     The  pectoralis  major  passes  from   the  pectoral  ridge  of  the 
humerus  to  the  inner  half  of  the  anterior  surface  of  the  clavicle,  the  corre- 
sponding half  of  the  anterior  surfVice  of  the  sternum,  the  cartilages  of  the 
first  six'inbs,  and  the  aponeurosis  of  the' external  oblique  muscle.     The  pedo- 
ralis  minor  passes  from  the  coracoid  process  of  the  scapula  to  the  upper  margin 
and  outer  surface  of  the  third,  fourth,  and  fifth  ribs  close  to  the  cartilages  and 
to  the  intercostal  aponeuroses.     The  pectorales  minores  and  the  costal  portion 
of  the  pectorales  majores  raise  the  ribs  when  the  shoulders  are  fixed.     The 
eredorc^  spince  are  composite  muscles  extending  along  each  side  of  the  spinal 
column,  each  consisting  of  the  sacro-lumbalis,  the  musculus  accessorius,  the 
cervicalis  ascendens,  the  longissimus  dorsi,  the  transversalis  cervicis,  the  trachelo- 
mastoid,  and  the  spinalis  dorsi.    The  erectores  spinse  straighten  and  extend  the 
spine  and  the  neck,  and  thus  tend  to  raise  the  sternum,  the  costal  cartilages, 
and  the  ribs.     The  infrahyoidei  may  also  be  included  among  the  muscles 
engaged  in  forced  inspiration,  since  they  may  aid  in  the  elevation  of  the  sternum. 
Summary  of  the  Actions  of  the  Chief  Muscles  of  Inspiration.— Dur- 
ing quid  inspiration  the  diaphragm  contracts,  thus  increasing  the  vertical  diam- 
eter of  the  thorax,  its  effectiveness  being  augmented  by  the  associated  actions 
of  the  quadrati  lumborum  and  the  serrafi  postici  inferiores,  the  former  fixing 
the  twelfth  ribs,  and  the  latter  fixing  the  ninth,  tenth,  eleventh,  and  twelfth 
ribs,  and  thus  preventing  the  muscular  slips  of  the  diaphragm  attached  to  these 
ribs  from  drawing  them  inward  and  upward  and  thus  diminishing  the  cavity 
of  the  thorax.     Coincidently  with  the  contractions  of  these  muscles  the  scaleni 
fix  the  first  and  second  ribs,  and  the  serrati  postici  superiores  aid  in  fixing  the 
second  ribs  and  elevate  the  third,  fourth,  and  fifth  ribs ;  the  intercostaks  extemi 
d  intercartilaginei  and  the  levatores  costarum  longi  d  breves  elevate  and  evert  the 
first  to  the  tenth  ribs,  inclusive,  throwing  the  lower  end  of  the  sternum  for- 
ward ;  and  the  levatores,  in  conjunction  with  the  quadrati  lumborum  and  the 
serrati  postici  inferiores,  aid  in  fixing  the  lower  ribs  and  even  draw  them  back- 
ward.   The  intercostales  extemi  also  serve  to  maintain  a  proper  degree  of  tension 
of  the  intercostal  tissues. 

During  forced  inspiration  the  scaleni  and  the  serrati  postici  s^iperiores  act 
more  powerfully  and  thus  raise  the  sternum  with  its  attached  costal  cartilages 
and  ribs,  being  assisted  bv  the  sterno-deido-mastoidei  and  the  infrahyoidei 
when  the  head  and  neck  are  fixed,  and  by  the  pectorales  majores  d  minores 

33 


514  A.y    AMERICAN    TEXT-BOOK    OE  PHYSIOLOGY. 

when  tlie  shoulders  are  fixetl  l)y  {\\ctrapezei  aiul  the  rhomboidei.     The  eredores 
spincc  further  assist  this  action  by  extending  the  spinal  column. 

Movements  of  Expiration. — During  (piiet  breathing  expiration  is  effected 
mainly  or  solely  by  tliL'  passive  return  of  the  (lis[)laeed  parts.  Normal  expi- 
ration is  therefore  essentially  a  passive  act,  although  it  may  be  assisted  by  the 
contraction  of  the  interosseous  portion  of  the  internal  intercostals.  The  most 
important  factors  are  unquestionably  the  elastic  tension  of  the  lungs,  costal 
cartilages,  intercostal  spaces,  and  abdominal  walls,  together  with  the  weight  of 
the  chest. 

The  lungs  after  quiet  expiration  are  in  a  state  of  elastic  tension  equal  to  a 
pressure  of  -f  1.9  to  +3.9  millimeters  of  mercury  (see  p.  505),  which  pressure 
during  inspiration  is  increased  in  proportion  to  the  depth  of  the  movement. 
As  soon,  therefore,  as  the  inspiratory  muscles  cease  to  contract,  this  tension 
comes  into  play,  and,  aided  by  elastic  and  mechanical  reactions  below  noted, 
forces  air  from  the  lungs.  This  elasticity,  and  the  facility  with  which  the  air 
is  expelled,  may  be  demonstrated  by  inflating  a  pair  of  excised  lungs  and  then 
suddenly  allowing  a  free  egrass  of  the  air:  collapse  occurs  with  remarkable 
rapidity,  with  a  force  proportionate  to  the  degree  of  distention.  The  elastic 
costal  cartilages  are  similarly  put  on  the  stretch  :  the  lower  borders  are  drawn 
outward  and  upward  and  are  thus  twisted  out  of  position,  so  that  as  soon  as 
the  inspiratory  forces  are  withdrawn  they  must  untwist  themselves,  further 
aiding  the  elastic  reaction  of  the  lungs.  The  intercostal  spaces,  excepting  the 
first  two,  are  widened  and  the  tissues  are  stretched,  and  the  diaphragm  during 
its  descent  presses  upon  the  abdominal  viscera,  rendering  the  abdominal  walls 
tense.  AVhen,  therefore,  inspiration  ceases  the  reaction  of  the  tense  and  elastic 
intercostal  tissues  aids  in  bringing  the  chest  into  the  position  of  rest,  while  the 
stretched  abdominal  walls  press  upon  the  abdominal  viscera  and  thus  force 
the  diaphragm  upward.  Finally,  the  chest-walls  by  their  weight  tend  to  fall 
from  the  positi<jn  to  which  they  have  been  raised,  adding  thus  another  factor 
toward  the  elastic  reaction  of  the  lungs,  costal  cartilages,  intercostal  tissues,  and 
abdominal  walls. 

Whether  or  not  the  interosseous  portion  of  the  internal  intercostal  nmscles 
assists  in  expiration  cannot  be  stated  with  positiveness.  The  fact  that  these 
muscles  contract  during  the  expiratory  phase  and  that  the  contraction  results 
in  an  approximation  of  the  ribs  leads  to  the  belief  that  they  are  expiratory. 
But,  as  before  stated  (p.  512),  this  activity  may  be  primarily  for  the  purpose 
of  maintaining  a  proper  degree  of  tension  of  the  intercostal  tissues.  In  the 
dog  these  muscles  are  not  active  until  dyspnoea  appeal's,  while  in  the  cat  they 
do  not  come  into  play  until  extreme  dyspnoea  has  set  in  (Martin  and  Hartwell). 
These  facts  certainly  militate  against  regarding  them  as  active  expiratory  fac- 
tors during  quiet  breathing,  while  during  forced  expiration  they  may  with 
accuracv  be  considered  as  being  in  part  at  least  ex]iiratory  in  function.  We  are 
therefore  justified  in  concluding  that  normal  quiet  expiration  is  essentially  a 
jiassivc  act  due  to  elastic  reaction  and  to  the  mechanical  replacement  of  dis- 
placed parts. 


RESPTRA  TTOX.  51o 

During  forced  expiration  c-ertain  muscles  may  l)e  active,  the  chief  being  the 
intereodales  intcrni  interossei,  tiie  Ir'uuKjalarcH  .stmii,  tiie  inujicnti  abdoiainalcs, 
and  the  levatovcs  aid.  The  intercostalcs  interni  inkrossei  are  pr(jl)ably  active 
expiratory  muscles  during  forced  expiration,  but  they  can  ]»rove  effective  only 
when  the  lower  part  of  the  thoracic  cagi;  is  fixed  or  drawn  down — an  act  which 
is  accomplished  chiefiy  by  the  abdominal  muscles. 

Tiie  triangulares  stenii  pass  outward  and  upward  from  the  lower  j)art  of 
the  sternum,  the  inner  surface  of  the  ensiform  cartilage,  and  the  sternal 
ends  of  the  costal  cartilages  of  the  two  or  three  lower  sternal  ribs,  to  the  lower 
and  inner  surfaces  of  the  cartilages  of  the  second  to  the  sixth  ribs,  inclusive. 
They  draw  the  attached  costal  cartilages  downward  during  expiration. 

The  abdominales  during  quiet  expiration  are  passive,  and  aid  in  the  expul- 
sion of  air  from  the  lungs  simply  by  their  elasticity  ;  but  during  forced  expi- 
ration, by  contraction,  they  are  active  expiratory  factors. 

The  ob/iqum  e.rterniis  arises  by  slips  on  the  outer  surface  and  lower  borders 
of  the  lower  eight  ribs,  and  is  inserted  into  the  outer  lip  of  the  anterior  half 
of  the  crest  of  the  ilium  and  into  the  broad  aponeurosis  which  blends  with 
that  of  the  opposite  side  in  the  linea  alba.  The  obliqmis  internus  passes 
from  the  outer  half  or  two-thirds  of  Poupart's  ligament,  the  anterior  two-thirds 
of  the  middle  lip  of  the  crest  of  the  ilium,  and  the  posterior  layer  of  the  lumbar 
fascia  to  the  cartilages  of  the  last  three  ribs  and  the  aponeurosis  of  the  anterior 
part  of  the  abdominal  wall.  The  rectus  abdominis  passes  from  the  crest  of  the 
pubes  and  the  ligaments  in  front  of  the  symphysis  pubis  to  the  cartilages  of 
the  fifth,  sixth,  and  seventh  ribs,  and  usually  to  the  bone  of  the  fifth  rib.  The 
transversalis  abdominis  passes  from  the  outer  third  of  Poupart's  ligament,  the 
anterior  three-fourths  of  the  inner  lip  of  the  iliac  crest,  by  an  aponeurosis 
from  the  transverse  and  spinous  processes  of  the  lumbar  vertebrae,  and  from 
the  inner  surface  of  the  sixth  lower  costal  cartilages  to  the  jiubic  crest  and  the 
linea  alba.  The  fibres  for  the  most  part  have  a  horizontal  direction.  The  pyram- 
idalis  passes  from  the  anterior  surface  of  the  pubes  and  the  pubic  ligament 
to  the  linea  alba.  It  is  obvious  from  the  points  of  origin  and  insertion  of  the 
abdominal  muscles  that  during  contraction  they  co-operate  toward  diminishing 
the  volume  of  the  thorax  in  three  ways :  (1)  By  offering  a  base  of  action  for 
the  internal  intercostals,  and  thus  aiding  in  the  approximation  of  the  ribs; 
(2)  by  depressing  and  drawing  inward  the  lower  end  of  the  sternum  and  the 
lower  costal  cartilages  and  rii)S ;  (3)  by  forcing  the  abdominal  viscera  against 
the  diaphragm,  thrusting  it  upward.  The  alxlominales  are  unquestionably 
the  chief  expiratory  muscles. 

The  levatores  ani  converge  from  the  pelvic  wall  to  the  inner  part  of  the  rec- 
tum and  the  prostate  gland.  They  form  the  largest  part  of  the  muscular  floor 
of  the  pelvic  cavity.  The  levatores  ani  are  important  during  forcible  exj>i- 
ration  by  resisting  the  downward  pressure  of  the  pelvic  viscera  caused  by  the 
powerful  contractions  of  the  abdominal  muscles,  but  they  must  be  regarded  rather 
as  associatefl  in  the  act  of  ex])iration,  and  not  as  true  expiratory  muscles. 

Summary  of  the  Actions  of  the  Chief  Muscles  of  Expiration. — During 


510  ^i;\^  AMERICAN  TEXT-BOOK   OF  PHYSIOLOGY. 

quiet  expiration  uo  muscular  factors  arc  involved,  unless  it  be  the  contraction 
of  the  intcreostalcs  intei'ni  interossei,  in  which  event  they  are  more  probably 
engaged  in  maintaining  the  tension  of  the  intercostal  tissues  tlian  in  actually 
diminishing  the  capacity  of  the  thorax. 

During  forced  expiration  the  abdominales  flex  the  thorax  upon  the  pelvis, 
force  (he  abdominal  viscera  against  the  diaphragm,  thrusting  it  uj)\vard,  and 
by  })ulling  u})()n  the  lower  margins  of  the  thoracic  cage  draw  them  inward 
and  at  the  same  time  oifer  a  base  from  which  the  intercostales  intenii  inter- 
ossei act  to  i)ull  the  ribs  downward ;  the  triangidares  sterni  contract  at  the 
same  time  and  pull  downward  the  cartilages  of  the  second  to  the  sixth  ribs, 
inclusive. 

Associated  Respiratory  Movements. — Associated  with  the  thoracic  and 
abdominal  movements  of  respiration  are  movements  of  the  face,  pharynx,  and 
larynx.  The  nostrils  are  slightly  dilated  during  insj)iration  and  passively 
return  to  their  condition  of  rest  during  expiration ;  the  soft  palate  moves  to 
and  fro  with  the  inflow  and  outflow  of  air,  and  the  glottis  is  widened  during 
inspiration  and  narrowed  during  expiration.  During  labored  inspiration, 
besides  the  above  movements,  the  mouth  is  usually  opened ;  the  muscles  con- 
cerned in  facial  expression  may  be  active,  giving  the  individual  an  apjwarance 
of  distress;  the  soft  palate  is  raised,  and  the  larynx  descends.  The  widening 
of  the  nares  and  the  glottis,  the  opening  of  the  mouth,  the  elevation  of  the  soft 
palate,  and  the  descent  of  the  larynx  during  inspiration  are  obviously  for  the 
purpose  of  lessening  the  resistance  to  the  inflow  of  air. 

Intrapulmonary  or  Respiratory  Pressure  and  Intrathoracic  Pressure. 
— The  tidal  flow  of  air  to  and  from  the  lungs  during  the  respiratory  move- 
ments is  due,  as  already  stated,  to  the  differences  between  the  jircssure  within 
the  lungs  and  that  outside  the  body.  During  inspiration  the  enlargement  of 
the  thorax  causes  an  expansion  of  the  lungs  and  a  consequent  diminution  of 
pressure  within  them,  so  the  air  is  forced  through  the  air-passages  until  the 
pressure  within  the  lungs  equals  that  of  the  atmosphere;  during  cx})iration 
there  occur  elastic  and  mechanical  reactions  whereby  the  pressure  within  the 
lungs  is  greater  tlian  that  of  the  atmosphere,  consequently  air  is  expelled  until 
an  equilibrium  is  again  established.  It  is  apparent,  then,  that  during  inspira- 
tion there  exists  within  the  lungs  a  condition  of  negative  pressure,  and  that 
during  expiration  the  pressure  is  positive.  If  a  manometer  be  so  arranged  as 
in  no  way  to  interfere  with  the  ingress  and  egress  of  air,  it  will  be  found  that 
during  inspiration  the  column  of  mercury  sinks,  while  during  expiration  it 
rises.  Donders  found  by  connecting  a  manometer  with  the  nasal  ])assage  that 
the  pressure  during  quiet  inspiration  was  — 1  millimeter  of  Hg,  and  during 
expiration  -}-2  to  3  millimeters.  Ewald  gives  as  corresponding  values  — 0.1 
millimeter  and  -fO.lB  millimeter,  and  IMundhorst,  — 0.5  millimeter  and  -1-5 
millimeters.  During  deep  inspiration  Donders  noted  a  pressure  of — 30  milli- 
meters, and  when  the  mouth  and  nose  were  closed,  — 57  millimeters.  During 
forced  expiration,  with  respiratory  passage  closed,  it  was  -}-87  millimeters;  but 
these  figures  have  been  exceeded. 


nESPTRATTOX.  517 

It  will  be  observed  that  during  quiet  respiration  intrapulmonary  pr&ssure 
(pressure  7cithin  the  lungs)  oscillates  between  negative  and  ])ositive  and  vice 
versd,  whereas  intrathoracic  pressure  (pressure  out.skJe  the  lungs)  is  pei'sistently 
negative,  the  amount  by  which  it  differs  from  atmospheric  pressure  becoming 
greater  during  inspiration  and  diminishing  to  the  j)revious  level  during  expi- 
ration (p.  5U5).  Under  forced  expirati(»n,  however,  when  the  air-i)assages  are 
obstructed  intrathoracic  pressure  may  become  positive.  This  may  be  demon- 
strated in  this  way:  If  a  manometer  be  connected  with  the  mediastinum  of 
a  cadaver,  and  the  chest  be  pulled  u])ward  in  imitation  of  deep  inspiration, 
intrathoracic  pre&sure  will  be  found  to  be  about  — 30  millimeters.  If  now  a 
second  manometer  be  connected  with  the  trachea,  and  air  be  forced  into  the 
lungs  through  a  tracheal  tube,  as  intrapulmonary  pressure  rises  intrathoracic 
pressure  falls,  so  that  when  the  former  reaches  +30  millimeters  the  intratho- 
racic negative  pressure  exerted  by  the  elastic  traction  of  the  lungs  is  counter- 
balanced and  the  pressure  within  and  outside  the  lungs  is  equal.  If  intra- 
pulmonary pressure  now  rise  above  this  limit,  intrathoracic  pressure  must 
proportionately  become  positive.  During  violent  coughing,  when  the  expira- 
tory blast  is  obstructed  and  the  muscular  effort  is  powerful,  intrapulmonary 
pressure  may  rise  to  +80  millimeters  or  more. 

The  intercostal  tissues  tend  to  be  drawn  inward  as  long  as  negative  intra- 
thoracic pressure  exists,  and  to  be  forced  outward  when  there  is  positive  intra- 
thoracic pressure ;  hence  during  inspiration  the  traction  becomes  more  marked 
with  the  rise  of  intrathoracic  pressure,  and  during  expiration  the  reverse; 
while  during  forced  expiration  with  obstructed  air-pa&sages  the  pressure  exerted 
by  the  effort  of  the  expiratory  muscles,  together  with  the  weight  of  the  chest 
and  the  elastic  reaction  of  the  costal  cartilages,  etc.,  may  be,  as  above  stated, 
far  more  than  sufficient  to  counterbalance  the  traction  exerted  by  the  distended 
elastic  lungs,  and  thus  cause  positive  intrathoracic  pressure. 

The  influences  exerted  by  changes  in  intrathoracic  and  intrapulmonary 
pressure  upon  the  circulation  are  marked  and  important,  and  may  be  so  pro- 
nounced as  to  cause  an  obliteration  of  the  pulse. 

Respiratory  Sounds. — During  the  respiratory  acts  characteristic  sounds 
are  heard  in  the  lungs.  A  study  of  these  sounds,  however,  properly  belongs 
to  physical  diagnosis. 

The  Value  of  Nasal  Breathing-. — Xasal  breathing  has  a  value  above 
breathing  through  the  mouth,  inasmuch  as  the  air  is  warmed  and  moistened 
and  thus  rendered  more  acceptable  to  the  lungs,  more  or  less  of  the  foreign 
particles  in  the  air  are  removed,  and  noxious  odors  may  be  detected. 

B.  The  Gases  in  the  Lungs,  Blood,  and  Tissues. 
Alterations  in  the  Gases  in  the  Lungs. — The  object  of  respiratory 
movements  is  to  renew  the  air  within  the  lungs,  which  air  is  constantly  being 
vitiated,  and  thus  supply  O  and  remove  COj  and  other  effete  substances.  The 
lungs  of  the  average  adult  man  after  quiet  expiration  contain  about  2800  cubic 
centimeters  (170  cubic  inches)  of  air.     During  quiet  respiration  there  is  an 


518 


A.X  AMERICAN    TKXT-JiOOK    OF   PHYSIOLOGY. 


iiiHow  ami  outflow  of  about  500  cubic  centimeters  (30  cubic  inches),  therefore 
from  one-sixth  to  one-fifth  of  the  air  in  the  kings  is  renewed  by  each  act. 
Since  tlie  respirations  occur  at  so  frequent  a  rate  as  16  to  20  per  minute,  it 
seems  apparent  tiiat  there  nnist  be  a  rapid  loss  of  O  and  a  gain  of  CO^.  This 
is  proven  by  analyses  of  inspired  and  ex])irc(l  air.  Inspired  air  is  under 
normal  circumstances  atmospheric  air,  composed  of  oxygen,  nitrogen,  argon,  and 
carbon  dioxide,  with  more  or  less  moisture,  traces  of  ammonia  and  nitric  acid, 
dust  and  micro-organisms,  etc.  The  es.sential  diflFerences  between  insj)ired 
and  expired  air  are  shown  by  the  following  table,  the  figures  for  the  gases 
being  in  volumes  per  cent.  Argon  constitutes  about  1  per  cent,  of  the  nitrogen 
as  ffiven  in  the  table : 


Inspired  air  . 
Expired  air   . 


0 

COa 

N 

20.81 
16.03 

0.04 
4.38 

79.15 
79.30 

4.78 

4.34 

0.15 

Watery  Vapor. 


Variable. 
Saturated. 


Temperature. 

Average,  about  20° 
Average,  about  36.3° 


Volume 
(Actual). 


Diminished 

2to2i%. 


Expired  air  is  therefore  4.78  volumes  per  cent,  poorer  in  O,  4.34  volumes  per 

cent,  richer  in  COj,  and  0.15  volume  per  cent,  richer  in  N;  it  is  saturated 

with  watery  vapor,  and  is  of  higher  temperature  and  of  less  actual  volume. 

In  addition,  expired  air  contains  various  effete  bodies,  such  as  organic  matter 

("crowd-poison"),  hydrogen,  marsh-gas,  etc. 

The  relative  quantities  of  O  absorbed  and  of  COg  given  oif  are  not  constant, 

and  the  ratio  is  known  as  the  respiratory  quotient.    This  is  obtained  by  dividing 

CO    4.34 
the  volume  of  COj  given  off  by  that  of  O  absorbed,    ^  ^'    ''     =  0.908.    Hence, 

for  each  volume  of  O  that  is  lost  0.908  volume  of  CO,  is  gained.  Various 
circumstances  affect  the  quotient  (p.  544).  The  quantity  of  N  given  oft'  is 
about  7  grams  per  diem. 

The  quantity  of  watery  vapor  lost  by  the  lungs  varies  inversely  with  the 
amount  contained  in  the  atmosphere  and  with  the  volume  of  air  respired.  The 
less  the  moisture  in  the  atmospheric  air  and  the  larger  the  volume  of  air 
respired,  the  greater  the  lo.ss.  Valentine,  in  experiments  on  eight  young  men, 
records  a  dailv  loss  varvine;  from  349.9  to  773.3  grrams,  or  an  average  of  540 
grams.  Vierordt  records  a  loss  of  330  grams,  while  Aschenbrandt  estimates 
a  daily  loss  of  526  grams. 

The  temperature  of  the  expired  air  varies  with  the  temperature  and  volume 
of  the  inspired  air  and  with  the  temperature  of  the  body.  Valentine  and 
Bruner  found  that  when  the  temperature,  of  inspired  air  was  from  15°  to  20°, 
that  of  expired  air  was  37.3°  ;  when  that  of  inspired  air  was  — 6.3°,  expired 
air  had  a  temperature  of  29.8°  ;  while  when  the  inspired  air  was  at»41.9°,  that 
of  expired  air  was  38.1°.  When  the  air  is  respired  through  the  nose  the 
expired  air  is  warmer  than  when  respiration  occurs  through  the  mouth,     l^loch ' 

^  Zeitschrijt  fur  OhrenheilJcunde,  1888,  vol.  xviii.  p.  215. 


RESPIIIATION.  519 

records  ;i  differoiicc  of  1.5°  to  2°,  The  fiii|;ures  by  other  observers  vary  froai 
0.5°  to  1.5°.  The  larger  tlie  volume  of  air  respired,  other  tliiugs  being  equal, 
the  less  the  increase  of  temperature. 

The  volume  of  expired  air  is  from  10  to  12  per  cent,  greater  than  that  of 
inspired  air,  this  increase  being  due  to  expansion  caused  by  the  increase  of  tem- 
perature. When  proper  deductions  are  made  for  tempei'ature  and  barometric 
pressure,  the  actual  or  corrected  volume  is  less  by  2  to  2^  per  cent. 

Lossen  estimated  that  0.0204  gram  of  ammonia  is  eliminated  per  diem  in 
the  expired  air,  but  Voit's  investigations  indicate  that  expired  air  usually  does 
not  contain  even  a  trace  of  ammonia. 

Alterations  in  the  Gases  in  the  Blood. — The  blood  in  the  pulmonary 
artery  is  of  the  typical  venous  color — that  is,  deep  bluish-red.  During  its 
passage  through  the  lungs  it  becomes  scarlet-red,  or,  commonly  speaking,  arte- 
rialized  or  aerated.  If  we  take  arterial  blood  and  deprive  it  of  oxygen,  the 
color  changes  to  a  venous  hue ;  if  now  we  shake  the  bluish-red  blood  in  air  or 
O,  the  scarlet- red  color  is  restored.  AVe  have  here  the  suggestion  that  the  blood 
while  passing  the  lungs  absorbs  O.  Analyses  show  that  not  only  does  absorp- 
tion of  O  occur,  but  that  there  is  simultaneously  with  this  an  elimination  from 
the  blood  of  CO2. 

Arterial  and  venous  blood  each  contains  approximately  60  per  cent,  volumes 
of  O  and  CO2 ;  that  is,  for  about  every  100  volumes  of  blood  60  volumes  of  gas 
will  be  obtained.  Such  analyses  demonstrate  also  that  while  the  total  volumes 
per  cent,  of  O  and  COg  are  about  the  same,  the  proportions  are  different.  The 
following  table,  after  Ellenberger,^  gives  the  volumes  per  cent,  of  gases  in  the 
arterial  blood  of  various  animals  : 

Animal.  Total.  O.  CO2.  N. 

Dog 57.9  19.8  37.0  1.9 

Cat 43.2  13.1  28.8  1.3 

Sheep 57.6  10.7  45.1  1.8 

Rabbit 49.3  13.2  34.0  2.1 

Man 63.5  21.6  40.3  1.6 

Fowl 58.8  10.7  48.1 

Pfliiger  obtained  as  averages  of  analyses  of  arterial  blood  of  dogs  58.3 
volumes  per  cent.,  consisting  of  22.2  volumes  per  cent,  of  O,  34.3  volumes 
per  cent,  of  COg,  and  1.8  volumes  per  cent,  of  N.  Venous  blood,  according 
to  estimates  by  Zuntz  based  on  a  large  number  of  analyses,  contains  7.15  vol- 
umes per  cent,  less  of  O  and  8.2  volumes  per  cent,  more  of  CO2.  The  quantity 
of  N  is  practically  the  same  in  both  arterial  and  venous  blood. 

The  proportions  of  O  and  CO2  in  arterial  blood  vary  but  little  in  speci- 
mens taken  at  random  from  the  arterial  system,  while  those  of  venous  blood, 
on  the  contrary,  differ  considerably  according  to  the  locality  of  the  vessel  as 
well  as  to  the  degree  of  activity  of  the  structures  whence  the  blood  comes. 
Thus,  venous  blood  from  an  active  secreting  gland  differs  very  little  in  its 
composition,  gaseous  and  otherwise,  from  typical  arterial  blood,  whereas  when 
'  Physiologie  der  Haussdugethiere,  1890,  vol.  i.  p.  204. 


020  AX  AMKRTCAX    TKXT-JiOOK    OF   PHYSIOLOGY. 

the  gland  is  inactive  tlie  l)lo(xl  is  distinctly  venous.  The  arterial  character  of 
the  venous  blood  in  tlie  former  case  is  due  to  the  considerable  increase  in  the 
(jnantitv  of  blood  j)assing  through  the  gland  during  activity,  the  result  i)eing 
that  the  loss  and  gain  of  substances  are  not  so  noticeable,  although  the  total 
quantities  of  O  and  CO,  exchanged  are  actually  greater  than  when  the  gland 
is  at  rest  and  the  blood  coming  from  it  has  the  typical  venous  characters. 

The  venous  blood  during  its  passage  through  the  lungs  acquires  O  and  loses 
CO.,.  After  the  blood  is  arterialized  it  passes  from  the  lungs  into  the  left  side 
of  the  heart,  from  which  it  is  forced  to  the  aorta  and  its  ramiiications  and  ulti- 
mately into  the  capillaries.  Here  it  undergoes  a  retrograde  change,  parting 
with  some  of  its  O  and  taking  in  exchange  COg ;  consequently  the  gaseous 
interchange  between  the  blood  and  the  tissues  is  the  reverse  of  that  occurring 
between  the  blood  and  the  air.  Thus  we  find  that  the  interchange  of  O  and  COj 
occurs  in  a  distinct  series  of  events:  (1)  Oxygen  is  carried  as  a  constituent  of 
the  atmospheric  air  to  the  alveoli ;  (2)  here  it  is  absorbed  by  the  venous  blood, 
which  at  the  same  time  gives  oif  CO,  to  the  air  in  the  alveoli;  (3)  O  is  now  in 
major  part  conveyed  to  the  ti&sues,  in  which  it  is  taken  up  and  utilized  in  pro- 
ce&ses  of  oxidation,  CO,  being  the  chief  effete  product,  which  is  formed  immedi- 
ately or  ultimately  and  given  to  the  blood  (a  part  of  the  O  is  consumed  by  the 
blood,  COg  being  one  of  the  results) ;  (4)  the  venous  blood  is  now  conveyed 
to  the  lungs,  COg  is  given  off'  and  O  is  received  in  exchange,  and  the  series  of 
events  is  repeated. 

The  Forces  Concerned  in  the  Diffusion  of  O  and  CO,  in  the  Lungs. — 
If  the  air  expired  be  collected  in  a  number  of  parts,  each  successive  portion  will 
be  found  to  contain  a  smaller  percentage  of  O  and  a  larger  percentage  of  COg. 
The  air  in  the  beginning  of  the  respiratory  tract  (nose  and  mouth)  varies  from 
atmospheric  air  but  little  in  composition,  while  that  in  the  alveoli  contains  con- 
siderably less  O  and  nuich  more  COg.  With  each  quiet  act  of  insj)iration  the 
quantity  of  air  breathed  is  from  three  to  four  times  greater  than  the  cajiacity  of 
the  trachea  and  bronchi,  so  that  with  each  respiratory  act  two-thirds  or  more 
of  the  fresh  air  is  carried  into  the  alveoli.  "When  expiration  occurs  a  similar 
volume  of  the  vitiated  air  within  the  alveoli  is  driven  into  the  bronchi  and 
trachea,  and  thus  a  certain  percentage  is  expelled  from  the  body.  Thus  the 
mere  volume  and  force  of  the  air-currents  must  obviously  be  of  great  value  in 
equalizing  the  composition  of  the  air  in  the  different  parts  of  the  respiratory 
tract. 

The  contractions  of  the  heart  exert  similar  mechanical  influences.  With  each 
contraction  intrathoracic  pressure  is  lessened,  so  that  there  is  a  slight  expansion 
of  the  lungs,  just  as  would  be  caused  had  the  thorax  been  slightly  enlarged, 
and  consequently  there  is  a  movement  of  air  toward  and  into  the  alveoli.  Dur- 
ing diastole  intrathoracic  pressure  returns  to  the  jn-evious  level,  the  volume 
of  the  lungs  is  diminished,  and  the  air  is  driven  from  the  alveoli.  Thus 
each  heart-beat  causes  a  to-and-fro  movement  (jf  the  air.  These  oscilla- 
tions, which  are  termed  carcJio-pnrinnntic  vwvemeyifs,  are  of  more  importance 
than  might  seem  at  first  sight,  for  it  has  been  shown  that  in  cases  of  suspended 


BESPIRA  TION.  521 

animation  and  in  hybernating  animals  they  aid  materially  in  pnlmonary  ven- 
tilation. 

Besides  these  mechanical  factors  there  is  present  the  important  factor  of  the 
ditt'nsion  of  gases,  O  diffnsing  toward  the  alveoli  and  COj  toward  the  anterior 
nares.  The  ra])idity  with  which  difFnsion  occnrs,  other  things  being  equal, 
depends  upon  the  differences  in  the  "  partial  pressure  "  of  the  gas  at  various 
regions.  Each  gas  forming  part  of  a  mechanical  mixture  exerts  a  partial 
pressure  proportional  to  its  percentage  of  the  mixture.  Thus,  atmosj)heric  air 
contains  20.81  volumes  per  cent,  of  (),  0.04  volumes  })er  cent,  of  COg,  and  79.15 
volumes  per  cent,  of  N.  If  the  air  exists  at  760  millimeters  barometric  pressure, 
each  gas  w'ill  exert  a  jx;/-^  of  the  total  pressure,  or  a  "  partial  pressure,"  equivalent 
to  its  respective  volume.     Should  we  wish  to  find  the  partial  pressure  of  O,  it 

.     ,    .      ,    ,        ,  .      20.81    ^  ,          ,                   20.81  X  760 
may  be  ascertained  simply  by  taking  oi  the  total  pressure= —^ 

=  158.15    millimeters;    similarly,  the   partial   pressure    of    COg   would   be 

0.04  X  760  ^^_  .„.  ^  1  .,  .  i.  AT  79.15X760  ._^  _ . 
r-— =  0.30  mdhmeter  ;  and  that  of  N,       ^r^ =  601.54 

millimeters.  Knowing,  then,  the  composition  of  any  mixture  of  gases  and  the 
total  pressure  under  which  it  exists,  it  is  a  matter  of  very  simple  calculation 
to  determine  the  partial  pressure  of  each  of  the  various  gases  constituting  the 
atmosphere.  Expired  air  is  poorer  in  O  and  richer  in  COg  than  inspired  air, 
and  alveolar  air  is  altered  even  to  a  greater  extent  than  expired  air;  hence 
the  partial  pressures  must  be  affected  similarly. 

The  first  portion  of  the  air  expired  contains  a  maximum  amount  of  inspired 
air  and  a  minimum  amount  of  the  air  contained  in  the  air-passages  previous  to 
the  inspiratory  act ;  but  as  expiration  continues  the  mixture  becomes  poorer  and 
poorer  in  inspired  air  and  similarly  richer  in  the  vitiated  air  from  the  smaller 
air-passages  and  the  alveoli ;  in  fact,  the  last  portion  of  expired  air  is  very 
similar  to,  if  not  identical  in  its  composition  with,  that  in  the  alveoli.  The 
following  partial  pressures  of  O  and  CO2  in  inspired  air  and  alveolar  air 
indicate  the  extent  to  which  the  composition  varies  in  different  parts  of  the 
respiratory  tract : 

Gas.  Inspired  Air.  Alveolar  Air. 

O 158.15  millimeters.  122  millimeters.^ 

COj 0.30  millimeter.  38  millimeters. 

Since  the  partial  pressure  of  O  in  inspired  air  is  about  158.15  millimeters,  and 
as  it  is  but  about  122  millimeters  in  the  alveoli,  and  as  the  air  is  poorer  in  O  as 
we  pass  from  the  nares  to  the  alveoli,  it  is  obvious  that  a  force  must  be  exerted 
constantly  to  cause  a  diffusion  of  O  from  the  larger  air-passages  to  the  bron- 
chioles and  from  the  bronchioles  to  the  alveoli — that  the  O  must  diffuse 
from  the  region  of  highest  pressure  to  that  of  lowest  pressure.  During  life 
an  equilibrium  can  never  be  established,  because  of  the  constant  supply  of 
fresh  air  and  the  continual  passage  of  O  from  the  alveoli  to  the  blood.     The 

•    ^  The  exact  per  cent,  composition  of  alveolar  air  is  not  known  ;  these  figures  are  estimates. 


522  AX  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

same  relations  of  partial  pressure  are  observed  in  connection  with  COj,  except 
that  the  air  in  the  alveoli  is  inces-santly  acquiring;  this  gas  from  the  blood,  causing 
the  per  cent,  composition  of  COj  to  be  much  in  excess  of  that  found  in  the 
atmosphere.  The  partial  pressure  of  CO2  in  the  alveolar  air  is  about  38.00 
niillimetci-s,  while  in  inspired  air  it  is  only  0.30  millimeter ;  hence  COj  must 
diffuse  from  the  alveoli  outward. 

There  are,  therefore,  three  important  factors  concerned  in  the  admixture 
and  purification  of  the  air  in  the  lungs:  (1)  The  tidal  movements  caused 
by  inspiration  and  expiration,  which  movements  bv  the  mere  force  of  air-cur- 
rents cause  a  partial  niixture  of  the  air ;  (2)  the  smaller  wave-movements  (car- 
dio-pneumatic)  produced  by  the  heart-beats,  and  similar  in  effect  to,  Ijut  much 
less  effective  than,  the  first ;  (3)  the  diffusion  of  O  and  CO^,  depending  upon  dif- 
ferences in  their  partial  pressures  in  the  various  parts  of  the  respiratory  tract. 

The  Forces  Concerned  in  the  Interchange  of  O  and  COj  between 
the  Alveoli  and  the  Blood. — The  gases  in  the  lungs  are  in  the  form  of 
a  mechanical  mixture,  while  in  the  blo(Kl  they  are  in  solution  or  in  chemical 
combination  ;  hence  we  now  have  to  deal  with  conditions  quite  different,  involv- 
ing the  consideration  of  the  relations  of  gases  to  liquids — a  relationship  of 
twofold  nature,  inasmuch  as  the  gas  may  be  found  not  only  in  solution,  but 
in  chemical  association. 

When  an  atmosphere  consisting  of  O,  COj,  and  N  is  brought  in  contact 
with  water,  each  gas  is  absorbed  independently  not  only  of  the  others,  but 
of  the  nature  and  quantity  of  all  other  gases  which  may  happen  to  be  in 
solution.  The  quantity  of  each  gas  dissolved  depends  upon  its  relative  solu- 
bilitv  as  well  as  upon  the  temperature  and  the  barometric  pressure.  The 
coefficient  of  absorption  of  any  fluid  is  the  quantity  of  gas  dissolved  at  a  given 
temperature  and  pressure,  and  is  in  inverse  relation  to  temperature  and  in  direct 
relation  to  pressure.  The  following  absorption-coefficients  of  water  for  O,  CO^, 
and  X  at  760  millimeters  of  Hg  have  been  obtained  by  Winkler:' 

Temperature.  O.  COj.  N. 

0° 0.04890  1.7967  0.02348 

15° 0.03415  1.0020  0.01682 

40° 0.02306  .  0.01183 

Thus,  at  0°  C  and  760  millimetei"s  pressure  each  volume  of  water  absorbs  0.0489 
volume  of  O;  at  15°,  0.03415  volume;  and  at  40°,  0.02306  volume.  The 
absorption-coefficient  falls,  it  will  be  observed,  with  the  increase  of  temperature. 
Comparing  the  solubilities  of  the  three  gases,  it  will  be  seen  that  at  the  same 
temperature  and  pressure  a  considerably  larger  quantity  of  COj  is  absorbed 
than  of  O — nearly  four  times  more — whereas  the  quantity  of  N  absorbed  is 
less  than  one-half  as  much  as  that  of  O. 

The  quantity  of  a  gas  absorbed  by  a  given  liquid  at  a  given  temperature  is 
proportionate  to  its  coefficient  of  solubility  and  to  the  pressure,  and  is  the  same 
whether  the  gas  exist  free  or  as  a  constituent  of  a  complex  atmosphere,  pro- 
'  Zeitschrift  fur  physikalische  Chemie,  1892,  vol.  9,  p.  173. 


BESPTRA  TION.  523 

vicled  that  the  pressure  exerted  by  the  gas  in  both  cases  be  the  same.  Thus, 
atmospheric  air  consists  of  20.81  volumes  per  cent,  of  O,  0.04  volume  per 
cent,  of  CO2,  and  79.15  volumes  per  cent,  of  N.  Each  gas  exerts  a  partial 
pressure  iu  proportion  to  its  percentage  of  the  mixture.  Assuming  that  the 
air  is  at  standard  atmospheric  pressure,  the  ])artial  pressure  of  O  is  20.81  per 
cent,  of  760  millimeters  of  Hg,  or  158.15  millimeters.  The  quantity  of  O 
absorbed  from  the  air  at  0°  C  and  760  millimeters  pressure  is  therefore  the  same 
as  when  the  atmosphere  consists  of  pure  O  at  a  pressure  of  158.15  millimeters. 

,    ,     20.81  X  0.0489        ^  ^,      , 
The  absorption-coefficient  must  consequently  be :^ =  0.01  vol- 
ume.    Therefore  100  volumes  of  water  at  0°  C.  and  760  millimeters  pressure 
absorb  from  the  air  1  volume  of  O. 

If  the  partial  pressure  of  O  be  increased  or  decreased,  the  quantity  absorbed 
will  rise  or  fall  accordingly.  From  this  it  is  obvious  that  O  must  exist  under 
a  certain  degree  of  pressure  to  prevent  its  passing  out  of  solution,  which 
is  expressed  by  the  term  tension  of  solution,  meaning,  in  a  word,  the  pres- 
sure required  to  keep  the  gas  in  solution.  If  the  partial  pressure  of  the  gas 
diminishes,  the  gas  in  solution  is  given  off  until  the  jxirtkd  jy-essure  of  the 
gas  in  the  air  and  the  tension  of  the  gas  in  solution  are  equal.  Conversely,  as 
the  partial  pressure  of  the  gas  in  the  air  increases,  the  gas  in  solution  will  be 
under  correspondingly  higher  tension. 

Tension  of  0.— The  absorption-coefficient  of  blood  for  O  is  nearly  the  same 
as  that  of  water,  so  that  blood  at  0°  should  absorb  from  the  atmosphere  about 
1  volume  per  cent,  of  O,  but  less  than  one-half  as  much  at  the  temperature 
of  the  body.  The  results  of  experiments  show,  however,  that  blood  contains 
considerably  more  than  this,  the  average  for  arterial  blood  being  22.2  volumes 
per  cent.,  or  very  much  more  than  can  be  accounted  for  by  the  laws  of  partial 
pressures  and  tensions.  Moreover,  when  the  blood  is  subjected  to  a  vacuum 
pump  there  is  evolved  a  small  amount  of  gas  consistent  with  the  diminution  of 
pressure,  but  the  great  bulk  of  it  does  not  come  off  until  the  pressure  has  been 
reduced  to  Jg-  to  j\  of  an  atmosphere.  Finally,  the  quantity  absorbed  is 
affected  but  little  by  changes  in  pressure  above  a  certain  standard.  These 
facts  indicate  that  almost  all  of  the  O  must  be  in  chemical  combination,  the 
combination  being  with  haemoglobin  in  the  form  of  oxyhseraoglobin.  This 
chemical  union  is  readily  dissociated  at  a  constant  minimal  pressure  which  is 
termed  the  tension  of  dissociation.  There  is  a  persistent  tendency  of  the  gas  in 
such  a  compound  to  become  disengaged,  so  that  when  oxyhsemoglobin  is  placed 
under  circumstances  where  the  tension  or  the  partial  pressure  of  O  is  less  than 
that  in  the  compound,  dissociation  occurs;  conversely,  when  htemoglobin  is 
brought  in  contact  with  O  at  a  pressure  above  the  minimal  constant  of  dissocia- 
tion (^  to  ^  of  an  atmosphere),  the  two  unite  to  form  oxyhemoglobin.  One 
gram  of  hemoglobin  combines,  according  to  Hiifner,^  with  1.59  cubic  centimeters 
of  O  at  0°  and  760  millimeters  pressure.  Assuming  that  100  volumes  of  blood 
contain  15  grams  of  hemoglobin  (p.  335),  if  oxidized  into  oxyhemoglobin  the 
1  Zeitschriftfur  physiobgische  Chemie,  1877-78,  vol.  ii.  p.  389. 


524  AX  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

quantity  of  gas  combined  witii  the  hfcmoglobiu  would  be  equal  to  23.38  vol- 
umes per  cent,  of  the  blood  ;  in  other  words,  arterial  blood  should  contain 
23.38  volumes  per  cent,  of  O.  This,  however,  is  more  than  is  found,  but  the 
deficit  is  accounted  for  by  the  fact  that  only  from  ^V  (Pfliiger)  to  -|-i  (Hiifner) 
of  the  haemoglobin  is  .saturated. 

Tiie  plasma  and  the  serum  absorb  but  very  small  quantities  of  O — according 
to  Pfiiiger,  only  0.26  volume  per  cent.  Owing  to  the  relatively  low  absor})tion- 
coefficient  of  the  plasma  compared  with  the  O-capacity  of  the  hsemoglobiu,  as 
well  as  to  the  fact  that  the  haemoglobin  is  practically  saturated  at  a  relatively  low 
pressure,  the  quantity  of  O  absorbed  is  not  materially  affected  by  an  increase  of 
pressure  above  the  level  of  the  tension  of  dissociation  :  the  slight  increase  which 
does  occur  is  due  chiefly  to  absorption  by  the  j)lasma. 

The  tension  of  O  in  arterial  and  venous  blood  must  be  ascertained  separately, 
inasmuch  as  each  contains  a  different  percentage.  Following  tliis  method, 
Strassburg^  records  the  following  averages:  Arterial  blood,  29.64  millimeters 
of  Hg,  or  3.9  percent,  of  an  atmosphere;  and  venous  blood,  22.04  millimeters, 
or  2.9  per  cent,  of  an  atmosphere. 

Tension  of  CO^. — Venous  blood  contains  about  45  volumes  per  cent,  of 
COg.  The  results  of  experiments  prove  that  only  about  5  per  cent,  of  this 
CO2  is  in  simple  solution,  that  from  10  to  20  per  cent,  is  in  firm  chemical 
combination,  and  that  from  75  to  85  per  cent,  is  in  loose  combination. 

When  the  blood  at  the  temperature  of  the  liody  is  sulijected  to  a  vacuum; 
all  of  the  CO2  is  given  off;  but  if  the  blood-corpuscles  be  removed  and  the 
plasma  and  corpuscles  each  in  turn  be  submitted  to  the  pump,  both  will  give 
off  COj,  the  plasma  yielding  a  larger  volume  than  the  corpuscles,  but  not  so 
much  as  when  they  are  together.  Plasma  and  serum  in  vacuo  give  off  only  a 
portion  of  their  COg ;  the  remainder  may,  however,  be  dissociated  by  adding 
acid  or  red  corpuscles.  The  red  corpuscles  therefore  act  as  an  acid  and  cause  the 
disengagement  of  all  the  gas  from  the  plasma ;  consequently,  not  only  do  the 
corpuscles  yield  up  the  CO2  contained  in  them,  but  they  are  also  active  agents 
in  bringing  about  the  dissociation  of  COj  which  is  in  chemical  combination  in 
the  plasma.  The  dissociation  is  due  in  part,  perhaps,  to  the  presence  of  phos- 
phates in  the  stromata  of  the  red  cor})uscles,  and  to  certain  proteids,  but  the 
observations  of  Preyer  and  Hoppe-Seyler  lead  to  the  conviction  that  it  is  due 
chiefly  to  oxyh?emoglobin  and  haemoglobin.  Phosphates,  proteids,  lijemoglubin, 
and  oxyhsemoglobiu  all  have  the  power  of  expelling  COj  from  sodium  car- 
bonate in  solution  in  vacuo,  but  this  fact  leaves  us  none  the  wiser  as  to  which, 
if  any,  is  active  in  this  way  in  the  blood.  Arterial  blood  gives  off  its  COj 
more  readily  than  venous  blood. 

Of  the  total  quantity  of  CO,,  about  5  per  cent,  is  in  simple  solution  and 
from  10  to  20  per  cent,  is  in  firm  chemical  combination  in  the  plasma,  the  latter 
requiring  the  addition  of  acid  or  of  haemoglobin,  etc.  to  cause  its  dissociation 
in  vacuo;  while  the  remainder,  constituting  nuich  the  larger  proportion,  is  in 
loose  chemical  union  in  both  the  plasma  and  the  corpuscles.     That  which  is  in 

'  Pfiiiger' s  Archlv  fiir  Physiologic,  vol.  vi.  p.  65. 


RESPIRATION.  525 

chemical  combination  in  the  plasma  is.  probably  in  part  combined  with  glob- 
ulin and  alkali,  and  in  part  with  sodium  as  carbonate  and  bicarbonate,  tiie 
proportion  of  each  varying  with  the  tension  of  the  COg.  The  wliite  blood- 
corpuscles,  so  far  as  they  contain  any  of  the  C()2,  hold  it  probably  in  combina- 
tion with  globulin  and  alkali  and  as  carbonates  of  sodium.  Tiie  great  bulk  of 
the  gas  disengaged  from  the  corpuscles  is  derived  from  the  red  cells,  but  in  what 
combination  or  combinations  it  exists  is  not  positively  known.  The  experiments 
of  Setschenow,  Zuntz,  Boiir,^  and  others  indicate  that  it  is  associated  in  some 
obscure  way  with  haemoglobin,  and  probably  with  a  third  body,  such  as  globulin 
or  alkaline  phosphates;  and  yet  haemoglobin  seems  to  have  the  power  to  hold 
the  CO2  in  tiie  absence  of  a  third  body.  This  latter  fact  has  been  shown  by 
the  experiments  of  Bohr,  who  compared  the  quantities  of  COj  absorbed  by 
pure  water  and  by  solutions  of  pure  crystallized  haemoglobin  at  constant  tem- 
perature and  varied  pressure.  He  found  that  the  weight  of  COg  absorbed  by 
the  water  increased  regularly  with  the  increase  of  pressure,  whereas  the  quan- 
tity absorbed  by  the  solution  of  haemoglobin  was  very  large  relatively  to  the 
lower  pressures  and  small  for  higher  pressures,  and  that  the  increments  of 
absorption  were  in  decreasing  ratio  to  the  rise  of  pressure.  The  absorption 
curve  is  therefore  steep  at  first,  becoming  less  and  less  so  with  the  increase  of 
pressure,  and  entirely  different  from  the  absorption  line  for  pure  water,  which 
is  straight.  Moreover,  the  quantity  of  CO2  dissolved  was  considerably  in 
excess  of  that  which  physical  laws  could  admit.  The  CO2,  in  \vhatever  form 
or  forms  it  may  exist  in  the  red  corpuscles,  is  in  looser  combination  than  in 
serum. 

Strassburg's  experiments  show  that  the  average  tension  of  COg  in  arterial 
blood  is  21.28  millimeters  of  Hg,  or  2.8  per  cent,  of  an  atmosphere,  and  in 
venous  blood  41.04  millimeters,  or  5.4  per  cent,  of  an  atmosphere. 

Tension  of  N. — The  quantity  of  nitrogen  in  the  blood  is  about  1.8  volumes 
per  cent.  It  is  in  simple  solution  in  the  blood-plasma,  and  the  quantity  in 
both  venous  and  arterial  blood  is  practically  the  same.  Its  presence  and  quan- 
tity are  not  of  physiological  importance. 

The  Interchang-e  of  O  and  COg  between  the  Alveoli  and  the  Blood. — 
Let  us  now  inquire  into  the  factors  which  bring  about  the  passage  of  O  from 
the  alveoli  to  the  blood  and  of  CO2  from  the  blood  to  the  alveoli.  If  we  have 
two  mixtures  of  the  same  gases,  but  in  unlike  proportions,  and  separate  them 
by  means  of  an  animal  membrane,  diffusion  will  occur  through  the  membrane 
until  the  partial  pressures  of  the  two  gases  are  the  same  on  the  two  sides  of  the 
membrane.  Now  modify  this  experiment  by  bringing  an  atmosphere  of  air 
in  contact  with  water  containing  O,  COj,  and  X  in  solution  or  in  chemical 
combination  :  if  the  partial  pressure  of  O  in  the  air  be  greater  than  the  tension 
of  O  in  the  water,  O  will  pass  to  the  water ;  if  the  partial  pressure  of  CO2  in 
the  air  be  less  than  the  tension  of  CO2  in  the  water,  COg  will  pass  to  the  air. 
If  now  we  interpose  an  animal  membrane  between  the  atmosphere  and  the 

1  Erper.  Uniermch.  u.  d.  Sauersioffaufnahme  d.  Blutfarbsioffes,  Kopenhagen,  1885  ;  Beitrdge  zwr 
Physiologic,  Festschr.  f.  C.  Ludwig,  1887,  pp.  164-172. 


526  AX  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

water,  the  interchange  of  gases  will  continue  as  before.  In  this  case  we  have 
conditions  analogous  totho.se  which  exist  iu  the  living  organism  :  In  the  alveoli 
tliere  is  an  atmosphere  consisting  of  O,  COj,  and  X ;  each  gas  is  under  a  par- 
tial pressure  proportional  to  its  volume  per  cent,  of  the  mixture;  the  pul- 
monary membrane  and  the  walls  of  the  capillaries  may  be  regarded  as  a  sini])le 
animal  membrane  separating  the  air  in  the  alveoli  from  the  blood  ;  finallv,  the 
blood  contains  O,  CO,,  and  N,  each  of  which  is  in  a  definite  and  inde])eiident 
degree  of  tension.  Whether  or  not  any  or  all  of  these  gases  will  pass  in  one 
direction  or  the  other  must  obviously  depend  upon  the  conditions  of  partial 
pressure  and  tension  of  each  gas  on  the  two  sides  of  the  membrane.  The  ten- 
sion of  O  in  venous  blood,  as  above  stated,  is  22.04  millimeters  of  Hg,  and  of 
CO,,  41.04  millimeters.  What  are  the  partial  pressures  of  these  gases  in  the 
alveoli?  The  precise  pressures  are  not  known,  but  it  is  estimated  that  the 
partial  pressure  of  O  is  about  122  millimeters,  and  of  COg  about  38  millimeters. 
Comparing  the  partial  pressures  and  the  tensions  of  these  two  gases  in  the 
alveoli  and  the  blood  respectively,  it  is  obvious  that  the  conditions  on  the  two 
sides  of  the  membrane  are  favorable  to  the  diffusion  of  O  and  COg,  and  in 
definite  but  opposite  directions.  This  is  illustrated  in  the  following  diagram- 
matic presentation : 


O.  COj. 

Tensions  in  alveolar  air 122.00  38.00 

Pulmonary  membrane + —\ — 

Tensions  in  venous  blood 22.04  41.04 


Since  the  gases  diffuse  from  the  point  of  higher  pressure  or  tension  to  that 
of  lower  pressure  or  tension,  O  passes  from  the  alveoli  to  the  blood,  while  CO, 
pas.ses  from  the  blood  to  the  alveoli. 

It  is,  however,  impo.ssible  under  certain  circumstances  to  account  for  the 
transmi.ssion  of  all  of  either  the  O  or  the  CO.,  by  the  laws  of  diffusion.  In 
regard  to  O,  physical  forces  are  active  to  the  extent  that  they  cause  a  diffusion 
of  O  to  the  blood-plasma,  where  it  is  brought  in  contact  with  the  haemoglobin 
of  the  blood-corjniscles.  The  chemical  union  of  O  Mith  haemoglobin  takes 
place  at  a  low  tension,  hence  the  quantity  of  O  taken  up  by  the  blood  does 
not  vaiy  matel'ially  with  the  amount  of  O  in  the  air  breathed,  no  more  O 
being  taken  up  when  pure  O  is  respired  than  from  atmospheric  air,  in  which  O 
constitutes  only  about  20  volumes  per  cent. ;  and  Frjinkel  and  Geppert  record 
that  the  quantity  of  O  in  arterial  blood  is  but  little  dimini.shed  even  when  the 
air-pressure  is  reduced  as  low  as  378-36o  millimeters.  But  Rolir  found  in 
experiments  on  dogs  that  the  tension  of  O  in  arterial  blood  may  even  be  higher 
than  it.-^  partial  pressure  in  the  alveolar  air;  and  Pfliiger  long  since  determined 
that  when  animals  breathe  pure  N  or  H,  no  O  passes  from  the  blood  into  the 
alveoli.  It  is  apparent  from  the^e  latter  facts  tliat  the  transmi.'^'sion  of  O  may 
not  be  entirely  a  matter  of  diffusion.  In  addition  to  the  phvsical  and  chemi- 
cal factors,  it  is  poasible,  as  suggested  by  Bohr,  that  the  ]uilmonary  tissue 
takes  an  active  part  as  a  specific  secretory  membrane   in   this  transmission. 

The  problem  in  connection  with  COj  is  also  complex.     It  is  commonly 


RESPIRATION.  527 

believed  tliat  the  passage  of  CO2  from  the  blood  to  the  alveoli  is  determined 
simply  by  the  laws  of  ditUision,  but  Bohr^  has  found  in  experiments  in  which 
analyses  of  the  blood  and  alveolar  air  were  made  simultaneously  that  the  par- 
tial pressure  of  COg  in  the  alveolar  air  may  be  less  than  the  average  tension  in 
the  blood.  Moreover,  Bohr  found  in  a  series  of  experiments  that  even  when 
the  quantity  of  COj  in  the  atmosphere  in  contact  with  the  blood  was  very 
small,  but  little  more  COg  diffused  from  the  blood.  Facts  of  this  kind  are 
explicable  on  the  hypothesis  that  the  pulmonary  membrane  is,  as  contended  by 
Ludwig,  Bohr,  and  others,  actively  engaged  in  the  process,  playing  a  specific 
excretory  role,  but  our  knowledge  is  as  yet  too  incomplete  to  require  the 
acceptance  of  such  an  hypothesis.  Under  ordinary  conditions  the  tension  of 
CO2  in  the  alveoli  is  less  than  in  the  blood,  and  the  transmission  of  CO^  from 
the  blood  to  air-cells  may  be  explained  satisfactorily  by  the  laws  of  diffusion. 

The  Forces  Concerned  in  the  Interchange  of  O  and  CO2  between  the 
Blood  and  the  Tissues. — Innumerable  facts  show  that  the  chief  seat  of  the 
chemical  processes  in  the  body  is  in  the  tissues,  and  that  the  decompositions 
are  essentially  of  an  oxidizing  character  whereby  COg  is  formed  as  one  of 
the  most  important  effete  products;  consequently  the  blood  as  it  is  carried 
through  the  capillaries  gives  up  O  and  receives  COj. 

Experiments  show  that  the  tissues  exert  a  strong  reducing  action,  and  that 
their  avidity  for  O  is  so  great  that  they  will  take  it  up  at  extremely  low 
pressures.  Moreover,  never  more  than  mere  traces  of  O  can  be  obtained 
from  the  tissues,  because  the  gas  upon  its  absorption  immediately  enters  into 
chemical  combination. 

The  tension  of  COg  in  the  tissues  is  considerably  higher  than  in  blood. 
Strassburg,^  in  a  loop  of  intestine  into  which  he  injected  atmospheric  air,  fcmnd 
that  the  tension  was  58.52  millimeters  of  Hg,  which  is  considerably  greater 
than  in  either  arterial  or  venous  blood.  Thus  we  find  that  the  tension  of  O  in 
the  tissues  is  nil,  owing  to  their  greediness  for  this  gas,  while  that  of  CO2  is 
very  high.  Comparing  the  tensions  of  these  two  gases  in  the  blood  and  the 
tissues,  it  will  be  observed  that  there  are  present  conditions  which  are  highly 
favorable  to  the  passage  of  O  to  the  tissues  and  of  CO2  in  the  reverse  direction  : 


O.  COo. 

Tensions  in  arterial  blood 29.64  21.28 

Blood-vessel  walls — + 1 

Tensions  in  tis.sues 0.00  58!25 


It  is  manifest  from  the  above  that  O  should  pass  from  the  blood  to  the  tissues, 
and  CO,  from  the  tissues  to  the  blood. 

The  lymph  is  probably  merely  a  passive  medium  in  this  interchange.  It 
contains,  according  to  Haramarsten,  only  traces  of  O,  from  37.5  to  47.1  vol- 
umes per  cent,  of  CO2,  and  from  1.1  to  1.63  volumes  per  cent,  of  N.  The 
mean  percentage  of  COg  is  lower  than  in  serum,  but  Gaule  has  shown  that  the 
tension  is  higher.     Doubtless  the  same  relations  hold  good  for  the  plasma  and 

'  Loc.  cit.  **  Loc,  cit. 


628 


AN  AMElilCAN   TEXT-BOOK    OF   PllYSlOLOaY. 


the  hlood,  so  that,  uotwithstaiuling  a  smaller  volume  per  cent,  of  CO2  in  the 
Ivmph,  CO2  passes  to  the  blood  because  of  the  higher  tension  in  the  Iyin])h. 

Extraction  of  Gases  from  the  Blood. — We  have  found  that  in  the  l)lood 
both  O  and  CO2  cxi.st  partly  in  solution  and  partly  in  chemical  combination. 
The  portion  in  solution  comes  off  regularly  with  a  diminution  of  pressure,  but 
that  which  is  in  chemical  combination  remains  so  until  the  pressure  is  reduced 
to  the  level  of  the  tension  of  dissociation.  Since  there  are  several  of  these 
combinations,  such  as  O  in  oxyhemoglobin  and  CO2  in  carbonates,  bicarbon- 
ates,  alkali  })hos2)hates,  etc.,  portions  of  each  of  these  gases  come  off  at  different 
pressures  in  accordance  with  their  different  tensions  in  the  several  chemical 
combinations.     The  portions  in  solution  may  be  removed  by  the  use  of  an 

ordinary  air-pump,  i)ut  those  in 
chemical  condjination  are  held  so 
firndy  that  the  more  powerful  mer- 
curial j)um])  is  required.  A  con- 
venient pump  of  this  kind  has  been 
devised  by  Dr.  Geo.  T.  Kemp,  the 
description  of  which  he  gives  as 
follows  : 

"  To  use  the  pump  the  reservoir 
bulb  lib  (Fig.  136),  the  bulb  /,  the 
cylinder  SR  and  S'R'  ^  and  the  ves- 
sel Pare  filled  with  mercury.  When 
the  bulb  Bli  is  raised  the  mercury 
rises  in  the  tube  AC  and  fills  B, 
driving  the  air  out  by  the  path 
FHOP,  the  stopcock  Q  being  closed. 
When  Bb  is  lowered  again  the  mer- 
cury flows  back  from  B  into  Bb, 
creating  a  Torricellian  vacuum  in 
B.  As  soon  as  the  mercury  has 
fallen  below  the  joint  D,  this 
vacuum  in  B  becomes  connected 
by  the  path  DEG  with  the  tubes 
TGIJG'T'  and  the  tube  VWYX,  and 
thence,  when  the  stopcock  is  open, 
with  the  vessel  to  be  exhausted.  The  air  in  this  then  diffuses  to  fill  the 
vacuum  in  B,  and  becomes  rarefied,  so  that  the  mercury  rises  from  the  cylin- 
ders SR  and  S'R'  in  the  outer  tubes  TG  and  T'G'.  The  small  inner  tubes 
RG  and  R'G'  are  made  so  high  that  even  when  there  is  a  complete  vacuum  in 
the  outer  tubes  TG  and  T'G'  the  mercury  will  not  rise  high  enough  to  cover 
them. 

"On  raising  Bb  again  the  mercury  rises  in  AC,  and  as  soon  as  the  joint  D  is. 
covered,  all  the  air  which  has  been  caught  in  B  is  forced  out  by  the  path  FHOP. 
Each  time  the  bulb  Bb  is  raised  and  lowered  a  certain  amount  of  air  is  ex- 


FiG.  136.— Kemp's  gas  pump. 


BESPIRA  TION. 


529 


tracted  from  the  receiver,  until  finally  a  vacuum  is  produced.  In  a  similar 
way,  when  the  receiver  connected  with  the  pump  at  Z  contains  any  gas  which 
we  wish  to  analyze — as,  for  example,  the  gases  given  off  by  the  blood  in  a 
vacuum — we  put  a  eudiometer  {Eii)  over  the  bend  of  the  tube  at  P,  which,  of 
course,  is  always  under  the  mercury,  and  collect  the  gases  as  they  are  forced  out. 

"  The  extraction  of  the  last  traces  of  gas  by  raising  and  lowering  Bh  is  a 
very  tedious  and  laborious  process,  so  that  the  final  extraction  of  the  gases  can 
best  be  accomplished  by  the  Sprengel  jnimp  LTKLMNIIOP.  The  bulb  and  stop- 
cock UK  are  made  separate,  as  shown  in  the  figure,  and  are  connected  with 
LMN  by  a  piece  of  rubber  tubing,  the  whole  being  under  mercury.  This  is 
accomplished  by  the  bend  JKLM,  which  is  made  so  as  to  allow  a  narrow  wooden 
box  filled  with  the  mercury  to  be  slipped  up  over  the  bend  high  enough  to 
cover  the  stopcock  and  thus  prevent  leakage  of  air.  The  same  arrangement  is 
shown  at  X,  aud  is  indicated  by  a  dotted  line  in  each  instance.  When  the 
stopcock  K  is  opened  the  mercury  flows  in,  drops  down  the  tube  NHOF,  and 
extracts  the  gases  at  H  in  the  well-known  manner  of  the  Sprengel  pump.  The 
large  bulb  is  for  rapid  exhaustion  down  to  the  last  few  millimeters  of  pressure, 
the  rest  being  accomplished  more  slowly  but  more  perfectly  by  the  Sprengel. 
In  extracting  blood-gases  the  oxygen  is  given  off  suddenly  and  the  CO2  slowly. 
The  great  desideratum  is  to  keep  the  tension  of  the  gases  in  the  blood-chamber 
down  as  near  zero  as  possible — certainly  below  20  millimeters  of  Hg.  This 
is  readily  done  with  the  large  bulb  when  the  O  is  evolved,  while  the  Sprengel 
is  able  to  remove  the  COg  as  it  is  given  oif,  thus  obviating  the  continued  rais- 
ing and  lowering  of  the  reservoir  bulb." 

The  gases  collected  are  driven  through  the  tube  P  into  a 
eudiometer  previously  filled  with  mercury  and  inverted. 
The  eudiometer  (Fig.  137)  is  a  calibrated  tube  in  which  the 
gases  are  measured.  In  the  upper  part  of  it  are  two  plati- 
num wires  by  means  of  which  an  electric  spark  is  brought 
in  contact  with  the  gases.  Hydrogen  is  introduced  into  the 
eudiometer  in. definite  quantity  (more  than  sufficient  to  com- 
bine with  all  of  the  O  to  form  HgO),  and  a  spark  is  gen- 
erated between  the  ends  of  the  platinum  wires,  causing  the 
O  and  the  H  to  combine.  The  diminution  in  volume  is  now 
noted,  one-third  of  which  diminution  is  equal  to  the  total 
volume  of  O  obtained  from  the  sample  of  blood.  The  quan- 
tity of  CO2  may  be  estimated  by  introducing  into  the  eudi- 
ometer a  piece  of  moistened  fused  potassium  hydrate,  which 
absorbs  the  COg,  forming  potassium  carbonate.  The  loss  in 
volume  is  the  volume  of  COg  obtained  from  the  blood.    The 


residual  gas  consists  of  N  and  H,  the  latter  being  the  excess 

not  combined  with  O.     The  total  quantity  of  H  introduced 

being  known,  and  also  the  quantity  which  combined  with 

O,  the  difference  is  deducted  from  the  volume  N  and  H,  the  remainder  being 

the  volume  N.     Accurate  analysis  necessitates  corrections  for  temperature,  for 
34 


Fig.  137.— Eudiometer. 


530         .Lv  AMKiurAN  TEXT-IK i< >K  OF  PTfYsrnr.oa Y. 

tension  of  aqueous  vapor,  and  for  atnios])heric  pressure,  as  well  as  adnition  to 
the  nianv  details  connected  with  jjas-analysis. 

Cutaneous  Respiration. — In  froj:;s  the  skin  is  a  nioic  important  i('sj)i- 
ratorv  organ  than  th(^  lungs,  as  is  illustrated  i)y  the  tact  that  asphyxia  is 
more  rapidly  })rodnced  hy  dipping  the  animal  in  oil,  and  thus  preventing  the 
interehangeof  O  and  CO2  through  the  skiu,  than  by  ligature  of  the  trachea; 
moreover,  the  investigations  of  Regnault  and  Reiset  show  that  in  these  animals 
nearly  the  same  quantities  of  O  are  absorbed  and  COg  eliminated  after  the 
lungs  are  excised  as  in  the  intact  animal.  In  man  the  reverse  is  the  case,  the 
cutaneous  interchange  being  insignificant  as  compared  with  that  in  the  lungs. 

The  quantity  of  COg  exhaled  through  the  skin  during  twenty-four  hours 
has  been  estimated  by  different  ob-servers  from  2.23  grams  to  as  much  as  32.08 
grams.  Compared  with  pulmonary  interchange,  the  ratio  of  O  absorbed  is 
probably  about  1  :  100-200,  and  of  CO2  eliminated,  1  :  200-250. 

Cutaneous  respiration  is,  as  a  rule,  subject  to  the  same  circumstances  that 
aifect  the  interchange  in  the  lungs,  and  is  accomplished,  moreover,  in  the  same 
w^ay.  In  some  instances,  however,  it  is  influenced  in  the  opposite  direction  ; 
for  instance,  it  is  increased  by  circumstances  that  hinder  pulmonary  respiration. 
Cutaneous  respiration  is  favored  by  moist  skin,  and  Ronehi  found  that  it  was 
inerea.sed  by  higher  external  temperature. 

Internal  or  Tissue-respiration. — The  main  object  of  the  respiratory  mech- 
anism is  to  supply  the  organism  with  O  and  to  remove  the  CO2  resulting  from 
tissue-activity.  The  organism  may  be  regarded  as  an  aggregation  of  living 
cells,  each  of  which  during  life  consumes  O  and  gives  off  COg.  Activity 
depends  essentially  upon  processes  of  oxidation ;  consequently,  not  only  is  oxi- 
dation necessary  for  existence,  but  the  quantity  of  O  absorbed  must  bear  a  direct 
relation  to  the  degree  of  activity.  The  avidity  of  the  different  tissues  for  O 
varies  greatly,  and  the  differences  are  doubtless  expressions,  broadly  speaking, 
of  the  relative  intensities  of  their  respiratory  processes.  Quinquaud  '  records 
the  following  absorption-capacities  of  100  grams  of  each  tissue,  submitted  for 
three  hours  to  a  temperature  of  38°  : 


Muscle 23  c.c. 

Heart 21    " 

Brain 12   " 


Spleen 8      c.c. 

Lungs 7.2     " 

Adipose  tissue 6       " 


Liver 10   "  Bone 5 

Kidney 10   "        I     Blood 0.8     " 

The  quantity  of  CO2  formed  in  each  case  was  approximately  proportional  to 
the  quantity  of  O  absorbed.  The  respiratory  value  of  blood  is  doubtless  too 
low.  The  blood  is  not  merely  a  carrier  of  O  and  COg  to  and  from  the  tissues, 
but  is  itself  the  .seat  of  active  disintegrations  which  involve  the  consumption 
of  O  and  the  production  of  COj  and  other  effete  matters.  Ludwig  and  his 
pupils  long  ago  showed  that  when  readily-oxidizable  substances,  such  as  lactate 
of  sodium,  are  mixed  with  the  blood,  and  the  blood  is  transfused  through  the 
lungs  or  other  living  tissues,  more  O  is  consumed  and  COj  given  off  than  by 

'  Compter  rendus  de  la  Societe  de  hiologie  (9),  1890,  2,  pp.  29,  30. 


RESPIBA  TION.  531 

blood  free  from  tlieni.  Tliese  results  Imvc  been  substantiated  by  the  recent 
researches  of  Bohr  and  Ilenriquez'  on  dogs;  tliese  experiments  have  further 
shown  that  a  considerable  portion  of  O  may  disappear  as  a  result  of  processes 
occurring  in  the  blood  during  its  passage  through  the  lungs,  and  a  large 
amount  of  COg  be  formed  as  one  of  the  products.  Thus  they  found  that  con- 
siderably more  O  was  absorbed  from  the  lungs  than  could  be  pumj)ed  from  the 
blood,  and  that  more  CO2  was  givx'u  to  the  air  in  the  lungs  than  was  lost 
by  the  venous  blood.  They  believe  that  the  tissues  deliver  to  the  blood  j)ar- 
tially-oxidized  substances  which  undergo  a  final  splitting  up  when  the  blood 
reaches  the  lungs.  If  this  be  so,  the  respiratory  capacity  of  the  blood,  apart 
from  its  capacity  as  a  carrier  of  0  and  COj  to  and  from  the  tissues,  must  be 
considerably  greater  than  indicated  by  Quinquaud's  figures. 

The  chief  chemical  product  of  the  oxidative  decompositions  in  the  blood 
and  tissues  is  CO2 ;  but  the  quantity  of  O  absorbed  is  not  necessarily  related 
to  the  amount  of  CO2  eliminated ;  that  is,  during  a  given  interval  the  quantity 
of  O  may  be  out  of  proportion  to  the  elimination  of  CO2,  and  vice  versd. 
Thus,  in  a  muscle  during  rest,  at  normal  bodily  temperature,  the  consumption 
of  O  is  greater  than  the  elimination  of  COg,  while  during  activity  the  propor- 
tion of  CO2  to  O  increases  and  may  exceed  that  of  O.  Rubuer's^  experiments 
on  the  resting  muscle  at  various  temperatures  accentuate  the  fact  that  the  for- 
mation of  CO2  may  be  independent  of  the  quantity  of  O  absorbed.  Thus,  at 
8.4°  the  respiratory  quotient  was  3.28  ;  at  28.2°,  1.01 ;  at  33.8°,  1.18  ;  and  at 
38.8'^,  0.91.  The  high  respiratory  quotient  at  low  temperatures  is  to  be 
explained  partly  by  direct  oxidation  and  partly  by  intramolecular  splitting, 
which  is  independent  of  oxidation.  It  is  probable  that  during  rest  O  is  util- 
ized to  some  extent  in  oxidations  which  are  not  at  once  carried  to  their  final 
stage  and  in  which  relatively  little  CO2  is  formed;  hence  during  activity  com- 
paratively little  O  is  required  to  cause  a  final  disintegration  of  the  now  par- 
tially broken-down  substances,  and  thus  to  give  rise  to  a  relatively  large 
formation  of  CO2.  (See  Effects  of  Muscular  Activity  on  Respiration  and 
Metabolism  of  Muscle,  etc.) 

0.  The  Rhythm,  Frequency,  and  Depth  op  the  Respiratory 

Movements. 

The  Rhythm  of  the  Respiratory  Movements. — During  normal  breathing 
the  respiratory  movements  follow  each  other  in  regular  sequence  or  rhythm. 
Various  instruments  have  been  devised  for  the  study  of  these  movements 
in  man ;  the  form  most  commonly  used  is  the  stethograph  or  pneumo- 
graph of  Marey.  The  respiratory  movements  are  communicated  by  a  system 
of  levers  to  a  tambour,  thence  through  a  rubber  tube  to  a  second  tambour 
having  attached  a  lever  which  records  upon  a  moving  surface.  In  animals 
a  tracheal  cannula  or  tube  (p.  554)  is  usually  inserted  into  the  trachea,  and 
a   tube   is   led    from   it   to   a  recording   tambour.     In   case   the  movements 

1  Comptes  rendus,  1892,  vol.  114,  pp.  1496-99. 

^  DuBoui-Reymond^ s  Archivfiir  Physioloffie,  1885,  pp.  38-66. 


532  ^l^V  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

of  the  ribs  are  especially  to  be  studied,  the  stethograph  may  be  employed ; 
if  the  movements  of  the  diaphragm,  a  loDg  probe  may  be  inserted 
through  the  abdominal  walls  so  that  one  end  rests  between  the  liver  and  the 
diaphragm  and  the  other  end  connects  with  a  recording  lever,  the  abdominal 
walls  serving  as  a  fulcrum.  A  tracing  obtained  by  one  of  the  above  methods 
shows :  (1)  That  inspiration  passes  into  expiration  without  an  appreciable  in- 
tervening pause ;  (2)  that  inspiration  is  shorter  than  expiration;  (3)  that  the 
curves  of  inspiration  and  expiration  diifer  in  certain  characters.  The  relative 
periods  of  inspiration  aud  expiration  vary  with  age,  sex,  and  other  conditions. 
The  inspiratory  phase  is  shorter  relatively  in  women  than  in  men,  and  in  chil- 
dren and  the  aged  than  iu  those  of  middle  life.  The  length  of  inspiration  as 
compared  to  expiration  is  subject  to  variations,  but  these  relations  are  affected 
chiefly  by  disease  and  by  other  abnormal  conditions.  After  section  of  the 
pneumogastric  nerves,  and  in  diseased  conditions  which  narrow  any  part  of  the 
air-passages,  inspiration  is  longer  than  expiration,  while  in  emphysema  the 
expiratory  phase  is  prolonged.  The  relative  periods  occupied  by  inspiration 
and  by  expiration  in  the  adult  differ  according  to  various  observers ;  at  one 
extreme,  the  ratio  according  to  Yierordt  aud  Ludwig  is  10  :  19-20,  and  at 
the  other  extreme,  according  to  Ewald,  11:12.  A  mean  ratio  is  5:6. 
Renuebaum  found  that  the  expiratory  phase  is  relatively  prolonged  by  an 
increase  in  the  respiration-rate,  the  ratio  being  9  :  10  at  13  respirations  per 
minute,  aud  9  :  13  at  46  per  minute.  In  the  new-born  the  ratio  is  1  :  2-3. 
Mosso  found  that  during  sleep  the  inspiratory  phase  is  lengthened  one-fourth. 

Inspiration  is  more  abrupt  than  expiration,  the  lever  moving  more  rapidly 
during  inspiration  than  during  expiration ;  consequently  the  curves  differ  in 
character.  We  may  volitionally  affect  the  rhythm  and  the  various  phases  of 
each  respiratory  act. 

A  pause  may  exist  between  expiration  and  inspiration  (expiratory  ])ause) 
when  the  respirations  are  abnormally  infrequent.  In  certain  diseases  an  inter- 
val may  be  observed  between  inspiration  and  ex])iration  (inspiratory  pause). 
Some  observers  look  upon  the  nearly  horizontal  part  of  the  respiratory  curve 
as  a  record  of  a  pause,  but  an  examination  of  tracings  of  normal  respirations 
shows  that  one  phase  passes  into  the  other  without  an  appreciable  interval. 

The  respiratory  acts  while  we  are  awake  and  quiet  are  rhytimiical,  but  this 
rhythm  is  more  or  less  disturbed  during  sleep,  especially  in  young  children 
and  in  the  aged.  In  the  latter  there  may  not  only  be  an  irregularity  in 
the  time-intervals  between  successive  acts,  but  occasionally  long  expiratory 
pauses,  giving  the  movements  a  peculiar  periodical  character.  In  the  so-called 
"  Cheyne-Stokes  respiration  "  the  rhythm  is  greatly  disturbed.  This  type  is 
characterized  by  groups  of  respiratory  movements,  each  grouj)  being  separated 
from  the  preceding  and  succeeding  ones  by  more  or  less  marked  pauses.  The 
first  respiration  in  each  group  is  very  shallow  and  is  followed  by  movements 
which  successively  become  deeper  and  deeper  until  a  maximum  is  reached; 
then  the  successive  movements  become  more  and  more  shallow  and  finally 
cease.     Each  group  commonly  consists  of  about  10  to  30  respirations,  and  is 


RESriRA  TIOX.  53:^ 

separated  from  the  preceding  aud  siicceetling  groups  by  a  variable  interval, 
usually  30  to  45  -seconds.  This  form  of  respiration  is  frcfjuently  observed  in 
urtemia,  after  severe  hemorrhage,  and  in  certain  diseases  of  the  heart  and  brain. 
Periodical  alterations  in  tlie  respiratory  rhythm  may  be  observed  in  the  last 
stages  of  asphyxia,  in  poisoning  by  chloral,  opium,  curare,  and  digitalis,  in  cer- 
tain septic  level's,  in  certain  animals  during  hybernation,  etc.  In  the  human 
organism,  excepting  during  sleep  and  in  the  aged  and  the  very  young,  such 
non-rhythmical  respirations  are  always  indicative  of  abnormal  conditions. 

In  Nvarm-blooded  animals  the  movements  are  generally  of  a  much  more 
rhythmical  character  than  in  cold-blooded  animals. 

The  Frequency  and  Depth  of  the  Respiratory  Movements. — The 
respiratory  rate  is  afiected  by  a  number  of  conditions,  chiefly  species,  age, 
posture,  time  of  day,  digestion,  activity,  internal  and  external  temperature, 
season,  barometric  pressure,  emotions,  the  composition  of  the  air,  the  composi- 
tion of  the  blood,  the  state  of  the  respiratory  centres  and  nerves,  etc. 

The  following  figures,  compiled  from  various  sources,  indicate  the  wide 
differences  in  various  species y  the  rates  being  per  minute  : 

Horse 6-10     I     Pig 15-20  i  Kabbit  ....  50-60 

Ox 10-15          Man 16-24  i  Sparrow    ...  90 

Sheep 12-20          Cat 20-30  Guinea-pig  .    .  100-150 

Dog 15-25         Pigeon 30  ■  Eat 100-200 

The  average  rate  in  man  varies  according  to  different  investigators,  from 
11.9  by  Yierordt  to  19.35  by  Ruef.  Hutchinson  noted  16-24  per  minute  as 
a  mean  of  2000  observations.  There  is  a  general,  but  not  an  absolute,  rela- 
tionship between  the  rate  and  the  size  of  the  body,  as  regards  both  different 
species  and  different  individuals  of  the  same  species :  as  a  rule,  the  smaller  the 
species  the  more  frequent  the  respirations;  the  same  holding  good  for  indi- 
viduals of  the  same  species. 

The  marked  influence  of  age  is  illustrated  by  the  records  of  the  observa- 
tions by  Quetelet  on  300  individuals  : 

Rate  per  Minute. 

Age.                                                            Maximum.  Minimum.  Mean. 

New-born 70  23  44 

1-  5  years 32  .  .  26 

15-20 '  "         24  16  20 

20-25     "        24  14  18.7 

25-30     "        21  15  16 

30-50     "         23  11  18.1 

Posture  exerts  a  marked  influence,  especially  in  those  enfeebled  by  disease. 
Guy  records,  in  normal  individuals,  13  while  lying,  19  while  sitting,  and  22 
while  standing. 

The  diurnal  changes  are  in  close  accord  with  those  of  the  pulse-rate  (p.  412). 
The  rate  is  less  frequent  by  about  one-fourth  during  the  night  than  during  the 
day,  and  more  frequent  after  meals,  especially  after  the  mid-day  meal.  Yier- 
ordt noted  the  following  variations:  9  a.m.,  12.1;  12  M.,  11.5;  2  p.m.,  13; 


531  AX  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

7  P.M.,  11.1.  Ciiiy  gives  tlie  mean  rate  in  tiie  morning  as  17  and  in  the 
evening  as  18. 

Tlie  rate  increases  with  an  increase  in  inuscular  adivUy  (p.  41  o). 

Changes  in  extermd  (surnxnuling)  tempcratare  have  very  little  iiiHuence. 
Vierordt  noted  a  rate  of  12.16  at  8.47°  C.  and  one  of  11.57  at  19.4°  C,  and 
that  an  increase  of  each  degree  C.  decreases  the  period  of  each  respiration 
0.054.  Alterations  of  into'nal  temperature  are  associated  with  marked 
changes,  as  is  well  illustrated  in  the  increase  in  the  rate  observed  in  fevers, 
which  increase,  in  turn,  is  closely  related  to  the  rise  in  the  pulse-rate  and 
the  bodily  temperature. 

Season  is  not  without  its  influence.  In  the  spring  the  rate,  according  to  E. 
Smith,  is  32  per  cent,  greater  than  at  the  end  of  summer. 

Ordinary  changes  in  atmospheric  pressure  exert  no  influence,  but  under  con- 
siderable variations  the  rate  rises  and  falls  inversely  with  the  pressure. 

The  frequency  of  the  respirations  may  be  profoundly  affected  by  our  emo- 
tions and  by  our  u-ill.  Mental  excitement  may  increase  or  decrease  the  rate, 
and,  as  is  well  known,  we  may  greatly  modify  not  only  the  rate  but  the  depth 
of  the  movements  by  volitional  effort. 

If  the  composition  of  the  inspired  air  becomes  so  altered  that  O  falls  below 
13  volumes  per  cent.,  the  respirations  ^re  increased  in  frequency  and  in  depth. 
In  the  same  way,  if  the  blood  becomes  deficient  in  O  or  overcharged  with  CO2, 
movements  of  respiration  are  increased. 

Excitation  and  depression  of  the  respiratory  centres  and  nerves  through  the 
agency  of  operations,  disease,  poisons,  etc.  effect  changes  in  the  respiratory  rate. 

The  rate  and  the  depth  of  the  respirations  bear  generally  an  inverse  relation 
to  each  other :  the  greater  the  rate  the  less  the  depth,  and  vice  versd  ;  but  the 
quantity  of  air  respired  during  a  given  period  does  not  necessarily  bear  any 
direct  relation  to  either  the  rate  or  the  depth  alone,  but  rather  to  both. 

A  general  relationship  exists  between  the  frequency  of  the  respirations  and 
the  pulse-rate.  Comparisons  of  a  large  number  of  observations  by  different 
investigators  give  a  ratio  at  twenty-five  to  thirty-five  years,  1  :  4-4.5  ;  at 
fifteen  to  twenty  years,  1  :  3.5 ;  at  six  weeks,  1  :  2.5. 

D.  The  Volumes  of  Air,  O,  and  CO..  Respired. 
During  quiet  respiration  there  occurs  an  inflow  and  outflow  of  air,  desig- 
nated tidal  air,  equal  to  about  500  cubic  centimeters,  or  30  cubic  inches.  The 
volume  of  ex})ired  air  is  a  little  in  excess  of  inspired  air,  owing  to  the  expan- 
sion caused  by  the  increase  of  tenijierature,  although  the  actual  volume  is  less 
(p.  519).  The  volume  of  air  respired  during  each  respiration  bears  generally 
an  inverse  relation  to  the  respiration-rate,  and  is  affected  by  the  position  of  the 
body;  thus,  if  in  the  lying  posture  the  volume  be  1,  when  sitting  it  will  be 
1.11,  and  when  standing  1.13  (Hutchinson).  Besides  the  term  tidal  air, 
others  are  used  to  express  definite  volumes  associated  with  the  capacity 
of  the  lungs  under  certain  circumstances.       Thus,  Hutchins<Mi  distinguishes 


RESPIRA  TION. 


535 


complemental  (lir,  or  the  volume  tlmt  cuii  he  inspired  after  the  completion  of  an 
ordinary  inspiration  (1500  ciihic  centimeters);  reserve  or  supplemental  air,  or 
the  vohime  that  can  ho  expelled  after  an  ordinary  expiration  (1 240-1  .SOO  ciil)ic 
centimeters);  residual  air,  or  the  vohinie  remaining  in  the  lungs  after  the  most 
forcible  expiration  (1 230-1040  cubic  centimeters);  and  stationary  air,  or  the 
volume  remaining  in  tlie  lungs  after  ordinary  expiration,  and  equal  to 
reserve  air  j)lus  residual  air  (2470-3440  cubic  centimeters).  The  volume  of 
residual  air  is  different  according  to  various  observers,  the  estimates  ranging 
from  538  cubic  centimeters  by  Kochs  to  19,800  cubic  centimeters  by  Neupauer. 
The  recent  researches  of  Hermann  and  Jacobson '  give  914.5  cubic  centimeters 
as  the  average  of  nine  observations,  the  lowest  measurement  being  434  (;ubic 
centimeters,  and  the  highest  1023.2  cubic  centimeters. 

Lung-capacity  is  the  tt)tal  quantity  of  air  the  lungs  contain  after  the  most 
forcible  inspiration,  and  is  equal  to  the  vital  capacity  plus  the  residual  air. 

Bronchial  capacity  is  the  capacity  of  the 
trachea  and  bronchi,  and  is  equal  to  about  140 
cubic  centimeters. 

Alveolar  capacity  is  the  volume  of  air  in 
the  smallest  air-passages  and  alveoli,  and  is 
greater  during  inspiration  than  during  expira- 
tion, and,  of  course,  is  altered  in  proportion  to 
the  depth  of  these  movements.  After  quiet 
expiration  it  is  equal  to  about  2000  to  3000 
cubic  centimeters ;  during  quiet  inspiration  it 
is  increased  about  500  cubic  centimeters,  and 
during  forced  inspiration  about  2000  cubic  cen- 
timeters; during  forced  expiration  it  is  dimin- 
ished about  1500  cubic  centimeters.  Between 
the  extremes  of  forced  inspiration  and  forced 
expiration  the  volume  diifers  about  3J  times. 

Vital  capacity  is  the  volume  of  air  that  can 
be  expired  after  the  most  forcible  inspiration. 
Averages  obtained  by  Vierordt  from  the  results 
of  the  observations  by  various  investigators  are 
3400  cubic  centimeters  for  men  and  2500  cubic 
centimeters  for  women.  Such  investigations 
are  conducted  by  the  aid  of  a  spirometer  (Fig. 
138),  Avhich  is  a  calibrated  gasometer  consisting 
of  a  bell-jar  submerged  in  water  and  counter- 
poised. Communicating  with  the  interior  of 
the  jar  is  a  tube  through  which  the  expired  air 

is  conducted.     The  subject  makes  the  deepest  possible  inspiration  and  then 
forcibly  expires   into  the  tube :  the  jar  rises  in  proportion  to  the  volume  of 
air  admitted,  and  the  extent  of  this  rise  may  be  read  from  the  scale. 
*  Pfliiger's  An-hiv  J'iir  Physiolor/ie,  1888,  vol.  43,  pp.  23G,  440. 


Fig.  138.— Wintrich's   modification  of 
Hutchinson's  spirometer. 


530  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

Vital  capacity  is  affected  by  various  circumstances,  especially  age,  stature, 
sex,  po.-turc,  occupation,  and  disease.  It  increases  with  age,  reaching  a  maxi- 
mum at  about  thirty-five  years,  after  which  there  occurs  an  annual  decrease  of 
about  32  cubic  centimeters  uj)  to  about  sixty-five  years.  In  proi)ortion  to 
the  length  of  the  body  it  increases  up  to  twenty-five  years  and  then  dimin- 
ishes. Wintrich  has  shown  that  vital  capacity  for  each  centimeter  of  height 
varies  at  different  ages;  thus  at  eight  to  ten  years  it  is  9  to  11  cubic 
centimeters  for  each  centimeter  of  height,  at  sixteen  to  eighteen  years 
20.65  cubic  centimeters,  and  at  fifty  years  21  cubic  centimeters.  Arnold 
estimates  that  in  the  adult  for  each  centimeter  of  increase  or  decrease  of 
height  beyond  a  mean  standard  there  is  a  corresponding  rise  or  fall  of  60  cubic 
centimeters  in  men  and  of  40  cubic  centimeters  in  women.  It  is  greater  in 
men  than  in  women  of  the  same  height,  the  ratio  being  about  10  :  7.5.  Hutch- 
inson found  that  it  was  affected  by  posture,  the  ratios  being  as  follows :  Lying 
on  chest  and  abdomen,  0.96;  lying  on  back  or  sitting,  1.11;  and  standing, 
1.13.  Wintrich  and  Arnold  both  have  found  that  vital  capacity  is  diminished 
during  starvation  100  to  200  cubic  centimeters.  Physical  exercise,  such  as 
running  and  other  forms  of  violent  exertion  that  increase  the  rate  and  depth 
of  respiration,  tends  to  increase  the  vital  capacity.  Occupation  also  exerts 
an  influence  upon  vital  capacity,  it  being  proportionately  greater  in  those  en- 
gaged in  active  physical  work  than  in  those  leading  a  sedentary  life.  All  cir- 
cumstances which  interfere  w^ith  the  full  and  free  expansion  of  the  thoracic 
cavity  diminish  vital  capacity,  as,  for  instance,  tight  clothing,  visceral  tumors, 
tuberculosis  of  the  lungs,  pneumothorax,  etc. 

The  Volumes  of  O  and  COg  Respired. — The  quantity  of  air  re- 
spired during  each  respiratory  act  is  about  500  cubic  centimeters,  or  30  cubic 
inches ;  and  since  the  normal  respiration-rate  in  man  is,  we  may  say,  for  the 
twenty-four  hours  about  15,  the  total  quantity  of  air  respired  per  diem  may 
readily  be  calculated : 

Per  minute,  500  c.c.        x  15  =    7,500  c.c,  or  7.5  liters. 
Per  hour,  7.5  liters  x  60  =       450  liters. 

Per  day,        450     liters  x  24  =  10,800  liters,  or  about  380  cubic  feet,  which  is  equal  to  a  volume 

about  220  centimeters  (7^  feet)  in  height,width,  and  thickness. 

With  these  figures  as  standards,  and  knowing  the  per  cent,  composition  of 
inspired  and  expired  air,  the  volumes  of  O  absorbed  and  of  COj  eliminated 
are  easily  found.  The  inspired  air  loses  4.78  volumes  per  cent,  of  O;  it  is 
obvious,  then,  that  the  quantity  absorbed  per  diem  is  4.78  volumes  per  cent, 
of  10,800  liters,  which  is  516  liters,  or  about  740  grams;  likewise,  the  ex- 
pired air  contains  an  exce&s  of  4.34  volumes  per  cent,  of  COj;  the  quantity 
expired  per  diem  is  4.34  volumes  per  cent,  of  10,800  liters,  or  470  liters  or 
925  grams.  These  figm-es,  while  not  strictly  accurate,  are  in  accord  with  those 
obtained  by  other  methods  of  estimation  and  by  experiments.  The  amount  of 
O  varies  from  600  to  1200  grams  per  diem,  and  that  of  CO^  from  700  to 
1400  grams — approximate  averages  being  about  750  grams  of  O  and  875 
grams  of  COj. 


RESPIRA  TION. 


637 


Tlie  quantities  of  O  and  of  CO2  exchanged,  although  in  a  general  way 
closely  related,  are  in  a  measure  independent  of  each  other,  but,  as  a  rule,  an 
increase  or  a  decrease  in  one  is  accompanied  by  a  rise  or  a  fall  in  the  other. 
The  most  important  conditions  affecting  the  quantities  of  O  absorbed  and  CO, 
given  off  are  species,  body-weight  and  body-surface,  age,  sex,  constitution,  rate 
and  depth  of  the  respirations,  the  period  of  the  day,  digestion,  food,  internal 
and  external  temperature,  activity,  atmospheric  pressure,  the  composition  of 
the  inspired  air,  and  the  condition  of  the  nervous  system. 

Most  of  the  studies  have  been  made  solely  by  determinations  of  the  quan- 
tities of  CO,  given  off,  the  results  being  taken  as  standards  for  tlie  relative 
volumes  of  O  absorbed ;  but  such  deductions  are  of  very  uncertain  value  and 
may  be  entirely  misleading.     (See  Respiratory  Quotient,  p.  544.) 

Respiratory  activity  in  different  species  in  proportion  to  body-weight  is  less 
in  cold-blooded  than  in  warm-blooded  animals,  the  difference  being  due  chiefly 
to  the  larger  supply  of  O  demanded  by  the  more  active  heat-producing  pro- 
cesses in  the  latter,  and  in  part  to  the  more  active  character  generally  of  the 
bodily  operations.  If  we  take  as  a  standard  for  cold-blooded  animals  the 
respiratory  activity  in  the  frog  (which  is  0.07  gram  of  O  per  kilogram  of  body- 
weight  per  hour),  and  compare  this  with  the  standards  for  warm-blooded  ani- 
mals, in  the  latter  it  will  be  from  6  to  18  times  greater,  according  to  the  species. 
Respiratory  activity  is  higher  in  proportion  to  body-weight  in  birds  than  in 
mammals.  The  following  tabular  statement  of  the  intensity  of  the  respiratory 
interchange  per  kilogram  of  body-weight  per  hour,  compiled  chiefly  from  the 
researches  of  Regnault  and  Reiset,  Zuutz  and  Lehmann,  Bossignault,  Herzog, 
and  Grouven,  illustrates  these  differences : 


Animal. 


Finch  . 
Sparrow 

Fowl .  . 

Frog  .  . 

Dog    .  . 

Cat     .  . 

Ox.    .  . 

Ass     .  . 

Calf    .  . 

Horse  . 

Sheep  . 

Rabbit  . 
Man 

Pig     .  . 


0. 

CO2. 

Grams. 

C.c. 

Grams. 

C.c. 

11.635 

1837 

11.540 

5857 

9.595 

6710 

10.492 

5334 

1.189 

831  ■ 

1.271 

678 

0.070 

49 

0.062 

37 

1.191 

847 

1.281 

652 

1.001 

699 

1.082 

549 

0.550 

382 

0.757 

383 

0.566 

394 

0.393 

394 

0.481 

336 

0.571 

290 

0.437 

303 

0.640 

323 

0.499 

347 

0.599 

304 

0.920 

642 

1.158 

588 

0.434 

302 

0.507 

257 

0.474 

331 

0.594 

302 

C02 
o 


0.72 
0.79 
0.82 
0.76 
0.77 
0.80 
1.00 
1.00 
0.86 
0.91 
0.88 
0.90 
0.85 
0.91 


As  a  rule,  the  smaller  the  species  the  greater  (relatively,  but  not  absolutely) 
is  the  intensity  of  respiratory  activity ;  for  instance,  the  consumption  of  O 
for  each  kilogram  of  body- weight  is  for  the  horse,  0.437;  ass,  0.566;  sheep, 
0.499;  rabbit,  0.92;  and  for  birds,  as  high  as  12.58.  For  different  species 
of  the  same  class  the  same  variations  are  observed ;  thus,  Richet  records,  as 
the  result  of  investigations  on  birds,  the  following  figures  as  the  number  of 


538 


A.\   AMERICAN    TEXT- BOOK    OF   PHYSTOLOGY. 


grains  of  COg  given  oil"  per  kilogram  ol"  hotly-w  eight  })er  lioiir:  Goijse,  1.4*J; 
fowl,  1.66;  duck,  2.27;  pigeon,  3.36;  and  finch,  12.58. 

In  the  same  species,  other  things  being  equal,  the  respiratory  interchange  is 
greater  in  smaller  animals,  because  in  relation  to  body-icciyht  the  body-surface 
is  greater,  causing  a  greater  })roportional  heat-loss,  which  in  turn  necessitates  a 
larger  consumption  of  O  for  oxidative  processes  to  produce  heat,  and  a  conse- 
quent increase  in  the  production  of  COg.  Richet'  has  shown  that  in  the  same 
species  the  quantity  of  COg  exhaled  (indicating  the  intensity  of  the  oxidation- 
processes)  is  inversely  proportional  to  the  body-weight  and  is  directly  ])r()p()r- 
tional  to  the  body-surface.  The  following  figures  illustrate  these  imiwrtant 
facts : 


Mean  Body-weight 
(kilograms). 

CO2  per  Kilogram 
per  Hour 
(grams). 

Body-surface 
(sq.  cm.). 

CO.,  per  100 
sq.  cm. 
(grams). 

24 

11.5 
6.5 
3.i 

1.020 
1.880 
1.624 
1.964 

9296 
5656 
3940 
2341 

2.65 
2.81 
2.69 
2.71 

Thus,  an  animal  weighing  24  kilograms  will  give  off  1.026  grams  of  COj 
per  hour  for  each  kilogram  of  body-weight,  while  one  weighing  3.1  kilograms 
will  give  off  1.964  grams,  or  nearly  twice  as  much,  for  equal  increments  of 
weight.  It  will  be  observed  by  comparing  the  quantity  of  CO2  and  the  body- 
surface  that  for  each  100  square  centimeters  of  surface  the  elimination  is  about 
the  same. 

Age  exercises  an  important  influence.  Until  full  growth  respiratory  activity 
is  higher  than  in  middle  life,  and  in  middle  life  it  is  higher  than  in  old  age. 
In  children  the  absolute  quantities  of  O  consumed  and  CO2  formed  are  less 
than  in  the  adult,  but  in  relation  to  body-weight  they  are  about  twice  as  much. 
During  middle  life  respiratory  activity  is  about  one-sixth  higher  than  during 
old  age.  In  the  young  the  quantity  of  O  in  relation  to  COj  is  higher  than  in 
the  adult. 

Andral  and  Gavarret  have  shown,  in  investigations  relative  to  sex,  that 
after  the  eighth  year  males  give  off  from  one-third  to  one-half  more  COg  than 
females,  the  difference  being  most  pronounced  at  puberty.  During  pregnancy 
and  after  the  menopause  the  relative  quantity  of  COg  rises. 

The  influence  of  constitution  is  manifest  by  a  greater  intensity  of  respi- 
ratory activity  in  the  robust  than  in  the  weak,  other  conditions  being  the 
same. 

The  rate  and  depth  of  the  respiratory  movehients  do  not  appreciably  affect 
the  volumes  of  O  and  COj  interchanged,  although  the  removal  of  COj  is  facili- 
tated by  an  increase  of  the  volume  of  air  respired,  because  of  the  better  ven- 
tilation of  the  lungis.  An  increase  in  the  rate,  the  depth  remaining  constant, 
increases  the  volume  of  air  respired  and  the  ab.solute  quantity  of  CO,  given 
off,  but  the  quantity  of  COj  in  relation  to  the  total  volume  of  air  is  Ic^s.  If 
'  Archiv  de  Physiologic  noi-male  et  pathologicpie,  vol.  22,  pp.  17-30. 


RESPTR ,  1  T/O  X.  539 

the  rate  remain  constant  ;iiul  tlio  clci)th  be  increased,  similar  results  are 
obtained. 

The  quantity  of  CO.^  eliminated  during  slow,  deep  respirations  is  larger 
than  during  rapid,  shallow  respirations. 

The  diunidl  rdriafions  are  in  accord  with  the  changes  in  the  respiratory 
rate — rising  after  we  awake,  falling  during  the  forenoon,  again  rising  after  the 
mid-day  meal,  again  falling  during  the  afternoon,  increasing  after  the  evening 
meal,  and  falling  to  a  minimum  during  the  night. 

Sunli(/Iit  exercises  a  marked  influence,  as  is  proven  by  the  results  obtained 
by  a  number  of  investigators.  In  frogs  the  elimination  of  COj  is  increased 
by  sunlight,  even  after  excision  of  the  lungs.  Fubini  and  Benedicenti,'  in 
experiments  upon  hybernating  animals,  found  that  the  comparative  quantities 
of  CO2  eliminated  under  the  influence  of  sunlight  and  of  darkness  were  as 
100  :  93.48.  Confirmatory  results  have  been  obtained  by  Ewald  on  curarized 
frogs. 

Respiratory  activity  is  affected  by  the  character  and  quantity  of  the  food. 
The  following  results,  obtained  by  Pettenkofer  and  Voit,  are  very  instructive : 

Non-nitrogenous  Nitrogenous 

Fasting.  Mixed  Diet.  j^jg^^  »  pj^j. 

O 743  grams.  867  grams.  808  grams.  1083  grams. 

CO., 695       "  930      "  839       "  850      " 

It  will  be  observed  that  respiratory  activity  is  lowest  during  fasting,  higher 
when  the  diet  is  non-nitrogenous,  still  higher  when  the  diet  is  mixed,  anJ 
highest  when  the  diet  is  purely  nitrogenous.  The  respiratory  quotient  is 
higher  when  the  diet  is  rich  in  carbohydrates  (p.  545),  while  it  falls  in  propor- 
tion to  the  percentage  of  nitrogenous  food.  Fasting  reduces  the  quotient  con- 
siderably, and  if  coupled  with  inactivity  (hybernation)  causes  it  to  fall  to  a 
minimum. 

During  digestion  the  gaseous  exchange  is  increased,  according  to  Loewy,'' 
from  7  to  30  per  cent.  Joylet,  Bergonie,  and  Sigalas^  obtained  the  following 
averages  of  seven  experiments  on  a  man  weighing  52  kilograms,  the  increase 
of  O  being  about  7  per  cent.,  and  of  CO2  about  6  per  cent. : 


o.  CO, 


CO2 
o 


Before  food 259  grams.  298.4  grams.  0.869 

After  food 275      "  317         "  0.867 

The  increase  of  respiratory  activity  during  digestion  may  be  due  to  the 
chemical  processes  involved  in  the  production  of  the  digestive  secretions,  to 
the  oxidation  of  the  products  of  digestion  after  absorption,  or  to  muscular 
activity  of  the   gastro-intestinal  walls.     Zuntz   and  Mering^  endeavored  to 

1  MolescMis  Untermch.  z.  Naturl.,  1887,  vol.  14,  pp.  623-629. 
^  Pfliir/ei-'s  Archivf.  Physiologle,  1888,  vol.  43,  pp.  515-532. 
s  Compt.  rend.,  1887,  vol.  105,  pp.  380,  675. 
*  Pfluyer's  Archiv  f.  Phy&iologie,  1883,  vol.  32,  pp.  173-221. 


540  AN  AMERICAN    TEXT-liOOK    OF   PHYSIOLOGY. 

settle  tliis  point  hv  making  three  series  of  expcriiuciits :  in  one  they  injected 
certain  readily  oxidizable  substances  into  the  blood  ;  in  another  the  substances 
were  injected  into  the  stomach  ;  and  in  another  sulphate  of  sodium  or  other 
purgative  was  given.  When  the  snbstances  were  injected  into  the  blood,  Zuntz 
and  Mering  found  as  a  general  result  that  the  absorption  of  O  was  not  increased, 
while  the  formation  of  VO.,  was  slightly  increased  ;  when  injected  into  the  stom- 
ach, no  marked  increase  in  respiratory  activity  occurred  unless  the  substances  were 
given  in  large  quantities.  When,  however,  in  addition  to  the  readily  oxidiz- 
able substances,  a  purgative  was  injected,  or  when  the  purgative  was  given 
alone,  the  absorption  of  O  and  the  elimination  of  COg  were  considerably  in- 
creased. They  were  therefore  led  to  conclude  that  the  increased  respiratory 
interchange  during  digestion  is  due  chiefly  to  the  muscular  activity  of  the 
intestinal  walls.  Loewy^  has  confirmed  this  conclusion,  and  has  clearly  shown 
that  the  increase  in  respiratory  activity  is  chiefly  related  to  the  intensity  of 
})eristalsis,  the  most  marked  increase  being  associated  with  excessive  peristaltic 
activity.  There  can  be  no  reasonable  doubt,  however,  that  an  insignificant 
portion  of  the  increase  is  due  both  to  glandular  activity  and  to  the  oxidation 
of  the  absorbed  products  of  digestion. 

The  volumes  of  O  absorbed  and  of  COj  produced  rise  with  an  increase  of 
bodily  temperature.  This  fact  has  been  illustrated  by  the  experiments  of 
Pfliiger  and  Colasanti  on  guinea-pigs,  in  which  they  found  that  the  quantity 
of  O  absorbed  at  a  bodily  temperature  of  37.1°  was  948.17  grams;  at  38.5°, 
1137.3  grams;  at  39.7°,  1242.6  grams.  Similar  results  have  been  obtained 
by  other  investigators  in  experiments  both  upon  the  human  subject  and  upon 
the  lower  animals  under  the  pathological  conditions  of  fever.  A  fall  of  bodily 
temperature  is  accompanied  by  a  decrease  in  the  intensity  of  respiration,  unless 
the  fall  is  accompanied  by  muscular  excitement,  such  as  shivering.  Speck  ^ 
has  seen  shivering  cause  the  consumption  of  ()  to  rise  from  302  to  496  cubic 
centimeters,  and  the  exhalation  of  COj  from  287  to  439  cubic  centimeters. 
The  primary  and  fundamental  effect  of  lowering  the  bodily  temperature  is  to 
diminish  respiratory  activity,  but  this  may  be  more  than  compensated  for  by 
involuntary  or  voluntary  excitement  of  the  muscles  (p.  541 ;  see  also  Tissue- 
respiration). 

The  effects  of  external  temperature  upon  warm-  and  cold-blooded  animals 
are  different:  Moleschott  found  that  frogs  produced  three  times  more  COj  at 
38.7°  than  at  6°,  while  in  warm-blooded  animals  the  opposite  is  the  cast — that 
is,  three  times  more  COg  is  formed  at  the  lower  temperature.  The  frog's  tem- 
])erature  rises  and  falls  with  changes  in  the  temperature  of  the  surroundings, 
while  that  of  warm-blooded  animals  remains  at  a  fairly  constant  standard ; 
he""ce  the  respiratory  intensity  in  the  frog  increases  with  the  rise  of  external 
temperature,  while  in  warm-blooded  animals  it  decreases,  owing  to  diminished 
heat-production.  But  in  warm-blooded  animals  the  alterations  in  respiratory 
activity  caused  by  changes  of  external  temperature  are  not  always  in  inverse 
relation.     Thus,  Voit  has  shown,  as  a  result  of  studies  in  man,  that  the  exhala- 

•  Loc.  cit.  »  Deutsehes  Archiv  f.  klin.  Med.,  1889,  vol.  33,  pp.  375,  424. 


RESPIRATION.  541 

tion  of  COj  diminishes  with  the  rise  of  external  temperature  from  4.4°  uiiiil 
the  temperature  reaehes  14.3°,  when  it  rises  slowly.  These  results  have  been 
substantiated  by  the  more  recent  investigations  of  Page/  who  found  in  ex])eri- 
ments  on  dogs  that  the  discharge  of  COg  was  at  a  mininuim  at  about  25° ; 
that  below  this  temperature  the  quantity  increased  as  the  temperature  fell ; 
and  that  above  this  temperature  the  discharge  increased,  and  became  greatly 
augmented  at  temperatures  of  40°  to  42°.  At  the  latter  temperatures  the 
increase  may  reach  3^  times  the  normal,  but  the  bodily  temperature  is  also 
incretised.  If  the  elimination  of  CO^  at  23°  to  24°  be  represented  by  100  as 
a  standard,  at  13°  it  will  be  about  128 ;  at  10°,  141  ;  and  at  18°,  177.  The 
researches  of  Speck,^  of  Loewy,^  and  of  Quinquaud  *  all  show  that  external 
cold  increases  respiratory  activity,  chiefly  by  causing  involuntary  muscular 
excitement  (shivering).  If  shivering  and  other  forms  of  nuiscular  activity  be 
absent,  the  exchange  of  O  and  COj  is  unaffected  or  diminished,  but  when 
present  the  increase  of  respiratory  activity  may  amount  to  100  per  cent,  not- 
withstanding a  fall  of  bodily  temperature  below  the  normal. 

Muscidar  activity  is  one  of  the  most  important  of  all  the  circumstances 
affecting  the  quantities  of  O  and  CO2  exchanged.  Involuntary  excitement, 
such  as  shivering,  may  of  itself  double  the  consumption  of  O  and  increase 
by  one-half  the  elimination  of  CO^,  but  the  volitional  effort  may  increase 
the  interchange  even  beyond  these  limits.  Hirn,  in  investigations  on 
four  men,  noted  during  rest  an  hourly  absorption  of  30.2  grams  of  O,  and 
during  work  120.9  grams;  and  Pettenkofer  and  Voit,  in  similar  studies, 
found  an  increase  of  O  from  867  grams  during  rest  to  1006  grams  during 
moderate  work,  and  from  930  grams*  of  CO2  to  1137  grams.  In  experiments 
on  the  horse  Zuntz  and  Lehmanu^  obtained  the  following  results,  which  show 
to  what  a  marked  extent  the  respiratory  interchange  may  be  increased  by 
muscular  activity : 

Liters  per  Minute. 

CO2 

O.  CO,.  -^^ 

Besting 1.722  1.570  0.92 

Walking ".    .    4.766  4.342  0.90 

Trotting      8.093  7.516  0.93 

Speck  ^  has  added  some  interesting  facts  to  our  knowledge  of  the  effects  of 
muscular  activity  on  the  respiratory  interchange.  Thus,  he  found  that  the 
increase  of  O  and  CO2  reaches  a  maximum  before  exertion  reaches  its  maxi- 
mum ;  that  the  increase  for  the  same  amount  of  work  can  be  varied  by  chang- 
ing the  position  of  the  body ;  that  if  a  given  amount  of  work  be  divided  into 
two  equal  parts,  the  increase  of  respiratory  activity  during  the  first  period  is 
greater  than  during  the  second  ;  that  the  greater  the  increase  of  CO^,  the  less, 

1  Journal  of  Physiology,  1879-80,  vol.  2,  p.  228.  ^  Loc.  cit. 

"  Pfluger^s  Arcfiiv  f.  Pliysiologie,  1890,  vol.  46,  pp.  189-224. 

*  Compt.  rend.,  1887,  vol.  104,  pp.  1542-1544. 

*  Journal  of  Physiology,  1890,  vol.  2,  p.  396. 

*  Deutsches  Archiv  f.  klin.  Med.,  1889,  vol.  45,  pp.  460-528. 


642  ^l.V   A3fEniCAN    TEXT-JiOOK    OF   PHYSIOLOGY. 

projx^rtioiiatcly,  is  tlic  iuoreasc  of  O,  so  that  the  respiratory  (juotient  rises 
more  and  more,  and  to  such  an  extent  that  the  COj  contains  more  O  than  is  at 
the  time  absorbed  ;  and  that  the  quantity  of  air  respired  is  so  intimately  related 
to  the  amount  of  CO^  given  off  that  he  regards  the  fpiantitv  of  this  gas 
formed  as  the  regulator,  as  it  were,  of  the  degree  of  activity  of  the  respii-atory 
movements. 

Griiber  ^  states  that  while  resj)iratory  activity  is  proportional  to  the  inten- 
sity of  muscular  activity,  "training"  diminishes  tlu."  (piaiitity  (»f  C()2  given 
off  for  the  same  amount  of  work.  Thus,  taking  1  as  a  standard  of  the 
amount  of  CO^  eliminated  during  rest,  he  obtained  the  following  ratios  in  two 
series  of  observations : 

Climbing  hills         Climbing  hills 
Resting.  Walking.  when  not  used         when  used  to 

to  it.  it. 

First  series 1  1.89  4.1  3.3 

Second  series J_  1.75  3.05  2.42 

Mean 1  1.82  3.07  2^86 

Training  therefore  reduces  the  output  about  20  per  cent. 

The  elimination  of  COg  is  about  one-fifth  less  during  sleep  than  while 
awake  and  quiet ;  from  one-fifth  to  one-half  greater  during  ordinary  exertion ; 
from  two  to  two  and  a  half  times  greater  during  violent  exercise ;  and  about 
three  times  greater  during  tetanus. 

During  hybernation  the  absorption  of  O  falls  to  -^^  and  the  elimination  of 
CO2  to  ^  of  the  normal  for  the  period  of  activity  (Valentine).  Relatively 
more  O  Ls  absorbed  than  CO2  given  off,  hence  the  respiratory  quotient  falls, 
reaching  as  low  as  0.50  to  0.75. 

A  diminution  of  the  barometric  pressure  increases  the  respiration-rate  and 
the  volume  of  air  respired,  but  both  Mosso  and  Marcet  have  shown  that  if 
allowances  be  made  for  the  increase  of  volume  of  the  air  at  the  lower  pressure, 
the  actual  volume  respired  is  less.  Conversely,  an  increase  of  pressure  lowers 
the  rate  and  the  volume  of  air  respired.  Extremes  of  pressure  severely  affect 
the  respiratory  and  other  functions  (p.  559). 

The  integrity  of  the  nervous  apparatus  which  governs  the  metabolic  pro- 
cesses in  the  tis.sues  is  obviously  of  fundamental  importance.  If  the  efferent 
nerve-fibres  of  a  muscle  be  cut,  the  interchange  of  O  and'COg  at  once  sinks, 
as  illustrated  by  the  following  results  obtained  by  Zuntz : 

O  consumed.  CO...  given  off. 

Before  section 13.2    c.c.  14.4  c.c. 

After  section 10.45  c.c.  10.1  c.c. 

After  section  (less) 2.75  c.c.  4.3  c.c. 

The  consumption  of  O  was  therefore  lessened  about  20  per  cent.,  and  the 
formation  of  COj  about  30  jier  cent. 

After  section  of  the  spinal  cord  in  the  dorsal  region  Quinquaud  ^  obtained 


'  Zeiischrift  f.  Biolof/ie,  1891,  vol.  28,  pp.  466-491. 
*  Cmipt.  rend.  Soc.  Biologic,  1887,  pp.  340-342. 


RESPIRATrOX.  643 

similar  results.  Before  the  section  the  hloml  in  the  crural  vein  contained  9.5 
per  cent,  of  ()  and  60  per  cent,  of  COj ;  after  section  it  contained  l.'i.o  per 
cent,  of  O  and  40  per  cent,  of  COj,  showinj^  that  the  consumption  of  O  by 
the  tissues  and  the  formation  of  COg  were  c(jnsiderably  leasened.  After  de- 
struction of  the  spinal  cord  res})iratory  activity  falls  to  a  minimum. 

The  study  of  the  eti'ects  of  a/fcrations  in  the  compo.sitlon  of  the  inspired  air 
on  the  absorptiou  of  O  and  the  elimination  of  CO2  are  of  great  importance. 
Nitrogen  is  merely  a  mechanical  diluent  of  the  inspired  air,  and  may  be 
replaced  by  H  or  by  other  inert  gas,  so  that  alterations  in  its  percentage  do 
not,  -per  se,  aifect  the  respiratory  phenomena ;  but  changes  in  the  percentages 
of  O  and  COj  may  cause  marked  disturbances  both  of  the  respiratory  move- 
ments and  of  the  gaseous  interchange. 

When  the  percentage  of  O  in  the  inspired  air  is  increased  up  to  40  volumes 
per  cent.,  Bert  found  that  there  occurred  an  increase  in  the  quantity  absorbed, 
and  both  Speck  and  Fredericq  have  noted  merely  a  transient  increase  under 
similar  circumstances ;  but  the  results  of  most  experimenters,  on  the  contrary, 
seem  to  show  quite  conclusively  that  an  increase  of  the  ])er  cent,  of  O  above 
the  normal  does  not  affect  the  quantity  absorbed.  Lnkjanow  ^  in  a  large 
number  of  experiments  could  not  detect  any  increase,  and  Saint-Martin,^  in 
researches  on  guinea-pigs  and  rats  with  an  atmosphere  containing  from  20  to 
75  volumes  per  cent,  of  O,  noted  the  same  result.  Even  in  an  atmosphere  of 
pure  O  animals  breathe  as  though  they  were  respiring  normal  atmospheric  air. 

A  decrease  in  the  percentage  of  O  is  without  influence  until  the  proportion 
falls  below  13  volumes  per  cent.  Worra-Miiller  long  ago  showed  that  animals 
breathe  quietly  in  air  containing  14,8  volumes  per  cent,  of  O,  and  that  if  the 
proportion  fell  to  7  volumes  per  cent.,  respiration  became  slow,  deep,  and  diffi- 
cult ;  with  4.5  volumes  per  cent,  marked  dyspnoea  occurred ;  and  when  there 
was  but  3  volumes  per  cent,  asphyxia  rapidly  supervened.  The  more  recent 
results  of  Speck  ^  not  only  confirm  the  main  facts  of  Worm-Miiller's  observa- 
tions, but  furnish  other  important  data.  He  has  shown  that  Avhen  the 
atmosphere  contains  18  volumes  per  cent,  of  O,  respiration  is  quiet  and  the 
quantity  of  O  absorbed  is  but  slightly,  if  at  all,  diminished,  and  that  even 
when  the  proportion  falls  to  9.65  volumes  per  cent,  breathing  is  carried  on  for 
a  long  time  without  inconvenience,  the  amount  of  O  absorbed,  however,  being 
diminished.  He  shows,  moreover,  that  when  the  volume  of  O  in  the  atmo- 
sphere falls  to  8  per  cent,  the  respiratory  movements  are  deep  and  are  but 
slightly  accelerated,  the  quantity  of  O  absorbed  being  very  much  diminished, 
and  that  the  animal  subjected  to  such  an  atmosphere  succumbs  in  a  few 
moments.  The  quantity  of  O  taken  into  the  lungs  falls  proportionately  with 
the  diminution  of  O  in  the  inspired  air  until  the  reduction  reaches  11.26  vol- 
umes per  cent.,  but  further  diminution  is  compensated  for  by  an  increase  in 
the  volume  of  air  respired.     As  the  volume  per  cent,  of  O  in  the  inspired  air 

1  Zeitschrifl  f.  Physiolog.  Oiemie,  1883-1884,  vol.  8,  pp.  31«-355. 

»  Compt.  rend.,  1885,  vol.  98,  pp.  241-243. 

'  Zeitschrift  f.  klin.  Med.,  1887,  vol.  12,  pp.  447-532. 


544  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

diminishes  the  relative  percentage  of  O  absorbed  increases,  and  tliis  continues 
until  the  volume  in  the  inspired  air  is  reduced  to  11.26  per  cent.,  27  per  cent, 
of  which  is  absorbed ;  below  this  point  no  further  increase  of  absorption 
occurs.  As  the  (piantity  of  O  absorbed  is  reduced  the  respiratory  (piotiont 
becomes  greaier,  and  may  reach  as  iiigh  as  2.218. 

When  the  quantity  of  O  remains  at  the  normal  standard  and  the  jK'rcentage 
of  COj  is  much  increased,  the  elimination  of  the  hitter  is  interfered  witli  ;  and 
Pfliiger  has  shown  that  if  the  percentage  of  COg  be  high,  dyspncea  ensues, 
notwithstanding  the  fact  that  the  blood  contains  a  normal  amount  of  O. 
When  air  contains  3  to  4  volumes  per  cent,  of  COg,  the  quantity  of  COg 
given  off  is  diminished  about  one-half.  Speck  ^  and  others  have  found  that 
the  elimination  of  COg  during  a  given  period  may  be  independent  of  b(»th 
the  percentage  of  O  in  the  inspired  air  and  the  quantity  absorbed.  An  atmo- 
sphere containing  10  volumes  per  cent,  of  COg  is  generally  believed  to  be  toxic, 
but  Wilson's^  investigations  show  that  air  having  even  as  much  as  25  to  30 
volumes  per  cent,  may  be  inhaled  with  impunity.  It  is  quite  probable  that 
in  those  cases  in  which  small  percentages  of  COg  in  the  inspired  air  have 
proven  poisonous  the  gases  were  contaminated  with  CO  (carbon  monoxide). 
Respiration  of  an  atmosphere  of  pure  COg  is  followed  within  two  or  three 
minutes  by  death. 

Worm-Miiller  found  that  when  animals  breathe  atmospheric  air  in  a  large 
closed  chamber  O  disappears  and  COg  accumulates,  and  death  finally  occurs, 
not  from  a  lack  of  O,  but  from  the  increase  of  COg,  as  is  shown  by  the  fact 
that  at  the  time  of  death  the  quantity  of  O  in  the  air  is  sufficient  to  sustain 
life.  He  has  also  shown  that  animals  placed  in  an  atmosphere  of  pure  O  die 
from  an  accumulation  of  COg  in  the  blood,  rabbits  succumbing  after  the  reten- 
tion of  a  volume  of  COj  equal  to  one-half  the  volume  of  the  body,  and  at  a 
time  when  the  atmosphere  contained  as  much  as  50  volumes  per  cent,  of  O. 

The  dyspnoea  occurring  in  an  animal  confined  in  an  air-tight  chamber  of 
miall  size  is  due  to  the  lack  of  O,  nearly  all  of  the  gas  being  ab^^orbed  before 
the  animal  dies.  If  a  cold-blooded  animal,  such  as  a  frog,  be  similarly  ex- 
posed, the  attraction  of  hemoglobin  for  O  is  so  strong  that  almo><t  every  ])ar- 
ticle  of  gas  will  pass  into  the  blood  long  before  death  occurs ;  and  even  after 
the  total  disappearance  of  O  the  elimination  of  COj  is  said  to  continue  at  the 
normal  rate. 

Animals  placed  in  a  confined  space  become  accustomed,  as  it  were,  to  the 
vitiated  air,  and  survive  longer  than  a  fresh  animal  suddenly  thrust  into  the 
poisonous  atmosphere. 

The  Respiratory  Quotient. — The  relation  between  the  (|uantities  of  O 
absorbed  and  Ci\  given  off  during  a  given  period  is  expressed  as  the  respira- 
tory quotient.  The  air  during  its  sojourn  in  the  lungs  loses  4.78  volumes  per 
cent,  of  O  and  acquires  4.34  volumes  per  cent,  of  COj,  hence  the  respiratory 

quotient    is    —~-     ._ -^  =  0.901.     This   quotient   is  subject   to  considerable 

•  Loc.  cit.  '  Amerimn  Joum.  Pharmacy,  1893,  p.  5(51. 


BESPJIiA  TION.  545 

variatioDS  not  only  in  tlifferont  species,  but  in  difTcrcnt  individuals  under 
varied  cireun»stances.     The  elilef  reasons  for  the  diHerences  are: 

First,  the  produetion  of  CO^  is  in  a  measure  independent  of  the  O  absorbed, 
as  is  proven  by  tlie  records  of  various  investigators,  showing  that  CO2  results 
both  from  oxidation-processes  and  from  intramolecular  splitting  (analogous  to 
fermentation-processes)  which  may  be  entirely  independent  of  each  other; 
that  the  quantity  of  COg  eliminated  may  continue  under  certain  circumstances 
at  the  normal  standard  even  after  the  absor[)tion  of  O  has  ceased ;  and  that 
the  quantity  of  O  contained  in  the  CO2  eliminated  during  a  given  time  may 
be  larger  than  the  actual  quantity  absorbed.  This  may  be  understood  in  a 
general  way  when  we  remember  that  the  COg  formed  in  the  body  is  not  the 
result  of  an  innnediate  oxidation  of  the  carbon-containing  material  of  the 
body ;  on  the  contrary,  some  of  the  O  absorbed  may  be  stored,  as  it  were,  in 
the  form  of  complex  compounds,  which  at  some  later  time  may  undergo  disin- 
tegration, with  the  formation  of  CO2 ;  or  the  complex  materials  introduced  as 
food  may  undergo  a  similar  disintegration  and  splitting  of  the  molecules,  with 
the  formation  of  COg  independently  of  the  direct  actiou  of  the  O  upon  them. 

Second,  a  larger  quantity  of  CO2  is  formed  per  unit  of  oxygen  from  the 
disintegration  of  certain  substances  than  from  others,  consequently  the  quotient 
must  be  affected  by  the  nature  of  the  substances  broken  down.  Thus,  in  the 
formation  of  COg  from  carbohydrates  all  of  the  O  consumed  in  the  disinte- 
gration of  the  molecules  is  used  in  forming  COj,  the  H  already  liaving  suffi- 
cient O  to  satisfy  it ;  but  in  the  case  of  fats  and  proteids  a  portion  of  the  O 
is  utilized  in  the  oxidation  of  H  to  form  HjO.  6  molecules  of  O  will  oxidize 
1  molecule  of  grape-sugar  (CgHijOg)  into  6CO2  +  GHgO ;  hence  the  quotient  is 

^^P-  =  1.     In  regard  to  fat,  if  we  take  olein,  C3H5  (0,8113302)3,  as  an  ex- 

6O2 

ample,  80  molecules  of  O  are  required  to  reduce  each  molecule  of  the  fat  to 

5  7  CO 
57  molecules  of  COg  and  52  molecules  of  H2O ;  hence  the  quotient  is  ^^^  ^ 

=  0.712.  In  the  disintegration  of  proteid  only  a  part  of  the  C  is  oxidized 
into  CO2,  the  remainder  being  eliminated  as  a  constituent  of  various  complex 
effete  bodies ;  but  it  is  estimated  that  the  quotient  for  proteids  (albumin)  is 
from  0.75  to  0.81,  depending  upon  the  completeness  of  disintegration. 

The  respiratory  quotient  varies  with  species,  food,  age,  the  time  of  day, 
internal  and  external  temperature,  muscular  activity,  the  composition  of  the 
inspired  air,  etc. 

In  regard  to  species,  the  quotient  is  higher  in  warm-blooded  (0.70  to  1.00) 
than  in  cold-blooded  animals  (0.65  to  0.75);  in  herbivora  (0.90  to  1.00)  than 
in  carnivora  (0.75  to  0.80) ;  and  in  omnivora  (0.80  to  0.90)  than  in  carnivora, 
but  lower  than  in  herbivora.  These  differences  are  due  essentially  to  diet, 
herbivora  feeding  largely  upon  carbohydrates,  omnivora  using  carbohydrates 
to  a  less  extent,  and  carnivora  practically  not  at  all.  These  observations  are 
substantiated  by  the  fact  that  during  fasting,  when  the  animal  is  feeding  ujion 
its  own  tissues,  the  respiratory  quotient  in  all  species  is  the  same  (0.7  to  0.75). 
35 


540  AN  AMERICAN   TEXT-HOOK   OF  PHYSIOLOGY. 

The  quotient  is  lowered  bv  an  animal  diet  and  increased  by  a  vegetable  diet, 
the  ratio  approximating  unity  if  the  diet  be  sufficiently  rich  in  carbohydrates. 
Hanriot  and  Ricliet '  in  observations  on  man  noted  that  before  feeding  the  quo- 
tient was  0.84  to  0.89;  when  meat  or  fat  was  given  tiie  consumption  of  ()  was 
increased,  but  there  was  no  increase  in  COg,  and  the  quotient  fell  to  0.76  ;  when 
given  potatoes  it  was  0.93;  and  when  the  diet  Was  of  glucose  it  reached  1.03. 
During  fasting  the  quotient  falls  rapidly.  The  exi)eriments  of  Zunt/  and 
Lehmann^  show  that  in  dogs  it  falls  as  low  as  0.65  to  0.68  on  the  second  day 
of  fasting,  and  that  on  the  resumption  of  food  it  rises  to  0.73  to  0.81. 

The  influence  of  age  is  manifest  in  the  fact  that  in  children  the  quotient  is 
lower  than  in  the  adult,  more  O  being  absorbed  in  proportion  to  the  COg  given 
off  than  after  full  growth  has  been  reached. 

The  quotient  undergoes  a  diurnal  variation.  The  day-time  is  more  favor- 
able than  the  night  for  the  discharge  of  CO2,  as  well  as  for  the  absor})tion  of 
O,  owing  mainly  to  greater  muscular  activity  :luring  the  day,  but  the  COj 
is  more  affected  than  the  O ;  hence  the  respirator}'  quotient  is  higher  during 
the  day.  In  the  recent  experiments  by  Saint-lNIartin '^  on  birds,  the  mean  quo- 
tient during  the  day  was  0.83  and  during  the  night  0.72 ;  the  ratio  for  CO2 
for  the  day  and  night  was  1  :  0.78,  and  for  O  1  :  0.9.  During  the  night  the 
elimination  of  COg  was  diminished  about  20  per  cent.,  while  the  absorption  of 
O  fell  only  about  10  per  cent. 

The  quotient  is  increased  by  a  rise  of  external  temper atm-e.  Thus,  Pfliiger 
and  Finkler  found  in  guinea-pigs  that  the  quotient  was  0.83  at  3.64°  and  0.94 
at  26.21°.  AVhen  the  bodily  temperature  is  increased,  as  in  fever,  the  respira- 
tory quotient  remains  practically  unaltered.  When  the  temperature  falls  below 
the  normal  the  respiratory  quotient  increases. 

Muscular  activity  is  also  an  important  factor.  During  rest  the  consumption 
of  O  by  muscles  is  greater  than  the  production  of  CO2,  while  during  contrac- 
tion the  difference  becomes  less  and  less  in  proportion  to  the  degree  of  activity, 
until  finally  more  CO2  may  be  given  off  than  there  is  O  consumed.  Sczelkow 
found  in  experiments  on  muscles  of  rabbits  at  rest  and  in  tetanus  that  the 
respiratory  quotient  was  decidedly  increased,  A  mean  of  six  experiments 
gives  as  the  quotient  during  rest  0.543  and  during  tetanus  0.933  ;  in  one-half 
of  the  experiments  it  went  above  1,  and  in  one  instance  to  1.13. 

During  sleep  the  output  of  CO2  is  diminished  more  than  the  consumption 
of  O  (p.  542),  so  that  the  respiratory  quotient  is  less  than  when  awake  and 
quiet. 

During  hybernation  the  quotient  falls  to  a  minimum — in  the  marmot  as  low 
as  0.49.  This  is  due  chiefly  to  the  more  decided  falling  off  in  the  quantity  of 
CO2,  the  CO2  being  reduced  to  j\,  and  the  O  to  only  ^L;  the  animal,  however, 
is  not  only  in  a  state  of  muscular' quiet,  but  fasting,  which,  it  will  be  remem- 
bered, is  an  important  factor  in  lowering  the  quotient. 

'  Compt.  rend.,  1888,  vol.  106,  pp.  496-498. 
. «  Berliner  klin.  Woch.,  1887,  p.  428. 
»  Compt.  rend.,  1887,  vol.  105,  pp.  1124-1128. 


RESPIRATION.  547 

When  the  paxentage  of  0  in  the  inspired  air  falls  so  low  as  to  cause  marked 
(lyspiKjea,  the  respiratory  quotient  ra[)i(lly  rises.  This  is  owing  ou  the  one 
hand  to  the  diminished  quantity  of  O  absorbed,  and  on  the  other  hand  to  the 
increased  production  of  COj  as  a  consequence  of  excessive  activity  of  the 
muscles  of  respiration.  Speck  (p.  543)  found  that  when  the  proportion  of  O 
was  very  low  the  quotient  rose  as  high  as  2.258. 

E.  Principles  of  Ventilation. 

Breathing  within  a  confined  space,  as  in  a  small  unventilated  room  or  in  a 
large  room  in  which  a  considerable  number  of  persons  are  assembled,  causes 
a  gradual  diminution  in  the  quantity  of  O  and  an  accumulation  of  CO,,  moist- 
ure, and  organic  matter.  In  regard  to  O,  even  in  the  worst  ventilated  rooms 
the  atmosphere  seldom  contains  as  little  as  15  volumes  per  cent.,  which  is  suffi- 
cient to  permit  of  undisturbed  respiration.  When  the  proportion  of  CO2 
exceeds  0.07  volume  per  cent,  the  air  becomes  disagreeable,  close,  and  stuffy — 
oflPensive  characters  which  are  due  neither  to  the  increase  of  COg  nor  to  a 
deficiency  of  O,  but  to  the  presence  of  organic  matter  termed  ^'  crowd-poison." 
Air  from  which  this  organic  exhalation  is  absent  may  contain  considerably 
more  COg  without  causing  any  unpleasant  etfects.  In  well- ventilated  rooms 
the  proportion  of  COg  does  not  exceed  0.05  to  0.07  volume  per  cent. ;  in 
badly-ventilated  rooms  it  may  reach  0.25  to  0.30  volume  per  cent. ;  while 
when  a  large  number  of  individuals  are  crowded  together,  as  in  lecture- 
rooms,  it  may  be  as  high  as  0.70  to  0.80  volume  per  cent.  This  vitiation  is 
further  increased  by  the  burning  of  gas  or  oil,  150  liters  of  ordinary  coal-gas 
(enough  to  supply  a  large  burner  for  about  an  hour)  consuming  all  the  O  in 
1200  liters  of  air,  or  as  much  O  as  is  required  by  the  average  individual 
in  eight  hours,  besides  loading  the  air  with  various  deleterious  products  of 
combustion. 

While  the  accumulation  of  CO2  even  in  the  worst  ventilated  rooms  is  not 
in  itself  pernicious,  its  percentage  is  a  practical  working  index  of  the  amount 
of  organic  matter  present,  and  therefore  of  the  degree  of  vitiation.  It  has 
long  been  recognized  that  the  atmosphere  of  crowded,  badly-ventilated  rooms 
is  poisonous,  but  the  precise  nature  of  the  toxic  element  is  unknown.  Brown- 
Sequard  and  d'Arsonval  condensed  the  moisture  of  the  expired  air  and  found 
that  from  20  to  40  cubic  centimeters  would  kill  a  guinea-pig;  but  their  results 
have  been  contradicted  positively  by  Dastre  and  Loye,  Lehmann,  Geyer,  and 
others.  The  poison  in  expired  air,  whatever  it  may  be,  is  of  an  impalpable 
nature,  and  is  neither  dissolved  nor  condensed  in  the  moisture  exhaled. 

The  quantity  of  fresh  air  required  during  a  given  period  depends  upon  the 
size  of  the  individual,  the  degree  of  activity,  and  the  size  of  the  air-space. 
Assuming  that  an  individual  eliminates  900  grams,  or  458  liters,  of  COj  per 
diem,  and  that  the  percentage  of  CO,  is  to  be  kept  at  a  standard  not  exceeding 
0.07  volume  per  cent.,  there  would  be  required  at  least  1,440,000  liters  of 
fresh  air  during  twenty-four  hours,  or  about  60,000  liters  (2000  cubic  feet)  per 


548  AN  AMUR/CAN   TEXT-BOOK   OF  PHYSIOLOGY. 

hour.  All  circumstances,  such  as  muscular  activity,  which  increase  the  outj)ut 
of  CO2  augment  the  demand  for  fresh  air.  When  confined  in  rooms,  every 
pei-sou  should  have  an  air-space  equal  to  about  28,000  litei-s,  or  1000  cubic 
feet,  the  floor-space  should  not  be  less  than  -^  of  the  cubic  capacity  of  the 
room,  and  the  air  should  be  renewed  as  often  as  twice  an  hour.  In  lecture- 
rooms,  school-rooms,  etc.  the  air-space  per  individual  is  usually  very  small,  so 
that  the  renewal  nnist  be  more  frequent  and  in  proportion  to  the  limitation  of 
space  per  individual. 

Ventilation  is  accomplished  by  natural  and  artificial  means.  The  forces  of 
the  wind,  the  differences  in  temperature  within  and  without  the  building,  the 
natural  diffusion  of  gases  owing  to  variations  in  composition,  etc.,  all  cause 
more  or  less  circulation.  Artificial  ventilation  is  effected  by  the  use  of  proper 
appliances  for  the  forced  introduction  of  air  into  and  expulsion  from  apartments. 

F.  The  Effects  of  the  Respiration  of  Various  Gases. 

The  respiration  of  pure  O  takes  place  without  disturbance  of  the  respiratory 
processes,  but  dyspnoea  is  developed  when  the  inspired  air  contains  less  than  13 
volumes  per  cent.  (p.  543).  Respiration  of  pure  CO2  (p.  544)  is  fatal  within 
two  or  three  minutes,  but  an  atmosphere  containing  as  much  as  25  to  30  per 
cent,  may  be  respired  for  a  few  minutes  without  ill  effect  (p.  544).  Nitrogen, 
hydrogen,  and  carburetted  hydrogen  (CHJ  may  be  inhaled  with  impunity  if 
they  contain  not  less  than  13  volumes  per  cent,  of  O.  The  respiration  of 
nitrous  oxide  or  of  air  containing  much  ozone  rapidly  produces  anaesthesia, 
unconsciousness,  and  death.  Carbon  monoxide  (CO)  and  cyanogen  are  decid- 
edly toxic,  combining  with  haemoglobin  and  displacing  oxygen.  Sulphuretted 
hydrogen,  phosphoretted  hydrogen,  arseniuretted  hydrogen,  and  antimoniu- 
retted  hydrogen  are  all  poisonous  and  are  all  destructive  to  ha?moglobin.  An 
atmosphere  containing  0.4  volume  per  cent,  of  sulphuretted  hydrogen  is  said 
to  be  toxic.  Air  containing  2  volumes  per  cent,  of  CO  (carbon  monoxide)  is 
quickly  fatal.  Certain  gases  and  vapors — as,  for  instance,  ammonia,  chlorine, 
bromine,  ozone,  etc. — produce  serious  irritation  of  the  respiratory  passages,  and 
may  in  this  way  cause  death. 

G.  Effects  of  the  Gaseous  Composition  of  the  Blood  on  the 

Respiratory  Movements. 

Certain  terms  are  employed  to  express  peculiarities  in  the  respiratory  phe- 
nomena :  Eupncea  is  normal,  fpiict,  and  easy  breathing,  ^pnoga  is  a  suspen- 
sion of  the  respiratory  movements.  Hijperpnoea  is  a  condition  of  increased 
respiratory  activity.  Poli/pnoea,  thcrmopoli/pnfra,  and  hcat-dyspncca  are  forms 
of  hyperpnoea  due  to  heating  the  blood  or  the  skin.  Dyspnoea  is  distinguished 
by  deep  and  labored  breathing ;  the  respiratory  rate  is  usually  less  than  the 
normal,  but  in  some  forms  it  may  be  higher.  Asphyxia  (suffocation)  is  cha- 
racterized by  infrequent,  feeble,  and  shallow  respirations. 

Eupnoea  is  the  condition  of  respiration  observed  during  bodily  and  mental 


BESPIRA  TION.  549 

([iiiet,  the  quantities  of  O  and  CO^  in  tlit'  hloocl  being  within  the  normal  mean 
limits. 

Apnoca  may  bo  produced  l)y  lapidly  repeated  respirations  of  atmospheric 
air,  under  \vhi<;li  circumstances  the  respiratory  movements  may  be  arrested  for 
a  period  vurvin*;-  from  a  few  seconds  to  a  minute  or  more.  This  condition  is 
produced  most  easily  upon  animals  which  have  been  tracheotomized  and  con- 
nected with  an  artificial  respiration  apparatus.  If  under  these  conditions  the 
lungs  are  repeatedly  inflated  with  sufficient  frequency,  and  the  blasts  are  then 
suspended,  the  animal  will  lie  quietly  for  a  certain  period  in  a  condition  of 
apncea.  The  respirations  after  a  time  begin,  usually  with  very  feeble  move- 
ments which  quickly  increase  in  strength  and  depth  to  the  normal  type.  The 
ultimate  cause  of  apncea  is  still  a  mooted  question,  and  the  heretofore  prevalent 
belief  that  it  is  due  to  hyperoxygenatiou  of  the  blood  is  almost  entirely  dis- 
carded. The  connection  between  the  quantity  of  O  in  the  blood  and  apnoea 
is,  however,  suggested  by  several  facts :  thus,  apnoea  is  more  marked  after  the 
respiration  of  pure  O  than  after  that  of  atmospheric  air,  and  less  marked  if  the 
air  is  deficient  in  O ;  moreover,  Ewald  states  that  the  arterial  blood  of  apnoeic 
animals  is  saturated  with  O.  These  facts  naturally  lead  to  the  inference  that  the 
blood  is  surcharged  with  O,  and  that  the  respiratory  movements  are  arrested 
until  the  excess  of  O  is  consumed  or  until  sufficient  COg  accumulates  in  the 
blood  to  excite  respiratory  movements.  But  Head  ^  has  shown  that  apnoea  can 
be  caused  by  the  inflation  of  the  lungs  with  pure  hydrogen  as  well  as  by  infla- 
tion with  air  or  with  pure  O,  although  the  apnoeic  pause  after  the  cessation  of 
the  infliations  is  not  so  long  or  may  be  absent  altogether ;  while  Ewald's  asser- 
tion as  to  the  saturation  of  the  blood  with  O  is  contradicted  by  Hoppe-Seyler, 
Gad,  and  others.  The  fact  that  the  apnoeic  pause  exists  for  a  longer  period 
when  O  is  respired  lends  confirmation  to  Gad's  theory  that  it  is  due  in  part  to 
the  large  amount  of  O  carried  into  and  stored  up,  as  it  were,  in  the  alveoli — 
an  amount  sufficient  to  supply  the  blood  for  a  certain  period  and  thus  to  dis- 
pense with  respiratory  movements.  Gad  found  that  even  when  apncea  follows 
the  inflation  of  the  lungs  with  air,  the  air  in  the  lungs  contains  enough  O  to 
supply  the  blood  during  the  period  occupied  by  the  blood  in  making  a  com- 
plete circuit  of  the  system.  The  fact,  however,  that  apnoea  can  be  caused 
by  the  inflation  of  the  lungs  by  an  indifferent  gas  such  as  hydrogen,  by 
which  every  particle  of  O  may  be  driven  from  the  lungs,  certainly  shows 
that  there  exists  some  important  factor  apart  from  theO;  and  this  assump- 
tion receives  support  in  the  observation  that  after  section  of  the  pneumo- 
gastric  nerves  (the  channels  for  the  conveyance  of  sensory  impulses  from 
the  lungs  to  the  respiratory  centre)  it  is  very  difficult  to  cause  apnoea  by  in- 
flation of  the  lungs  with  air,  while  if  pure  hydrogen  is  used  violent  dyspnoea 
results.  It  seems,  then,  that  apnoea  cannot  be  produced  after  division  of  the 
vagi  unless  there  be  an  accumulation  of  O  in  the  lungs.  These  facts  suggest 
that  the  frequent  forced  inflations  of  the  lungs  excite  the  pulmonic  peripheries 
of  the  pneumogastric  nerves,  thus  generating  impulses  which  inhibit  the  inspi- 
^  Journ.  Physiology,  1889,  vol.  10,  pp.  1,  279. 


ooO  ^.V  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

ratoiy  discharges  from  the  respiratory  centre.  This  view  receives  further  su[i- 
port  in  several  facts  :  first,  that  the  same  number  of  inflations,  whether  of  pure 
O,  of  air,  or  of  H,  causes  apncea,  the  only  difference  l)eing  the  length  of  the 
apna?ic  pause  after  the  cessation  of  artificial  respiration,  which  pause  lasts  for 
the  longest  period  when  O  is  used,  and  for  the  shortest  period,  or  not  at  all, 
when  II  is  employed;  second,  that  apiuea  cannot  be  caused  by  inflation  of  the 
lungs  with  H  if  the  pneumogastric  nerves  be  previously  divided  ;  third,  that  the 
arrest  of  respiration  which  occurs  during  swallowing  ("  deglutition-apncea  ") 
is  due  to  an  inhibition  of  the  respiratory  centre  by  impulses  generated  in  the 
terminations  of  the  glosso-pharyngeal  nerves  (p.  570).  It  therefore  seems  evi- 
dent that  apncea  may  be  due  to  either  gaseous  or  mechanical  factors,  or  to  both, 
the  former  being  effective,  not  because  of  the  blood  being  saturated  with  O, 
but  because  of  the  increased  amount  of  O  in  the  alveoli — a  quantity  sufficient 
for  a  time  to  aerate  the  blood  ;  while  the  mechanical  factors  give  rise  to  inhibi- 
tory impulses  which  suspend  for  a  longer  or  shorter  period  the  rhythmical 
inspiratory  discharges  from  the  respiratory  centre,  doubtless  by  depressing  the 
irritability  of  this  centre  (p.  563).  From  the  experiment  quoted  it  seems  that 
the  first  of  these  factoi'S  may  alone  be  sufficient  to  cause  apnoea,  but  that  apncea 
is  more  easily  produced,  and  lasts  longer,  when  both  factors  act  together,  as  is 
usually  the  case. 

Polypnoea,  thermopolypnoea,  and  heat-dyspncea  are  due  to  a  direct  excitation 
of  the  respiratory  centres  through  an  increase  of  the  temperature  of  the  blood, 
or  reflexly  by  excitation  of  the  cutaneous  nerves  by  external  heat.  This  con- 
dition may  be  produced,  as  was  done  by  Goldstein,  by  exposing  the  carotids 
and  placing  them  in  warm  tubes,  thus  heating  the  blood ;  or,  as  was  done  by 
Richet  and  others,  by  subjecting  the  body  to  high  external  heat.  Richet  in 
employing  this  latter  method  found  that  dogs  so  exposed  may  have  a  respira- 
tory rate  as  high  as  400  per  minute.  Ott  records  marked  polypncea  as  a  result 
of  direct  irritation  of  the  tuber  cinereum.  This  form  of  hyperpn(ea  is  entirely 
independent  of  the  gaseous  composition  of  the  Ijlood ;  moreover,  an  animal  in 
heat-dyspnoea  cannot  be  rendered  apnoeic,  even  though  the  blood  be  so  thor- 
oughly oxygenated  that  the  venous  blood   is  of  a  bright  arterial  hue. 

Dyspnoea  is  generally  characterized  by  slow,  deep,  and  labored  respiratory 
movements,  although  in  some  instances  the  rate  may  be  increased.  Several 
distinct  forms  are  observed :  "  O-dyspnnoa,"  due  to  a  deficiency  of  O ; 
"  COj-dyspnoea,"  due  to  an  excess  of  COg  in  the  blood ;  a  form  of  dyspnoea 
due  to  substances  imparted  to  the  blood  by  the  muscles  during  activity ;  and 
cardiac  and  hemorrhar/ic  dyspnoeas,  belonging  to  the  O  category. 

Dys])noeas  due  to  the  gaseous  composition  of  the  blood  maybe  caused  either 
by  a  deficiency  of  O  or  by  an  excess  of  CO^,  but  are  generally  due  to  both. 
Dyspnoea  from  a  deficit  of  O  is  observed  when  an  animal  is  j^laeod  within  a 
small  closed  chamber,  or  when  an  indifferent  gas,  such  as  pure  hydrogen  or 
nitrogen,  is  respired.  Under  the  latter  circumstances  dyspnoea  occurs  even 
though  the  quantity  of  COj  in  the  blood  be  below  the  normal.  If,  on  the 
contrary,  the  animal  be  compelled  to  breathe  an  atmosphere  containing  10  vol- 


RESPIRA  TION.  551 

limes  per  cent,  of  COg,  dyspnoea  occurs,  notwithstanding  an  abundance  of  O 
(p.  544)  both  in  the  air  and  in  the  blood  ;  indeed,  the  quantity  of  O  in  the 
blood  maybe  above  the  normal.  Fredericq  •  in  ingenious  experiments  has 
directly  demonstrated  the  influence  of  the  quantity  of  CO^  in  the  blood  upon 
the  respiratory  movements.  He  took  two  rab))its  or  dogs,  A  and  H,  ligated  the 
vertebral  arteries  in  each,  exposed  the  carotids,  and  ligated  one  in  each  animal. 
The  other  carotid  in  each  was  cut,  and  the  peripheral  end  of  the  vessel  of  one 
was  connected  by  means  of  a  cannula  with  the  central  end  of  the  vessel  of  the 
other,  so  that  the  blood  of  animal  A  supi)lied  the  head  (respiratory  centre)  of 
animal  B,  and  vice  versd.  When  the  trachea  of  animal  A  was  ligated  or  com- 
pressed the  animal  b  showed  signs  of  dyspnoea,  because  its  respiratory  centre 
was  now  supplied  with  the  venous  blood  from  A.  Ou  the  contrary,  animal  a 
exhibited  (piiet  respirations,  almost  apnoeic,  because  its  centre  received  the 
thoroughly  arterialized  blood  from  B,  in  which  the  respiratory  movements  were 
augmented.  In  a  second  series  of  experiments  blood  was  transfused  through 
the  head :  when  the  blood  was  laden  with  COa  marked  dyspnoea  resulted ; 
when  arterial  blood  was  transfused  the  normal  respirations  were  restored. 

While  dyspnoea  may  be  caused  by  the  respiration  of  an  atmosphere  either 
deficient  in  O  ("  O-dyspnoea ")  or  containing  an  excess  of  CO^  ("  C^Og-dysp- 
noea  "),  the  phenomena  in  the  two  cases  are  in  certain  respects  different :  When 
an  animal  breathes  pure  N,  thus  causing  O-dyspnoea,  the  dyspnoea  is  character- 
ized especially  by  frequent  respiratory  movements  with  vigorous  insjjirations, 
whereas  if  the  atmosphere  be  rich  in  O  and  contain  an  excess  of  COg  the 
respirations  are  especially  marked  by  a  slower  rate  and  by  the  depth  and  vigor 
of  the  expirations ;  O-dyspnoea  continues  for  a  long  time  before  death  ensues, 
and  is  more  severe ;  in  O-dyspnoea  the  absorption  of  O  is  diminished,  but  the 
excretion  of  COg  is  practically  unaffected  ;  in  O-dyspnoea  the  attendant  rise  of 
blood-pressure  (p.  555)  is  more  marked  and  lasting ;  in  O-dyspnoea  death  is 
preceded  by  violent  motor  disturbauces  which  are  absent  in  COg-dyspnoea. 
Blood  poor  in  O  (O-dyspnoea)  affects  chiefly  the  inspiratory  portion  of  the 
respiratory  centre  (p.  565),  while  blood  rich  in  COg  (COa-dyspnooa)  affects 
chiefly  the  expiratory  portion  ;  hence  in  the  former  the  dyspnoea  is  manifest 
especially  in  an  increase  in  the  fi-eqnency  of  the  respirations  (hyperpnoea)  and 
in  the  vigor  of  the  inspirations,  while  in  the  latter  it  is  manifest  in  a  lessened 
rate,  strong  expirations,  and  expiratory  pauses. 

The  marked  increase  in  the  depth  of  the  respiratory  movements  in  COg- 
dyspnoea  is  not  solely  due  to  the  direct  action  of  COg  upon  the  respiratory 
centre,  for  Gad  and  Zagari^  have  shown  that  COj  in  abundance  in  inspired  air 
acts  upon  the  terminations  of  the  sensory  nerves  of  the  larger  bronchi  and 
thus  reflexly  excites  the  respiratory  centre.  In  a  research  on  dogs  these  ob- 
servers opened  the  trachea  and  passed  glass  tubes  through  the  trachea  and  the 
larger  bronchi  to  the  smaller  bronchi.  Before  the  tubes  were  inserted  the 
inhalation  of  COg  caused  a  considerable  deepening  of  the  respiratory  move- 

i  Bull.  Acnd.  Roy.  Med.  Belgique,  vol.  13,  pp.  417-421. 
*  DuBois-Reymond's  Archiv  f.  Pkysiologie,  1890,  p.  588. 


5r)2  AN  AMERICAN    TEXT- HOOK   OF   PHYSIOLOGY. 

nieuts,  l)iit  after  tlio  insertion  of  the  tubes,  by  means  of  \vbi(  li  the  gas  was 
earried  directly  to  the  smaller  brondii,  the  characteristic  action  of  the  CO^  wits 
no  lon<;er  observed.  From  the  results  of  these  experiments  we  may  con- 
clude that  the  marked  increase  in  the  depth  of"  the  respiratory  mctvements 
in  COg-dyspnoea  is  due  in  part  to  the  irritation  of  the  sensory  nerve-fibres  of 
the  mucous  membrane  of  the  larger  bronchi. 

Till'  form  of  dyspnani  due  to  miisoular  activifi/  is  owing  to  the  action  upon 
the  re.si)iratory  centre  of  certain  substances  which  are  formed  in  the  muscles 
during  contraction  and  are  given  to  the  blootl.  Muscular  activity,  as  is  well 
known,  is  accompanied  by  an  increase  in  the  rate  and  depth  of  the  respiratory 
movements,  and  when  the  exercise  is  violent  more  or  less  marked  dyspuwa 
may  occur.  Some  physiologists  have  been  led  to  the  belief  that  the  respiratory 
centre  is  connected  directly  or  indirectly  with  the  muscles  by  means  of  afferent 
nerve-fibres  which  convey  im})ulses  to  the  centre  and  thus  excite  it  to  activity; 
while  others  have  regarded  a  ditninution  of  O  and  an  increase  of  COg  in  the 
blood  as  the  cause,  the  active  nmscles  rapidly  consuming  the  O  in  the  blocxl 
and  giving  oil"  COg  in  great  abundance;  but  Gepj)ert  and  Zuntz  ^  have  clearly 
shown  that  neither  of  these  theories  is  tenable,  and  that  the  respiratory  excita- 
tion is  due  to  products  of  muscular  activity  which  are  given  to  the  blood  and 
which  act  as  powerful  excitants  to  the  respiratory  centre.  The  precise  nature 
of  the  bodies  is  unknown,  but  it  is  probable  that  they  are  of  an  acid  character, 
for  Lehmann  ^  found  that  there  was  a  distinct  lessening  of  the  alkalinity  of 
the  blood  after  muscular  exercise.  It  is  likely  that  the  bodies  are  broken  up 
in  the  system,  because  the  results  of  Loewy's'  investigations  indicate  that  they 
are  not  removed  by  the  kidneys. 

Cardiac  and  hemorrharjic  dyspnoeas  are  chiefly  due  to  tlie  deficiency  in  the 
supplv  of  O — the  former,  to  the  poor  supply  of  blood  due  to  the  enfeebled  action 
of  the  heart ;  and  the  latter,  l)oth  to  this  and  to  the  reduced  quantity  of  blood 
(haemoglobin).  All  circumstances  which  enfeeble  the  circulation  or  lessen  the 
quantity  of  hrcmoglobin  therefore  tend  to  cause  dyspnoea  ;  hence  individuals 
Avith  heart  troubles  or  weakened  by  disease  or  with  certain  forms  of  anaemia 
are  apt  to  suffer  from  dyspmea  uj)on  the  least  exertion. 

All  circumstances  which  interfere  with  the  interchange  of  O  and  the 
elimination  of  CO2  in  the  lungs  are  favorable  to  the  production  of  dyspnoea, 
as  in  pneumonia,  pulmonary  tuberculosis,  growths  of  the  larnyx,  abdominal 
tumors,  etc.,  especially  so  upon  exertion. 

Asphyxia  is  literally  a  state  of  pidselcssness,  but  the  term  is  now  used  to 
express  a  series  of  phenomena  caused  by  the  deprivation  of  air,  as  by  j)lacing 
an  animal  in  a  closed  chamber  of  moderate  size.  These  phenomena  may  be 
divided  into  three  stages:  the  first  is  one  of  hyperpnoea ;  the  second,  of 
developing  dyspnoea,  and  finally  of  convidsions ;  and  the  third,  of  collapse. 
During  the  first  stage  the  ins])iratory  portion  of  the  respiratory  centre 
especially  is  excited,  the  respirations  being  increased   in  frequency  and  dejUh. 

'  Pfluger's  Archiv  f.  Physiologic,  1888,  vol.  A2,  p.  189.  ''  Ibid.,  p.  284. 

'IbicLy,.  -JSl. 


RESPIRA  TION.  553 

During  the  second  stage  the  excitation  of  the  expiratory  portion  of  the  respiratory 
centre  is  more  intense  tlian  that  of  the  inspiratory  portion,  so  that  the  respira- 
tions become  slow  and  deep,  prolonged  and  convnlsive,  and  tiie  moven)ents  of 
inspiration  are  feeble  and  in  striking  contrast  to  the  violent  spasmodic  expira- 
tory efforts.  During  the  third  stage  the  dyspno'a  is  followed  by  general 
exhaustion  ;  the  resi)irations  are  shallow  and  occur  at  longer  and  longer  inter- 
vals, the  pupils  become  dilated,  the  motor  reflexes  disappear,  consciousness  is 
lost,  the  inspiratory  muscles  contract  spasmodically  with  each  ins})iratory  act, 
convulsive  twitches  are  observed  in  the  muscles  of  the  extremities  and  else- 
where, gasping  and  snapping  respiratory  movenients  may  be  present,  the  legs 
are  rigidly  outstretched  and  the  head  and  body  are  arched  backward,  feces  and 
urine  are  usually  voided,  respiratory  movements  cease,  and  finally  the  heart 
stops  beating.  During  these  stages  the  circulation  has  undergone  considerable 
disturbances.  During  the  first  and  second  stages  the  blood  has  been  robbed 
of  nearly  all  its  O,  the  gums,  lips,  and  skin  become  cyanosed,  and,  owing  to  the 
venous  condition  of  the  blood,  the  cardio-inhibitory  centre  has  been  decidedly 
excited,  so  that  the  heart's  contractions  are  rendered  less  frequent ;  the  vaso- 
constrictor centre  for  the  same  reason  has  also  been  excited,  causing  a  con- 
striction of  the  capillaries  and  an  increase  of  blood-pressure.  During  the 
third  stage  these  centres  are  depressed  and  finally  are  paralyzed. 

If  asphyxia  be  caused  by  ligating  the  trachea,  the  whole  series  of  events 
covers  a  period  of  four  to  five  minutes,  the  first  stage  lasting  for  about  one 
minute,  the  second  a  little  longer,  and  the  third  from  two  to  three  minutes. 
If  asphyxia  be  produced  gradually,  as  by  placing  an  animal  within  a  relatively 
large  confined  air-space,  death  may  occur  without  the  appearance  of  any  motor 
disturbances  (p.  544). 

The  heart  usually  continues  beating  feebly  for  several  minutes  after  the 
cessation  of  respiration,  so  that  by  means  of  artificial  respiration  it  is  possible 
to  restore  the  respiratory  movements  and  other  suspended  functions.  After 
death  the  blood  is  very  dark,  almost  black.  The  arteries  are  almost  if  not 
entirely  empty,  while  the  veins  and  lungs  are  engorged. 

Death  from  drowning  occurs  generally  from  the  failure  of  respiration, 
occasionally  from  a  cessation  of  the  heart's  contractions.  It  is  more  difficult 
to  revive  an  animal  asphyxiated  in  this  way  than  one  which,  out  of  water,  has 
simply  been  deprived  of  air  for  the  same  length  of  time.  Dogs  submerged 
lor  one  and  a  half  minutes  can  rarely  be  revived,  but  recovery  can  usually  be 
accomplished  after  deprivation  of  air,  out  of  water,  for  a  period  four  to 
five  times  longer.  After  a  person  has  been  submerged  for  five  minutes  it  is 
extremely  difficult  to  effect  resuscitation. 

H.  Artificial  Respiration. 

Effective  methods  for  maintaining  ventilation  of  the  lungs  are  important 
alike  to  the  experimenter  and  to  the  clinician.  In  the  laboratory  the  usual 
method  is  to  expose  the  trachea,  insert  a  cannula  (Fig.  139),  and  then  period- 
ically force  air  into  the  lungs  by  means  of  a  pair  of  bellows  or  a  pump.     Some 


554         ^AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

of  the  forms  of  ajiparatus  arc  very  simple,  wliile  others  are  complicated.     An 
ordinarv  pair  of  bellows  does  very  well  for  short  experiments,  but  for  longer 

study,  especially  when  it  is  necessjuy 
that  the  supply  of  air  should  be  uniform, 
the  bellows  are  operated  by  power. 
Some  of  these  instruments  are  so  con- 
structed that  air  is  alternately  forced 
into  and  withdrawn  from  the  lungs. 

Periodical    in  Hat  ion   of  the  lungs  is 

termed  po.sitire  ventilation ;  the  period- 

Fi.;.  i:'.'.i.-r;iiiiiuhL  for  au-s  ^-M  aiui  for  cats       ical  withdrawal   of  air  from  the  lungs 

rabbits  (b).  y^^^  suction  is  negative  ventilation  ;  and 

alternate  inflation  and  suction   is  compound  ventilation. 

In  practising  artificial  respiration  we  should  imitate  the  normal  rate  and 
depth  of  the  respiratory  movements.  Long-continued  positive  ventilation 
causes  cerebral  anaemia,  a  fall  of  blood-pressure,  and  decrease  of  bodily  tem- 
perature. 

In  human  beings  it  is  not  practicable,  except  under  extraordinary  circum- 
stances, to  inflate  the  lungs  by  the  above  methods,  so  that  we  are  dependent 
upon  such  means  as  Avill  enable  us  to  expand  and  contract  the  thoracic  cavity 
without  resorting  to  the  knife.  One  method  is  to  place  the  individual  on  his 
back,  the  operator  taking  a  position  on  his  knees  at  the  head,  facing  the  feet. 
The  lower  ribs  are  grasped  by  both  hands  and  the  lower  antero-latei'al  portions 
of  the  thorax  are  elevated,  thus  increasing  the  thoracic  capacity,  with  a  conse- 
quent drawing  of  air  into  the  lungs;  the  ribs  and  the  abdominal  muscles  are 
then  pressed  upon  in  imitation  of  expiration.  These  alternate  movements  are 
kept  up  as  long  as  necessary. 

The  methods  of  Marshall  Hall  and  Sylvester  are  now  classic,  and  should 
be  learned  thoroughly  by  every  jihysician.  Marshall  Hall's  method  is  as 
follows  :  "  After  clearing  the  mouth  and  throat,  place  the  patient  on  the  face, 
raising  and  supporting  the  chest  well  on  a  folded  coat  or  other  article  of  dress. 
Turn  the  body  very  gently  on  the  side  and  a  little  beyond,  and  then  briskly 
on  the  face,  back  again,  repeating  these  measures  cautiously,  efficiently,  and 
perseveringly  about  fifteen  times  in  the  minute,  or  one  every  four  or  five 
seconds,  occasionally  varying  the  side.  By  placing  the  patient  on  the  chest 
the  weight  of  the  body  forces  the  air  out ;  when  turned  on  the  side  this  pres- 
sure is  removed  and  air  enters  the  chest.  On  each  occasion  that  the  body  is 
replaced  on  the  face,  make  uniform  but  efficient  pressure  with  brisk  move- 
ments on  the  back,  between  and  below  the  shoulder-blades  or  bones  on  each 
side,  removing  the  })ressure  immediately  before  turning  the  body  on  the  side. 
During  the  whole  of  the  operations  let  one  person  attend  solely  to  the  move- 
ments of  the  head  and  of  the  arm   placed  under  it." 

The  following  is  Sylvester's  method  :  "  Place  the  patient  on  the  back,  on  a 
flat  surface  inclined  a  little  upward  from  the  feet;  raise  and  support  the  head 
and  shoulders  on  a  small  firm  cushion  or  folded  article  of  dress  placed  under 


BESPIRA  TION.  555 

the  shoulder-blades.  Draw  forward  the  patient's  tongue,  and  keep  it  project- 
ing bevond  the  lips ;  an  elastic  band  over  the  tongue  and  under  the  chin  will 
answer  this  purpose,  or  a  piece  of  string  or  tape  may  l)e  tied  around  them,  or 
bv  raising  the  lower  jaw  tiic  teeth  may  be  made  to  retain  the  tongue  in  that 
position.  Remove  all  tight  clothing  from  about  tlie  neck  and  chest,  especially 
the  braces  ",...*'  To  imitate  the  movements  of  breathing  :  {Standing  at  the 
patient's  head,  grasp  the  arms  just  above  the  elbows,  and  draw  the  arras  gently 
and  steadily  upward  above  the  head,  and  keep  them  stretched  u])\\ard  for  two 
seconds.  By  this  means  air  is  drawn  into  the  lungs.  Then  turn  down  the 
patient's  arms,  and  press  them  gently  and  firndy  for  two  seconds  against  the 
sides  of  the  chest.  By  this  means  air  is  pressed  out  of  the  lungs.  Repeat 
these  measures  alternately,  deliberately,  and  perseveringly  about  fifteen  times 
in  a  minute,  until  a  spontaneous  effort  to  respire  is  perceived,  immediately 
upon  Avhich  cease  to  imitate  the  movements  of  breathing,  and  proceed  to 
induce  circulation  and  warmth." 

The  restoration  of  respiratory  movements  is  usually  facilitated  by  periodical 
traction  of  the  tongue,  which  acts  as  a  reflex  stimulus  to  the  respiratory  centre. 

I.  The  Effects  of  the  Respiratory  Movements  on  the 

Circulation. 

The  respiratory  movements  are  accompanied  by  marked  changes  in  the  cir- 
culation. If  a  tracing  be  made  of  the  blood-pressure  and  the  pulse  (Fig.  140), 
and  at  the  same  time  the  inspiratory  and  expiratory  movements  be  noted,  it 


Fig.  140.— Blood-pressure  and  pulse  tracing  showing  the  changes  during  inspiration  (is.)  and  expi- 
ration (EX.). 

will  be  seen  that  the  blood-pressure  begins  to  rise  shortly  after  the  onset  of 
inspiration,  commonly  after  a  period  occupied  by  one  to  three  heart-beats,  and 
reaches  a  maximum  after  the  lapse  of  a  similar  brief  interval  after  the  begin- 
ning of  expiration,  when  it  begins  to  fall,  reaching  a  minimum  after  the 
beginning  of  the  next  inspiration.  During  inspiration  the  pulse-rate  is  more 
frequent  than  during  expiration  and  the  character  of  tlie  pulse-curve  is  some- 
what different. 

The  Effects  on  Blood-pressure. — The  changes  in  blood-pressure  are 
mechanical  effects  due  to  the  actions  of  the  respiratory  movements.  When  it 
is  remembered  that  the  lungs  and  the  heart  with  their  great  blood-vessels  are 
placed  within  an  air-tight  cavity,  that  the  lungs  become  inflated  through  the 
aspiratory  action  of  the  muscles  of  inspiration,  and  that  during  inspiration 


55(3  AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

intrathoracic  negative  pressure  is  increased,  it  is  easy  to  understniid  liuw  the 
action  wliich  causes  inflation  oi"  the  hnigs  must  affect  in  like  manner  such 
hollow  clastic  structures  as  the  heart  and  the  great  blood-vessels,  and  tlms 
influence  the  circulation.  It  is  obvious,  however,  that  this  influence  must  make 
itself  felt  to  a  more  marked  degree  n])on  the  vessels  than  upon  the  heart,  and 
upon  tlie  flaccid  Avails  of  the  veins  than  upon  the  comparatively  rigid  walls  of 
the  arteries.  JNIoreover,  the  effects  upon  the  flow  of  blood  tlirough  the  vessels 
entering  and  leaving  the  thoracic  cavity  must  be  different :  the  inflow  through 
the  veins  must  be  favored,  and  the  outflow  through  the  arteries  hindered  ;  but 
it  is  upon  the  flaccid  veins  chiefly  that  the  mechanical  influences  of  insj)i ration 
are  exerted.  If  the  thoracic  cavity  be  freely  opened,  movements  of  ins])iration 
no  longer  cause  an  expansion  of  the  lungs,  nor  is  there  a  tendency  to  distend 
the  heart  and  the  large  blood-vessels;  if,  however,  in  an  intact  animal  the  out- 
let of  the  thorax  be  restricted,  as  by  pressure  upon  the  trachea,  the  force  of  the 
inspiratory  movement  would  make  itself  felt  chiefly  u])on  the  heart  and  the 
vessels,  and  it  is  under  such  circumstances  that  the  maximal  influences  of  in- 
spiration upon  the  circulation  are  observed.  The  lungs  on  the  one  hand  and 
the  heart  and  its  large  vessels  on  the  other  may  be  regarded  as  two  sacs  placed 
within  a  closed  expansible  cavity,  the  former  having  an  outlet  communicating 
with  the  external  air,  and  the  latter  having  inlets  and  outlets  communicating 
with  the  extrathoracic  blood-vessels,  both  being  dilated  when  the  thorax  ex- 
pands and  constricted  when  it  contracts.  Moreover,  the  blood-vessels  in  the 
lungs  may  be  compared  to  a  system  of  delicate  tubes  jilaccd  within  a  closed 
distensible  bag  and  communicating  with  tubes  outside  of  the  bag,  simulating 
the  communication  of  the  vense  cavse  and  the  aorta  with  the  extrathoracic 
vessels.  "When  such  a  bag  is  distended  the  tubes  also  must  be  distended 
and  their  lumina  in  consequence  be  enlarged.  The  lungs  in  the  same  way, 
when  expanded  by  the  act  of  inspiration,  are  accompanied  by  a  simultaneous 
dilatation  of  the  intrapulmonary  vessels,  increasing  their  capacity,  with  the 
natural  physical  result  of  lessened  resistance  to  the  flow  of  blood. 

During  expiration  negative  intrathoracic  pressure  becomes  less,  so  that  there 
is  a  gradual  return  of  the  expanded  intrathoracic  vessels  to  that  condition 
wdiich  existed  at  the  beginning  of  ins})iration ;  at  the  same  time  the  intrajiul- 
monary  vessels  are  not  only  subjected  to  the  passiv^e  influence  of  the  declining 
intrathoracic  pressure,  but  are  actively  squeezed,  as  it  were,  between  the  air  in 
the  lungs  on  one  side  and  the  expiratory  forces  expelling  the  air  on  the  other. 
Thus  we  have  during  ex})iration  passive  and  active  agents  combining  to  bring 
about  constriction  of  the  intrapulmonary  vessels. 

The  mechanical  effects  of  the  movements  of  respiration  upon  blood-pressure 
maybe  demonstrated  by  means  of  Hering's  device  (Fig.  141).  The  chamber 
A  represents  the  thorax ;  the  rubber  bottom  b,  the  diaphragm  ;  c,  the  opening 
of  the  trachea;  ED,  a  tube  leading  from  the  thoracic  cavity  to  the  manometer 
I,  by  means  of  which  intrathoracic  pressure  is  measured;  G  is  a  vessel  contain- 
ing water,  colored  blue  in  imitation  of  venous  blood,  communicating  by  means 
of  a  tube  with  an  oblong  flaccid  bag  f,  in  imitation  of  the  heart  and  the  intra- 


RESPIRATION.  557 

thoracic  vessels,  and  iiiially  witli  tla-  vessel  ii  ;  v' and  v  arc  valves  in  imitation 
of  valves  in  the  heart  and  j)ulnu)naiv  vein  and  aorta.  Jt'  now  the  knob  K 
which  is  fastened  to  the  centre  of  the  diaiihra^m  he  pidled  down,  rarefaction 
of  the  air  witiiin  the  chamber  occnrs,  so  that  the  greater  external  pressure 
forces  air  throngh  the  tube  c  into  the  two  rubber  bags  (lungs);  at  the  same 
time  and  for  the  same  reason  water  is  forced  from  tlie  vessel  G  iuto  f,  which  is 
distended.  The  diaphragm  upou  being  released  is  drawn  up  in  [)art  by  virtue 
of  its  own  elasticity  and  in  part  by  the  negative  pressure  within  the  chamber. 
The  rubber  bags  are  emptied  by  their  own  natural  elastic  reaction.     At  the 


Fig.  141. — Hering's  device  to  illustrate  the  influence  of  respiratory  movements  upon  the  circulation. 

same  time  the  distended  bag  F  contracts  on  its  contained  fluid,  forcing  it  into 
the  vessel  h,  the  valve  v  preventing  a  back-flow  into  g.  The  degree  of  force 
exerted  by  the  traction  on  the  diaphragm  is  read  from  the  scale  on  the  man- 
ometer. 

This  simple  contrivance  teaches  us  that  during  the  entire  phase  of  in.spira- 
tion  there  is  a  condition  of  progressively  increasing  negative  pressure  within 
the  thorax,  and  that  not  only  is  air  aspirated  into  the  lungs,  but  that  blood  is 
drawn  into  the  large,  flaccid  vense  cavse ;  and  that  during  expiration  there  is  a 
gradual  diminution  of  negative  pressure  during  which  air  is  expelled  from  the 
lungs  and  blood  from  the  expanded  venae  cavte. 

The  increased  flow  iuto  the  thoracic  cavity  during  inspiration  is  favored  in 
its  progress  through  the  pulmonary  vessels  by  the  attendant  dilatation  of  the 
lung-capillaries  and  by  the  fact  that  the  increased  negative  pressure  affects  the 


558  AX  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

tliiu-walled  and  sliglitly  distended  pulinuiiary  veins  mure  than  the  thiei<-\valled 
and  more  distended  puhnonary  arteries,  so  that  the  "driving  force"  of  the  lung 
circulation,  which  is  essentially  the  difference  in  pressure  between  the  blood  in 
the  pulmonary  arteries  and  that  in  the  veins,  is  thereby  increased  during  inspi- 
ration and  the  blood-current  is  driven  with  greater  velocity.  More  blood  thus 
l>eing  brought  into  the  chest,  and  consequently  to  the  heart,  during  ingpiration, 
and  less  resistance  being  offered  to  the  flow  of  the  blood  through  the  lungs, 
more  blood  must  ultimately  find  its  way  to  the  left  side  of  the  heart,  and  con- 
sequently into  the  general  circulation.  If,  therefore,  the  general  capillary 
resistance  in  the  systemic  circulation  remains  the  same,  it  is  evident  that  an 
increased  blood-supply  to  the  left  ventricle  must  cause  the  general  blood-pres- 
sure to  "rise.  That  this  rise  does  not  become  manifest  immediately  at  the 
beginning  of  inspiration  is  doubtless  owing  to  the  filling  of  the  flaccid  and 
partially  collapsed  large  veins  and  to  the  dilatation  of  the  pulmonary  capil- 
laries. The  continuance  of  the  rise  for  a  short  time  after  the  cessation  of  in- 
spiration is  due  apparently  to  the  partial  emptying  of  the  now  distended  lung- 
vessels,  whereby,  owing  to  the  arrangement  of  the  heart-valves,  the  excess  of 
blood  is  forced  toward  the  left  side  of  the  heart. 

Besides  the  above  factors,  the  flow  of  blood  to  the  right  side  of  the  heart  is 
favored  bv  the  pressure  transmitted  from  the  conjoint  actions  of  the  diaphragm 
and  the  abdominal  walls  tlirough  the  abdominal  viscera  to  the  al)dominal 
vessels.  The  pressure  upon  the  arteries  tends  to  drive  the  Ijlood  toward  the 
lower  extremities  and  to  hinder  the  flow  from  the  heart ;  in  the  veins,  however, 
the  flow  toward  the  heart  is  encouraged,  Avhile  that  from  the  extremities  is 
hindered.  The  rigid  walls  of  the  arteries  protect  them  from  being  materially 
affected,  but  the  flaccid  veins  are  influenced  to  a  marked  degree;  while,  there- 
fore, the  flow  from  the  left  side  of  the  heart  is  not  materially  interfered  with, 
that  through  the  veins  toward  the  right  side  is  appreciably  facilitated,  and  thus 
the  supply  of  blood  to  the  heart  is  increased.  The  effects  of  these  movements 
may  be  seen  after  section  of  the  phrenic  nerves,  which  causes  paralysis  of  the 
diaphragm,  when  it  will  be  noted  that  the  blood-pressure  curves  are  much  re- 
duced.. This  diminution  is  attributed  to  two  causes — the  enfeebled  respiratory 
movements,  which  are  now  confined  to  the  ribs  and  the  sternum,  and  the 
absence  of  the  pressure  transmitted  from  the  diaphragm  through  the  abdominal 
organs  to  the  veins.  If  in  such  an/ animal  the  abdomen  be  periodically  com- 
pressed, in  imitation  of  the  effects  produced  by  the  contraction  of  the  dia- 
]ihragm,  the  respiratory  curves  may  be  restored  to  their  normal  height. 

During  expiration,  since  the  conditions  are  reversed  the  effects  also  must  be 
reversed.  The  increased  negative  intrathoracic  pressure  occasioned  by  inspira- 
tion now  gives  place  to  a  gradual  diminution,  and  with  this  a  lessening  of  the 
aspiratory  action  due  to  the  sub-atmospheric  intrathoracic  pressure  ;  the  blood- 
supply  is  further  reduced  because  of  the  lessened  amount  of  blood  coming 
through  the  inferior  vena  cava;  the  abdominal  veins,  instead  of  being  com- 
pressed and  their  contents  forced  chiefly  toward  the  heart,  are  now  being 
filled;  finally,  during  the  shrinkage  of  the  lungs  the  intrapulmonary  vessels 


BESPIRA  TION.  559 

become  constricted,  and  tlius  offer  greater  i-esistance  to  the  flow  from  the  right 
side  of  the  heart  through  the  lungs  to  tlie  left  side  of  the  heart,  and  subse- 
quently into  the  general  circulation. 

Another  factor  believed  by  some  to  be  involved  in  the  respiratory  undula- 
tions in  blood-pressure  is  a  rhythmical  excitation  of  the  vaso-constrictor  centre 
in  the  medulla  oblongata,  asserted  to  occur  coincidently  with  the  inspiratory 
discharge  from  the  respiratory  centre.  This  has,  however,  been  disproved. 
Others  have  held  that  the  blood-pressure  changes  are  due  to  the  pressure  ex- 
erted by  the  expanding  lungs  u[)on  the  heart;  while  others  contend  that 
rhythmical  alterations  in  the  heart-beats  are  important.  This  latter  factor  is 
of  importance  in  man  and  in  the  dog,  in  which  there  is  a  distinct  increase  in 
the  rate  of  the  heart-beat  during  inspiration,  and  co-operates  in  producing  the 
general  rise  of  pressure  during  inspiration. 

The  Effects  on  the  Pulse. — During  inspiration  the  pulse-rate  is  more 
rapid  than  during  expiration.  If  we  cut  the  pneumogastric  nerves,  it  will  be 
seen  that,  while  the  rate  is  increased  as  the  result  of  the  section,  the  diiference 
during  ins[)iration  and  expiration  is  abolished  ;  on  the  other  hand,  if  the  thorax 
be  widely  opened,  but  the  pneumogastric  nerves  are  left  intact,  the  inspiratory 
increase  in  the  rate  still  occurs.  This  indicates  that  the  cardio-inhibitory 
centre  is  either  less  active  during  inspiration  or  more  active  during  expiration, 
and  that  there  is  an  associated  activity  of  the  respiratory  and  cardio-inhibitory 
centres.  Why  this  sympathy  sliould  exist  between  the  respiratory  and  cardio- 
inhibitory  centres  we  do  not  know,  but  it  has  been  suggested  that  during  expi- 
ration the  blood  reaching  the  centres  is  less  highly  arterialized  than  during 
the  inspiratory  phase,  and  that  the  cardiac  centre  is  so  sensitive  to  the  difference 
as  to  be  affected,  and  thus  its  activity  is  somewhat  increased  during  the  expira- 
tory phase,  W'itli  the  consequent  decrease  in  the  pulse-rate. 

During  inspiration  the  pulse-rate  is  not  only  higher  than  during  expiration, 
but  the  form  of  the  ])ulse-wave  is  affected.  The  systolic,  dicrotic,  and  sec- 
ondary waves  are  smaller  and  the  dicrotic  notch  is  more  pronounced,  so  that 
the  dicrotic  character  of  the  curves  is  better  marked. 

The  Effects  of  Obstruction  of  the  Air-passag-es  and  of  the  Respira- 
tion of  Rarefied  and  Compressed  Air  on  the  Circulation. — The  blood- 
pressure  undulations  produced  during  quiet  breathing  become  marked  in  pro- 
portion to  the  depth  of  the  respiratory  movements.  Inspiration  or  expiration 
against  extraordinary  resistance — as  after  closing  the  mouth  and  nostrils,  or 
respiring  rarefied  or  compressed  air — may  materially  modify  the  eircul»t<jry  phe- 
nomena. When  we  make  the  most  forcible  inspiratory  effort,  the  air  passages 
being  fully  open,  not  only  is  there  a  full  expansion  of  the  lungs,  but  great 
diastolic  distention  of  the  heart  and  dilatation  of  the  intrajjulmonary  and  intra- 
thoracic vessels;  yet,  notwithstanding  that  this  powerful  aspiratory  action  en- 
courages the  flow  of  an  extraordinarily  large  amount  of  blood  into  the  thoracic 
vessels,  the  heart-beats  may  be  very  small,  because  intrathoracic  negative 
pressure  is  so  great  that  the  thin-walled  auricles  meet  with  great  resistance 
while  contracting;  in  consequence,  then,  of  this  forced  inspiratory  effort  little 


5G0  AX  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

blood  is  driven  throiiiih  tho  lungs  to  the  left  auricle  and  by  the  left  ventricle 
into  the  general  circulation.  If  we  make  the  greatest  possible  expiratory 
effort,  and  niaintaiu  the  expiratory  phase  with  air-passages  open,  the  heart- 
beats are  small,  owini;  to  the  small  amount  of  blood  which  flows  throuirh 
the  vena^  cavjo  to  the  right  auricle,  and  to  the  resistance  ofVered  by  the  con- 
stricted intrapulmouary  vessels. 

If,  after  a  most  p(i\verful  expiration,  we  close  the  mouth  and  nostrils  and 
make  a  powerful  inspiratory  etibrt,  the  aspiratory  effect  of  inspiration  on  the 
heart  and  the  blood-vessels  is  manifest  to  its  utmost  degree  :  the  heart  and  the 
vessels  tend  to  undergo  great  dilatation,  the  blood-flow  to  the  right  auricle  and 
ventricle  is  increased,  the  intrapulmouary  vessels  and  the  heart  become  en- 
gorged, and,  owing  to  the  powerful  traction  of  the  negative  pressure  upon  the 
heart,  especially  upon  the  right  auricle,  very  little  blood  is  forced  through  the 
lungs  to  the  left  auricle  and  ventricle  and  subsequently  into  the  general  circu- 
lation, thus  causing  a  fall  of  blood-pressure ;  indeed,  the  heart-sounds  and  the 
pulse  may  disappear.  If  now  we  make  the  most  forcible  inspiratory  effort, 
close  the  glottis,  and  make  a  powerful  expiratory  effort,  not  only  is  the  air  in 
the  lungs  subjected  to  high  positive  pressure,  but  the  heart  and  the  great 
vessels  partake  in  the  pressure-effects,  the  blood  being  forced  from  the  pul- 
monic circulation  into  the  left  auricle,  thence  by  the  v^entricle  into  the  aorta, 
with  the  result  of  a  temporary  rise  of  blood-pressure.  The  pressure  upon  the 
intrathoracic  veins  is  so  great  that  the  flow  of  blood  into  the  chest  is  almost 
shut  off,  hence  the  veins  outside  the  thorax  become  very  much  distended,  as 
seen  in  the  superficial  veins  of  the  neck,  and  the  heart  is  pressed  upon  to  such 
an  extent  that,  together  with  the  lessened  supply  of  blood,  the  heart-sounds 
and  the  radial  pulse  may  disappear  and  the  blood-pressure  falls. 

The  respiration  into  or  from  a  spirometer  (p.  535)  containing  rarefied  or 
compressed  air  modifies  the  blood-pressure  curves.  Inspiration  of  rarefied  air 
causes  a  greater  rise  of  blood-pressure  than  when  respiration  occurs  at  normal 
pressure,  while  during  expiration,  although  the  blood-pressure  falls,  it  may 
remain  somewhat  above  the  normal.  The  increase  of  pressure  is  due  to  the 
aspiratory  effort  required  to  draw  the  air  into  the  lungs,  which  effort  also  makes 
itself  felt  to  a  more  marked  degree  upon  the  heart  and  the  intrathoracic  and 
intrapulmouary  vessels,  thus  increasing  the  blood-flow  through  the  pulmonary 
circulation.  During  expiration  air  is  aspirated  from  the  lungs  into  the  spi- 
rometer, tending  to  dilate  the  intrathoracic  and  intrapulmouary  vessels  and  the 
heart  and  thus  to  aid  the  pulmonary  circulation.  After  a  time,  however,  there 
is  a  fall  of  blood-pressure  on  account  both  of  the  engorgement  of  the  thoracic 
vessels  and  the  accompanying  depletion  of  the  general  circulation,  :u)d  of  the 
distention  of  the  heart  and  interference  with  its  contractions. 

Inspiration  of  compressed  air  lessens  the  extent  of,  and  may  prevent,  the 
inspiratory  rise,  or  it  may  cause  a  fall.  If,  U})()n  the  respiration  of  compressed 
air,  the  pressure  of  the  air  be  above  that  exerted  by  the  elastic  tension  of  the 
lungs,  no  effort  of  the  inspiratory  muscles  is  required,  the  chest  being  expanded 
by  the  pressure  of  the  air.     Therefore,  instead  of  an  increase  of  negative  intra- 


BESPIRA  TION.  56 1 

thoracic  pressure,  as  in  normal  inspiration,  there  is  a  decrease,  and  negative 
intrathoracic  pressure  is  replaced  by  positive  pressure.  As  a  result,  the  blood- 
vessels and  the  heart,  instead  of  being  dilated  by  an  as[»irat()rv  action,  are 
pressed  upon,  forcing  the  blood  into  the  general  circulation,  and  thus  causing  a 
transient  rise  of  pressure,  which  is,  however,  succeeded  by  a  iall  (hu;  to  obstruc- 
tion to  the  flow  of  blood  through  the  heart  and  the  pulmonary  vessels.  Ex- 
piration into  compressed  air  causes  at  first  a  transient  increase  of  blood-pressure 
followed  by  a  fall,  the  former  being  due  to  the  forcing  of  some  of  the  blood 
from  the  intrathoracic  and  intrapulmonary  vessels  into  the  general  circulation, 
and  the  latter  to  obstruction  to  the  blood-flow  through  the  heart  and  the  pul- 
monary circulation. 

When  individuals  are  exposed  to  compressed  air,  as  in  a  pneumatic  cabinet, 
or  to  rarefied  air,  as  in  ballooning,  the  effects  on  the  circulation  become  of  a 
very  complex  character,  owing  chiefly  to  the  additional  influences  of  the 
abnormal  pressure  upon  the  peripheral  circulation ;  moreover,  the  effects  of 
breathing  against  obstructions  or  of  respiring  rarefied  or  compressed  air  may 
be  materially  influenced  by  secondary  effects  resulting  from  excitation  of  the 
cardiac  and  vaso-motor  mechanisms. 

In  artificial  respiration,  as  ordinarily  performed  in  the  laboratory,  air  is 
periodically  forced  into  the  lungs  by  a  pair  of  bellows  or  a  pump,  and  is  ex- 
pelled from  the  lungs  by  the  normal  elastic  and  mechanical  factors  of  expira- 
tion. When  the  lungs  are  inflated  the  pulmonary  capillaries  are  subjected  to 
opposing  forces — the  positive  pressure  of  the  air  within  the  lungs  on  one  hand, 
and  the  resistance  of  the  thoracic  walls  on  the  other — so  that  the  blood  is 
squeezed  out,  thus  momentarily  increasing  the  blood-pressure,  but  subsequently 
retarding  the  current  and  consequently  lowering  the  pressure.  During  expira- 
tion the  pressure  is  removed  and  the  blood-flow  is  encouraged ;  there  is,  there- 
fore, a  temporary  fall  during  the  filling  of  the  pulmonary  vessels,  followed  by 
a  rise  due  to  the  removal  of  the  obstruction.  If  the  air  is  aspirated  from  the 
lungs,  the  rise  of  the  pressure  is  augmented,  owing  to  the  further  dilatation  of 
the  intrapulmonary  capillaries ;  hence,  in  artificial  respiration,  during  the  in- 
spiratory phase  the  blood-pressure  curves  are  reversed,  there  being  a  primary 
transient  rise  followed  by  a  fall,  and  during  the  expiratory  phase  a  transient 
fall  followed  by  a  rise.  In  normal  respiration  the  oscillations  are  due  essen- 
tially to  changes  in  negative  intrathoracic  pressure,  while  in  artificial  respira- 
tion, as  above  noted,  they  are  due  to  changes  in  positive  intrapulmonary 
pressure. 

J.  Special  Respiratory  Movements. 

The  rhythmical  expansions  and  contractions  of  the  thorax  which  we  under- 
stand as  respiratory  movements  have  for  their  object  the  ventilation  of  the 
lungs.  There  are,  however,  other  movements  which  possess  certain  respiratory 
characters,  but  which  are  for  entirely  different  purposes,  hence  they  are  spoken 
of  as  special  or  modified  respiratory  movements.  Some  of  these  movements 
are  purposeful  in  character,  others  are  spasmodic ;  some  are  voluntary  or  in- 

36 


502  .l.V   AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

vi»liintarv,  or  possess  both  volitional  and  iiivolitional  characteristics;  some  are 
peculiar  to  certain  species,  etc.  Ainoiit;  such  movements  are  coughing,  hawking, 
sneezing,  laughing,  crying,  sobbing,  sighing,  yawning,  snoring,  gargling,  hic- 
cough, neighing,  braying,  growling,  etc. 

In  coughing  a  preliminary  inspiration  is  followed  by  an  expiialion  which  is 
frequently  interrupted,  the  glottis  being  partially  closed  at  the  time  of  the 
occurrence  of  each  interruption,  so  that  a  series  of  characteristic  sounds  are 
cau.sed.  The  air  is  forcibly  ejected  through  the  mouth,  and  thus  foreign  parti- 
cles, such  as  mucus  in  the  respiratory  passages,  may  be  expelled.  Coughing 
may  be  either  voluntary  or  reflex. 

Hawking  is  somewhat  similar  to  coughing.  The  glottis  is,  however,  open 
during  the  expiratory  act,  and  the  expiration  is  continuous.  The  current  of 
air  is  forced  through  the  contracted  j>assage  between  the  root  of  the  tongue 
and  the  soft  palate.     Hawking  is  a  vohmtary  act. 

In  sneezing  a  deep  inspiration  is  followed  by  a  forcible  expiratory  blast 
directed  through  the  nose;  the  glottis  is  open,  and  should  the  oral  passage  be 
open,  which  is  not  usually  the  case,  a  portion  of  the  blast  is  forced  through  the 
mouth.  Sneezing  is  usually  a  reflex  act  commonly  excited  by  irritation  of  the 
fibres  of  the  nasal  branches  of  the  fifth  pair,  of  cranial  nerves.  Peculiar  sen- 
sations in  the  nose  give  us  a  premonition  of  sneezing;  at  such  a  time  the  act 
may  be  prevented  by  firmly  pressing  the  finger  upon  the  upper  lip. 

In  laughing  there  is  an  inspiration  followed,  as  in  coughing,  by  a  repeatedly- 
interrupted  expiration  during  which  the  glottis  is  open  and  the  vocal  cords  are 
thrown  into  vibration  with  each  expiratory  movement.  The  expirations  are 
not  as  forcible  as  in  coughing,  the  mouth  is  wide  open,  and  the  face  has  a 
characteristic  expression  due  to  the  contraction  of  the  muscles  of  expression. 

Crying  bears  a  close  relationship  to  laughing — so  much  so  that  at  times  it 
is  impossible  to  distinguish  between  the  two ;  hence  one  may  readily  pass  into 
the  other,  as  frequently  occurs  in  cases  of  hysteria  and  in  young  children. 
The  chief  differences  between  the  two  are  in  the  rhythm  and  the  facial  expres- 
sion. A  secretion  of  tears  is  an  accompaniment  of  crying,  but  not  so  of 
laughing,  except  during  very  hearty  laughter.  Crying  normally  is  involun- 
tary; laughing  may  be  cither  voluntary  or  involuntary. 

Sobbing,  which  is  apt  to  follow  a  long  period  of  crying,  is  characterized  as 
being  a  series  of  spasmodic  inspirations  during  each  of  which  the  glottis  is 
partially  closed,  and  the  series  is  followed  by  a  long,  quiet  ex]>iration.  This  is 
usually  involuntary,  but  may  sometimes  be  arrested  volitionally.  In  sighing 
there  is  a  long  inspiration  attended  by  a  peculiar  plaintive  sound.  The  mouth 
may  be  either  closed  or  partially  open.     Sighing  is  usually  voluntary. 

Yawning  has  certain  features  like  the  j)receding.  There  occurs  a  long, 
deep  inspiration  during  which  the  mouth  is  stretched  wide  open,  and  there  is 
usually  a  simultaneous  strong  contraction  of  certain  of  the  muscles  of  the 
shoulders  and  the  back  ;  the  glottis  is  wide  open,  and  inspiration  is  accompa- 
nied by  a  peculiar  sound  ;  expiration  is  short.  Yawning  may  be  either  volun- 
tary or  involuntary. 


RESPIRA  TION.  563 

In  snoring  the  mouth  is  open,  and  the  inflow  and  outflow  of  air  throws  the 
uvuhi  and  tiie  soft  palate  into  vibration.  The  sound  produced  is  more  marked 
during  inspiration,  and  may  even  he  absent  during  exj)iration.  It  is  more  apt 
to  occur  when  the  individual  is  lying  on  his  back  than  wlien  in  any  other 
posture.     Snoring  is  usually  involuntary,  but  it  may  be  volitional. 

In  gargling  the  fluid  is  held  between  the  tongue  and  the  soft  palate  and  air 
is  exj)ire(l  through  it  in  the  form  of  bul)bles. 

In  hiccough  there  is  a  sudden  inspiratory  effort  caused  by  a  spasmodic 
twitch  of  the  diaphragm  and  attended  by  a  sudden  closure  of  the  glottis,  so 
that  the  inspiratory  movement  is  suddenly  arrested,  thus  causing  a  characteris- 
tic sound.  Hiccough  is  sometimes  not  only  distressing,  but  may  be  even  seri- 
ous or  fatal  in  its  consequences.  It  is  especially  apt  to  occur  in  cases  of  gastric 
irritation,  in  certain  forms  of  hysteria,  in  alcoholism,  in  urremia,  etc. 

Besides  the  above  special  respiratory  movements,  others  are  observed  in 
certain  species  of  animals,  such  as  whining,  neighing,  braying,  roaring,  bellow- 
ing, bawling,  barking,  purring,  growding,  etc. 

Of  all  these  modified  respiratory  movements,  coughing  possesses  to  the 
clinician  the  most  interest,  because  it  not  only  may  express  an  abnormal  condi- 
tion of  some  portion  of  the  lungs,  trachea,  or  larynx,  but  may  indicate  irrita- 
tion in  even  remote  and  entirely  unassociated  parts.  Thus,  coughing  may  be 
the  result  of  irritation  in  the  nose,  ear,  pharynx,  stomach,  liver,  spleen,  intes- 
tines, ovaries,  testicle,  uterus,  or  mamma.  Coughs  which  are  not  dependent 
upon  irritation  of  the  larynx,  trachea,  or  lungs  are  distinguished  as  sympa- 
thetic or  reflex  coughs.  The  term  "■  reflex  "  is  a  bad  one,  however,  inasmuch 
as  all  coughs  are  essentially  or  solely  reflex. 

K.  The  Nervous  Mechanism  of  the  Respiratory  Movements. 

The  movements  of  respiration  are  carried  on  involuntarily  and  automati- 
cally— that  is,  they  recur  by  virtue  of  the  activity  of  a  self-governing  mech- 
anism. Each  respiratory  act  necessitates  a  finely  co-ordinated  adjustment  of 
the  contractions  of  a  number  of  muscles,  which  adjustment  is  dependent  upon 
the  operations  of  a  dominating  or  controlling  nerve-centre  located  in  the 
medulla  oblongata,  and  known  as  the  resjyiratory  centre.  Besides  this  centre, 
others  of  minor  importance  have  been  asserted  to  exist  in  certain  parts  of  the 
cerebro-spinal  axis;  these  centres  are  distinguished  as  subsidiary  or  subordinate 
respiratory  centres.  Connected  with  the  respiratory  centre  are  afferent  and 
efferent  respiratory  nerves. 

The  Respiratory  Centres. — After  removal  of  all  parts  of  the  brain  except 
the  spinal  bulb,  rhythmical  respiratory  movements  may  still  continue,  but  after 
destruction  of  the  lower  part  of  the  bulb  they  at  once  cease.  These  facts  indi- 
cate that  the  centre  for  these  movements  is  in  the  medulla  oblongata,  and  this 
conclusion  is  substantiated  by  the  results  of  other  experiments  upon  this 
region.  According  to  the  observations  of  Flourens,  the  respiratory  centre  is 
located  in  an  area  about  5  millimeters  wide  between  the  nuclei  of  the  pneumo- 
gastric  and  spinal  accessory  nerves  in  the  lower  end  of  the  calamus  scriptorius. 


564  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

When  this  region  was  destroyed  he  found  that  respiratory  movements  ceased 
and  death  ensued,  consequently  he  termed  it  the  nceud  vital,  or  vital  knot. 
The  results  of  various  investigations  show,  however,  that  Flourens'  area,  as 
well  as  certain  other  parts  of  the  medulla  oblongata  that  have  been  looked 
upon  by  others  as  being  respiratory  centres,  are  nut  such,  but  arc  largely  or 
wholly  collections  of  nerve-fibres  which  arise  chiefly  in  the  roots  of  the  vagal, 
s])inal  accessory,  glosso-pharyngcal,  and  trigeminal  nerves,  and  which  there- 
fore are  probably  nerve-paths  to  and  from  the  respiratory  centre.  Moreover, 
excitation  of  the  no^id  vital  does  not  excite  respiratory  movements,  but  simply 
increases  the  tonicity  of  the  diaphragm ;  nor  is  the  destruction  of  the  area 
always  followed  by  a  cessation  of  respiration.  While  the  precise  location  of 
the  centre  is  still  in  doubt,  there  is  abundant  evidence  to  justify  the  belief  in 
its  existence  in  the  lower  portion  of  the  spinal  bulb. 

The  centre  is  bilateral,  one  half  being  situated  on  each  side  of  the  median 
line,  the  two  parts  being  intimately  connected  by  commissural  fibres,  thus  con- 
stituting physiologically  a  single  centre.  This  union  may  be  destroyed  by 
section  along  the  median  line.  Each  half  acts  more  or  less  independently  of, 
although  synchronously  with,  the  other,  and  each  is  connected  with  the  lungs 
and  the  muscles  of  respiration  of  the  corresponding  side.  These  facts  are 
rendered  manifest  in  the  following  observations :  If  a  section  be  made  in  the 
median  line  so  as  to  cut  the  commissural  fibres,  the  respiratory  movements  on 
the  two  sides  continue  synchronously  ;  if  now  the  portion  of  the  centre  on  the 
one  side  be  destroyed,  the  respiratory  movements  on  the  corresponding  side  tem- 
porarily or  permanently  cease.  If  after  section  in  the  median  line  one  pneumo- 
gastric  nerve  be  divided,  the  sensory  impulses  conveyed  from  the  lungs  on  the 
side  of  section  to  the  corresponding  half  of  the  respiratory  centre  are  prevented 
from  reaching  the  centre,  causing  the  movements  of  the  respiratory  muscles  on 
the  same  side  to  be  slower  and  the  inspirations  stronger  as  compared  with  those 
on  the  opposite  side  ;  if  both  pneumogastrics  be  divided,  and  the  central  end  of 
one  of  the  cut  nerves  be  excited  high  in  the  neck  by  a  strong  current,  the  respi- 
ratory movements  on  the  same  side  may  be  arrested,  yet  they  may  continue  on 
the  opposite  side.  These  facts  indicate  that  each  half  is  in  a  measure  inde- 
pendent of  the  other.  The  operations  in  the  two  parts  are,  however,  inti- 
mately related,  as  shown  by  the  fact  that  if  the  commissural  fibres  between 
the  halves  are  intact,  excitation  or  depression  of  one  half  is  to  a  certain  degree 
shared  by  the  other.  Thus,  after  section  of  one  vagus  not  only  are  the  respi- 
ratory movements  less  frequent  and  the  inspirations  stronger  on  the  side  of 
the  section,  but  there  is  a  corresponding  condition  on  the  opposite  side;  simi- 
larly, excitation  of  the  central  end  of  the  cut  nerv€  increases  the  respiratory 
rate  both  on  the  same  and  on  the  opposite  side.  Consequently,  while  there  is 
more  or  less  indej)endence  of  the  halves,  the  two  are  physiologically  so 
intimately  associated  as  to  constitute  a  common  or  single  centre. 

Moreover,  each  of  the  halves  may  be  supposed  to  consist  of  two  distinct 
portions,  one  of  M^hich,  upon  excitation,  gives  rise  to  contraction  of  insi)irat()ry 
muscles,  the  other  to  contraction  of  expiratory  muscles ;  hence  they  are  spoken 


RESPIRA  TION.  565 

of  IIS  ins})iratorv  and  expiratory  j)arts  of  the  respiratory  centre,  or  as  inspi- 
nitory  and  expiratory  ventres.  Moderate  e.\<'itati()n  of  the  inspiratory  centre 
causes  not  only  contraction  of  inspiratory  muscles,  but  an  increase  in  the 
respiratory  rate ;  and  if  tiie  irritation  be  sufficiently  strong,  there  occurs  a 
spasmodic  arrest  of  the  res})iratory  movements  in  the  inspiratory  phase.  On 
the  contrary,  excitation  of  the  expiratory  centre  causes  couti'action  of  expi- 
ratory nuiscles  and  diminishes  the  respiratory  rate;  powerful  excitation  of  the 
same  centre  is  followed  by  arrest  of  movements  in  the  expiratory  phase. 
The  inspiratory  portion  may  therefore  be  regarded  not  only  as  being  spe- 
cifically connected  with  ins])irat()i"v  nuiscles,  but  in  the  sense  of  an  accelerator 
centre;  and  the  expiratory  portion  maybe  regarded  as  being  similarly  con- 
nected Avith  expiratory  nuiscles,  and  as  being  an  Inliihitory  centre.  When  the 
two  are  conjointly  excited  the  accelerator  eifcct  prevails,  because  under  ordinary 
circumstances  the  accelerator  element  of  the  centre  seems  more  excitable  and 
potent  than  the  inhibitory ;  therefore,  when  the  centre  as  a  whole  is  irritated, 
it  manifests  an  accelerator  character. 

In  addition  to  this  centre,  the  existence  of  subsidiary  centres  is  claimed, 
situated  both  in  the  brain  and  in  the  spinal  cord.  One  centre  has  been  located 
in  the  rabbit  in  the  tuber  cinereum,  which  has  been  named  a  polypnosic  centre, 
because  when  excited  the  respirations  are  rendered  extremely  frequent.  The 
sensitiveness  of  this  centre  is  readily  demonstrated  by  subjecting  an  animal 
to  a  high  external  tem])erature,  when  a  marked' increase  of  the  respiratory  rate 
follows;  if  now  the  tuber  cinereum  be  destroyed,  there  occurs  an  immediate 
cesssation  of  the  accelerated  movements.  Another  area  has  been  located  in 
the  optic  thalamus  in  the  floor  of  the  thii'd  ventricle ;  this  centre  is  believed 
to  be  excited  by  impulses  carried  by  the  nerves  of  sight  and  hearing,  and 
when  irritated  causes  an  acceleration  of  the  respiratory  rate,  and  when  strongly 
excited  arrests  respiration  during  the  inspiratory  phase ;  hence  it  is  regarded 
as  an  inspiratory  or  accelerator  centre.  Another  centre  has  been  located  in 
the  anterior  pair  of  the  corpora  quadrigemina  ;  it  causes  expiratory  and  inhibi- 
tory eifects,  and  may  therefore  be  placed  among  the  expiratory  or  inhibitory 
centres.  An  inspiratory  or  accelerator  centre  has  been  recorded  as  existing  in 
the  posterior  pair  of  the  corpora  quadrigemina  and  the  j^ons  Varolii.  The 
nuclei  of  the  trigemini  are  also  said  to  act  as  inspiratory  or  accelerator  centres. 
Respiratory  centres  are  likewise  claimed  to  exist  in  the  brain-corte.v.  It  is 
very  doubtful,  however,  whether  or  not  these  so-called  subsidiary  respiratory 
centres  should  be  regarded  as  being  of  a  specific  character.  In  any  event,  we 
cannot  suppose  that  these  centres  are  capable  of  evoking  directly  respiratory 
movements.  If  they  exist,  they  are  probably  connected  with  the  medullary 
centre,  through  which  they  exert  their  influence  on  the  respiratory  movements. 
The  existence  of  a  respiratory  centre  in  the  spinal  cord,  is  also  doubtful. 
The  chief  reasons  for  the  claim  of  its  existence  is  that  respiratory  movements 
may  for  a  time  be  observed  after  section  of  the  cerebro-spinal  axis  at  the  junc- 
tion of  the  spinal  cord  and  bulb.  In  new-born  animals  after  such  section 
respiratory  movements  may  continue  for  some  time,  strychnine  rendering  them 


5GG  AX  AM  ERICA  X   TEXT-BOOK    OF  PHYSIOLOGY. 

moi'C  proiioLinccil,  Again,  animals  in  which  respiration  has  been  artilieially 
maiutoiued  for  a  long  time  may,  after  section  of  the  cord  at  the  junction  with 
the  bulb,  exhibit  respiratory  movements  after  artificial  respiration  has  been 
suspended.  The  resjiiratory  movements  mider  these  circumstiinces  are,  how- 
ever, of  a  spasmodic  character,  and  distinctly  unlike  the  co-ordinated  rhythmi- 
cal movements  observed  in  normal  animals ;  the  movements  are  rather  of  the 
nature  of  spasms  simulating  normal  respirations. 

The  Wiytlnnie  Acticlty  of  the  Retiipiriitory  Centre. — The  rhythmic  sequence 
of  the  respiratory  movements  is  due  to  periodic  discharges  from  the  respiratory 
centre.  The  cause  of  this  periodicity  is  still  obscure,  but  the  fact  that  the 
rhythm  continues  after  the  combined  section  of  the  vagi  and  the  glosso-pharyu- 
geal  nerves,  of  the  spinal  cord  in  the  lower  cervical  region,  of  the  posterior 
roots  of  the  cervical  spinal  nerves,  and  of  the  spinal  bulb  from  the  parts 
above,  indicates  that  the  rhythm  is  inherent  in  the  nerve-cells,  and  is  not 
caused  by  external  stimuli  carried  to  the  centre  through  afferent  nerve-fibres. 
Loewy  ^  has  shown  that  under  the  above  circumstances,  when  the  centre  is  iso- 
lated from  afferent  nerve-impulses,  the  rhythmical  activity  of  the  centre  is  due  to 
the  blood,  which,  while  acting  as  a  continuous  excitant,  causes  discontinuous  or 
periodic  discharges,  so  that,  although  we  usually  speak  of  the  activity  of  the 
respiratory  centre  as  being  automatic — that  is,  not  immediately  dependent  upon 
external  stimuli — yet  as  a  mutter  of  fact  the  apparently  automatic  discharges 
are  in  reality  due  to  the  stimulation  by  the  blood ;  the  centre  is  therefore  auto- 
matic only  with  reference  to  external  nerve-stimulation. 

The  rhythm  as  well  as  the  rate,  force,  and  other  characters  of  the  discharges 
may  be  affected  materially  by  the  will  and  emotions ;  by  the  composition, 
supply,  and  temperature  of  the  blood ;  and  especially  by  certain  afferent  im- 
pulses, pre-eminently  those  originating  in  the  pneumogastric  nerves.  As  to 
the  influence  of  the  Avill  and  emotions,  we  are  able,  as  is  well  known,  to  modify 
voluntarily  to  a  certain  extent  the  rhythm  and  other  characters  of  the  respira- 
tions, while  the  striking  effect  of  emotions  upon  respiratory  movements  is  a 
matter  of  almost  daily  observation.  The  importance  of  the  composition  of 
the  blood  is  manifested  by  the  marked  effect  upon  the  respirations  when  the 
blood  is  deficient  in  O,  when  it  contains  an  exce&s  of  COo,  ;^nd  during  muscu- 
lar activity,  when  in  the  blood. there  is  a  relative  abundance  of  certain  products 
resulting  from  muscular  metabolism.  If  the  blood-supply  to  the  centre  is 
diminished,  as  after  severe  hemorrhage  or  after  clamping  the  aorta  so  as  to 
interfere  with  the  cerebral  circulation,  the  respirations  are  less  frequent  and 
the  rhythm  is  affected,  the  form  of  breathing  having  a  Cheyne-Stokes  char- 
acter (p.  532) ;  conversely,  an  increase  in  the  blood-supply  causes  an  increase 
in  the  rate.  An  increase  or  decrease  in  the  temperature  of  the  blood  induces 
corresponding  changes  in  the  rate;  thus,  in  fever  tiie  frequency  of  the  move- 
ments increases  almost  pari  passu\\\t\\  the  augmentation  of  temperature,  while 
if  the  temperature  of  the  blood  be  reduced  by  applying  ice  to  the  carotids,  the 
rate  is  lessened. 

>  Pjiuger's  Archivf.  Physiologie,  1889,  vol.  xlii.  pp.  245-281. 


RESPIRA  TION.  567 

Afferent  impulses  exercise  an  important,  and  practically  a  continuous,  influ- 
ence. After  section  of  one  pneunioj^astric  iicrve  the  respirations  are  somewhat 
less  frequent;  after  section  of  botli  nerves  the  respirations  become  considerably 
less  frequent  and  deei^er  and  otherwise  changed.  If  we  stinudate  the  central 
end  of  one  of  these  cut  nerves  below  the  origin  of  the  laryngeal  branches  by 
a  current  of  electricity  of  moderate  intensity,  the  respiratory  rate  may  be  in- 
creased, and  we  may  be  able  to  restore,  or  even  exceed,  the  normal  frequency. 
The  fact  that  section  of  these  nerves  is  followed  by  a  dimiimtion  of  tiie  rate 
and  that  excitation  of  the  central  end  of  the  cut  nerve  causes  an  increase  leads 
us  to  l)elicve  that  the  pneumogastric  nerves  are  continually  conveying  impulses 
from  the  lungs  to  the  respiratory  centre,  which  impulses  in  some  way  increase 
the  number  of  discharges,  and  thus  the  respiratory  rate.  The  centre  may  be 
excited  or  depressed  by  excitaticm  of  the  cutaneous  nerves  and  the  sensory 
nerves  in  general ;  thus,  external  heat  accelerates,  while  a  dash  of  cold  water 
may  either  accelerate  or  inhibit,  respiratory  movements.  Excitation  of  the 
glosso-pharvngeal  nerves  inhibits  the  respirations.  Such  inhibition  occurs 
during  deglutition  to  avoid  the  risk  of  introducing  foreign  bodies  into  the 
larynx.  Similar  respiratory  inhibition  may  be  induced  by  excitation  of  the 
superior  laryngeal  nerves,  when,  if  the  degree  of  irritation  be  sufficiently 
strono-,  complete  arrest  of  the  respiratory  movements  may  occur.  Strong  irri- 
tation of  the  olfactory  nerves  and  of  the  fibres  of  the  trigemini  distributed  to 
the  nasal  chambers  excites  expiration  and  may  be  fcjUowed  by  complete  inhibi- 
tion of  the  respiratory  movements ;  strong  irritation  of  the  optic  and  auditory 
nerves  excites  inspiratory  activity ;  and  irritation  of  the  sciatic  nerve  causes  an 
increase  of  the  rate,  and  may  or  may  not  affect  the  depth  of  breathing. 

The  study  of  the  rhythmic  activity  of  the  respiratory  centre  is  further 
complicated  Ijy  the  fact  that  there  is  not  only  a  rhythmic  sequence  of  the  res- 
pirations, but  a  rhythmic  alternation  of  iusi)iratory  and  expiratory  move- 
ments. While  it  is  true  that  in  ordinary  quiet  expiration  but  little  of  the 
muscular  element  is  present,  yet  forced  ex])iration  is  a  well-defined  co-ordinated 
muscular  act.  The  mechanism  whereby  this  alternation  is  brought  about  is 
not  understood.  Some  believe  that  the  pneumogastric  nerves  contain  both 
■  inspiratory  and  exj)iratory  fibres  which  are  connected  with  corresponding  parts 
of  the  respiratory  centre  and  alternately  convey  their  respective  impulses  to 
the  centre,  inspiratory  impulses  being  excited  during  expiration  and  expiratory 
impulses  during  inspiration  (p.  505).  These  impulses  are,  however,  not  indis- 
pensable to  the  alternation  of  inspiration  and  expiration,  because  these  acts 
follow  each  other  regularly,  even  after  the  isolation  of  the  respiratory  centre 
from  the  lungs  by  section  of  the  pneumogastric  nerves. 

Thus  we  may  conclude  that  the  rhythmical  discharges  from  the  centre  are 
due  primarily  to  an  inherent  property  of  periwlic  activity  of  the  nerve-cells 
constituting  the  respiratory  centre  and  maintained  by  the  blood,  and  that  the 
rhythm,  ra'te,  and  other  Characters  of  these  discharges  may  be  affected  by  the 
will  and  the  emotions,  by  the  composition,  supply,  and  temperature  of  the 
blood,  and  bv  various  afferent  impulses.     The  chief  factors  are,' under  ordi- 


568  A.X  AMERICAN   TEXT-BOOK   OE  PJIYSIOLOGY. 

iiarv  circumstances,  the  quantities  of  O  and  COj  in  the  blood,  and  the  inipnlses 
conveyed  from  tlie  lungs  by  tiie  fibres  of  the  pneumogastric  nerves. 

The  Afferent  Respiratory  Nerves. — The  chief  of  these  nerv(is  are  the 
■pncuinoijnstrH',  (jlosxo-plmryngcdl,  triytiainal,  and  cidaneoua  'iirrvcs.  The  im- 
j)()rtant  part  taken  by  them  in  the  regulation  of  the  respiratory  movements  has 
frequently  been  alluded  to  in  connection  with  the  respiratory  centres.  Their 
functions,  however,  are  of  sufficient  importance  to  demand  special  and  detailed 
consideration. 

The  j)neuinogastvic  verves  are  pre-eminently  the  most  important.  Their 
functions  juay  be  studied  by  comparing  the  ])lienomena  before  and  after  section 
of  one  or  of  both  nerves,  and  from  the  results  following  excitation  by  stimuli 
of  varying  quality  and  strength  under  normal  and  abnormal  conditions. 

Section  of  ojie  pneumogastric  may  be  without  effi'ct  or  be  followed  by  a 
transitory,  slight  diminution  of  the  resi)iratory  rate ;  by  slower  and  deeper 
movements;  by  stronger,  deeper,  and  longer  inspirations;  by  unaltered  or 
longer  or  shorter  expirations;  and  probably  by  active  expirations.  Tliese 
effects  are  transient,  and  the  normal  respiratory  niovements  are  usually  restored 
within  a  half  hour.  Section  of  both  nerves  is  sooner  or  later  followed  by  a 
diminution  of  the  resi)iratorv  rate ;  by  slow,  deep,  ]iowerful  inspirations ;  by 
active  expiration ;  and  by  a  pause  between  ex])iration  and  inspiration.  The 
immediate  results  are  variable  unless  certain  precautions  are  taken  to  prevent 
irritation  of  the  central  ends  of  the  cut  nerves.  If  the  ends  are  allowed  to 
fall  back  into  the  wound,  the  respirations  may  become  irregular ;  or  they  may 
be  le&s  frequent,  with  weakened  inspirations,  spasmodic  expirations,  and  pro- 
longed expiratory  pauses.  The  explanation  of  these  variable  results  is  found 
in  the  fact  that  the  expiratory  fibres  are  more  sensitive  to  vev}/  veak  stimidus 
than  the  inspiratory  fibres,  and  that  the  mechanical  irritation  caused  by  the 
section,  and  the  excitation  due  to  the  electric  current  in  the  cut  ends  of  the 
nerves  that  is  established  when  the  central  end  of  the  nerve  is  replaced  in  the 
wound,  excite  ex})iratorv  impulses  and  cause  expiratory  phenomena;  if  the 
irritation  be  stronger,  both  inspiratory  and  expiratory  impulses  are  excited, 
thus  causing  uncertain  results,  varying  as  one  or  the  other  is  the  stronger.  If 
irritation  be  prevented,  section  is  at  once  followed  by  typical  slow,  deep 
respirations. 

Stimulation  of  the  central  end  of  the  cut  vagus,  the  other  nerve  being 
intact,  is  followed  by  variable  results  dependent  ujwn  the  character  of  the 
stimulus.  Chemical  stimuli,  such  as  a  solution  of  sodium  carbonate,  excite 
the  expiratory  fibres;  mechanical  stimuli,  the  inspiratory  fibres;  electrical 
stimuli,  expiratory  or  ins]Mratory  fibres  or  both,  according  to  the  strength  of 
tha  current.  Single  induction  shocks  are  without  cfTect,  but  a  tetanizing 
current  is  very  effective.  Should  that  current  which  will  elicit  the  least 
response  be  used,  the  breathing  is  rendered  less  frequent,  the  inspirations  are 
weakened,  and  the  expirations  may  be  active  and  lengthened  ;  in  other  words, 
there  are  present  the  same  phenomena  which  often  immediately  follow  section 
of  both  nerves  when  the  cut  ends  are  allowed  to  fall  back  into  the  wound  and 


resi'/hatiox.  500 

thus  establish  an  exciting  electric  current  whidi  affects  expiratory  fibres.  If 
the  strcnoftli  of  the  current  bo  increascil,  these  elfects  give  place  to  those  of  an 
ojjpo.site  ciiaracter,  the  respirations  becoming  more  freijucnt  and  tiie  inspi- 
rations more  marked  in  depth  and  force,  the  exi)hiiiati<)M  of  this  difference 
being  that  the  stronger  current  has  also  excited  inspiratory  fibres,  so  that  now 
both  expiratory  and  inspiratory  impulses  are  generated,  Ijut  the  latter,  being 
more  potent  in  their  influences,  cause  acceleration  of  the  rate  and  accentuated 
inspirations.  The  effects  following  stimulation  of  the  central  end  of  the  cut 
vagus  by  a  current  of  moderate  strength  are  best  observed  after  l)oth  nerves  have 
been  divided  and  when  there  exist  slow,  deep,  powerful  respirations.  Under 
such  circumstances  stimulation  of  the  central  end  of  one  of  the  vagi  is  followed 
at  once  by  an  increase  in  the  respiratory  rate  and  a  return  of  the  general  char- 
acters of  the  inspiratory  and  expiratory  phases  toward  the  normal ;  and  if  the 
degree  of  excitation  be  properly  adjusted,  the  normal  rate  and  normal  charac- 
ter  of  breathing  mav  be  restored.  Still  stronger  excitation  further  accelerates 
the  rate,  causing  the  respiratory  acts  to  follow  each  other  with  sucii  frequency 
that  inspiration  begins  before  the  expiratory  act  (relaxation  of  the  inspiratory 
muscles)  has  been  completed.  The  inspiratory  muscles  are  therefore  never 
completely  relaxed.  With  a  further  increase  of  stimulus  the  expiratory 
relaxation  becomes  less  and  less,  until  finally  the  respirations  are  brought  to  a 
standstill  in  the  inspiratory  phase,  the  inspiratory  muscles  being  in  tetanus. 

If  the  nerves  be  fatigued  from  over-excitation  or  if  the  animal  be 
tiioroughly  chloralized,  stimuhition  of  the  central  end  of  the  cut  nerve  by  a 
strong  current  is  no  longer  followed  by  inspiratory  stimulation,  but  is  followed 
by  expiratory  stimulation  (the  inspirations  being  shortened  and  weakened,  the 
expirations  prolonged  and  spasmodic)  and  by  long  pauses  between  expiration 
and  inspiration.  If  the  excitation  be  sufficiently  strong,  arrest  of  respiration 
occurs  in  the  expiratory  phase. 

It  will  be  observed  from  the  above  results  that  electrical  irritation  of  the 
central  end  of  the  cut  pneumogastric  may  be  followed  by  eftects  of  an  oppo- 
site character,  extremely  w^eak  irritation  causing  expiratory  stimulation  (weaker 
and  shorter  inspirations,  prolonged  and  active  expirations,  expiratory  pauses, 
and  diminished  respiratory  rate) ;  whereas  moderate  irritation  causes  inspiratory 
stimulation  (stronger  and  deeper  inspirations  and  increased  respiratory  rate). 
These  diverse  results  are  explained  by  the  fact  that  tliese  nerves  contain  two 
kinds  of  fibres  having  opposite  functions  :  fibres  of  one  kind  convey  impulses 
which  affect  the  expiratory  centre ;  those  of  the  other  kind  convey  impulses 
which  affect  the  inspiratory  centre.  The  former  are  more  susceptible  to  weak 
electrical  stimulation,  and  thus  their  presence  may  be  elicited  by  the  weakest 
stimulus  capable  of  causing  any  response.  At  the  same  time  they  are  less 
readily  exhausted,  so  that  if  the  vagi  be  subjected  to  prolonged  stimulation 
by  a  strong  current,  the  inspiratory  fibres  are  exhausted  before  the  expiratory 
fibres.  For  moderate  and  strong  currents  the  inspiratory  fibres  are  affected 
to  a  greater  degree  than  the  expiratory  fibres,  therefore  inspiratory  stimula- 
tion predominates. 


570  ^.V  AMERICAN   TEXT- BOOK    OF   PIIYSIOLOdY. 

Both  sets  of  fibres  convey  iiupulses  which  liavc  their  origin  essentiallv  in 
the  peripheries  of  the  pneuniogastric  nerves  in  the  kings;  but  expiratory 
impulses  may  arise  in  tlie  fibres  of  the  supei-ior  and  inferior  huyngeal  nerves, 
especially  in  the  former.  The  impulses  which  arise  in  the  lungs  are  under 
ordinary  circumstances  produced  mechanical ly  by  the  movements  of  the  lungs, 
although  it  is  believed  by  some  that  the  composition  of  the  gases  in  the  alveoli 
is  an  important  factor.  According  to  the  latter  view,  when  the  lungs  are  in 
the  expiratory  phase  the  accummulation  of  CO^  in  the  air-cells  excites  the 
peripheries  of  the  inspiratory  fibres,  thus  giving  rise  to  impulses  which  are 
carried  to  the  inspiratory  ])ortion  of  the  res])iratory  centre,  and  exciting  inspi- 
ration ;  whereas  the  stretching  of  the  lungs  during  inspiration  is  held  to  excite 
the  peripherics  of  the  expiratory  fibres,  generating  impuses  which  are  conveyed 
to  the  ex})irutory  portion  of  the  ex])iratory  centre,  causing  expiration.  There 
is,  however,  no  sufficient  evidence  to  lead  us  to  believe  that  the  presence  of 
CO2  in  normal  percentages  influences  in  any  way  either  set  of  fibres.  On  the 
contrary,  the  mechanical  eifects  of  the  movements  of  the  lungs  are  of  great 
importance,  as  is  apparent  from  the  fact  that  inflation  excites  active  expi- 
ration, whereas  aspiration  or  collapse  excites  inspiration;  moreover,  if  the 
movements  of  one  lung  be  prevented  by  occlusion  of  the  bronchi  or  by  free 
opening  of  the  pleural  sac,  the  effects  are  the  same  as  though  the  vagus  of  the 
same  side  were  cut ;  if  now  the  other  nerve  be  severed,  the  results  are  the  same 
as  when  both  nerves  are  cut.  The  movements  of  the  lungs  therefore  generate 
alternate  inspiratory  and  exj)iratory  impulses,  collavpse  causing  inspiratory 
impulses,  and  expansion  causing  expiratory  impulses.  The  inspiratory 
impulses,  however,  not  only  excite  inspiration,  but  concurrently  limit  the 
duration  of  expiration  ;  Mdiile  the  expiratory  impulses  excite  expiration  and 
concurrently  limit  inspiration. 

Excitation  of  the  snperior  laryngeal  nerve  causes  expiratory  stimulation, 
and  there  may  occur  respiratory  arrest  in  the  expiratory  phase.  These  fibres 
are  extremely  sensitive;  and  they  are  of  considerable  physiological  import- 
ance, as  is  illustrated  by  the  fact  that  the  entrance  of  foreign  bodies  into 
the  larynx  during  deglutition  causes  an  immediate  arrest  of  inspiration,  and 
even  a  forced,  spasmodic  expiration.  The  foreign  particles,  coming  in 
contact  with  the  keenly  sensitive  fibres  of  these  nerves,  generate  impulses 
which  arrest  inspiration,  thus  being  prevented  from  being  carried  to  the 
lungs. 

The  fibres  of  the  r/losso-pharyngeal  nerves  act  similarly.  Their  excitation 
is  followed  by  an  arrest  of  respiration  which  lasts  for  a  period  e(|ual  to  that 
occupied  bv  al)OUt  three  of  the  preceding  respiratory  acts.  The  value  of  such 
an  inhibitory  influence  is  obvious:  During  swallowing  breathing  is  arrested, 
evidently  for  the  purpose  of  preventing  the  aspiration  of  food  and  drink  into 
the  larynx.  This  act  is  purely  reflex,  and  is  due  to  the  excitation  of  fibres  of 
these  nerves  by  the  fluid  or  the  bolus  of  food  after  the  act  of  deglutition  has 
begun.  Such  impulses  flow  to  the  respiratory  centre,  immediately  arresting 
the  inspiratory  discharge  in  whatever  phase  the  inspiratory  movement    may 


RESPlHATrOX.  571 

happen  to  bo.     Wlien  ^^wallowinj;  has  bwii  accoinphshed  the  inhibitory  influ- 
ence is  removed  and  respiration  is  resumed. 

The  inhalation  of  irritating  gases  may  cauM'  respiratory  arrest  by  excituig 
either  the  sensory  fibres  of  the  trigeminal  iierves  in  the  nose  or  the  pueumo- 
gastric  fibres  in  the  larynx  and  lungs.  Some  gases  affect  the  former,  some 
the  latter,  others  both.  In  the  rabbit,  for  example,  the  introduction  of  tobacco- 
smoke  into  the  lungs  through  a  tracheal  opening  produces  no  effect  upon  the 
respirations,  but  if  injected  into  the  nose  respiration  is  at  once  arrested.  When 
ammonia  is  similarly  introduced  into  the  lungs  the  respirations  may  be  either 
accelerated  or  diminished,  and  may  be  arrested  in  the  inspiratory  or  the  expi- 
ratory phase,  but  when  drawn  into  the  nose  expiratory  arrest  follows.  Some 
irritating  gases  arrest  respiration  in  the  inspiratory  phase,  others  in  the  expi- 
ratory phase.  Odorous  gases  which  are  powerful  and  disagreeable  may  simi- 
larly cause  arrest  by  acting  upon  the  olfactory  nerves.  Excitation  of  the 
splanchnic  nerves  causes  expiratory  arrest ;  stimulation  of  the  sciatic  and  sea- 
sonj  nerves  in  general  usually  increases  the  number  of  respirations,  yet  under 
certain  circumstances  it  may  cause  a  decrease  and  final  arrest  during  expi- 
ration. 

Stimulation  of  the  cutaneous  nerves,  as  by  a  cold  douche,  slapping,  etc., 
causes  primarily  a  tendency  to  an  increase  in  the  number  and  depth  of  the  res- 
pirations, but  finally  causes  cessation  in  the  expiratory  phase.  It  is  stated  that 
excitation  of  these  nerves  is  more  effective  in  causing  respiratory  movements 
than  irritation  of  the  vagi.  The  influence  of  external  heat  is  very  powerful, 
and  is  perhaps  the  most  potent  means,  under  ordinary  circumstances,  of  exciting 
the  respiratory  centre.  The  respiratory  movements  caused  by  cutaneous  irrita- 
tion, are,  however,  of  the  character  of  reflex  spasms  rather  than  of  normal 
movements,  and  when  the  excitation  is  sufficiently  strong  the  movements  may 
be  distinctly  convulsive. 

Finally,  afferent  (intercentral)  fibres  connect  the  brain-cortex,  and  probably 
the  ganglia  at  the  base  of  the  brain,  with  the  respiratory  centres. 

The  Efferent  Respiratory  Nerves.— During  ordinary  respiration  the  only 
efferent  or  motor  nerves  necessarily  involved  are  the  phrenics,  and  certain  other 
of  the  spinal  nerves,  and  the  pneumogastrics.  Section  of  one  phrenic  nerve  causes 
paralysis  of  the  corresponding  side  of  the  diaphragm ;  section  of  both  phrenics 
is  followed  by  paralysis  of  the  entire  diaphragm.  So  important  are  these 
nerves  in  respiration  that  in  most  cases  after  section  death  occurs  from  asphyxia 
wathin  several  hours.  In  such  cases  not  only  is  the  work  of  inspiration  thrown 
upon  the  other  inspiratory  muscles,  but  the  effectiveness  of  the  latter  is  greatly 
compromised  by  the  relaxed  condition  of  the  diaphragm,  which  permits  of  its 
being  drawn  into  the  thoracic  cavity  with  each  inspiration,  thus  hindering  the 
expansion  of  the  lungs.  If  section  be  made  of  the  spinal  cord  just  below  the 
exit  of  the  fifth  cervical  nerve,  costal  movements  cease,  but  diaphragmatic  con- 
tractions continue.  The  level  of  the  section  is  just  below  the  origin  of  the  roots 
of  the  phrenics,  so  that  the  motor  fibres  for  the  diaphragm  are  left  intact,  but 
the  motor  impulses  which  would  have  gone  out  to  other  inspiratory  muscles 


r>72  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

tliroiigli  the  spinal  nerves  below  the  point  of  section  are  cut  off.  If  the  cord 
be  out  just  below  the  medulla  oblongata  or  above  the  origin  of  the  phrenics, 
both  costal  and  diai)liragniatic  movements  immediately  or  very  soon  cease,  but 
respiratorv  movements  may  continue  in  the  larynx,  and  when  dyspntt-a  occurs 
thev  may  be  observed  in  the  muscles  of  the  face,  neck,  and  mouth.  In  rare 
cases,  after  section  at  the  junction  of  tlie  mcidulla  ()l)l(»ngata  and  the  spinal  cord, 
respiratory  movements  may  continue  in  tlu;  thorax  and  the  abdomen,  but  these 
instances  are  exceptional  and  the  movements  are  of  the  nature  of  reflex  spasms. 

During  each  respiratory  act  there  flow  to  the  larynx  impulses  which  open 
the  glottis  during  inspiration.  The  pathway  of  these  impulses  is  through  the 
laryngeal  branches  of  the  vagi,  almost  solely  through  the  recurrent  or  inferior 
laryngeal  nerves.  (See  section  on  the  Physiology  of  the  Voice.)  If  the  pneu- 
mogastrics  are  cut  above  the  origin  of  these  brancdies,  res[)iratory  movements 
in  the  larynx  cease,  and,  owing  to  the  paralysis  of  the  laryngeal  muscles,  the 
vocal  cords  are  flaccid,  the  glottis  is  no  longer  widened,  and  thus  great  resist- 
ance is  offered  to  the  inflow  of  air,  causing  difflculty  during  ins})iration. 

During  forced  breathing,  besides  the  above  nerves  a  number  of  others  may 
be  involved,  especially  the  spinal  nerves,  which  supply  the  extraordijaary  respi- 
ratory muscles  of  the  chest,  abdomen,  pelvis,  and  vertebral  column,  and  the 
facial,  hypoglossal,  and  spinal  aecessorii  nerves. 

L.  The  Condition  of  the  Respiratory  Centre  in  the  Fetus. 

During  intra-uterine  life  the  child  receives  O  from  and  gives  CO2  to  the 
blood  of  the  mother.  No  attempt  is  made  by  the  child  to  breathe,  because  the 
centre  is  in  an  apnoeic  condition,  due  to  a  low  condition  of  irritability  and  to 
the  relatively  large  amount  of  O  in  the  blood.  The  fetal  blood  contains  a 
larger  percentage  of  haemoglobin  than  the  blood  of  the  mother;  Quinquaud 
has  shown  that  the  fetal  blood  has  a  larger  respiratory  capacity  than  adidt's 
blood  ;  and  Regnard  and  Dubois  have  proven  the  same  to  be  true  of  the  calf 
and  the  cow.  Were  it  not  for  these  two  conditions,  the  child  would  continu- 
ally attempt  to  breathe.  While  such  efforts  do  not  occur  under  normal  cir- 
cumstances, they  may  be  present  if  we  interfere  in  any  way  with  the  supj)ly  of 
oxygen,  as  by  pressure  upon  the  umbilical  vessels.  The  child  has  been  seen 
to  make  respiratory  efforts  while  within  the  intact  fetal  membranes.  It  seems 
evident,  therefore,  that  all  that  is  necessary  to  excite  the  respiratory  centre  to 
activity  is  a  venous  condition  of  the  blood.  In  utero,  and  as  long  as  the  child 
is  bathed  in  the  amniotic  fluid,  respiratory  movements  cannot  be  carried  on 
even  though  the  res])iratory  centre  be  excited  to  activity,  the  reason  being  that 
with  the  first  movement  of  inspiration  amniotic  fluid  is  drawn  into  the  nasal 
chamber;  the  fluid  acts  as  a  powerful  excitant  to  the  sensory  fibres  of  the 
nmcous  membrane,  thus  causing  inhibitory  resjiiratory  impulses.  From  this 
fact  we  learn  the  practical  application  that  it  is  desirable  immediately  after  birth 
of  a  child,  if  spontaneous  respirations  do  not  immediately  and  effectively  occur, 
to  carefully  remove  mucus  or  other  matter  from  the  nose,  so  that  the  inhibitory 
influences  generated  by  nasal  irritation  shall  be  discontinued. 


BESPIBA  TION.  573 

When  the  exchange  of  O  and  COg  is  interfered  witli  for  a  long  period,  as 
in  cases  of  prolonged  labor,  the  respiratory  centre  may  become  so  de})ressed 
that  spontaneous  respirations  do  not  occur  upon  the  birth  of  the  child.  In 
such  a  case  respirations  may  usually  be  initiated  by  irritation  of  the  skin,  as 
by  slapping,  sprinkling  with  iced  water,  etc.  Respirations  may  also  be  carried 
on  successfully  by  artificial  means  (see  p.  553). 

In  utero  the  lungs  arc  devoid  of  air ;  the  sides  of  the  alveoli  and  of  the 
small  air-passages  are  in  apposition,  although  the  lungs  completely  fill  the 
compressed  thoracic  cavity.  During  the  first  inspiration  comparatively  little 
air  is  taken  into  the  lungs,  because  of  the  force  necessary  to  overcome  the 
adhesion  of  the  sides  of  the  alveoli  and  of  the  smaller  air-tubes,  but  as  one 
inspiration  follows  another  inflation  increases  more  and  more  until  full  disten- 
tion is  accomplished.  The  vigorous  crying  which  so  generally  occurs  immedi- 
ately after  birth  doubtless  is  of  value  in  facilitating  this  expansion.  If  once 
the  lungs  have  been  filled  with  air,  they  are  never  completely  emptied  of  it, 
either  by  volitional  effort  or  by  collapse  after  excision. 

M.  The  Innervation  of  the  Lungs. 

The  nerves  of  the  lungs  are  derived  from  the  pneumogastrics,  the  sympa- 
thetics,  and  the  upper  dorsal  nerves.  Scattered  along  the  paths  of  distribution 
of  these  fibres  are  many  small  ganglia. 

The  Pneumogastric  Nerves. — The  pulmonary  branches  of  the  pneumogas- 
tric  nerves  contain  not  only  fibres  which  convey  impulses  that  affect  the  gen- 
eral characters  of  the  respiratory  movements,  but  other  fibres  that  are  of 
great  importance  to  the  respiratory  mechanism.  Setting  aside  the  effects  on 
the  respiratory  movements  following  section  and  stimulation  of  one  or  of  both 
vagi,  there  are  observed  phenomena  which  are  of  an  entirely  different  character, 
and  which  are  due  to  excitation  or  paralysis  of  certain  other  specific  nerve- 
fibres.  Among:  these  fibres  are  efferent  and  afferent  broncho-constrictors  and 
broncho-dilators.  Roy  and  Brown  ^  found  in  investigations  upon  dogs  that 
stimulation  of  one  vagus  caused  constriction  of  the  bronchi  in  both  lungs; 
section  of  one  vagus  was  followed  by  expansion  of  the  bronchi  in  the  corre- 
sponding lung,  which  expansion  was  sometimes  preceded  by  a  slight  contraction 
owing  to  the  temporary  irritation  caused  by  the  section ;  stimulation  of  the 
peripheral  end  of  the  cut  nerve  caused  a  contraction  of  the  bronchi  in  both 
lungs;  stimulation  of  the  central  end  of  the  cut  nerve  was  followed  by  a  con- 
traction of  the  bronchi  in  both  lungs,  but  not  so  marked  as  when  the  peripheral 
end  was  stimulated  ;  stimulation  of  sensory  nerves  other  than  the  vagus  rarely, 
and  then  only  to  a  slight  extent,  caused  contraction ;  atropine  paralyzed  the 
constrictor  fibres ;  nicotine  in  small  doses  had  a  powerful  expansive  effect  on 
the  bronchi ;  after  etherization  stimulation  of  either  the  central  or  the  periph- 
eral end  of  the  cut  pneumogastric  nerve  was  often  followed  by  broncho-dilata- 

1  Journal  of  Physiologrj,  vol.  6,  1885  {Proceedings  of  the  Phydologkal  Society,  iii.  p.  xxi.) ; 
Einthoven,  Pftiiger's  Archiv  fiir  Physiologie,  1892,  vol.  51,  p.  367  ;  Sandeman,  Bu  Bois-ReymomT a 
Archiv  fiir  Physiologie,  1890,  p.  252. 


57  4  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

tion  ;  asphyxia  causes  broncho-constrict iun,  hut  not  after  section  of  the  pnou- 
niogastric  nerves ;  after  section  of  bt)th  vagi  it  is  impossible  to  rause  reflex 
bronclio-coustriction  or  broncho-dihitation ;  the  constriction  of  tlie  bronchi 
niav  be  so  great  as  to  reduce  their  calibres  to  one-half  or  one-third,  or  even 
more.  The  above  results  are  very  instructive,  and  show — (1)  That  broncho- 
constriction  or  broncho-dilatation  can  l)e  obtained  bv  stimulating  the  peri])heral 
end  of  the  vagus,  and  tliat  these  changes  occur  in  the  bronchi  of  both  lungs 
when  only  one  nerve  is  excited,  thus  })roving  tliat  each  nerve  supplies  l)Oth 
kinds  of  fibres  to  both  lungs;  (2)  that  the  same  results  can  be  obtained  by  ex- 
citation of  the  central  end  of  the  cut  nerve,  tiuis  showing  that  the  ])iienmogas- 
trics  contain  both  atfereut  constrictor  and  afferent  dilator  fibres  ;  (3)  that  reflex 
broncho-constriction  and  broncho-dilatation  cannot  be  produced  after  section 
of  the  vagi,  thus  proving  that  all  of  the  efferent  fibres  pass  through  the  pneu- 
mogastrics;  (4)  that  asphyxia  and  the  inhalation  of  COg  cause  broncho-con- 
striction, but  not  after  section  of  the  vagi,  thus  indicating  that  under  these 
circumstances  the  effects  on  the  bronchi  are  reflex ;  (5)  that  certain  poisons 
affect  one  or  the  other  of  these  two  sets  of  fibres. 

The  presence  of  efferent  vaso-motor  fibres  in  the  vagi  has  been  disproved  by 
the  results  of  experiments  by  Bradford  and  Dean,^  and  others.  These  observers 
have  shown,  however,  that  the  vagi  contain  afferent  prei^sor  fibres,  irritation  of 
which  is  followed  by  constriction  of  the  pulmonary  vessels  that  may  or  may 
not  be  accompanied  by  constriction  of  the  systemic  vessels,  the  efferent  fibres 
in  this  case  reaching  the  lungs  through  the  sympathetic  nerves. 

The  existence  of  trophic  fibres  is  generally  admitted.  After  section  of  one 
pneumogastric  nutritive  changes  immediately  begin  in  the  lung  of  the  corre- 
sponding side,  which  changes  are  manifest  in  the  appearance  of  inflammation 
in  the  middle  and  lower  lobes.  Section  of  both  nerves  is  followed  by  inflam- 
mation in  the  middle  and  lower  lobes  of  both  lungs. 

The  vagi  contain  sensori/  fibres  for  the  larynx,  trachea,  and  lungs,  after  sec- 
tion of  which  fibras  there  is  an  absolute  loss  of  sensibility  in  these  parts. 

It  is  probable  that  the  vagi  contain  secretori/  fibres  for  the  mucous  glands. 

Thus  we  find  that  the  pneumogastric  nerves  supply  the  lungs  with  (1) 
afferent  inspirator)/  and  expiratorn  fibres ;  (2)  afferent  and  efferent  broncho- 
constrictor  and  broncho-dilator  fibres;  (3)  afferent  pressor  fibres;  (4)  general 
sensory  fibres;  (5)  trophic  fibres;  (6)  and  probably  secretory  fibres  for  the 
mucous  glands. 

The  Sympathetic  Xerves. — The  sympathetics  supply  trophic  and  efferent 
vaso-motor  fibres.  The  efferent  vaso-motor  fibres  pass  from  the  spinal  cord  in 
the  anterior  roots  of  the  second  to  the  seventh  dorsal  nerve,  inclusive,  to  join 
the  sympathetics,  thence  through  the  fii-st  thoracic  ganglia  to  the  lungs. 

The  Ganglia. — Nothing  is  known  of  the  functions  of  the  ganglia. 
'  Jow-nal  of  Physiology,  1894,  vol.  16,  p.  70. 


IX.  ANIMAL   HEAT. 


A.   Bodily  Temperature. 

Homothermous  and  Poikilothermous  Animals. — Animal  organisms  are 
divided  as  regards  bodily  temperature  into  two  classes,  homothermous  and 
poikilothermous.  The  temperature  of  homothermous  (warm-blooded)  animals 
is  constant  within  narrow  limits  and  is  not  materially  aifected  by  alterations 
of  the  temperature  of  the  medium  in  which  the  organism  lives.  The  tempera- 
ture of  poikilothermous  (cold-blooded)  animals  normally  ranges  from  a  frac- 
tion of  a  degree  to  several  degrees  above  that  of  the  surrounding  medium,  and 
under  ordinary  circumstances  rises  and  falls  with  corresponding  changes  of  sur- 
rounding temperature.  The  old  terms  warm-blooded  and  cold-blooded  imply 
that  the  difference  between  the  two  classes  is  one  of  absolute  temperature,  the 
•former  having  a  temperature  higher  than  the  latter,  and  although  this  is  gener- 
ally the  case  it  is  not  necessarily  so.  For  instance,  Landois  has  recorded  that  a 
frog  (cold-blooded)  in  water  at  a  temperature  of  20.6"^  C.  had  a  temperature  of 
about  20.7°  C,  and  that  when  the  water  was  at  41°  C.  his  temperature  rose  to 
about  38°  C,  which  is  higher  than  the  mean  temperature  of  man  (warm- 
blooded). The  temperature  of  cold-blooded  animals  may,  therefore,  be  higher 
than  that  of  warm-blooded  animals.  The  difference  therefore  is  relative  and 
not  absolute,  the  chief  distinguishing  feature  being  that  the  temperature  of 
homothermous  animals  is  practically  constant,  while  that  of  poikilothermous 
animals  fluctuates  with  the  temperature  of  the  medium  in  which  the  organism 
exists.  The  class  of  homothermous  animals  includes  mammals  and  birds  ;  and 
that  of  poikilothermous  animals,  fish,  reptiles,  amphibia,  and  invertebrates. 

Temperatures  of  Different  Species  of  Animals. — The  temperature  of 
every  animal  varies  in  different  parts  of  the  organism,  so  that  in  making  com- 
parisons it  is  necessary  that  the  observations  be  made  in  the  same  region  of  the 
body  of  the  different  individuals,  and  as  far  as  possible  under  the  same  internal 
and  external  conditions.  As  a  rule,  rectal  temperatures  are  preferable,  and 
in  making  them  it  is  especially  desirable,  in  order  to  ensure  practical  accuracy, 
that  the  bulb  of  the  thermometer  be  inserted  well  into  the  pelvis,  and  that  it 
does  not  rest  within  a  mass  of  fecal  matter.  The  depth  to  which  the  bulb  is 
inserted  is  also  of  importance,  as  shown  by  Finkler,  who  found  in  experiments 
on  a  guinea-pig  that  the  temperature  was  36.1°  C.  at  a  depth  of  2.5  centimeters, 
38.7°  C.  at  6  centimeters,  and  38.9°  C.  at  9  centimeters.  The  following  records 
of  mean  bodily  temperature  of  various  species  have  been  derived  from  various 
sources,  chiefly  from  the  compilations  of  Gavarret : 

575 


576 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


Mammals. 

Centigrade. 

Mouse 41.1" 

Sheep 37.3-40.5° 

Ape 35.5-39.7° 

Rabbit 39.6-40.0° 

Guinea-pig  ....  38.4^39.0° 

Dog 37.4-39.6° 

Cat 38.3-38.9° 

Horse 36.8-37.5° 

Rat 38.8° 

Ox 37.5° 

Ass 36.95° 


Birds. 

Centigrade. 

Birds 44.03" 

Duck 42.50-43.90" 

Goose 41.7° 

Gull 37.8° 

Guinea 43.90° 

Turkey 42.70° 

Sparrow    ....  39.08-42.10° 
Chicken    ....  43.0° 
Crow 41.17° 


Reptiles  and  Fish.* 

Centigrade. 

Frog 0.32-2.44° 

Snakes 2.5-12.0° 

Fish 0.5-3.0° 

Invertebrates.! 

Crustacea 0.6° 

Cephalopods     -    .    .  0.57° 

Medusa 0.27° 

Polyps 0.21° 

Molluscs 0.46° 


The  Temperature  of  the  Different  Regions  of  the  Body. — The  quanti- 
ties ol"  lieat  produced  aud  di.'^sipated  bv  different  parts  of  the  eeonomv  vary, 
con.sequently  there  must  continually  be  a  transmission  of  heat  from  the  warmer 
to  the  cooler  parts  to  establi.'^h  throughout  the  organism  an  equilibrium  of  tem- 
perature. Heat  is  distributed  by  direct  conduction  from  part  to  part,  but  prob- 
ably chiefly  by  the  circulating  blood  and  lymph.  The.se  means  of  distril>utiun 
are,  however,  not  sufficiently  active  to  establish  a  uniform  temperature.  Thus 
we  find  that  the  internal  parts  of  the  body  have  a  higher  temperature  than  the 
external  parts;  that  some  internal  organs  are  considerably  warmer  than  others; 
that  every  organ  is  warmer  when  active  than  when  at  rest ;  that  the  tempera- 
ture varies  in  different  regions  of  the  surface  of  the  body,  etc.  The  following 
figures  by  Kunkel '"  instance  some  of  these  differences,  the  temperature  of  the 
room  being  20°  C. : 

Centigrade. 

Sternum 34.4° 

Pectorales 34.7° 

Right  iliac  fossa 34.4^ 

Left  iliac  fossa 34.6° 

Os  sacrum 34.2° 

Eleventh  rib  (back) 34.5° 

Tuberosity  of  ischium 32.0° 

Upper  part  of  thigh 34.2° 

!  Calf 33.0° 

The  temperature  of  the  skin  is  higher  over  an  artery  than  at  some  di.'^tauce 
from  it ;  it  is  higher  over  muscle  than  over  sinew ;  it  is  higher  over  an  organ 
in  activity  than  when  at  rest;  it  is  higher  in  the  frontal  than  in  the  parietal 
region  of  the  head,  and  on  the  left  side  of  the  head  than  on  the  right,  etc. 

Temperature  observations  are  usually  made  in  the  rectum,  in  the  mouth 
under  the  tongue,  in  the  axilla,  and  in  the  vagina,  the  rectum  being  preferable, 
although  in  the  human  being  the  temperature  is  usually  obtained  in  the  mouth 
and  axilla.  In  the  same  individual  when  records  are  taken  .'simultaneously  in 
all  four  regions  appreciable  differences  will  be  noted.  The  temperature  in  the 
axilla  is,  according  to  Hunter  37.2°  C,  to  Davy  37.3°  C.,to  Wunderlich  36.5° 
to  37.25°  C.  (mean  37.1°  C),  to  Liebermeister  36.89°  C,  to  Jiirgensen  37.2°  C, 

^  Temperatures  above  that  of  the  surrounding  medium. 
*  Zeitschrift  fur  Biologie,  1889,  vol.  25,  pp.  69-73. 


Centigrade. 

Forehead 34.1°-34.4° 

Cheek  under  the  zygoma     ....  34.4° 

Tip  of  ear 28.8° 

Back  of  hand 32.5°-33.2° 

Hollow  of  the  hand  (closed)    .    .    .  34.8°-35.1° 
Hollow  of  the  hand  (open)  ....  34.4°-34.8° 

Forearm 33.7° 

Forearm  (higher) 34.3° 


ANIMAL   HEAT.  577 

and  to  Jaeger  37.3°  C.  'V\\v  inean  axillary  temperature  may  be  put  down  as 
being  about  37.1°  C.  (98.8°  F.),  the  normal  limits  being  3(5.25°  to  37.5°  C. 
(97.2°  to  99.5°  F.)  The  temperature  in  tiie  mouth  is  about  0.2°  to  0.5°  C. 
higher  than  in  the  axilla,  in  the  reetura  from  0.3°  to  1.5°  C.  higher,  and  in  the 
vagina  from  0.5°  to  1.8°  C.  higher. 

The  temperature  of  different  tissues  varies.  Davy,  as  results  of  observa- 
tions on  a  fresh-killed  sheep,  gives  the  temperature  of  the  brain  as  about  40° 
C;  of  the  left  ventriele  41.G7°  C;  of  the  right  ventricle  41.11°  C. ;  of  the 
liver  41.39°  C.  ;  of  the  rectum  40.56°  C.  According  to  Bernard,  the  liver  is 
the  warmest  organ  in  the  body,  and  then  the  following  in  the  order  named- 
brain,  glands,  muscles,  and  lungs. 

The  temperature  of  the  blood  varies  considerably  in  different  vessels.  In 
the  carotid  it  is  from  0.5°  to  2°  C.  higher  than  in  the  jugular  vein;  in  the 
crural  artery,  from  0.75°  to  1°  C.  higher  than  in  the  corresponding  vein  ;  in 
the  right  side  of  the  heart  about  0.2°  C.  higher  than  in  the  left ;  in  the  hepatic 
vein  0.6°  C.  higher  than  in  the  portal  vein  during  the  intervals  of  digestion, 
and  as  much  as  1.5°  to  2°  C  or  more  during  periods  of  digestion ;  the  venous 
blood  coming  from  internal  organs  is  warmer  than  the  arterial  blood  going  to 
them,  but  the  blood  coming  from  the  skin  is  cooler  than  that  going  to  it ;  the 
blood  coming  from  a  muscle  in  a  state  of  rest  is  about  0.2°  C,  and  during 
activity  as  much  as  0.6°  to  0.7°  C,  warmer  than  that  supplied  to  the  muscle. 
The  mean  temperature  of  the  blood  as  a  whole  is  about  39°  C.  (102°  F.) ;  of 
venous  blood  about  1°  C.  (1.8°  F.)  lower  than  of  arterial  blood.  The  warm- 
est blood  in  the  body  is  that  coming  from  the  liver  during  the  period  of  diges- 
tion ;  the  coolest  blood  is  that  coming  from  the  tips  of  the  ears  and  nose  and 
similarly  exposed  parts. 

Conditions  affecting  Bodily  Temperature.— The  mean  temperature  of 
the  body  is  subjected  to  variations  which  depend  chiefly  upon  age,  sex,  consti- 
tution, the  time  of  day,  diet,  activity,  season  and  climate  (surrounding  tem- 
perature), the  blood-supply,  disease,  drugs,  the  nervous  system,  etc. 

The  temperature  of  a  new-born  child  (37.86°  C.)  is  from  0.1°  to  0.3°  C. 
higher  than  that  of  the  vagina  of  the  mother;  it  falls  about  1°  C.  during  the 
first  few  hours  after  birth,  and  then  rises  within  the  next  twenty-four  hours  to 
about  37.4°  to  37.5°  C.  The  mean  temperature  of  an  infant  a  day  or  two 
old  is  about  37.4°  C.  It  very  slowly  sinks  until  full  growth  is  attained,  when 
the  normal  mean  temperature  of  adult  life  is  reached  (37.1°  C),  a  standard 
which  is  maintained  until  about  the  age  of  forty-five  or  fifty,  when  it  declines 
until  about  the  age  of  seventy  (36.8°  C),  and  then  slowly  rises  and  approaches 
in  very  old  people  (eighty  to  ninety  years)  the  temperature  of  very  young 
infants'  (37.4°  C).  It  is  important  to  observe  that  during  the  early  weeks  of 
life  the  temperature  may  undergo  considerable  variations,  and  that  it  is  readily 
affected  bv  bathing,  exposure,  crying,  pain,  sleep,  etc.,  and  by  many  circum- 
stances which  have  little  or  absolutely  no  influence  upon  the  temperature  of 

the  adult. 

The  mean  temperature  of  the  female  is  said  to  be  slightly  lower  than  that 

37 


578  AN  AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 

of  llie  niak'.  In  ob.servatioii.s  on  childrou  Soinnier  noted  a  ditiercnce  of  0.05° 
C,  and  Feliling  a  difference  of  0.33°  C. 

Individuals  with  vigorous  constitutions  have  a  somewhat  higher  temper- 
ature than  those  who  are  weaii. 

Records  obtained  by  various  European  investigators  indicate  that  tlie  bodily 
temperature  is  subjected  to  regular  diurnal  variations.  The  limits  of  variation 
in  health  are  from  1°  to  2°  C.  The  maximum  temperature  observed  is  usu- 
ally from  5  to  8  p.  M.  (mean,  about  7  p.  m.)  ;  the  minimum,  from  2  to  6  A.  M. 
(mean,  about  4  A.  M.).  Carter's '  experiments  on  rabbits,  cats,  and  dogs  show 
that  rhythmical  temperature-changes  occur  in  these  animals  which  agree  with 
those  noted  by  Jiirgensen  in  man.  This  same  rhythm  is  stated  to  occur  during 
fasting,  so  that  the  ingestion  and  the  digestion  of  food  cannot  be  claimed  to 
account  for  it;  moreover,  it  is  prestiiit  in  fever  and  not  disturbed  by  muscular 
activity  and  by  cold  baths.  If  an  individual  works  at  night  and  sleeps  during 
the  day,  thus  reversing  the  prevailing  custom,  the  temperature  curve  is 
reversed,  the  lowest  temperature  being  noted  in  the  evening  and  the  highest 
in  the  morning. 

Insufficient  diet  causes  a  lowering  of  the  temperature ;  a  liberal  diet  tends 
to  cause  a  rise  slightly  above  the  normal  mean,  especially  during  forced  feeding 
or  when  the  food  is  particularly  rich  in  fats  and  carbohydrates.  There  is  a 
rise  during  digestion  which  is  usually  slight,  but  it  may  reach  0.2°  or  0.3°,  the 
increase  being  due  chiefly  to  the  activity  of  the  intestinal  muscles  (see  p.  540). 
Although  considerably  more  heat  is  produced  during  the  periods  of  digestion 
than  during  the  intervals,  the  excess  is  dissipated  almost  as  rapidly  as  it  is 
formed,  so  that  but  little  heat  is  permitted  to  accumulate  and  thus  cause  a  rise 
of  temperature.  Hot  drinks  and  solids  tend  to  augment,  and  cold  drinks  and 
solids  to  lower  bodily  temperature.  In  the  nursing  child  Demme  found  that  the 
rectal  temperature  sinks  during  the  first  half-hour  after  taking  food,  then  rises 
during  the  next  sixty  to  ninety  minutes  to  a  point  from  0.2°  to  0.8°  C.  higher 
than  the  temperature  before  feeding,  and  falls  again  during  the  next  thirty  to 
sixty  minutes. 

All  conditions  which  increase  metabolic  activity  are  favorable  to  an  increase 
of  temperature.  Thus,  during  the  activity  of  the  brain,  glands,  muscles,  etc., 
more  heat  is  produced  than  when  the  tissues  are  at  rest;  indeed,  so  abundant 
is  heat-production  during  severe  muscular  exercise  that  the  temperature  of  the 
body  may  rise  as  much  as  0.5°  to  1.5°  C.  (1°  to  2.7°  F.).  During  sleep  the 
temperature  falls  from  0,3°  to  0.9°  C.  or  more  in  young  children. 

During  the  summer  the  mean  bodily  temperature  is  from  0.1°  to  0.3°  C. 
hi<rher  than  durino;  the  winter.  In  warm  climates  it  is  about  0.5°  C.  hijjher 
than  in  cold  climates,  but  the  difference  is  not  due  to  race,  since  it  is  observed 
in  individuals  who  have  changed  their  habitations  from  one  climate  to  another. 
Continued  exposure  to  excessively  high  or  low  temperatures  is  inimical  to 
life.  Exposure  in  dry  air  at  a  temperature  of  100°  to  130°  C.  may  cause 
the  bodily  temperature  to  increase  as  much  as  1°  to  2°  C.  within  a  few  minutes, 
'  Journal  of  Nervous  and  Mental  Diseases,  1890,  vol.  xvii.  p.  782. 


ANIMAL   HEAT.  579 

and  the  temperature  may  rise  so  rapidly  as  to  cause  fatal  symptoms  within  ten 
or  fifteen  minutes.     A  hot  moist  air  is  far  more  opi)ressive  and  dangerous  than 

hot  drv  air. 

Baths  exercise  a  potent  influence  on  bodily  temperature,  hot  baths  increasmg 
and  cold  baths  decreasing  it.     The  effect  of  a  cold  bath  is  less  if  it  follows  a 
hot  bath.     Thus  Dill '  found  that  his  morning  temperature  varied  from  33.7° 
to  36.6°  C,  after  a  hot  bath  (40°-41°  C.)  it  rose,  in  one  instance,  as  high  as 
39.5°  C,  and  after  a  cold  bath  it  remained  at  37°  C.     When,  however,  the 
hot  bath 'was  omitted  the  cold  bath  reduced  the  temperature  to  35.4°  C.     Bal- 
jakowski  ^  has  recorded  some  very  interesting  results  which  show  that  the  local 
application  of  heat  causes  the  bodily  temperature  to  sink  and  the  cutaneous 
temperature  of  the  part  experimented  upon  to  rise.     The  experiments  were 
conducted  on  youug  men,  whose  arms  and  legs  were  encased  in  hot  sand  at  a 
temperature  of  55°  C.  When  the  arm  was  used  the  axillary  temperature  sunk 
an  average  of  0.13°  C.  during  the  bath  and  subsequently  0.24°  C,  the  corre- 
sponding" records  of  average  rectal  temperature  being  0.23°  and  0.31°  C.     In 
case  of  the  leg  bath  the  corresponding  records  were  axillary  0.06°  and  0.32° 
C;  and  rectal  0.21°  and  0.25°  C.     The  cutaneous  temperature  of  the  limb 
expei-imented  upon  increased  materially,  the  average  rise  varying  from  0.73° 
to  1.20°  C,  according  to  the  part  of  the  limb.     Long-continued  severe  exter- 
nal cold  may  prove  fatal,  but  this  is  not  necessarily  due  to  the  effect  on  bodily 
temperature,  for  Milne-Edwards  ^  has  shown  that  rabbits  die  within  five  or  six 
days  when  exposed  to  a  temperature  of  -10°  to  -15°  C,  without  the  bodily 
temperature  falling  more  than  1°  C. 

There  is  a  general  relationship  between  tiie  frequency  of  the  heart's  beat  and 
the  bodily  temperature,  especially  in  fever.  Barenspruug  noted  such  a  coinci- 
dence between  the  diurnal  variations  of  the  pulse  and  bodily  temperature  ;  and, 
in  fever,  Aiken  found  that  for  each  increase  of  0.55°  C.  (1°  F.)  above  the  mean 
normal  temperature  the  pulse-rate  was  increased  about  ten  beats  per  minute. 
But  the  variations  in  the  two  do  not  always  correspond  either  quantitively  or 
qualitatively.  Liebermeister  found  in  man  that  for  a  rise  of  each  degree  from 
37°  to  42°  C.  the  increase  in  the  pulse-rate  was  12.6,  8.6,  8.7,  11.5,  and  27.5 
beats  per  minute  respectively.  Beljakowski's  *  experiments  show  that  the 
bodily  temperature  mav  fall  and  the  pulse-rate  rise— in  one  set  of  experiments 
the  rectal  temperature  "falling  on  an  average  0.23°  C.  and  the  pulse  increasing 
on  an  average  6.85  beats  per  minute.  After  the  local  hot  bath  the  temperature 
remained  subnormal,  and  the  heart-beats  became  less  frequent,  and  finally  were 
on  an  average  from  2.7  to  3.1  beats  per  minute  less  than  the  normal  rate. 

:^rore  important,  however,  than  the  pulse-rate  is  the  effect  of  the  amount 
of  blood  supplied  to  any  given  part  of  the  body.  The  mere  lowering  or  rais- 
ing of  the  arm  is  sufficient  to  alter  the  blood-supply  to  the  part ;  thus  Romer 
found  that  keeping  the  arm  elevated  for  five  minutes  was  sufficient  to  reduce 

*  British  Medical  Journal,  1890,  vol.  i.  p.  1136. 

2  Vratch,  1889,  p.  436 ;  Provincial  Medical  Journal,  1890,  p.  113. 

3  Cmnptes  rendus  de  la  Sac.  de  Biologic,  1891,  vol.  112,  pp.  201-205.  .     ♦  Loc.  cit. 


580  AX  AMERICA  iV  TEXT- BO  OK    OF   PHYSIOLOGY. 

the  tempfcrature  of"  the  hand  0.19°  C,  and  that  if  tlje  period  was  doubled  the 
fall  amounted  to  0.38°  C.  Compression  of  the  veins  of  the  arm  may  diminish 
the  tonij)cratnre  of  the  hand  as  innrh  a^  0.25°  to  2.-45°  C,  while  compression 
of  the  brachial  artery  may  eanse  a  fall  of  2.4°  within  fifteen  minutes.  A  larger 
supply  of  blood  to  the  cutaneous  surface  increases  cutaneous  temperature  and 
tends  to  decrease  internal  temperature,  while  a  lessened  supply  causes  the 
opposite  effects. 

In  abnormal  conditions  the  temperature  may  be  increased  or  decreased  :  in 
cholera,  diabetes,  and  in  the  last  stages  of  insanity,  it  mav  be  lowered  6°  or 
8°  C.  or  even  more.  In  fever  it  is  increased,  usually  ranging  between  37.5° 
and  41.5°  C.  (99.4°  and  106.7°  F.),  but  in  very  rare  cases  it  may  reach  44°  to 
45°  C.  (111°  to  113°  F.)  just  before  death.  A  temperature  of  42.5°  C. 
(108.5°  F.)  maintained  for  several  hours  is  almost  inevitably  fatal.  In  frogs, 
the  highest  temperature  consistent  with  life  for  any  length  of  time  is  below 
40°  C. ;  in  birds,  from  48°  to  50°  C,  and  in  dogs,  from  43°  to  45°  C.  Ex- 
ceptional cases  are  on  record  of  people  having  survived  extraordinarily  high 
or  low  bodily  temperature,  Riehet  having  reported  one  in  which  the  tempera- 
ture several  times  was  46°  C.  (114.8°  F.),  while  Teale  records  an  axillary  tem- 
perature of  50°  C.  (122°  F.)  in  an  hysterical  (?)  woman.  Frantzel  noted  a 
temperature  of  24.6°  C.  (76.2°  F.)  in  a  drunken  man,  and  Kosiirew  a  temper- 
ture  of  26.5°  C.  (79.7°  F.)  in  a  man  having  a  fractured  skull. 

Bodily  temperature  may  be  variously  influenced  by  drugs  and  other  sub- 
stances, micro-organisms,  etc.  Some  increase  it,  others  decrease  it,  others  are 
without  any  marked  influence,  while  others  exert  primary  and  secondary 
actions.  Among  those  which  increase  bodily  temperature  are  cocain,  atropin, 
strychnin,  brucin,  caffein,  veratrin,  etc.,  and,  as  shown  by  Krehl'  and  others,  a 
large  number  of  other  organic  substances  and  micro-organisms.  Temperature 
is  decreased  by  anaesthetics,  morphin  and  other  hypnotics,  quinin,  various 
antipyretics,  large  doses  of  alcohol,  etc. 

Among  the  most  important  of  the  conditions  which  affect  bodily  tempera- 
ture are  disturbances  of  the  nervous  systetu.  Injury  or  irritation  of  almost 
any  part  of  the  nerve-centres  and  of  certain  nerves  may  give  rise  directlv  or 
indirectly  to  alterations  of  temperature,  and  there  are  some  parts  which  are 
very  sensitive  in  this  respect,  especially  certain  areas  of  the  brain  cortex,  the 
striated  bodies,  the  pons  Varolii,  the  spinal  bulb,  and  the  cutaneous  nerves. 
The  results  of  injury  or  stimulation  of  these  as  well  as  of  other  })arts  will 
be  considered  later  on  (p.  600). 

Temperature-regulation. — The  fact  that  during  life  the  organism  is  con- 
tinxially  producing  and  losing  heat,  and  that  the  Ixxlilv  temperature  of  homo- 
thermous  animal  is  maintained  at  an  almost  uniform  standard,  notwithstanding 
considerable  mutations  of  surrounding  temperature,  renders  it  evident  that 
there  exists  an  important  mechanism  whereby  the  regulation  of  the  relations 
between  heat-production  and  heat-di.<sipation  is  effected.  It  must  be  evident 
that  when  the  variations  in  heat-production  and  heat-di.ssipation  balance,  bodily 

■  Archil'  fur  experimentelle  PcUhologie  und  Pharmakologie^  1895,  vol.  35,  pp.  222-268. 


ANIJfAL  HEAT.  581 

temperature  must  remain  unaltered,  and  that  if  the  clianges  in  one  exceed 
tlio.se  in  the  other  the  temperature  rises  or  falls,  depending  upon  whether  more 
or  less  heat  is  produced  than  is  dissipated.  It  does  not  follow  that  because 
luat-production  is  increased  the  bodily  temperature  must  similarly  be  affected, 
since  hcat-dissi])ation  may  be  increased  to  the  same  extent  and  thus  effect  a 
compensation,  'J'herefore  an  alteration  in  heat-production  or  in  heat-dissipation 
bv  no  means  implies  that  the  temperature  must  be  affected.  Moreover,  when 
the  temperature  is  increased  or  diminished  the  change  may  be  caused  by 
various  alterations  in  the  quantities  of  heat  produced  or  lost,  singly  or  com- 
bined, and  the  temperature  may  remain  constant  even  when  both  processes  are 
materially  affected.  Thus,  the  temperature  remains  comtant  when  both  heat- 
production  and  heat-dissipation  are  normal,  and  when  both  are  increased  or 
decreased  to  the  same  extent.  The  temperature  is  increased  when  heat-pro- 
duction is  normal  and  heat-dissipation  diminished ;  when  both  heat-production 
and  heat-dissipation  are  diminished,  but  when  heat-production  is  diminished 
to  a  less  extent  than  heat-dissipation  ;  when  heat-production  is  increased  and 
heat-dissipation  remains  normal ;  when  both  heat-production  and  heat-dissipa- 
tion are  increased,  but  when  heat-production  is  increased  to  a  greater  extent 
than  heat-dissipation  ;  and  when  heat-production  is  increased  and  heat-dissipa- 
tion is  diminished.  The  temperature  is  diminished  when  heat-production  is 
normal  and  heat-dissipation  is  increased ;  when  heat-production  is  diminished 
and  heat-dissipation  remains  normal ;  when  heat-production  and  heat-dissipa- 
tion are  diminished,  but  when  heat-production  is  diminished  to  a  greater  extent 
than  heat-di&sipation ;  when  heat-production  is  diminished  and  heat-dissipa- 
tion is  increased ;  and  when  both  heat-dissipation  and  heat-production  are 
increased,  but  when  heat-production  is  increased  to  a  less  extent  than  heat- 
dissipation. 

It  is  generally  regarded  by  clinicians  that  bodily  temperature  varies  directly 
with  heat-production — that  is,  that  a  rise  means  increased  production,  and  a 
fall  diminished  production ;  but  the  fallaciousness  of  such  a  conclusion  must 
be  apparent.  It  may,  however,  be  accepted  as  a  fact  that  in  fever,  as  a  rule, 
an  increase  of  bodily  temperature  is  a  concomitant  of  increased  heat-produc- 
tion, and  diminished  temperature  of  diminished  heat-production;  but  it  must 
also  be  observed  that  pyrexia,  although  generally  due  to  increased  he^it- 
production,  may  also  be  due  partly  or  wholly  to  diminished  heat-dissipation. 
It  is  obvious,  therefore,  that  temperature  variations  simply  show  that  the 
balance  between  heat-production  and  heat-dissipation  is  disturbed,  without 
positively  indicating  how  the  processes  of  heat-production  and  heat-dissipation 
are  affected. 

The  mechanism  concerned  in  the  adjustment  of  the  relations  between  heat- 
production  and  heat-dissipation  will  be  considered  under  another  heading 
(p.  602). 

B.  Income  and  Expenditure  of  Heat. 

Broadly  speaking,  the  source  of  animal  heat  is  in  the  potential  energy  of 
organic  food-stuffs — so  little  relatively  being  obtained  from  the  heat  of  warm 


582  ^l^V  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

food  and  drink  and  directly  from  external  sources,  such  as  tlie  sun's  rays,  that 
these  sources  may  be  disregarded.  This  potential  energy  of  food  may  ije 
converted  into  Unixi  dircdhi  or  indirectly  ;  directly,  as  an  immediate  result  of 
chemical  decomposition  ;  and  indirectly,  by  mechanical  movements,  such  as 
muscular  contraction,  the  flow  of  the  blood,  the  friction  of  the  joints,  etc. 
Abont  90  })er  cent,  of  the  heat  of  the  organism  results  directly  from  chemical 
decompositions,  and  about  10  per  cent,  results  indirectly  from  mechanical 
movements.  The  potential  energy  of  the  food  is  transformed  into  kinetic 
energy  (heat  and  work)  essentially  by  processes  of  oxidation.  The  energy- 
yielding  food-stuffs  enter  the  body  in  the  form  of  proteids,  fats,  and  carbo- 
hydrates. The  proteid  is  oxidized  into  urea,  CO2,  HjO,  and  various  extrac- 
tives ;  and  the  fats  and  carbohydrates  are  reduced  to  CO2  and  HgO.  Dining 
these  oxidative  processes,  by  which  the  potential  energy  of  the  molecules  is 
transformed  into  kinetic  energy,  the  total  amount  of  energy  evolved  by  the 
complete  oxidation  of  a  given  amount  of  any  substance  is  the  same  whether 
the  processes  are  carried  at  once  to  the  final  stages,  that  is,  to  the  final  disin- 
tegration products,  or  whether  they  pass  through  an  indefinite  number  of 
intermediate  stages,  provided  that  the  final  product  or  products  are  the  same. 
In  other  words,  the  amount  of  heat  evolved  by  the  oxidation  of  1  gram  of 
proteid  into  urea,  CO2.,  and  HgO  is  the  same  when  the  molecule  is  oxidized 
immediately  into  these  substances  as  when  the  decomposition  is  carried  through 
a  number  of  intermediate  stages.  Similarly  1  gram  of  carbon  oxidized  into 
CO2,  or  1  gram  of  H  oxidized  into  HgO,  yields  a  definite  amount  of  heat, 
1  gram  of  C  yielding  8080  calories  (see  p.  584  for  definition  of  calorie), 
and  1  gram  of  H  34,460  calories;  1  gram  of  proteid  oxidized  into  CO2 
and  HgO  yields  5778  calories;  1  gram  of  fat  oxidized  into  CO2  and  H2O 
yields  9312  calories;  and  1  gram  of  carbohydrate  oxidized  into  COg  and  HjO 
yields  4116  calories  (see  Potential  Energy  of  Food,  p.  302). 

Income  of  Heat. — Since  the  energy-yielding  food-stuffs  are  essentially 
proteids,  fats,  and  carbohydrates,  and  composed  of  C,  H,  O,  and  N,  and  since 
the  products  of  their  disintegration  are  essentially  urea,  COj,  and  HgO,  the 
amount  of  energy  yielded  by  the  oxidation  of  the  food-stuffs  can  readily  be 
determined  if  we  know  the  quantity  and  quality  of  the  food  and  excreta.  Since 
the  energy  of  the  organism  is  manifested  essentially  in  the  form  of  heat  and 
work,  and  as  under  ordinary  circumstances  but  a  fraction  of  it  is  manifested  as 
work,  we  may  in  making  this  estimate,  as  a  matter  of  convenience,  consider 
that  the  total  available  energy  of  the  food  appears  in  the  form  of  heat. 

The  income  of  energy  may  be  estimated  by  determining — (1)  the  quantity 
of  oxygen  consumed  ;  (2)  the  amounts  of  C  and  H  that  are  oxidized  in  the 
body  into  COj  and  H2O;  (3)  the  quantity  and  quality  of  the  food,  and  the 
energy  yielded  by  the  oxidation  of  the  same  substances  outside  the  body  when 
they  are  decompospd  into  the  same  residual  products  as  appear  in  the  body  ; 
(4)  the  quantity  of  heat  produced,  by  the  aid  of  a  calorimeter,  the  individual 
being  kept  quiet  so  that  as  little  as  possible  of  the  energy  expended  appears 
as  work. 


ANIMAL  HEAT. 


583 


The  first  two  methods  have  fallen  into  disuse.     According  to  the  third 
method  it  is  necessary  that  we  know  the  kind  and  quantity  of  food  ingested, 
the  Hnal  ,)rodaets  of  disintegration,  and  the  quantity  of  energy  evolved  by  the 
oxidation  of  each  of  the  food-stuffs  to  their  nornial  residual  substances.    As  tiie 
basis  of  the.e  calculations  wc  have  the  fact  that  during  the  complete  oxidation 
of  any  -iven  substance  a  definite  amount  of  energy  is  given  off,  and  that  when 
the  oxidation  is  but  partial  only  a  portion  of  energy  is  evolved,  the  proportion 
bein-  in  accordance  with  the  stage  of  oxidation.     The  complete  oxidation  of 
1  ci^m  of  proteid  yields  5778  calories;  of  1  gram  of  fat,  9312  calor^s;  and 
of'l  gram  of  carbohvdrate,  4116  calories  (see  Potential  Energy  of  Food,  p 
302)      If  these  substmices  be  completely  oxidized  in  the  body,  the  amount  of 
enei-v  evolved  will  be  the  same  as  though  the  oxidation  occurred  outside 
of  the  body,  provided  that  the  final  products  are  the  same  in  both  cases.     As 
far  as  fats  and  carbohydrates  are  concerned,  we  are  justified  in  assuming  that 
they  are  completely  oxidized  in  the  body  into  CO,  and  H,0 ;  but  the  proteids, 
a.  already  pointed  out,  undergo  only  partial  oxidation,  each  gram  yielding 
about  one-third  of  a  gram  of  urea.     The  results  of  experiments  show  tha 
each  gram  of  urea  contains  potential  energy  equivalent  to  2523  calories,  and 
since  each  gram  of  proteid  yields  one-third  of  a  gram  of  urea  representing 
841  calories,  each  gram  of  proteid  yields  to  the  organism  only  49o7  calories. 
The  available  energy  from  the  proteid  would,  therefore,  be  equivalent  to  the 
total  amount  of  energy  derivable  from  the  complete  oxidation  of  the  proteid 
minus  the  amount  represented  in  the  urea.     With  these  facts  in  view  it  is  a 
simple  matter  to  determine  the  total  income  of  cniergy,  should  the  diet  be 
known      Thus,  if  the  diet  consists  of  120  grams  of  proteids,  90  grams  of  fat, 
and  330  of  carbohydrates,  the   absolute   and  available   amounts  of  energy 
ingested  are—  ^^^^^  ^^^^^.^^  calories. 

Proteids  •    •  120         x         ^778  693,360 

I'T  .    90         X         9312  837,080 

^     ,    ,•    ; ooA         ^         4116  1,358,280 

Carbohydrates ^^"^^         ^         ^^^"  '^^  — 

2,888,720 

Deduct  the  proteid  energy  in  40  grams  of  urea,  40  x  2523=   J^m 

Total  daily  heat-production ■    ■    •    2,78/, 800 

Thfe  is  assuming  that  the  entire  quantity  of  proteids,  fats,  and  carbohydrates 
is  digested,  absorbed  and  ultimately  broken  down  into  CO,,  H.O,  and  urea. 
Thislssumption,  however,  is  not  justified  by  facts,  since  we  know,  for  instance, 
that  more  or  less  food  escapes  digestion.  In  practice,  therefore,  it  is  necessary 
to  ascertain  from  the  excreta  of  the  animal  (see  section  on  Nutrition)  just  how 
much  of  the  ingested  food  has  been  absorbed  and  completely  or  partially 

destroyed  in  the  body.  . 

Calorimetric  investigations  also  afford  us  indirect  information  as  to  the 
income  of  heat  by  showing  the  quantities  of  heat  produced  and  dissipated. 
Such  data  are  of  much  value,  since  it  is  evident  that  should  the  energy  of  the 
body  be  maintained  in  a  condition  of  equilibrium  from  day  to  day,  and  should 
the  energy  resulting  from  the  transformation  of  potential  energy  be  manifested 


584  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

solely  in  the  form  ot"  iieat,  it  follows  that  the  mean  daily  heat-production  and 
income  of  available  cncr»i;:y  must  balance.  lint  it  caimot  be  considered  that  this 
balance  is  maintained  at  a  constant  standard  from  hour  to  hour,  nor  from  day 
to  day;  on  the  contrary,  the  fluctuations  are  undoubtedly  considerable,  as  is 
obvious  by  the  fact  that  we  are  continually  expending  energy  and  only  periodi- 
cally (at  meal-times)  acquiring  energy.  During  fasting  there  is  absolutely  no 
income  of  energy,  yet  the  output  of  heat  may  be  subnormal,  normal,  or  hvi)er- 
normal ;  on  the  other  hand,  if  an  excess  of  energy  be  ingested,  as  in  excessive 
eating,  it  is  not  by  any  means  implied  (hat  there  is  a  similar  excess  in  heat-pro- 
duction, because  some  of  the  food  in<iested  mav  be  lost  as  undiirested  food  or  as 
partially  oxidized  excrementitious  matters,  or  may  be  stored  in  the  body  in  the 
form  of  carbohydrate,  fat,  or  proteid  ;  nor  does  an  excess  of  heat-pi'oduction 
imply  an  excess  of  income  of  energy,  because  the  storcd-up  energy  may  be 
drawn  upon.  (For  results  of  the  ealorimetric  method  see  p.  589.)  The  results 
of  the  various  methods  are  in  close  accord,  and  indicate  that  in  the  adult  the 
total  income  of  available  energy  is  about  2,500,000  calories. 

Expenditure  of  Heat. — Assuming  that  the  energy  of  the  organism  is 
expended  in  the  form  of  heat,  and  that  the  total  income  of  available  energy  is 
2^00,000  calories,  it  has  been  estimated  by  Vierordt  that  about — 

1.8  per  cent,  is  lost  in  the  urine  and  feces 47,500  calories. 

3.5         "  "  "      expired  air 84,500        " 

7.2        "  '-'  "      evaporation  of  water  from  the  lungs  •  182,120        " 

14.5        "  "         "  "  "  "         skin.     364,120 

73.0        "  "  "       radiation  and  conduction  from  skin  1,791,820        " 

2,500,000  calories. 

Therefore,  about  87.5  per  cent,  is  lost  by  the  skin,  10.7  per  cent,  by  the  lungs, 
and  1.8  per  cent,  in  the  urine  and  feces. 

C.  Heat-production  and  Heat-dissipation. 

Calorimetry. — The  intensity  of  heat  of  any  substance  is  measured  by  means 
of  a  thermometer  or  thermopile ;  the  quantity  of  heat  present  is  estimated  by 
the  weight,  the  specific  heat,  and  the  mean  temperature  of  the  body  ;  the  quan- 
tity of  heat  dissipated  is  measured  by  the  calorimeter ;  and  the  quiuitity  of 
heat  produced  is  determined  by  the  quantity  dissipated  plus  any  addition  of 
heat  to  that  of  the  body  or  miiuis  any  that  is  lost  (j).  588).  The  caloric,  or  heat 
unit,  is  the  (juantity  of  heat  that  is  necessary  to  raise  the  tem])erature  of  one 
gram  o\'  water  1°  C. ;  the  mechanical  unit,  or  grammcter,  is  the  quantity  of 
energy  required  to  raise  one  gram  a  height  of  one  meter,  and  is  equal  to  424.5 
calories;  a  kiloealorie  or  kilogramdcgvec  is  equal  to  1000  calories,  and  a  hilo- 
grammeter  to  1000  gramraeters.  By  specific  heat  is  meant  the  quantity  of  heat 
required  to  raise  the  temperature  of  any  substance  1°  C,  this  quantity  varying 
considerably  for  different  substances.  If  water  be  taken  as  1,  as  a  standard  of 
comjiarison,  the  specific  heat  of  the  animal  body  may  be  regarded  as  being 
about  0.8 ;  in  other  words,  0.8  of  the  quantity  of  heat  will  be  required  to  heat 
the  same  weight  of  the  animal  body  as  to  heat  the  water.    Knowing  the  weight, 


AXr.UAL    ir/'JAT.  585 

specific  heat,  and  teinponitiirc  of"  any  siihstaiicc  the  total  quantity  of  heat  stored 
in  it  at  a  giv-'ii  tcniiKM-ature  may  hv.  readily  calculated.  Thus,  if  the  animal 
oxperimcnted  uj)()u  weii;']!  20  kilos,  its  specific  heat  he  0.8,  and  its  temperature 
be  39°,  the  total  quantity  of  heat  stored  would  he  20  X  0.8  X  39°  =  62.4  kilo- 
g-ramdci^rees.  In  calorimetric;  work  the  total  heat  in  the  organism  is  seldom 
considered,  but  the  specific  heat  of  the  organism  is  of  importance  in  determin- 
ing the  quantity  of  heat  involved  in  a  change  of  the  animal's  temperature.  For 
instance,  should  the  animal  weigh  20  kilograms  and  its  temperatm-e  be  increased 
or  decreased  0.2°,  the  cpiantity  of  heat  added  to  or  taken  from  the  heat  of  the 
body,  as  the  case  may  be,  would  be  20X0.8X0.2=3.20  kilogramdegrees. 
These  calculations  are  of  fundamental  importance  in  studying  heat-production 
and  heat-dissipation. 

In  making  estimates  of  the  dissipation  of  heat  no  regard  is  paid  usually  to 
the  quantity  lost  in  the  urine  and  feces,  because  the  error  involved  is  so  slight, 
but  the  quantities  imparted  to  the  air,  both  in  warming  the  inspired  air  and  in 
eva])orating  water  from  the  lungs  and  skin,  represent  important  percentages. 

Calorimetry  is  spoken  of  as  direct  and  indirect.  The  former  method  is 
the  direct  determination  of  the  amount  of  heat  produced  and  dissipated ;  the 
latter  is  the  indirect  determination  based  upon  estimates  of  the  quantities  of  O 
absorbed  and  CO2  eliminated,  or  upon  the  amount  of  potential  energy  ingested 
in  the  food  and  probably  transformed  into  kinetic  energy  within  the  body 
(p.  582).^ 

Calorimeters  of  various  forms  have  been  employed,  some  of  which  have 
been  devised  to  study  the  body  as  a  whole,  while  others  are  adapted  only  for 
studying  parts,  such  as  a  leg  or  arm.  They  may  be  classified  as  ice,  air,  and 
tvater  calorimeters  in  accordance  with  the  chief  medium  employed  to  absorb 
the  heat.  They  consist  essentially  of  an  insulated  jacket  of  ice,  air,  or  water, 
which  encloses  the  animal  and  serves  to  absorb  the  heat.  The  ice  calorimeter 
is  impracticable  for  physiological  uses  because  the  animal  is  placed  under 
such  abnormal  temperature  conditions ;  the  air  calorimeter  has  many  inherent 
defects,  and  until  very  recent  years  has  found  but  little  acceptance ;  the  water 
calorimeter  is  the  form  of  apparatus  usually  employed,  having  been  first  used 
by  Crawford  in  1788;  it  has  been  materially  modified  by  Despretz  and 
Dulong  and  subsequent  investigators.  The  now  classical  instrument  of 
Dulong  consists  of  two  concentric  cases.  The  animal  is  placed  within  the 
smaller  case,  which  is  submerged  in  the  water  contained  in  the  larger  case, 
this  in  turn  being  placed  within  a  large  box,  between  which  and  the  calorime- 
ter some  non-conducting  material  such  as  feathers  or  wool  is  packed.  Suit- 
able openings  are  made  for  the  proper  supply  of  fresh  air  and  for  the  agitation 
of  the  water  in  the  calorimeter  so  that  an  equalization  of  the  temperature  of 
the  instrument  can  be  obtained.  This  apparatus  has  certain  serious  defects, 
however,  which  render  it  troublesome  for  expeditious  and  accurate  work.  An 
improved  form  devised  by  the  author  ^  which  is  now  in  general  use  meets 
every  essential  requirement  for  a  satisfactory  instrument.  The  apparatus  con- 
*  Reichert:    University  Medical  Magazine,  1890,  vol.  2,  p.  173. 


586 


AN  AMERICAN    TEXT- HOOK    OF  PHYSIOLOGY. 


sists  of  two  concentric  boxes  of  sheet  metal  which  are  fastened  together  so  that 
there  is  space  of  about  one  and  a  lialf  inches  between  them  filled  with  water 
(Fig.  142).     The  outer  box  is  fifteen  inches  in  height  and  width,  and  eighteen 


Fig.  142. — Reichert's  water  calorimeter. 

inches  in  length.  An  opening  (A)  nine  inches  in  diameter  is  made  in  one  end 
for  the  entrance  and  exit  of  the  animal.  It  is  also  perforated  with  three  small 
holes  in  the  top  corners,  and  a  slit-like  opening  in  the  top  on  one  side.  Two  of 
the  holes  are  for  the  tubes  for  the  entrance  and  exit  of  air  {EN^  EX),  the  entrance 
tube  being  carried  close  to  the  bottom,  while  the  exit  tube  extends  only  to 
the  top  of  the  box,  and  is  placed  in  the  opposite  diagonal  corner,  thus  ensuring 
adequate  ventilation.  In  the  third  hole  a  thermometer  {C  T)  is  inserted, 
by  means  of  which  the  temperature  of  the  calorimeter  (jacket  of  metal  and 
water)  is  obtained.  The  opening  in  the  side  is  for  the  insertion  of  a  stirrer  (.S), 
which  is  for  the  purpose  of  thoroughly  mixing  the  water  and  thus  equalizing 
the  temperature  of  both  water  and  metal — in  other  words,  of  the  calorimeter. 
Before  using  the  apparatus  the  calori metric  equivalent  mu:^t  he  deierm'inedj 
that  is,  the  amount  of  heat  required  to  raise  the  temperature  of  the  in.strument  1°. 
This  may  be  obtained  indirectly  by  knowing  the  different  substances  used  in 
the  construction  of  the  in.strument,  their  weights,  and  their  specific  heats,  and 
estimating  from  these  data.  It  is  better,  however,  to  make  the  determination 
by  burning  a  definite  amount  of  absolute  alcohol  or  hydrogen  within  the  instru- 
ment, or  bv  using  a  sealed  vessel  of  hot  water  of  a  known  temperature  and 
allowing  it  to  cool  to  a  definite  extent.  The  process  is  simple;  for  instance, 
each  gram  of  alcohol  or  each  liter  of  hydrogen  completely  oxidized  yields  a 
definite  number  of  calories  ;  similarly,  a  definite   weight  of  water  cooled  a 


ANIMAL  HEAT.  587 

definite  number  of  degrees  gives  off  a  definite  quantity  of  heat.  The  heat  thus 
generated  by  the  oxidation  of  the  alcoliol  or  hyth-ogen  or  given  off  by  the  cool- 
ing of  the  water  is  imparted  to  the  calorimeter  and  increases  its  temperature. 
Knowing  the  quantity  of  heat  given  to  the  calorimeter  and  the  increase  of 
temperature  of  the  instrument,  the  determination  of  the  ciilori metrical  equiva- 
lent may  be  easily  made.  Thus,  1  gram  of  alcohol  yields  in  round  numbers 
9000  calories ;  if  we  burn  10  grams  of  absolute  alcohol,  90,000  calorics  will 
result ;  if  the  temperature  of  the  calorimeter  be  increased  1°,  the  calorimetric 
equivalent  will  be  90,000  calories  or  90  kilogramdegrees ;  in  other  words,  for 
each  degree  of  increase  of  the  temperature  of  the  calorimeter  a  quantity  of 
heat  equivalent  to  90  kilogramdegrees  is  absorbed. 

The  heat  dissipated  by  an  animal  is  only  in  part  absorbed  by  the  calori- 
meter, another  portion  being  given  to  the  air  which  passes  from  the  instrument, 
and  another  portion  to  water  which  is  evaporated  from  the  lungs  and  skin. 
Three  estimates,  therefore,  are  necessary — (1)  of  the  heat  given  to  the  calori- 
meter, (2)  of  the  heat  given  to  the  air,  and  (3)  of  the  heat  given  off  in  the 
evaporation  of  water. 

The  estimate  of  the  heat  given  to  the  air  necessitates  the  measurement  of 
the  quaiitity  of  air  supplied  to  the  calorimeter,  and  of  the  temperature  of  the 
air  on  entering  and  leaving  the  calorimeter;  while  the  estimate  of  the  heat  lost 
in  evaporating  water  involves  the  measurement  of  samples  of  the  air  entering 
and  leaving  the  instrument  and  of  the  quantities  of  water  in  both  cases,  the 
total  quantity  of  water  evaporated  from  the  animal  being  estimated  from  these 
data. 

The  conduct  of  such  experiments  is  not  attended  with  any  material  dif- 
ficulties. The  water  of  the  calorimeter  is  stirred  for  a  sufficient  length  of 
time  in  order  to  obtain  a  uniform  temperature.  The  temperature  of  the 
animal  is  taken  and  the  animal  then  placed  within  the  animal  chamber.  The 
temperatures  of  the  calorimeter  and  of  the  air  entering  and  leaving  the  instru- 
ment, and  readings  of  the  three  gas-meters  are  recorded.  During  the  progress 
of  the  experiment  air  temperatures  are  recorded  at  regular  intervals  of  ten  or 
fifteen  minutes  and  the  water  stirred  for  a  few  seconds  each  time.  At  the 
conclusion  of  the  experiment  there  are  recorded — the  temperature  of  the  calori- 
meter, the  temperatures  of  the  air  entering  and  leaving  the  calorimeter,  the 
quantities  of  air  passing  through  the  three  gas-meters,  and  the  temperature  of 
the  animal. 

The  quantity  of  heat  given  to  the  calorimeter  is  now  determined  by  multi- 
plying the  increase  of  temperature  of  the  instrument  by  the  calorimetric 
equivalent.  If  the  rise  of  temperature  be  0.6°  C.  and  the  calorimetric  equiva- 
lent be  90  kilogramdegrees,  the  quantity  of  heat  imparted  to  the  water  jacket 
will  be  90  X  0.6°  =  54  kilogramdegrees. 

The  quantity  of  heat  imparted  to  the  air  is  determined  by  finding  first  the 
corrected  volume  of  the  air,  then  reducing  the  corrected  volume  to  weight, 
then  multiplying  the  weight  by  the  specific  heat  of  air  at  0°  C,  and  finally 
multiplying  by  the  increase  of  temperature.     The  corrected  volume  may  be 


588  A  A  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

V       P 

uhtuiiicd  l)v  tlu!  lollowing   formula:  V= ,  where  V  is 

760  (1  +  0.003665  t) 
the  reqiiirt'd  volume  at  0°  C  and  760  mm.  barometric  pressure,  V  the  ob- 
served volume,  P  the  observed  pressure,  aud  t  the  observed  mean  temperature : 
760  (1  +  0.003665)  is  conveniently  obtained  from  standard  tables.  The  errors 
incident  to  changes  in  barometric  pressure  and  in  aqueous  tension  are  so  slight 
tiiat  they  are  not  usually  taken  into  consideration.  Assuming  that  the  quan- 
tity of  air  suj)plied  amounted  to  6000  liters,  and  that  the  mean  temperature 
of  the   air  was  20°,  the   corrected  volume   would    be,  omitting  l)arometric 

V  6000 

pressure  and  aqueous  tension,  V  = = —  5590  liters 

(1  +  0.0036656  t)  1,0733 
at  0°  C.  One  litre  of  dry  air  at  0°  C.  weighs  0.001293  kilogram  ;  therefore, 
5590  liters  x  0.001293  =  7.228  kilograms.  If  we  assume  that  the  air  during 
its  passage  through  the  calorimeter  had  its  temperature  increased  3°,  and  the 
specific  heat  of  air  is  0.2377,  the  quantity  of  heat  imparted  to  the  air  must 
have  been  7.228  X  3  X  0.2377  =  5.152  kilogramdegrees. 

The  next  estimate  is  of  the  quantity  of  lieat  lost  in  the  evaporation  of 
ivater.  This  is  determined  by  finding  the  difference  between  the  quantities 
of  water  in  the  samples  of  the  air  passing  into  aud  from  the  calorimeter,  and 
estimating  from  these  results  the  amount  of  moisture  imparted  to  the  total  air 
leaving  the  chamber.  Assuming  that  10  grams  of  water  were  thus  evaporated, 
since  each  gram  requires  about  582  calories  or  0.582  kilogramdegree,  the  quan- 
tity of  heat  evolved  would  be  equal  to  10  X  0.582  =  5.82  kilogramdegrees. 

The  total  quantity  of  heat  dissipated  would  therefore  be  the  sum  of  the 
quantities  given  to  the  calorimeter,  to  the  air,  aud  to  the  \vater  evaporated  : 

Given  to  tlie  calorimeter 54,00U  kilogramdegrees. 

Given  to  the  air 5,152  " 

Lost  in  evaporating  water 5,820  '' 

Total  heat-dissipation 64,y72  " 

The  quanttf)/  of  heat  produced  is  determined  by  adding  to  or  subtracting 
from  the  quantity  dissipated  the  amount  of  heat  that  may  have  been  gained 
or  lost  by  the  organism.  It  is  obvious  that  any  difierence  between  the 
quantities  of  heat  dissipated  and  produced  must  be  represented  by  an  increase 
or  decrease  of  the  mean  temperature  of  the  animal.  If  the  animal's  teiupera- 
ture  reiuains  unchanged,  the  quantity  of  heat  produced  is  the  same  as  the 
quantity  lost ;  if,  however,  the  animal's  temperature  increases,  less  heat  is 
dissipated  than  is  ])roduced  ;  if  it  falls,  ince  versa.  The  quantity  of  licat 
involved  in  a  change  of  body-temperature  is  determined  by  the  product  of 
the  change  in  temperature  into  the  animal's  weight  and  specific  heat.  Assum- 
ing that  the  animal's  temperature  at  the  beginning  of  the  experiment  was 
38.95°  C.  and  at  the  end  39.32°  C,  the  temperature  being  increased  0.37°  C, 
that  the  animal's  weight  was  25  kilograms,  and  that  the  animal's  specific  heat 
was  0.8,  the  quantity  of  heat  would  be  0.37  X  25  x  0.8  ^-  7.4  kilogramdegrees. 


ANIMAL  HEAT. 


589 


The  quantity  of  heat  produced  would,  tlierefore,  be  the  total  quantity  dissipated 
phis  tlu>  (luantity  of  heat  added  to  the  heat  of  the  organism  at  the  time  the 
oxperimciit  begun  ;  therefore,  the  heat-produetion  was  04.972  +  7.4  =  72.372 
kilograiudegrees.  If  the  animal's  temperature  had  fallen,  more  heat  would 
have  been  dissipated  than  produeed,  beeause  the  total  quantity  of  heat  in  the 
organism  was  greater  at  the  beginning  than  at  the  end  of  the  experiment; 
therefore,  the  cpiantity  of  heat  represented  in  the  change  of  temi)erature  would 
have  been  deducted  from  the  (piantity  of  heat  dissipated. 

While  calorimetric  experiments  do  nut  generally  involve  any  special  diffi- 
culties, accurate  results  can  only  be  ensured  by  the  strict  observation  of  certain 
details :  (1)  The  temperatures  of  the  calorimeter  and  room  should  be  as  nearly 
as  possible  alike  and  kept  as  far  as  possible  constant.  (2)  The  thermometers 
employed  should  be  so  sensitive  that  readings  can  be  made  in  hundredths  of  a 
degree,  and  they  should  respond  very  quickly,  so  that  rectal  temperatures  can 
be'obtained  within  three  minutes.  (3)  Rectal  temperatures  are  to  be  preferred, 
the  thermometer  always  being  inserted  to  the  same  extent  and  held  in  the 
same  position,  care  being  exercised  to  prevent  the  burying  of  the  bulb  in  fecal 
matter.  (4)  The  animal  during  the  taking  of  its  temperature  nmst  on  no 
account  be  tied  down,  but  gently  held,  and  all  circumstances  seduously  avoided 
that  tend  to  excite  the  animal.  The  chief  sources  of  error  in  the  calorime- 
try  are  in  failures  to  obtain  accurate  temperatures  of  the  calorimeter  and  of 
the  animal.  In  the  latter  case  inaccuracy  is  to  some  extent  absolutely  una- 
voidable, chiefly  because  of  normal  fluctuations  which  occur  frequently  and  are 
often  very  marked. 

Conditions  affecting  Heat-produetion.— The  quantity  of  heat  produced 
must  necessarily  vary  with  many  circumstances.  Estimates  of  heat-production 
in  the  adult  range  in  round  numbers  from  2000  to  3000  kilogramdegrees  per 
diem  according  to  the  method  and  incidental  circumstances,  llius,  according 
to— 


Scharling 3169  kilogramdegrees 

Vogel 2400 

Him 3725 

Ley  den 2160 

Hemholtz 2732  " 

Rosenthal 2446 

Danilesky 3210  " 

Ludwig 3192 


Ranke 2272  kilogramdegrees 

Rubner 2843 

Ott 103 

per  hour  during  tlie  afternoon  (weight  of 
man  87.3  kilograms). 

Lichatschew  .  .  •  ■  33.072  to  38.723  kilo- 
gramdegrees per  kilogram  of  body-weighl 
per  diem.' 


The  chief  conditions  which  affect  heat-production  are  age,  sex,  constitution, 
body-weight  and  body  surface,  species,  respiratory  activity,  the  condition  of 
the  circulation,  internal  and  external  temperature,  food,  digestion,  time  of  day, 
muscular  activity,  the  activity  of  heat-dissipation,  nervous  influences,  drugs, 
abnormal  and  pathological  conditions. 

1  The  fi-ures  bv  Ott  {New  York  Medical  Journal,  1889,  vol.  16,  p.  29)  and  Lichatschew 
{Diss.  inm,luralis/st.  Petersburg,  1893;  quoted  in  Hermann's  Jahresberichte  der  Physiologic, 
1893,  p.  99)  were  obtained  by  means  of  a  water  calorimeter. 


590  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

Yoiinj;  animals  produce  more  heat,  weight  for  weiglit,  than  the  mature.  Tliis 
is  owing  chiefly  to  the  greater  activity  of  the  metabolic  processes  in  the  former, 
autl  iu  part  to  the  relatively  larger  body  surface,  young  animals  generally 
being  smaller  than  the  matured  and  thus  having,  in  proportion  to  body-weight, 
larger  radiating  surfaces. 

Heat-productiou  is  more  active  in  the  robust  than  in  the  weak,  other  con- 
ditions being  the  same. 

The  weight  of  the  body  is  obviously  a  most  important  factor  in  relation  to 
the  quantity  of  heat  produced,  especially  as  regards  the  weight  of  the  active 
tissues  iu  relation  to  inactive  structures  such  as  bone,  sinew,  and  cartilage. 
Two  animals  of  the  same  weight  may  produce  very  different  quantities  of 
heat  per  diem,  other  things  being  equal.  Thus,  a  fleshy  animal  should 
naturally  be  expected  to  produce  more  heat  than  one  Avith  very  little  flesh  and 
an  abundance  of  fat,  which  is  an  inactive  heat-producing  structure.  While, 
therefore,  the  relation  of  heat-production  to  body-weight  does  not  seem  to  be 
definite,  yet  the  experiments  by  Reichert^  and  by  Carter^  indicate  that  heat- 
production  bears,  broadly  speaking,  a  direct  relation  to  body-weight. 

Heat-production  is  greater  relatively  in  homotherraous  than  in  poikilother- 
mous  animals ;  it  varies  materially  in  intensity  in  different  species,  especially  in 
warm-blooded  animals ;  and  it  is  closely  related  to  the  intensity  of  respiration. 
Moreover,  it  is  probable  that  each  species,  and  even  each  individual  of  the 
species,  has  its  own  specific  thermogenic  coefficient,  that  is,  a  mean  standard  of 
heat-production  for  each  kilogram  of  body-weight  or  for  each  square  centime- 
ter of  body-surface.  The  following  figures  giving  the  heat-production  per 
kilogram  per  hour,  compiled  by  Munk,^  are  of  interest  both  as  regards  species 
and  size  and  weight  of  the  animal  in  relation  to  heat-production  : 


Horse 1.3  kilogramdegrees. 

Man 1.5 

Child  (7  kilograms)  .    .  3.2  " 

Dog  (30  "       )  .    .  1.7 

Dog     (3  "       )  .    .  3.8 

Guinea-pig 7.-5  " 


Duck 6.0  kilogramdegrees. 

Pigeon 10.1 

Rat 11.3 

Mouse 19.0 

Sparrow 35.5  " 

Greenfinch 35.7  " 


These  figures  have  an  additional  interest  when  compared  with  the  respira- 
tory activity  of  different  species  (p.  537).  The  intensity  of  respiration  has  a 
marked  significance  both  in  connection  with  the  species  and  the  individual. 
The  larger  the  quantity  of  oxygen  consumed  the  greater  relatively  is  the 
activity  of  oxidation  processes,  and,  consequently,  the  more  active  is  heat-pro- 
duction (see  p.  537).  Therefore,  all  circumstances  w'hich  affect  respiratory 
activity  tend  to  affect  thermogenesis.  The  intensity  of  respiratory  activity  and 
the  extent  of  body-surface  in  relation  to  body- weight  are  closely  related  (p. 
538). 

Increased  activity  of  the  circulation  is  favorable  to  increa.sed  heat-produc- 

'  University  Meflical  Magazine,  1890,  vol.  2,  p.  225. 

'  Journal  of  Nervom  and  Menial  Diseases,  1890,  vol.  17,  p.  782. 

'  Physiologie  des  Menschen  und  der  Saugethiere,  1892,  p.  302. 


ANIMAL  HEAT.  591 

tion,  this  being  duo  to  several  factors:  (1)  A  more  abmulant  supply  of  blood 
may  be  accompanied  by  increased  metabolic  activity.  (2)  Increased  circulatory 
activity  is  favorable  to  incn'ascd  heat-dissipation  by  causing  a  larger  supply 
of  blood  to  the  skin,  thus  facilitating  loss  by  radiation  and  indirectly  tending  to 
increase  thermogenesis.  (3)  Increased  circulatory  activity  also  excites  the  respi- 
ratory movements  and  the  secretion  of  sweat,  thus  increasing  heat-loss  and  in- 
directly favoring  heat-production.  (4)  The  more  active  the  circulation  the 
larger  the  amount  of  heat  produced  by  the  heart  and  the  movement  of  the 
blood.  The  diurnal  fluctuations  of  the  pulse-rate  are  said  to  be  more  or  less 
closely  related  to  similar  changes  of  body  temperature. 

A  rise  of  internal  temperature  (bodily  temperature)  is  favorable  to  increased 
metabolic  activity  (p.  540)  and,  therefore,  to  an  increase  of  heat-production ; 
conversely,  a  fall  of  bodily  temperature  reduces  heat-production.  The  influ- 
ences of  bodily  temperature  are,  as  a  whole,  less  important  than  those  of  ex- 
ternal temperature. 

The  influences  of  external  temperature  are  in  a  measure  different  upon  homo- 
thermous  and  poikilothermous  animals.  In  the  former,  heat-production  is  in 
inverse  relation  to  the  temperature  of  the  surrounding  medium,  so  that  the 
cooler  the  ambient  temperature  the  greater  the  heat-production  ;  in  the  latter 
heat-production  increases  with  an  increase  of  external  temperature,  because 
with  the  rise  of  the  latter  bodily  temperature  increases,  which  in  turn  increases 
metabolic  activity  (pp.  540,  541).  Consequently,  in  warm-blooded  animals  heat- 
production  is  greater  in  cold  climates  and  seasons  than  in  the  opposite  conditions, 
while  in  cold-blooded  animals  the  opposite  is  the  case.  Cold  applied  to  the  skin 
increases  heat-production  by  reflexly  exciting  muscular  activity  (shivering,  etc., 
p.  541) ;  moderate  heat  exerts  the  opposite  influence  unless  the  bodily  tem- 
perature is  affected,  as  shown  by  the  results  of  studies  of  respiration  (p.  541). 
The  character  of  the  food  is  important.  Danilewsky^  has  estimated  that  the 
following  quantities  of  heat  are  produced  under  different  diets,  etc. : 

On  a  minimum  diet 1800  kilogramdegrees. 

On  a  leduced  diet  (absolute  rest) 1989 

On  a  non-nitrogenous  diet 2480 

On  a  mixed  diet  (moderate  work) 3210 

On  an  abundant  diet  (hard  work) 3646  " 

On  an  abundant  diet  (very  laborious  work) 3780 

The  influence  of  the  quantity  and  quality  of  the  diet  must  be  potent  when 
it  is  remembered  that  1  gram  of  proteid  yields  about  4937  calories,  1  gram  of 
fat  about  9312  calories,  and  1  gram  of  carbohydrate  about  4116  calories.  In 
cold  climates  fats  enter  very  largely  into  the  diet  because  of  the  greater  loss 
of  heat  and  the  consequent  increased  demand  for  heat-producing  substances. 

During  the  periods  of  digestion  more  heat  is  produced  than  during  the  in- 
tervals, this  increase  being  due  chiefly  to  the  muscular  activity  of  the  intestinal 
walls  (p.  540).  Langlois'  experiments  indicate  that  during  digestion  heat- 
production  may  be  increased  35  to  40  per  cent. 

I  Pfiiigei-'s  Archivfiir  Physioloffie,  1883,  vol.  xxx.  p.  19a 


592  AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

It  is  said  that  heat-prodiietion  undergoes  diurnal  variations  wiiich  eorre- 
spond  with  the  fluctuations  of  bodily  t^fmijerature,  but  this  is  doubtful. 

All  structures  produce  more  heat  during  activity  than  during  rest.  Heat- 
production  has  been  e-tiniated  to  be  from  two  and  a  half  to  three  times  greater 
when  awake  and  resting  than  when  asleep,  and  from  one  and  a  half  to  three 
times  more  when  active  than  when  at  rest,  in  jiroportion  to  the  degree  of 
activity.  During  hybernation  the  absorption  of  O  falls  considerably  (p.  542), 
consequently  heat-protluctiou  is  believed  to  decline  to  a  like  degree. 

All  circumstances  which  affect  heat-dissipation  (p.  601)  tend  indirectly  to 
influence  heat-production. 

The  most  important  of  the  factors  influencing  heat-production  is  the  ner- 
vous mechanism  which  controls  the  heat-producing  processes  (p.  598). 

Various  drugs  exert  more  or  less  potent  influences  directly  or  indirectly  upon 
heat-production.  Cocain,  strychnin,  brucin,  and  other  motor  excitants  increase 
heat-production ;  while  chloroform,  most  antipyretics,  narcotics  generally,  bro- 
mides, and  motor  depressants  decrease  heat-production. 

Heat-production  is  diminished  in  most  forms  of  anaemia,  after  severe  hem- 
orrhage, and  in  most  non-febrile  adynamic  conditions.  It  is  usually  increased 
in  fevers,  especially  so  in  infectious  fevers.  According  to  Liebermeister,  the 
increase  in  fever  is  probably  about  6  per  cent,  for  each  increase  of  1°  C.  of 
bodily  temperature,  so  that  were  the  increase  of  temperature  3°  C.  the  increase 
of  heat-production  would  be  18  per  cent. 

Conditions  affecting  Heat-dissipation. — The  loss  of  heat  from  the  body 
occurs  through  several  channels — in  the  urine,  feces,  sweat,  and  expired  air, 
and  by  radiation  and  conduction  from  the  skin ;  hence,  all  conditions  which 
affect  the  loss  of  heat  in  the  above  ways  must  influence  heat-dissipation.  The 
chief  of  these  are :  Age,  sex,  species,  the  quantity  of  subcutaneous  fat,  the 
nature  of  the  surrounding  medium,  clothing,  internal  and  external  tempera- 
ture, activity  of  heat-production,  body-surface,  the  condition  of  the  circulation, 
respiration,  sweat,  activity,  radiating  coefficient,  nervous  influences,  drugs,  and 
abnormal  conditions. 

The  young  di.ssipate  and  produce  more  heat  in  proportion  to  body- weight 
than  the  adult,  this  being  due  chiefly  to  the  relatively  greater  metabolic 
activity  and  the  larger  proportional  body-surface  (p.  538),  and  consequent 
greater  radiation,  in  the  young. 

Sex  per  se  does  not  seem  to  exert  any  influence,  although  the  adult  human 
female,  weight  for  weight  and  for  an  equivalent  bodily  surface,  probably  dissi- 
pates less  heat  than  the  male,  because  of  her  relative  abundance  of  subcu- 
taneous fat,  which  hinders  heat-dis«ipation.  No  difference  so  far  as  sex  is 
concerned  has  been  noted  in  the  lower  animals. 

Heat-dissipation  varies  greatly  in  different  species,  owing  chiefly  to  relative 
size  and  respiratory  activity,  to  the  nature  of  the  medium  in  which  the  animal 
lives,  and  to  the  character  of  the  bo<ly-covering.  Heat-dissipation  is  more 
active  in  homothermous  animals  than  in  poikilothermous  animals,  because  of 
the  greater  activity  in  the  former  of  heat-production.     In  amphibia  heat-dissi- 


ANI^fAL   HEAT.  693 

pation  is  greater  when  the  animal  is  in  the  water  than  when  exposed  to  the  air 
if  both  water  and  air  be  of  the  same  temperature,  because  water  is  a  better 
conductor  of  heat  and  conse^piently  withdraws  heat  from  the  body  more 
rapidly.  The  hij^her  the  temperature  of  the  surroundings  the  higher  the 
bodily  temperature  of  cold-blooded  animals,  consequently  the  greater  are  heat- 
production  and  heat-dissipation.  In  warm-blooded  animals  the  effect  o!i  botii 
heat-production  and  heat-dissipation  is  in  inverse  relation  to  the  surrounding 
temperature  (unless  tiie  bodily  temperature  is  affected),  external  heat  decreasing 
both  heat-dissipation  and  heat-production,  and  internal  heat  increasing  both. 

Subcutaneous  fat  is  a  poor  conductor  of  heat,  consequently  the  greater  the 
abundance  of  it  the  greater  the  hindrance  offered  to  the  dissipation  of  heat. 
The  value  of  fat  in  this  respect  is  illustrated  in  water- fowl,  which,  as  a  rule, 
are  far  more  abundantly  supplied  with  fat  than  other  species ;  and  by  the  ex- 
ceptional abundance  of  subcutaneous  fat  in  species  of  fowl  which  inhabit  very 
cold  waters.  Bathing  the  skin  with  grease  hinders  radiation,  and  is  adopted 
by  swimmers  both  to  conserve  the  bodily  heat  and  to  protect  the  skin. 

When  air  and  water  are  of  the  same  temperature,  heat-dissipation  is  greater 
when  the  animal  is  exposed  to  the  water,  because  the  latter  is  a  better  con- 
ductor. Heat-loss  is  greater  in  dry  than  in  moist  air,  other  things  being 
equal,  because  in  the  former  the  evaporation  of  sweat  from  the  body  and  the 
loss  of  water  from  the  lungs  are  favored,  the  vaporization  of  water  affecting 
heat-dissipation  more  decidedly  than  the  moisture  of  the  air.  Heat-dissipation 
is  more  active  in  cold  moist  air  than  in  cold  dry  air.  Cold  air  is  not  favorable 
to  the  vaporization  of  water,  whereas  cold  moist  air  has  a  higher  si^ecific  heat 
than  the  dry  air,  and  thus  tends  to  carry  off  heat  more  rapidly. 

The  character  of  the  covering  of  the  body  is  of  great  importance.  This 
is  illustrated  in  the  changes  which  occur  in  the  natural  covering  of  animals 
during  warm  and  cold  seasons,  and  in  the  characters  of  the  fur  of  species 
which  inhabit  very  cold  or  very  warm  climates.  During  the  winter  the  fur 
is  longer  and  thicker  than  during  the  summer.  Animals  living  in  cold  or  hot 
climates  are  supplied  with  a  relatively  greater  or  less  abundance  of  fur  or 
feathers  and  subcutaneous  fat.  Man  provides  for  changes  of  the  seasons  by 
modifying  the  quantity  and  quality  of  his  clothing.  In  the  adaptation  of 
dress  to  climate,  the  conductivity,  radiating  coefficient,  hygroscopic  capacity, 
porosity,  weight,  and  color  of  the  clothing  are  important  factors.  The  poorest 
conductors,  other  things  being  equal,  make  the  warmest  clothing;  fur  and 
wool  are  poor  conductors  and  therefore  are  adapted  especially  for  cold  seasons 
and  climates,  while  cotton  and  linen  are  good  conductors  and  therefore  make 
cool  clothing.  The  radiating  coefficient  depends  upon  the  conductivity  of  the 
material  and  the  character  of  the  radiating  surface.  The  coarser  the  material 
the  better  the  radiating  surface,  hence  the  better  the  conductor  and  the  cooler 
the  clothing.  The  hygroscopic  character  of  the  clothing  is  of  far  more 
importance  than  is  generally  believed.  Articles  of  clothing  having  a  large 
capacity  for  absorbing  and  retaining  moisture  are,  other  things  being  equal, 
of  more  value,  especially  for  underwear,  than  those  possessing  the  o])posite 

38 


r)04  AN  AMERICAN   TEXT-BOOK    OF  I'llYSlOLOQY. 

(jiialitv.  Woollen  goods  compared  with  lliosi;  made  of  cotton  not  only  have 
a  far  greater  absorptive  capacity  but  retain  moisture  for  a  longer  tinu.'.  \\'hen 
the  clothing  is  of  wool  people  are  less  apt  to  catch  cold  from  exjHtsure  to 
draughts  and  sudden  cold  than  when  it  is  of  linen  or  cotton,  the  wool  pre- 
venting a  too  rapid  evaj)oration  of  moisture,  thus  guarding  against  chilling. 
Porosity  is  a  comparatively  subsidiary  factor.  The  greater  the  weight  of  the 
clothing,  other  things  being  equal,  the  more  is  heat-dissipation  hindered.  Tiie 
color  of  the  outer  apparel  has  a  certain  influence  owing  to  the  relative  heat- 
absorbing  cajiacities,  black  clothing  being  warmer  than  white,  etc.,  hence  the 
general  use  of  white  or  light-colored  clothing  in  warm  climates  and  seasons. 

A  rise  of  internal  temperature  (bodily  temperature)  is  favorable  to  an  in- 
crease of  heat-diasipation,  for  several  reasons:  (1)  Heat-production  tends  to 
be  increased  and  thus  cause  an  effort  of  the  system  to  get  rid  of  the  excess  of 
heat.  (2)  The  activity  of  the  circulation  is  increased,  causing  a  larger  amount 
of  l)lood  to  be  brought  to  the  cutaneous  surface  where  it  is  subjected  to  the 
influence  of  the  cooler  surroundings.  (3)  Respiratory  movements  are  increased 
so  that  heat-dissipation  is  favored  by  the  larger  amount  of  air  respired  and 
larger  amount  of  moisture  carried  off.  (4)  The  temperature  of  the  body  is 
higher  in  relation  to  that  of  the  surroundings  and  thus  heat-dissipation  by 
radiation  and  conduction  is  facilitated.  The  influences  of  external  tempera- 
ture are  even  more  potent  in  their  effects  than  those  of  internal  temperature, 
chiefly  because  of  the  much  wider  range  of  temperature  to  which  the  organism 
is  subjected.  Bodily  temperature  under  ordinary  circumstances  does  not  vary 
more  than  1°  to  2°  C.  during  the  twenty- four  hours,  but  external  temperature 
may  vary  as  much  as  40°  C,  or  more.  External  heat  tends  by  exciting  cuta- 
neous nerves  to  reflexly  diminish  heat-production  and  thus  indirectly  dimin- 
ish heat-dissipation  ;  but  this  is  to  some  extent  antagonized  by  a  dilatation  of 
the  blood-vessels  of  the  skin,  an  excitation  of  respiration,  and  increase  in  the 
quantity  of  sweat,  all  of  which  tend  to  increase  heat-dissipation,  but  which 
are  unable  to  balance  the  opposite  effects.  Cold,  on  the  other  hand,  accelerates 
both  heat-dissipation  and  heat-production.  The  loss  of  heat  from  the  body 
is  increased  because  of  the  greater  difference  in  the  temperatures  of  the  body 
and  the  surroundings ;  but,  on  the  other  hand,  the  cutaneous  vessels  are  con- 
tracted, the  circulation  is  less  active,  and  the  quantity  of  sweat  is  lessened,  all 
of  which  are  unfavorable  to  heat-dissipation.  Yet  while  these  latter  altera- 
tions tend  to  diminish  heat-loss,  they  are  not  sufficient  to  compensate  for  the 
increased  expenditure  by  radiation  and  for  the  greater  loss  by  respiration. 

Circumstances  which  increase  heat-production  above  the  normal  tend  indi- 
rectly to  increase  heat-dissipation.  Other  things  being  equal,  the  greater  the 
quantity  of  heat  produced  the  greater  the  heat-dissipation,  unless  the  bodily 
temperature  be  below  the  normal,  in  which  case  heat-production  may  be  in- 
creased and  yet  heat-dissipation  remain  unaffected,  or  even  be  diminished,  until 
sufficient  heat  has  accumulated  to  bring  the  bodily  temperature  up  to  the 
mean  standard. 

The  larger  the  surface  of  the  body  ex])osed  to  the  normally  cooler  sur- 


ANIMAL    HEAT. 


595 


roundings,  the  greater  is  the  loss  of  heat.  Tlie  larger  the  animal  the  greater  the 
body-surface,  and  thorelbre  the  greater  is  heat-dissipation  ;  l)nt  in  proportion 
to  bodv-weight  smaller  animals  have  larger  body-surfaces,  therefore  heat-dissi- 
pation' is  relatively  greater,  although  not  absolutely  so  (see  p.  537).  The  area 
of  body-surface  involved  in  heat-dissipation  is  affected  by  the  position  of  the 
individual.  Thus,  bv  bringing  the  arms  and  legs  in  contact  with  the  body 
the  total  surface  exposed  is  lessened.  On  the  other  hand,  animals  which 
habitually  have  their  legs  in  apposition  with  the  trunk  have  their  radiating, 
surfaces  increased  when  their  legs  are  extended.  For  instance,  in  the  rabbit 
extension  of  the  legs  enormously  increases  heat-dissipation,  so  that  the  bodily 
temperature  is  profoundly  affected. 

The  condition  of  the  vascular  system  exercises  an  important  influence. 
Circumstances  that  excite  the  circulation  affect  heat-dissipation  both  directly 
and  indirectly.  Thus,  heat-loss  is  directly  increased  by  the  excitation  of  the 
respiratory  movements,  by  the  increased  secretion  of  sweat,  and  by  the  larger 
supply  and  increased  temperature  of  the  blood  to  the  skin.  Increased  activity 
of  the  circulation  also  increases  heat-production,  and  thus  indirectly  affects  heat- 
dissipation.     Opposite  conditions,  of  course,  lessen  heat-dissipation. 

The  larger  the  quantity  of  air  respired,  other  things  being  equal,  the  larger 
the  loss  of  lieat  by  this  channel.  The  heat-loss  occurs  both  in  warming  the 
air  and  in  the  evaporation  of  water  from  the  lungs,  so  that  the  cooler  and 
drier  the  air  inspired  the  larger  relatively  is  the  heat-loss.  The  importance 
of  respiration  as  a  heat-dissipating  factor  is  illustrated  by  the  fact  that  about 
10.7  per  cent,  of  the  total  heat-dissipation  occurs  in  this  way  (see  p.  584). 

Next  in  importance  to  radiation  is  the  amount  of  ^vater  evaporated  from 
the  skin.  Each  gram  of  water  requires  582  calories  to  vaporize  it,  and  it  is 
estimated  (p.  584)  that  364,120  calories  are  dissipated  in  this  way,  or  14.5 
per  cent,  of  the  total  heat-dissipation.  An  increase  of  external  temperature 
increases  the  irritability  of  the  sudoriparous  glands,  thus  favoring  secretion  and 
heat-dissipation.  The  value  of  sweat,  however,  as  a  means  of  carrying  off 
heat,  is  materially  affected  by  the  temperature  of  the  air  as  well  as  by  the 
amount  of  moisture  present. '  The  higher  the  temperature  and  the  less  the 
moisture  the  more  rapidly  evaporation  occurs,  and  consequently  the  greater 
the  loss  of  heat ;  when  air  is  moist  and  of  high  temperature  evaporation  takes 
place  relatively  slowly,  if  at  all.  Therefore,  individuals  can  withstand  sub- 
jection to  dry  air  of  a  higher  temperature  and  for  a  longer  period  than  when 
the  atmosphere  is  moist.  In  the  former  case  sweat  is  rapidly  secreted  and 
vaporized,  and  thus  a  marked  rise  of  internal  temperature  may  be  prevented. 
James  found  that  a  vapor  bath  at  44.5°  C.  (112°  F.)  was  insufferable,  while 
dry  air  at  80°  C.  (176°  F.)  caused  little  inconvenience.  AVhen  air  is  of  high 
temperature  and  loaded  with  moisture  we  say  that  it  is  "sultry,"  but  dry  air 
of  the  same  temperature  is  not  unpleasant. 

I^Iuscular  activity  increases  heat-production,  excites  the  circulation  and 
respiration,  and  increases  the  secretion  of  sweat,  all  of  which  directly  or  indi- 
rectly increase  heat-dissipation. 


596  AN  AMERICAN   TEXT- BOOK   OF  PHYSIOLOGY. 

Tlie  .surface  of  the  body  as  a  radiating  surface  cannot  be  rejL^anled  in  the 
same  light  as  an  indifferent,  inanimate  surface,  such  as  metal  or  wood.  The 
coeffidcnt  of  radiation  (the  quantity  of  heat  emitted  during  a  unit  of  time  at  a 
standard  temperature  from  a  given  area)  in  an  inanimate  body  remains  fixed, 
because  the  surface  itself  is  virtually  unchangeable ;  but  the  coefficient  for  the 
living  organism  is  subject  to  material  alterations.  These  alterations  depend 
chiefly  (1)  upon  the  actions  of  tlie  pilo-motor  mechanism  whereby  the  relation 
of  the  natural  covering  (hair  or  feathers  in  the  lower  animals)  of  the  body  to 
the  skin  is  effected ;  (2)  upon  changes  in  the  conductivity  of  the  skin  owing  to 
variations  of  the  blood-supply  ;  (3)  upon  the  varying  thickness  of  the  skin  in 
different  species,  in  different  individuals,  and  in  different  parts  of  the  body ; 
(4)  upon  the  temperature  of  the  surroundings;  (5)  upon  the  extent  of  the 
body-surface  exposed ;  (6)  upon  the  character  of  the  clothing.  When  the 
arrector  pili  muscles  contract  the  skin  is  made  tense  and  the  cutaneous  blood- 
vessels are  pressed  upon  and  rendered  anaemic,  thus  lessening  the  quantity  of 
fluid  in  the  skin  and  as  a  consequence  lowering  the  coefficient  of  dissipation  ; 
moreover,  in  animals  whose  natural  covering  is  fur  or  feathers,  these  fibres 
cause  an  erection  of  one  or  the  other,  as  the  case  may  be,  and  in  this  way 
affect  the  radiating  coefficient.  The  coefficient  is  enormously  increased  by 
removing  the  natural  covering,  such  as  the  fur  of  the  rabbit,  under  which  cir- 
cumstances, even  though  the  animal  be  subjected  to  a  relatively  high  external 
temperature,  heat-dissipation  is  so  enormously  increased  that  death  ensues  within 
two  or  three  days.  When  one  side  of  the  body  of  a  horse  was  shaved  and  the 
animal  subjected  to  an  atmosphere  having  a  temperature  of  0°  C,  the  tem- 
perature of  the  skin  of  the  shaven  side  fell  8°  in  forty  minutes,  while  the 
temperature  of  the  unshaven  side  fell  only  0.5°. 

The  coefficient  is  diminished  where  there  is  excessive  sebaceous  secretion, 
and  where  grease  is  artificially  applied,  and  by  an  accumulation  of  subcutaneous 
fat ;  it  is  increased  by  wetting  the  skin,  as  by  sweat  or  bathing ;  and  it  is 
affected  by  many  other  circumstances. 

Through  the  operations  of  the  nervous  system  heat-dissipation  may  be 
affected  directly  or  indirectly  by  action  upon  the  heat-dissipating  and  heat- 
producing  processes — circulation,  respiration,  sudorific  and  sebaceous  glands, 
and  arrector  pili  muscles. 

There  are  many  drugs  which  directly  or  indirectly  affect  heat-dissipation. 
Drugs  which  cause  dilatation  of  the  cutaneous  vessels  tend  to  increase  heat- 
dissipation  ;  conversely,  those  which  cause  contraction  of  the  blood-vessels 
hinder  dissipation.  Diaphoretics  increase  heat-loss  essentially  by  increasing 
the  amount  of  sweat.  Respiratory  excitants  increase  the  loss  of  heat  by  means 
of  the  increased  volume  of  air  respired.  Drugs  which  increase  heat-jiroduction 
tend  to  indirectly  increase  heat-dissipation. 

All  pathological  states  which  affect  heat-production  tend  to  similarly  disturb 
heat-dissipation.  Conditions  of  malnutrition  favor  heat-dissipation  by  causing 
a  loss  of  subcutaneous  fat,  but  this  is  to  a  greater  or  less  extent  compensated 
or  by  the  eufeebleraent  of  the  circulation,  respiration,  and  metabolic  processes 


ANIMAL  HEAT.  597 

in  general.  In  fever,  both  heat-prodnction  and  heat-dissipation  are  generally 
increased,  the  fbrnier  being  afJ'ected  more  than  the  latter,  so  that  the  bodily- 
temperature  rises.  In  some  forms  of  fever  the  rise  of  temperature  is  essentially 
due  to  diminished  heat-dissipation. 

D.  The  Heat-mechanism. 

The  heat-mechanism  consists  of  two  fundamental  parts,  one  being  concerned 
in  heat-production,  and  the  other  in  heat-dissipation.  Heat-production  is 
briefly  expressed  as  tlwrmogenesis ;  and  heat-dissipation,  as  fhermolyfiis.  The 
operations  of  these  mechanisms  are  so  intimately  related  that  fluctuations  in  the 
activity  of  one  are  rapidly  compensated  for  by  reciprocal  changes  in  the  other, 
so  that  under  normal  conditions  heat-production  and  heat-dissipation  so  nearly 
balance  that  thd  mean  bodily  temperature  is  maintained  within  narrow  limits. 

The  regulation  of  the  relations  between  heat-production  and  heat-dissipation 
is  termed  thermotaxis,  which  regulation  may  be  effected  by  alterations  in  either 
thermogenesis  or  thermolysis. 

The  Mechanisra  concerned  in  Thermogenesis. — The  portion  of  the  heat- 
raechanism  concerned  in  heat-production  consists  of  (1)  thermogenic  tissues, 
(2)  thermogenic  nerves,  and  (3)  thermogenic  centres. 

The  Thermogenic  Tissues. — Almost  if  not  every  tissue  of  the  body  may  be 
regarded  as  being  a  heat-producing  structure.  The  very  fact  that  oxidative 
processes  lie  at  the  bottom  of  all  forms  of  vital  activity,  and  that  heat-produc- 
tion is  a  concomitant  of  oxidation,  leads  inevitably  to  the  conclusion  that  as 
long  as  cells  possess  life  they  must  produce  heat.  There  are,  however,  certain 
of  the  bodily  structures,  especially  the  skeletal  muscles  and  the  glands,  which 
are  exceptionally  active  as  heat-producers.  Indeed,  in  the  case  of  the  skeletal 
muscles  the  heat-producing  processes  are  of  such  a  character  as  to  justify  the 
belief  that  with  them  thermogenesis  is  a  specific  function,  because  heat  is  pro- 
duced not  merely  as  an  incidental  product  of  activity  but  as  a  specific  product. 
When  a  muscle  contracts,  heat  is  evolved  as  an  incident  of  the  performance  of 
work,  and  when  it  is  at  rest  heat  is  produced  not  only  as  an  incident  of  growth 
and  repair  but  as  the  result  of  a  specific  act.  This  latter  is  proved  by  the  fact 
that  when  the  muscles  have  been  in  a  state  of  prolonged  rest,  when  the  chemi- 
cal changes  concerned  in  growth  and  in  repair  of  waste  are  inactive,  heat-pro- 
duction continues  to  a  marked  degree.  Moreover,  the  quantity  which  is  pro- 
duced varies  with  the  immediate  needs  of  the  economy  and  bears  a  reciprocal 
relationship  to  the  quantity  of  heat  formed  in  other  structures,'  and  is  regulated 
apparently  by  specific  nerve-centres. 

When  the  muscles  are  contracting  less  than  one-fifth  of  the  energy  apj.^ears 
as  work,  and  more  than  four-fifths  as  heat.  The  contractions  of  the  heart  also 
furnish  an  appreciable  percentage  of  heat  as  an  accompaniment  of  contraction ; 
and  considerable  heat  is  formed  indirectly  by  the  resistance  oifered  by  the 
the  blood-vessel  walls  to  the  blood  current.  Indeed,  the  entire  work  of  the 
heart  becomes  converted  into  heat,  representing  from  5  to  10  per  cent,  of  the 
^  Riibner :  Siizungsberichte  d.  konigl.  Bayer.  A  kad.  der  Wissenschaften,  1885,  Heft  4. 


598  AN  AMERICAN   TEXT-BOOK    OF   PHYSIO  LOGY. 

total  heat-})ruduction.  The  quantity  IViniied  as  by-prodiicts  of  tlie  activity  of 
various  structures  during  a  state  of  muscular  quiet  is  doubtless  small  compared 
witli  the  rjuautity  produced  by  the  muscles. 

The  TJicnnofjcnic  Nvnrn  and  Centres. — Heat-production  may  occur  intlc[)cnd- 
ently  of,  but  under  normal  circumstances  it  is  regulated  by,  the  nervous  system. 
A  muscle  separated  from  all  nervous  influences  continues  to  produce  heat,  but  con- 
siderably less  than  before,  and  it  ceases  to  respond  to  the  demands  of  the  system 
for  more  or  less  heat  as  do  muscles  with  their  nerves  intact.  Injuries  to  certain 
parts  of  the  cerebro-spiual  axis  affect  heat-production  in  muscles,  in  some  in- 
stances causing  an  increase  and  in  others  a  decrease ;  but  these  changes  do  not  occur 
if  the  nervous  communication  between  the  centres  and  muscles  is  destroyed. 

Thennogenic  Nerves. — Specific  •  thermogenic  nerve-fibres  have  not  as  yet 
been  isolated,  although  the  researches  by  Kemp^  and  Reichert^  indicate  that 
such  fibres  exist.  In  muscles  probably  two  kinds  of  katabolic  processes 
go  on,  one  subservient  to  muscular  contraction  and  the  other  to  heat-produc- 
tion. From  the  fact  that  there  may  be  two  kinds  of  katabolic  processes  we 
are  led  to  the  conclusion  that  two  corresponding  sets  of  nerve-fibres  con- 
trol them,  and  it  seems  probable  that  the  katabolic  processes  which  give  rise  to 
muscular  contraction  and  its  accompanying  heat-production  are  due  to  im- 
pulses carried  to  the  muscles  by  motor  nerves,  while  those  specifically  con- 
cerned in  the  production  of  heat  are  transmitted  by  nerve-filjres  of  an  entirely 
different  character,  possibly  those  fibres  subserving  muscular  tone.  Upon  this 
hypothesis  the  latter  fibres  might  be  designated  as  specific  thermogenic  fibres — 
in  other  words,  they  are  specifically  engaged  in  conveying  impulses  from  the 
nerve-centres  to  the  muscles,  bringing  about  katabolic  changes  which  have  for 
their  especial  object  the  production  of  heat.  According  to  another  hypothesis 
both  muscular  contraction  and  muscular  tone  are  subserved  by  the  motor  nerves, 
whether  or  not  contraction  results  being  a  question  of  intensity  of  the  impulses. 

Our  knowledge  of  the  character  of  the  afferent  fibres  which  carry  impulses 
that  reflexly  affect  thermogenesis  is  very  unsatisfactory.  There  can  be  no 
doubt  that  sensory  impulses  arise  in  various  parts  of  the  organism,  especially  in 
the  skin,  which  exercise  important  influences  upon  the  heat-producing  pro- 
cesses. Thus,  cooling  the  skin  reflexly  excites  heat-production,  which  cannot 
be  attributed  to  indirect  influences  upon  other  functions,  but  whether  or  not 
there  exist  specific  afferent  thermogenic  fibres  is  not  known.  It  is  })ossible  that 
the  temperature  nerves  of  the  skin,  the  cold  and  the  heat  nerves,  may  be 
responsible  for  reflex  excitation  or  depression  of  heat-production. 

The  Thermogenic  Centres. — The  existence  of  specific  thermogenic  centres  has 
for  many  years  been  conceded,  but  it  has  only  been  recently  that  hypothesis 
has  given  place  to  fact.  The  most  important  results  of  recent  research  may  be 
generalized  as  follows:  (1)  That  the  irritation  of  the  skin  by  heat  or  cold  is 
followed  by  marked  changes  in  thermogenesis,  which  effects  are  to  a  certain 
extent  entirely  independent  of  vasomotor  and  other  incidental  changes,  and 
which,  therefore,  are  due  in  part  to  an  increase  of  heat-production  dependent 

»  Therapeutic  GazeUe,  1889,  p.  155.  '  Ibid.,  1891,  p.  151. 


ANIMAL  HEAT.  599 

directly  upon  eiferent  tlierinogenie  impulses.  (2)  That  injury  or  excitation  of 
certain  parts  of  the  brain  is  followed  by  an  increase  of  heat-production,  (3) 
That  injury  or  excitation  of  certain  other  parts  of  the  brain  is  fallowed  by 
diminished  heat-production.  (4)  That  injury  of  the  spinal  cord  may  be  fol- 
lowed by  an  increase  or  decrease  of  heat-production  which  cannot  be  entirely 
accounted  for  by  vaso-motor  and  other  attendant  alterations.  (5)  That  after 
operations  upon  certain  parts  of  the  cerebro-spiual  axis  there  follows  an  increase 
or  decrease  in  the  quantity  of  COj  formed,  indicating  a  corresponding  effect  on 
the  heat-producing  processes. 

The  results  of  recent  calorimetric  work  show  that  there  are  definite  regions 
of  the  cerebro-spinal  axis  which  are  apparently  specifically  concerned  in  ther- 
mogenesis ;  that  the  effects  of  excitation  or  destruction  of  each  region  are  more 
or  less  characteristic ;  and  that  the  different  regions  seem  to  be  so  intimately 
related  to  one  another  as  to  constitute  a  co-ordinate  mechanism.  Certain  of  these 
regions  when  irritated  give  rise,  as  a  direct  result,  to  increased  thermogenesis, 
hence  they  are  of  the  nature  of  thermo-accelerator  centres ;  and  others  to 
diminished  thermogenesis,  hence  are  thermo-inhibitory  centres.  Both  kinds  of 
centres  seem  to  be  associated  with  and  to  govern  a  third  kind  which  is  dis- 
tinguished as  the  general  or  automatic  thermogenic  centres.  The  mechanism 
may  be  theoretically  expressed  in  this  form  :  The  general  thermogenic  centres 
may  be  regarded  as  maintaining  by  virtue  of  independent  activity  a  fairly  con- 
stant standard  of  thermogenesis,  and  as  being  influenced  to  increased  activity  by 
the  thermo-accelerator  centres  and  to  diminished  activity  by  the  thermo-inhib- 
itory  centres.  The  finer  or  smaller  variations  in  thermogenesis  are  presumably 
effected  by  the  general  centres,  whereas  the  grosser  variations  are  probably  ef- 
fected by  the  influences  of  the  thermo-accelerator  and  therrao-inhibitory  centres. 

Specific  heat-centres  (thermogenic  and  thermolytic)  have  by  various  ob- 
servers been  held  to  exist  in  certain  regions  of  the  brain  cortex,  in  the  base  of 
the  brain  just  in  front  of  and  beneath  the  corpus  striatum,  in  the  corpus  stri- 
atum, in  the  septum  lucidum  and  the  tuber  ciuereum,  in  the  optic  thalamus, 
in  the  corpora  quadrigemina,  in  the  pons  and  medulla  oblongata,  and  in  the 
spinal  cord.  Some  of  these  centres  have  been  regarded  as  being  thermogenic 
and  others  as  being  thermolytic.  Many  errors  in  deduction  have,  however, 
been  made  because  of  the  many  inherent  difficulties  attending  experimenta- 
tion upon  the  cerebro-spiual  axis,  and  because  almost  all  the  methods  used 
necessarily  involve  injury  or  excitation  of  contiguous  parts.  The  methods 
adopted  of  studying  these  various  regions  have  been  chiefly  destruction  or 
injury  by  means  of  a  probe,  actual  cautery,  excision,  and  the  injection  of 
cauterants ;  by  transverse  incisions  across  the  cerebro-spinal  axis  so  as  to  sepa- 
rate higher  from  lower  portions  of  the  cerebro-spinal  axis ;  and  by  excitation 
by  small  punctures,  electricity,  etc. 

In  classifying  these  centres  we  are  governed  by  the  results  which  follow 
excitation  and  destruction.  When  irritation  or  destruction  directly  affects 
thermogenesis,  the  centre  is  regarded  as  being  thermogenic,  but  if  heat-dissi- 
pation is  the  process  directly  affected,  the  centre  is  regarded  as  being  thermo- 


600  AiX  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

lytic.  In  classifying  thermogenic  centres  we  wonld  regard  the  centre  as  being 
a  general  thermogenic  centre  if  it  is  capable,  after  the  destruction  of  other 
thermogenic  centres,  of  causing  the  normal  output  of  heat ;  a  thermo-acceler- 
ator  centre  is  distinguished  by  the  fact  that  excitation  increases  thermogenesis, 
while  destruction  does  not  diminish  thermogenesis,  unless  the  centre  happens 
to  be  active  at  the  time,  and  further  by  the  fact  that  after  its  destruction  the 
normal  output  of  heat  may  continue  ;  a  thermo-inhibitory  centre  is  distinguished 
by  a  decrease  of  heat-})roduction  following  stimulation  and  by  the  absence  of 
any  permanent  effect  on  thermogenesis  when  the  centre  is  destroyed.  The 
general  or  reflex  thermogenic  centres  are  undoubtedly  continuously  active,  the 
degree  of  activity  varying  according  to  the  immediate  demands  of  the  organism 
for  heat ;  while  the  thermo-accelerator  and  thermo-inhibitory  centres  are  prob- 
ably only  intermittently  active,  coming  into  play  when  the  general  centres  are 
of  themselves  unable  to  effect  a  sufficiently  rapid  compensation. 

While  it  must  be  admitted  that  our  knowledge  of  the  precise  locations, 
physiological  peculiarities,  and  correlations  of  the  thermogenic  centres  is  by  no 
means  complete,  we  have  at  our  disposal  some  most  important  and  significant 
data.  The  general  thermogenic  centres  have  been  shown  by  Reichcrt  *  to  be 
located  in  the  spinal  cord.  The  thermogenic  centres  in  the  brain  are  either 
thermo-accelerator  or  thermo-inhibitory.  Thermo-accelerator  centres  ]>robably 
exist  in  the  caudate  nuclei  (possibly  also  in  the  tuber  cinereum  and  optic 
thalami),  pons,  and  medulla  oblongata.^ 

Excitation  of  any  one  of  these  regions  is  followed  by  a  pronounced  rise  of 
heat-production  ;  destruction  of  any  one  region  may  or  may  not  be  followed 
by  a  decrease  of  heat-production,  and  if  a  decrease  does  occur  it  may  in  most 
cases  be  attributed  to  incidental  causes,  such  as  shock  and  other  attendant 
conditions.  The  centre  which  is  common  to  the  pons  and  medulla  is  for  the 
most  part  probably  located  in  the  latter,  but  it  is  not  so  powerful  in  its  influ- 
ences on  thermogenesis  as  the  thermo-accelerator  centres  in  the  basal  regions 
of  the  cerebrum.  These  cerebral  centres  are  affected  by  agents  which  have 
little  or  no  effect  on  the  heat  centres  of  the  spinal  cord.  Thermo-inhibitory 
centres  have  been  located  in  the  dog  in  the  region  of  the  sulcus  cruciatus  and 
at  the  junction  of  the  supra-Sylvian  and  post-Sylvian  fissures.^  Irritation 
of  either  of  them  is  followed  by  a  decrease  of  heat-production,  while  their 
destruction  may  be  followed  by  a  transient  increase  of  heat-production.  The 
cruciate  centre  is  the  more  powerful.     None  of  these  cerebral  centres  exercises 

^  University  Medical  Magazine,  1894,  vol.  v.  p.  406. 

^Reichert:  University  Medical  3Iafjnzine,  1894,  vol.  6,  p.  303.  Ott :  Journal  of  Nervous  and 
Mental  Diseases,  1884,  vol.  11,  p.  141;  1887,  vol.  14,  p.  154;  1888,  vol.  15,  p.  85;  Therapeutic 
Gazette,  1887,  p.  592;  Fever,  Thermotaxia,  and  Calorimetry,  1889.  Aronsohn  and  Sachs:  Pjliiger's 
Archiv  fiir  Physioloc/ie,  1885,  vol.  37,  p.  232.  Girard :  Archiv  de  Phjsiologie  nonnale  ct  patholo- 
gique,  1886,  vol.  8,  p.  281.  Baginsky  iind  Lehmann  :  Virchou's  Archiv  fiir  Pathnlofjie,  1886,  Bd. 
106,  p.  258.  White:  Journal  of  Physiolor/y,  1890,  vol.  11,  p.  1  ;  1891,  vol.  12,  p.  233.  Baculo: 
Centri  temici,  1890,  1891,  and  1892.    Tangl :  Pjim/er's  Archiv  fiir  Physiologic,  1895,  vol.  68,  p.  559. 

'Wood:  "Ye\eT,"  Smithsonian  Contributions  to  ivnou;W<7e,  1880,  No.  357.  0*-t>;  Journal  of 
Nen-ous  and  Menial  Duieases,  1888. 


ANIMAL  HEAT.  601 

any  influence  on  thermogenesis  after  section  of  the  spinal  cord  at  its  junction 
with  the  niedulhi  oblongata. 

Theoretically,  these  centres  are  associated  in  this  way  :  The  general  thermo- 
genic centres  are  in  the  spinal  cord,  and  while  they  are  perhaps  impressionable 
to  impulses  coming  to  them  tlirough  various  sensory  nerves,  they  are  not 
apparently  in  the  least  influenced  by  cutiuieous  impulses  caused  by  changes  iu 
external  temperature  nor  by  changes  of  the  temperature  of  the  blood.  It  is 
not  improbable  that  these  centres  are  in  the  anterior  cornua  of  the  spinal  cord. 
The  thermo-accelcrator  and  thermo-inhibitory  centres  are  connected  with  the 
general  centres  by  nerve-tibres,  the  former  influencing  the  general  centres  to 
increased  activity,  and  the  latter  to  diminished  activity.  The  thermo-accel- 
erator  and  thermo-inhibitory  centres  seem  to  be  especially  affected  by  cuta- 
neous impulses  which  are  generated  by  changes  in  external  temperature,  and 
to  be  influenced  by  alterations  of  the  temperature  of  the  blood.  It  is  doubtless 
through  these  centres  that  changes  in  external  and  internal  temperature  are 
able  to  affect  the  heat-producing  processes.  Presumably  both  an  increase  of 
temperature  of  the  blood  and  cutaneous  impulses  generated  by  an  increase  of 
external  temperature  excite  the  thermo-inhibitory  centres,  and  thus  inhibitory 
impulses  are  sent  to  the  general  centres,  lessening  their  activity ;  on  the  other 
hand,  both  a  fall  of  temperature  of  the  blood  and  cutaneous  impulses  gener- 
ated by  cold  presumably  excite  the  thermo-accelerator  centres  and  thus  cause 
impulses  to  be  sent  to  the  general  centres,  exciting  them  to  greater  activity. 

The  Mechanism  concerned  in  Thermolysis. — The  loss  of  heat  by  the  body 
is  in  a  large  measure  incidental  to  attendant  conditions  and  is  not  a  reflex 
result  of  the  activity  of  a  thermolytic  mechanism ;  in  other  words,  the  loss 
occurs  essentially  by  virtue  of  the  same  conditions  as  would  cause  inanimate 
bodies  to  lose  heat.  The  living  homothermous  organism  differs  as  regards  the 
loss  of  heat  from  dead  matter,  chiefly  in  that  the  rapidity  with  which  heat- 
dissipation  occurs  is  regulated  to  a  material  extent  by  vital  processes.  The 
regulation  of  the  loss  of  heat  is  effected  by  the  operations  of  a  complex  mech- 
anism—that is,  one  consisting  of  a  number  of  distinct  although  correlated  parts. 
A  study  of  this  mechanism,  which  is  designated  the  thermolytic  mechanism, 
includes  a  consideration  of  all  of  the  processes  by  which  heat  is  lost,  of  the 
nervous  mechanisms  which  govern  thera,  and  of  the  conditions  which  affect 
them,  but  especially  of  those  processes  and  mechanisms  which  act  reciprocally 
in  conjunction  with  the  thermogenic  mechanism  to  maintain  the  mean  bodily 
temperature.  Practically  all  of  the  heat  lost  by  the  organism  occurs  by  radia- 
tion and  conduction  from  the  skin,  by  the  evaporation  of  water  from  the  skm 
and  lungs,  and  in  warming  the  food,  drink,  and  inspired  air.  From  these  facts  we 
believe  that  mechanisms  which  affect  the  blood-supply  to  the  skin,  the  quantity 
of  sweat  secreted,  the  condition  of  the  surface  of  the  skin,  and  the  quantity  of 
air  inspired  must  in  a  large  measure  regulate  thermolysis.  For  instance,  if  the 
temperature  of  the  organism  be  materially  increased  there  occur  increased  activ- 
ity of  the  heart,  peripheral  vascular  dilatation,  increased  respiratory  activity,  and 
(except  in  fever)  an  increase  in  the  secretion  of  sweat.     The  increase  of  the 


602  .l.V   AMERICAN    TEXT- BOOK    OF   PHYSIOLOGY. 

activity  of  the  heart  together  with  the  dihitation  uf  the  cutaneous  blood-vessels 
increases  the  quantity  of  blood  supplied  to  the  skin  ;  the  cutaneous  blood-vessels 
are  dilated,  exposing  a  larger  surface  of  blood  to  the  cooler  external  surround- 
ings, and  thus  materially  favoring  the  loss  of  heat  by  radiation  ;  the  increase  in 
the  (juantity  of  sweat  is  favorable  to  an  increase  in  the  amount  of  ^vater  evaporated, 
and  thus  to  a  larger  loss  of  heat  in  this  way  ;  an  increase  of  respiratory  activity 
means  a  larger  volume  of  air  respired,  a  greater  expenditure  of  heat  in  warming 
the  air  and  in  the  evaporation  of  water  from  the  lungs.  In  man  the  pilo-motor 
mechanism  plays  a  subsidiary  and  unimportant  part  in  the  regulation  of  heat- 
dissipation,  but  in  some  lower  animals,  as  in  certain  Ijirds,  it  is  of  considerable 
importance.  The  thermolytic  mechanism  therefore  includes  the  cardiac,  vaso- 
motor, respiratory,  sweat,  and  pilo-motor  mechanisms.  All  these  are  affected 
directly  or  indirectly  by  the  temperature  of  the  blood  and  skin.  An  increase 
in  the  temperature  of  the  blood  and  skin  excites  all  of  them  so  that  changes 
are  brought  about  which  favor  heat-loss.  The  respiratory  movements  especially 
may  be  rendered  intensely  active,  and  in  certain  animals  to  such  a  marked 
degree  that  they  may  become  more  frequent  than  the  heart-beats. 

Thennotaxis. — Thermotaxis  or  heat-regulation  is  effected  by  reciprocal 
changes  in  heat-production  and  heat-dissipation  brought  about  by  the  inter- 
vention of  the  thermogenic  and  thermolytic  centres,  just  as  the  regulation 
of  arterial  pressure  is  effected  by  the  reciprocal  relations  of  the  cardio- 
inhibitory  and  vaso-motor  mechanisms.  If  heat-production  is  more  active 
than  heat-dissipation,  thermolysis  is  so  affected  that  the  heat-loss  is  increased, 
and  thus  the  mean  bodily  temperature  maintained  ;  if  heat-production  is  sub- 
normal, heat-dissipation  also  falls.  Similarly,  if  heat-dissipation  is  increased, 
the  heat-producing  })rocesses  are  excited  to  greater  activity  to  make  up  the  loss ; 
conversely,  if  heat-dissipation  is  decreased,  heat-production  also  tends  to  be 
decreased.  These  reciprocal  actions  depend  essentially  or  wholly  upon  the 
influence  of  cutaneous  impulses  and  the  temperature  of  the  blood.  For 
instance,  an  increase  of  the  temperature  of  the  blood  increases  the  activity 
of  the  thermolytic  processes,  thus  effecting  a  compensation.  If  we  subject  an 
animal  to  a  moderately  cold  atmosphere,  as  in  the  winter,  heat-dissipation  is 
increased,  but  cutaneous  impulses  are  generated  which  excite  the  tliermogenic 
centres  so  that  heat-production  is  also  increased,  and  thus  the  bodily  temperature 
is  maintained  practically  unaffected.  It  is  only  under  abnormal  conditions  or 
under  conditions  of  intense  muscular  activity  that  this  reciprocal  relation- 
ship is  so  disturbed  that  changes  in  one  process  are  not  quickly  compensated 
for  by  changes  in  the  other. 

Thermotaxis  is  effected  in  a  large  measure  reflexly,  especially  by  cutaneous 
impulses  generated  by  external  cold  and  heat,  b(jth  thermogenic  anil  thermo- 
Ivtic  processes  being  affected.  Cold  ap})lied  temporarily,  as  in  the  form  of  a 
douche,  bath,  sponging,  etc.,  causes  constriction  of  the  cutaneous  capillaries. 
This  lessens  both  the  quantity  and  temperature  of  the  blood  passing  through 
the  skin,  the  effect  of  which  tends  to  decrease  the  dissipation  of  heat  by  radia- 
tion and  conduction.     Moreover,  a  lessened  blood-supply  causes  the  skin  to 


ANIMAL   HEAT,  603 

become  poorer  in  fluid,  .so  tluit  tiie  conduction  of"  iioat  from  the  warmer  inner 
parts  is  lessened.  The  conductivity  of  the  skin  is  further  decreased  by  the 
action  of  the  pilo-motor  muscles,  which  when  in  contraction  or  in  a  state  of 
greater  tonicity  render  the  skin  tenser  and  thus  j)ress  out  the  blood  and  tissue 
juices.  The  secretion  of  sweat  is  diminished,  so  that  the  quantity  of  heat  lost 
in  the  vaporization  of  water  is  decreased.  On  the  other  hand,  heat-dissipation 
tends  to  be  materially  increased  by  the  greater  radiation  of  heat  due  to  the 
greater  diiference  between  the  temperature  of  the  body  and  of  the  douche,  bath, 
etc.,  and  the  tendency  to  an  increase  in  this  way  is  much  greater  than  the 
opposite  tendency  depending  upon  the  factors  above  noted,  therefore  heat- 
dissipation  is  increased.  Bathing  the  skin  with  cold  water  increases  heat-loss 
by  the  vaporization  of  water  as  well  as  by  conduction. 

The  excitation  of  the  cutaneous  nerves  by  cold  reflexly  increases  thermo- 
genesis,  and  to  such  an  extent  that  heat-production  may  even  exceed  the 
quantity  dissipated,  thus  causing  an  increase  of  bodily  temperature.  This  rise, 
which  is  transient,  may  amount  to  0.2°  C.  or  more,  and  is  followed  by  a  re- 
action in  which  the  temperature  may  fall  0.2°  C.  or  more  below  the  normal,  and 
continue  subnormal  for  some  hours ;  this  fall  in  turn  is  succeeded  by  a  supple- 
mentary reaction  in  which  the  temperature  may  rise  slightly  above  the  normal. 

The  chief  reactions  brought  about  by  moderate  external  cold  are  constriction 
of  the  cutaneous  blood-vessels,  a  diminution  of  the  quantity  of  sweat  secreted, 
increased  tonicity  of  the  pilo-motor  muscles,  and  increased  tonicity  of  the 
skeletal  muscles.  The  action  upon  the  latter  muscles  may  be  so  marked  as 
to  cause  shivering,  which  increases  respiratory  activity  (see  p.  540)  and 
presumably  similarly  increases  heat-production. 

Moderate  external  heat  causes  dilatation  of  the  -cutaneous  vessels,  excites 
the  general  circulation  and  thus  increases  the  blood-supply  to  the  skin,  excites 
respiratory  movements  and  the  sweat-glands,  but  decreases  thermogenesis. 
Owing  to  the  dilatation  of  the  blood-vessels  of  the  skin  and  the  excitation  of 
the  circulation  the  temperature  and  the  quantity  of  the  blood  supplied  to  the 
skin  are  increased,  so  that  conditions  are  caused  which  are  favorable  to  an 
increased  loss  of  heat  by  radiation.  Increased  activity  of  the  respiratory 
movements  means  a  larger  volume  of  air  respired,  and  consequently  a  greater 
loss  of  heat  in  warming  the  air  and  in  the  evaporation  of  the  larger  quantity 
of  water  from  the  lungs.  The  increase  in  the  quantity  of  sweat  formed  also 
favors  heat-dissipation  by  means  of  the  larger  amount  of  water  evaporated 
from  the  skin.  When,  however,  the  external  temperature  is  higher  than  that 
of  the  body,  loss  of  heat  by  radiation  and  conduction  cannot  occur,  so  that 
heat  not  only  accumulates  as  a  result  of  the  interference  with  heat-dissipation, 
but  by  absorption. 

The  chief  reactions  brought  about  by  moderate  external  heat  are  a  dilata- 
tion of  the  cutaneous  blood-vessels,  excitement  of  the  general  circulation,  an  in- 
crease in  the  number  of  respiratory  movements,  increase  in  the  amount  of  sweat, 
diminished  tonicity  of  the  muscles,  and  diminished  thermogenesis  which  is  prob- 
ably due  to  a  lessening  of  the  activity  of  the  chemical  changes  in  the  muscles. 


604  AN  A3fEBICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

"Wlien  external  temperature  is  excessive  and  continued,  heat-regulation  is 
rendered  impossible  :  if  extreme  cold,  heat-dissipation  takes  place  more  rapidly 
than  heat-production,  so  that  bodily  temperature  falls  until  death  results;  if 
verv  hot,  heat-dissipation  is  so  interfered  with  that  heat  rapidly  accumulates 
within  the  organism,  causing  a  continuous  rise  of  tenj})eraturc  which  finally 
causes  death. 

Abnormal  T/icrmoidxis. — By  this  term  is  meant  the  regulation  of  the  heat- 
processes  under  conditions  in  which  the  mean  bodily  temperature  is  maintained 
at  a  standard  above  or  below  the  normal,  as  in  i'ever  and  in  animals  from 
which  the  hair  has  been  shaved.  It  is  assumed  that  under  normal  conditions 
the  heat-centres  are  "  set/'  as  it  were,  for  a  given  temperature  of  the  blood, 
and  that  when  the  temperature  of  the  blood  goes  above  or  below  this  standard 
a  compensatory  reaction  occurs,  so  that  thermogenesis  and  thermolysis  are 
properly  affected  to  bring  about  an  adjustment.  In  fever  it  may  be  considered 
that  the  centres  are  set  for  a  higher  temperature  than  the  normal ;  the  higher 
the  fever,  the  higher  the  adjustment.  The  centres  may  be  set  for  subnormal 
temperatures,  as  in  the  case  of  a  rabbit  shaved,  whose  temperature  may  remain 
2°  or  3°  below  the  normal  for  a  week  or  more.  When  the  cause  of  the  ab- 
normal condition  disappears,  the  centres  are  readjusted  to  the  normal  standard. 

E.  Post-mortem  Rise  of  Temperature. 

A  rise  of  temperature  after  death  is  not  uncommon ;  indeed,  in  case  of 
violent  death  of  healthy  individuals,  and  after  death  following  convulsions, 
a  rise  in  temperature  is  almost  invariable.  This  increase  is  due  to  continued 
heat-production  and  to  diminished  heat-dissipation.  Heat-production  after 
d(»ath  may  be  due  to  continued  chemical  activity  in  the  muscles  and  other 
structures  which  are  not  dead  but  simply  in  a  moribund  state.  There  is,  as  it 
were,  a  residual  metabolic  activity  which  remains  in  the  cells  until  their  tem- 
])erature  has  been  reduced  to  such  a  standard  that  the  molecular  transforma- 
tions cease — in  other  words,  until  the  death  of  the  cells  occurs.  Consequently, 
the  higher  the  temperature  of  the  individual  at  the  time  of  somatic  death  (the 
cessation  of  the  circulation  and  respiration),  the  longer  heat-production  con- 
tinues, because  the  longer  the  time  required  to  cool  the  cells  to  such  a  degree 
that  their  chemical  processes  no  longer  go  on.  Heat  is  also  produced  during 
the  development  of  rigor  mortis.  The  more  quickly  rigor  sets  in,  and  the 
more  intense  it  is,  the  greater  is  the  abundance  of  heat  produced. 

The  tendency  to  an  increase  of  bodily  temperature  is  favored  by  the  marked 
diminution  of  heat-dissipation  which  occurs  immediately  upon  the  cessation  of 
of  the  circulation  and  respiration.  Therefore,  while  both  heat-production  and 
heat-dissipation  fall  at  once  and  enormously  at  the  time  of  death,  heat-dissipa- 
tion may  be  decreased  to  a  more  marked  degiee  than  heat-production,  so  that 
heat  may  accumulate  and  the  bodily  temperature  rise. 

Temperature  Sense. — (See  Cutaneous  Sensibility,  in  the  section  on  Special 
Senses.) 


X.  CENTRAL  NERVOUS  SYSTEM. 


Introduction. 


The  Unity  of  the  Central  Nervous  System. — The  human  nervou.s  system 
is  formed  by  a  muss  of  separate  but  contiguous  nerve-cells.  As  each  nerve- 
cell  is  always  in  close  relations  with  some  other  nerve-cell,  this  system  differs 
from  those  formed  by  the  bones,  muscles,  or  glands,  since  these  tissues  are  dis- 
tributed through  the  body  in  masses  more  or  less  isolated.  Isolated  groups  of 
nerve-cells  do  not  occur.  Indeed  a  group  of  nerve-cells  disconnected  from  the 
other  nerve-tissues  of  the  body,  as  the  muscles  or  glands  are  disconnected, 
would  be  without  physiological  significance.  It  is  desirable,  therefore,  to 
emphasize  the  fact  that  by  dissection  the  nervous  system  is  found  to  be  con- 
tinuous throughout  its  entire  extent. 

Subdivisions  Artificial. — When,  therefore,  the  nervous  system  is  described 
as  formed  of  a  central  and  a  peripheral  portion,  and  the  peripheral  portion  is 
further  analyzed  into  its  spinal  and  sympathetic  components,  the  parts  distin- 
guished are  found  to  have  no  sharply  marked  boundaries  separating  them,  but 
really  to  merge  one  into  the  other. 

The  convenience  of  these  subdivisions  is  undoubted,  but  the  physiological 
processes  which  it  is  our  purpose  to  study,  overstep  in  so  large  a  measure  such 
conventional  limits,  that  the  picture  of  events  in  the  central  nervous  system 
would  be  very  incomplete,  should  they  be  traced  only  within  such  prescribed 
anatomical  boundaries. 

By  virtue  of  its  continuity,  the  nervous  system  puts  into  connection  all  the 
other  systems  of  the  body.  Conforming  as  it  does  in  shape  to  the  framework 
of  the  body,  its  branches  extend  to  all  parts.  These  branches  form  pathways 
over  which  nerve-impulses  travel  toward  the  central  system — the  brain  and 
spinal  cord,  enclosed  in  the  cranial  cavity  and  vertebral  canal — and  in  conse- 
quence of  the  impulses  that  come  in,  there  pass  out  from  the  central  system 
other  impulses  to  the  muscles,  glands,  and  blood-vessels. 

All  incoming  impulses  must  reach  the  central  system.  ]\Iost  important  in 
this  arrangement  is  the  absence  of  any  device  for  short-circuiting  the  incoming 
impulses.  It  is  a  fact  of  the  greatest  significance,  that  until  they  have  entered 
the  central  system  the  incoming  impulses  do  not  give  rise  to  those  outgoing, 
and  thus  all  incoming  impulses  are  first  brought  to  the  spinal  cord  and  brain, 
and  the  outgoing  impulses  are  there  aroused  and  co-ordinated  by  them. 

By  means  of  the  central  system  there  are  established  reactions  in  those  tis- 
sues not  directly  affected  by  the  variation  of  the  external  conditions,  and  thus 


605 


606  A^'  AMKlilCAX    TEXT-BOOK    OF  PIIYSIOLOUY. 

there  follows  an  amount  and  variety  of  response  in  the  organism  as  a  whole 
out  of  all  proportion  to  the  strength  of  the  physical  stimuli  employed.  Owing 
also  to  the  wide  connections  of  the  nervous  system  and  the  conduction  of  all 
incoming  impulses  to  its  central  part  a  measure  of  harmony  is  maintained 
between  the  various  activities  of  the  several  systems  composing  the  hody. 
Thus  not  only  the  various  systems  forming  the  body  are  in  this  manner  con- 
trolled, biu  the  body  as  a  whole,  in  relation  to  all  things  outside  of  it  and 
forming  its  environment,  is  even  more  ]ilainly  under  the  guidance  of  these 
administrative  cells. 

Gro-wth  and  Organization. — In  this  connection,  it  is  fitting  to  emphasize 
a  character  of  the  central  system  which  is  both  unique  and  highly  important. 
The  phvsiological  connections  existing  between  the  nerve-elements  in  youth 
are  very  incomplete  and  poorly  established,  more  so  than  in  any  other  system 
of  the  bodv;  in  the  history  of  the  growth  of  the  nervous  system,  the  increase 
in  weight  and  change  in  shape  run  })arallel  with  an  increase  in  its  organiza- 
tion— /.  e.  in  the  connections  between  its  constituent  cells.  This  organization 
results  in  better  and  more  numerous  physiological  pathways  which  permit  the 
system,  as  a  whole,  not  only  to  do  more  perfectly  at  maturity  those  things 
which  it  could  do  in  some  degree  at  an  earlier  age,  but  also,  by  virtue  of  its 
increased  complexity,  to  do  at  maturity  those  things  which  previously  it  could 
not  do  at  all. 

Growth  in  the  case  of  this  system  implies,  therefore,  an  increase  in  com- 
plexity such  as  nowhere  else  occurs,  and  since  this  growth  can  be  modified  by 
the  experience  of  the  individual  during  the  growing  period,  the  importance 
of  understanding  it  and  its  relation   to  organization  is  evident. 

Phenomena  Involving  Consciousness. — It  is  with  the  nervous  system 
that  the  phenomena  of  consciousness  are  most  closely  linked.  Strictly,  physi- 
ologv  concerns  itself  at  present  with  the  reactions  of  the  nervous  system,  which 
can  be  studied  without  an  appeal  to  consciousness.  A  moment's  consideration 
shows,  however,  that  in  the  physiology  of  the  brain  the  assistance  to  be 
obtained  by  passing  beyond  the  limit  thus  laid  down  is  of  more  value  than 
any  boundary,  and  hence,  although  the  field  of  consciousness  is  sacred  to  psy- 
chology, physiology  should  not  be  deprived  of  any  of  the  advantages  which 
come  from   the  privilege  of  occasional   trespass. 

Plan  of  Presentation. — In  accordance  with  these  facts,  it  has  seemed  best 
to  first  present — 

Part  I.  The  physiology  of  the  nerve-cell,  considered  as  a  peculiar  kind  of 
tissue-element,  endowed  with  special  physiological  characters. 

Part  II.  The  activities  of  the  simplest  groups  of  these  elements.  The 
phvsiological  grouping  is  of  course  mainly  dependent  on  the  anatomical 
arrangement,  and,  as  must  always  be  the  case,  the  activities  of  one  group 
modify  those  of  others.  Stated  in  general  terms,  the  problem  in  this  part  is 
that  of  the  ixdhway  of  any  impulse  through  the  central  system. 

Part  III.  The  reactions  of  the  system  taken  as  a  whole.  Here  its  capa- 
bilities as  a  unit  are  contrasted  with  those  of  the  other  tissue-systems,  and  its 


CENTRAL    NERVOUS  SYSTEM. 


607 


growth,  organization,  and    rhytlims  of   rest  and  activity,  are  more  properly 
presented  as  functions  of  all  its  parts  than  as  I'unctions  of  special  subdivisions. 

PART    I.— PHYSIOLOGY   OF   THP]   NERVE-CELL. 

A.  Anatomical  Characteristics  of  the  Nerve-cell. 

Form  of  Nerve-cells. — Morphologically,  the  mature  ncrvc-cell  is  regarded 
as  composed  of  a  cell-body,  containing  a  nucleus  together  witli  other  modified 
inclusions  and  possessed  of  one  or  more  outgrowths  or  branches.  Some  of 
these  branches  may  be  very  long,  such  for  instance  as  those  which  form  nerve- 
fibres  ;  other  branches  are  short  and  differ  from  the  nerve-fibres  in  their  structure. 

The  terms  employed  in  describing  the  nerve-elements  are  as  follows :  To 
the  entire  mass  under  the  control  of  a  given  nucleus  and  forming  both  cell- 
body  and  branches,  the  term  nerve-cell  is  applied.  The  inclusions  within  the 
cell-body  have  the  usual  designations.  Nerve-cells  differ  greatly  in  the 
number' of  the  branches  arising  from  them.  In  some  cells  there  appear 
to  be  two  nerve-fibres  arising  from  the  cell-body,  in  others  only  one.  For 
convenience  the  description  about  to  be  given  will  apply  to  the  latter  group 
only.  From  most  cells  there  arises  one  principal  branch,  which  when  con- 
sidered alone  is  described  as  a  nerve-fibre,  but  when  considered  as  the  out- 
growth of  the  cell-body  from  which  it  originates,  is  called  a  neuron}  Cells 
with  one  neuron  are  called  raononeuric.  Cells  with  two  neurons,  dineuric. 
The  neuron,  in  many  cases,  has  branches,  both  near  its  origin  from  the  cell- 
body  and  also  along  its  course.  These  branches  are  designated  as  coUatei-als. 
Contrasted  with  this  principal  outgrowth  are  the  other  branches  of  the  cell, 


Fig.  143.— a  group  of  human  nerve-cell  bodies,  drawn  to  scale  ;  X  200  diameters  :  A,  cell-body  from 
the  ventral  horn  of  the  spinal  cord,  longitudinal  section ;  C,  the  same,  transverse  section ;  B,  cell  from 
the  third  layer  of  cerebral  cortex ;  D,  cell  from  the  column  of  Clarke  ;  E,  cell  from  the  ganglion  of  the 
spinal  nerve-root,  with  neuron  :  F,  "solitary"  cell  from  the  dorsal  horn  of  the  spinal  cord  ;  G,  granule 
from  the  cortex  of  the  cerebellum  (modified  from  Waller,  Human  Physiology). 

which  are  individually  much  less  extensive  and  which  divide  dichotomously 
at  frequent  intervals.  From  the  tree-like  form  which  they  thus  acquire  they 
have  been  designated  dcndrons. 

The  accompanying  illustration  (Fig.  143)  shows  the  features  just  described 
and  also  gives  some  idea  of  the  variations  in  the  size  of  the  cell-bodies  as  found 

»  Schafer,  Brain,  1893. 


608 


^l^V   AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


in  mail.  The  nerve-cell  body  is  usually  ovoid  in  shape,  although  this  type  is 
much  modified  in  many  cases.  As  will  be  seen  from  Figure  14o,  the  diam- 
eters of  nerve-cells  range  from  10-100  //,'  and  in  some  instances,  in  the  spinal 
cord,  cells  of  even  larger  diameter  are  found. 

The  Structure  of  the  Nerve-cell  Body. — NissPhas  shown  that  in  nerve- 
cells  hardened  in  strong  alcohol  there  art;  two  substances — one  whith  is  not 
stained  by  a  basic  aniline  dye,  and  the  sirond  which  is.  The  first  forms  a  frame- 
work continuous  with  the  fibrillie  of  tiie  nerve-fibre  and  enclosing  the  staiuable 
substance  in  its  meshes  in  small  masses  or  granules.  These  granules  are  physio- 
logically very  sensitive,  and  the  study  of  them  under  a  variety  of  conditions  has 
already  revealed  changes  in  the  nerve-cells  where  none  had  previously  been  found. 
Peculiarities  of  Nerve-cells. — As  compared  with  the  other  cells  of  the 
body,  the  best  developed  nerve-cells  are  of  large  size,  but  the  nucleus,  pro- 
portionately to  the  cell-body,  is  not  large,  its  value  decreasing,  as  a  rule,  with 
the  increase  in  the  size  of  the  entire  cell.  The  most  striking  feature  of  the 
nerve-cell,  however,  is  the  great  length  to  which  its  chief  branch,  the  neuron, 
may  attain,  for  in  no  other  tissue  does  anything  like  so  great  a  proportion  of  the 
cell-substance  occur  as  a  branch.     The  form  of  cell  represented  in  Figure  144  is 

one  in  which  the  neuron  shows  a  very  short 
stem  between  the  cell-body  and  its  terminal 
twigs.  In  such  an  instance  the  entire  exten- 
sion of  the  neuron  may  be  less  than  a  milli- 
meter. With  this  are  to  be  contrasted  those 
forms  in  which  the  neuron  is  very  long  and 
its  mass  great.  What  its  greatest  length 
may  be  is  easily  determined.  Within  the 
central  system  there  are  cells  whose  neurons 
extend  from  the  cerebral  cortex  to  the  lumbar 
enlargement  (60  centimeters),  and  again  in  the 
peripheral  system  there  are  cell-bodies  in  the 
lumbar  enlargement  of  the  spinal  cord  the 
neurons  of  which  extend  to  the  skin  and 
muscles  of  the  foot  a  distance  of  100  centi- 
meters. These  are  the  extreme  cases,  but  as 
the  neurons  are  distributed  to  all  inter- 
mediate points  both  in  the  central  and  pe- 
ri])heral  system,  every  interme<liate  length 
between  these  and  the  cells  with  very  short 
neurons  previously  mentioned,  is  to  be 
found. 
Volume  Relations. — Calculation  shows  that  the  volume  of  the  cell-body 
of  a  pyramidal  cell  in  the  human  cerebral  cortex  having  a  basal  diameter  of 

1  fi  =  0.001  of  a  millimeter. 

"  Allgemeiner  Zeitschrijt  fur  Psychialrie,  1896,  Bd.  Hi.  S.  1147.    (A  condensed  statement  of  pre- 
vious work.) 


Fig.  144.— a  cell  with  a  short  neuron 
giving  off  many  branches.  In  such  a  cell 
the  neuron  is  less  in  volume  than  the  cell- 
body.  This  is  the  extreme  form  of  the 
"central  cell"  (Ram6n  y  Cajal).  D,  den- 
drons ;  N,  neuron. 


CENTRAL    NERVOUS  SYSTEM. 


609 


16  a,  is,  when  calcuUue.l  as  a  cone,  approximately  4266  cubic  /i.  The  neuron 
from  such  a  cell  would  have  a  diauKter  of  at  U-ast  2  /i,  the  medullary  sheath 
being  indudi'd.  This  gives  un  area  for  the  cross  se(;tion  of  the  neuron,  of  6.3 
squat-e  /i.  Thus  in  the  case  chosen  a  portion  of  the  neuron  680  /z  long  would 
have  a  volume  ecpial  to  the  cell-body.  We  may  assume  this  neuron  to  be 
15  centimeters  =  150,000 /^  long.  Dividing  the  entire  length  of  the  ueuron 
by  the  length  of  the  piece  having  the  volume  of  the  cell,  it  appears  that  the 
volume  of  the  neuron  is  220  times  that  of  the  cell-body. 

Repeating  the  same  process  with  a  cell  from  the  lumbar  enlargement  of  the 
spinal  cord,  taking  a  medium  cell  with  a  diameter  of  46 /i  and  a  volume  (calcu- 
lated as  a  sphere)  of  50,000  cubic  //,  a  neuron  with  a  diameter  of  10  //,  and 
a  length  of  100  centimeters,  the  relation  of  the  volume  of  the  neuron  to  that 
of  the  cell-body  is  1570  to  1. 

This  estimate  of  the  volume  of  the  neuron  includes,  in  addition  to  the  axis- 
cylinder,  the  enclosing  medullary  sheath.  The  volumes  of  these  two  portions  are 
approximately  equal,  so  that  either  the  axis-cylinder  or  the  medullary  sheath 
exceeds  the  cell-body  in  volume  about  half  as  many  times  as  does  the  entire 
neuron.  It  is  extremely  difficult  to  estimate  the  mass  of  the  dendrons.  In 
some  instances,  as  in  the  cells  of  the  spinal  ganglia  (Fig.  147)  they  are  absent, 
while  in  the  large  cells  of  the  cerebellum— Purkinje's  cells— they  form  a  mass 
which  must  be  many  times  greater  than  that  of  the  cell-body  proper.  In  most 
cells,  however,  the  dendrons  have  at  best  a  mass  several  times  as  great  as  that 

of  the  cell-body. 

Size  of  Nerve-cells  in  Different  Animals.— In  discussing  the  size  and 
form  of  cells  in  man  it  becomes  of  interest  to  determine  how  far  the  observa- 
tions apply  to  the  lower  mammals.  The  facts  are  briefly  these  :  It  can  be  said 
that  the  smaller  mammals  usually  have  the  smaller  nerve-cells,  but  the  decrease 
in  the  mass  of  the  nerve-cells  is  not  proportional  to  the  decrease  in  the  mass 
of  the  entire  body.  For  example,  Kaiser^  has  shown  that  the  cell-bodies 
occupying  the  ventral  horn  in  the  cervical  enlargement  of  the  spinal  cord  of 
the  bat,  the  rabbit,  and  the  monkey  are  in  many  cases  as  large  or  larger  than 
those  found  in  man. 

Size  of  the  Neurons  in  Different  Animals.— Though  the  volume  of  the 
cell-body  and  the  diameter  of  the  associated  neuron  are  approximately  similar 
in  any  two  animals  of  different  size,  as  for  instance  in  a  bat  and  in  man,  it  is 
also  evident  that  the  ueuron  could  nevertheless  not  have  the  length  in  the  bat 
that  it  does  in  man,  and  that  in  this  last  dimension  at  least  there  is  a  diminu- 
tion corresponding  to  the  size  of  the  animal.  Nevertheless,  the  volume  of  the 
entire  cells— cell-body  plus  neuron— still  remains  iwopoHionately  very  large  in 
the  smaller  mammals. 

The  bearing  of  this  fact  on  the  comparative  physiology  of  the  nervous  sys- 
tem is  evident,  for,  under  these  conditions,  as  the  volume  of  the  entire  nervous 
system  is  diminished,  the  number  of  cell-elements  constituting  it  must  also  be 
1  Die  Funktinnen  der  Ganglienzellen  des  Halsmarkes,  Haag,  1891. 


39 


610 


AN  AMERICAN   TEXT- BOOK    OF  PHYSIOLOGY. 


diminished,  and  thus  the  structure  ol'  tliis  system   in  the  smaller  mummals 
becomes  numerically  simj)liHcd. 

Size  and  Function. — Histology  shows  us  the  nerve-cell  prolonging  itself 
into  branches  often  nuich  sulxlivided,  the  dendrons  and  the  neuron.  Such  a 
cell  contains  a  mass  of  living  substances  capable  of  being  broken  down  and 
built  up  chemically,  and  there  is  nothing  against  the  inference  that  the  larger 
the  cell  the  greater  is  the  (piantity  of  these  living  substances,  and  hence  the 
larger  the  amount  of  stored .  energy  represented  by  it.  The  larger  cells  are 
therefore  those  capable  of  setting  free  the  greater  amount  of  energy.  The 
energy-producing  changes  are  in  the  greatest  measure  to  be  associated  with  the 
cell-body,  rather  than  with  any  of  the  branches.  Ou  the  other  hand,  the 
nerve-cells  with  large  cell-bodies,  sending  out  as  they  do  branches  which  are 
more  voluminous  than  those  nerve-cells  that  are  small,  furnish  a  greater 
amount  of  material  to  form  the  ultimate  twigs  into  which  these  branches 
finally  split.     From  this  it  follows  that  in  general  the  large  nerve-cells  have 

more  points  of  connection  with  the  structures 
about  them,  as  well  as  the  capacity  for  the  lib- 
eration of  a  greater  amount  of  energy. 

Gro-wth  of  Nerve-cells. — During  growth 
and  development  the  nerve-cells  may  present 
many  changes  in  appearance  (Fig.  145). 

The  nerve-elements  are  derived  from  ger- 
minal cells  found  in  the  epiblast  of  the  embryo. 
Amid  the  columnar  epiblastic  elements  forming 
the  medullary  tube  these  spherical  cells  appear 
in  man  about  the  third  to  the  fourth  week  of 
fetal  life.*  They  divide  rapidly  and  in  such 
a  way  that  one  daughter-cell  continues  as  the 
germinal  cell,  while  the  other  moves  away 
from  the  primitive  surface  of  the  body  and 
becomes  without  iurther  division  a  young 
nerve-cell  or  neuroblast.  The  formation  of 
neuroblasts  in  man  ceases  or  becomes  very 
slow  and  unimportant  by  the  end  of  the  third 
month  of  fetal  life. 

Two  chai-acters  of  the  neuroblast  are 
worthy  of  careful  consideration.  First,  there 
is  good  indirect  evidence  that,  in  early  life  at  least,  and  before  their  branches 
have  been  formed,  they  are  migratory,  moving  in  an  amoeboid  manner. 
This  being  .so,  the  perfection  with  which  they  arrange  themselves  in  the  adult 
sy.stem  depends  on  the  accuracy  with  which  they  respond  to  those  condi- 
tions that  determine  their  migration  as  well  as  upon  the  normal  character  of 
these  directing  influences  (mechanical  strain;^  chemotaxis  or  nutritive  attrac- 

'  His:  Archiv  fiir  Anatomie  und  Physiologie,  Anat.  Abthlg.,  1889. 
'  His :  Unsere  Korperfonn,  1874. 


Via.  145.— PorUon  of  developing  medul- 
lary tube  (human)  seen  in  frontal  section 
X  1100  diameters  (His) :  (;,  germinal  cell ; 
N,  neuroblasts. 


CENTRAL    NERVOUS  SYSTEM.  611 

tiou).^     But  with  so  nuuh  lil,erty  of  movement  and  with  directing  influences 
that  are  so  complicated,  the  chances  for  deviation  from  a  fixed  arrangement  are 

mucli  enhanced. 

Polarization  of  Neuroblasts.— Moreover,  very  early  in  the  history  of  the 
neuroblast  the  point  on  the  cell-body  from  which  the  neuron  will  grow  ai)pears 
in  many  cases  to  be  fixed,  and  the  cell  is  thus  physiologically  polarized.^  This 
polarity  being  established,  the  direction  in  which  the  neuron  first  grows  is 
determ'ined,  and  where  the  cells  are  misplaced  this  polarization  can  lead^to 
the  confusion  of  arrangement  found  in  the  brains  of  some  congenital  idiots.^ 

The  volume  of  either  the  germinal  cell  or  of  the  first  form  of  the  neuro- 
blast was  found  by  His  *  to  be  697  cubic  /i  in  a  human  fetus  (embryo  R-length 
5.5  millimeters,  aged  3  to  3.5  weeks).  It  has  jjreviously  been  shown  that  the 
volume  of  a  spinal-cord  nerve-cell  is,  taken  altogether,  78,500,000  cubic  fx, 
and  that  of  this  the  neuron  occupies  78,450,000  cubic  fx,  and  the  cell-body 
50,000  cubic  11.  If  we  take  half  of  this  total  volume,  it  gives  under  the  con- 
ditions chosen  an  increase  in  volume  between  the  neuroblast  and  the  mature 

cell  of  57,456-fold. 

Maturing  of  the  Nerve-ceU.— The  maturing  of  the  nerve-cell  involves 
several  changes.  First,  the  outgrowth  of  the  neuron  or  neurons ;  next,  the 
formation  of  the  dendrons ;  and  finally,  in  some  cases,  the  medullation  of  the 
neuron,  while  simultaneously  and  with  greater  or  less  rapidity  the  absolute 
amount  of  substance  in  both  cell-body  and  neuron  is  being  increased,  together 
with  a  chemical  differentiation  of  the  contents  of  the  cytoplasm  and  the 
nucleus.  The  time  in  the  life-history  of  the  individual  at  which  these  several 
events  occur  is  variable,  and  may  be  delayed  beyond  puberty  at  least,  while 
the  rate  at  which  they  occur  is  different  in  different  cases.  Furthermore,  many 
nerve-cells  never  develop  beyond  the  first  stages  of  immaturity  (Fig.  146).^ 

Form  of  the  Neuron  as  a  Means  of  Classification.— Of  the  various 
devices  used  to  classify  nerve-cells,  the  form  of  the  neuron  is  the  most  useful. 

Physiologically,  the  nerve-cell  is  significant  as  a  pathway  for  the  nerve- 
impulse.  tIic  current  conception  of  the  change  called  the  nerve-impulse  is 
that  it  begins  at  one  point  of  the  cell  and  travels  from  there  to  the  other  parts ; 
one  of  the  other  parts  is  the  neuron,  and  along  this  the  impulse  can  be  shown 
to  pass.  Although  it  cannot  be  directly  demonstrated,  there  is  reason  to  think 
that  primitively  all  the  branches  of  a  cell  had  similar  physiological  powers. 
Indeed,  the  nerve-cell  body  stimulated  at  any  point  may  be  responsive  just  as 
an  amoeba  is  responsive  at  any  portion  of  its  surface.  When,  however,  the 
branches  are  formed  they  become  the  channels  through  which  the  impulses 
pass,  and  hence  assume  a  special  significance  without  indicating  any  funda- 
mental change  in  the  structure  of  the  cell.     Where  the  cell  has  well-developed 

1  Davenport :   Bulletin  of  the  3/u.seHm  of  Comparative  Zoology,  Harvard  College,  Nov.,  1895; 
Herbst :  Biologviche  Centralblatt,  1894,  Bd.  xiv. 

*  Mali :  Journal  of  Morphology,  1893,  vol.  viii. 

»  Koster:  Neurologische  Centralblatt,  1889,  Bd.  viii. 

*  Archivfiir  Anatomie  tind  Physiologie,  1889. 


(312 


.l.V  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 


brandies  we  expect  an  arraii<^ena'nt  of  thcin  such  tliat  the  impulse  .shall  enter 
the  cell-body  by  one  branch  and  leave  it  by  another. 

On  examining  tlie  mature  nerve-cells  of  man  with  this  idea  in  mind,  two 
types  arc  found.     The  first  type  may  be  exemplified  by  tlu!  pvraniidal  cortical 


Fig.  146  — ^-Z),  showing  the  pliylogcnetic  development  of  mature  nerve-cells  in  a  series  of  ver- 
tebrates;  a-e,  the  ontogenetic  development  of  growing  cells  in  a  typical  mammal;  in  both  cases  only 
pyramidal  cells  from  the  cerebrum  are  .shown;  .1,  frog;  i;,  lizard;  f'.rat;  D.man;  a,  neuroblast  without 
dendrons;  6,  commencing  dendrons ;  c,  dendrons  further  developed;  d,  first  ajjpearance  of  collateral 
branches ;  e,  further  development  of  collaterals  and  dendrons  (from  S.  Ram6n  y  Cajal). 

cells  shown  in  Figure  146.  Plere,  from  a  pyramidal  body  {D)  there  arise  a 
number  of  dendrou.s,  while  from  the  lower  portion  of  the  cell  the  neuron  grows 
out  and  branches.    In  the  other  type  the  neuron  alone  grows  out.    Its  branches 


Fig.  147.— Spinal  ganglion  of  an  embryo  duck  ;  composed  of  dineuric  nerve-cells  (van  Gehuchten). 

are  but  two  in  number  and  both  are  medullated.  They  pass  in  opposite  direc- 
tions and  in  this  type  there  are  no  dendrons.  To  understand  the  arrangement 
in  these  cases,  recourse  must  be  had  to  the  facts  of  development.     The  second 


CENTRAL    NERVOUS  SYSTEM.  613 

type  begins  its  development  as  :i  bipolar  cell,  a  neuron  growing  from  each  pole 
(Fig.  147).  In  the  adult  spinal  ganglion  of  tlie  higher  mannnuls,  however, 
no  such  bii)olar  cells  are  to  be  found,  but  only  cells  having  a  single  neuron 
which  soon  divides  into  two  branches. 

Figure  14<S  beautifully  illustrates  the  phases  of  this  change  as  seen  in  a 
sin<:;le  section.  At  first  one  nciuron  arises  from  each  pole  of  the  ovoid  cell- 
bodv.  Later  the  cell-body  occupies  a  position  at  the  side  of  the  two  neurons, 
which  appear  to  run  into  one  another.  Finally  the  cell-body  is  separated  from 
the  two  neurons  by  an  intervening  stem.  The  stem  has  the  characters  of  a 
nerve-fibre  and  from  the  end  of  it  the  original  two  neurons  pass  off  as  branches. 

From  this  mode  of  development  it  is  jilain  that  the  single  stem  must  be 
looked  upon  as  containing  a  double  pathway,  although  it  appears  to  be  in  all 
ways  a  single  fibre,  for  on  the  one  hand  it  contains  the  path  for  the  incoming 
and  on  the  other  for  the  outgoing  im- 
pulses. Recent  investigations  have 
shown  in  a  striking  way  that  cells 
modified  in  this  manner  are  by  no 
means  limited  to  the  spinal  ganglia, 
but  occur  in  the  cortex  of  the  cerebel- 
lum and  elsewhere.     The  study  of  this 

^•t!.      j^:^,,    U«;r.^c  -nri'fVi  I'f  flio    fnllnw  Fig.  148.— Dineuric  changing  into  mononeuric 

modification  brings  with  it  the  toUow-     ^^^^^   ^^^^  ^^^^  ^^^^^^.^^  ^^^^^.^^  ^^  ^  ^^^.^^^p. 

ing    suggestion  :    If  the    single    stem    in       ing  guinea-pig  (van  Oehuchten). 

the  modified  spinal  ganglion-cells  must 

by  virtue  of  its  development  contain  a  double  pathway,  it  is  fair  to  inquire 
whether  the  same  may  not  be  true  of  the  other  forms  of  the  nerve-cell  in  which 
the  neuron  also  appears  to  be  single.  Among  the  cortical  cells  the  arrange- 
ment of  the  branches  is  such  that,  for  aught  that  is  known,  the  stem  of  the 
neuron  may  functionate  in  the  manner  suggested,  and  contain  more  than  one 

pathway. 

Classifying  the  nerve-cells,  therefore,  in  the  light  of  these  facts,  we  find— 
(1)  The  pyramidal  type,  in  which  the  dendrons  and  neuron  are  both  well 
developed,  and  in  which  the  greater  part  of  the  impulses  most  probably  enter 
the  cell  by  way  of  the  dendrons  and  leave  by  way  of  the  neuron ;  (2)  The 
spinal  ganglion  type,  in  which  originally  the  impulse  passes  in  at  one  pole  of 
the  cell  and  out  at  the  other,  but  in  the  course  of  development  the  hvo  neurons 
become  attached  to  the  cell-body  by  a  single  stem,  and  by  inference  there  must 
be  in  this  stem  a  double  pathway.     In  this  special  case  there  are  no  dendrons. 

Growth  of  Branches.— After  the  cells  have  taken  on  their  type  form,  the 
branches  still  continue  to  grow,  not  only  in  length,  but  in  diameter.  In  man, 
for  example,  the  diameter  of  the  nerve-fibres  (neurons)  taken  from  the  periph- 
eral nerves  at  birth  is  1 .2-2  fx  for  the  smallest,  up  to  7-8  //  for  the  largest,  with 
an  average  of  3-4  ji,  while  at  maturity  it  is  10-15  //  for  the  larger  fibres.^ 

In  the  second  spinal  nerve  of  the  frog,  Birge  found  the  fibres  ^  to  increase 

1  Westphal :  Neurologische  Centralblatt,  1894,  No.  2. 
'■^  Birge :  Archiv  fiir  Anatomie  und  Physiologie,  1882. 


614  AiX  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

in  average  diameter  from  7.6  [jl  to  12.6  fi,  as  the  total  weight  ol'  tiie  frog 
increased  from   1.5  to  63.0  grams. 

The  branch  which  forms  the  neuron  contains  an  axis-cylinder  surrounded  by 
a  meilullarv  sheath.  There  are  two  views  coiioerniug  the  constitution  of  the 
axis-cyliuder — one'  that  tiie  axis  is  composed  of  slender  thread-like  fil^rillae 
floating  in  a  coagulable  plasma,  these  fibrillae  being  the  conductors  of  the  nerve- 
impulses.  The  opposing  view  is  that  advocated  by  Leydig,^  Nansen,^  and 
Schiifer/  to  the  effect  that  the  axis-cylinder  is  formed  by  a  spongy  framework 
in  the  meshes  of  which  is  a  semi-fluid  plasma.  According  to  this  latter  view 
the  plasma  is  the  substance  through  which  the  impulses  ]>ass,  Xeitiier  view  is 
bevond  criticism,  nor  does  either  of  them  admit  of  detailed  correlation  with  the 
physiological  facts.  The  conception  of  the  axis-cylinder  as  composed  of  fibrillae 
appears  at  first  sight  to  offer  an  anatomical  arrangement  for  a  number  of  isolated 
pathways  within  a  single  fibre,  but  the  fibrillae  cannot  be  unbrauched  from  one 
end  of  their  course  to  the  other,  since  many  nerve-fibres  near  their  final  distribu- 
tion divide  a  number  of  times,  the  diameter  of  the  individual  fibrillae  remaining 
the  same;  and  the  combined  cross  sections  of  the  axis-cylinders  in  the  subdivis- 
ions demand,  therefore,  a  far  greater  number  of  fibrillar  than  is  contained  in  the 
main  stem  of  the  fibre.  On  the  other  hand,  the  conception  of  the  axis-cylinder 
as  a  series  of  tubes  interosculating  at  very  acute  angles  does  away  at  the  start 
with  any  notion  of  structural  isolation  of  the  pathways  within  the  fibres. 
This  latter  view  is,  however,  the  better  supported  histologically. 

"When  the  axis-cylinder  increases  in  diameter,  it  must,  under  this  view,  be 
by  the  formation  of  more  of  these  tubes,  for  their  size,  though  variable,  is  not 
directly  in  proportion  to  the  diameter  of  the  fibre.  While  the  neuron  is  growing 
as  a  naked  axis-cylinder  it  is  usually  slightly  enlarged  at  the  tip  (Cajal),  sug- 
gesting that  it  is  specially  modified  at  that  point.  The  nutritive  exchange  on 
which  the  increase  of  the  entire  neuron  depends  appears  to  take  place  along 
its  whole  extent,  and  not  to  be  entirely  dependent  on  material  passed  from  the 
cell-body  into  the  neuron. 

Medullation. — After  the  production  of  its  several  branches  the  next  step 
in  the  growth  of  the  cell  is  the  formation  of  the  medullary  sheath.  Not  all 
neurons  have  a  medullary  sheath,  nor  is  any  neuron  completely  niedullated. 
In  the  sympathetic  system  there  is  a  very  large  proportion  of  unmeduUated  fibres. 
In  the  central  system  the  number  is  very  large  although  their  mass  is  small. 
Of  the  significance  of  the  medullary  sheath  we  know  nothing.  The  suggestion 
that  it  acts  to  insulate  the  nerve-impulse  within  a  given  axis-cylinder  has  little 
or  no  evidence  in  its  favor.  The  suggestion  that  it  is  nutritive  is  plausible,  but 
important  differences  in  the  physiological  reactions  of  the  two  classes  of  nerve- 
fibres  have  not  yet  been  found. 

In  studving  the  effect  of  stimulation  and  of  changes  in  temperature  on  the 

^  Kuppfer  und  Boveri :  Abhnndlungen  d.  k.  bayer.  Akad.  den  Wissenschaften,  Miinchen,  1885. 
2  Zelle  und  Gewebe,  Bonn,  1885. 

*  The  Structure  and  Combination  of  the  Histological  Elements  of  the  Central  Nervous  System, 
Bergen,  1887.  *  Quain's  Anatomy,  10th  edition,  vol.  i.  pt.  2,  1891. 


CENTRAL    NERVOUS  SYSTEM.  615 

irritability  and  conductivity  oi'  nerve-fibres*  it  was  found  that  certain  nerve- 
fibres,  notably  tiie  vaso-constrictor  fibres  and  the  sweat-fibres  in  the  sciatic  nerve 
of  the  cat,  when  they  were  subjected  to  a  faradic  current  continued  for  several 
minutes,  lost  their  irritability,  completely  or  in  part,  at  the  point  of  stimula- 
tion. This  "stimulation  fati<;:ue"  is  not  known  to  be  produced  in  nerves 
which  ai-e  unquestionably  medullated.  It  does  occur  where  the  nerves  are 
iinmcdullated,  but  it  also  occurs  where  the  absence  of  medullation  lias  not  been 
proved,  and  hence  cannot  be  put  forward  as  a  differential  character  distinguish- 
ing these  two  sorts  of  nerves.  The  medullated  neurons  are  in  their  early  history 
unmedullated,  and  only  later  acquire  this  sheath,  so  that  medullation  might  be 
taken  to  represent  a  final  step  in  the  highest  development  of  the  nerve-cell.  The 
fact  that  certain  groups  of  fibres  are  not  functional  till  after  they  are  medullated 
hardly  bears  on  the  question,  for  the  following  reason  :  Until  a  group  of  fibres 
has  established  a  physiological  connection  with  the  tissues  which  it  is  to  control, 
it  cannot  be  expected  to  influence  them,  and  it  has  yet  to  be  shown  that  the 
appearance  of  functional  activity  and  the  beginnings  of  medullation  are  not 
both  of  them  the  result  of  such  growth-changes  at  the  distal  end  of  the  axis- 
cylinder.  The  changes  involved  in  establishing  physiological  connections  are 
those  by  which  the  tips  of  the  branches  formed  by  the  neuron  of  one  cell  come 
into  such  relation  with  other  branches  of  a  second  cell  or  some  non-nervous 
tissue  that  the  nerve-impulse  can  pass  between  them.  At  the  same  time  the 
non-medullated  neurons  establish  connections  with  the  tissues  controlled  by 
them  just  as  well  as  do  those  which  are  to  be  medullated,  but  why  one  goes 
on  to  the  acquisition  of  the  sheath  and  the  other  remains  without  it,  is  not 
explained.  Neither  is  it  known  how  far  one  of  these  forms  may  re})lace  the 
other,  although,  it  is  not  improbable  that  the  proportions  of  medullated  and 
unmedullated  fibres  in  different  persons  may  be  very  unlike. 

Gro-\^h  of  Medullary  Sheath. — Whatever  may  be  the  significance  of  the 
medullary  sheath  it  is  usually  formed  before  the  nerve-element  as  a  whole  has 
attained  its  full  size.  In  the  peripheral  system  it  depends  on  the  presence  of 
cells  which  envelop  the  axis-cylinder,  forming  a  tube  about  it.  Each  ensheath- 
ing  cell  is  physiologically  controlled  by  a  nucleus  which  becomes  situated  about 
midwav  between  its  extremities.  The  cell-substance  is  largelv  transformed  into 
myelin,  and  the  line  of  junction  between  two  of  these  sheathing  cells  forms  a 
node  of  the  nerve-fibre.  In  the  sheath  of  a  growing  nerve-cell  at  least  two 
changes  are  clearly  marked :  As  the  axis  increases  in  diameter  the  medul- 
lary sheath  becomes  thicker.  The  change  is  such  that  in  the  peripheral 
system  the  areas  of  the  axis-cylinder  and  of  the  medullary  sheath  as  shown 
in  cross  sections  remain  nearly  equal  (Fig.  149).  On  the  other  hand  the  length 
of  the  internodal  segments  tends  to  increase  with  an  increase  in  the  diameter 
of  the  nerve-fibre,  and  for  nerves  of  the  same  diameter  it  is  less  in  man  than 
in  the  lower  mammals.  In  a  given  fibre  the  segments  are.  shorter  at  the  extreme 
peripheral  end  (Key  and  Retziu.s).  In  the  young  fibres,  also,  they  are  shorter 
and  increase  in  length  with  age. 

'  Howell,  Budgett,  and  Leonard:  Journal  of  Physiology,  1894,  toI.  xvi. 


616  AN  A  mi:  RICA  N    TEXT-BOOK    OF  PHYSIOLOOY. 

A  jiliysiological  significance  attaches  to  these  scgmeuts,  because,  as  Ranvier 
long  since  pointed  out,  it  is  at  the  nodes  that  various  staining  reagents  most 

I'asily  reach  the  axis-cylinder.  This  sug- 
gests that  normal  nutritive  exchanges  may 
follow  the  same  path  and  thus  short  inter- 
nodal  segments  giving  rise  to  many  nodes 
would  represent  tlie  condition  most  favor- 
able to  exchange  between  the  axis  and  the 

1  1...  ;i;'.— l,..u,L;ii,i.uii,u  ^y;.  ami  tr!insvi.Tse(,-l)  p       i-   .    i      • 

sections    of  nerve-fibrcs.     The    lu-avy  border  SUrrOUndmg  plasma.      illUS  lar,  histologl- 

represents  the  medullary  sheath,  which  be-  ^^^  observation  showS  the  more  numcrOUS 
comes  thicker  in  the  larger  fibres.     Human 

sciatic  nerve.    X  200  diameters  (modified  from  nodcS    where    the    pliysiological    proCCSSeS 

van  Gehuchtcn).  ^^.^  presumptivelv  most  active,  and  hence 

supports  the  hypothesis  suggested.  Cases  of  the  interjiolation  of  new  sheath- 
ing cells  to  form  additional  segments  between  those  originally  laid  down  have 
also  been  described.^ 

Medullation  in  Central  System. — Concerning  the  relation  of  the  medul- 
lary sheath  to  the  axi.s-cylinder  in  the  central  system,  our  information  is  less 
complete.  The  elements  which  give  rise  to  the  medullary  substance  are  not 
known  and  the  myelin  is  not  enclosed  in  a  primitive  sheath.  There  are  no 
internodal  nuclei  regularly  placed,  yet  Porter^  has  demonstrated  in  both  the 
frog  and  the  rabbit  the  existence  of  nodes  in  fibres  taken  from  the  spinal  cord. 
The  conditions  which  there  exist  must  be  further  studied  before  any  general 
statements  concerning  the  medullary  suKstance  in  the  nerve-centres  can  be  ven- 
tured, yet  it  is  an  important  observation,  that  whereas  medullation  in  the 
peripheral  system  is  mainly  completed  during  the  first  five  years  of  life,  the 
process  continues  in  the  central  system,  and  especially  in  the  cerebral  cortex, 
to  beyond  the  thirtieth  year. 

AVhatever  views  may  be  held  concerning  the  capacities  of  a  medullated  fibre, 
it  is  to  be  remembered  that  the  medullary  sheath  does  not  cover  the  first  part 
of  the  neuron  on  its  emergence  from  the  cell-body,  nor  are  ultimate  branches 
of  the  neuron  medullated  in  the  region  of  their  final  distribution. 

The  acquisition  of  this  sheath  occurs  in  response  to  a  i)hysiological  change 
that  appears  at  the  same  time  along  the  entire  length  of  the  fibre.  The  pro- 
cess, therefore,  is  not  a  progressive  one,  but  practically  simultaneous. 

What  has  just  been  said  applies  to  the  main  stem  of  the  neuron.  As  shown 
in  Figure  146,  the  neuron  often  has  branches  near  its  origin,  and  according  to 
the  ob.^ervations  of  Flechsig^  these  may  become  medullated.  Concerning  the 
time  of  the  medidlation  of  these  branches  there  are  no  direct  observations,  but 
if  it  is  controlled  by  the  same  conditions  which  appear  to  control  the  process  in 
the  main  stem,  then,  as  the  branches  form  their  physiological  connections  later 
than  the  main  stem,  it  would  follow  that  their  medullation  should  also  occur 
later,  and  the  studies  on  the  progressive  medullation  of  the  cerebral  cortex 
favor  such  a  view. 

1  Yignal :  Archives  de  Physiologic,  1883.        *  Quarterly  Journal  Microscopical  Science,  1890. 
'  Archivfiir  Anatomie  und  Physiologie,  1889. 


CJ:.\  til  1  L    XI'JR  VO  T  \S  S  YSTEM. 


617 


Changes  in  the  Cytoplasm, — While  the  nerve-cell  is  passing  from  the 
immature  to  the  inatiirc  form,  inorcasino;  in  mass  and  in  the  number  of  its 
branches,  as  well  as  aecjuiring  its  medullary  sheath,  it  is  also  undergoing  vari- 
ous ehemical  changes.  The  chromatic  substance  in  the  cytoplasm  becomes 
more  abundant  at  maturity  and  the  pigment-granules  increase  in  <|uantity.' 

Old  Age  of  Nerve-cells. — But  the  nerve-cell,  though  possessing,  in  most 
cases,  a  life-history  co-extensive  with  that  of  the  entire  body,  eventually  exhibits 
regressive  changes.  These  changes  of  old  age  consist,  in  some  measure,  in  a 
reversal  of  those  jirocesses  most  evident  during  active  growth.  The  cell-body, 
together  with  the  nucleus  and  its  subdivisions,  becomes  smaller,  the  chromatic 
substance  diniinishes,  the  jiigment  increases,  the  cytoplasm  exhibits  vacuoles,  the 


C  D 

Fig.  150.— Toshow  the  changes  in  nerve-cells  due  to  age:  A,  spinal  ganglion-cells  of  a  still-born  male 
child ;  B,  spinal  ganglion-cells  of  a  man  dying  at  ninety-two  years  ;  n,  nuclei.  In  the  old  man  the  cells 
are  not  large,  the  cytoplasm  is  pigmented,  the  nucleus  is  small,  and  the  nucleolus  much  shrunken  or 
absent.  Both  sections  taken  from  the  first  cervical  ganglion,  X  250  diameters ;  C,  nerve-cells  from  the 
antennary  ganglion  of  a  honey-bee,  just  emerged  in  the  perfect  form  ;  D,  cells  from  the  same  locality  of  an 
aged  honey-bee.  In  Cthe  large  nucleus  (black)  is  surrounded  by  a  thin  layer  of  cytoplasm;  in  D  the 
nucleus  is  stellate,  and  the  cell-substance  contains  large  vacuoles  with  shreds  of  cytoplasm  (Hodge). 

dendrons  atrophy,  and  the  neurons  also  probably  diminish  in  mass.  In  some 
instances  the  entire  cell  is  absorbed.  Some  of  these  facts  are  illustrated  by  the 
observations  of  Hodge  ^  on  the  spinal  ganglion-cells  of  an  old  man  of  ninety- 
two  years  as  compared  with  those  of  a  new-born  child  (see  Fig.  150).     The 

^  Vas :  Archiv  filr  mikroskopische  Anatomic,  1892. 
'  Journal  of  Physiology,  1894,  vol.  xvii. 


618  AiX  AMEBICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

changes  in  the  outline  of  the  nucleus  are  also  to  be  noted,  as  well  as  the 
decrease  in  their  volume.  The  figures  for  the  decrease  in  the  volume  of  the 
nucleus  are  given  in  the  following  table,  showing  the  ])rin('ij)al  differences 
observed  on  comparing  the  s[)inal  ganglion-cells  (first  cervical  ganglion)  from 
a  child  at  birth  with  those  from  a  man  dying  from  old  age  at  ninety-two  years 
(Hodge)  : 

Child  at  birth  ;  male.  Old  man. 

Volnine  of  nucleus 100  per  cent.  64.2  per  cent. 

Nucleoli  visible o.'i    "      "  5       "      " 

Deep  pigmentation 0    "      "  67       "      « 

Slight  i)igmentation 0    "      "  33       "      " 

Analogous  changes  were  found  by  this  investigator  in  the  antennary  gan- 
glia of  old  honey-bees  as  compared  with  the  corresponding  ganglia  taken  from 
those  which  had  ju.st  emerged  in  the  perfect  form.  These  are  also  shown  in 
Figure  150. 

Since  Nvith  the  chemical  and  morphological  variations  which  occur  during  the 
entire  growth-cycle  there  must  go  variations  in  the  physiological  powers,  we 
are  led  therefore  to  anticipate  in  old  age  a  correlation,  on  the  one  hand,  between 
the  decrease  in  the  quantity  of  functional  substance  in  the  cyto|)lasm  and  a 
decrease  in  the  energy-producing  power  of  the  cells,  and,  on  the  other,  between 
the  absorption  of  the  cell-branches  and  a  limitation  in  the  extent  of  the  mflu- 
ence  exerci.sed  by  a  given  cell.  Both  of  which  defects  are  characteristic  of  the 
nervous  system  during  old  age. 

B.  The  Nerve-impulse  ■within  a  Single  Nerve-cell. 

The  Nerve-impulse. — Xerve-cells  form  the  pathways  along  which  nerve- 
impuLses  travel.  As  introductory,  therefore,  to  the  study  of  the  composite 
pathways  in  the  central  system,  comprising  as  they  do  several  elements 
arranged  in  series,  it  becomes  important  to  study  the  behavior  of  the  nerve- 
impulse  within  the  limits  of  a  single  cell-element. 

Experimentally  it  is  found  that  the  nerve-impulse  is  revealed  by  a  wave  of 
molecular  change  in  the  form  of  an  electrical  variation  which  passes  along  the 
nerve-fibre  in  both  directions  from  the  point  of  stimulation.  Under  normal 
conditions  the  intensity  of  the  electrical  change  does  not  vary  in  transit,  but 
it  does  change  with  changes  in  the  strength  of  the  initial  stimulus.  It  moves 
in  the  peripheral  nerves  of  the  frog  in  the  form  of  a  wave  some  18  rcillime- 
ters  in  length,  at  the  mean  rate  of  30  meters  per  second,  and  this  rate  can  be 
somewhat  retarded  by  cooling  the  nerves,  and  accelerated  by  warming  them. 
In  mammals,  the  rate  in  the  peripheral  nerves  has  been  found  by  Helm- 
holtz  and  Baxt  to  be  3-1  meters  per  second.  The  nerve-impulse  can  be 
aroused  at  any  point  on  a  nerve-fibre  provided  a  sufficient  length  of  fibre  be 
subjected  to  stimulation.  Mechanical,  thermal,  chemical,  and  electrical  stimuli 
may  be  used  to  arouse  it,  but  just  how  the  impulse  thus  .started  differs  from 
that  normally  passing  along  the  fibres  as  a  consequence  of  changes  in  the  cell- 
bodies  of  Avhich  these  fibres  arc  outgrowths  is  not  known.     It  appears,  how- 


CENTRAL   NERVOUS  SYSTEM.  619 

ever,  that  tlie  impulses  roused  by  artificial  stimuli  are  usually  accompanied  by 
a  much  stron<j;er  electrical  variation  than  accompanies  the  normal  impulses. 

In  the  peripheral  system  the  nerve-impulse,  when  once  started  within  a 
fibre,  is  confined  to  that  track  and  does  not  difiiise  to  other  fibres  running  par- 
allel with  it  in  the  same  biuidie.  In  other  words,  throughout  this  portion  of 
its  course  the  conduction  of  the  impulses  is  isolated. 

The  above-mentioned  facts  have  been  observed  on  the  peripheral  nerves, 
and  these  morphologically  are  but  parts  of  the  medullated  neurons,  the  cell- 
bodies  of  which  are  located  either  in  the  central  system  proper  or  in  the  spinal 
or  sympathetic  ganglia. 

The  observations  apply  therefore  to  but  one  portion  of  the  nerve-cell,  and 
our  present  purpose  is  to  determine  how  far  it  is  possible  to  extend  them  so 
that  they  apply  to  the  entire  nerve-cell,  noting  at  the  same  time  the  modifica- 
tions introduced  by  this  extension. 

Conditions  Surrounding-  the  Extension  of  the  Nerve-impulse. — 
Owing  to  the  small  size  of  nerve-cell  bodies,  there  are  of  course  very  few 
instances  in  which  a  single  nerve-cell,  or  part  of  such  a  cell,  has  been  the 
object  of  direct  physiological  experiment. 

Groups  of  elements  are  usually  employed  like  those  represented  in  the 
groups  of  neurons  forming  the  various  peripheral  nerves,  and  w4iere  these 
have  common  functions,  the  inference  may  be  made  from  the  changes  in  the 
mass  to  changes  in  the  constituent  units.  This  method  can  be  used  without 
serious  error,  and  it  is  possible,  therefore,  to  speak  of  events  occurring  in  the 
individual  elements,  although  the  experiments  were  made  upon  masses  of 
them. 

Direction  of  the  Nerve-impulse. — In  the  case  of  a  given  nerve-cell,  the 
impulses  which  we  usuall}'  consider  pass  in  one  direction  only.  For  instance, 
along  the  ventral  nerve-roots  of  the  spinal  cord  the  impulses  pass  from  the 
cord  to  the  periphery,  while  in  the  dorsal  roots,  so  far  as  they  take  origin 
from  the  cells  of  the  spinal  ganglia,  these  impulses  travel  in  the  opposite 
direction.  At  the  same  time  experiment  has  shown  that  if  a  nerve-trunk  be 
stimulated  at  a  given  point,  then  the  nerve-impulse  can  be  demonstrated  as 
passing  away  from  the  point  of  stimulation  in  both  directions. 

We  are  therefore  led  to  inquire  what  limits  are  set  to  the  passage  of  im- 
pulses in  a  direction  opposite  to  the  usual  one.  The  narrowest  limits,  it 
appears,  are  those  of  the  single  cell  in  which  the  impulse  has  originated.  The 
experimental  observations  are  as  follows :  When  the  fibres  forming  tli^  ven- 
tral root  of  the  spinal  cord  are  stimulated  electrically,  and  the  cross  section  of 
the  cord,  somewhat  cephalad  to  the  level  at  which  the  root  joins  it,  is  explored 
with  an  electrometer,  there  is  not  found  any  evidence  of  nerve-impulses  pass- 
ing cephalad  in  the  substance  of  the  cord.  The  arrangement  of  the  cells  in 
the  cord  is  such,  however,  that  the  cell-bodies  which  give  origin  to  the  fibres 
forming  the  ventral  root  are  physiologically  connected  with  fibres  running 
toward  them  from  every  portion  of  the  cord,  and  under  normal  conditions 
these  fibres  convey  impulses  to  them.     The  experiment  shows  that  when,  under 


620 


^^Y  AMEniCAN   TEXT-BOOK   OF  PHYSIOLOGY. 


the  ooiulitions  named,  an  ini])ul.se  enters  the  ecll-budy  bv  way  of  the  ventral 
root-fibre  to  wliieli  it  gives  origin,  it  does  not  pass  out  of  tliis  cell-budy  into 
tlie  other  elements  of  the  cord  causing  an  electric  change  detectable  as  a  nega- 
tive variation.  It  appeal's,  therefore,  that  the  connection  between  the  fibres 
of  the  cord  and  the  cell-bodies  in  question  is  such  that  though  impulses 
readily  pass  from  the  former  to  the  latter,  they  do  not  jms.s  in  tiie  reverse 
direction,  thus  showing  that  in  this  instance  the  cell-boundary  sets  a  limit  to 
the  reversed  impulse.* 

With  the  elements  forming  the  dorsal  spinal  root,  the  case  is  at  first  glance 
apparently  different,  though  in  reality  it  is  the  same.     These  elements  are 

those  having  the  cell-body  located  in  the  spinal 
ganglion.  The  cells  are  essentially  dineuric 
(Fig.  148) ;  one  neuron  extends  from  the 
point  of  division  toward  the  periphery,  and 
the  other  enters  the  spinal  cord  to  distribute 
itself  as  a  fibre  coursing  longitudinally  for  some 
distance  within  it  (see  Fig.  151).  The  normal 
direction  of  the  eftective  impulses  is  from  the 
periphery  toward  the  cord,  and  Avithin  the  cord 
they  are  delivered  to  other  elements  which  cany 
them  in  all  directions.  It  is  therefore  to  be  ex- 
pected that  the  stimulation  of  the  dorsal  root- 
fibres  would  give  rise  to  impulses  })assing  in  both 
directions  in  the  dorsal  columns  of  the  cord. 
When,  however,  the  dorsail  columns  of  the  cord 
are  electrically  stimulated  in  across  section  made 
just  above  the  level  of  the  entrance  of  a  dorsal 
root,  then  it  is  found  that  the  electrical  varia- 
tion is  to  be  detected  in  the  nerve-fibres  on  the 
distal  side  of  the  spinal  ganglion.  These  im- 
pulses have  therefore  passed  in  a  direction  the 
reverse  of  that  usually  taken.  The  fibres  which 
are  stimulated  in  this  instance  in  the  cross  sec- 
tion of  the  cord  are,  however,  outgrowths  of  the 
spinal  ganglion-cells,  and  thus,  although  the 
stimulation  of  the  cord  does  give  rise  to  an  im- 
pulse in  the  peripheral  nerve,  nevertheless  the 
impulse  is  continually  within  the  limits  of  one 
cell-element.  The  question  of  whether  the  re- 
versed impidse  can  traverse  the  cell-body  is 
here  answered  in  the  affirmative,  for  these  cells 
are  virtually  dineuric,  and  everything  jioints  to  the  passage  of  the  impulse 
through  the  cell-body  in  passing  from  one  neuron  to  the  other.  There  is, 
however,  no  evidence  that  the  stimulation  of  the  dorsal  columns  of  the  cord 
^  Gotch  and  Horsley  :  Proceedings  of  the  Royal  Society,  1888. 


Fig.  lol.— a  longituditml  section 
of  the  cord  to  show  the  branching  of 
incoming  root-fihres  in  dorsal  col- 
umns. At  the  left  are  three  />  R 
root-fibres,  each  of  which  forms  two 
princii)al  branches.  These  give  off 
at  right  angles  other  branches,  col- 
laterals, Col,  which  terminate  in 
brushes.  C  C,  central  cells,  whose 
neurons  give  off  similar  collaterals 
(Ram6n  y  Cajal). 


CENTRA Fj    nervous  SYSTEM.  621 

produces  outgoing  impulses  in  the  dorsal  nerve-roots  except  when  the  stiinuhis 
is  applied  to  the  neurons  whieli  ai'c  outgrowths  of  tiie  (;ells  of  the  dorsal  ganglia. 

Arrangement  in  the  Central  System. — As  will  be  shown  later  on,  there 
is  reason  to  picture  tiic  passage  of  the  uerve-inipulse  through  the  central 
system  as  accomplished  by  a  series  of  relays  in  which  each  cell-body  is  roused 
to  discharge  its  own  impulse  as  the  consequence  of  an  impidse  received  from 
some  other  cell. 

When  therefore  an  impulse  is  brought  by  one  neuron  to  a  cell-body,  and 
passed  on  by  way  of  it  to  another  neuron  which  is  a  part  of  the  stimulated  cell, 
there  is  no  escape  from  the  conclusion  that,  if  in  this  case  the  cell-body  is 
physiologically  significant,  it  rather  originates  the  impulse  which  traverses 
the  second  neuron  than  acts  merely  as  the  conductor  for  it. 

This  is  suggested  by  the  changes  caused  in  the  cell-body  as  the  result  of 
stimulating  it.  At  the  same  time  there  is  an  appreciable  delay  (0.036  second) 
in  the  passage  of  the  nerve-impulse  through  the  cell-body  in  the  case  of  those 
cells  which  form  the  spinal  ganglion.' 

Double  Pathways. — If  the  view  is  correct,  that  in  passing  through  the 
spinal  ganglion  the  impulse  enters  the  cell-body,  then  the  nerve-impulse  passes 
to  and  fro  along  the  common  stem  which  joins  the  cell-body  with  the  two 
neurons  {vide  Fig.  148).  In  such  a  case,  the  impulse  going  toward  the  cell 
must  travel  either  through  the  entire  stem,  or  through  a  part  of  it  only.  This 
stem  is  conceived  as  homologous  with  the  bases  of  the  two  neurons  which 
originally  arose  from  the  dineuric  cell,  thus  morphologically  representing  a 
double  pathway,  although  in  the  mature  cell  there  is,  from  the  histological 
side,  absolutely  no  trace  of  this  duplicity. 

The  same  arrangement  must  exist  in  the  case  of  cells  like  those  represented 
in  Figure  152,  in  which  the  neuron  arises  from  the  base  of  a  dendron  at  some 


Fig.  152.— Showing  the  relations  between  the  terminal  branches  of  the  dendrons  (D)  and  of  the 
neurons  [N')  of  the  optic  fibres  where  they  come  together  in  the  superficial  layer  of  the  optic  lobe  of 
the  chick ;  also  showing  the  origin  of  the  neuron  (iV)  from  a  dendron  (van  Gehuchten). 

distance  from  the  cell-body,  and  in  which  nerve-impulses  arriving  over  the 
dendron  and  leaving  by  the  neuron  must  follow  the  portion  of  the  cell-branch 
which  is  common  to  both,  passing  along  it  first  in  one  direction  and  then  in 
the  other.  It  appears  not  improbable,  therefore,  that  some  outgrowths  of  the 
cell-body  which  morphologically  are  simple,  really  contain  more  than  one 
physiological  pathway. 

^  Gad  and  Joseph  :  Archiv  fur  Anatomie  und  Physiologic,  1889, 


622  AX  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

Significance  of  Shape. — Since  tlie  outgoing  nerve-impulses  pass  along 
the  efferent  cell-branches  to  their  tijw,  it  follows  that  if  the  impulses  are 
destined  to  leave  the  cell  limits  they  will  do  so  at  the  extremities  of  the 
branches.  This  leads  to  the  question  how  far  the  j)ossession  of  branches  is 
necessary  to  the  functional  activity  of  a  nerve-cell  either  for  the  reception  or 
transmission  of  an  impulse.  Since  it  has  been  pointed  out  that  the  spinal  cord 
of  the  newt  and  fish*  is  capable  of  conduotiug  impulses  even  before  the  den- 
drons  of  the  cells  composing  it  are  developed,  it  follows  that  the  transmission 
of  impulses  is  in  some  way  dependent  on  the  condition  of  the  cell-wall  inde- 
pendent of  cell-branches.  This  modification  of  the  cell-wall  may  exist  at 
points  where  there  are  no  branches,  or  during  this  early  period  be  a  general 
property  of  the  wall  and  only  later  become  the  peculiar  property  of  that  por- 
tion Avhich  forms  the  tips  of  the  branches.  But  not  only  the  ciipacity  to 
receive,  but  also  the  capacity  to  deliver  impulses  is  a  function  of  the  ends  of 
the  branches,  and  the  cell-wall  at  these  points  must  therefore  be  peculiarly 
modified  with  a  still  further  differentiation  determining  the  direction  in  which 
the  impulses  may  pass.  If,  therefore,  the  mature  cell  is  thus  arranged,  its 
shape  and  the  number  of  its  branches  have  a  meaning.  Each  dendron  repre- 
sents at  least  one  pathway  by  which  impulses  reach  the  cell-body.  If,  then, 
there  are  many  dendrons,  the  cell-body  is  subject  to  a  more  complicated  series 
of  stimuli  than  if  the  branches  are  few.  It  will  be  ■  remembered  that  the 
young  nerve-cell  has  no  dendrons,  that  the  first  branch  to  be  formed  is  the 
neuron,  and  that  the  completion  of  the  full  numl^er  of  dendrons  is  a  slow 
process.  The  j)athways  formed  by  the  dendrons  are,  therefore,  continually 
increasing  up  to  maturity. 

Effect  of  Impulses. — The  impulses  which  arrive  at  the  cell-body  produce 
there  chemical  changes.  These  changes  when  they  reach  a  given  volume  and 
intensity  cause  a  nerve-impulse  which  leaves  the  cell-body  by  way  of  the 
neuron.  If  the  nerve-impulse  is,  as  we  a.ssume,  dependent  on  the  chemical 
changes  occurring  in  the  cytoplasm,  then  the  nerve-impulse  must  vary  accord- 
ing to  these  changes,  which  in  turn  can  hardly  be  similar  when  the  incoming 
impulses  that  arouse  them  arrive  along  different  dendrons. 

Concerning  the  modifications  in  the  nerve-impulse  as  de|)endent  on  the 
cell-body,  there  are  thus  far  known  only  the  variations  in  the  intensity  of  the 
negative  variation,  this  being  greater  with  the  stronger  stimulus.  When  the 
nerve-impulses  leave  a  cell-b(xly  after  momentary  stimulation,  they  depend  not 
upon  a  single  event  but  a  series  of  events,  varying  slightly  for  the  different 
groups  of  cells.  Experiments  showing  the  multiple  character  of  the  impulses 
aroused  within  the  central  sy.stem  have  been  made  by  Gotch  and  Hoi"sley.* 
When  the  motor  cortex  of  a  monkey  was  stimulated  (Fig.  153)  by  means  of 
the  faradic  current,  the  muscles  which  by  this  means  were  made  to  respond 
showed  a  long  tonic  contraction  followe<^l  by  a  series  of  shorter  clonic  ones 
(Fig.  154,  D).     When  the  spinal  cord  had  been  cut  across,  the  cortex  was 

•  His:  Archiv  fur  Anatomie  und  PhynoloyU,  1890. 

*  Proceedings  of  the  Royal  Society,  London,  1888. 


CENTRAL    NERVOUS  SYSTEM. 


623 


again  stiinulalcd  and  tlio  changes  in  the  fibres 
of  the  cord  which  convey  the  impulses  from 
tlie  cortex  to  the  spinal  centres  were  investigated 
by  means  of  the  capillary  electrometer.  By  this 
means  a  curve  (Fig.  154,  D)  was  obtained  as  a 
record  of  the  negative  variations  passing  along 
these  fibres.  This  latter  curve  corresponds 
with  the  record  for  the  muscular  contraction 
and  hence  the  relation  between  the  two  series 
of  events  is  evident.  It  appears,  therefore, 
that  the  cortical  cells  after  the  cessation  of  the 
stimulus  still  continue  to  discharge  in  a  rhyth- 
mical manner.  The  attempt  was  also  made 
to  determine  the  rhythmic  character  of  the 
negative  variations  in  the  motor  nerve-trunk 
between  the  cord  and  the  contracting  muscle, 
but  the  changes  there  present,  though  sufficient 
to  cause  contractions  of  the  muscle,  were  not 
strong  enough  to  be  recorded  by  a  delicate 
capillary  electrometer.  This  result  suggests 
that  the  impulses  sent  out  from  the  spinal  cord 
by  the  normal  discharge  of  the  motor  nerve- 
cells  in  it  may  differ  from  the  impulses  artifi- 
cially aroused  in  the  lesser  intensity  of  the 
electrical  changes  that  accompany  them.  The 
rate  at  which  the  nerve-cells  discharge,  as 
shown  by  the  number  of  impulses  which  pro- 
duce tetanus  of  a  muscle  indirectly  excited, 
either  by  artificial  stimulation  of  the  nerve- 
elements  in  animals  or  by  voluntary  impulses 

in    man,  is    about 


Mercury. 


,'SuIjjhHric  acid  10  fc. 


Microscope. 


^i 


ten  per  second.  It 
appears  thatat  least 
the  cortical  cells 
and  those  of  the 
spinal  cord  have 
the  same  rate  of 
discharge,  and  that 
this  rate  is  the  same 
in  some  mammals 
(dogs,  cats,  rabbits, 
and  monkeys)  as  in 

man.    Hence  a  tendency  to  discharge  about  ten  times  a  second  may  be  assumed 

as  characteristic  of  the  mammalian  nerve-cell.^ 

'  Scbiifer  and  Horeley:  Journal  of  Physiology,  1885,  vol.  vii.     Schiifer:  Ibid. 


I Mercuri/. 


Fig.  153.— Schema  illustrating  the  experiment  for  determining  the  num- 
ber of  separate  nerve-impulses  passing  down  the  spinal  cord  upon  stimula- 
tion of  the  cortex  (from  experiments  on  the  monkey ;  Horsley) :  E,  E,  elec- 
trodes, intended  to  be  on  the  "  leg  area."  Wliere  the  cord  is  interrupted  one 
non-polarizable  electrode  is  placed  over  the  cut  end  of  the  pyramidal  fibres 
going  to  the  lumbar  enlargement ;  the  other,  on  the  side  of  the  cord.  These 
lead  to  the  capillary  electrometer,  in  which  the  column  of  mercury  moves 
each  time  an  impulse  passes. 


624  AX   AMEllTCAN   TEXT-BOOK    OF   PJIYSfOLOGY. 

Points  at  which  the  Nerve-impulse  can  be  Aroused. — It  appears  pro- 
bable that  the  excitation  oi"  any  part  of  a  nerve-cell  is  capable  of  producing 


D 


I      Excitation. 


I    1  Sec.    I 


E.rcilutioii. 


I  I  I  I  I  I  I  I  I      ^  ■'''«•.   I 

Fig.  15-1.— From  a  photographic  record  of  the  movements  of  the  coliiinn  of  mercury  in  a  capillary 
electrometer  (Gotch  and  llorsley).  The  arrow  shows  the  direction  in  which  the  record  is  to  be  read. 
The  upper  curve  (B)  shows  the  period  of  excitation  by  the  interrupted  current ;  this  is  followed  by  a  series 
of  waves  in  the  record  showing  a  number  of  separate  impulses  sent  down  from  the  cortex  after  electrical 
stimulation  has  ceased.  In  the  lower  curve  the  exciting  electrodes  were  a|)plied  to  the  white  matter 
directly,  the  corte.v  having  been  removed.  The  record  shows  that  in  this  case  no  impulses  pass  after  the 
stimulation  has  ceased. 

a  nerve-impulse,  Miicther  the  stimulus  be  applied  at  the  tips  of  the  dendrons 
or  to  the  neuron  in  its  course. 

There  is,  however,  no  indisputable  evidence  that  within  the  central  nervous 
system  the  cell-bodies  of  nerve-cells  can  be  made  to  discharge  by  the  direct 
application  of  electrical  or  other  artificial  stimuli  to  them,  for  there  is  no 
locality  suited  for  such  isolated  stimulation.  In  every  place  where  such  cell- 
bodies  are  found  they  always  lie  more  or  less  imbedded  in  the  terminals  of 
neurons  that  have  originated  elsewhere,  and  hence  present  methods  are  not 
fitted  to  decide  whether  the  impulse  is  aroused  in  these  cases  indirectly  by  the 
stimulation  of  the  terminals  or  directly  by  the  passage  of  the  stimulus  through 
the  cell-body  alone.  That  artificial  stimuli  do  in  some  way  arouse  the  cell- 
bodies  to  discharge  is  amply  shown  by  the  fact  that  when  the  cortex  is  stimu- 
lated under  the  conditions  just  mentioned,  the  impulses  continue  to  come  from 
the  cortex  after  the  stimulus  itself  has  ceased  to  act. 

If  after  such  a  reaction  the  cortical  layer  containing  tlie  cell-bodies  be  cut 
away,  exposing  the  cut  ends  of  the  fibres  which  have  originated  from  them, 
and  the  stimulus  be  again  applied,  an  impulse  is  to  be  detected  in  these  fibres 
so  long  as  the  stimulation  is  continued,  but  the  impulses  cease  when  the 
stimulus  stops.  This  diiference  in  the  time-relations  and  the  form  of  the 
impulses  according  to  the  presence  or  absence  of  the  cortical  layer  is  taken  as 
an  indication  that  in  the  first  instance  the  cell-bodies  were  stimulated,  but  it 
still  leaves  the  question  of  directness  of  the  stimulation  undecided. 

Probably  every  nerve-element  in  all  its  parts  is  to  some  degree  irritable, 
and  the  reports  to  the  effect  that  the  cell-bodies  cannot  be  directly  stimulated 
are  not  supported  by  satisfactory  proof  that  no  nerve-impulses  passed  from  the 
point  to  which  the  stimulus  was  applied. 

Irritability  and  Conductivity. — In  general,  parts  of  the  system  which  are 
irritable  are  also  conductive,  but  there  are  special  cases  in  which  the  irrita- 
bility of  the  nerve-fibre  can  be  distinctly  separated  from  its  conductivity,  the 
latter  being  present  while  the  former  is  absent. 

It  is  an  old  observation  that  on  stripping  down  the  phrenic  nerve  by  com- 


CENTRAL   NERVOUS  SYSTEM.  625 

pressing  it  between  the  tluimb  and  forefinger  and  sliding  these  along  the 
nerve,  ti  contraction  of  the  diaphragm  is  cansed.  The  part  of  the  nerve  thns 
stinndated  is  soon  exhausted.  If,  now,  the  same  operation  is  repeated  on  a 
portion  of  the  nerve  lying  nearer  the  spinal  cord,  contraction  of  the  diaphragm 
again  follows.  This  result  was  originally  used  to  support  the  theory  of  a 
nerve-fluid,  and  wius  held  to  demonstrate  that  after  the  nerve-tubes  in  the 
portion  of  the  trunk  compressed  had  been  emptied  so  that  no  reaction  followed 
further  pressure,  then  if  the  pressure  were  applied  still  nearer  the  cord  the 
fluid  from  that  part  of  the  nerve  could  be  driven  forward  and  a  contraction 
of  the  diaphragm  would  result.  The  notion  of  a  nerve-fluid  in  the  sense  in 
which  that  terra  was  used  by  the  earlier  physiologists  has  long  since  been 
abandoned,  but  for  our  purpose  the  experiment  is  important  as  showing  that 
irritability  and  conductivity  do  not  under  such  treatment  disappear  at  the 
same  time,  but  that  the  fibres  remain  conductive  after  they  cease  to  be  irrita- 
ble, as  is  shown  by  the  flict  that  the  peripheral  part  of  the  nerve,  though  irre- 
sponsive, still  permits  the  impulses  aroused  nearer  the  cord  to  pass  through  it. 

It  has  been  also  shown  ^  that  in  young  regenerating  motor  fibres  it  often 
happens  that  while  no  response  is  to  be  obtained  by  the  direct  stinndation  of 
the  regenerated  peripheral  portion,  yet  the  stimulation  of  the  central  and  fully 
grown  portion  does  cause  a  contraction  of  the  muscles  controlled  by  these 
fibres.  In  this  case  the  newly  formed  fibres  can  conduct  an  impulse  which 
gives  rise  to  a  contraction,  although  such  an  impulse  cannot  be  aroused  by 
directly  stimulating  them. 

In  the  case  of  the  cell-body  certain  conditions  must  be  present  in  order 
that  an  impulse  sufficient  to  cause  an  evident  response  shall  be  aroused. 
There  is  certainly  no  evidence  that  stimuli  which  for  one  reason  or  another 
do  not  cause  such  responses  are  without  any  effect  whatever.  At  the  same 
time  all  cases  in  which  there  may  be  marked  delay  in  the  response  occur 
where  the  impulse  passes  from  one  cell  to  another,  and  hence  the  question  can 
always  be  raised  as  to  the  exact  point  at  which  delay  occurs. 

Number  of  Stimuli  necessary  to  Elicit  a  Response. — In  an  isolated 
portion  of  a  nerve-cell,  like  a  nerve-fibre  for  instance,  a  single  stimulus 
is  followed  by  a  single  nerve-impulse ;  on  the  other  hand,  the  studies  which 
have  been  made  to  determine  the  number  of  weak  stimuli  necessary  to  dis- 
charge a  series  of  cell-elements  indicate  that  there  is  a  summation  of  stimuli, 
i.  e.  the  discharge  does  not  follow  until  a  series  of  stimuli  has  been  given. 
These  experiments  have  been  made  for  the  most  part  with  reflex  frogs,  and 
they  indicate  that  with  very  weak  stimuli  that  can  be  individualized,  like 
mechanical  impacts  or  single  induction  shocks,  a  given  reaction  can  be  obtained 
with  remarkable  regularity  after  a  given  number  of  stimuli,  while  the  intervals 
between  the  single  shocks  may  be  varied  within  comparatively  wide  limits 
without  modifying  the  number  required.^ 

^  Howell  and  Hiiber:  Journal  of  Physiolocpj,  1892,  vol.  xiii. 

*  Ward  :  Archiv  fiir  Analomie  und  Physiologie,  1880 ;  Stirling :  Arbeiten  aiis  der  physiologischen 
Anstalt  in  Leipzig,  1874. 
40 


t)26 


A^"  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


WhetlicT,  liowever,  the  delay  in  tlie  response  is  due  to  the  failure  of  the 
cytoplasm  oi'  the  reeeiviiig  cell  to  discharge  until  i-cpcatcd  itupulses  liave 
reached  it,  or  whether  the  inoditieation  of  the  cell  which  causes  the  delay  is 
a  process  taking  place  at  the  point  where  the  inipulse  passes  over  from  the 
branches  of  one  cell  to  those  of  another,  is  not  directly  determined  by  the 
experiments.  The  indirect  evidence  is,  however,  entirely  in  favor  of  the  view 
that  the  delay  which  is  notable  in  the  arousal  of  a  reflex  response  occurs  at 
the  point  where  the  impulse  i)asses  from  one  cell  to  another. 

0.  The  Nutrition  of  the  Nerve-cell. 

The  metabolic  processes  within  the  nerve-cell  are  continuous,  and  the 
chemical  changes  there  taking  place  involve  not  only  those  prerequisite  to  the 

enlargement  of  the  cell  during 
J>»f^^^^^^_  growth,  but  also  those  leading 

1^  A  to  the  formation  of  such  sub- 

stances as  by  their  breaking 
down  release  the  energy  that 
appeal's  in  the  nerve-impulse. 
The  passage  of  the  nerve- 
impulses  probably  alters  the 
osmotic  powers  of  the  cell- 
wall  toward  the  surrounding 
j)lasnia,  and  this  of  course  is' 
fundamental  to  the  nutritive 
exchange.  It  follows,  there- 
fore, that  the  passage  of  nerve- 
impulses  is  one  factor  deter- 
mining the  nutrition  of  these 
cells. 

Cell-body. — Histologically 
we  look  uj)on  the  cell-bodies 
as  the  part  in  which  the  most 
active  changes  occur,  since  the 
network  of  blood-vessels  is 
most  dense  about  these,  indi- 
cating that  the  metabolic  pro- 
cesses are  here  most  active ' 
(Fig.  155). 

Chemical  Changes. — For 
the  direct  micro-chemical  de- 
termination of  special  sub- 
stances within  the  nerve-cells  there  are  but  few  methods,  though  some  phos- 
phorus-bearing substances  (nuclein.s)  can  be  demonstrated,^  and  the  occurrence 

^  Shimamura:  Neurologische  Centrdlhlatt,  1894,  Bd.  xiii. 

^  Lilienfeld  und  Monti:  Zeitschrift fiir physiologiache  Chemie,  1892,  Bd.  xvii. 


Fig.  155.— Frontal  sections  through  the  human  mid-brain 
at  A,  level  of  the  anterior  quadrigeminum ;  J!,  level  of  the 
posterior  quadrigeminum  (Shimam)ira).  On  the  left  side  the 
Vjlood-vessels  have  been  injected  ;  on  the  riglit  the  gray  mat- 
ter is  indicated  by  the  heavy  lines.  It  apjiears  by  this  that 
the  blood-vessels  are  most  abundant  in  the  gray  matter. 


CENTRAL    NERVOUS  SYSTEM. 


627 


of  chemical  changes  due  to  activity  and  to  age  are  very  evident.  The  nature 
of  these  latter  changes  is  quite  unknown.  Tiiere  is  general  consensus  that 
the  alkalinity  of  the  nerve-tissues  is  decreased  during  activity,  and  this  decrease 
in  alkalinity  may  amount  at  times  to  a  positively  acid  reaction.'  This  change, 
too,  is  better  suj)ported  by  the  observations  made  where  the  cell-bodies  are 
numerous,  than  by  those  made  where  the  fibres  are  alone  present. 

Trpphic  Influences. — W'lien  a  nerve-cell  is  not  kept  active  by  the  passage 
of  nerve-impulses  through  it,  it  usually  atrophies  and  may  degenerate.  The 
reason  for  this  appears  to  lie  in  the  fact  that  the  loss  of  those  changes 
which  accompany  the  nerve-impulses  decreases  the  vigor  of  the  nutritive 
exchange  with  the  result  of  causing  a  steady  diminution  in  the  volume  of  the 
cell  or  even  its  disintegration.  Such  changes  are  found,  for  instance,  in  the 
nerves  after  the  amputation  of  the  limb  to  which  they  were  supplied.^ 

The  result  of  an  amputation  is  that  portions  of  the  neurons  originating  from 
cell-bodies  located  either  in  the  ventral  horns  of  the  spinal  cord,  or  in  the 
cells  of  the  spinal  ganglion,  are  removed.  In  the  latter  case  the  normal 
pathway  for  the  incoming  impulses  is  interrupted  at  its  peripheral  end,  and  in 
the  former  the  last  part  of  the  pathway  by  which  the  impulse  is  delivered  at 
the  periphery  is  destroyed  (see  Fig.  156). 


Fig.  156.— Cross  section  of  the  spinal  cord  of  the  chick,  X  100  diameters  (van  Gehuchten) :  D,  dorsal 
surface ;  V,  ventral  surface ;  d.  r,  dorsal  root ;  v.  r,  ventral  root ;  g,  spinal  ganglion.  On  the  left  the  arrows 
indicate  the  direction  of  the  larger  number  of  impulses  in  the  dorsal  and  ventral  roots  respectively.  The 
small  arrow  on  the  right  dorsal  root  calls  attention  to  the  fact  that  some  neurons  arising  in  the  ventral 
plate  emerge  through  the  dorsal  root  and  convey  impulses  in  the  direction  indicated. 


The  disturbance  caused  in  the  two  sets  of  cells  is,  however,  not  the  same. 
In  the  case  of  the  cells  of  the  spinal  ganglion  the  chief  pathway  by  which  they 
are  stimulated  under  normal  conditions,  is  so  far  mutilated  that  only  a  com- 
paratively small  number  of  impulses  passes  over  them.  That  some  do  pass, 
is  indicated  by  the  sensations  apparently  coming  from  the  lost  limbs — sensa- 
tions which  are  often  very  vivid  and  minutely  localized.^ 

^  Gscheidlen :  Archiv  fur  die  gesammte  Physiologie,  1874,  Bd.  viii. 

^  Grigoriew :  Zeitschrift  fur  Heilkunde,  1894,  Bd.  xv. 

*  Weir-Mitchell :  Injuries  of  Nenes,  Philadelphia,  1872. 


628  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

Oil  analyzing  th6  condition  thus  established  by  an  amputation  it  is  seen 
that  the  cells  located  in  the  spinal  cord  are  deprived  by  such  an  operation  of 
one  principal  group  of  incoming  impulses,  namely  those  which  arrive  through 
the  dorsal  root-fibres  that  are  most  closely  associated  with  them  ;  but  at  the 
same  time  there  remain  many  other  ways  in  which  these  same  cells  are  nor- 
mally stimulated.  The  efferent  pathway  from  these  cells  is  incomplete,  and 
the  impulses  which  must  pass  along  the  stumps  are  inefficient.  That  im- 
pulses do  pass  along  the  stumps  of  the  efferent  roots  is  beyond  question,  since, 
when  the  distal  portion  of  an  efferent  nerve  is  cut  off  the  cell  can  be  shown 
to  still  discharge  through  the  portion  of  the  fibres  connected  with  the  cell- 
bodies.  Moreover,  the  muscles  of  any  stump  tend  to  execute  the  associated 
contraction  w'hicli  they  normally  perform,  thus  showing  that  the  group  of 
cells  is  fully  innervated,  although  its  discharge  is  without  mechanical  signifi- 
cance, and  finally  there  is  always  a  tendency  to  the  regeneration  of  the  cut 
fibre  which  indicates  activity  through  its  entire  length. 

It  is  therefore  not  improbable  that  after  amputation' impulses  do  pass  down 
even  those  fibres  which  end  without  physiological  connections.  It  is  explica- 
ble from  this  that  in  the  case  named  the  spinal  ganglion  cells  should  be  more 
affected  than  those  of  the  spinal  cord.  Further,  since  the  efferent  cells  of  the 
leg  are  more  commonly  innervated  bilaterally  than  are  those  of  the  arm,  we 
might  expect  the  efferent  cells  in  the  cervical  region  to  be  more  readily  affected 
by  an  amputation. 

Wherever  in  the  central  system  a  group  of  fibres  forms  the  chief  pathway 
for  the  impulses  arriving  at  a  given  group  of  cells,  then  the  destruction  of 
these  afferent  fibres  brings  about  the  more  or  less  complete  atrophy  of  the 
cells  with  which  they  are  secondarily  associated,  and  this  effect  is  the  more 
marked  the  younger  the  animal  at  the  time  of  injury.  Examples  of  this 
relation  are  found  in  the  "  nuclei "  of  the  sensory  cranial  nerves. 

Thus  the  activity  of  a  given  cell  has  the  value  of  contributing  to  the 
strength  of  its  own  nutritive  processes,  and  different  cell-elements,  so  far  as 
they  are  physiologically  united,  stand  in  a  nutritive  or  trophic  relation  to  one 
another  such  that  the  cell  receiving  impulses  is  in  some  measure  dependent  for 
its  nutrition  on  the  cell  which  delivers  the  impulses  to  it. 

Fatigue. — It  is  a  familiar  fact  that  living  tissues  may  be  fatigued.  In 
the  nervous  system  the  signs  of  fatigue  are  both  physiological  and  histological, 
but  it  is  to  the  latter  changes  only  that  attention  will  be  here  directed. 

Not  only  is  the  food-supply  to  the  nerve-cells,  as  represented  by  the  quality 
and  quantity  of  the  plasma,  variable,  but  the  cells  themselves  are  subject  to 
wide  variations  in  their  power  to  use  the  surrounding  substances. 

When  in  a  nerve-trunk  containing  both  afferent  and  efferent  spinal  root- 
fibres  passing  to  a  limb,  the  afferent  fibres  are  stimulated  by  a  faradic  current 
applied  intermittently,  changes  in  the  cell-bodies  in  the  spinal  ganglion  are  to 
be  observed  (Hodge). 

When  this  experiment  is  made  on  a  cat,  and,  after  death,  the  sections 
from  the  stimulated  are  compared  with  those    from  the   corresponding  but 


CENTRAL   NERVOUS  SYSTEM. 


629 


unstimulated  spinal  ganglion,  a  picture  like  that  represented  by  Figure  157  is 
obtained.* 

The  sections  indiciitc  that  the  cytoi)lasm  together  with  the  enclosed  nucleus 
and  nucleolus  as  well  as  the  nuclei  of  the  enclosing  capsule  of  the  cell,  have 


Fig  157.-TWO  sections,  A  and  B,  from  the  first  thoracic  spinal  ganglion  of  a  cat.  B  is  from  the  gan- 
glion which  had  been  electrically  stimulated  through  its  nerve  for  five  hours.  A,  from  the  correspond- 
ing resting  ganglion.  The  shrinkage  of  the  structures  connected  with  the  stimulated  cells  is  the  most 
marked  general  change,    n,  nucleus ;  n.  s,  nucleus  of  the  capsule ;  v,  vacuole ;  X  500  diameters  (Hodge). 

all  suffered  change  by  this  treatment.  The  stimulus  was  applied  for  only 
fifteen  seconds  of  each  minute,  the  remaining  forty-five  seconds  being  given  to 
rest.  In  this  way  the  cells  here  figured  had  been  stimulated  over  a  period  of 
five  hours.  The  nuclei  of  the  sheath  are  flattened,  the  cytoplasm  somewhat 
shrunken  and  vacuolated.  With  osmic  acid  the  nuclei  of  the  stimulated  cells 
stain  more  darkly  and  the  cytoplasm  less  darkly  than  in  a  resting  cell.  The 
nucleus  is  shrunken  and  crenated,  and  the  nucleolus  is  also  diminished  in  size. 
In  the  first  experiments  the  attempt  was  made  to  demonstrate  a  measurable 
change  within  the  nerve  cell-bodies  as  the  result  of  stimulation.  Assuming  the 
nuclei  of  these  cells  to  be  approximately  spherical,  and  calculating  their  vol- 
ume as  spheres,  the  shrinkage  amounted  to  that  shown  in  the  following  table : 
1  Hodge :  Journal  of  Morphology,  1892. 


630 


l.V   AMIJBICAX    TEXT-BOOK    O/     I'l I VSIOLOGY. 


2\ihk  sJtou-iiKj  the  Ikcreaac  in  the  \'oluinc  of  the  Nadeua  of  iSthaulated  iSpuial 
Ganc/lion-cells  of  Cats.  Stimulation  for  fifteen  seconds  alternating  with 
rest  for  forty-Jive  seconds  (Hodge). 


stimulation  cont 

mied 

^hriukaKc  in  the  volume  of  the  nuclei 

for- 

of  thf  .stiinuluted  cells. 

1      hour 

22  per  cent. 

2.5  hours 

21     "      " 

5 

24     "      " 

10 

44    "      " 

This  table  further  shows  that  the  shrinkage  is  greater,  the  greater  the  time 
during  which  the  stiinuhis  was  applied.  There  is  thus  established  not  only 
the  fact  of  a  change  in  tiie  cell,  but  al.'^o  a  connection  between  the  amount  of 
this  change  and  the  length  of  time  during  which  the  stimulus  was  allowed  to 
act.     The  results  when  expressed  by  a  curve  yield  the  following : 


Per 

cent. 

100 

\\ 

• 

90 

\\ 
"\\ 

80 

\^  \ 

^.^ 

* — V 

\ 

^ 

70 

60 

- 

\ 

\^ 

50 

1      1 

\^ 

1         1 

1 

1 

L_ 

2i 


10      IIV 


23 


29 


Fig.  158.— The  broken  line  indicates  the  volume  of  the  nuclei  of  the  spinal  ganglion-cells  of  a  cat 
after  stimulation  for  the  times  indicated.  The  solid  line  indicates  the  volume  of  the  nuclei,  first  after 
severe  stimulation  for  five  hours,  and  then  in  other  cats,  also  stimulated  for  five  hours,  but  subsequently 
allowed  to  rest  for  different  periods  of  time.  The  period  of  rest  is  found  by  subtracting  five  hours  from 
the  time  at  which  the  record  is  made.  After  twenty-four  hours  of  rest  the  nucleus  is  seen  to  have 
regained  its  normal  volume  (Hodge). 


Table  to  show  Influence  of  Rest. 

Right  brachial  plexus  of  each  Cat  stimulated  in  the  same  manner  for  five  hours, 
to  rest  for  a  variable  time  after  the  stimulation  had  been  stopped. 


Cat  allowed 


Nuclei. 


Cat,  17 
Cat,  16 
Cat,  21 
Cat,  19 
Cat,  18 
Cat,  7 


Rest. 
0  hours. 


6.5  hours. 


{ 

12  hours.  <. 

18  hours.  < 

24  hours.  <, 
Normal. 


Mean  diameter  of  nuclei  in  m. 

16.40  Left,  normal. 

12.93  Riglit.  stimulated. 

16.70  Left,  normal. 

\o.0U  Right,  stimulated. 

16.34  Left,  normal. 

14.73  Right,  stimulated. 

17.08  Left,  normal. 

16.03  Right,  stimulated. 

17.01  Left,  normal. 

17.11  Right,  stimulated. 
(  114.20  Left. 
\  1 14. 54  Right. 


Shrinkage. 

I     48.8% 
}     26% 
}      26% 
j      18% 
[      +2% 
+  6.9% 


Cells. 


Mean    diam- 
eter in  ft.. 

f  57. 

\  52. 

j  56 

I  54 

f  55 

1  51 

f  56 

1  55 


Whether  these  changes  could  be  considered  similar  to  the  normal  physi- 


CENTRAL    NERVOUS  SYSTEM. 


631 


ological  variations  (1(|mii(1((1  on  \vli»'tli<  r  it  was  possible  to  demonstrate  recov- 
ery from  them.     This  was  accomplished  in  the  followin*^  manner. 

Under  fixed  conditions  a  cat  was  stimulated  in  the  usual  way  and  the 
amount  of  shrinkage  in  the  nuclei  of  the  spinal 
gangliou-cells  was  determined.  This  was  found  to 
be  almost  oO  per  cent.  Four  other  cats  were 
similarly  treated  and  then  allowed  various  periods 
(six  and  a  half,  twelve,  seventeen,  and  twenty-four 
hours)  in  which  to  recover.  The  results  appear  in 
Figure  158  and  the  table  on  page  030. 

The  effects  of  stimulation  described  were  found 
not  only  in  the  nerve-cells  of  cats,  but  also  in  tluxse 
of  frogs  which  had  been  stimulated  in  a  similar 
manner. 

Having  thus  shown  that  the  change  was  physio- 
logical in  the  sense  that  it  was  one  from  which  the 
cells  could  recover,  it  remained  to  be  shown  that 
the  features  of  the  change  were  discernible  in  the 
living  cell,  and  were  not  caused  secondarily  by  the 
actions  of  the  reagents  employed  in  preparing  the 
sections. 

For  the  study  of  the  living  cell,  frogs  were 
chosen,  and  the  cells  of  the  sympathetic  ganglia 
examined.  In  these  experiments  cells  from  dif- 
ferent frogs  were  prepared  under  two  different 
microscopes  and  kept  alive  in  the  same  way  by  irri- 
gation with  a  nutrient  fluid.  In  one  case,  however, 
the  cell  was  stimulated  by  electricity,  while  in  the 
other  no  stimulation  was  applied.  During  the  time 
of  the  experiment  the  cell  which  was  not  stimulated 
remained  unchanged,  while  the  stimulated  cell  went 
through  the  series  of  changes  exhibited  in  Figure 
159.^ 

So  far  as  the  main  features  are  concerned  the 
shrinkage  and  crenulation  of  the  nucleus  was  essen- 
tially similar  to  that  found  in  the  nuclei  of  the 
spinal  ganglion  cells  of  cats.  These  results  demon- 
strated therefore  the  natural  character  of  those 
changes  in  the  nerve-cells  which  had  been  found 
after  treatment  with  histological  reagents. 

It  followed  that  if  these  changes  were  really 
significant  of  normal  processes  they  should  be  found 
in  the  nerve-cells  of  those  animals  which  show 
well-marked  periods  of  activity,  alternating  with  periods  of  rest 

^  Hodge:  Journal  of  Morphology,  1892,  vol.  vii. 


Fig.  159. — Showing  the  changes 
in  the  form  of  the  nucleus  result- 
ing from  the  direct  electrical 
stimulation  of  the  living  sym- 
pathatic  nerve-cell  of  a  frog. 
The  hour  of  observation  is  given 
within  each  outline.  The  experi- 
ment lasted  six  hours  and  forty- 
nine  minutes.  A  control  cell 
treated  during  this  time  in  the 
same  manner,  except  that  it 
was  not  stimulated,  showed  no 
changes  (Hodge). 


To  deter- 


632 


AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 


mine  this,  birds  and  bees  were  examined,  one  set  of  preparations  being  made 
from  animals  which  were  killed  at  the  beginnin<r  of  the  day,  after  a  night  of 
rest,  and  the  other  froni  those  killed  at  the  end  of  the  day,  after  a  period  of 
activity.  Similar  changes  were  fonnd  in  the  cells  of  the  spinal  ganglia  of 
l^'.nglisli  sparrows,  of  the  cerebrnm  of  pigeons  and  cerebellum  of  swallows,  and 
of  the  antennary  lobes  of  bees  (see  Fig.  160). 


^  ■•?#Pii■y^^•■•X)C^;■o■ 


^•-f?^\••  ■';:•■■■  i=^*;.'".'v5.'  ■ 


Fia.  160.— Spinal  ganglion-pclls  from  English  sparrows,  to  show  the  daily  variation  in  the  appearance 
of  the  cells  due  to  normal  activity  :  A,  appciirance  of  cells  at  the  end  of  an  active  day  :  B,  appearance  of 
cells  in  the  morning  after  a  night's  rest.  The  cytoplasm  is  filled  witli  clear  lenticular  masses  which  are 
much  more  evident  in  the  rested  cells  than  in  those  fatigued  (Hodge). 

A  study  of  these  figures  shows  the  cells  to  be  turgid  with  large  round 
nuclei,  at  the  beginning  of  the  day  after  a  night  of  rest,  and  on  the  other 
hand  that  they  are  vacuolated  and  shrunken  and  with  altered  nuclei  at  the 
end  of  an  active  period.  These  observations  therefore  justify  the  conclusions 
drawn  from  the  apjiearauces  following  direct  stimulation. 

Other  observers '  have  obtained  similar  results.  The  motor  cells  of  the 
spinal  cord  and  cells  of  the  retina  (dogs,  INIann)  have  been  added  to  the  list 
of  those  showing  changes.  After  a  short  period  of  stimulation  of  the  sympa- 
thetic cells  of  the  rabbit,  both  Vas  and  Mann  have  found  a  preliminary  swell- 
ing of  the  cell,  and  the  same  has  been  noted  by  Mann  in  the  case  of  retinal 
cells  in  the  dog. 

The  application  of  these  ob.servations  to  changes  in  the  human  nervous 
system  has  thus  far  been  made  only  in  a  casual  way,  but  enough  has  been 
already  observed  to  make  certain  that  the  results  are  applicable. 

It  will  be  noted  that  the  changes  described  follow  variations  in  the  amount 
of  stimulation,  the  nutrient  conditions  represented  by  the  surrounding  plasma 
remaining  nearly  constant.  This  latter,  however,  may  undergo  alteration,  and 
recent  observations  show  that  in  various  forms  of  poisoning  by  inorganic  sub- 

*  Vas:  Archiv  fiir  mikroskopische  Anatomie,  1892;  Mann:  Journal  of  Anatomy  and  Physiology, 
1894. 


CENTRAL    NERVOUS  SYSTEM.  633 

stances  or  iu  zymotic  diseases,  the  nervous  system  and  especially  the  cell-bodies 
are  aflected  early  and  in  a  profound  manner.* 

With  the  establishment  of  these  facts  conccrnintj^  the  cell-body  the  question 
at  once  arises  whether  the  nerve-fibres  are  in  a  like  manner  altered  as  a  result 
of  their  activity. 

The  matter  has  been  tested  in  this  way  :  In  a  cat  or  dog  a  nerve-trunk  was 
stimulated  by  a  measured  induction  current,  and  the  contraction  of  the  muscle 
controlled  by  it,  recorded.  The  physiological  connection  between  the  nerve  and 
muscle  was  then  interrupted  by  the  giving  of  curare  and  the  nerve  was  tcta- 
nized.^  The  stimulation  of  the  nerve-trunk  was  continued  in  some  cases  for 
five  hours.  On  the  complete  disappearance  of  the  curare  effects,  a  stimulus 
similar  to  that  employed  in  the  first  instance  was  found  to  produce  muscular 
contraction,  thus  showing  that  the  continuous  stimulation  of  the  nerve-trunk 
during  this  interval  had  not  seriously  diminished  its  power  to  transmit  the 
nerve  impulses  aroused  in  it. 

Histological  changes  have  also  been  souo;ht  for  in  the  nerve-fibres  after 
prolonged  stimulation,  but  thus  far  they  have  not  been  demonstrated.  Chemi- 
cal changes  in  the  nerve-fibres,  if  present,  must  be  extremely  small,  and  the 
thermal  variations  which  occur  amount  to  less  than  0.0005°  C,  or,  in  other 
words,  are  not  demonstrable.^  Histological  and  chemical  changes  due  to 
activity  have  therefore  been  seen  in  the  cell-bodies  alone. 

Degeneration  and  Regeneration  of  Nerve-elements. — All  parts  of  a 
nerve-cell  are  under  the  control  of  that  portion  of  the  cell-body  which  con- 
tains the  nucleus;  in  this  respect  the  nerve-tissues  are  similar  to  other  tissues 
which  have  been  studied,  and  iu  which  the  nucleated  portion  of  the  cell  is 
found  to  be  the  more  important.  It  was  shown  by  Waller^  that  a  nerve- 
fibre  belonging  to  the  peripheral  nerves  when  separated  from  the  cell  of  which 
it  was  an  outgrowth  soon  degenerated  from  the  point  of  section  to  its  final 
distribution.  The  process  is  often  designated  as  Walleriau  degeneration. 
According  to  recent  studies  on  this  subject,^  this  degenerative  change  occurs 
practically  simultaneously  along  the  entire  length  of  the  portion  cut  off.  The 
changes  following  the  section  consist  in  a  fragmentation  of  the  axis-cylinder 
followed  by  its  disappearance,  enlargement  and  multiplication  of  the  nuclei 
of  the  medullary  sheath,  and  absorption  of  the  medullary  substance,  so  that 
in  the  course  of  the  fibres  there  is  left  at  the  completion  of  the  process  the 
primitive  sheaths  together  with  the  sheath-nuclei.  In  the  early  stages  of  this 
process  the  medullary  sheath,  moreover,  undergoes  some  changes,  the  result  of 
which  is  that  it  stains  more  deeply  with  osmic  acid,  and  hence  appears  very 
black  in  comparison  with  the  normal  fibres  about  it  (Marchi). 

Degeneration  of  Non-meduUated  Fibres. — Concerning  the  progress  of 

'Schaflfer:  Ungarisehes  Archiv  filr  Mediein,  189^ ;  Pandi:  Ibid.,  1894;  Popoff:  Virchovfs 
Archiv,  1894;  Tschistowitsch  :  Petersburger  medicinische  Wochenschrift,  1895. 

*  Bowditch  :  Archiv  fur  Anatomie  und  Physiologic,  1890. 
'  Stewart :  Journal  of  Physiology,  1891,  vol.  xii. 

*  Nouvelle  methode  anaiomique  pour  investigation  du  Systhne  nerveux,  Bonn,  1851. 
^  Howell  and  Huber  :  Journal  of  Physiology,  1892,  vol.  xiii. 


634 


AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


degenerative  changes  in  the  non-nieihilluted  fibres  iuformatiou  is  scanty. 
Bowditch  and  Warren^  observed  that  when  the  sciatic  nerve  of  the  cat  was 
sectioned,  degeneration  of  the  motor  and  vaso-constrictor  fibres  in  the  periph- 
eral portion  went  on  at  about  the  same  rate.  Stimulation  of  the  peripheral 
part  of  the  nerve  gave  a  vaso-dilator  reaction  after  the  vaso-constrictor  reac- 
tion had  entirely  disappeared,  suggesting  that  the  constrictor  fibres  degenerate 
more  rapidly  than  do  the  dilators,  although  it  is  not  improbable  that  tlie 
dilator  fibres  in  this  location  really  belong  to  the  medullated  class  (Howell). 
After  five  dayS  no  vaso-motor  reaction  at  all  could  be  obtained.  In  a  recent 
study  by  Tuckett^  of  the  degeneration  of  the  non-medullated  fibres  contained 
in  the  branches  springing  from  the  superior  cervical  ganglion,  it  is  stated  that 
the  degeneration  as  traced  by  histological  and  physiological  methods  is  com- 
plete within  thirty  to  forty  hours  after  section  of  the  fibres,  and  that  the 
degenerative  changes  involve  only  the  core  of  the  fibres,  the  outside  sheath 
and  nuclei  being  unaffected. 

Degeneration  in  the  Central  System. — In  the  central  system,  the  distal 
portion  of  the  fibres  separated  from  the  cell-body  degenerate  as  at  the  periph- 
ery, and  this  reaction  has  therefore  formed  a  means  by  which  to  study  the 
architecture  of  the  central  system.  The  details  of  the  process  are,  however, 
not  well  understood. 

So  far,  then,  as  the  principal  outgrowth  of  the  nerve-cell  is  concerned,  it  is 
found  to  be  always  under  the  nutritive  control  of  the  cell-body  from  which  it 
springs.  The  changes  which  take  place  when  the  spinal  roots  are  cut  will  serve 
to  illustrate  this  control  (see  Fig.  161).    Section  of  the  dorsal  root  at  the  distal 


Fig.  161.— Schema  of  a  cross  section  of  the  spinal  cord,  showing  the  dorsal  and  ventral  roots  and  the 
points  at  which  they  may  be  interrupted  :  D  R,  dorsal  root ;  V R,  ventral  root ;  G,  ganglion  :  M,  muscle ; 
S,  skin  ;  1,  lesion  between  ganglion  and  cord  ;  2,  lesion  between  muscles  and  cord;  3,  lesion  between  skin 
and  ganglion  ;  4,  combination  of  2  and  3. 

side  of  the  spinal  ganglion  at  3  causes  a  degeneration  of  all  the  fibres  which 
form  the  dorsal  nerve-root  distal  to  the  ganglion.  Section  of  the  dorsal  root 
at  1  causes  degeneration,  central  to  the  section,  of  those  nerves  which  are  out- 
growths from  the  cell-bodies  of  the  spinal  ganglion.  Section  of  the  ventral 
root  at  2  causes  a  degeneration  distal  to  the  point  of  section  in  those  fibres 
which  form  the  ventral  root  and  which  arise  from  the  cells  within  the  spinal 
cord.  In  each  case,  therefore,  the  degeneration  occurs  ou  one  side  only  of  the 
section,  and  that  is  the  side  away  from  the  cell-body. 

'  Journal  of  Physiology,  1885,  vol.  vii.  ^  TuckeU:  Journal  of  Physiology,  1896,  vol.  xix. 


CENTUM.    NERVOUS  SYSTEM.  035 

It  is  sometiinos  stated  that  degeneration  takes  place  in  the  direction  of  the 
uerve-inipulse.  In  a  general  way  this  is  trne,  since  the  impulses  usually 
travel  from  the  cell-body  along  the  neuron.  In  the  case  of  the  fibres  arising 
from  the  cells  of  the  spinal  ganglion  it  is  not  true,  since  the  section  at  the 
distal  side  of  the  ganglion  causes  degeneration  away  from  the  spinal  cord,' 
while  that  on  the  })roximal  side  of  the  ganglion  causes  degeneration  toward 
the  spinal  cord  ;  yet  in  both  neurons  the  impulse  is  in  the  same  direction — 
namely,  always  toward  the  cord. 

The  distal  portions  of  the  nerve  may  be  regenerated,  or,  under  other  con- 
ditions, the  remainder  of  the  neuron  together  with  the  cell-body  from  which 
it  springs  may  atrophy,  and  this  latter  process  may  result  in  even  the  complete 
destruction  of  the  nucleated  ))()rti()n. 

Degeneration  of  Nucleated  Portion. — In  any  case  the  internodal  seg- 
ment of  the  peripheral  nerve-fibre  which  has  been  directly  injured  by  the 
section  degenerates  centrally  as  far  as  the  next  node  of  Ranvier.  Whether 
beyond  this  point  any  marked  change  is  to  occur  depends  on  several  circum- 
stances. When  regeneration  is  prevented,  the  younger  the  animals  on  which 
the  operation  has  been  made  the  more  marked  are  the  involutionary  changes. 
These  consist,  first,  in  a  stoppage  of  growth-processes  in  the  elements  affected ; 
second,  in  a  simple  atrophy.  Such,  for  example,  are  the  changes  taking  place 
in  the  cells  of  the  spinal  cord  after  the  amputation  of  a  limb.  Sometimes  also 
true  degeneration  follows.  That  these  effects  may  be  very  plain  in  man,  the 
amputation  should  be  one  near  the  trunk — i.  e.  involving  a  great  number  of 
nerve-fibres,  and  be  of  long  standing — i.  e.  more  than  one  year.^ 

It  was  discovered  by  von  Gudden  ^  that  when  nerves  in  young  animals 
are  pulled  away  from  their  attachment  with  the  central  system,  they  most  fre- 
quently break  just  at  the  point  where  they  emerge  from  the  cord  or  brain  axis. 
When  an  efferent  nerve  is  thus  broken,  in  animals  just  born  or  very  young, 
the  remaining  portion — i.  e.  the  cell-bodies  with  so  much  of  their  neurons  as 
lie  within  the  central  system — atrophies  to  complete  disappearance.  The  cause 
of  this  complete  disappearance  in  the  case  of  very  young  animals  thus  injured, 
seems  to  lie  in  the  intense  struggle  for  nutriment  among  the  nerve-elements 
themselves.  Thus  young  cells  meeting  with  injury  are  unable  to  compete 
with  those  about  them  for  nourishment,  and  so  perish.  The  bearing  of  such 
a  fact  is  very  direct.  If  in  man  there  is  reason  to  think  that  an  injury  was 
suffered  during  fetal  life,  there  is  a  possibility  that  the  injury  may  not  only 
have  prevented  the  further  development  of  the  cells  involved,  but  may  also 
have  caused  the  complete  destruction  of  some  of  them,  in  which  case,  of 
course,  the  architecture  of  the  region  is  necessarily  abnormal. 

Such  complete  disappearance  as  the  result  of  early  injury  has  not  been 
shown  for  cells  which  lie  entirely  within  the  central  system,  or  for  those  form- 
ing the  spinal  ganglia.  In  the  case  of  those  central  cells  which  form  the 
sensory  nuclei,  like  the  sensory  nucleus  of  the  fifth  nerve,  or  of  the  vagus, 

^  Grigoriew :  Zeitschrift  fur  Heilkunde,  1894,  Bd.  xv. 
*  Archiv  fur  Psychiatrie,  1870,  Bd.  ii. 


636  AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

pullin<2;  out  tlie  nerve-trunk  causes  only  tin  atr()])hy  of  the  central  cells,  and 
not  their  complete  disappearance.^ 

Regeneration. — When  the  two  ends  of  the  sectioned  nerve  are  brought 
together  under  favorable  conditions,  the  peripheral  portion  of  the  trunk  may 
be  regenerated.  This  occurs  in  the  following  steps  as  described  bv  Howell 
and  Huber.^ 

While  the  fragmentation  and  absorption  of  the  myelin  in  the  distal  portion 
of  the  cut  nerves  is  going  on,  the  protoplasm  in  the  neighborhood  of  the 
sheath-nuclei  tends  to  increase.  These  enlarged  masses  of  protoplasm  then 
apjiear  as  a  thread  of  substance  within  the  old  nerve-sheath.  A  new  sheath 
is,  however,  soon  formed  on  the  jn-otoplasniic  thread,  and  the  whole  consti- 
tutes an  "embryonic  fibre."  Tiie  embryonic  fibres  lying  on  one  side  of  the 
cut  unite  with  those  on  the  other,  union  taking  })lace  in  the  intervening  cica- 
tricial tissue.  Next  the  myelin  appears  in  isolated  drops,  usually  near  the 
nuclei,  and  these  subsequently  unite  to  form  a  continuous  tube,  the  formation 
of  the  myelin  proceeding  centrifugally  from  the  wound.  Then  follows  the 
outgrowth  of  the  new  axis-cylinder  slightly  behind  the  organization  of  the 
myelin  into  the  tubular  form. 

It  must  not  be  forgotten  that  the  last  act,  the  formation  of  the  axis-cylin- 
der, is  the  important  event,  and  while  the  whole  process  of  repair  may  require 
many  months,  the  rate  at  which  the  axis-cylinder,  when  started,  grows  out 
from  the  central  end  may  be  comparatively  rapid.  If  this  explanation  be 
correct,  namely  that  the  axis-eylinder  is  an  outgrowth  from  the  central  end, 
then  the  regeneration  of  the  neuron  is  in  so  far  but  a  repetition  of  the  events 
by  which  it  was  originally  formed.  The  development  of  the  medullary  sheath 
in  its  relation  to  the  axis  is,  however,  different  in  the  two  cases.  When  first 
regenerated,  the  fibres  resemble  normal  young  fibres  in  being  small,  but 
whether  they  later  attain  the  size  of  those  which  they  replace  has  not  been 
shown.  Moreover,  it  appears  that  the  two  functions  of  irritability  and  con- 
ductivity do  not  both  return  at  the  same  time.  The  newly  formed  fibres  are 
capable  of  conduction  before  they  become  sufficiently  irritable  to  respond  to 
artificial  stimuli  directly  applied  to  them.  In  the  first  stages  of  irritability, 
also,  the  young  fibres  responded  more  readily  to  slight  mechanical  stimuli 
than  to  induction  shocks — a  differentiation  in  reaction  which  serves  to  suggest 
the  complexity  of  the  changes  involved  in  the  re-formation  of  the  fibres. 

Regeneration  of  this  sort  which  is  found  in  the  peripheral  system  is  not 
knoA^  to  occur  in  the  central  system,  although  in  many  ways  the  conditions 
of  such  regeneration  seem  there  most  favorable.  This  fact  also  has  its  ai)pli- 
cation  in  the  use  of  the  method  of  degeneration  for  determining  architectural 
relationships ;  for  when  once  caused  to  degenerate,  the  bundles  of  fibres  thus 
altered  can  be  tracked  through  the  central  system  without  fear  that  new  growth- 
changes  will  obscure  them. 

The  dorsal  spinal  root  degenerates  when  the  section  is  made  between  the 

'  Forel :  Festschrift  zur  von  Ndgeli  und  von  Kollikcr,  Zurich,  1891. 
^  Journal  of  Physiology,  1892,  vol.  xiii. 


CENTRAL   NERVOUS  SYSTEM.  637 

cord  and  the  spinal  ganglion.  Study  of  its  develo[)Mic'nt  has  shown  that  in 
the  first  instance  the  spinal  ganglion  becomes  connected  with  the  cord  by  the 
outgrowth  from  the  cells  of  tlie  ganglion  of  those  fibres  which  form  tiie  dorsal 
root.  It  would  follow  that  as  the  cells  of  the  spinal  ganglion  can  regenerate 
the  fibres  which  pass  toward  the  periphery,  they  should  also  be  able  to  regen- 
erate those  which  form  the  dorsal  root,  but  as  yet  there  have  not  been  reported 
any  cases  where  a  dorsal  root  has  been  thus  re-formed. 

That  the  regeneration  is  due  to  an  outgrowth  of  the  central  stump  has 
been  clearly  shown  by  Huber,'  who  iuserted  a  bone  tube  between  the  two  ends 
of  the  sciatic  nerve  of  the  dog,  and  obtained  regeneration  of  the  nerve  with 
a  return  of  function  although  the  initial  interval  between  the  two  parts  of  the 
nerve  was  more  than  three  centimeters.  The  rate  of  growth  from  the  central 
end  has  been  specially  studied  by  Vanlair.^  In  the  facial  nerve  of  the  rabbit, 
function  was  restored  in  eight  months  after  section,  and  in  the  pneumogastric 
and  ischiadic  nerves  of  the  dog  in  about  eleven  months.  In  the  latter  case, 
this  gives  an  average  rate  of  growth  of  about  1  millimeter  a  day.  In  the 
scar-tissue  between  the  two  parts  of  the  nerve  the  rate  is  not  more  than  0.25 
millimeter  a  day,  and  hence  the  return  of  function  tends  to  be  delayed  by  any 
increase  in  the  distance  between  the  cut  ends  of  the  nerve.  It  appears  also 
that  the  return  of  the  cutaneous  sensibility  is  more  rapid  than  the  return  of 
motion  (Howell  and  Huber). 

On  testing  the  capacity  of  the  sciatic  nerve  for  repeated  regeneration 
Vanlair  found  that  in  a  dog,  when  it  was  cut  a  second  time,  it  not  only  regen- 
erated but  did  so  more  rapidly  than  in  the  first  case. 

Much  interest  has  always  attached  to  the  exact  course  taken  by  the  regen- 
erating fibres.  They  appear  in  a  general  way  to  be  guided  by  the  old  sheaths 
of  the  peripheral  portion.  But  the  peripheral  nerves  contain  both  afferent  and 
efferent  fibres,  and  it  would  appear  most  probable  that  in  the  process  of  re-for- 
mation these  should  undergo  much  rearrangement.  Since  the  peripheral  por- 
tion of  the  nerve  acts  as  a  guide  to  the  growing  fibres,  the  experiment  has 
been  tried  of  cross-suturing.  Thus  Howell  and  Huber  ^  having  cut  both  the 
median  and  ulnar  nerves  in  dogs,  sutured  the  central  end  of  one  nerve  to  the 
peripheral  end  of  the  other,  and  obtained  reunion  with  extensive  return  of 
sensation  and  movement,  and  without  iuco-ordi nation  to  be  attributed  to  the 
unusual  arrangement  of  the  nerve-fibres.  Such  a  rearrangement  without 
inco-ordination  is  not  easy  to  explain  in  view  of  the  association  of  certain 
functions,  such  as  the  control  of  a  given  set  of  muscles,  with  a  special  cell- 
group  in  the  cord.  The  most  remarkable  observation,  however,  on  the  regen- 
eration of  nerve-trunks  has  recently  been  reported  by  Langley.*  The  pre- 
ganglionic nerve  going  to  the  superior  cervical  ganglion  of  the  cat  is  composed 
of  fibres  with  several  functions.  These  fibres  are  derived  frt)m  the  first 
thoracic  nerve,  which   mainly  controls  those  cells  in  the  ganglion  that  are 

^  Journal  of  Morphology,  1895,  vol.  xi. 

*  Archiv  de  Fkysiologie  normale  et  pathologique,  1894. 

^  Loc.  cit.  *  Journal  of  Physiology,  1895,  vol.  xviii. 


638  AN  AMJ'JRICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

connec'tod  witli  the  pupil  and  (lie  nictitating  membrane ;  from  the  second 
thoracic  nerve,  wiiich  is  mainly  associated  with  the  cells  controlling  the 
blood-vessels  of  the  car  and  in  a  less  measure  the  nictitating  membrane;  from 
the  third  thoracic,  which  connects  with  a  few  cells  which  control  the  ])upil  ; 
from  the  fourth  thoracic,  which  connects  mainly  with  cells  controlling  the 
erection  of  the  hairs  on  the  face  and  neck  ;  from  the  fifth  thoracic,  which  cou- 
uects  with  the  cells  controlling  the  vessels  of  the  car,  and  also  the  hairs  of  the 
face  aud  neck ;  and  from  the  sixth  and  seventh  thoracic,  supplying  hairs  only. 
When  the  pre-ganglionic  fibres  were  cut,  therefore,  and  allowed  to  regenerate, 
various  things  might  happen.  The  newly-formed  fibres  might  grow  past  the 
ganglion,  or  they  might  form  novel  connections  with  the  cells  there  contained, 
or  finally,  they  might  repeat  the  original  connections.  As  a  matter  of  fact, 
the  last  arrangement  is  the  one  accomplished,  and  in  the  case  of  the  cat  used 
in  this  experiment,  stimulation  of  the  nerve-roots  above  mentioned  gave  after 
regeneration  the  reactions  characteristic  for  the  several  roots.  It  would  ap- 
pear, therefore,  that  in  some  way  each  group  of  the  regenerating  pre-gangli- 
onic fibres  had  selected  those  cells  which  they  had  originally  controlled. 

The  reg-eneration  which  has  thus  far  been  described  has  been  that  of  the 
non-nucleated  neuron  by  that  portion  of  a  nerve-cell  which  was  nucleated. 
The  regenerated  portion  always  lies  in  the  peripheral  nervous  system.  Con- 
cerning the  regeneration  of  the  dendrous  there  are  no  observations. 

The  possibility  of  the  formation  of  entirely  new  cell-elements  in  the  pro- 
cess of  repair  remains  to  be  mentioned.  When  the  central  system  is  injured 
it  sometimes  happens  that  mature  nerve-cells  there  ]>resent  show  in  their 
nuclei  those  changes  which  are  characteristic  of  nuclei  about  to  divide,  but 
division  does  not  take  place  ^  either  in  the  nuclei  or  in  the  cell-bodies.  In 
mammals  there  is  no  convincing  record  of  the  formation  of  new  nerve-cells 
in  the  central  nervous  system  of  the  mature  animal.  In  some  lower  verte- 
brates (lizards)  regeneration  of  the  spinal  cord  has  been  reported,  and  in  the 
newt  such  regeneration  has  been  obtained  in  the  retina,  but  the  result  in  both 
cases  ap})ears  to  be  due  rather  to  the  enlargement  of  embryonic  cells  still 
remaining  in  these  regions  than  to  an  exhibition  in  the  mature  cells  of  powers 
absent  from  the  corresponding  cells  of  the  mammalia.  At  various  times  and 
in  several  places  the  idea  has  been  advanced  that .  in  the  peripheral  nervous 
system  at  least  there  was  in  progress  a  continuous  process  of  degeneration  and 
regeneration,  as  though  this  portion  of  the  system  was  being  continually  reno- 
vated. What  is  knoM'n  of  the  fixity  of  the  central  system  and  of  the  relation 
between  the  central  system  and  that  of  the  periphery,  very  strongly  supports 
the  idea  that  change  in  one  would  necessitate  change  in  the  other,  and  for 
central  changes  of  this  sort  the  evidence  has  never  been  advanced.  To  be 
sure,  slow  srrowth-chamz-es  occur  in  the  central  svstcm  until  after  the  thirtieth 
year,  but  the  additions  which  are  thus  made  result  from  the  enlargement  of 
nerve-cells  tTiere  present  as  structural  units  from  a  very  early  age,  and  such 

*  Sanarelli :  "  I  processi  riparativi  nel  Cervello  e  nel  Cervelleto,"  R.  Accademia  del  Lincei, 
1891. 


CENTRAL    NERVOUS  SYSTEM.  639 

repair  as  is  nuulo  ofciirs   in   ihc  peripheral  system   only,  wliile  a  cell  once 
(l:uii:ii:;ed  by  injury  to  its  nucleated  portion  is  not  to  he  replaeed. 


PART  II.— THE  PHYSIOLOGY  OF  GROUPS  OF  NERVE-CELLS. 

A.    Organization    and  Architecture    of  the  Central  Nervous 

System. 
The  reactions  of  groups  of  associated  nerve-cells  have  usually  furnished 
the  largest  mass  of  facts  presented  under  the  title  of  the  physiology  of  the 
central  nervous  system.  When  it  was  recognized  that  the  nerves  formed 
pathways  by  which  the  sensory  surfaces  of  the  body  were  put  into  connection 
with  the  central  system,  and  also  the  pathways  by  which  this  system  was  in 
turn  rendered  capable  of  controlling  the  tissues  of  expression,  it  became  at 
once  important  to  determine  over  what  nerves  the  impulses  arrived  at  the 
central  organ,  how  they  travelled  through  that  organ,  and  by  what  other 
nerves  they  were  again  delivered  at  the  periphery. 

Both  anatomical  and  physiological  research  have  been  directed  to  this  end. 
The  arrangement  of  these  paths  as  found  in  the  adult  human  nervous  system 
is  our  principal  object ;  at  the  same  time  it  should  not  be  forgotten  that  the 
reactions  of  simpler  mammalian  systems  have  furnished  the  greater  number  of 
facts,  and  if  the  pitfalls  surrounding  the  assumption  that  the  reactions  found 
in  the  nervous  system  of  a  rabbit  or  monkey  hold  true  in  all  detail  for  that 
of  man  can  be  avoided,  no  danger  and  much  gain  will  follow  from  the  use  of 
the  facts  of  comparative  physiology. 

Physiological  Unity  of  the  Central  Nervous  System. — So  far  as  its 
physiology  is  concerned,  the  nervous  system  of  any  mammal  must  be  regarded 
as  a  unit.  Custom,  however,  sanctions  a  division  into  a  central  and  peripheral 
nervous  system.  The  central  system  is  usually  taken  as  that  enclosed  within 
the  bony  cavities  of  the  cranium  and  vertebral  canal,  excluding  the  dorsal 
root-ganglia ;  the  peripheral,  that  formed  by  the  spinal  and  cranial  nerves  and 
the  ganglia  associated  with  them.  Neither  of  these  parts  has  an  independent 
significance,  and  furthermore  the  central  system  is  largely  penetrated  by  nerve- 
fibres  from  the  dorsal  spinal  roots,  fibres  which  have  an  origin  outside  of  those 
cells  which  form  the  walls  of  the  medullary  tube  and  constitute  the  central 
system  in  the  strict  morphological  sense.  On  the  other  hand,  the  retina,  which 
is  in  large  measure  morphologically  a  i)art  of  the  medullary  system,  is,  as  a 
rule,  not  counted  as  belonging  to  this  system,  but  is  put  down  as  a  peripheral 
sense-organ.  These  facts  are  here  mentioned  solely  to  emphasize  the  point  that 
gross  anatomy  has  found  convenient  certain  methods  of  division  which,  if 
strictly  followed,  confuse  the  morphological  relations.  Yet,  for  many  purposes, 
the  subdivision  into  central  and  peripheral  portions  is  advantageous. 

General  Arrangement  of  the  Central  Nervous  System. — The  general 
architecture  of  the  central  system  is  best  understood  by  means  of  schemas 
(Figs.  162  and  163).  As  the  typical  arrangement  is  found  in  the  spinal  cord, 
a  cross  section  through  this  part  will  most  readily  express  the  facts. 


640 


AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


The  dorsal  root-fibres  among  the  spinal  and  cranial  nerves,  together  with 
their  homologues  in  the  retina  and  tiie  olfactory  region,  are  the  only  channels  for 
the  entrance  of  impulses  into 
the  central  system.  Once  having 
arrived  there,  the  impulses  cause 
other  cells  to  discharge,  and  these 
in  turn  still  others,  through  an 
indefinite  series.  The  original 
impulse  may  thus  arouse  many 
other  impulses  within  the  system, 
antl  these  spread  until  some  of 
them  reach  cell-bodies  which  give 
rise  to  efferent  fibres  and  which 
discharge  awav  from  the  central 
system.  The  efferent  fibres  pass 
out  mainly  by  the  ventral  roots,  but 
in  part  by  the  lateral  (when  pre- 
sent) or  by  the  dorsal  roots  (Fig. 
163).  Such  efferent  fibres  end 
either  directly  in  striated  muscle 
tissue,   or    in   the   neighborhood 

D.G 


DP    y-^ 

Fig.  162.— Schema  of  the  arrangement  of  the 
human  spinal  cord  ^s  seen  in  cross  section ;  for 
clearness  the  afferent  fibres  arc  shown  on  the 
left  side  only,  efferent  and  central  cells  on  the 
right  side  only  (von  Lenhossek) :  D.  li,  dorsal 
root;  V.  i?,  ventral  root;  D.  P,  direct  pyramidal 
fibres ;  C.  P,  crossed  pyramidal  fibres ;  (',  direct 
cerebellar  tract ;  A.  Z,,  antero-lateral  tract:  D.  C, 
dorsal  columns.  The  various  classes  of  cell- 
bodies  are  indicated  by  the  manner  of  draw- 
ing. 


Fig.  163.— Schema  of  the  distribution  of  the 
efferent  fibres  of  the  spinal  roots.  A,  afferent 
fibres  in  the  dorsal  root  only ;  E,  E,  efferent  fibres 
in  both  dorsal  and  ventral  roots.  In  the  ventral 
root  one  group  of  efferent  fibres  goes  to  .V,  the 
striped  muscles ;  another  group  to  ganglion  cells, 
S,  forming  a  single  sympathetic  ganglion,  or  to  S', 
cells  located  in  more  than  one  sympathetic  gan- 
glion, but  all  connected  with  one  efferent  fibre  by 
means  of  its  collaterals ;  P,  peripheral  plexuses 
into  which  the  neurons  of  some  sympathetic  cells 
run. 


of  ganglia  (sympathetic  ganglia).  The  fibres  from  the  ganglia,  in  turn, 
very  often  connect  with  a  peripheral  plexus,  such  as  the  double  plexus  of 
Meissner  and  Auerbach,  or  the  plexuses  about  the  blood-vessels. 

The  evidence  for  the  foregoing  statements  is  briefly  the  following :  The 


CENTRAL    NERVOUS   SYSTEM.  641 

experiments  and  observations  of  Sir  Cliarles  Bell  (1811)  and  Majeudie  (1822) 
showed  that  sensation  followed  the  stimulation  of  the  central  ends  only  of  the 
dorsal  nerve-roots,  and  that  direct  contractions  of  the  skeletal  nniscles  occurred 
only  when  the  peripheral  portions  of  the  ventral  and  lateral  roots  were  stim- 
ulated. 

It  had  previously  been  shown  by  Hales  and  Whytt  (1768)  that  even 
though  both  roots  were  intact,  destruction  of  the  spinal  cord  prevented  the 
excitation  of  the  dorsal  roots  from  causing  a  reflex  response,  and  hence  the 
cord  was  to  be  regarded  as  forming  part  of  the  pathway.  Moreover,  it  had 
been  shown  by  the  earlier  investigators,  before  Bell,  that  the  excitation  of  the 
ventral  roots  produced  a  response.  Brown-Sequard '  showed  that  section  of 
the  (last  six  thoracic  and  first  two  lumbar)  dorsal  roots  caused  (in  guinea-pig, 
rabbit,  and  dog)  a  vascular  dilatation  and  a  rise  of  1°  to  3°  C.  in  the  hind 
limbs.  Strieker  showed  that  stimulation  of  the  peripheral  ends  of  the  cut 
dorsal  nerves  caused  a  rise  in  the  temperature  of  the  foot ;  and  Morat  showed 
that  stimulation  of  the  peripheral  end  of  a  cut  dorsal  root  produced  vaso- 
dilatation. The  studies  in  the  degeneration  of  the  nerve-fibres^  siiow  a  small 
group  in  the  dorsal  root  which,  upon  section  of  the  root  between  the  ganglion 
and  cord,  degenerates  toward  the  periphery  and  remains  intact  toward  the 
cord — a  behavior  which  is  precisely  opposite  to  that  which  occurs  in  the  case 
of  the  fibres  taking  origin  from  the  spinal  ganglion-cells. 

Finally,  van  Gehuchteu  and  others  have  shown,  that  in  histological  prep- 
arations (chick),  these  fibres  can  be  traced  through  the  ganglion  itself  (see  Fig. 
163).  In  the  dorsal  roots  of  the  lumbar  region  of  the  monkey,  Sherring- 
ton ^  was  unable  to  find  any  efferent  fibres.  The  connection  of  some  of  the 
ventral  roots  with  sympathetic  ganglia  was  established  by  Budge  (1851),  and 
physiological  as  well  as  histological  observations  show  that  the  further  con- 
nection of  these  ganglion-cells  with  the  elements  which  they  ultimately  control 
is  in  many  instances  by  way  of  the  peripheral  plexuses. 

Classification  of  Nerve-elements. — In  accordance  with  this  arrangement 
of  the  nervous  system,  the  elements  which  compose  it  fall  into  three  groups  : 
(1)  The  afferent  cells,  those  whose  function  it  is  to  convey  impulses  due  to 
external  stimuli  from  the  periphery,  including  the  muscles  and  joints,  to  the 
central  system.  The  expression  "  external  stimuli "  is  in  this  case  intended  to 
include  also  such  stimuli  as  act  within  the  tissues  of  the  body,  for  example, 
those  acting  on  tendons  and  muscles,  and  affecting  the  afferent  nerves  which 
terminate  in  them.  (2)  The  central  cells,  those  the  neurons  of  which  never 
leave  the  central  system,  and  the  function  of  which  is  to  distribute  within  this 
system  the  impulses  which  have  there  been  received.  (2)  The  efferent  cells, 
or  those  the  neurons  of  which  pass  outside  of  the  central  system,  and  which 
carry  impulses  to  the  periphery.  In  this  last  group,  again,  two  minor  divisions 
may  be  made,  namely,  («)  the  efferent  elements  the  cell-bodies  of  which  lie 

'  Gazette  medicale  de  Paris,  1856. 

'  Gad  and  Joseph :  Archivfur  Atiatomie  und  Physiologie,  1889. 
^  Journal  of  Physiology,  1895,  vol.  xvii. 
41 


642  .l.V   AMKRirAX    TEXT-BOOK    OF   PlTYSlOJ.OCiY. 

within  the  central  system,  as  is  the  case  with  those  giving  rise  to  the  ventral 
root< ;  ili)  tliose  forming  tlic  periphoral  ganglia  entirely  outside  of  the  central 
svstem — the  sympathetic  ganglia  and  tiie  more  <jr  less  solitary  cells  which  tidce 
part  in  the  formation  of  the  peripheral  plexuses. 

Relative  Development  of  Different  Parts. — The  bulk  of  the  three  sub- 
divisions which  have  been  named  is  by  no  means  equal.  The  central  .system 
is  far  more  massive  than  the  afferent  and  efferent,  taken  together,  but  the 
relation  cannot  be  stated  with  any  exactness,  since  the  ma.ss  of  the  peripheral 
system  is  not  definitely  known.  The  afferent  and  efferent  groups  are,  how- 
ever, about  equal  in  weight,  so  that  the  comparatively  small  ma.ss  of  either  of 
them,  taken  alone,  is  apparent.  When  in  addition  to  this  disproportion  it  is  fur- 
ther recalled  that  in  both  the  groups  last  named  the  number  of  cell-elements 
is  small  as  compared  with  the  number  which  compose  the  central  .«y.stem,  the 
disproportion  is  still  further  emphasized.  That  the  central  or  distributive 
division  of  the  nervous  .system  is  thus  the  most  important  is  indicated  also  by 
the  fact  that,  in  tiie  vertebrate  series,  as  the  complexity  of  the  entire  nervous 
system  increases,  the  proportional  development  of  the  group  of  central  ele- 
ments is  mo.st  marked. 

Moreover,  if  we  take  the  areas  of  the  cross  sections  of  the  various  spinal 
and  cranial  nerve-trunks  as  a  measure,  it  is  found  that  the  areas  for  the  afferent 
are  greater  than  those  for  the  efferent  elements,  and  that  the  area  of  afferent 
nerves  increases  from  the  cord  toward  the  encephalon. 

Organization. — During  early  fetal  life  all  the  cells  are  isolated  from  each 
other.  Either  they  are  without  branches  as  in  the  earliest  state,  or  the  branches, 
although  formed,  have  not  come  into  such  relations  with  the  neighboring  ele- 
ments that  nerve-impulses  are  able  to  pass  by  way  of  them.  The  series  of 
changes  by  which  the  elements  are  put  into  the  most  perfect  physiological 
connection  which  they  will  ultimately  attain  may  be  designated  as  orf/anization. 

This  change  is  dependent  on  two  structural  conditions — («)  the  number  of 
the  dendritic  branches,  and  of  the  terminal  and  collateral  branches  of  the 
neurons,  and  (6)  the  relations  in  which  these  dendrons  and  terminal  and  col- 
lateral branches  stand  to  one  another. 

In  the  case  of  cells  like  tho.se  of  the  cortex,  it  is  to  be  seen  from  the 
instructive  figure  of  Cajal  (see  p.  612),  that  in  the  vertebrate  series  the  cor- 
tical cells  tend  to  possess  more  branches  the  higher  the  animal  stands  in  the 
.series,  i.  e.  the  more  complicated  and  adaptable  its  reactions.  Further,  the 
same  figure  .shows  that  in  the  development  of  the  individual  cells  it  passes 
from  a  condition  in  which  it  has  few  to  that  in  which  it  has  many  branches. 
Certainly  the  disposition  of  the  cell-substance  in  the  form  of  branches  in- 
creases the  surface  thus  exposetl,  and,  assuming  that  the  nutrition  of  the  cell 
takes  place  over  this  surface  generally,  they  increa.se  its  nutritive  capacity. 
There  is,  however,  another  and  more  important  standpoint  from  which  they 
may  l)e  regarded.  Cajal  has  sugge.sted  that  the  dendrons  are  the  pathways 
by  which  impulses  enter  the  cells.  If  this  is  true,  then  the  number  of  den- 
drons characteristic  of  any  group  of  cells  may  Ije  taken  as  an  index  of  the 


CENTRAL    NERVOUS  SYSTEM. 


643 


variety  of  incoming  impulses  to  wliicli  they  are  subject.  In  the  case  of  the 
afferent,  central,  and  efferent  groups  of  cells,  the  following  can  be  stated: 
Unless  the  l)raneh  whicii  passes  toward  the  ])eriphery  from  the  cells  of  the 
spinal  ganglia  be  considered  as  homologous  with  the  dendrons — because  it  car- 
ries incoming  impulses — tiiese  cells  are  without  dendrons  but  possess  two 
neurons.  In  either  case  they  are  subject  to  but  one  group  of  impulses — those, 
namely,  which  enter  the  cell  over  the  peripheral  neuron.  The  central  neuron 
ramifies  widely  within  the  central  system. 

Among  the  central  cells  we  have  the  greatest  variety  of  arrangement,  the 
dendrons  being  insignificant  in  certain  cells  of  the  dorsal  horns  of  the  gray 
matter,  and  abundant  in  the  large  pyramidal  cells  of  the  cortex ;  or  again,  the 
granules  of  the  cerebellar  cortex  with  few  dendrons  may  be  contrasted  with  the 
large  cells  of  Purkiuje  having  many — these  being  taken  merely  as  examples. 

Finally,  the  bodies  of  efferent  calls  are  characteristically  supplied  with  a 
large  number  of  dendrons — again  an  arrangement  which  fits  with  the  physio- 
logical demands,  as  they  must  react  to  many  stimuli  though  they  discharge 
but  one  way  and  with  but  one  sort  of  effect. 

Connections  between  Cells. — In  determining  the  connection  between 
cells,  the  fact  that  the  neuron  is  the  outgrowth  of  a  cell-body  and  that  each 
cell  is  an  independent  morphological  unit  forms  the  point  of  departure.  Under 
these  circumstances  the  question  of  the  connection  between  cells  takes  the 
more  explicit  form  of  the  question  whether  cell-branches  become  continuous 
by  secondary  union.  In  mammals,  man  included,  there  is  no  good  histo- 
logical evidence  that  such  secondary 
union  occurs  in  the  central  system, 
A  close  apj)roximation  of  the  parts 
of  two  nerve-cells  is  alone  to  be 
seen.  The  means  by  which  the  cells 
are  brought  close  together  are  not 
always  the  same.  If  the  branching 
of  the  neurons  in  the  neighborhood  of 
the  dendrons  of  the  large  pyramidal 
cells  is  subject  to  the  interpretation 
that  the  impulses  act  across  the  small 
intervals  that  separate  these  two  struc- 
tures, then,  when  it  is  found  that  the 
neurons  in  some  cases  end  in  an  en- 
closing basket  or  frame  about  the 
bodies  of  the  cells  of  Purkinje,  it 
would  be  correct  to  infer  that  the  ac- 
tion took  place  between  the  terminals 
of  the  neuron  and  the  bodij  of  the  cell 
which  they  surround.  If  this  infer- 
ence is  correct,  then  the  dendrons  are  not  necessarily  the  sole  pathways  for  the 
impulses  which  affect  a  given  cell  (see  Fig.  164). 


Fig.  164.— Showing  at  the  lower  edge  of  the  figure 
a  series  of  basket-like  terminations  of  neurons 
which  surround  the  bodies  of  the  great  cells  of 
Purkinje  in  the  cortex  of  the  cerebellum  (Ram6n 
y  Cajal) :  C,  cell-body ;  N,  neurons ;  B,  basket-like 
terminations  arising  from  cell  C,  and  enclosing  the 
cells  of  Purkinje. 


644 


AN  AMERICAN    TEXT- BOOK    OF  PHYSIOLOGY. 


Theories  of  the  Passage  of  the  Nerve-impulse. — Accej)tiug  the  view 
tliat  the  nervous  system  is  composed  of  discontinuous  l)ut  closely  apju'oxi- 
mated  cell-elements,  it  remains  to  explain  how  impulses  arising  within  the 
limits  of  one  element  are  able  to  influence  others. 

As  an  hypothesis,  this  may  be  assumed  as  dependent  on  chemical  changes 
set  up  at  the  tips  of  the  terminals  and  affecting  the  surrounding  substance, 
which,  thus  affected,  acts  to  stimulate  the  neighboring  dendrons.  As  this  is 
only  an  hypothesis,  it  may  be  left  with  the  statement  that  it  seems  to  fit  in 
large  measure  the  group  of  facts  which  it  is  necessary  to  explain. 

The  structural  changes  which  permit  the  stimulation  of  one  element  to 
affect  another  are  com})leted  slowly,  and,  as  we  shall  later  see,  these  changes 
continue  in  some  parts  of  the  human  nervous  system  up  to  middle  life. 

From  what  has  just  been  stated  it  follows  that  the  nervous  system  of  the 
immature  person  is  quite  a  different  thing  from  that  of  one  mature,  since  in 
the  former  it  is  more  schematic,  more  simple,  the  details  of  the  pathways  not 
having  been  as  yet  filled  out.  Moreover,  considering  the  slow  and  minute 
manuer  in  which  the  central  system  is  organized  by  the  growth  of  the  cell- 
branches,  it  is  the  last  ]>lace  where  there  should  be  expected  structural  uni- 
formity in  the  details  of  arrangement. 

B.    The  Physiological  Anatomy  of  the  Nervous  System. 

It  follows  from  what  has  already  been  stated  concerning  the  relations  of 
cell-elements,  that  the  impulse  which  enters  the  central  system  along  a  given 
dorsal  neuron  is  bound  to  be  first  delivered  to  those  cells  in  the  neighborhood 
of  which  the  branches  of  the  neuron  terminate. 

Therefore,  in  determining  the  course  that  the  impulses  take,  the  determina- 
tion of  the  mode  in  which  the  dorsal  root-fibres  are  distributed  is  the  first  step. 


Fig.  165.— Schema  of  the  humau  spinal  cord :  D.  R,  dorsal  root,  right  side  ;  Col,  collaterals  from  the 
dorsal  root- fibres;  Z).  C,  dorsal  columns ;  P,  crossed  pyramid ;  P",  direct  pyramid ;  C,  direct  cerebellar 
tract;   A,  antero-lateral  tract.  ^ 

Afferent  Roots. — The  manner  of  this  termination  is  shown  in  Figures  151 
and  165. 

Here  the  afferent  neuron  having  entered  into  the  cord  is  seen  to  divide,  and 


CENTRAL  NERVOUS  SYSTEM.  645 

send  one  branch  caudad,  while  the  otlier  [)a.s.ses  ceplialad  (Fig.  151).  The 
length  of  these  branches  is  dillicult  of  determination,  but  it  ai)|)ears  that  the 
one  passing  eephahid  is  probably  the  longer  as  a  rule,  and  tliat  it  may  extend 
over  nearly  the  entire  length  of  the  cord.  By  means  of  collaterals,  these  main 
branches  are  connected  with  cells  witliin  the  cord,  probably  both  efferent  and 
central.  Through  the  central  cells  arranged  in  series,  pathways  are  formed 
by  which  the  incoming  impulses  may  produce  an  effect  at  parts  of  the  system 
remote  from  the  point  of  entrance,  as  well  as  pass  almost  directly  to  the  effer- 
ent cells  in  the  neighborhood  where  they  enter. 

Of  these  afferent  roots  there  are  thirty-one  on  either  side,  and  for  each 
dorsal  root  there  is  a  corresponding  ventral  one.  Due  allowance  being  made 
for  components  which  liavc  failed  to  develop,  the  cranial  nerves  can  be 
homologized  with  them.  Considering,  then,  the  longitudinal  extension  of 
the  cord,  it  falls  into  a  .series  of  segments  marked  on  each  side  by  a  pair  of 
spinal   nerves. 

Sag-mentation. — The  segmentation  thus  indicated  is  most  evidently 
marked  by  the  arrangement  of  the  efferent  or  ventral  spinal  nerves.  The 
studies  on  the  relations  between  the  efferent  nerve-fibres  and  the  cell-bodies 
which  o-ive  orig-in  to  them  indicate  that  the  latter  are  located  at  the  same  level 
in  the  cord  as  that  at  which  the  fibres  springing  from  them  emerge.  This 
permits  us  to  infer  that  the  cells  of  origin  for  any  ventral  root  tend  to  concen- 
trate in  the  segment  from  which  that  root  springs. 

The  afferent  nerve-fibres  have  in  part  at  least  a  somewhat  extended  course 
through  the  cord,  and  are  less  strictly  limited  to  the  segment  with  which  they 
make  their  superficial  connections.  At  the  same  time,  a  number  of  central 
cells  belong  to  each  segment,  and  must  be  more  closely  connected  with  the 
dorsal  and  ventral  nerves  with  which  they  are  immediately  associated,  than 
with  any  others.  Nevertheless  the  human  spinal  cord  shows  but  poorly 
the  segmental  disposition  of  the  elements  in  it  wdien  compared  with  that 
of  lower  vertebrates,  like  the  snakes  for  example,  in  which  the  concentra- 
tion of  the  nerve-cells  about  the  region  of  emergence  of  the  roots  is  more 
evident. 

Bilateral  Symmetry. — The  body  being  in  the  main  bilaterally  symmet- 
rical, it  is  to  be  expected  that  the  nervous  system  which  controls  it  will  be 
constructed  in  the  same  manner.  Such  is,  indeed,  the  case.  Architecturally 
this  symmetry  is  not  perfect,  since  each  cell  on  one  side  is  not  exactly  bal- 
anced by  a  corresponding  cell  on  the  opposite  side,  but  the  number  of  cells 
in  corresponding  regions  is  approximately  the  same,  and  for  physiological 
purposes  the  bilateral  symmetry,  is  quite  complete.  Yet  this  arraugeAient  is 
not  without  exception. 

Dorsal  and  Ventral  Plates. — In  the  human  fetus  the  shape  of  the  me- 
dullary tube,  — the  tube  from  which,  later,  the  brain  and  spinal  cord  are 
developed — is  shown  in  cross  section  in  Figure  166. 

Sl'io-ht  indentations  on  either  side  of  the  tube  are  here  evident  on  the  inner 
wall.     They  divide  each  side  of  the  tube  into  a  dorsal  and  ventral  portion. 


{)46 


.l.V  AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 


Ti^d.r 


anil  His'  has  followed  these  two  portions,  with  a  gn^ove  dividing  thera 
througii  the  entire  length  of  the  tube.  The  dorsal  plate  {d.p)  he  designates 
as  the  /'7//</c//>/a/^' (literally,  wing-plate),  and  the  ventral  plate  (u. p.)  as  the 
Grundplatte  (literally,  foundation-plate).  The  interest  attaehing  to  these  sub- 
divisions resides  iu  the  fact  that  the  parts  of  the 
tube  thus  marked  off  are  loci  for  cells  having 
well-marked  and  different  physiological  func- 
tions. The  incoming  neurons  arriving  from 
the  cells  of  the  spinal  ganglia  are  limited  in 
the  distribution  of  the  main  branches  to  the 
dorsal  plate,  and  the  cell-bodies  which  give 
rise  to  the  efferent  fibres  are  to  be  found  in  the 
ventral  plate  only.  The  central  cells  are  pres- 
ent in  both  plates,  though  grouped  in  the  local- 
ity where  the  two  plates  come  together,  and 
being  rather  more  abundant  in  the  dorsal  one. 
The  collaterals  of  the  afferent  fibres  are  distrib- 
uted to  both  plates.  There  is  thus  in  the  cord 
a  general  arrangement  whereby  the  central  cells 
are  located  between  the  afferent  neuron  and  the 
efferent  cell-bodies.  Far  more  important  than 
this,  however,  is  the  relation  which  becomes  evi- 
dent as  we  pass  cephalad — namely,  that  the  cerebellum,  quadrigemina,  and 
almost  the  entire  mass  of  the  basal  ganglia,  together  with  the  hemispheres, 
are  the  homologues  of  the  dorsal  plates,  and  contain  central  cells  only  (Fig. 
167). 


Fig.  1G6.— Cross  section  in  the  cer- 
vical region  of  a  fetal  human  spinal 
cord  at  the  sixth  week;  X  50 diameters 
(Kolliker) :  c,  central  canal ;  a,  a, 
groove  separating  the  two  plates ;  d.p, 
dorsal  plate ;  v.p,  ventral  plate,  in 
which  alone  are  located  nerve-cells 
the  neurons  of  which  leave  the  central 
system ;  d.r,  dorsal  root ;  v.r,  ventral 
root. 


Fig.  167.— Schema  showing  the  encephalon  and  cord  ;  the  unshaded  portion  is  that  derived  from  the 
dorsal  plate ;  the  shaded  that  from  the  ventral  (from  Minot) :  C,  cerebrum ;  Cb,  cerebellum ;  F,  foramen 
of  Monro;  /,  infundibulum ;  .V,  bulb;  0,  olfactory  lobe;  P,  pons;  Q,  quadrigemina;  Sp.c,  spinal  cord; 
III,  third  ventricle ;  IV,  fourth  ventricle. 

1  His :  Abhandlungen  d.  maXh.-phya.  Clause  d.  kiinigl.  Sdcfus.  Geeellschafl  dcr  Wissemcha/Un, 
1889. 


CENTIiAL    NERVOUS  SYSTEM. 


647 


/// 


There  arc  then  to  We  expeeted  from  tlu-se  cells,  ioniiiiig  as  they  do  the 
great  bulk  of  the  central  system,  reactions  of  the  same  order  as  those  occurring 
amony;  the  eentral  cells  of  the  cord. 

Decussation.— All  through  the  central  system  neurons  pa.ss  from  one 
lateral  half  to  the  other,  witness  for  example  the  arrangements  of  the  optic 
chiasma,  the  eallosum,  the  decussation  of  the 
pyramidal  fibres  and  the  ventral  commissure 
in  the  cord  itself.  It  is  to  be  noted,  however, 
that  the  bulk  of  the  commissures  is  small  as 
comj)ared  with  the  masses  which  they  connect. 
So  far  as  known,  the  neurons  of  the  dorsal  roots 
that  have  entered  the  dorsal  colunni  of  the  cord 
on  one  side  of  the  middle  line  do  not  cross,  by 
their  main  stems  at  least,  to  the  other  side.  As 
regards  the  efferent  cells,  it  appears  that  the 
neurons  of  some  of  these  do  cross  in  the  ventral 
commissure,  but  in  the  instances  above  given, 
and  in  the  case  of  the  greater  number  of  fibres 
belonging  to  the  ventral  commissure,  the  ueurons 
concerned  are  the  outgrowths  of  central  cells 
(Fig.  168).  In  the  case  of  the  central  cells 
the  decussation  may  be  effected  by  the  entire 
neuron  or  by  a  principal  branch  from  it.  Such 
is  the  arrangement  in  the  case  of  certain  cortical 
cells  which  send  one  branch  to  the  eallosum 
(Cajal).  Besides  these  connections  between 
parts  lying  symmetrically  on  either  side  of 
the  middle  line,  there  are  of  course  dorso-ven- 
tral  connections,  but  the  neurons  by  which  this 
is  effected  do  not  run  in  bundles  and  are  there- 
fore less  obvious  and  probably  less  important. 


Fig.  168.— Illustrating  the  partial 
and  complete  decussation  of  the 
fibres  of  the  third  and  fourth  cranial 
nerves,  and  the  absence  of  decussa- 
tion in  the, case  of  the  sixth:  ///, 
root  of  the  third  cranial  nerve;  IV, 
of  the  fourth ;  VI,  of  the  sixth. 


O.   Pathway  op  the  Impulses. 

Conditions  of  Stimulation. — In  speaking  of  the  nerve-impulses  we  regard 
them  as  always  initially  arou.sed  at  the  periphery,  using  this  last  term  in  a 
wide  sen.se.  The  conditions  necessary  for  this  arousal  are  an  external  stimulus, 
acting  on  an  irritable  nerve-end.  While  life  exists,  stimulation  of  varying 
intensity  is  always  going  on,  aird  hence  there  is  no  moment  at  which  the 
nervous  system  is  not  stimulated  and  no  moment  at  which  the  effectiveness 
of  this  stimulus  is  not  varied.  The  response  to  this  continuous  and  ever- 
varying  stimulation  is  not  neces.sarily  observable,  but  occasionally  the  variation 
in  the  stimuli  is  so  wide  that  an  evident  reaction  follows. 

Though  the  foregoing  statements  suggest  that  the  chief  variable  is  that 
represented  by  the  stimulus,  the  strength  of  which  changes,  yet  as  a  matter  of 


648  AN  AMERICAN    TEXT- BOOK   OE  PHYSIOLOGY. 

fact  the  variations  in  the  j)iiy.si()l()gic'al  (cheniica!)  condition  of  tlio  nerve-cells 
arc  eqnally  important,  and  neither  factor  can  be  studied  independently. 

The  term  central  stimulation  is  sometimes  employed.  For  example,  the 
spasmodic  movements  of  the  young  child,  when  there  is  no  change  noticeable 
in  the  external  stinndi  acting  upon  it,  are  sometimes  attributed  to  this  cause; 
but  these,  although  doubtless  due  to  central  changes,  altering  the  irritability 
of  the  cells,  are  most  properly  classed  with  the  reactions  which  follow  the 
external  stimulus.  The  misconceptions  here  to  be  avoided  are  those  of  sup- 
posing that  the  nervous  system  is  at  any  time  unstimulated,  and  that  the 
evident  responses  follow  a  change  of  the  external  stimulus  only. 

Strength  of  Stimulus  and  Strength  of  Response. — AVhere  the  im})ulse 
does  not  traverse  more  than  one  nerve-element,  there  is  a  direct  relation  be- 
tween the  strength  of  the  stimulus  and  the  strength  of  the  response.  The 
negative  variation  in  the  isolated  nerve  increases  with  the  intensity  of  the 
stimulus  which  is  sent  through  it.  The  same  is  true  for  submaximal  stimuli 
a}>plied  to  the  nerve  when  the  nerve  is  still  attached  to  a  muscle,  and  the 
height  of  the  muscular  contraction  is  measured. 

When,  however,  the  impulse  in  one  cell-element  is  used  to  arouse  an  impulse 
in  another,  as  in  all  experiments  where  the  nerve-cells  are  arranged  in  a  physio- 
logical series,  the  strength  of  the  impulse  from  the  second  is  less  easy  to  pre- 
dict. This  is  explained  as  due  to  variations  in  the  ease  with  which  the  impulse 
in  one  element  stimulates  the  next,  and  also  to  the  variations  in  the  second 
cell  of  those  conditions  which  determine  the  intensity  with  which  it  may 
discharge. 

When  an  impulse  has  once  entered  the  central  system  the  arrangement 
of  the  pathways  involves  the  distribution  of  it  to  a  larger  and  larger  number 
of  elements.     This  may  be  illustrated  by  Figure  169. 

At  the  same  time  that  the  impulse  is  thus  distributed  it  tends  to  die  out. 
If,  as  we  assume,  it  is  a  wave  of  molecular  change  that  passes  along  the  neuron, 
then  when  the  neuron  divides  the  energy  in  the  main  stem  is  distributed  to 
the  mass  of  substance  which  forms  the  branches,  and  if  the  mass  of  these, 
as  is  usually  the  case,  is  greater  than  that  of  the  main  stem,  then  the  energy 
in  any  branch  will  be  less  than  in  the  main  stem. 

In  the  case  of  some  of  the  cells  about  Avhich  the  branches  of  the  neuron 
end  the  impulse  will  not  be  adequate  to  cause  in  them  a  discharge,  although 
it  may  still  produce  a  certain  amount  of  chemical  change  in  them.  The 
impulse  thus  tends  to  disappear  within  the  system,  by  producing  in  j)art  chem- 
ical changes  strong  enough  to  cause  a  discharge,  and  in  part  similar  changes 
of  a  less  intensity. 

Diffusion  of  Central  Impulses. — Thus  the  general  result  of  sending  an 
impulse  into  the  central  system  is  that  it  tends  to  be  distributed  and  at  the 
same  time  to  become  weaker.  Finally,  by  one  or  more  of  the  central  paths  it 
reaches  an  efferent  cell  which  is  in  a  condition  to  discharge  so  as  to  produce 
an  evident  reaction. 

If  the  previous  description   has  been  correct,  two  very  important  events 


CENTRAL    NERVOUS  SYSTEM. 


649 


occur:  in  the  first  place,  the  impulse  reaches  a  far  greater  number  of  cells 
than  evidently  discharge,  an.l  in  the  second,  the  pathway  followed  by  the  nn- 


( ^ 


FIG  169 -schema  to  show  how,  by  means  of  the  collaterals  and  the  central  cells,  several  Paths  are 
openTo  aS  impure  coming  in  over  A,A,  also  showing  how  an  impulse  may  arrive  at  a  gjven  part  of  a 
efferent  ceU  by  more  than  one  pathway  among  the  central  cells :  C,C,  CC  .    C  C  ,  neurons 
cells  the  bodies  of  which  are  located  in  other  segments  ;  E,  efferent  cell. 

pulses  which  do  produce  the  discharge  is  by  no  means  the  only  pathway  over 
which  the  impulses  can  or  do  travel.  u    •     i 

The  most  convenient  illustration  of  this  process  of  diffusion  can  be  obtained 
by  a  study  of  the  knee-kick  or  knee-jerk  as  it  is  more  commonly  called. 
The  reaction  in  question  consists  in  a  contraction  of  extensor  muscles  of  the 
knee  in  consequence  of  a  blow  on  the  tendon  just  below  the  knee-pan.  As 
a  result  of  this  contraction,  the  leg  is  extended,  and  a  kick  of  greater  or  less 
extent  is  made  from  the  knee  joint.  Very  careful  studies  of  the  conditions 
controlling  this  response  have  been  made  by  a  number  of  mvest.gators 
notably    Westphal,^    Lombard,^    Bowditch    and    Warren,^   Weir-Mitchell, 


1  Archiv  filr  Psychiatrk,  1875. 
»  Joumd  of  Physiology,  1890. 


2  American  Journal  of  Psychology,  1887. 
*  Philadelphia  Medical  News,  Feb.,  1886. 


650 


AK  AMERICAN  TEXT-BOOK    OF  PHYSIOLOGY. 


Fig.  170.— Record  of  the  knee-kick  of  a  tk'ineiited 
patient.  The  knee  wa.s  tapped  at  regular  intervals  of 
five  seconds.  While  the  patient  was  asleep  and  all 
about  was  quiet,  no  response  was  obtained ;  after  such 
an  irresponsive  period  the  sound  of  some  one  walking 
on  the  floor  below  caused  at  ^  a  series  of  kicks  which 
gradually  diminished ;  the  same  at  B.  At  C  two  taps 
with  a  pencil  and  a  distant  locomotive-whistle  produced 
a  longer  series.  The  arrow  indicates  the  direction  in 
which  the  record  is  to  be  read  (Noyes). 


Noyes.^  It  is  fouiul  tlmt  under  given  conditions,  the  variations  in  the 
extent  of  the  kick  can  be  referred  to  variations  in  the  excitability  of  tliat 
portion  of  the  spinal,  cord  from  which  the  fibres  controlling  the  muscles  take 

their  origin,  namely,  the  second, 
third,  and  fourth  lumbar  seg- 
ments. 

In  the  same  individual  under 
constant  conditions  and  for  short 
periods  of  time,  the  knee-kick 
may  be  fairly  constant  in  its  ex- 
tent, but  the  normal  extent  for 
different  individuals  may  vary 
widely,  all  the  way  from  those 
cases  in  which  this  reaction  is  nor- 
mally absent  to  those  in  which  it  is 
normally  very  large.  In  the  same 
individual  there  are  also  variations 
from  day  to  day,  variations  com- 
parable for  in.stance  to  those  in  the 
condition  of  athletes  whose  capacity 
for  performing  a  given  feat  is,  as 
we  know,  by  no  means  constant. 
Experimentally  the  most  marked  variation  which  is  observed  in  the  extent 
of  the  knee-kick  occurs  when  the  patient  passes  from  the  waking  to  the 
sleeping  state,  or  vice  versa.  The  regulated  blow  of  a  hammer  automatically 
released,  and  striking  the  same  point  of  the  tendon,  will  produce  little  or  no 
reaction  when  the  patient  is  asleep,  whereas  in  full  wakefulness  the  reaction 
may  be  very  evident.     Figures  170,  171  illustrate  such  variations. 

Attention  was  first  directed  to  this  peculiar  reaction  for  the  reason  that  in 
some  degree  it  could  be  used  to  test  the  physiological  condition  of  the  spinal 
cord,  it  being  found  that  the  knee-kick  M'as  usually  abolished  in  those  condi- 
tions in  which  the  lumbar  portion  of  the  cord  is  damaged  or  its  connections 
with  the  higher  centres  interrupted,  whereas  it  was  much  exaggerated  in  those 
conditions  in  which  disturbance  in  the  higher  centres  tended  to  cause  excessive 
stimulation  of  the  cord.  As  soon,  however,  as  the  reaction  was  studied  with 
greater  care  in  normal  persons,  it  became  evident  that  the  condition  of  this 
part  of  the  spinal  cord  was  subject  to  remarkable  ^uctuations,  and  that  these 
fluctuations  depended  in  a  measure  on  circumstances  which  coidd  be  controlled. 
For  example,  there  are  here  given  (Fig.  171)  six  records  showing  respectively 
the  increase  in  the  extent  of  the  knee-kick  after  the  subject  was  suddenly 
awakened;  on  repeating  Browning's  Poem,  "How  they  brought  the  good 
news  from  Ghent  to  Aix ; "  as  the  result  of  talking ;  in  consequence  of  the 
crying  of  a  child  in  the  next  room  ;  and  immediately  after  swallowing.  The 
point  here  insisted  upon  and  for  which  illustration  is  sought  by  the  accom- 
'  American  Journal  of  Fsycholoyy,  1892. 


CENTRAL    NERVOUS   SYSTEM. 


651 


panying  figures,  is  simply  this  :  that  an  extra  stimulus  caused  by  the  condi- 
tions just  enumerated  and  sent  into  the  central  system,  often  at  one  very  def- 


70 


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Fig.  171.— a  series  of  small  figures  showing  various  reinforcements  of  the  knee-kick  (Lombard);  curves 
constructed  from  the  original  records.  Numbers  at  the  left  indicate  the  height  of  kick  in  millimeters :  A, 
subject  asleep,  when  the  curve  is  lowest;  *  reinforcement  after  being  called;  B,  first  part  of  curve  low; 
*  reinforcement  in  the  knee-kick  on  repeating  Browning's  poem,  "How  they  brought  the  good  news  from 
Ghent  to  Aix."  C,  *  reinforcement  as  the  result  of  talking ;  D,  *  reinforcement  due  to  itching  of  the  ear; 
E,  *  reinforcement  due  to  the  crying  of  a  child  in  the  next  room ;  F,  *  reinforcement  due  to  swallowing. 

inite  point,  does  not  limit  its  influence  to  that  immediate  portion  of  the  system, 
but  in  all  these  cases  the   nerve-cells  located  iu  that  portion  of  the  spinal 


052  AK  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

cord   which  controls  the  knee-kick   are  so  modified  that   the  extent  of  the 
kick  is  noticeably  altered. 

There  is  little  doubt  that  if"  there  were  a  means  of  measuring  other  motor 
reactions  and  testing  their  variability  as  determined  by  variations  in  the 
incoming  stimuli,  results  concordant  with  these  just  given  could  be  obtained. 
Thev  illustrate  a  fundamental  condition  in  the  reactions  of  the  central  system 
— namely,  that  every  stimulus  which  falls  upon  it  alters  its  responsiveness,  and 
that  it  is  continually  in  a  state  of  tension  due  to  the  effect  of  many  stimuli 
which  we  often  fail  to  recognize.  If  we  follow  strictly  the  anatomical  inter- 
pretation, it  appears,  as  a  consequence  of  these  observations,  that  any  nerve- 
impulse  arriving  over  the  afferent  pathways  can  and  does  affect  to  a  varying 
degree  all  the  efferent  cell-elements,  that  there  must  be  a  pathway  for  the 
nerve-impulses  from  some  of  the  terminals  of  each  afferent  fibre  to  the  neigh- 
borhood of  each  cell  giving  rise  to  efferent  impulses. 

Variations  in  Diffusibility. — The  degree  to  which  any  set  of  incoming 
impulses  modifies  the  responsiveness  of  the  central  system  depends  in  the 
first  instance  on  the  physiological  connections  of  the  fibres  by  which  they 
travel,  and  in  the  second,  on  the  particular  condition  in  which  the  central 
cells  happen  to  be  found.  As  to  the  first  point,  we  should  expect  the  afferent 
nerves  with  the  widest  central  connections,  such  as  the  olfactory,  optic,  and 
auditory  nerves,  to  be  the  most  efficient  in  this  respect,  and  this  is  the  case. 
Concerning  the  second,  it  is  observed,  for  example,  that  by  means  of  drugs  it 
is  possible  to  alter  the  diffusibility  of  incoming  stimuli  to  an  enormous  extent. 
Strychnin  and  drugs  with  a  similar  physiological  action  have  this  as  one  of 
their  effects. 

Influence  of  Strychnin. — The  experimental  study  of  strychnin-poisoning 
shows  the  following  relations:  A  frog  poisoned  by  the  injection  of  this  drug 
is  easily  thrown  into  tetanus  whether  the  brain  is  intact  or  has  been  removed 
previous  to  the  injection.  The  drug  is  found  to  have  accumulated  in  the  sub- 
stance of  the  spinal  cord.'  The  peculiar  change  wrought  in  the  nervous  sys- 
tem is  such  that  a  slight  stimulus  will  cause  an  extended  and  prolonged  tetanic 
contraction  of  the  skeletal  muscles,  i.  e.  the  diffusion  of  impulses  within  the 
cord  is  very  wide  and  efficient  to  an  unusual  degree.  The  direct  application 
of  strychnin  to  the  spinal  cord  has  been  carefully  studied  by  Houghton  and 
Muirhead.^  AVhen  the  strychnin  solution  was  applied  locally  to  the  brachial 
enlargement  of  the  spinal  cord  of  a  brainless  frog,  a  subsequent  stimulation  of 
the  skin  of  the  arms  produced  tetanic  contractions  of  the  arms,  and  later,  after 
the  poison  had  acted  for  a  time,  of  the  entire  trunk  and  legs.  On  the  other 
hand,  stimulation  of  the  legs  in  such  a  case  produced  a  slight  reflex  or  none 
at  all.  Since  in  order  to  cause  contraction  of  the  leg  muscles  the  efferent  cells 
controlling  the  muscles  of  the  leg  must  be  discharged — and  in  the  one  case 
Avhen  the  stimulus  was  applied  to  the  arm  region  these  cells  discharged  so  as 
to  cause  a  tetanic  spasm,  while  in  the  other,  wdien  the  stimulus  was  applied  to 
the  legs,  they  discharged  only  slightly — the  alteration  in  the  cord  produced  by 
1  Lovett :  Journal  of  Physiology,  1888,  vol.  ix.  *  The  Medical  News,  June  1,  1895. 


CENTRAL    NERVOUS  SYSTEM.  653 

the  drug  must  affect  some  other  group  thau  these  efferent  cells.  Since,  more- 
over, a  tetanus  of  the  legs  could  be  caused  by  the  stimulation  of  the  skin  of 
the  arm,  the  application  of  the  drug  being  to  the  brachial  enlargement  only, 
it  appears  that  the  central  cells,  or  those  conducting  the  impulses  entering  by 
the  dorsal  root-fibres  in  the  brachial  region  to  the  nuclei  of  the  lumbar  en- 
largement, arc  probably  affected  ;  and  further,  that  it  is  the  bodies  of  these 
cells  on  which  the  drug  must  act,  since  they  alone  were  in  the  locality  at 
which  the  drug  was  applied.  The  application  of  the  drug  to  the  dorsal  root- 
ganglia  and  to  the  nerve-roots  between  the  ganglia  and  the  cord  proved  to 
be  without  effect,  so  that  the  two  parts  which  can  possibly  be  influenced  are 
the  terminations  of  the  sensory  afferent  nerves  within  the  cord  and  the  bodies 
of  the  central  cells  with  which  these  terminations  are  associated.  But  whether 
the  change  is  in  both  these  structures  or  only  in  one  cannot  now  be  determined. 

The  diffusion  of  impulses  in  the  central  system  depends  anatomically  not 
only  on  the  amount  of  branching  among  the  neurons  of  the  individual  cen- 
tral cells,  but  also  on  the  association  of  many  cells  together  so  as  to  accomplish 
this  wide  distribution  of  the  impulses.  In  the  case  of  the  afferent  elements, 
as  we  have  seen,  the  diffusion  depends  on  the  branching  of  the  neurons 
alone. 

Peripheral  Diffusion. — Turning  next  to  the  efferent  system,  we  find  the 
conditions  for  diffusion  dependent  on  the  arrangement  of  several  cells  in 
series.  When  a  group  of  efferent  cells  discharges,  we  know  from  the  arrange- 
ment of  the  ventral  roots  that  the  impulses  leave  the  cord  mainly  along  the 
fibres  which  comprise  these  roots,  but  where  the  lateral  root  is  present  they 
may  also  pass  out  over  it,  as  well  as  over  the  few  efferent  fibres  found  in  the 
dorsal  roots.  These  neurons  carrying  the  outgoing  impulses  have  two  desti- 
nations :  (1)  The  voluntary  or  striped  muscle-fibres ;  (2)  the  sympathetic 
nerve-cells,  grouped  in  masses  to  form  the  vagrant  ganglia  (see  Fig.  163). 

In  the  case  of  those  neurons  passing  to  the  voluntary  muscles,  the  impulses 
are  distributed  to  the  muscle-fibres  to  which  the  final  branches  of  the  neuron 
extend,  but  there  is  no  evidence  that  in  these  localities  the  impulses,  having 
entered  a  given  muscle-cell,  necessarily  pass  beyond  the  limits  of  that  cell  by 
conduction  through  the  muscle-substance.  It  thus  happens  that  one  part  of 
a  large  muscle  can  be  innervated  by  one  bundle  of  fibres  and  another  part  by 
a  different  bundle,  or  that  the  same  parts  of  a  muscle  may  be  innervated 
by  fibres  which  reach  it  through  more  than  one  ventral  nerve-root,  and  also 
that  with  a  given  stimulus  the  strength  with  which  a  muscle  contracts  depends 
on  the  proportion  of  the  neurons  stimulated,  and  therefore  on  the  proportion 
of  the  muscle-fibres  thrown  into  contraction.^ 

When  the  impulses  are  thus  sent  out  there  is  in  the  case  of  motor  nerves  no 
diffusion,  the  effect  being  limited  to  the  peripheral  distribution  of  the  efferent 
nerve-elements  by  way  of  which  the  impulses  leave  the  central  system.  The 
fibres  going  to  the  voluntary  muscles  form,  however,  but  one  portion,  which 

^  Gad  :  "  Ueber  einige  Beziehungen  zwischen  Nerv,  Muskel,  und  Centrum,"  Wiirzburger  Fest- 
fchrift,  1882. 


654  A\   AMF.RKAN    TEXT-BOOK    OF  PHYSIOLOGY. 

lias  just  been  indicated  as  gnnij)  1.     The  connections  of  the  remaining  group 
(2)  are  still  to  be  examined. 

Sympathetic  System. — Associated  with  the  efferent  neurons  of  the  cerebro- 
spinal system,  and  with  these  alone,  is  the  series  of  vagrant  ganglia  and  also 
of  peripheral  plexuses  containing  ganglion-cells,  which  taken  together  form 
the  sympathetic  system.'  This  system  is  composed  of  nerve-cells  always  mono- 
neuric  but  sometimes  with  and  sometimes  without  well-marked  dendrons. 
The  cells  are  more  or  less  grouped  in  ganglia,  and  these  ganglia  interpolated 
between  the  efferent  neurons  of  the  spinal  nerve-roots  on  the  one  hand  and 
the  peripheral  plexuses  or  secreting  cells  on  the  other.  The  number  of  cells 
in  the  ganglia  is  greater  than  tiie  number  of  spinal  neurons  going  to  them, 
and  hence  their  interpolation  in  the  course  of  the  ventral  fibres  increases  the 
number  of  pathways  toward  the  periphery,  as  is  shown  in  Figure  103.  In 
speaking  of  the  fibres  concerned  it  is  desirable  to  distinguish  l)etween  the 
pre-ganglionic,  or  those  originating  in  the  medullary  centres  and  ])assing  to 
the  ganglia,  and  the  post-gangl ionic  fibi'cs,  or  those  originating  in  the  cells 
of  the  ganglia  and  passing  to  the  peripiiery. 

Following  the  histological  observations  of  Ga.skell '  and  the  jjhysiological 
studies  of  Langley,^  previously  quoted,  an  outline  of  the  relations  of  the  sym- 
pathetic cells,  based  on  those  found  in  the  cat,  is  briefly  as  follows : 

Pre-ganglionic  fibres,  i.  e.  those  growing  out  of  cell-bodies  located  in  the 
cord,  arise  from  the  first  thoracic  to  the  fourth  or  fifth  lumbar,  and  from  these 
segments  only  (Gaskell).  The  fibres  are  medullated.  Langley's  experiments 
indicate  that  no  sympathetic  cell  sends  a  branch  to  any  other  sympathetic  cell. 
It  has  been  shown  that  the  pre-ganglionic  fibres  are  interrupted  in  the  ganglia. 
The  post-ganglionic  fil)i-es  are  in  part  medullated,  though  sometimes  medulla- 
tion  occurs  only  at  intervals,  but  in  the  main  they  are  gray  or  unmedullated. 

The  cerebro-spinal  neurons  end  in  the  ganglia  in  such  a  manner  that  the 
branches  of  the  pre-ganglionic  neuron  are  distributed  to  a  number  of  the 
ganglion  cell-bodies,  and  these  cells  in  turn  send  their  neurons  either  directly 
to  the  peripheral  structures  controlled  by  the  sympathetic  elements  or  to  the 
plexuses  such  as  are  found  in  the  intestine  and  about  the  blood-vessels. 

The  same  pre-ganglionic  fibre  may  have  connections  with  several  cells  in 
one  ganglion,  or,  by  means  of  collaterals,  connect  with  one  or  more  cells  in  a 
series  of  ganglia  (Langlcy). 

Manner  of  Diffusion. — It  has  been  found  that  while  the  cells  in  a  sympa- 
thetic; ganglion  are  so  arranged  that  one  ])re-ganglionic  fii)re  may  be  in  con- 
nection with  a  group  of  cells,  and  thus  the  impulses  which  pa.ss  out  of  the 
ganglion  be  more  numerous  than  those  which  entered  it,  yet  the  several  r/roiips 
of  cells  within  tlie  ganglion  are  not  connected.  In  the  peripheral  plexuses 
there  appears  to  be  a  different  arrangement.^ 

'  Gaskell:  Journal  of  Physiolofjy,  188o,  vol.  vii. ;  von  Kolliker:  "Ueber  die  feinere  Anat- 
omie  und  die  physiologische  liedeutung  des  syinpathisclieii  Nervensystems,"  Verhandlungen 
Oeselischnfl  deidscher  Naturforscher  und  Aerzte,  194,  Allgenieiner  Theil,  1894. 

^  Langley  :  "A  Short  Account  of  the  Sympathetic  System,"  Physiological  Congress,  Berne,  1895. 

^  Berkeley  :  Anatomischer  Anzeiger,  1892. 


CENTIiAL    XKliVorS   SYSTEM.  055 

It  has  been  observed  upon  stimulation  of  the  branches  of  the  coeliac  plexus 
in  the  (lou;,  tliat  the  several  branches,  thonj^h  unlike  in  size,  bring  about  nearly 
the  same  ([uantitative  reaction,  in  the  constriction  of  the  veins,  from  which  we 
infer  tliat  tliounh  enterin-i-  the  peripheral  plexus  by  diiferent  channels,  the 
impulses  find  their  way  to  the  same  elements  at  the  end,  owing  to  a  multi- 
plicity of  i)athways  within  the  plexus.' 

Experiments  with  strychnin  on  the  more  proximal  sympathetic  ganglia  do 
not  show  anv  increased  (liifusibility  following  the  apjdication  of  the  drug,  but 
on  the  other  hand,  Langley  and  Dickinson  Miave  shown  that  nicotin  apjjlied 
to  various  sympathetic  ganglia  of  the  cat  produces  a  condition  whereby  elec- 
trical stimulation  below  the  ganglion,  which  in  the  normal  animal  is  followed 
bv  dilatation  of  the  pupil,  is  without  effect.  Since  the  application  of  the  drug 
to  the  nerve-fibres  on  either  side  of  the  ganglion  is  ineffective,  when  at  the 
same  time  the  application  to  the  ganglion  itself  is  effective,  it  is  inferred  that 
tlie  drug  acts  by  altering  some  peculiar  relation  existing  within  the  ganglion, 
and  the  relation  which  is  assumed  to  be  thus  modified  is  that  between  the 
fibres  terminating  in  the  ganglion  and  the  cells  which  they  there  control. 
The  relation  between  the  post-gauglionic  fibres  and  the  peripheral  plexuses  is 
not  interrupted  by  nicotin,  and  hence  is  different  from  that  between  the  pre- 
ijanglionic  fibres  and  the  cell-bodies  which  they  control. 

Evidence  for  Continuous  Outgoing  Impulses. — Under  normal  condi- 
tions, striped  and  unstriped  muscular  tissues  are  always  in  a  condition  of 
slight  contraction.  When  the  nerves  controlling  any  such  set  of  muscles  are 
cut,  or  their  central  connections  injured,  the  muscles  at  first  relax. 

If  a  frog,  rendered  reflex  by  the  removal  of  the  brain,  the  cord  remaining 
intact,  be  huug  up  vertically,  it  is  fouud  that  the  legs  are  slightly  flexed  at 
the  hip  and  knee.  If  now  the  sciatic  nerve  be  cut  upon  one  side,  the  leg  on 
the  side  of  the  section  hangs  the  straighter,  indicating  that  the  muscles  have 
relaxed  a  little  as  the  result  of  the  section  of  the  nerve  ;  if,  in  the  same  animal, 
the  smaller  arteries  in  the  web  of  the  foot  be  examined  both  before  and  after 
the  section,  it  is  found  that  after  the  section  they  have  increased  in  diameter. 
Conversely,  artificial  stimulation  of  the  peripheral  stump  causes  a  contraction 
of  the  vessels,  but  it  is  not  possible  in  so  rough  a  way  to  imitate  the  tonic  con- 
traction of  the  skeletal  muscles. 

It  is  inferred  from  these  experiments  that  normally  there  pass  from  the 
central  system  along  some  of  the  nerve-fibres  impulses  which  tend  to  keep  the 
muscles  in  a  state  of  slight  contraction.  Destruction  of  the  entire  cord  abolishes 
all  outgoing  impulses,  and  produces  a  complete  relaxation  of  these  muscles. 

Though  the  intensity  of  these  outgoing  impulses  is  normally  always  small, 
yet  it  is  subject  to  significant  variations.  The  diflerence  between  the  tone  of 
the  muscles  of  an  athlete  in  prime  condition  and  those  of  a  patient  recovering 
from  a  prolonged  and  exhausting  illness  is  easily  recognized,  and  this  differ- 
ence is  in  a  large  measure  due  to  the  difference  in  the  intensity  of  the  impulses 

•  Mall :   Archivfiir  Anatomie  und  Physiologic,  1892. 

*  Proceedings  of  the  Royal  Society,  1889,  vol.  xlvi. 


656  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

passing  out  of  the  cord.  Among  tlie  insane,  too,  the  variations  in  this  tonic 
condition  follow  in  a  marked  way  the  nutritive  changes  in  the  central  system, 
and  both  facial  and  bodily  expression  have  a  value  as  an  index  of  the  strength 
and  variability  of  those  impulses  on  which  the  tone  of  the  skeletal  muscles 
depends.  Indeed,  so  wide  in  the  insane  is  the  variation  thus  brought  about, 
that  when  the  expressions  of  the  same  individual  at  one  time  in  a  phase  of 
mental  exaltation  and  at  another  in  that  of  mental  depression  are  com- 
pared, it  appears  hardly  j)ossible  that  they  can  be  those  of  the  same  person. 

This  continuous  outflow  of  impulses  from  the  central  system  is  indicated 
also  by  the  continuous  changes  within  glands,  and  the  variations  in  these 
metabolic  processes  according  to  the  activities  of  the  central  system. 

Rigor  Mortis. — Even  in  the  very  act  of  dying,  the  influence  of  these  im- 
pulses can  be  again  traced.  The  death  of  the  central  nerve-tissues  being  ex- 
pressed as  a  chemical  change,  causes  impulses  to  pass  down  the  efferent  nervesj 
and  these  impulses  modify  those  chemical  changes  which,  in  the  muscles  of  a 
frog's  leg  for  examjjle,  lead  to  rigor  mortis.  It  thus  ha[)pens  that  a  frog  sud- 
denly killed  and  then  left  until  the  onset  of  rigor,  will  under  ordinary  condi- 
tions show  this  at  about  the  same  time  in  both  legs.  If,  however,  the  sciatic 
nerve  on  one  side  be  cut  immediately  after  the  death  of  the  animal,  the  begin- 
ning of  rigor  in  that  leg  is  much  delayed  ;  thus  showing  that  the  nervous  con- 
nection is  an  important  factor  in  modifying  the  time  of  this  occurrence 
(Hermann). 

Summary. — In  their  most  general  form  the  activities  of  the  nervous  sys- 
tem can  therefore  be  pictured  as  follows  :  The  peripheral  termini  of  the  sensory 
or  afferent  nerves  are  isolated  and  there  pass  into  the  central  system  at  least 
as  many  distinct  impulses  as  there  are  nerves  that  have  been  stimulated.  The 
point  of  entrance  of  these  impulses  is  in  each  case  the  point  at  which  the  affer- 
ent nerve  connects  with  the  cerebro-spinal  system,  and  these  points  taken  all 
together  form  a  corresponding  projection  of  the  sensory  surfaces  upon  the  cen- 
tral system.  Once  entered  into  the  central  system  and  transmitted  to  the  cen- 
tral cells  by  the  collaterals  and  terminals  of  the  afferent  fibre,  such  an  incom- 
ing impulse  has  open  to  it  many  pathways  among  the  central  cells,  and  by  these 
pathways  it  can  reach  any  group  of  efferent  cells.  That  all  the  pathways  by 
which  it  can  travel  are  traversed  by  it,  and  that  all  the  efferent  cells  are  in 
some  measure  affected,  is  very  probable.  Both  the  diffusion  and  the  response 
are,  however,  subject  to  wide  modifications. 

The  evident  response  which  we  commonly  regard  as  the  reaction  to  any 
stimulus,  arises  from  a  more  or  less  localized  group  of  efferent  cells  and 
emerges  as  a  series  of  impulses  which  pass  by  the  efferent  nerves  either  to  find 
a  comparatively  limited  expression  in  the  contractions  of  the  voluntary  muscles 
or  enter  into  the  series  of  ganglia  and  plexuses  forming  the  sympathetic  system 
to  be  distributed  in  a  diffuse  manner  to  the  unstriped  muscles  and  the  secret- 
ing tissues. 

In  brief,  then,  the  impulses  enter  the  cerebro-spinal  system  according  to 
the  fixed  anatomical  relation  of  the  afferent  nerves.     They  leave  this  system 


CENTRA L    NERVOUS  SYSTEM.  657 

according  to  similar  auatoinical  restrict  ions  imposed  by  tlie  arrangement  of  the 
efferent  cells,  and  along  the  etierent  pathway  they  are  directed  by  isolated 
fibres  either  to  the  voluntary  muscles,  or  by  means  of  other  fibres  to  the 
ganglia  of  the  sympathetic.  In  this  latter  subdivision  the  arrangement  is 
for  diffusion  from  the  proximal  to  the  distal  members  of  the  series,  and  here 
the  area  of  tissue  finally  atlected  is  large  as  compared  with  the  part  of  the 
efferent  system  from  which  the  outgoing  impulse  may  have  started.  Yet 
the  point  at  which  the  most  significant  diffusion  of  the  impulses  occurs  is  the 
central  system. 

The  afferent  elements  being  single  cells  only,  the  amount  of  diffusion  which 
may  occur  is  limited  to  the  branches  of  this  one  group  of  elements  alone. 
The  efferent  subdivision  of  the  nervous  system,  so  far  as  it  connects  with 
skeletal  muscles,  represents  a  single  element,  but  so  far  as  it  is  connected  with 
the  sympathetic  system  there  are  at  least  two  elements  arranged  in  series.  The 
arrangement  of  the  central  system,  however,  is  but  an  elaboration  of  this  latter 
in  so  far  as  the  number  of  elements  involved  may  be  increased  above  two. 
Any  incoming  impulse  entering  the  central  system  at  any  point  tends  to  be 
diffused  over  a  large  portion  of  the  central  cells  and  by  them  to  all  the 
efferent  elements,  but  the  path  between  the  point  of  the  arriving  impulse  and 
that  at  which  the  evident  discharge  originates  in  the  efferent  cells  is  variable. 
The  permeability  of  the  central  system  is  therefore  inconstant,  and  probably 
this  inconstancy  depends  on  the  one  hand  on  the  ease  with  which  the  incoming 
impulses  are  transferred  to  it  and  from  it,  as  well  as  the  ease  with  which  they 
pass  among  the  elements  constituting  this  subdivision  itself.  The  chief  prob- 
lem in  the  physiology  of  the  central  system  is,  therefore,  to  determine  how 
the  nerve-impulses  find  their  way  among  the  central  cells  and  at  what  point 
they  pass  over  to  the  efferent  cells  so  as  to  cause  an  evident  response. 

D.  Reflex  Action. 

The  simplest  and  most  constant  of  the  co-ordinated  reactions  of  the  nerv- 
ous system  are  reflex.  The  term  involves  the  idea  that  the  response  is  not 
accompanied  by  consciousness,  and  is  dependent  on  anatomical  conditions  in 
the  central  system  which  are  only  in  a  slight  degree  subject  to  physiological 
modifications.  This  view  of  reflex  activities  is  in  a  large  measure  justified  by 
the  facts,  but  at  the  same  time  it  must  be  held  subject  to  many  modifications, 
and  it  is  not  possible  to  make  a  hard  and  fast  line  between  reflex  and  voluntary 
reactions. 

The  principal  features  of  a  reflex  act  may  be  illustrated  by  following  a 
typical  experiment. 

Typical  Reflex  Response. — If  the  central  nervous  system  of  a  frog  be 
severed  at  the  bulb,  so  as  to  separate  from  the  spinal  cord  all  of  the  portions 
of  the  central  system  above  it,  the  animal  is  for  a  time  in  a  condition  of  col- 
lapse. If,  after  twelve  hours  or  more,  such  a  frog  be  suspended  by  the  lip,  it 
will  remain  motionless,  the  fore  legs  extended  and  the  hind  limbs  pendent, 
though  very -slightly  flexed.    If  such  a  frog  were  dissected  down  to  the  nervous 

42 


058  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY^ 

system,  tlicre  would  be  f'oiuul  the  following  arrangement:  Aifcrciit  lil)i-('.s  run- 
ning from  the  .skin,  muscles,  and  tendons,  and  forming  the  dorsal  nerve-root 
with  its  ganglion.  The  central  mass  of  the  cord  in  which  these  roots  end,  each 
root  marking  the  middle  of  a  segment.  From  each  segment  of  the  cord  go 
the  ventral  root-tibres  passing  to  the  muscles  lying  beneath  the  skin  to  which 
the  sensory  nerves  are  distributed,  as  well  as  to  the  ganglia  of  the  sympa- 
thetic system.  The  mechanism  demanded  for  a  reflex  response  is  au  afferent 
j)ath  leading  to  the  cord  ;  cells  in  the  cord  by  which  the  incoming  impulses 
shall  be  distributeil ;  and  a  third  set  of  efferent  elements  to  carry  the  outgoing 
impulses.  It  is  important  to  consider  in  detail  what  occurs  in  each  portion 
of  this  reflex  arc. 

In  a  frog  thus  prepared,  stimulation  of  the  skin  in  any  part  supi)lie(l  by 
the  sensory  nerves  originating  from  the  spinal  cord  causes  a  contraction  of 
some  muscles. 

Influence  of  Location  of  Stimulus. — The  muscles  which  thus  contract 
tend  to  be  those  innervated  from  the  same  segments  of  the  cord  that  receive 
the  sensory  nerves  that  have  been  stimulated.  Thus  stimulation  of  the  skin 
of  the  breast  causes  movements  of  the  fore  limbs,  and  stimulation  of  the  rump 
or  legs  corresponding  movements  of  the  hind  limbs.  It  is  noticeable,  how- 
ever, that  wherever  the  stimulus  is  applied,  the  hind  limbs  have  a  tendency 
to  move  at  the  same  time  that  the  muscles  most  directly  concerned  contract. 

Segmental  Reactions. — In  attempting  to  explain  this  associated  contrac- 
tion of  the  leg  muscles,  it  must  be  remembered  that  the  hind  limbs  are,  par 
e.vcellence,  the  motile  extremities  of  the  frog,  and  therefore  all  general  move- 
ments involve  their  use.  We  infer  from  this,  moreover,  that  the  arrangement 
in  the  spinal  cord  of  the  frog  is  not  such  that  the  sensory  impulses  coming 
into  any  segment  tend  to  rouse  exclusively  the  muscles  innervated  by  that 
segment,  bijt  that  these  incoming  impulses  are  diffused  in  the  cord  unevenly 
and  in  such  a  way  as  to  easily  involve  the  segments  controlling  the  legs.  As 
reflex  co-ordinating  centres,  therefore,  the  several  segments  of  the  cord  have 
not  an  equal  value. 

When  the  stimulus  is  applied  on  one  side  of  the  median  plane,  the  re- 
sponses first  appear  in  the  muscles  of  the  same  side,  and  if  the  stimulus  is 
slight  they  may  appear  on  that  side  only.  The  incoming  impulses  are  there- 
fore first  and  most  effectively  distributed  to  the  efferent  cells  located  on  the 
same  side  of  the  cord  as  that  on  which  these  impulses  enter.  Such  a  state- 
ment is  most  true,  however,  when  the  stimulus  enters  the  cord  at  the  level 
Avhere  the  nerves  to  the  limbs  are  given  off.  At  other  levels  the  diffusion  to 
the  limb  centres  may  take  place  more  readily  than  to  the  cells  in  the  opposite 
half  of  the  same  segment.  When  the  muscles  of  the  side  opposite  contract 
it  is  found  that  those  there  contracting  correspond  to  the  group  of  muscles 
giving  the  initial  response.  The  diffiision  then  tends  to  be  across  the  cord 
and  to  involve  the  cells  located  at  the  same  level  as  that  at  which  the 
incoming  impulses  enter  it. 

There  is  some  reason  to  think   that   the  i)ath  by  which  the  diffusion  takes 


CENTRAL    NERVOUS   SYSTEM.  659 

place  is  not  the  shortest  one  between  the  two  groups  of  cells,  but  a  path  in 
which  the  actual  crossinj^  of  the  inipulsfs  occurs  t(jwar(l  the  cephalic  end  of  the 
cord,  so  that  tiicy  must  pass  up  the  cord  on  one  side  and  down  on  the  other. 

Strength  of  Stimulus. —  In  a  reflex  response  the  strength  of  the  stimulus 
intlncnccs  the  extent  to  which  the  muscles  are  contracted  ;  the  number  of 
muscles  taking  part  in  the  contraction,  and  the  length  of  time  during  which 
the  coutraetion  continues.  That  the  strength  of  the  stimulus  influences  the 
extent  to  which  the  contraction  of  a  given  group  of  muscles  takes  place  is 
easily  shown  when,  for  example,  tlie  toe  of  a  reflex  frog  which  has  been  sus- 
pended is  stimulated  by  pinching  it  or  dipping  it  in  dilute  acid.  In  this  case, 
if  the  stimulus  be  slight,  the  leg  is  but  slightly  raised,  whereas  if  the  stimulus 
be  strong  it  is  drawn  up  high.  In  the  same  way  by  altering  the  stimulus  the 
muscles  which  enter  into  the  contraction  may  be  only  those  controlling  the 
joints  of  the  foot,  whereas,  with  stronger  stimuli,  those  for  the  knee  and  hip 
are  successively  aflTected,  thereby  involving  a  nuich  larger  number  of  muscles. 
Here,  too,  we  infer  a  spread  of  the  incoming  impulses  which  is  orderly,  since 
the  several  joints  of  the  limb  are  moved  in  regulai  sequence. 

The  responses  which  are  thus  obtained  are  not  spasmodic,  but  are  contrac- 
tions of  muscles  in  regular  series,  giving  the  appearance  of  a  carefully  co- 
ordinated movement — a  movement  that  is  modified  in  accordance  both  with 
the  strength  of  the  stimulus  and  its  point  of  application.  Moreover,  such  a 
movement  may  occur  not  only  once  but  a  number  of  times,  the  leg  being 
alternately  flexed  and  extended  during  an  interval  of  several  seconds,  although 
the  stimulus  is  simple  and  of  much  shorter  duration. 

Continuance  of  Response. — The  continuance  of  the  response  after  the 
stimulus  has  been  withdrawn  must  be  of  course  the  result  of  a  long-continued 
chemical  change  at  some  point  in  the  pathway  of  the  impulse,  and  it  appears 
probable  by  analogy  with  the  results  obtained  from  the  direct  stimulation  of 
the  central  cortex,  that  in  these  cases  the  stimulating  changes  are  taking  place 
in  the  central  cells. 

Latent  Period. — It  has  been  observed  that  in  the  case  of  a  reflex  frog  an 
interval  of  varying  length  elapses  between  the  application  of  a  stimulus  and 
the  appearance  of  a  reaction.  The  modifications  of  the  interval  according  to 
variations  in  the  stimulus  have  been  carefully  studied.  When  dilute  acid  is 
used  as  a  stimulus,  this  latent  interval  decreases  as  the  strength  of  the  acid  is 
increased.  When  separate  electrical  or  mechanical  stimuli  are  employed,  the 
reaction  tends  to  occur  after  a  giv€f)i  number  of  stimuli  have  been  applied, 
although  the  time  intervals  l)etween  the  individual  stimuli  may  be  varied 
within  wide  limits.  The  experimental  evidence  for  electrical  stimuli  shows 
that  the  time  intervals  may  range  between  0.05  second  and  0.4  second,^  while 
the  number  of  stimuli  required  to  produce  a  response  remains  practically  con- 
stant. 

Summation  of   Stimuli. — A  single  stimulus  very  rarely  if   ever  calls 
forth  a  reaction  if  the  time  during  which  it  acts  is  very  short,  and  hence  there 
*  Ward  :  Arehiv  fiir  Analomie  und  Physiologie  (Physiol.  Abthl.),  1880. 


660  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

has  deveU)|K(l  tlio  idea  of  tlie  sumuiatioii  of  stiimili,  implying  at  some  |)art  of 
the  pathway  a  piling  np  of  the  effects  of  the  separately  inefiicieut  stimuli  to 
a  point  at  whicli  they  ultimately  become  effective. 

The  details  of  the  changes  involved  in  this  summation  and  the  place  at 
whicii  the  changes  occur  are  both  obscure,  but  it  would  seem  most  probable 
that  summation  is  an  exj>ression  of  changes  in  the  relations  between  the  final 
twigs  of  the  aliei'ent  elements  and  the  cell-bodies  of  the  central  or  efferent 
elements,  which  permit  the  better  passage  of  the  impulse  from  one  element  to 
the  other,  for  the  evidence  strongly  indicates  that  the  course  of  the  impulse  can 
be  interrupted  at  these  junctions.  The  foregoing  paragraphs  are  concerned, 
therefore,  with  changes  occurring  in  the  afferent  portion  of  the  patliway. 

Next  to  be  considered  is  the  amount  of  central  nervous  matter  which  must 
be  present  in  tlie  frog's  spinal  cord  in  order  that  the  reactions  can  take  place. 

Reactions  from  Fractions  of  the  Cord. — U  the  construction  of  the  cord 
was  strictly  segmental  in  the  sense  that  each  segment  contained  the  associated 
nerves  for  a  given  band  of  skin  and  muscle,  there  should  be  no  disturbance  on 
dividing  the  cord  into  its  anatomical  segments,  and  practically,  among  the 
invertebrates,  where  the  ganglionic  chain  is  thus  arranged,  the  single  segments 
can  perform  alone  all  the  reactions  of  which  they  are  capable  under  normal 
conditions.  In  such  invertebrates  the  only  change  effected  by  the  combination 
of  the  segments  is  that  of  co-ordinating  in  time  and  in  intensity  the  reactions 
of  the  series.  If,  on  the  other  hand,  the  segments  of  the  cord  were  more  or 
less  dependent  upon  one  another,  and  not  physiologically  equivalent,  modifica- 
tions of  various  degrees  would  arise  according  to  the  segments  isolated.  It  has 
been  found  that  the  spinal  cord  of  the  frog  may  under  special  conditions  be 
reduced  to  three  segments  and  reactions  still  be  obtained. 

During  the  breeding  season  the  male  frog  by  means  of  his  fore  legs  clasps 
the  female  vigorously  and  often  for  days.  If  at  this  season  there  is  cut  out 
from  the  male  the  region  of  the  shoulder  girdle  bearing  the  fore  limbs  together 
with  the  connected  skin  and  muscles  and  the  three  upper  segments  of  the 
spinal  cord,  then  an  irritation  of  the  skin  will  cause  a  reflex  clasping  move- 
ment similar  to  that  characteristic  for  the  normal  male  at  this  season.^ 

The  Efferent  Impulses. — Incessantly  the  efferent  impulses  pass  out  from 
the  cord  to  the  muscles  and  glands.  With  each  fresh  afferent  imjndse  those 
which  go  out  are  modified  in  strength  and  in  their  order,  but  just  how  they 
shall  be  co-ordinated  is  de])endent  on  so  many  and  such  delicate  conditions  that 
even  in  the  simplest  case  the  results  are  to  be  predicted  only  in  a  general  way. 

The  attempt  to  determine  the  spread  of  the  impulse  in  the  cord  by  deter- 
mining the  order  in  M'hich  the  various  muscles  of  the  thigh  and  leg  contracted 
in  response  to  thermal  stimuli  was  made  by  Lombard.^  In  a  reflex  frog  the 
tendons  of  the  leg  and  thigh  muscles  were  exposed  at  the  knee,  and  each 
attached  to  a  writing  rod  in  so  ingenious  a  manner  that  simultaneous  records 
of  fifteen   muscles   could  sometimes  be  obtained.     The  stimulus  was  a  metal 

'  (ioltz  :   Crntrcdblatt  fiir  die  medicinische  Wi.fucnscha/ten,  1865. 
*  Archiv  fur  Aiiutomie  mid  Physiologic^  1885. 


CENTRAL   NERVOUS  SYSTEM.  661 

tube  filled  with  warm  water  at  47°  to  61°  C'.,  \\\\\v\\  was  applied  to  the  skiu. 
Uuder  these  conditions  it  was  remarkable  that  a  continuous  stinudus  was 
often  followed,  not  by  a  single  contraction  of  the  muscles,  but  by  a  scries  of 
contractions,  suggesting  that  in  the  central  system  the  cells  are  roused  to  a 
discharge  and  then  ai'c  for  a  time  concerned  with  the  preparation  for  sending 
out  new  impulses,  and  that  during  this  latter  period  the  muscles  were  relaxed. 

Aj)parently  a  high  degree  of  uniformity  in  the  conditions  was  obtained  in 
these  experiments,  but  at  the  same  time  the  reactions  were  far  from  uniform, 
in  either  the  latent  time  of  contraction  or  the  order  in  which  the  contrac- 
tion of  the  several  muscles  followed,  although  certain  muscles  tended  to  con- 
tract first,  and  certain  series  of  contractions  to  reappear.  The  co-ordination 
of  the  contractions  is  therefore  variable  in  time,  even  under  these  condi- 
tions. These  variations  are  probably  due  either  to  the  fact  that  the  impulses 
are  not  distributed  in  the  centre  in  the  same  manner  on  each  occasion,  or  if 
they  are  thus  distributed,  the  central  and  efferent  cells  vary  from  moment 
to  moment  in  their  responsiveness.  That  these  cells  should  so  vary  is  easy 
to  comprehend,  lor  all  the  cell-elements  in  such  a  reflex  frog  are  slowly  dying. 
In  this  process  they  are  undergoing  a  destructive  chemical  change,  and  with 
these  destructive  changes  are  generated  weak  impulses  sufficient  to  cause  their 
physiological  status  continually  to  vary,  thus  modifying  the  effects  of  any 
special  set  of  incoming  impulses  acting  upon  them. 

It  is  not  to  be  overlooked  also  that  the  dissection  of  the  muscles  tested, 
and  the  removal  of  the  skiu  about  them,  deprived  the  spinal  cord  of  the 
incoming  impulses  due  to  the  stretching  of  the  skiu  by  the  swelling  of  the 
contracting  muscles  and  disturbed  the  order  and  intensity  of  such  sensory  im- 
pulses as  come  in  from  the  tendons  and  the  muscles  themselves.  However 
much  these  impulses  may  add  to  the  regularity  of  the  muscular  responses,  as 
apparently  they  do,  in  the  case  of  an  intact  leg,  these  experiments  indicate 
that  the  regularity  thus  obtained  is  dependent  rather  on  the  constancy  of  the 
incoming  stinudi  than  on  any  fixed  arrangement  in  the  nerve-centres  them- 
selves. It  is  thus  evident  that  the  discharge  of  one  efferent  cell  is  not  neces- 
sary in  order  that  another  efferent  cell  may  discharge,  but  that  each  dis- 
charging cell  stands  at  the  end  of  a  physiological  pathway  and  may  react 
independently. 

Purposeful  Character  of  Responses. — When  the  muscular  responses  of 
a  reflex  frog  to  a  dermal  stimulus  are  studied,  they  are  seen  to  have  a  purpose- 
ful character,  in  that  they  are  often  directed  to  the  removal  of  the  irritation. 
This  is  demonstrated  by  placing  upon  the  skin  on  one  side  of  the  rump  a 
small  square  of  paper  moistened  with  dilute  acid.  As  a  result  the  foot  of  the 
same  side  is  raised  and  the  attempt  made  to  brush  the  paper  away ;  if  the  first 
attempt  fails,  it  may  be  several  times  repeated.  When  the  irritation  has  been 
removed,  the  frog  usually  becomes  quiet.  If  the  leg  of  the  same  side  be  held 
fast  after  the  application  of  the  stimulus,  or  if  the  first  movements  fail  to 
brush  away  the  acid  paper,  then  the  leg  of  the  opposite  side  may  be  contracted 
and  appropriate  movements  be  made  by  it.    Emphasis  has  been  laid  by  various 


662  AN  AMERICAN    TEXT-BOOK    OF    PHYSIOLOGY. 

physiolotjists  upon  reactions  of  this  sort  as  sliowin^  a  capability  of  choice  on 
tlie  part  of  the  sj)inal  cord,  tiius  grantinj^  to  the  cord  psychical  poxv-ers. 
Against  such  a  view  it  must  be  urged  that  the  movements  of  the  leg  on  the 
side  opposite  to  the  stimulus  do  not  occur  until  after  the  muscles  of  the  leg 
on  the  same  side  have  responded.  When  these  responses  are  inefficient  be- 
cause the  leg  is  prevented  from  moving  or  because  they  fail  to  remove 
the  stimulus,  the  prime  fact  remains  that  the  stimulus  continues  to  act  and 
the  diffusion  of  the  impulses  in  the  cord  goes  on,  involving  in  either  case 
the  nerve-cells  controlling  the  muscles  of  the  opposite  leg.  The  adjustment 
of  the  reaction  of  the  leg,  on  whichever  side  it  occurs,  is,  however,  far  from 
precise ;  and  although  the  movements  of  the  leg,  when  the  stimulus  is  applied 
far  up  on  the  rump,  differ  from  those  which  follow  the  application  of  the 
stimulus  to  the  lower  part  of  the  thigh,  yet  in  either  case  they  are  very  wide, 
and  in  both  cases  the  foot  is  brushed  across  a  large  part  of  both  the  rump  and 
\eg.  Considering,  therefore,  the  rather  general  character  of  these  movements, 
and  the  fact  that  the  movement  of  the  opposite  leg  only  follows  after  a  con- 
tinued stimulus  to  the  leg  of  the  same  side  has  produced  an  ineffective  response, 
it  is  best  to  explain  the  result  by  the  diffusion  of  the  im])ulses  within  the  cord, 
leaving  quite  to  one  side  the  psychical  element.  Such  reflex  actions  are  in  a 
high  degree  predictable,  but  in  reality  this  has  little  significance,  since  there  is 
but  one  general  movement  that  a  frog  in  such  a  condition  can  make,  whether 
the  stimulus  be  applied  to  the  toes  or  the  rump — namely,  the  flexion  of  the 
leg — so  that  under  these  circumstances  the  prediction  of  the  kind  of  movement 
is  a  simple  matter.  The  extent  of  the  contraction  is  related  to  the  intensity 
of  the  stimulus,  and  is  in  turn  dependent  on  the  excitability  of  the  central 
system,  which  can  be  increased  or  diminished  in  various  ways.  The  modifi- 
cation of  the  reaction  as  dependent  on  the  location  of  the  stimulus  can  be  in  a 
measure  predicted,  but  the  modification  is  wanting  in  precision  just  in  so  far 
as  the  movements  themselves  are  wanting  in  this  quality. 

Periodic  Reflexes. — Not  all  reflexes  are  to  be  obtained  from  the  same 
animal  with  equal  intensity  at  different  times.  In  genei-al,  frogs  in  the  spring- 
time and  in  early  summer,  after  reviving  from  their  winter  sleep,  are  highly 
irregular  in  their  reflex  responses — so  irregular  that  students  are  advised  not  to 
attempt  the  study  of  these  reactions  at  this  season.  On  the  other  hand,  it  is 
during  the  spring  that  the  mating  occurs,  and  during  this  period  the  male 
clasps  the  female  and  exhibits  the  peculiar  reflex  which  has  already  been 
described.  Comparable  with  this  variation  in  the  frog  must  be  the  changes 
which  occur  in  the  spinal  cords  of  migratory  birds  which  both  in  the  spring 
and  in  the  fall  are  capable  of  such  extended  flights,  or  in  the  svstem  of  hiber- 
nating mammals  and  all  animals  exhibiting  extensive  periodic  variations  in 
their  habits  of  life. 

General  Applicability  of  these  Resiilts. — There  are  manv  reptiles  and 
fishes  in  which  the  arrangement  of  the  S])inal  cord  is  more  simple  than  that  in  the 
frog  ;  such  are  the  animals  in  which  the  actions  of  locomotion  are  verv  uniform, 
and  in  which  these  locomotory  actions  represent  the  principal  responses  of  the 


CENTRAL    NERVOUS  SYSTEM.  663 

muscles  whatever  the  stiniuhis.  In  these  cases  small  segments  of  the  body 
will  perform  the  hx'oiiiotor  reactions  when  the  segments  of  the  spinal  cord 
belonging  to  thcin  are  intact  (Stciner).^  Tarchanow  has  shown  tliat  l)eheaded 
ducks  can  still  swim  and  tly  in  a  co-ordinated  manner,  and  among  mammals 
(dog  and  rabbit)  Goltz  and  others  have  demonstrated  that  if  the  lumbar  region 
be  separated  from  the  rest  of  the  cord  by  a  cut  and  the  animal  allowed  to 
recover  from  tiie  operation,  it  will  with  proper  care  live  for  many  months, 
and  not  only  are  the  legs  responsive  to  stimulation  of  the  skin,  but  the  reflexes 
of  defecation  and  urination  are  easily  induced  by  slight  extra  stimulation.  An 
instructive  reaction  occurs  when  such  animal  is  held  up  so  that  the  hind  legs 
hang  free.  When  thus  held  the  legs  slowly  extend  by  their  own  weight  and 
then  are  flexed  together.  The  reaction  becomes  rhythmic  and  may  continue 
for  a  long  time.  It  is  assumed  in  this  case  that  the  .stretching  of  the  skin  and 
tendons  due  to  the  weight  of  the  pendent  legs  acts  as  the  stinmlus,  and  in  con- 
sequence the  legs  are  flexed.  This  act  in  turn  removes  the  stimulus,  and  as  a 
result  they  extend  again,  to  be  once  more  stimulated  and  drawn  up. 

In  man,  as  a  rule,  death  rapidly  follows  the  complete  separation  of  any 
portion  of  the  cord  from  the  rest  of  the  central  system,  especially  if  the  sep- 
aration be  sudden,  as  in  the  case  of  a  wound.  But  Gerhardt^  has  recorded 
the  retention  of  the  reflexes  in  the  case  of  compression  of  the  cord  by  a  tumor, 
the  case  having  been  under  observation  for  four  and  a  half  years  ;  and  Hitzig ' 
a  case  in  which  a  total  separation  between  the  last  cervical  and  first  thoracic 
segments  had  been  survived  for  as  long  as  seven  years.  The  principal  reac- 
tion to  be  observed  in  such  cases  is  a  contraction  of  the  limb  muscles  in 
response  to  stimulation  of  the  skin,  such  as  a  drawing  up  of  the  legs  when 
the  soles  of  the  feet  are  tickled.  No  elaborate  reflexes  are,  however,  retained 
in  connection  with  the  muscles  of  locomotion.  In  the  normal  individual 
reflexes  involving  striped  muscles  are  found  in  the  tendon  reflexes,  of  which 
the  knee-kick  is  an  example,  in  winking,  and  the  whole  series  of  reflex  modi- 
fications of  respiration,  such  as  coughing,  sneezing,  and  the  like. 

The  activities  of  the  alimentary  tract  are  examples  of  reflex  actions  in- 
volving the  peristaltic  contraction  of  unstriped  muscles  in  deglutition,  defe- 
cation, and  similar  peristaltic  movements  in  other  hollow  viscera.  So,  too, 
micturition,  the  cremaster  reflex,  emission,  and  vaginal  peristalsis  and  the 
reactions  of  parturition  are  to  be  classed  here.  Moreover,  the  entire  vascular 
system  is  controlled  in  this  manner,  the  contraction  and  distention  of  the 
small  arteries  being  in  a  large  measure  in  response  to  stimuli  originating  at  a 
distance ;  while  as  a  third  group  we  have  the  glands,  the  activity  of  which  is 
almost  entirely  reflex. 

It  thus  appears  that  the  reflex  responses,  namely,  simple  reactions  unac- 
companied by  consciousness,  are  in  man  mainly  given  by  the  unstriped  mus- 
cle-tissue and  by  glands,  and  only  in  a  minor  degree  by  the  striped  muscles. 
Moreover,  while  the  typical  reflex  is  a  reaction  over  which  we  cannot  exercise 

'  Die  Functionen  des  Centralnervensystems  der  Fuiche,  Braunscliweig,  1888. 

»  Neurobgische  Centrcdblait,  1894,  S.  502.  '  Loc.  cU. 


I)u4  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

direct  control,  the  normal  individual  has  some  power  over  many  of"  these 
reactions ;  for  example,  the  impulse  to  micturition  or  defecation  can  be  thus 
delayed,  respiration  arrested,  and  in  some  instances,  so  remote  a  reaction  as 
the  beat  of  the  heart  either  accelerated  or  slowed  at  will. 

It  is  of  interest  to  note  that  many  reflexes  which  in  the  young  are  not 
controlled,  as  micturition  for  instance,  become  so  gradually — a  change  most 
j)robal)ly  dependent  on  the  growth  of  neurons  from  the  ce})halic  centres  into 
the  cord,  thus  subjecting  the  cord-cells  to  a  new  set  of  impulses  which  modify 
their  reactions.  That  such  is  the  case  is  indicated  by  the  fact  that  extreme 
fright  or  anaesthetics  which  diminish  the  activities  of  the  higher  centres  often 
cause  these  reactions  to  take  place  involuntarily.  Other  reflexes  are  present 
in  early  life,  but  disappear  later;  such  are  the  sucking  reflex  of  an  infant,  and 
the  remarkable  clinging  power  of  the  hands,  by  which  a  young  child  is 
enabled  to  hang  from  a  bar,  thus  supporting  the  weight  of  its  entire  body, 
often  for  several  minutes.  This  last  capacity  soon  begins  to  wane,  and  usually 
disappears  by  the  second  month  of  life  (Robinson,  Nineteenth  Century,  1891). 

The  Nervous  Background. — We  return  now  to  the  conditions  which 
modify  the  spread  of  the  imj)ulses  within  the  central  system,  when  this 
system  is  represented  by  the  spinal  cord  of  a  reflex  frog.  Admittedly,  there 
is  here  j)resent  but  a  fraction  of  the  central  system.  It  lias  been  shown  that 
all  incoming  impulses  tend  to  spread  over  a  large  part  of  the  central  system. 
In  a  reflex  frog,  therefore,  the  cord  is  cut  ofiF  from  the  remote  effects  of 
impulses  which  normally  enter  the  system  by  way  of  cells  located  in  the  por- 
tion removed.  Moreover,  in  the  complete  nervous  system,  the  incoming 
impulses  tend  to  be  transmitted  to  the  cephalic  end,  and  in  some  measure 
give  rise  to  impulses  returning  within  the  central  system  and  afi'ecting  the 
efferent  cells.  In  a  fragment  of  the  central  system  like  the  cord,  such  im- 
pulses taken  up  by  the  central  cells  must  pass  so  far  as  the  neurons  are  intact, 
but  as  these  end  at  the  level  of  the  section,  such  impulses  are  lost,  in  the 
physiological  sense,  at  that  point. 

The  fact,  therefore,  that  the  experiments  with  sj)inal  reflexes  are  conducted 
on  a  portion  of  the  central  system  has  two  im])ortant  j)hysiological  conse- 
quences. In  the  first  place,  there  are  w^anting  incoming  imjndses,  direct  or 
indirect,  from  the  portion  removed  ;  on  the  other  hand,  through  the  section 
of  the  afferent  neurons,  in  their  course  w-ithin  the  central  system,  there  is  a 
direct  diminution  in  the  number  of  the  pathways  by  which  the  impulses  arriv- 
ing at  the  cord  may  be  there  distributed.  It  is  most  probable  that  in  the  frog, 
at  least,  the  reduction  of  the  central  mass  does  not  so  much  diminish  the  num- 
ber of  pathways  by  whi(!h  the  impulses  may  be  immediately  distributed  by  way 
of  the  afferent  and  central  elements,  as  it  diminishes  the  number  of  impulses 
wdiich  by  way  of  the  portion  removed  arrive  at  the  efferent  cells  and  modify 
their  responsiveness. 

The  modification  of  the  responsive  cells  under  more  than  one  impulse  is 
well  illustrated  by  an  experiment  of  Exner :'  A  rabbit  was  so  prepared  that  an 
'  Arckiv  fiir  die  gesammte  Physiologic,  Bd.  xxvii. 


CENTRAL    NERVOUS  SYSTEM. 


665 


electric  stimulus  could  We  uppliiil  to  the  cerebral  cortex  at  a  j)()int  the  excita- 
tion ot"  wliifli  caused  colitractiou  of  certain  muscles  of  the  foot.  One  of  these 
muscles  was  attached  to  a  lever  so  that  its  contraction  could  be  recorded,  and 
a  second  electrode  a})})lied  to  the  skin  of  the  foot  overlying  the  muscle.  The 
discharging  efferent  cells  in  the  cord  were  in  this  case  subject  to  impulses  from 
two  directions,  one  from  the  cortex  and  one  from  the  skin  of  the  foot.  With 
a  current  of  given  strength  stimulation  of  the  cortex  alone  caused  a  contrac- 
tion of  the  muscle,  and  stimulation  of  the  skin  of  the  foot  alone,  a  similar 
contraction.  When  both  were  stimulated  simultaneously,  the  extent  of  the 
contraction  was  greater  than  when  either  was  stimulated  alone.  If  now  the 
strength  of  the  stimulus  applied  to  the  skin  was  so  reduced  that,  alone,  it  was 
inefficient,  then  a  stimulus  from  the  cortex,  which  produced  a  reaction,  as 
indicated  by  the  first  cortical  stimulus  in  Figure  172  (^1,  a),  put  the  efferent 


Moremeiil  of  pmr. 

' 

stimulation  of  cortex. 

»"' 

A 

»" 

JJ;  b'      "  paw. 

^h 

Time  in  .feanids. 

i     L_r- 

"\_A 

\_\ 

\_\     ^_r 

rAHHrlrirlrViiirii 


Fig.  172.— To  show  the  reinforcing  influence  of  stimuli  applied  to  the  cerebral  cortex  and  to  the  skin 
of  the  paw,  on  tlie  movements  of  the  paw  of  a  rabbit  (Exner).  The  arrows  indicate  the  direction  in 
which  the  curves  are  to  be  read.  In  curve  A  the  cortical  stimulus  at  a  causes  a  movement  of  the  paw. 
Dermal  stimulus,  within  a  second,  at  b  causes  a  movement  of  the  paw.  Cortical  stimulus  at  a'  causes  a 
movement  of  the  paw.  Dermal  stimulus  several  seconds  later  at  b'  is  ineffective.  In  curve  B  dermal 
stimulus  at  b  is  ineffective.  The  cortical  stimulus  at  a  several  seconds  later  is  also  ineffective.  The 
dermal  stimulus  at  b'  is  ineffective,  but  if  followed  within  0.13  second  by  a  cortical  stimulus  at  a' a  move- 
ment of  the  paw  occurs. 

cells  in  such  a  condition  that  the  stimulus  from  the  skin  {A,b)  Figure  172, 
applied  within  0.6  second,  produced  a  second  contraction  of  the  muscle, 
although,  alone,  the  stimulus  from  the  skin  had  proved  inefficient.  Here  the 
first  efficient  stimulus  from  the  cortex  had  rendered  the  discharging  cell,  for  a 
short  period  of  time,  more  excitable.  In  the  same  figure  the  record  shows  that 
if  a  longer  interval,  here  more  than  three  seconds,  be  allowed  to  elapse,  then 
the  second  stimulus  from  the  skin  remains  inefficient.  A  similar  relation  be- 
tween the  two  incoming  impulses  is  also  found  to  hold,  when  the  stimulus 
from  the  skin  is  made  to  precede.  The  curve  B,  Fig.  172,  shows  the  results 
when  both  stimuli  are  inefficient.  In  this  the  stimuli  {b  and  a)  produce  no 
effect  when  given  several  seconds  apart,  but  when  they  occur  within  a  short 
interval  (6'  and  a') — in  this  case  0.13  second — a  contraction  of  the  muscle 
follows.  These  various  experiments,  taken  together,  show  in  a  beautiful  way 
that  in  the  cases  chosen  the  two  sets  of  impulses  tend  to  reinforce  each  other, 
whether  they  are  efficient  or  inefficient,  and  without  regard  to  the  order  iu 
which  they  come. 

This  relation  between  the  discharging  cell  and  those  by  way  of  which  it  is 
stimulated  can  be  illustrated  in  still  another  way.     It  was  observed  by  Jen- 
drassik  ^  that  when  a  patient  was  being  tested  for  the  height  of  his  knee-kick, 
^  DeiUsches  ArcMv  fUr  hlinische  Mcdicin,  Bd.  xxxiii. 


6GG 


.l.y  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 


a  voluntary  muscular  contraction,  or  an  extra  sensory  stimulus  occurrini;  about 
the  same  time  that  the  tendon  was  struck,  had  the  eil'ecf  of"  increasing  the  height 
of  the  kick.  This  was  studied  in  detail  by  Bowditch  and  Warren/  and  they 
were  able  with  great  exactness  to  measure  the  interval  between  the  contraction 
of  the  muscle  used  for  reinforcement  and  the  time  at  which  the  tendon  was 
struck.     The  curve  shown  iu  Fig.  173  represents  the  results  of  these  experi- 


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Xnrinal. 


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OrOZ"     0.4" 


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1.7- 


FiG.  173.— Showing  in  millimeters  the  amount  by  which  the  "  reinforced  "  knee-kick  varied  from  the 
normal,  the  level  of  which  is  represented  by  the  horizontal  line  at  0,  "  normal."  The  lime  intervals 
elapsing  between  the  clenching  of  the  hand  (which  constituted  the  reinforcement)  and  the  tap  on  the 
tendon  are  marked  below.  The  reinforcement  is  greatest  when  the  two  events  are  nearly  simultaneous. 
At  an  interval  of  0.4"  it  amounts  to  nothing:  during  the  next  0.6"  the  height  of  the  kick  is  actually 
diminished  the  longer  the  interval,  after  which  the  negative  reinforcement  tends  to  di.sappear;  and 
■when  1.7"  is  allowed  to  elapse  the  height  of  the  kick  ceases  to  be  affected  by  the  clenching  of  the  hand 
(Bowditch  and  Warren). 

ments.  It  indicates  that  in  general  the  closer  together  these  two  stimuli  occur, 
the  greater  the  reinforcement.  At  an  interval  of  0.4  second  no  effect  is  pro- 
duced by  the  muscular  contraction.  Increasing  the  interval  only  very  slightly 
has,  however,  the  effect  of  greatly  diminishing  the  height  of  the  knee-kick — 
i.  e.  decreasint;  the  strength  of  the  discharge  of  the  efferent  cells — and  this 
effect  is  not  lost  until  the  interval  is  increased  to  1.7  second,  when  the  volun- 
tary muscular  contraction  ceases  to  modify  the  response.  A  given  efferent  cell 
is  thus  modified  in  its  discharge  according  to  the  several  stimuli  that  act  upon  it. 
Effects  of  Disuse. — Studies  on  inactivity  show  that  a  certain  amount  of 
exercise  in  any  given  cell  is  necessary  for  its  proper  nutrition,  and  if  the  exci- 
tation fall  below  the  point  which  causes  this,  the  responsiveness  of  the  cell  is 
diminished. 

For  example,  a  strychnized  reflex  frog  on  being  dipped  into  a  solution  of 
cocaine  loses  iu  so  large  a  measure  its  irritability  that  its  responsiveness  falls 
far  below  that  of  a  normal  frog.^  In  this  case  the  central  system  is  deprived 
by  the  action  of  the  cocaine  of  the  impulses  which  even  in  the  absence  of  any 
special  form  of  irritation  normally  arrive  from  the  .>^kin,  and  the  abolition  of 
these  impulses  causes  a  diminution  iu  central  responsiveuess.     Effects  which 

^Journal  of  Physiology,  1890,  vol.  xi. 

*  PoulssoD  :  Archil'  J'iir  Palholofjie  und  eiperimenielle  Pharmakologie,  1885,  Bd.  xivi. 


CENTRAL   NERVOUS  SYSTEM.  667 

cau  tluis  be  accomplished  in  a  few  seconds  by  cutting  off  the  afferent  impulses 
from  the  skin  may  of  course  follow  any  slow  diminution  in  these  impulses, 
althougii  all  such  slow  changes  are  nuu-h  more  likely  to  be  accompanied  by 
some  sort  of  compensation  whereby  other  alferent  impulses  in  a  measure  take 
the  place  of  those  which  have  been  sup})resse(l.  The  loss  of  these  impulses 
which  rouse  the  cells  to  activity  is  usually  a  more  important  condition  than 
direct  nutritive  change,  and  must  for  this  reasou  always  be  kept  in  view. 

Inhibition. — On  the  other  hand,  let  one  leg  of  a  reflex  frog  be  stimulated 
in  the  usual  manner  by  pinching  or  by  acid,  and  then  the  experiment  repeated, 
while  the  other  leg  is  lightly  pinched  at  the  same  time,  and  it  will  be  found 
that  either  the  latent  period  preceding  the  response  is  increased  or,  with  the 
strength  of  stimulus  employed,  the  reaction  does  not  occur.  This  is  an  ex- 
ample of  inhibition  which  can  be  caused  by  the  simultaneous  excitement  of  a 
nerve-cell  in  several  ways. 

To  obtain  inhibition  there  nuist  be  at  least  two  pathways  by  which  impulses 
reach  a  given  cell,  and  the  two  stimuli  must  tend  to  excite  different  reactions. 
When  they  tend  to  excite  the  same  reaction  a  reinforcement  follows.  The  inhi- 
bition, therefore,  is  connected  with  the  effect  of  these  two  sets  of  impulses  upon 
the  responding  cell,  and  that  is  always  associated  with  the  fact  that  as  the  two 
paths  end  in  different  relations  to  the  cell,  the  impulses  must  enter  it  at  differ- 
ent points,  and  hence  in  the  first  instance  tend  to  act  on  different  portions  of 
the  cell-contents. 

Though  at  the  present  time  it  is  not  possible  to  give  a  theory  of  inhibition 
that  will  be  general  and  satisftictory,  there  is  enough  known  to  indicate  that 
this  effect,  when  developed  in  the  central  nervous  system,  is  not  produced  by 
a  special  set  of  nerve-fibres,  but  is  the  result  of  the  action  of  several  incom- 
ing impulses,  arriving  by  different  paths,  on  the  responsiveness  of  a  given 
cell. 

E.  Voluntary  Actions. 

On  attempting  to  distinguish  between  a  voluntary  and  reflex  act  from  the 
physiological  standpoint,  we  find  the  chief  difference  to  be  that  the  voluntary 
act  is  not  predictable,  because,  according  to  the  capabilities  of  the  animal,  it 
may  be  more  variable  in  form  than  is  the  reflex  response,  and  also  because,^ 
instead  of  occurring  within  a  short  interval  after  the  stimulus,  as  does  the 
reflex,  the  voluntary  response  may  be  delayed  even  for  years.  For  example, 
we  read  in  a  book  some  statement  that  makes  us  desire  to  question  the  author. 
The  question  is  a  response  to  the  stimulus  given  by  the  printed  page,  and  it 
may  be  carried  out  by  writing  a  letter  within  a  few  hours,  or  delayed  until  a 
meeting  with  the  author  years  hence.  During  this  interval,  and  in  the  absence 
of  the  author,  the  reaction  which  will  take  the  form  of  a  question  remains 
incomplete,  while  his  presence  is  sufficient  to  set  in  motion  the  train  of  stimuli 
which  shall  cause  it.  Moreover,  consciousness  enters  as  an  element  into  such 
reactions,  and  there  is  present  a  mental  image  of  the  act  to  be  accomplished, 
together  with  some  remembrance  of  its  execution. 


61)8 


.l^y  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


For   the   most  complex   vuluiitiiry  reactious  tlic  entire   central  .sy.stem  is 
necessary,  aud  especially  the  cortex  of  the  cerebral  hemispheres,  while  it  has 

already  been  shown  that  the  impulses 
which  cause  reflex  actions  can  make 
their  circuit  in  a  very  limited  portion 
of  the  spinal  cord.  In  the  case  of  vol-, 
untary  reactions  the  impulses  take  a 
longer  pathway  and  involve  a  larger 
number  of  nerve-elements,  since  from 
the  point  at  which  they  enter  the  sys- 
tem they  must  pass  to  the  cephalic  end. 
At  the  same  time,  in  a  voluntary  reac- 
tion a  greater  number  of  impulses  com- 
bine to  modify  the  discharge  from  the 
efferent  cells. 

Tracts  in  the  Central  System. — 
How  this  result  is  accomplished  has 
been  studied  both  in  mammals  and  in 
man.  Histology  shows  us  the  fibres  of 
the  dorsal  root  entering  the  cord  and 
sending  one  branch  cephalad  and  the 
other  caudad,  both  branches  giving  off 
collaterals  (Fig.  174).  In  man  and  the 
higher  mammals  the  dorsal  root-fibres 
enter  the  cord  in  three  groups — a  me- 
dian group,  an  intermediate  group  of 
large  fibres,  and  a  lateral  group  of 
very  fine  fibres,  the  bundle  of  Lissauer. 
When  the  dorsal  root  is  sectioned  be- 
tween the  ganglion  and  the  cord,  all 
these  fibres  degenerate. 
The  degeneration  extends  in  the  doreal  columns  down  the  cord  two  or 
three  centimeters  from  the  level  of  the  section,  and  also  up  the  cord  as  far  as 
the  nuclei  of  the  dorsal  columns,  located  at  the  commencement  of  the  bulb. 
If  the  section  is  made  near  the  caudal  end,  the  degeneration  may  in  conse- 
quence run  through  the  entire  length  of  the  cord.  Moreover,  it  occurs  only 
on  the  side  of  the  cord  to  which  the  sectioned  nerves  belong.  Take,  for 
example,  the  area  of  degeneration  caused  by  the  section  in  a  dog  of  the  dorsal 
roots  on  the  left  side  between  the  sixth  lumbar  and  second  sacral  nerves. 
The  degeneration  in  the  lower  lumbar  region  is  represented  in  Figure  175,  A, 
in  the  upper  lumbar  region  in  B,  and  in  the  thoracic  in  C.  On  passing 
cephalad  the  area  of  degeneration  becomes  smaller.  This  is  interpreted  to 
mean  that  all  along,  between  the  caudal  and  cephalic  limits,  fibres  are  given 
off  from  the  main  bundle  to  the  intermediate  segments  of  the  cord.  Here  is 
evidence  of  an  arrangement  that  is  always  to  be  kept  in  view.     Though  a 


Fig.  174. — Schema  showing  pathway  of  the  sen- 
sory impulses.  On  the  left  side  8,  S'  represent 
afferent  spinal  nerve-fibres ;  C,  an  afferent  cranial 
nerve-fibre.  This  fibre  in  each  case  terminates 
near  a  central  cell,  the  neuron  of  which  crosses 
the  middle  line  and  ends  in  the  opposite  hemi- 
sphere (van  Gehuchten). 


CENTRAL    NERVOUS  SYSTEM.  669 

number  of  fibres  among  those  degenerating  after  section  of  the  dorsal  roots 
may  run  tlie  longer  course,  the  larger  portion  run  a  short  or  an  intermediate 
course,  and  are  therefore  distributed  at  different  points  between  tlie  termini. 
Injury  to  the  dorsal  roots  at  different  levels  shows,  moreover,  that  the  fibres 


Fig.  175.— Sections  showing  the  degeneration  in  the  dorsal  columns  of  the  dog's  spinal  cord  when  the 
dorsal  roots  from  the  sixth  lumbar  to  the  second  sacral  have  been  cut  on  the  left  side  (Singer) :  A,  level 
of  the  sixth  lumbar;  B,  level  of  the  fourth  lumbar;  C,  level  of  the  sixth  thoracic.  Degenerated  area  in 
black. 

from  a  given  level  which  run  the  length  of  the  dorsal  columns  do  not  mingle 
indiscriminately  with  those  from  other  levels,  but  form  a  bundle,  and  that 
this  bundle  in  the  cephalic  part  of  the  cord  tends  to  lie  nearer  the  middle  line 
the  more  caudad  the  level  from  which  it  arises. 

From  these  relations  it  is  evident  that  comparatively  few  of  the  dorsal 
root-fibres  run  the  entire  length  of  the  dorsal  columns.  If,  then,  it  is  remem- 
bered that  in  describing  the  arrangements  of  the  cord  emphasis  is  usually 
placed  on  the  very  short  pathways  formed  in  part  by  collaterals  and  con- 
cerned in  the  simpler  reflexes,  and  on  the  longest  pathways  concerned  in  the 
voluntary  reactions,  as  two  extremes  between  which  are  to  be  found  a  more  or 
less  complete  series  of  intermediate  arrangements,  the  unevenness  of  the  pre- 
sentation can  be  corrected. 

Since  these  fibres  in  the  dorsal  columns  of  the  cord  degenerate  on  destruc- 
tion of  the  dorsal  roots,  it  is  inferred  that  they  must  be  morphologically  con- 
tinuous with  certain  fibres  in  the  roots,  and,  since  the  dorsal  roots  are  aflFerent 
pathways,  they  too  must  form  part  of  the  afferent  pathway  in  the  cord. 

It  is  of  course  a  portion  only  of  the  afferent  pathway  that  is  thus  formed, 
for  both  the  intermediate  and  lateral  groups  of  root-fibres  enter  the  gray 
matter  of  the  dorsal  horn,  and  must  there  come  into  physiological  connection 
with  otlier  nerve-cells  both  central  and  efferent.  The  fact  that  the  connection 
is  only  physiological  accounts  for  the  arrest  of  the  Wallerian  degeneration  at 
these  points  after  section  of  the  dorsal  roots. 

The  continuation  of  the  paths  for  the  afferent  impulses  must  therefore  be 
formed  by  the  neurons  of  the  central  cells  with  which  the  dorsal  root-fibres 
connect. 

Degeneration  after  Hemisection  of  Cord. — Upon  heraisection  of  the 
cord  involving  one  lateral  half  the  ascending  fibres  which  degenerate  appear 
in  the  dorsal  columns,  in  the  dorso-lateral  a.scending  tract,  and  in  the  ventro- 
lateral ascending  tract.  The  number  of  degenerated  fibres  is  large  on  the  side 
of  the  lesion,  but  on  the  opposite  side  there  are  also  degenerated  fibres  in  all 


(JTo  AN  AMERICAN    TEXT-BOOR'    OF  J'HVSIOLOGY. 

these  localities,  although  thoy  aiv  hy  no  means  so  imiiiorous.     It  is  interred 
that  all  the  fibres  which  thus  degenerate  form  paths  for  the  aflPerent  impulses. 

The  impulses  which  come  in  over  a  dorsal  root  on  one  side  can  therefore 
find  their  way  cephalad  either  hy  the  direct  continuations  of  the  dorsal  root- 
fibres  running  in  the  dorsal  column  of  the  same  side,  or  bv  wav  of  central 
cells  in  the  lateral  column  of  the  same  side  of  the  cord,  and  also  to  a  less 
degree  in  the  lateral  and  dorsal  columns  of  the  opposite  side. 

The  tracts  which  undergo  Wallerian  degeneration  after  this  treatment 
inelude.  therefore,  those  formed  by  the  neurons  arising  from  central  cells. 
These  cells  have  their  cell-bodies  arranged  in  a  column  running  the  length 
of  the  cord.  In  the  neighborhood  of  this  column  some  of  the  dorsal  root- 
fii)res  terminate.  In  the  bulb  we  are  familiar  with  such  groups  of  cells,  well 
marked  as  the  "  nuclei  of  the  sensory  nerves,"  and  these  cells  in  the  cord, 
though  far  less  clearly  segregated,  are  the  homologues  of  those  in  the  bulb. 
If  this  is  granted,  then  the  fibres  which  are  continued  from  these  central  cell- 
groups,  whether  in  the  cord  or  bulb,  are  also  homologous. 

Corroborative  of  what  has  been  said  on  the  subject  of  afferent  pathwavs  in 
the  cord  are  the  results  of  Pellizzi.^  He  studied  dogs,  making  use  of  the 
method  of  Marchi,  whereby  the  nerve-sheaths  of  fibres  beginning  to  degen- 
erate or  the  nutrition  of  which  is  disturbed  give  a  characteristic  reaction  ;  he 
found,  after  heraisection  of  the  cord,  the  same  lesions  that  have  been  described 
above,  with  the  addition  that  the  changes  could  also  be  followed  in  some  of 
the  fibres  of  the  ventral  roots.  More  significant,  however,  is  the  fact  that 
section  of  the  lumbar  and  sacral  dorsal  roots,  without  direct  injury  to  the 
cord,  gave  rise  to  modifications  of  the  medullary  sheaths,  detectable  by  the 
method  of  Marchi,  in  all  the  localities  just  named. 

A  distinction  must  be  made  at  this  point.  Wallerian  degeneration  in  the 
central  system  means  eventual  de.struction  of  the  severed  fibre.  The  method 
of  Marchi  shows  a  characteristic  change  in  fibres  entering  upon  this  degen- 
eration, but  this  method  also  shows  changes  in  the  sheaths  of  elements  which 
are  only  physiologically  connected  with  those  about  to  undergo  Wallerian 
degeneration,  but  which  themselves  are,  as  a  "rule,  not  ultimately  destroyed. 
Under  the  usual  conditions  of  experiment  Wallerian  degeneration  is  confined 
within  the  morphological  limits  of  a  single  cell-element,  but  the  physiological 
changes  in  the  cells  overstep  this  limit,  as  shown  by  Marchi's  reaction.  It  is 
proper  to  add,  also,  that  Wallerian  degeneration  may  under  some  conditions 
extend  to  a  group  of  nerve-cells  only  j)hysiologically  connected  with  those 
suffering  the  initial   injury. 

Physiological  Observations  on  Afferent  Path-ways. — Making  use  of 
the  fact  that  strong  stimulation  (jf  the  sensory  fibres,  such  as  those  in  the 
sciatic  nerve,  causes  a  rise  in  blood-pressure,  Woroschiloff''^  sought  to  block 
the  passage  of  the  impulses  causing  this  reaction  by  section  of  the  cord  in 
different  ways  in  the  upper  lumbar  region  of  the  rabbit.     It  appears  that  in 

'  Archives  Ilaliennes  de  Biologie,  1895,  Bd.  xxiv. 

^  Berichte  der  math.-phys.  Clause  d.  k.  Gesellsch.  d.   Wissen.  zu  Leipzig,  1874. 


CENTRAL    NERVOUS   SYSTEM.  671 

this  animal  the  reaction  was  most  diminishccl — that  is,  stimulation  of  the 
sciatic  produced  least  rise  in  the  blood-pressure — when  the  lateral  columns  of 
the  cord  had  been  cut  through ;  and  that  the  effect  of  section  of  the  lateral 
column  on  the  side  opposite  to  that  on  which  the  stimulus  was  applied  was 
greater  than  that  following  section  of  the  column  on  the  same  side.  These 
experiments  are  open  to  the  criticism  that  tiie  results  are  proved  only  for  a 
very  limited  set  of  conditions,  and  hence  it  would  be  unwise  to  make  any 
broad  inference  from  them  ;  yet  at  the  same  time  they  form  a  very  definite 
part  of  the  evidence  which  directs  our  attention  to  the  lateral  columns  of 
the  cord  as  a  principal  afferent  pathway. 

The  phvsiological  observations  of  Gotch  and  Horsley '  indicate  that  when 
in  a  monkey  a  dorsal  root  is  stimulated  electrically,  then  80  per  cent,  of  the 
impulses  pass  cephalad  on  the  same  side  of  the  cord,  while  the  remainder  cross. 
Of  the  20  per  cent,  that  cross,  some  15  per  cent,  pass  up  in  the  dorsal  columns. 
The  dorso-ventral  median  longitudinal  section  of  the  cord  in  the  monkey 
(sixth  lumbar  segment)  -  shows  an  ascending  degeneration  in  a  small  part  of 
the  dorsal  area  of  the  direct  cerebellar  tracts  and  of  the  ventro-lateral  tracts, 
as  well  as  in  the  columns  of  Goll.  This  would  indicate  that  the  section  had 
cut  fibres  which  crossed  the  middle  line  and  ran  cephalad  in  these  localities. 

These  investigations  all  point  to  the  several  tracts  most  closely  connected 
with  the  dorsal  nerve-roots  as  the  paths  for  the  sensory  impulses.  The  experi- 
mental results,  taken  together,  are  by  no  means  accordant,  but  not  necessarily 
mutually  exclusive :  confusion  must,  therefore,  not  be  permitted  to  enter  here 
through  any  unwarranted  attempt  to  combine  observations  which  should  really 
be  kept  apart,  and  the  failure  of  which  to  harmonize  is  in  large  degree  an  ex- 
pression of  the  physiological  complexity  of  the  cord. 

Osawa  ^  found  that  when  the  cord  in  a  dog  was  hemisected  (in  the  upper 
lumbar  or  lower  thoracic  region)  the  animal  showed  for  the  most  part  no  per- 
manent disturbance  of  sensation  or  motion. 

If  the  cord  is  first  hemisected  on  one  side,  and  later  on  the  other  side,  the 
second  hemisection  being  made  a  short  distance  above  or  below  the  first,  sen- 
sation and  motion  persist  behind  the  section,  although  they  are  somewhat 
damaged.  After  three  hemisections,  alternating  and  at  different  levels,  there 
still  remained  a  trace  of  co-ordinated  movement  possible  to  the  hind  legs, 
although  the  sensibility  of  the  parts  could  not  be  clearly  demonstrated.  The 
path  thus  marked  out  for  any  afferent  impulses  is  certainly  a  tortuous  one. 
These  observations  were  followed  by  a  number  of  others,  the  most  important 
of  which  in  this  connection  are  the  following : 

Section  of  all  parts  of  the  cord  except  the  two  lateral  columns  (in  the  lower 
thoracic  region,  Fig.  176)  was  without  influence  on  the  sensibility  or  move- 
ments of  the  hind  legs.  After  section  of  the  entire  cord,  with  the  exception  of 
the  dorsal  and  ventral  columns  and  the  intervening  gray  matter,  sensation  was 

^  Croonian  Lectures,  Philosophical  Transactions  Royal  Society,  1891. 

^  Griinbaum  :  Journal  of  Physiology,  1894,  vol.  xvi. 

'  Untersuchungen  Uber  die  Leitiingsbahnen  im  Riickenmark  des  Hundes,  Strassburg,  1882. 


672 


AX  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


nearly  destroyed,  while  the  voluntary  niovemeuts  of  the  leg  were  but  slightly 
disturbed  (Fig,  177),  After  section  of  the  entire  cord,  with  the  exception  of 
the  dorsal  columns,  both  sensation  and  motion  were  lost  (Fig,  178), 


Fig,  176.— Outline  of  the 
spinal  cord  of  a  dog; 
the  shaded  portion  indi- 
cates the  extent  of  the 
lesion.  The  lateral  col- 
umns of  the  cord  are  in- 
tact (Osawa). 


Fig.  177.— Outline  of  the  spi- 
nal cord  of  a  dop;  the  shaded 
portion  indicates  the  extent 
of  the  lesion.  The  dorsal  and 
ventral  columns,  together 
with  the  intermediate  gray 
matter,  are  intact  (Osawa). 


Fig.  178.— Outline  of  the  spi- 
nal cord  of  a  dog;  the  shaded 
portion  indicates  the  extent 
of  the  lesion.  The  dorsal 
columns  alone  are  intact 
(Osawa). 


Here  are  a  number  of  very  striking  results.  It  is  to  be  noted  that  the 
lateral  columns  of  the  cord  form  the  important  pathway  for  all  the  impulses 
which  influence  sensation  and  motion  caudad  to  the  section,  but,  at  the  same 
time,  section  of  them  causes  a  marked  diminution  of  sensation  alone.  On  the 
other  hand,  the  preservation  of  the  dorsal  columns  alone  does  not  preserve 
sensation. 

It  will  be  understood,  of  course,  that  the  motion  in  question  is  executed 
by  muscles  lying  caudad  to  the  section  and  is  co-ordinated  with  that  of  the 
structures  lying  in  front  of  it.  Similarly  sensation  was  inferred  from  move- 
ments executed  in  front  of  the  level  of  the  section  and  caused  by  stimulation 
behind  it. 

A  double  hemisection  of  the  spinal  cord  as  described  above  seems  to  involve 
an  interruption  of  all  the  long  pathways.  Yet  the  nervous  impulses  pass 
such  a  block  in  both  directions.  Probably  within  the  central  system  as 
elsewhere  the  amount  of  information  conveyed  is  not  directly  dependent  on 
the  number  of  nerve-fibres  stimulated.  In  general,  a  very  small  number — 
those  brought  into  action  by  pulling  out  a  single  hair — are  as  efficient  in 
co-ordinating  our  re.spon.ses  as  would  be  the  stimulation  of  a  thousand  times 
the  number.  Such  being  the  ca.se,  it  is  not  impossible  that  although  after  the 
sections  of  the  cord  both  the  number  and  intensity  of  the  impulses  that  pass 
the  point  of  section  may  be  diminished,  yet  they  may  still  remain  sufficient  to 
modify  the  reactions  of  the  caudal  portion  of  the  cord,  which  is  in  no  very 
great  degree  dependent  on  such  modifying  impulses.  That  the  impulses  may 
pass  along  a  cord  twice  hemisected  on  opposite  sides  demands  the  aid  of  the 
gray  matter,  and  we  at  once  refer  to  the  short  fibre-tracts  as  the  pathway. 

It  is  a  drawback  to  such  a  view  that  physiologists  have  not  been  accustomed 
to  lay  much  weight  on  the  connections  established  by  these  short  tracts,  but 
from  the  anatomical  side  there  is  no  inherent  difficulty  in  accounting  for  many 


CENTRAL    NERVOUS  SYSTEM.  673 

reactions  by  means  of  them.  It  is  evident  that,  so  far  as  the  dog  is  copcerned, 
the  long  and  preferred  pathways  in  the  spinal  cord  are  by  no  means  the  only 
pathways,  and,  though  probably  the  human  cord  offers  fewer  possible  alter- 
natives, the  arrangeuR'ut  is  j)resumi)tively  according  to  the  same  plan. 

Specific  Nerves. — In  order  to  analyze  the  afferent  pathways  still  further, 
we  next  inquire  whether  among  the  dorsal  nerve-roots  which  pass  between  the 
cord  and  periphery  there  are  separate  nerve-fibres  for  eacli  of  the  modes  of 
sensation  represented  by  pressure,  heat,  cold,  pain,  and  the  nmscle-sensation. 
The  data  available  for  determination  of  this  question  are  not  of  the  best,  but 
are  still  of  some  value. 

The  number  of  dorsal  root  nerve-fibres  on  both  sides  was  found  (in  a 
woman  twenty-six  years  of  age)  by  Stilling  to  be  approximately  500,000, 
which  is  probably  an  underestimate.^  The  area  of  the  skin  in  a  man  of  62 
kilograms  (136  pounds),  and  twenty-six  years  of  age,  was  found  by  Meeh 
to  be  1,900,000  square  millimeters.^  Taking  three-fifths  of  the  number  of 
the  dorsal  root-fibres  (300,000)  as  the  portion  going  to  the  skin,  the  other 
two-fifths  going  to  the  muscles  and  joints,  there  is  evidently  one  nerve-fibre 
to  innervate,  on  the  average,  about  6  square  millimeters  of  skin. 

It  is  recognized  that  dermal  innervation  is  extremely  unequal,  as  the  experi- 
ments on  tactile  discrimination  and  the  like  all  indicate.  The  average  distri- 
bution which  has  just  been  suggested  must  therefore  be  subject  to  local  modi- 
fications that  are  very  wide.  Moreover,  Woischwillo  ^  has  determined  that  in 
man  the  skin  of  the  arm  is  three  times  better  supplied  with  sensory  nerves 
than  that  of  the  leg.  In  both  arm  and  leg  the  relative  abundance  of  the 
sensory  nerves  increases  toward  the  extremity  of  the  limb.  This  increase  is 
specially  marked  in  the  leg.  Assuming,  however,  one  nerve-fibre  to  6  square 
millimeters  to  be  the  average  relation,  it  becomes  a  serious  matter  to  postulate 
separate  groups  of  fibres  for  each  mode  of  dermal  sensation,  since  each  time 
a  new  set  of  fibres  is  admitted  the  area  of  the  skin  innervated  by  any  one 
fibre  with  a  given  function  is  thereby  increased. 

The  histological  evidence  for  the  area  of  skin  innervated  by  a  single  sen- 
sory fibre  has  still  to  be  gathered,  but  in  the  mean  time  physiological  observa- 
tions indicate  that  the  area  controlled  by  a  single  fibre  cannot  be  indefinitely 
extended,  and  the  suggestion  of  a  new  category  of  nerve-fibres  needs  very 
ample  evidence  to  make  it  plausible.  This  being  the  case,  there  is  good  reason 
to  limit  the  number  of  categories  of  nerve-fibres. 

In  every  case  the  fibres  carrying  the  impulses  which  come  from  the  skin 
arise  as  outgrowths  of  the  spinal  ganglion-cells.  Trophic  nerves  as  a  special 
category  are  not  recognized,  nor  reflex  nerves,  the  functions  attributed  to  the 
latter  being  now  explained  by  the  collaterals  of  the  afferent  fibres.  At  pres- 
ent it  is  sometimes  maintained  that  there  must  be  special  nerves  for  pain,  pres- 

^  Stilling :  Neue  Untersuchungen  iiber  den  Bau  des  Riickenmarks,  Cassel,  1859. 
^  Zeitschrift  fiir  Biologie,  1879,  Bd.  xv. 

*  "  Ueber  das  VerhJiltniss  des   Kalibers  der  Nerven   zur   Haul  und  den  Muskeln   des 
Menschen,"  Inaug.  Diss.  (Russian),  1883,  vide  Centralblatt  fiir  Nervenheilkunde,  1883,  Bd.  vi. 
43 


674  AN   AMKRHWN   TEXT-JiOOK    OF    Pll  YSIOIJXI  Y. 

sure,  lioat,  and  cold.  Tlie  evidence  foe  lliose  of  pressure  and  heat  and  cold  i.s 
the  most  satisfactory. 

Pain. — Upon  severe  stimulation  of  the  skin  or  muscles  the  noi-mal  person 
exj)eriences  a  distinct  sensation  of  j)ain.  There  is,  however,  threat  variation 
in  the  intensity  of  this  sensation  when  the  same  stimulus  is  ai)plied  to  dill'erent 
pereons. 

If  we  include  abnormal  persons,  it  is  found  that  while  in  a  few  cases  com- 
plete absence  of  painful  sensations  has  been  noted — the  other  sensations 
remaining  normal — there  are  at  the  other  end  of  the  scale  those  cases  in  which 
pain  is  produced  by  many  stimuli,  wdiich  would  not  have  this  effect  on  persons 
in  ordinary  health.  The  capability  of  a  given  stiniulus  to  ]iroduce  pain  is 
therefore  subject  to  w'ide  variations  according  to  the  general  condition  of  the 
subject.^  The  same  stimulus  has  different  effects  in  a  given  individual  accord- 
ing to  several  circumstances.  Peripheral  irritation,  such  as  an  inflammatory 
process  in  the  skin,  greatly  increases  the  intensity  of  the  pain  caused  by  the 
stimulation  of  the  nerves  supplying  the  locality.  Continued  stimulation  of 
the  sensory  nerves  of  the  muscles  and  viscera  has  the  same  effect.^  Local 
anaesthetics,  such  as  cocaine,  may  reduce  the  sensibility  to  zero,  and  the  same 
follows  the  general  anaesthesia  produced  by  chloroform,  ether,  nitrous  oxide, 
morphia,  and  similar  drugs.  Painful  sensations  are  distinct  and  powerful 
only  Avhen  the  stimulus  is  applied  to  general  sensory  nerve-trunks — /.  e.  those 
mediating  cutaneous,  muscular,  and  visceral  sensibility — while  the  nerves 
which  mediate  the  special  sensations  of  light,  sound,  taste,  and  smell  do  not 
give  pain  even  on  excessive  stimulation. 

Limiting  our  observation,  therefore,  to  the  nerves  of  cutaneous  sensibility, 
it  is  found  that  the  sensations  of  pressure,  heat,  and  cold  may  all  be  present  to 
a  normal  degree,  and  yet  increasing  the  stimulus  be  without  effect  in  causing 
any  painful  sensations  whatever.  This  would  represent  a  condition  of  com- 
plete analgesia.  Moreover,  the  capacity  of  the  skin  to  cause  abnormal  painful 
sensations  upon  the  adequate  stimulation  of  each  of  these  groups  of  nerves 
may  be  associated  (in  lesions  of  the  central  system)  with  any  one  group  alone, 
the  abnormal  pain-sensations  thus  produced  being  either  those  of  excess  or 
deficiency. 

We  advance  the  hypothesis,  therefore,  that  each  of  these  three  sensations, 
if  pushed  to  excess,  is  usually  accompanied  by  pain  of  gradually  increasing 
intensity.  Therefore  it  is  most  probable  that  these  nerves  when  slightly 
stimulated  mediate  their  proper  sensations,  but  when  this  stimulus  is  pushed 
to  excess  they  can  give  rise  to  j)ain  also,  and  that  in  the  last  instance  this  sen- 
sation of  })ain  may  prove  exclusive  of  any  other.  If  this  view^  is  correct  it 
appears  improbable  that  special   pain-nerves  exist. 

As  various  experiments  show,  increasing  either  the  strength  of  the  periph- 
eral stimulus,  the  number  of  fibres  to  which  it  is  applied,  or  the  irritability  of 
the  terminals  of  the  fibres,  will  assist  in  arousing  palnftd  sensations.     In  the 

'  Strong:   P.v/cholofjirnl  Rei-ieu',  1895,  vol.  ii.  No.  4. 

^  Gad  uiid  Goldscheider :  Zcituclirift  fiir  klinischc  Mcdicin,  Bd.  xx. 


CENTRAL    NERVOUS  SYSTEM.  675 

last  analysis  the  pljysiological  condition  for  pain  is  excessive  stimulation, 
which  by  all  analogy  must  mean  excessive  discharge  within  the  central  system. 
The  changes  following  this  discharge  into  the  central  system  are  not  such  as 
lead  to  co-ordinatt'd  muscular  responses,  but  to  convulsive  reactions  of  a  very 
irregular  character.  Where  this  process  takes  place  in  the  central  system  we 
do  not  know,  because  we  can  only  determine  the  existence  of  this  sensation 
when  conscious.  As  to  normal  analgesia,  it  must  be  looked  upon  as  depend- 
ent on  a  condition  in  which  excessive  stimulation  cannot  be  produced ;  and  we 
find  this  condition  normally  present  in  the  case  of  the  nerves  of  special  sense. 

Ilcturning  now  to  the  arrangements  by  which  the  several  dermal  sensations 
are  mediated,  the  hypothesis  may  be  entertained  that  one  peripheral  twig 
of  a  dermal  nerve  may  be  modified  for  thermal  and  another  for  mechanical 
stimulation,  and,  though  they  run  by  way  of  the  same  ganglion-cell,  may  yet 
find  a  different  distribution  in  the  centre,  and  thus  lead  to  different  sensations. 

Since  in  the  pathological  cases  the  one  sort  of  sensibility  may  be  lost  while 
the  others  remain,  it  has  been  inferred  that  there  were  separate  fibres  for  the 
conveyance  of  each  sort  of  sensation.  This  idea  was  expressed  in  the  law  of 
the  specific  energies  of  nerves  as  formulated  by  Johannes  Miiller,  who  jwinted 
out  that  in  many  cases  the  same  nerve  might  be  stimulated  in  any  way,  me- 
chanically, electrically,  or  chemically,  as  well  as  in  the  normal  physiological 
manner,  and  that  in  all  cases  the  mode  of  the  response  was  the  same — a  sen- 
sation of  light  or  taste  or  contact,  as  the  case  might  be.  Hence  it  was  argued 
that  the  mode  of  the  sensation  was  independent  of  the  kind  of  stimulus,  but 
dependent  on  the  nature  of  the  central  cells,  among  which  the  afferent  fibres 
terminated.  It  will  be  seen,  however,  that  this  argument  does  not  touch  the 
character  of  the  nerve-impulses  in  any  two  sets  of  nerves,  and  we  have  no 
observations  by  which  to  decide  whether  the  nerve-impulses  passing  along 
the  optic  nerve-fibres  are,  for  example,  similar  or  dissimilar  to  those  which 
pass  along  the  auditory  fibres. 

If  the  nerve-impulses  are  always  all  alike,  there  seems  no  escape  from  the 
inference  that  separate  nerve-fibres  convey  the  different  sorts  of  impulses  to  the 
cord.  At  the  same  time,  it  is  just  possible  that  the  nature  of  the  impulses  and 
of  the  resultant  sensation  is,  in  the  nerves  of  cutaneous  sensibility,  determined 
by  the  form  of  the  peripheral  stimulus,  and  that,  as  a  consequence,  different 
branches  of  the  same  nerve-fibres  may  be  conceived  of  as  susceptible  to  differ- 
ent forms  of  stimulation,  and  thus  the  two  different  sensations  follow  from  the 
partial  stimulation  of  the  same  nerve-fibres. 

Pathway  of  Impulses  in  the  Spinal  Cord. — The  question  arises  how 
these  impulses  are  distributed  among  the  afferent  tracts  which  are  recognized 
in  the  cord,  and  whether  these  tracts  form  special  paths  for  the  impulses  that 
rouse  the  several  sensations  of  pressure,  temperature  (heat  and  cold),  and  pain. 
Since  it  is  necessary  to  know  the  sensations  of  the  subie(!t,  this  problem  can  be, 
in  some  ways,  best  studied  in  man.  Here,  owing  to  wounds  or  disease,  it  may 
so  happen  that  some  of  these  sensations  are  lost  or  greatly  diminished,  and  it 
is  to  be  determined  whether  this  loss  is  constantly  associated  with  the  inter- 


676  .l.V  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

ruptiou  of  defiuite  tracts.     Unfortunately,  however,  the  material-  for  such  a 
study  is  very  meagre. 

The  weight  of  evidence  indicates  that  the  result  of  a  lesion  in  one  lateral- 
half  of  the  spinal  cord  in  man  and  in  the  higher  animals  is  followed  by  a  loss 
or  impairment  of  motion  on  the  same  side,  and  a  loss  of  sensation  which  is 
greatest  on  the  side  opposite  to  the  lesion.  As  just  cited,  there  are  cases  in 
dogs  where  the  damage  caused  by  the  hemisection  is  apparently  transient, 
and  no  permanent  loss  can  be  demonstrated,  but  in  man  the  loss  of  function 
tends  to  be  far  more  persistent. 

On  the  basis  of  a  case  ^  in  which  the  lateral  column  of  the  cord  and  the 
gray  matter  of  both  horns  on  the  same  side  was  the  seat  of  damage,  and  in 
which  there  was  a  total  loss  of  pain  on  the  opposite  side  of  the  body  without 
impairment  of  tactile  sensibility,  it  may  be  inferred  that  the  pain-impulses 
cross  soon  after  entering  the  cord,  and  pass  cephalad  by  some  path  lying  within 
the  damaged  area.  A  second  case  ^  is  recorded  in  which  a  stab- wound  divided 
all  of  one-half  of  the  cord  plus  the  dorsal  column  of  the  other  half.  There 
was  here  a  loss  of  sensibility  to  pain  on  the  side  opposite  the  lesion,  together 
Nvith  the  loss  of  tactile  sensibility  on  both  sides,  pointing,  therefore,  to  the 
dorsal  columns  as  the  paths  for  the  tactile  impulses. 

The  observations  of  Turner^  on  monkeys,  in  which  hemisection  of  the  cord 
had  been  made  in  the  lumbar  and  thoracic  regions  indicate  that  all  sensory 
impulses  cross  immediately  after  entering  the  cord,  yet  section  in  the  cervical 
region  showed  that  the  impulses  roused  by  touching  the  skin  pass  in  part  on 
the  same  side  of  the  cord  as  the  section,  the  other  sensory  impulses  being, 
however,  completely  crossed. 

On  the  other  hand,  from  his  work  on  hemisection  of  the  dorsal  cord  of 
the  monkey  at  different  levels,*  Mott  found  the  disturbance  of  sensibility  of  all 
forms  mainly  on  the  side  of  the  section.  The  evidence  for  the  path  of  the 
cutaneous  impulses  is  therefore  contradictory. 

In  addition  to  the  cutaneous  impulses  there  are  the  sensory  impulses  from 
the  viscera,  muscles  and  tendons,  which  find  their  path  cephalad  probably  along 
the  direct  cerebellar  tract  as  well  by  the  other  pathways  conducting  cephalad. 
After  hemisection  of  the  cord  the  "  muscular  "  sensations  are  usually  lost  on 
the  side  of  the  section. 

Since,  then,  the  dorsal  and  lateral  columns  of  the  cord  appear  to  contain 
the  chief  afferent  paths  for  the  sensory  impulses,  the  next  step  in  following 
the  pathway  is  to  find  the  terminations  of  these  tracts. 

The  long  tracts  in  the  dorsal  columns  are  connected  with  the  nuclei  of 
those  columns  (nuclei  of  GoH  and  of  Burdach)  on  the  same  side.  The  cells 
of  these  nuclei  send  their  neurons  cephalad ;  in  part  they  decussate  in  the 
sensory  crossing  and  contribute  to  the  formation  of  the  lemniscus,  by  way  of 
which  they  pass  either  directly  to  the  cerebral  cortex  or  reach  this  only  after 

^  Gowers :  Clinuxd  Society's  Transactions,  1878,  vol.  xi. 

*  Miiller  :  Beitrage  zur  pathologische  Anatomic  und  Physiologic  des  Rilckenmarkcs,  Leipzig,  1871. 

'  Brain,  1891.  *  Mott:  Journal  of  Physiology,  1891,  vol.  xvii. 


CENTRAL    NKin'OrS   SySTEAf. 


677 


interruption  in  the  thalamus.'     Fig.  179,  a.s  will  be  observed,  shows  no  fibres 
running  directly  to  the  cortex  without  interruption  in  the  thalamus.     It  will 


f'ortex. 


luternitclear  fibre. .- 


j'  Nucleus 
<  of  dorsal 
{^columns. 


Fig.  179.— To  illustrate  the  pathway  of  a  sensory  impulse  arriving  at  the  nuclei  of  the  dorsal  columns 
"  d"  or  the  gray  matter  of  the  pons  and  bulb  "  c."  The  impulse  is  represented  as  passing  over  to  a  new 
element  "a"  in  the  thalamic  nuclei,  and  from  thence  to  the  cortex.  In  the  other  direction  the  cortex 
is  shown  as  connected  with  the  thalamic  cells  by  the  neuron  b';  only  the  fibres  arising  from  the  nuclei 
of  the  dorsal  columns  cross  the  middle  line  "meson"  (von  Monakow). 

be  noted  that  these  fibres  of  the  dorsal  columns  are  physiologically  joined  with 
the  contralateral  thalamus  and  hemisphere.  In  part,  however,  the  neurons  from 
the  dorsal  nuclei  enter  the  cerebellum  by  the  inferior  peduncle  of  the  same  side. 
The  ascending  fibres  in  the  lateral  columns  of  the  cord  pa.-s  to  the  cerebellar 
hemisphere  of  the  same  side  by  way  of  the  inferior  peduncle  of  the  cerebel- 
lum, and,  although  the  paths  out  of  the  cerebellum  are  not  clearly  marked, 
the  general  relation  of  the  hemispheres  of  the  cerebellum  to  that  of  the  cere- 
brum is  a  cro.ssed  one.  Some  of  the  fibres  by  which  this  crossed  connection 
is  accomplished  pass  from  the  cerebral  hemisphere  along  the  crus  of  the  same 
side  to  the  olivary  body,  and  thence  by  way  of  the  arcuate  fibres  of  the  pons 
and  the  middle  peduncle  to  the  opposite  cerebellar  hemisphere. 

It  is  with  the  "  motor  "  region  of  the  cerebral  hemisphere  that  this  con- 
nection of  the  cerebellum  appears  to  be  most  marked.     If  this  really  repr<^ 
^  von  Monakow  :  Archiv  fur  Psychiatrie  und  Nervenkrankheiten,  1895,  Bd.  xxvii. 


678 


AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 


sents  the  path  for  the  sensory  impulses  finding  their  way  by  the  antero-lateral 
tract,  then  the  impulses  are  finally  delivered  to  the  hemisphere  on  the  same 
side  of  the  system  as  that  on  which  they  enter. 

The  direct  cerebellar  tracts  pass  by  the  way  of  the  restifoiin  body  to  the 

A 
N.D.S.  ST.MI'D.D. 

T.Af!  '      ST.MED.S.  ^'-'M''- ^^4— — ^    T.A.D. 


VIII.R.P.S. 
(ATE.)-" 


VIII.R.P.D. 


N.D.S. 
T.A.8.  \     FiT.MED.R. 


N.D.D. 


C.R.^ 


Fig.  180.— Sections  of  the  bulb  of  a  rabbit  after  lesion  of  the  cochlear  portion  of  the  eighth  nerve 
(Onufrowicz) :  A,  section  at  the  level  of  the  posterior  root  of  the  eighth  nerve  ;  H,  section  at  the  level  of 
the  accessory  ganglion  of  tlie  eighth  nerve.  In  the  designations  the  final  S^  "  left  "  and  tlie  final  D  — 
"  right."  C.R,  restiforme  ;  N.D,  dorsal  nucleus ;  1',  pyramids  ;  St.  Med,  strite  mcdullares  ;  r..l,  tubcrculum 
acusticum  (atrophied  on  the  left  side) ;  Gl.Ac,  accessory  ganglion  (atrophied  on  the  left  side) ;  VIII.R.P, 
posterior  root  of  the  eighth  nerve  (atrophied  on  the  left  side):  VIII.R.A,  anteriorrootof  the  eighth  nerve  ; 
VII.G,  knee  of  the- seventh  nerve ;  VII. K,  nucleus  of  the  seventh  nerve ;   V,  root  of  the  fifth  nerve. 

middle  lobe  of  the  cerebellum,  mainiy  on  the  same  side  ;  from  here,  by  way 
of  the  superior  peduncle,  there  is  a  crossed  connection  with  the  more  cephalic 
cell-masses. 

On  passing  up  the  axis  the  sensory  cranial  nerves  appear.  Those  which 
depart  most  from  the  type  of  the  dorsal  spinal  nerves  are  the  eighth  or  audi- 


CENTUAL    NERVOUS  SYSTEM.  679 

tory,  the  second  or  optic,  and  the  first  or  olfactory  ;  and  these  require  special 
comment. 

Eighth  Nerve,  Heainng. — The  eightli  nerve  goes  to  the  ear.  The  gau- 
gliou-eells  appear  in  two  groups,  the  accessory  ganglion  Gl.Ac.  and  the  spiral 
ganglion  of  the  cochlea.  This  latter  is  definitely  associated  with  the  cochlear 
braneii  of  the  autlitory  nerve  which  has  to  do  with  the  organ  of  Corti.  The 
other  branch  of  the  auditory  nerve,  the  vestibular,  is  associated  with  the  semi- 
circular canals,  the  functions  of  which  are  not  auditory,  but  concerned  with  the 
maintenance  of  equilibrium  (see  Fig.  180). 

The  branch  for  the  semicircular  canals  and  that  for  the  cochlea  have  dif- 
ferent central  connections.^  The  auditory  fibres  proper  arising  from  the  cells 
of  the  spiral  ganglion  in  the  cochlea  and  from  those  of  the  anterior  auditory 
nucleus  [Gl.  ac),  first  connect  with  the  cells  of  the  tuberculum  acusticura 
{T.A.),  and  are  thence  continued  by  the  striae  acusticse  {St.  med.)  into  the 
lemniscus  of  the  opposite  side  ;  through  this  with  the  posterior  quadrigemi- 
nuni  and  the  internal  geniculate  body  of  that  side,  probably  the  thalamus  also, 
and  thence  by  the  internal  capsule  toward  its  occipital  end,  with  the  cortex 
of  the  more  occipital  portions  of  the  first  and  second  temporal  convolutions. 

This  path  is  indicated  by  comparative  anatomy  (Spitzka),  by  experimental 
degeneration  practised  on  animals  (von  Monakow),  and  by  pathological  observa- 
tions on  man  where  the  pathway  has  become  injured  or  diseased  in  one  of  its 
parts. 

By  the  two  latter  forms  of  evidence  it  appears  that  the  portion  of  the  cere- 
bral cortex  is  also  associated  with  the  lateral  nucleus  of  the  thalamus  of  the 
same  side,  for  injury  to  the  cortex  causes  atrophy  of  this  part  of  the 
thalamus. 

Second  Nerve,  Optic. — As  has  long  been  recognized,  the  optic  nerve,  so 
called,  is  a  cerebral  tract  morphologically  equivalent  to  such  tracts  as  connect 
any  portion  of  the  cerebral  cortex  with  a  primary  centre,  the  retina  being  in 
part  the  representative  of  the  cerebrum,  and  the  pulvinares,  the  quadrigemina, 
and  genieulata  externa  being  the  primary  centres. 

At  the  chiasma  where  the  two  optic  nerves  come  together  their  fibres  inter- 
mingle, and  then  emerge  as  the  optic  tracts,  which  contain  not  only  the  fibres 
connected  with  the  retina,  but  others  added  from  the  superposed  parts  of  the 
brain. 

In  the  higher  mammals  it  was  shown  by  von  Gudden  ^  tiiat  in  the  chiasma 
the  majority  of  tlje  fibres  forming  one  optic  nerve  pass  to  the  tract  of  the 
opposite  side,  but  that  a  portion  of  the  fibres  remain  in  the  tract  of  the  same 
side. 

This  was  inferred  because  removal  of  one  optic  bulb  caused  in  young 
rabbits  a  degeneration  in  the  associated  optic  nerve  and  also  in  both  optic 
tracts — most  marked,  however,  in  the  tract  of  the  side  opposite  to  the  lesion. 

^  Onufrowicz :  "  Exper.  Beitrag  zur  Kenntniss  des  centralen  Urspriinges  des  Nervus  acus- 
ticus,"  Inaug.  Diss.,  1885. 

^  von  Gudden  :   Gesammelle  und  hinterlassene  Abhandlangen,  Wiesbaden,  1889. 


680 


AN   AMERirAA    TEXT- HOOK    OF   PIIYSIOhOQY. 


Conversely,  the  section  of  one  optic  tract  causes  a  degeneration  in  both  optic 
nerves,  the  nerve  of  tlio  side  opposite  to  the  lesion  being  most  affected,  and  a 
smaller  degeneration  a])pearing  in  the  nerve  of  the  same  side  (see  Fig.  181). 


Pig.  181— Illustrating  the  relations  of  the  afferent  fibres  in  the  optic  nerve.  The  crossed  fibres  are 
indicated  by  solid  lines,  the  uncrossed  fibres  by  broken  lines  :  A',  nasal  side  of  the  right  eye ;  T,  temporal 
side  of  the  same  ;  G.  E,  geniculutum  externum  :  P,  pulvinar ;  C  Q,  quadrigeminum  antcrius. 


It  appears  from  this  that  in  the  higher  mammals  an  optic  tract  is  composed 
of  fibres  from  both  optic  nerves,  but  mainly  of  fibres  from  the  nerve  of  the 
opposite  side.  In  the  fish,  amphibia,  reptiles,  and  birds — except  the  owls' — 
as  well  as  in  the  lower  mammals  (mouse  and  guinea-pig,  for  example)  the 
decussation  appears  to  be  complete.^  For  the  partial  decussation  in  the  owls 
the  evidence  is  physiological.     This  distribution  of  the  optic  fibres  was  asso- 

'  Ferrier :  The.  Croonian  Lectures  on  Cerebral  Localization,  London,  1890,  p.  70. 
'  Singer  und  Miinzer:  Denkschriflen  der  math.-naturuiss.  Classe  der  kais.  Akademie  der  Wissen- 
achaften,  1888,  Ed.  Iv. 


CENTRAL    NERVOUS  SYSTEM.  681 

ciated  by  von  Guddon  with  the  position  of  the  eyes  in  tlic  head.  The  extreme 
lateral  position  of  the  eyes  as  it  occurs  in  the  lower  nminnials  permits  of  but 
little  combination  of  the  two  visual.fields ;  whereas  the  position  in  man,  in  a 
frontal  plane,  permits  a  combination  of  the  fiehls  to  a  much  greater  degree.  It 
was  in  accordance  with  this  principle  that  partial  decussation  of  these  nerves 
was  anticipated  by  von  Guddeu  in  the  owl,  although  the  histological  evidence 
for  it  was  not  obtained  by  him. 

In  man  the  evidence  from  degeneration  in  the  optic  nerve  j)oints  to  the 
presence  of  a  crossed  and  an  uncrossed  bundle  of  fibres  in  each  optic  nerve, 
the  uncrosse<l  being  much  the  smaller  of  the  two  bundles.  The  contrary  view 
of  complete  decussation  has  been  maintained  by  Michel.^  Tlie  central  ends 
of  the  afterent  optic  fibres  forming  an  optic  tract  are  distributed  between  the 
anterior  quadrigemimim,  the  geniculatum  externum,  and  the  ])ulvinar  of  the 
same  side.  By  central  cells  located  in  these  latter  structures  tlie  pathway  is 
continued  to  the  occipital  cortex  of  the  hemisphere  of  the  same  side,  by  the 
fibres  passing  in  the  occipital  end  of  the  internal  capsule  and  forming  the 
optic  radiation.  It  must  be  remembered,  however,  that  between  the  cortex 
and  the  primary  centres,  and  again  between  these  centres  and  the  bulb,  there 
are  pathways  conducting //-o?/!  the  cortex  to  the  primary  centres,  and  also  from 
the  primary  centres  to  the  retina.* 

As  the  result  of  partial  decussation  it  will  be  seen  that  the  relations  of  the 
two  bulbs  to  the  cortex  is  this:  The  nasal  or  crossed  bundle  of  the  contra- 
lateral bulb  and  the  temporal  or  uncrossed  bundle  of  the  bulb  of  the  same 
side  come  together  in  the  optic  tract  of  one  side,  and  are  associated  with  the 
occipital  lobe  of  that  side.  Hence  it  would  appear  that  hemianopsia  or 
blindness  in  the  corresponding  halves  of  the  two  eyes  following  a  lesion 
of  the  optic  pathway  anywhere  behind  the  chiasma  would  be,  in  some 
measure,  explained  by  this  anatomical  arrangement.  If  strictly  interpreted 
an  approximately  equal  number  of  fibres  would  be  expected  for  each  half 
of  the  retina.  Such,  however,  has  not  been  established  as  the  relation  be- 
tween the  areas  of  the  bundles.  It  is  to  be  added,  nevertheless,  that  ana- 
tomical arrangements  such  as  decussations  are  probably  open  to  wide  indi- 
vidual variations,  and  hence  that  many  more  observations  are  required  before 
we  can  say  what  is  the  usual  relation  between  these  two  bundles. 

With  a  view  to  determining  the  exact  location  of  the  cortical  centres  in 
man  many  observations  have  been  made.  The  cuneus  and  immediately  sur- 
rounding parts  of  the  cortex  are  those  most  concerned.  Heuschen^  indicates 
the  calcarine  fissure  and  its  immediate  neighborhood  as  the  most  important 
locality.  Observations  on  the  arrest  in  the  development  of  the  cortex  due  to 
early  blindness  following  destruction  of  the  bulb  in  the  case  of  the  blind  deaf- 
mute  Laura  Bridgman  show  the  entire  cuneus  to  be  the  central  and  funda- 
mental portion,  while  the  associated  portions  extend  some  distance  on  to  the 

'  Kolliker's  Festschrift,  Wiirzburg,  1887. 

*  von  Monakow  :  Archivf.  Psychiatrie,  1890,  Bd.  xx.  H.  3. 

'  Experimentelle  und  pathologiscke  Untersuchungen  iiber  der  Gehirn,  Upsala,  1890-92. 


682  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

convex  surface  of  the  hciui.spliei'e.^  Ferrier^  from  the  .study  of  monkeys  em- 
phasizes the  importance  of  the  cortex  of  the  angular  gyrus ;  l»ut  these  various 
results  must  ultimately  be  harmonized  through  studies  of  degeneration  in  man 
and  the  monkeys  which  will  show  the  relative  values  of  the  several  parts,  all 
of  which  are  in  some  degree  involved. 

First  Nerve. — Comparative  anatomy  indicates  that  the  parts  of  the  en- 
cephalon  mediating  the  .sense  of  smell  are  most  clo.sely  connected  with  the 
cerebral  hemispheres,  in  the  sen.se  that  phylogenetically  the  first  development 
of  the  hemispheres  was  in  connection  with  the  central  terminations  of  the 
olfactory  tracts.^  It  happens  in  man,  however,  that  although  the  cerebral  hem- 
ispheres are  proportionately  much  more  massive  than  in  the  lower  mammals, 
yet  the  olfactory  bulbs  and  tracts  are  at  the  same  time  but  poorly  developed. 
The  pathway  of  the  olfactory  impulses  is  from  the  olfactory  area  in  the  nose 
to  the  olfactory  bulb  of  the  same  side,  thence  via  the  olfactory  tract  to  its 
termination  in  front  of  the  anterior  perforated  space,  one  branch  of  the  tract 
passing  directly  into  the  substance  of  the  gyrus  fornicatus  at  this  point,  and 
the  other  going  into  the  more  lateral  portion  represented  in  man  by  the  tem- 
poral end  of  the  gyrus  hippocampi.  The  cortical  areas,  together  with  the 
olfactory  lobe  and  tract,  form  the  rhiuencephalon  of  the  comparative  anat- 
omists. It  has  been  shown,  nevertheless,  by  Hill  ^  that  in  anosraic  mammals 
the  fascia  dentata  alone  varies  with  the  development  of  the  olfactory  apparatus. 
The  experimental  pathological  evidence  is  very  meagre  in  relation  to  these 
nerves,  but,  on  the  other  hand,  the  anatomical  evidence  is  of  the  best. 

The  brief  sketches  of  the  pathways  for  incoming  impulses  indicate  that 
with  the  exception  of  those  coming  by  the  olfactory  tract,  they  arrive  ulti- 
mately at  the  cerebral  cortex  over  the  fibres  forming  the  internal  capsule, 
most,  if  not  all,  passing  by  way  of  the  thalamus.  In  the  cerebral  cortex  are 
found  the  terminal  branches  of  the  last  cell-groups  furnishing  neurons  which 
conduct  toward  the  cerebrum,  and  these  are  arranged  in  several  layers  corre- 
sponding to  the  various  strata  of  fibres  which  the  cortex  always  shows. 

F.  Localization  of  Cell-groups  in  the  Cerebral  Cortex. 

The  foregoing  .section  has  brought  to  light  the  fact  that  groups  of  incom- 
ing impulses  find  their  way  to  the  cerebral  cortex.  The  path  to  the  cerebrum 
is  best  developed  in  the  higher  animals.  In  any  case,  the  impulse  in  order  to 
produce  evident  responses  must  finally  escape  from  the  central  .sy.stera  into  the 
tissues  controlled,  and  using  the  reactions  of  the  expressive  tissues  as  a  guide, 
it  is  our  present  purpose  to  trace  the  impulses  in  those  cases  in  which  the  cor- 
tex forms  part  of  the  path.  We  turn,  therefore,  to  the  study  of  those  parts 
of  the  cerebral  cortex  the  direct  stimulation  of  which  produces  impulses  that 
pass  to  cell-groups  lying  more  or  less  caudad  in  the  central  system. 

'  Donaldson :  American  Journal  of  Psychology,  1892,  vol.  iv.  No.  4. 
-  The  Croonian  Lectures  on  Cerebral  Localization,  London,  1890. 

*  Sir  William  Turner:  Journal  of  Anatomy,  1890;  Edinger:  Anatomische  Anzeiger,  1893. 

*  Philosophical  Transactions  of  the  Royal  Society,  1893,  vol.  clxxxiv. 


CENTRAL    NERVOUS   SYSTEM. 


683 


Earlier  Observations. — It  wiis  demonstrated  by  Fritsch  and  Hitzig  in 
1870 '  that  if  a  constant  current  was  applied  to  the  surface  of  the  dog's  brain, 
it  was  possible  by  interrupting  it  to  obtain  movements  of  the  limbs  and  face 
when  the  electrodes  were  placed  on  certain  parts  of  the  cerebral  cortex,  and 
the  reaction  varied  according  to  the  place  of  stimulation,  a  constant  rela- 
tion subsisting  between  the  two.  From  this  time  on,  active  investigations 
of  the  relations  thus  suggested  have  been  pursued,  both  by  stimulating  small 
areas  in  the  cortex  of  various  aiiinials,  including  the  monkey  and  man,  and 
by  the  removal  of  various  parts  of  the  cerebral  hemispheres  and  cortex, 
together  with  the  study  of  the  effects  of  pathological  lesions  in  man.  The 
results  following  removal  of  parts  are  complicated  by  the  transitory  effects 
of  the  lesion,  and  can  best  be  treated  by  themselves  later  on.  The  results 
following  the  stimidation  of  the  cortex  are  the  simplest,  and  will  next  be 
described. 

Stimulation  of  Cortex. — The  common  method  of  experiment  is  to  apply 
the  faradic  current  by  means  of  fine  but  blunt  electrodes,  the  ends  of  which 
are  but  two  or  three  millimeters  apart,  to  the  exposed  surface  of  the  cerebral 
hemispheres,  the  pia  being  undisturbed.  Rabbits,  dogs,  and  monkeys  have 
been  the  animals  most  commonly  studied. 

If  the  current  be  slight,  its  application  for  one  or  more  seconds  causes  a 
response  in  the  shape  of  movements  of  muscles,  which  are  thrown  into  co- 
ordinated contraction.  The  contraction  continues  for  some  time  after  the 
stimulus  has  been  removed.  When  the  stimulus  is  very  strong,  instead  of  a 
limited  and  co-ordinated  response,  there  may  be  a  widespread  contraction  of 
many  muscles,  resembling  an  epileptic  convulsion.  This,  however,  occurs 
more  commonly  in  the  lower  than  in  the  higher  mammals.  On  the  other 
hand,  the  irritability  of  the  cortex  is  easily  reduced,  so  that  it  becomes  irre- 
sponsive, and  often  immediately  after  the  first  exposure  of  the  brain  there  is  a 
time  during  which  a  response  cannot  be  obtained. 

Turning  to  the  areas  of  the  cortex  which  are  occupied  by  the  extension  of 


Fig.  182.— Lateral  view  of  a  human  hemisphere.    The  cortical  visual  area  on  this  aspect  is  shaded  ( V). 


the  pathways  from  the  special  sense-organs,  it  is  found  that  the  visual  area 
alone  exhibits  any  elaboration  when  examined  by  the  method  of  stimulation. 

^Arehiv  fur  Anatomie  und  Physiologic,  1870. 


684 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


Fig.  183.— Mesial  view  of  a  human  hemisphere.  The  corti- 
cal visual  area  is  shaded,  )',•  cortical  area  for  smell,  S. 


To  be  sure,  Ferrier'  very  early  pointed  out  tliat  stimulation  of  the  other  sen- 
sory areas  causes  movements.      It  was  by  means  of  the  movements  tiius  ob- 
tained that  he  sought  to  localize  the  sensory  centres,  assuming  that  the  move- 
ments were  in  response  to  sensations  caused  by  the  irritation  of  the  cortex. 
As  the  result  of  stimulation  of  a  sensory  area  tlie  muscles  of  the  sense 

organ  itself  or  those  immediately 
associated  with  it  respond  (see  Figs. 
182,  183). 

Shiifer^has  shown  in  the  mon- 
key that  the  dorsal  portion  of  the 
visual  area  is  associated  with  the 
upper  portion  of  the  retina,  the 
eye  being  turned  downward  as  the 
result  of  stimulating  this  portion. 
This  is  interpreted  as  a  movement 
of  the  eye  intended  to  bring  a 
stimulus  falling  on  the  upper  part  of  the  retina  into  the  centre  of  the  field  of 
vision.  When  the  stimulus  is  applied  to  the  ventral  portion  of  the  area  a 
corresponding  upward  movement  of  the  eye  occurs,  and  the  corresponding 
relation  holds  for  the  stimulation  of  the  lateral  and  mesial  portions  of  the 
area.  These  movements  occur  in  both  eyes,  although  the  stimulus  is  applied 
to  one  lobe  only,  and  hence  the  two  retinal  fields  appear  to  be  superposed  in 
the  visual  cortex  of  each  hemisj)here. 

The  experiments  on  the  stimulation  of  the  other  sensory  areas  show,  in 
the  first  place,  that  these  areas  contain  cells  the  stimulation  of  which  causes 
the  contraction  of  certain  mu.scles  immediately  associated  with  the  organ  of 
sense,  and,  in  the  second  place,  that  while  each  of  the  areas  is  pre-eminently 
concerned  with  the  reception  of  impulses  from  a  particular  sense-organ,  yet 
no  one  of  them  is  exclusively  sensory. 

Deferring  for  a  moment  the  other  evidence  by  which  the  sensory  charac- 
ters have  been  established,  and  also  the  arrangements  within  the  cortex  by 
which  any  group  of  muscles  can  be  made  to  respond  to  stimuli  arriving  at  any 
sensory  area,  we  shall  follow  out  the  distribution  of  those  cortical  cells  the 
stimulation  of  which  causes  contractions  of  the  skeletal  muscles. 

The  results  here  presented  were  obtained  from  the  electrical  stimulation  of 
the  monkey's  brain  by  Beevor  and  Horsley^  (see  Figs.  184,  185).  These 
experimenters  explored  the  exposed  surface  of  the  hemisphere  with  the  elec- 
trodes, moving  them  two  millimeters  at  a  time,  and  at  each  point  noting  the 
muscle-group  first  thrown  into  contraction. 

As  the  result  of  many  observations  on  the  monkey,  it  is  possible  to  map  out 
the  cerebral  cortex  in  the  following  way :  The  surface  of  the  hemispheres  is 
divided  into  regions  (motor  and  sensory  regions),  which  are  the  largest  sub- 

'  The  Functions  of  the  Brain,  1876. 

*  Proceedings  of  the  Royal  Society,  London,  1888,  vol.  xliii. 

^Philosophical  Transactions  of  the  Royal  Society,  1888-90. 


CENTRAL    NERVOUS  SYSTEM. 


(J85 


Fig.  184.— Brain  of  the  macaque  monkey,  showing  the  sensory  and  motor  areas.  In  the  sensory  region 
the  name  of  the  sensation  is  over  the  locality  most  closely  associated  with  the  corresponding  sense-organ ; 
in  the  motor  region  the  name  of  the  part  is  written  over  the  portion  of  the  cortex  which  controls  it.  The 
upper  figure  gives  a  lateral  view  of  the  hemisphere,  and  the  lower  a  dorsal  view  (Beevor  and  Horsley). 

divisions.     These  are  subdivided  into  areas  for  the  muscle-groups  belonging 
to  different  members  of  the  body — arms,  head,  trunk,  etc.,  or  those   areas 


PoF. 


Fig.  185.— Mesial  surface  of  the  brain  (monkey).  The  localization  of  motor  functions  is  indicated 
along  the  shaded  portion  of  the  marginal  gyrus.  The  location  of  the  visual  area  is  indicated  at  the  tip  of 
the  occipital  lobe,  and  the  location  of  the  olfactory  area  at  the  tip  of  the  temporal  (Horsley). 


(J8G  ^liV  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

witliiu  M'liicli  all  the  impulses  from  a  given  seuse-orgau  reach  the  cortex. 
The  areas  in  turu  may  be  marked  off  into  centres,  formed  by  the  groups  of 
cells  which,  for  example,  control  the  smaller  masses  of  muscle  belonging  to  a 
given  segment  of  a  limb,  or  in  the  visual  area  are  represented  by  those  cells 
especially  connected  with  one  part  of  the  retina.  There  is  thus  a  motor  region 
the  stimulation  of  which  gives  rise  to  the  more  evident  bodily  movements. 
AVithin  this  are  several  subdivisions,  the  stimulation  of  one  of  which  is  fol- 
lowed by  movements  of  groups  of  muscles — for  instance,  those  controlling  the 
arm — and  within  such  an  area  in  turu  come  the  smaller  centres,  or  those 
the  stimulation  of  which  is  first  followed  by  movements  at  one  joint  only. 

Another  method  of  studying  the  cortex  is  to  regard  the  character  of  the 
movement  obtained  by  stimulating  a  single  area,  as  that  of  the  arm.     Figure 


Fig.  186.— Showing  in  the  arm-area  (monkey's  brain)  the  localization  of  movements  having 
different  characters  (after  Horsley). 

186  shows  that  stimulation  of  the  upper  arm-area  gives  rise  in  the  first  in- 
stance to  movements  of  extension,  whereas  the  lower  arm-area  yields  those  of 
flexion.  This  basis  of  subdivision  is,  however,  not  so  useful  as  the  analysis 
into  centres.  As  the  smallest  subdivisions,  the  centres  are  most  convenient 
for  further  study. 

If  a  vertical  incision  be  carried  around  such  a  centre  so  as  to  isolate  it  from 
the  other  parts  of  the  cortex,  the  characteristic  reactions  still  follow  the  stimu- 
lation of  it,  indicating  that  tiie  special  effect  can  be  produced  l)y  the  passage 
of  impulses  from  the  point  of  stimulation  toward  the  infracortical  structures. 
If,  in  addition,  a  cut  be  made  below  the  cortex  and  parallel  with  its  surface, 
then  stimulation  of  the  cortex  above  this  section  is  ineffective,  thus  indicating 
that  the  impulses  pass  from  the  cortex  directly  into  the  substance  of  the  hem- 
isphere along  certain  nerve-tracts,  which  by  this  operation  were  sectioned. 
Further,  if  the  bit  of  cortex  thus  separated  from  the  underlying  white  sub- 
stance be  removed  and  the  faradic  current  be  applied  to  the  white  substance 
beneath,  a  reaction  of  the  same  type  and  involving  the  same  muscles  can  be 
obtained,  although  it  differs  from  that  to  be  gotten  from  the  cortex  it.self,  in 


CENTRAL    NERVOUS  SYSTEM. 


687 


the  fii*st  place  by  being  less  co-ordinated,  in  the  second  by  continuing  only  so 
long  as  the  stimulus  lasts,  and  in  the  third  place  by  giving  rise  to  less  intense 
electrical  changes  connected  witii  the  passing  impulse. 

These  facts,  taken  together,  lead  to  the  conclusion  that  when  the  cortex  is 
stimulated  the  impulses  concerned  in  producing  the  muscular  contractions 
traverse  cell-bodies  at  the  ])oint  of  stimulation,  and  are  transmitted  thence 
through  the  underlying  fibres.  We  shall  see  later  that  this  direct  course 
probably  does  not  represent  the  sole  pathway  for  these  impulses. 

Secondary  Degeneration. — The  course  of  these  impulses  is  next  inferred 
from  the  relation  between  the  removal  of  different  parts  of  the  cortex  and 
the  consequent  secondary  degenerations  throughout  the  length  of  the  central 
nervous  system.  When  the  part  of  the  cortex  removed  is  taken  from  the 
motor  area,  then  the  degeneration  occurs  in  the  internal  capsule  and  in  the 


Fig.  187.— Schema  of  the  projection  fibres  within  the  brain  (Starr) ;  lateral  view  of  the  internal  cap- 
sule :  A,  tract  from  the  frontal  gyri  to  the  pons  nuclei,  and  so  to  the  cerebellum ;  B,  motor  tract ;  C,  sen- 
sory tract  for  touch  (separated  from  B  for  the  sake  of  clearness  in  the  schema) ;  D,  visual  tract ;  E,  audi- 
tory tract;  F,  G,  E,  superior,  middle,  and  inferior  cerebellar  peduncles ;  J,  fibres  between  the  auditory 
nucleus  and  the  inferior  quadrigeminal  body :  K,  motor  decussation  in  the  bulb ;  Vt,  fourth  ventricle. 
The  numerals  refer  to  the  cranial  nerves.  The  sensory  radiations  are  seen  to  be  massed  toward  the 
occipital  end  of  the  hemisphere. 

callosum.     The  path  of  the  fibres  forming  outgrowths  of  the  cortical  cells 
can  be  followed  thence  through  the  crusta  and  pyramids  to  the  spinal  cord. 
After  removal  of  the  motor  region  of  one  cerebral  hemisphere  the  degeu- 


688  AX   AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 

eration  is  niainlv  in  the  internal  capsule  and  erusta  of  the  same  side,  though 
bv  wav  of  fibres  crossing  in  the  callosuni  it  may  be  traced  on  the  other  side  also. 
At  the  decussation  of  the  pyramids  the  fibres  occupying  the  internal  capsule 
of  the  same  side  as  the  lesion,  for  the  most  part  cross  the  middle  line  (see  Fig. 
187).  The  portion  which  remains  uncrossed  passes  as  the  direct  pyramidal 
tract  of  the  ventral  columns  in  man,  while  the  crossed  bundle,  which  is  much 
the  larger,  lies  in  the  dorso-lateral  field  of  the  lateral  column,  forming  the 
crossed  pyramidal  tract.  This,  however,  is  only  the  principal,  but  not  the  com- 
plete, distribution  of  the  degenerated  fibres. 

The  direct  pyramidal  tracts  disappear  in  the  cervical  region, .having  entered 
the  substance  of  the  cord  by  way  of  the  ventral  commissure,  and  probably 
having  there  undergone  decussation.  The  crossed  pyramidal  tract  shows  the 
greatest  diminution  in  area  after  passing  caudad  of  the  cervical  and  lumbar 
enlargements,  and  hence  it  is  inferred  that  the  pyramidal  fibres  largely 
terminate  in  these  regions  of  the  cord.  Most  important,  however,  is  the 
observation  of  Sherrington,^  that  even  with  a  unilateral  cortical  lesion  degen- 
eration occurs  in  both  crossed  pyramidal  tracts,  and  that  at  the  level  of  the 
two  enlargements  the  degenerations  in  the  crossed  pyramidal  tract  on  the  same 
side  as  the  lesion  is  larger  than  above  or  below  these  enlargements,  thus 
showing  a  local  increase  in  the  degenerated  fibres  running  on  this  side. 
Sherrington's  first  explanation  of  this  bilateral  degeneration  in  the  pyramidal 
tracts  was  based  on  the  assumption  that  fibres  which  had  once  crossed  at  the 
decussation  of  the  pyramids  recrossed  at  lower  levels.  If,  however,  such 
were  the  case,  the  recrossiug  would  carry  a  number  of  the  degenerated  fibres 
across  the  middle  line,  and  decrease  by  so  many  the  fibres  in  the  opposite 
half.  The  diminution  of  the  fibres  in  number  on  the  first  side  of  the  cord 
does  not  warrant  this  inference :  Sherrington  therefore  put  forward  the  view 
that  the  pyramidal  fibres  recrossing  in  the  cord  are  derived  in  large  part  from 
a  division  of  the  pyramidal  fibres  into  two  branches,  one  of  which  may  cross 
to  the  opposite  side  of  the  cord,  while  the  other  continues  its  first  course; 
such  dividing  fibres  he  designates  as  "geraiual  fibres,"  the  number  of  which 
is  by  no  means  small. 

The  observations  of  Sherrijigton  were  made  on  monkeys  (Macacus)  and 
dogs,  and  probably  tiie  arrangements  of  these  fibres  in  man  is  similar.  The 
observations  are  particularly  significant  as  giving  an  anatomical  basis  for  the 
control  of  the  movements  in  both  halves  of  tiie  body  from  each  cerebral 
hemisphere. 

The  continuous  degeneration,  coupled  with  the  histological  evidence  for 
the  absence  of  intervening  nerve-cells,  indicates  that  the  cell-bodies  in  the  cortex 
have  neurons  that  extend  all  the  way  to  the  cell-grou})s  of  the  spinal  cord, 
even  as  far  as  the  sacral  region.  The  neurons  of  one  group  of  these  cortical 
cells  pass,  however,  to  the  cell-groups  in  the  cervical  enlargement,  while  those 
from  others  pass  to  the  groups  in  the  lumbar  enlargement.  It  thus  happens 
that  if  the  spinal  cord  be  cut  across  in  the  middle  of  the  thoracic  region,  and 
1  Journal  of  Physiology,  1889,  vol.  x. 


CENTRAL   NERVOUS  SYSTEM.  689 

then  the  lef]:;-area  (see  Fig.  153)  be  stimulated,  an  electrometer  applied  to  the 
cut  end  of  the  cord  will  show  the  passage  of  nerve  impulses,  because  the 
electrometer  is  applied  to  a  tract  of  fibres  on  their  way  to  the  lumbar  enlarge- 
ment, and  the  fibres  originate  in  cortical  cells  within  the  region  stinmlated. 
When,  however,  the  cortical  stimulus  is  made  in  the  arm-area,  the  electrometer 
being  applied  as  before,  no  electric  change  occurs,  for  the  neurons  of  the  cells 
in  the  arm  terminate  in  the  part  of  the  cord  containing  the  cell-groups  which 
control  the  muscles  of  the  arm,  and  these  all  lie  cephalad  to  the  point  of 
section  of  the  cord.  It  is  evident,  therefore,  that  the  arrangement  is  a  com- 
paratively simple  one — namely,  an  extension  of  the  neurons  of  the  several 
groups  of  cortical  cells  from  the  different  areas  for  the  leg,  arm,  face,  etc.,  to 
the  axial  cell-groups  which  control  the  muscles  of  these  parts,  and  which 
are  situated  in  the  cord.  Sherrington  reports  ^  a  degeneration  of  some  fibres 
as  far  as  the  lumbar  enlargement  even  when  the  lesion  is  confined  to  the 
cortical  area  for  the  arm.  Assuming  .the  correctness  of  this  observation,  it  is 
to  be  harmonized  with  the  preceding  statements  to  the  effect  that  stimulation 
of  the  arm-area  does  not  produce  an  electrical  variation  in  an  electrometer 
applied  to  the  crossed  pyramidal  tracts  in  the  mid-thoracic  region  by  the  fact 
that  the  number  of  these  long  fibres  is  small. 

The  cortical  cells  in  the  motor  region  belong  to  the  group  of  central  cells 
— i.  e.  their  neurons  never  leave  the  central  system — and  hence  they  are 
engaged  in  distributing  impulses  within  it.  To  the  axial  cell-groups  in  the 
cord  they  bring  impulses,  and  therefore  from  the  standpoint  of  these  latter 
may  be  considered  as  afferent,  whereas,  owing  to  the  fact  that  they  carry 
impulses  away  from  the  cortex,  they  are  sometimes  called  efferent.  Confusion 
can  be  avoided,  however,  by  refraining  from  either  term.  Just  how  these  two 
sets,  the  cortical  and  the  cord  elements,  are  related  still  requires  to  be  worked 
out.  The  number  of  fibres  in  the  pyramidal  tracts  indicates  that  there  cer- 
tainly is  not  one  fibre  for  each  cell  in  the  axial  cell-groups,  because  the  num- 
ber of  pyramidal  fibres  is  very  much  less  than  is  the  number  of  cells  which 
they  control.  This  discrepancy  is  in  some  measure  relieved  by  the  formation 
of  "  geminal "  fibres  already  described.  Moreover,  the  branching  of  the  pyr- 
amidal fibres  near  their  termination  is  very  probable,  and  the  most  plausible 
view  at  present  is  that  each  pyramidal  fibre  by  means  of  its  collaterals  comes 
into  physiological  connection  with  a  considerable  number  of  efferent  cells,  and 
probably  the  cells  controlled  by  any  one  fibre  at  its  terminus  form  more  or  less 
compact  groups. 

Mapping  of  the  Cortex. — Having  sketched  the  relations  of  the  pyramidal 
cells  forming  the  motor  region  of  the  cerebral  cortex  to  the  parts  lying  below, 
it  will  be  important  to  study  the  arrangement,  size,  subdivisions,  and  com- 
parativ^e  anatomy  of  this  region,  and  then  to  examine  the  relation  of  it  to  the 
other  parts  of  the  cortex.  The  observations  here  quoted  are  those  on  the 
monkey  only. 

On  glancing  at  Figure  184  it  is  evident,  first,  that  the  areas  for  the  head 
^  Journal  of  Physiology,  1869,  vol.  x. 
44 


690 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


and  i'acc  :n-e  widely  separated  from 
each  otlier — that  tlie  ann-area  lies  her 
tweeu  them,  and  that  the  area  for  the 
trunk,  though  less.soiiematieall y  plaeed, 
is  located  between  the  arm  and  leg. 
This  arranjreujent  is  more  typically 
represented  on  the  mesial  (Fij^.  18o) 
than  on  the  conv-ex  surface  of  the 
hemisphere. 

The  muscle-groups  M'hen  enumer- 
ated cephalo-caudad  being  those  for 
the  head,  arm,  trunk,  and  legs,  the 
serial  order  of  the  cortical  areas  is 
thus  in  correspondence  with  the  order 
of  the  muscle-groups  which  they  con- 
trol. 

The  Size  of  the  Cortical  Areas. — 
Evidently  there  is  no  direct  relation 
between  the  extent  of  a  cortical  area 
and  the  mass  of  muscles  which  it  con- 
trols; certaiidy  in  man  the  mass  of 
muscles  in  the  leg  is  five  times  greater 
than  that  in  the  arm,  and  this  many 
times  greater  than  that  in  the  face  and 
head  ;  yet  it  is  for  the  last  area  that 
the  greatest  cortical  extension  is  found. 
Mass  of  muscle  and  extent  of  cortical 
area  do  not  therefore  go  together. 

When  the  movements  effected  by 
the  muscles  in  these  several  areas  are 
considered,  we  find  that  such  move- 
ments become  more  complex  and  more 
accurate  as  we  apj)roach  the  head,  and 
it  therefore  accords  with  the  facts  to 
consider  the  extension  of  the  motor 
areas  as  correlated  with  the  refinement 
of  the  movements  which  they  control — 
a  relation  which  may  be  expressed  ana- 
tomically as  an  increase  in  the  number 
of  cortical  cells  controlling  the  related 
cel]-grou])s  in  the  cord. 

Subdivision  of  Areas. — The  areas 
which  have  been  described  are  further  subdivided,  the  subdivisions  in  the  arm- 
area  being  the  clearest.  Here  it  is  found  that  the  stimulation  of  the  upper 
part  of  the  arm-area  gives  rise  to  movements  which  start  at  the  shoulder, 


Fig.  188.— Horizontal  section  of  the  Iniinan  cere- 
brum, showing  the  internal  capsule  on  the  left 
side:  F,  frontal  region;  G,  knee  of  the  cup.siile ; 
JVC,  NC,  caudate  nucleus ;  NL,  lenticular  nucleus ; 
O,  occipital  lobe :  TO,  thalamus ;  X,  X,  lateral  ven- 
tricle. In  the  internal  capsule  the  letters  indicate 
the  probable  position  of  tlie  bundles  of  fibres  which 
upon  stimulation  give  rise  to  movements  of  the 
parts  named  or  which  convey  special  sets  of  in- 
coming impulses;  E,  eyes;  //,  head;  7,  tongue;  M, 
mouth  ;  /-, shoulder;  li.  elbow  ;  D,  digits  ;  A,  abdo- 
men; P.  hip;  A",  knee;  f,  toes;  .S  temporo-occip- 
ital  tract ;  OC,  fibres  to  the  occipital  lobe ;  OP,  optic 
radiation  (based  on  Horsley). 


CEXTI!.  1  /.    NKR  VO  US   SYSTEM. 


G91 


while  stimulation  at  the  lower  part  of  this  area  gives  rise  to  movements  first 
involvino;  the  fingers,  and  especially  the  thumb.  The  centres  from  which 
these  several  reactions  may  he  obtained  occupy,  as  Fi<j;ure  184  shows,  narrow 
fields  across  the  cortex  in  a  fr(»nt()-(K('i[)it:il  direction.  Moreover,  the  centre 
for  the  most  proximal  joint  of  the  arm  is  farthest  removed  from  that  fin*  the 
most  distal,  while  (ho  intermediate  joints  are  represented  by  their  several  cen- 
tres lying  in  reoujar  order  between  these  two.  A  similar  arrangement  appears 
in  the  subdivisions  of  the  leg,  and  in  the  face-area  as  well. 

Interpreting  these  facts  in  the  terms  of  nerve-cells  and  their  arrangement, 
it  appears  that  in  the  shoulder  centre  the  neurons  of  the  cortical  cells  that  dis- 
charge downward  pass  predominantly  to  the  efferent  cell-groups  which  in  the 
spinal  cord  directly  control  the  muscles  of  the  shoulder,  and  that  a  similar 
arrangement  obtains  for  the  other  centres  in  this  region  with  the  correspond- 
ing cell-groups  in  the  cord.  The  stimulation  of  the  different  portions  of  the 
internal  capsule  where  it  is  composed  of  bundles  of  fibres  coming  from  the 
motor  region  shows  (observations  on  orang-utang)  that  the  fibres  running  to 
the  several  lower  centres  are  here  aggregated,  and  are  ranged  in  the  same 
order  as  the  cortical  centres  themselves  (see  Fig.   188). 

Separateness  of  Areas  and  Centres. — As  we  ascend  in  the  mammalian 
series  there  is  an  increase  in  the  perfection  with  which  cells  forming  the  sev- 
eral centres  are  segregated,  though  the  areas  in  the  different  forms  tend  to 
hold  the  same  relative  positions.* 

Figures  189,  190  give  the  localizations  recently  obtained  in  the  rabbit's 
brain  by  stimulation  (Mann).     The  various  areas  occupy  a  large  propoi'tion 

of  the  cortex,  and  in  some  cases  come 
very  close  together,  so  that  they  are 
not  easily  separated    by  experiment. 


Fig.  189.— Rabbit's  brain,  dorsal  view.  The 
areas  indicated  are  those  the  stimulation  of  which 
causes  a  movement  of  the  parts  named  (Mann). 


Fig.  190.— Rabbit's  brain,  lateral  view.  The 
areas  indicated  are  those  the  stimulation  of  which 
causes  a  movement  of  the  parts  named  (Mann). 


In  the  lower  monkeys  {Macacus  sinicus)  these  cell-groups  are  segregated, 
so  that  those  associated  with  the  cervical  portion  of  the  cord  and  forming  the 
arm-area  are  much  more  together,  and  quite  separate  from  those  associated 
with  the  lumbar  region,  leg-area.  In  the  orang-utaug,^  and  to  a  greater 
extent  in  man,  a  further  separation  occurs,  so  that  they  come  to  be  surrounded 

*  Mann:  Journal  of  Anatomy  and  Phyxiolof/y,  189o,  vol.  xxx. 

*  Beevor  and  Horsley :  Proceedings  of  the  Royal  Society  of  London,  1890-91,  vol.  xlviii. 


692 


AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


Fig.  191. — Lateral  view  of  the  left  hemisphere  of  an  orang-utang,  showing  the  motor  area  about 
the  central  fissure  (Beevor  and  Horsley). 

by  parts  of  the  cortex  from  which  no  response  can  be  obtained  upon  direct 
stimulation  (see  Fig.  191). 


Fig.  192.— Lateral  view  of  a  left  human  hemisphere,  showing  the  motor  areas  in  man.  The  schema 
is  based  on  the  observations  on  the  monkey,  on  pathological  records,  human,  and  on  direct  experiments 
on  man.  It  is  to  be  remembered  that  in  the  human  brain  the  excitable  localities  are  surrounded  by 
rather  extensive  areas  not  directly  excitable  (Dana). 


Fig.  193.— Mesial  view  of  a  human  hemisphere,  showing  motor  areas.    Formed  in  the 
same  way  as  Figure  192. 

By  a  few  direct  experiments  and  by  many  pathological  observations  some- 
thing is  known  of  the  motor  centres  in  the  human  cerebral  cortex.    When 


CENTRAL    NERVOUS  SYSTEM, 


693 


the  results  are  plotted  they  give  a  distribution  such  as  is  shown  in  Figure  1 92. 
At  the  same  time  all  such  figures  are  largely  compiled  from  results  obtained 
ou  the  monkey.  It  is  here  seen  that  the  two  central  gyri  are  the  principal 
seat  of  these  areas,  and  that  it  is  ouly  along  the  great  longitudinal  fissure  divid- 
ing the  hemisjMiores  that  the  motor  areas  extend  beyond  this  limit  in  a  cephalo- 
caudad  tlirection.  Perhaps  the  relation  most  wortiiy  of  remark  is  the  com- 
paratively small  fraction  of  the  cortex  concerned  with  the  direct  control  of  the 
spinal  cord  cells.  The  motor  areas  in  man  are  elaborated,  not  so  much  by 
the  increase  in  the  number  of  the  cells  controlling  the  lower  centres,  as  by  an 
increase  in  the  number  of  those  cells  under  the  influence  of  which  these  areas 
react.     The  relation  of  the  areas  in  a  frontal  section  is  shown  iu  Figure  194. 


Fig.  194.— Frontal  section  of  the  human  cerebrum  on  the  left  side.    The  fibres  forming  the  internal 

capsule  ( ),  the  callosum  ( ),  and  the  anterior  commissure  (.  —  .—  .  —  .—)  have  been 

indicated.  T,  cortical  area  for  the  trunk ;  L,  cortical  area  for  the  leg ;  A,  cortical  area  for  the  arm ;  F, 
cortical  area  for  the  face  ;  A,  anterior  commissure ;  C,  callosum ;  CO,  optic  chiasma ;  NC,  caudate  nucleus ; 
NL,  lenticular  nucleus ;  R,  fornix ;  TO,  thalamus ;  X,  lateral  ventricle. 


Sensory  and  Motor  Regions. — If  an  attempt  is  made  to  unify  the  con- 
struction of  the  entire  cortex  by  bringing  the  motor  and  sensory  areas  under 
a  common  law,  it  must  be  based  on  the  fact  that  the  system  of  neurons  bring- 
ing impulses  to  the  motor  region  forms  part  of  the  aiferent  pathways  from  the 
skin  and  muscles.  To  Munk  ^  is  due  the  credit  of  having  from  the  first  looked 
upon  the  responsive  cortex  as  marked  off  into  areas  within  which  certain  groups 
of  afferent  fibres  terminated,  so  that  apart  from  the  sensory  areas  named  from 
the  special  senses,  he  calls  the  area  which  controls  the  skeletal  muscles  the 
"  Fuhlsphare,"  on  the  assumption  that  in  it  end  the  fibres  bringing  in  impulses 
*  Ueher  der  Functionen  der  GrosshiiTirinde,  1881. 


G94  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

from  tlie  skin  and  nnisclcs.  It  has  been  supjgested,  to  be  sure,  that  separate 
localities  were  the  seat  lor  the  dernial  and  nuisenhir  sensations.  Ferrier'  in- 
dicated the  limbic  lobe,  especially  the  hii)i)ocampal  gyrus,  wliile  Horslev  and 
Schafer'  argued  for  the  gyrus  foruicatus.  At  present  the  weight  of  evidence 
is  iu  favor  of  the  location  of  the  centres  for  dermal  and  muscular  sensations 
in  the  same  area  as  that  from  which  the  muscles  of  the  trunk  and  limbs  can 
be  made  to  contract.^  Botii  in  monkeys  and  in  man  defects  in  sensation  are 
not  permanent  after  limited  lesions  of  the  cortex,  but,  as  suggested  by  Mott, 
the  wide  distribution  of  the  incoming  impulses  would  explain  this  result. 

Thus  the  entire  portion  of  the  cortex  to  which  a  definite  function  can  be 
assigned  must  be  looked  upon  as  made  up  of  fibres  which  bring  ini[)ulses  into 
it  and  cell-bodies  which  by  their  discharge  send  impulses  to  other  divisions  of 
the  central  system  as  well  as  to  other  parts  of  the  cortex  itself  All  parts  of 
the  cortex  having  assigned  functions  give  rise  on  stimulation  to  movements, 
but  in  the  case  of  the  movements  aroused  by  the  stimulation  of  the  sensory 
areas,  so  called,  they  involve  the  contractions  of  only  those  muscles  controlling 
the  external  sense-organ,  as  the  eyeball,  external  ear,  tongue,  and  nostrils,  and, 
though  physiologically  important,  and  in  the  case  of  the  eye  at  least  reaching 
a  high  degree  of  refinement,  they  are  quantitatively  very  insignificant  as  com- 
pared with  the  responses  to  be  obtained  from  stimulating  the  "  motor  region," 
from  whicii  contractions  of  the  larger  skeletal  muscles  are  obtained.  Hence 
the  significance  of  the  usual  terms  "  sensory  "  and  "  motor  "  in  describing  the 
respective  regions. 

Multiple  Control  from  the  Cortex. — It  has  been  found  that  stimulation 
of  the  cortex  in  the  region  of  the  frontal  lobes  marked  "eye"  (Fig.  184)  was 
followed  by  movements  of  the  eye.  Schafer  *  has  shown  that  very  precise 
movements  of  the  eye  also  follow  the  stimulation  of  the  temporal  and 
various  parts  of  the  occipital  cortex.  Since  the  efferent  fibres  which  control 
the  muscles  concerned  start  from  the  cell-groups  of  the  third,  fourth,  and 
sixth  cranial  nerves,  it  w'ould  appear  most  probable  that  in  both  parts  of  the 
cortex  there  are  located  cells  the  neurons  of  which  pass  to  those  groups  and 
are  capable  of  exciting  them.  An  alternative  hypothesis — namely,  that  the 
impulses  M'hich  produced  the  movements  when  the  occipital  region  was 
stimulated,  travelled  first  to  tiie  cortical  cells  in  the  frontal  lobe  and  thence 
by  way  of  them  to  the  efferent  cell-groups — was  at  one  time  considered,  for 
the  latent  period  of  contraction  of  these  muscles  was  less  by  several  hun- 
dredths of  a  second  when  the  stimulus  was  applied  in  the  frontal  region  than 
M'hen  applied  elsewhere.  The  experiments  of  Schafer  show,  however,  that 
when  the  occipital  and  frontal  lobes  are  separated  from  one  another  by  a  sec- 
tion severing  all  the  association  fibres,  still  the  reactions  can  be  obtained  by 
stimulation  in  the  former  locality, — showing  that  the  connections  of  the  two 

>  Tht  Functions  of  the  Brain,  1876. 

*  Philosophical  Transactions  of  the  Royal  Society,  1888,  vol.  cxxix. 

*  Mott :  Journal  of  Physiology,  1894,  vol.  xv. 

*  Proceedings  of  the  Royal  Society,  1888,  vol.  xliii. 


CENT  HAL  xi:nvoj\'^  SYSTE^^.  695 

cortical   areas   witli    the  cell-o;r()nps   coiitrolliiifr  the   muscle.s  of  the  eye   are 
iiulepeiuh'nt  of"  eaeh  other. 

This  instance  of  the  ilireet  control  of  the  same  axial  c-ell-groiips  from  dif- 
ferent areas  of  the  cortex  is  analogous  to  the  control  of  efferent  cell-groups  in 
the  spinal  cord,  either  by  impulses  coming  down  from  the  cerebrum  or  by 
those  entering  the  cord  directly  through  the  dorsal  roots,  and  the  instance 
here  cited  is  typical  of  a  general  arrangement. 

Cortical  Control  Crossed. — Where  the  stimulation  of  the  cerebral  cortex 
causes  a  response  on  one  side  only,  that  response  is  on  the  side  opposite  to  the 
stimulated  hemisphere.  It  sometimes  happens,  however,  that  two  groups  of 
symmetrically  placed  muscles  both  respond  to  the  stimulus  applied  to  one 
hemisphere  only,  but  these  cases: — the  conjugate  movements  of  the  eyes; 
movements  of  the  jaw  muscles  or  those  of  the  larynx, — always  depend  on  the 
response  of  muscles  which  are  naturally  contracted  together. 

This  reaction  depends  on  the  arrangement  of  the  fibres  in  the  cord,  since 
in  lower  mammals  (dog  and  rabbit,  for  example)  it  is  not  seriously  disturbed 
by  the  removal  of  one  hemisphere. 

Course  of  Impulses  Leaving-  the  Cortex. — In  the  higher  mammals,  as 
w^ell  as  in  man,  it  is  by  way  of  the  pyramidal  fibres  that  impulses  travel  from 
the  cortex  to  the  cell-groups  of  the  axis.  The  pyramidal  tracts  by  definition 
form  in  part  of  their  course  the  bundles  of  fibres  lying  on  the  ventral  aspect 
of  the  bulb,  caudad  to  the  pons,  ventrad  to  the  trapezium,  and  between  the 
olivary  bodies.  According  to  Spitzka,^  these  are  absent  in  the  case  of  the 
elephant  and  porpoise.  It  has  been  pointed  out,  too,  that  removal  of  a  hemi- 
sphere causes  in  the  dog  and  most  rodents  a  degeneration  of  other  parts  of 
the  cord  (dorsal  columns)  than  those  occupied  by  the  pyramidal  tracts  in  man.^ 
The  fibres  passing  from  the  cortex  to  the  efferent  cell-groups  in  the  cord  do 
not,  therefore,  hold  exactly  the  same  position  in  various  mammals. 

Size  of  Pyramidal  Tracts. — It  has  been  clearly  shown  that  if  the  cross 
sections  of  the  cords  of  the  dog,  monkey,  and  man  be  drawn  of  the  same  size, 
the  pyramidal  fibres  being  indicated,  then  the  area  of  this  bundle  is  propor- 
tionately greatest  in  man  and  least  in  the  dog,  the  monkey  being  intermediate 
in  this  respect.  The  relations  thus  indicated  are  evident — namely,  that  the 
number  of  fibres  controlling  the  cell-groups  in  man  is  the  largest,  and  is  much 
larger  than  that  in  the  lower  animals. 

•  The  relative  areas  of  the  pyramidal  tract,  the  area  of  the  entire  cord  being 
taken  as  100  per  cent,  at  corresponding  levels,  are  given  by  v.  Lenhossek  ^  for 
the  following  animals  : 

Mouse 1.14  per  cent. 

Guinea-pig 3.0 

Rabbit 0.3 

Cat 7.76       « 

Man 11.87       " 

^  Journal  of  Comparative  Medicine  and  Surgery,  1886,  vol.  vii. 

^  von  Lenhossek  :  Anatomischer  Anzeiger,  1889. 

^  Diefeiner  Bau  des  Nervensystems  im  Lichte  neuester  Forschunyen,  Basel,  1893. 


69() 


AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 


This  relation  is  to  be  carefiiUy  noted,  for  with  it  is  correlated  the  degree 
of  the  disturbances  in  the  reactions  of  the  entire  nervous  system  following 
removal  of  parts  of  tiie  encephalon,  the  effect  being  slight  when  the  encephalou 
is  connected  with  the  cord  by  a  small  number  of  Hbres,  and  serious  when  the 
connection  is  by  many  fibres,  as  in  the  case  of  man  and  the  highest  mammals. 


G.  Pathways  within  the  Hemispheres. 

If  the  guiding  idea  of  the  })atliway  of  the  nervous  impulse  through  the 
central  system  had  been  rigidly  followed,  the  association  tracts  in  the  cerebral 
hemispheres  would  have  come  up  for  discussion  immediately  after  the  descrip- 
tion of  the  afferent  pathways.  The  knowledge  of  the  arrangement  in  the 
cerebral  cortex  which  has  been  obtained  from  the  stimulation  of  it  is,  how- 
ever, so  much  less  complicated  than  that  obtained  by  other  methods  of  inves- 
tigation that  the  observations  on  this  head  were  made  introductorv  to  the 
whole  matter  of  localization,  although  in  so  doing  the  strict  sequence  of  the 
presentation  was  interrupted  and  the  emphasis  put  on  the  cell-groups  which 
discharge  from  the  cortex  to  the  lower  centres. 

Determination  of  Sensory  Areas. — The  determination  of  the  sensory 
areas  in  man  has  been  through  the  study  of  brains  modified  by  destructive 
lesions  or  congenital  defects. 

The  cortical  centre  for  smell,  inferred  from  comparative  anatomy  and 
physiology  to  be  at  the  tip  of  the  temporal  lobe  and  closely  connected  with 

the  hippocampal  gyrus  and  the 
uncus,  has  been  similarly  located 
in  man  on  the  basis  of  pathologi- 
cal observations ;  but  the  evidence 
is  indirect  and  incomplete  (see 
Fig.  195).  Concerning  the  loca- 
tion of  taste  sensations  even  less 
is  known.  Both  of  these  senses, 
it  must  be  remembered,  are  insig- 
nificant in  man,  and  hence  their 
central  locations  have  not  been 
studied  with  great  care. 

On  the  other  hand,  the  cortical 
areas  for  hearing  and  sight  have 
been  located  with  much  more  precision  and  certainty. 

Damage  to  the  first  and  second  temporal  gyri  in  man  causes  deafness  in 
the  opposite  ear,  and  concordantly  conditions  of  the  ear  wdiich  early  in  life 
lead  to  deafness  and  deaf-mutism  are  accompanied  by  a  lack  of  development 
in  these  gyi'i.^  Destruction  of  these  temporal  gyri  on  one  side  always  causes 
deafness  in  the  opposite  ear,  but  there  has  not  yet  been  reported  a  case  of  com- 
plete deafness  due  to  a  double  cortical  lesion  alone. 

*  Donaldson :  American  Jownul  of  Psychology,  1891. 


Fig.  195.— Lateral  view  of  a  human  hemisphere.  The 
cortical  area  for  smell  is  shaded  (S ) ;  the  cortical  area 
for  hearing  is  shaded  ( II). 


CENTRAL    NERVOUS  SYSTEM.  697 

lu  the  case  of  the  visual  areas  in  man  there  is  tiie  same  sort  of  evidence, 
but  somewhat  more  exact.  Tlie  destruction  of  the  area  represented  by  the 
cuueus  and  the  surrounding  cortex  (see  Figures  182  and  183)  always  injures 
vision,  and  the  faihirc  of  the  eyes  to  grow  arrests  the  deveh)pment  of  this 
portion  of  the  hemisphere.' 

Hemianopsia. — It  is  found,  moreover,  that  injury  to  tlie  visual  area  in  one 
hemisphere  })roduces  usually  a  hemianopsia  or  partial  defect  of  vision  in  both 
retinas.  The  homonymous  halves  are  aifected  on  the  same  side  as  the  lesion, 
and  the  dividing  line  is  usually  vertical.  The  clinical  })icture  corresponds  to 
a  semi-decussation  of  the  optic  tract  and  the  representation  of  the  homon- 
ymous halves  of  each  retina  in  both  hemispheres.  At  the  same  time  the  rela- 
tion is  much  more  complicated  than  at  first  sight  appears,  for  the  point  of 
most  acute  vision  is  often  unaffected  in  such  cases ;  and  for  this  peculiarity  we 
have  no  anatomical  explanation.^ 

In  neither  vision  nor  hearing  do  we  find  in  man  any  subcortical  cell-groups 
capable  of  acting  as  centres ;  that  is,  after  the  removal  of  the  appropriate  cor- 
tical region  the  corresponding  sensations  and  reactions  to  the  stimuli  which 
arouse  these  sensations  are  completely  and  permanently  lost. 

From  these  facts,  therefore,  it  appears  that  the  impulses  which  give  rise  to 
visual  and  auditory  sensations  are  delivered  in  certain  parts  of  the  cerebral 
cortex,  and  unless  they  arrive  there  the  appropriate  sensations  are  absent. 

Association  Fibres. — Common  experience  shows  us  that  we  can  volun- 
tarily contract  any  group  of  muscles  in  response  to  any  form  of  stimulus — 
dermal,  gustatory,  olfactory,  auditory,  or  visual.  When,  therefore,  the  hand 
is  extended  in  response  to  a  visual  stimulus,  the  nerve-impulses  pass  first  to 
the  visual  region,  and  then  are  transferred  to  the  cortical  cells  controlling  the 
muscles  of  the  hand.  This  connection  is  accomplished  through  the  so-called 
association  fibres  of  the  cortex.  These  fibres  are  formally  described  as  those 
which  put  into  connection  different  parts  of  one  lateral  half  of  any  subdivis- 
ion of  the  central  system  (see  Fig.  196). 

The  bundles  which  are  thus  shown  in  the  cerebral  hemisphere  must  be 
looked  upon  as  typical  of  the  arrangement  throughout  the  entire  cortex,  and, 
further,  the  arrangement  in  the  cortex  is  typical  of  that  in  other  parts  of 
the  central  system.  Anatomy  would  suggest,  and  pathology  bears  out  the 
suggestion,  that  it  is  by  these  tracts  that  the  impulses  travel  from  one  area 
to  another. 

Aphasia. — The  development  of  the  ideas  bearing  on  this  subject  has  been 
slow.  After  the  publication  of  the  great  work  of  Gall  and  Spurzheim  (1810- 
19)  on  the  brain,  some  pathologists  (Bouillaud,  1825;  Dax,  1836),  especially 
in  France,  were  in  search  of  evidence  touching  the  doctrine  of  the  localization 
of  function.  At  the  same  time  the  subject  of  phrenology,  as  put  forward  by 
Grail  and  Spurzheim,  was  not  in  good  repute,  and  anything  which  looked  that 
way,  even  in  a  slight  degree,  was  generally  scouted.     Broca,  however,  pub- 

'  Donaldson :  American  Journal  of  Psychology,  1892,  vol.  iv. 
*  Noyes:  New  York  Medical  Record,  1891. 


698  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

lished  (18G1)  the  iinjxjrtant  ubservatiou  that  when  the  most  ventral  or  the 
thirtl  frontal  convolution  in  tlie  left  hemisphere  (often  designated  Broca's  con- 
vulutiou)  was  thrown  out  of  function,  the  power  of  expression  by  spoken 
words  was  lost,  and  hence  the  name  of  "  speech-centre  "  has  been  applied  to 
this  convolution. 

Since  this  discovery,  which  links  the  nourohitjy  of  the  first  part  of  the 


Fig.  196.— Lateral  view  of  a  human  hemisphere,  showing  the  bundles  of  association  fibres  (Starr): 
A,  A,  between  adjacent  gj'ri ;  B,  between  frontal  and  occipital  areas  ;  C,  between  frontal  and  temporal 
areas,  cingulum  ;  D,  between  frontal  and  temporal  areas,  fasciculus  uncinatus  ;  E,  between  occipital  and 
temporal  areas,  fasciculus  longitudinalis  inferior;  C,  X,  caudate  nucleus;  O,  T,  optic  thalamus. 

century  with  that  of  to-day,  and  also  forms  a  fundamental  observation  in  the 
modern  doctrine  of  cerebral  physiology,  many  steps  have  been  taken. 

It  was  early  observed  that  although  in  such  cases  the  capacity  for  spoken 
language  was  lost,  nevertheless  the  muscles  which  were  used  in  the  act  of 
phonation  were  by  no  means  paralyzed.  This  relation  is  due  probably  to  the 
fact  that  the  speech-centre  of  Broca  does  not  contain  cells  which  connect 
directly  with  the  lower  nuclei  controlling  the  mu.scles  of  phonation. 

The  interesting  observation  was  also  made  that  in  the  ordinary  person 
the  mu.scles  could  not  be  controlled  for  ])houation  from  the  right  hemisphere. 
Thus  the  symmetrical  portion  of  the  right  hemisphere  has  not  the  same  physi- 
ological value. 

Besides  this  lesion,  which  involves  the  cortex  frontad  to  the  motor  region 
proper,  numerous  other  lesions — namely,  those  which  involve  the  tracts  run- 
ning between  the  areas  of  special  sensation  (vision  and  hearing,  for  example), 
and  the  motor  or  expressive  region — produce  corresponding  results  (see  Fig. 
197). 

An  individual  in  whom  the  association  tracts  between  the  visual  and  motor 
areas  have  been  interrupted  can,  for  instance,  see  an  object  presented  to  him  in 


CENTRAL    NERVOUS  SYSTEM. 


699 


H 

Fig.  197.— Lateral  view  of  a  human  hemisphere  ;  cor- 
tical area  V,  damage  to  which  produces  "mind-blind- 
ness;" cortical  area  H,  damage  to  which  produces 
"  mind-deafness ; "  cortical  area  S,  damage  to  which 
causes  the  loss  of  audible  speech ;  cortical  area  W,  dam- 
age to  which  abolishes  the  power  of  writing. 


the  sense  that  he  gets  :i  visiuil   impres.sion,  but  because  of  the  interruption  of 
the  association  fibres  the  object  is  not  recognized,  and  the  impulses  reaching  this 
sensory   area   elicit    no   response 
from    the    jnuscles,    the     motor 
areas  for  which  are  located  else- 
where. 

Of  these  connections  between 
sensory  and  motor  areas  a  suffi- 
cient number  have  been  studied 
to  suggest  that  the  typical  ar- 
rangement of  the  cells  in  the 
cerebral  cortex  is  the  following : 
The  afferent  impulses  ai'e  dis- 
tributed in  the  sensory  cortical 
areas  among  several  classes  of 
cells.  Some  of  these,  through 
their  neurons,  form  association 
tracts  by  which  the  impulses  are 
transferred  from  the  sensory  to 
the    motor  regions.     Concerning 

the  exact  manner  in  which  the  impulses  arrive  at  these  associating  cells,  or 
concerning  the  layer  in  the  cortex  which  represents  them,  information  is 
meagre,  but  the  observations  on  the  distribution  of  the  fibres  in  the  cortex 
suggest  that  the  short  association  tracts  must  be  at  the  level  of  the  superficial 
fibre-layers,  while  the  longer  tracts  extend  far  below  the  cortex,  and  would 
most  naturally  be  associated  with  the  deepest  layers  of  cells.^  Upon  attempt- 
ing to  carry  out  this  arrangement  to  anything  like  the  completeness  demanded 
by  the  physiological  reactions,  it  is  necessary  to  postulate  the  existence  of  such 
pathways  between  each  sensory  and  each  motor  area,  and  thus  there  must  be  a 
pathway  extending  from  every  sensory  to  every  motor  area.  This  arrange- 
ment is  of  course  to  be  pictured  as  modified  in  several  ways. 

In  the  first  place,  the  connection  between  a  given  motor  and  a  given  sen- 
sory area  is  by  no  means  proportionate  in  the  several  instances.  The  connec- 
tion, for  example,  between  the  visual  area  and  the  motor  area  for  the  arm  is 
probably  represented  by  more  nerve-elements,  and  these  better  organized,  than 
the  connection  between  the  gustatory  area  and  that  for  the  movements  of  the 

leg. 

When,  therefore,  it  is  said  that  such  connections  exist,  it  must  be  added 
always  that  the  nexus  is  different  for  the  several  regions  concerned,  and,  what 
is  more,  that  in  man,  at  least,  it  is  different  for  the  two  hemispheres. 

The  Relative  Functions  of  the  Two  Hemispheres. — "When  the  subject 
is  right-handed,  it  appears  that  in  man  injury  to  the  left  cerebral  hemisphere 
is  more  productive  of  disturbance  than  injury  to  the  right  hemisphere.  At 
the  same  time,  lesion  of  the  left  hemisphere  is  far  more  frequent  than  that  of 

^  Andriezen  :  Brain,  1894. 


700  AiY  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

the  right.  So  far  as  can  bo  judged  from  experiments  ou  man,  tlie  higher 
sense-organs,  the  eye  and  the  ear,  are  more  perfect,  physiologically,  on  the  right 
side.  Since  the  connection  of  the  sense-organs  is  largely  with  the  cortex  of  the 
contralateral  hemisphere,  this  nieans  tliat  the  impulses  going  mainly  to  the  left 
hemisphere  are  better  differentiated  than  those  going  to  the  right.  For  these 
impulses  to  reach  a  motor  area  in  the  same  hemisphere  would  ap|)ear  to  be 
easier  than  to  reach  the  corresponding  area  on  the  opposite  side,  and  it  is  thus 
possible  to  see  how,  on  the  basis  of  the  slightly  better  sense-organs  of  the  right 
side,  the  left-brained  man  might  have  been  developed.  The  observations  of 
Flechsig'  on  the  pyramidal  tracts  also  show  that  this  tract,  before  mcdullation 
at  least,  may  be  unevenly  developed  on  two  sides  of  the  cord,  and  the  ease  of 
control  may  thus  be  rendered  unequal — a  condition  which  must  be  dominant 
in  the  determination  of  the  side  of  the  body  which  shall  be  exercised. 

Doubtless  there  are  other  factors  concerned,  and,  moreover,  it  has  yet  to  be 
demonstrated  that  the  sense-organs  of  the  left  side  are  superior  in  persons  left- 
handed.  Nor  has  the  inequality  of  the  crossed  pyramidal  tracts  in  the  adult 
been  established  wath  reference  to  these  questions.  Be  this  as  it  may,  the 
lesions  which  cause  aphasia  or  apraxia  (inability  to  determine  the  meaning  and 
use  of  objects)  arc  predominantly  in  the  left  hemisphere  in  persons  who  are 
right-handed,  while  there  is  some  evidence  that  the  right  hemisphere  is  more 
important  in  left-handed  persons. 

In  the  adult,  damage  to  one  hemisphere  is  usually  followed  by  a  permanent 
loss  of  function,  but  this  loss  may  be  transient  when  the  lesion  occurs  in  the 
very  young  subject,  so  that  during  the  growing  period  the  sound  hemisphere 
can  in  a  measure  take  up  the  function  of  the  one  that  has  been  injured. 

Assuming  this  general  plan  for  the  arrangement  of  the  cortex  to  be  correct, 
it  is  evident  that  a  given  cell,  the  neuron  of  which  forms  part  of  the  pyrami- 
dal tract,  must  in  the  human  cortex  be  subject  to  a  large  series  of  impulses 
coming  to  it  over  as  many  paths.  Schematically,  it  would  be  as  represented 
in  Figure  198. 

The  discharging  cell  may  be  destroyed ;  then,  of  course,  the  muscles  con- 
trolled by  it  become  more  or  less  paralyzed.  The  discharging  cell  may,  how- 
ever, remain  intact,  but  the  pathways  by  which  impulses  arrive  at  it  be  dam- 
aged. This  is  the  type  of  lesion  which  produces  symptoms  of  aphasia.  When 
an  interruption  of  associative  pathways  occurs  some  one  or  more  of  these  tracts 
is  broken,  and  hence  this  discharging  cell  does  not  receive  a  stimulus  adequate 
to  cause  a  response. 

The  physiological  simplicity  of  the  elements  in  any  part  of  the  central  sys- 
tem, either  when  different  portions  of  the  system  from  the  same  animal  or 
when  the  corresponding  portions  of  different  animals  are  compared,  depends 
on  the  number  of  paths  by  which  the  impulses  are  brought  to  the  discharging 
cells. 

Composite  Character  of  Incoming  Impulses. — To  these  conclusions 
based  on  the  anatomy  are  to  be  added  others  suggested  by  clinical  observa- 
'  Leilungsbahnen  im  Qehim  und  Rikkenmark,  1876. 


CENTRAL    NERVOUS  SYSTEM. 


701 


tious.  That  a  patient  suttering  from  a  lesion  between  the  visual  and  motor 
areas  may  be  able  to  recognize  an  object  and  to  indicate  its  use,  it  is  sometimes 
necessary  that  the  object  shall  apjieal  to  several  senses.  For  example,  the 
name  and  use  of  a  knife,  when  seen  alone,  may  not  be  recalled,  but  when  it  is 


rtotoi-T' 


Fig.  198.— Schema  showing  in  a  purely  formal  manner  the  different  sort  of  afferent  impulses  which  may 
influence  the  discharge  of  a  cortical  cell. 


taken  into  the  hand — that  is,  when  the  dermal  and  muscular  sensations  are 
added  to  the  visual  one — the  response  is  made,  though,  acting  alone,  any  one 
set  of  sensations  is  inadequate  to  produce  this  result. 

Just  where  the  block  occurs  in  such  a  case  it  is  not  possible  to  say  with 
exactness,  but  the  lesion  lies,  as  a  rule,  between  the  sensory  and  motor  areas 
concerned,  and  by  the  damage  to  the  pathway,  it  is  assumed  that  one  or  more 
groups  of  impulses  are  so  reduced  in  intensity  that  they  are  alone  insufficient 
to  })roduce  a  reaction ;  and  therefore  it  is  only  when  the  impulses  from  several 
sides  are  combined  that  a  response  can  be  obtained. 

Variations  in  Association. — It  is  a  familiar  fact  that  individuals  differ 
in  no  small  degree  in  the  acuteness  of  their  senses — i.  e.  in  the  power  to  dis- 
criminate small  diiferences,  and  this,  too,  when  the  sense-organs  are  normal. 
Further,  the  powers  of  those  best  endowed  are  by  no  means  to  be  attained  by 
others,  however  conscientious  their  training.  Moreover,  the  central  sensory 
pathways  differ  widely.  The  inference  is  fair,  therefore,  that  those  who  think 
in  terms  of  visual  images,  as  compared  with  those  who  think  in  auditory 
terms,  do  so  by  virtue  of  the  fact  that  in  the  former  case  the  central  cells  con- 


702  .l.V  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

cenicd  iu  vision  arc  distinctly  the  bctlvr  oPiranizod,  wliilr  in  the  latter  ease  it 
is  those  concerned  in  hearinL;:. 

In  the  same  way,  tlie  power  ot"  expression  varies  iu  an  etjually  marked 
degree,  and  the  capacity  for  the  expression  of"  ideas  by  means  of  the  hand  iu 
writing  is  by  no  means  necessarily  equal  to  the  power  of  expression  by  means 
of  spoken  words.  In  the  former  case  we  have  the  results  of  the  play  of  im- 
pulses from  the  several  sensory  centres  on  the  motor  area  for  the  hand,  and 
this  is  reinforced  by  the  sight  of  that  which  has  been  written,  whereas  in  the 
latter  case  impulses  from  these  same  sensory  centres  play  upon  the  area  wiiich 
controls  the  muscles  of  phonation,  and  the  reaction  is  reinforced  by  the  sound 
of  the  words  uttered.  Of  course  in  the  case  of  a  defective,  like  a  blind-deaf- 
mute,  the  expression  of  thought  is  by  movements  of  the  fingers,  and  this  is  rein- 
forced by  the  tactile  and  muscular  sensations  which  follow  these  movements. 

It  is  not  by  any  means  to  be  expected  that  the  anatomical  connections 
which  render  such  reactions  possible  will  be  equally  perfect  for  the  different 
sensori-motor  combinations  or  the  same  combinations  in  different  persons,  and 
hence  the  powers  of  the  individual  will  be  modified  by  the  perfection  of 
these  paths  in  the  several  cases.  From  this  it  also  follows  that'  the  same 
lesion  as  grossly  determined  will  not  produce  identical  results  in  the  two  per- 
sons, for  it  will  not  efRnit  the  damage  of  structural  elements  which  are  strictly 
comparable. 

Path-w^ays  through  Gray  Matter. — Moreover,  what  is  true  of  the  spinal 
cord  is  also  probably  true  of  the  cortex — viz.  that  while  the  long  tracts  are 
the  usual  and  preferred  pathways  between  centres,  shorter  tracts  formed  by  a 
large  series  of  cells  often  serve  as  the  pathway,  and  impulses  may  under  some 
conditions  find  their  way  from  one  part  of  the  cortex  to  another  by  way  of 
these  more  complex  tracts. 

Latent  Areas. — It  has  been  plain  from  an  examination  of  the  foregoing 
figures,  as  well  as  from  the  descriptions,  that  there  must  be  a  large  portion  of 
the  cortex  which,  so  far  as  has  been  observed,  may  be  called  latent.  These 
regions,  which  include  nearly  the  entire  ventral  surface  of  the  hemispheres,  a 
large  part  of  the  mesial  surface,  and  on  the  dorsal  and  lateral  aspects  a  large 
portion  of  the  frontal  and  temporal  lobes,  certainly  require  a  word. 

The  various  forms  of  investigation  yield  negative  results.  The  speech- 
centre  is,  strictly  speaking,  neither  a  motor  nor  a  sensory  portion  of  the  cortex, 
and  yet  when  it  is  damaged  the  function  of  speech  is  disturbed.  We  have 
come  to  look  upon  the  speech-centre  as  containing  cells  by  way  of  which  im- 
pulses pass  to  the  centres  controlling  the  muscles  of  phonation.  This  relation 
su2:s:ests  that  the  rest  of  the  cortex  called  latent  mav  act  in  a  similar  manner, 
and  that  by  way  of  it  pass  impulses  which  modify  the  discharge  of  the  motor 
areas  proper.  From  any  one  portion  of  the  latent  area,  however,  the  connec- 
tions are  not  massive  enough  to  permit  of  impulses  which  will  cause  a  contrac- 
tion, and  hence  these  impulses  coming  from  one  locality  to  a  discharging  cell 
form  only  a  fraction  of  the  impulses  which  control  it ;  and  for  this  reason  the 
significance  of  these  parts  fails  to  be  clearly  evident  upon  direct  experiment. 


CENTRAL  NERVOUS  SYSTEM.  703 

The  corlex  of"  tlio  froiilal  lohcs  has  some  connections  with  the  nuclei  of  the 
pons,  and  so  with  the  cerehelhnn.  The  more  recent  experiinents  on  tlie  func- 
tions of  this  region  are  by  Bianchi  ^  and  Grosglil<,^  the  former  on  monkeys 
and  dogs  and  the  latter  on  dogs  alone. 

These  experimenters  found  that  the  removal  of  one  frontal  lobe  is  com- 
paratively insignificant  in  its  effects,  while  when  both  are  removed  the  change 
is  profound.  On  removing  the  frontal  lobe  on  one  side  only  there  is  no  dis- 
turbance of  vision,  hearing,  intelligence,  or  character.  There  do  occur  both 
sensory  and  motor  disturbances,  but  these  are  for  the  most  part  transient.  On 
the  side  o])posite  to  the  lesion  there  is  in  the  limbs  a  blunting  of  all  sensations 
and  some  paresis.  Moreover,  there  is  a  hyperaesthesia  combined  with  a  paresis 
of  the  muscles  of  the  neck  and  trunk  which  move  these  parts  away  from  the 
side  of  the  lesion. 

These  several  effects  of  the  operation  tend  to  pass  off,  and  if  then  the 
remaining  frontal  lobe  be  removed  from  a  dog  or  monkey,  not  only  do  the 
symptoms  just  described  appear  on  the  other  side  of  the  body,  but  still  more 
fundamental  changes  occur.  A  ceaseless  wandering  to  and  fro,  such  as  Goltz"* 
observed  in  those  dogs  in  which  the  anterior  half  of  the  brain  had  been 
removed,  characterizes  the  animals ;  curiosity,  affection,  sexual  feeling,  pleasure, 
memory,  and  the  capacity  to  learn  are  at  the  same  time  abolished,  and  the 
expressions  of  the  animal  are  those  of  fear  and  excessive  irritability.  That, 
therefore,  the  frontal  lobes  play  an  important  role  in  the  total  reactions  of  the 
central  system  is  amply  evident,  but  this  by  no  means  justifies  the  conclusion 
that  they  are  the  seat  of  the  intelligence. 

H.  Comparative  Physiology  of  the  Central  Nervous  System. 

For  the  better  comprehension  of  the  conditions  found  in  man  and  the 
monkey,  it  will  be  of  importance  to  briefly  review  the  comparative  physiology 
of  the  central  nervous  system  in  vertebrates  below  the  monkey.  This  system 
in  the  lower  vertebrates  is  usually  composed  of  a  very  much  smaller  number 
of  cells  than  is  found  in  that  of  man,  and  also  cephalization,  or  the  massing 
of  the  elements  toward  the  head  and  in  connection  with  the  principal  sense- 
organs,  has  gone  on  to  a  far  less  extent. 

It  must  not  be  thought,  however,  because  it  is  the  custom  to  emphasize 
the  reflex  activities  of  the  lower  vertebrates,  and  to  show  that  these  reflexes 
can  be  carried  out  even  by  fractions  of  the  spinal  cord  alone,  that  therefore 
the  spinal  cord  is  particularly  well  developed  in  them.  Comparative  anatomy 
shows  in  the  lower  vertebrates  a  simplicity  in  the  structure  of  the  cord  quite 
comparable  with  that  found  in  the  brain,  and  as  we  ascend  the  vertebrate 
series  both  parts  of  the  central  system  increase  in  complexity.  In  this  increase, 
however,  the  cephalic  division  takes  the  lead,  and  further,  by  means  of  the 
fibre-tracts,  the  cell-groups  in  the  cord  are  more  and  more  brought  under  the 

'  Archives  Italiennes  de  Biologie,  1895,  t.  xii. 
'  Archivfiir  Anatomie  und  Physiologie,  1895. 
'  Ueber  die  Verrichtangen  des  Grosshinis,  1881. 


704  ^iV^  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

influence  of"  the  special  sense-organs  which  connect  with  the  encephalon.  The 
physiological  reactions  of  the  higher  vertebrates  are  especially  modified  hy  this 
latter  arrangement.  It  is  therefore  true  that  the  cord,  as  well  as  the  brain,  is, 
in  man,  more  complicated  anatomically  than  in  any  of  the  lower  forms,  and 
this  in  spite  of  the  fact  that  the  independent  reactions  of  the  human  cord  are 
so  imperfect. 

One  result  of  this  concentration  of  the  nerve-elements  toward  the  head, 
and  the  dependence  of  the  rest  of  the  system  on  the  encc]>halon,  is,  as  we  shall 
see,  that  the  cephalic  division  becomes  thereby  a  more  necessary  portion  of  the 
pathway  for  the  incoming  impulses,  and,  conversely,  as  cephalization  fails  to 
take  place  the  several  parts  of  the  system  remain  more  independent. 

Reactions  of  Portions  of  Spinal  Cord. — When  an  amphioxus  is  cut 
into  two  pieces  and  then  put  back  in  the  water,  a  slight  dermal  stimulus 
causes  in  both  of  them  locomotory  movements,  such  as  are  made  by  the 
entire  animal. 

When  a  shark  (Scyllium  canicula)  is  beheaded  the  torso  swims  in  a  co-ordi- 
nated manner  when  returned  to  the  water.  Separation  of  the  cord  from  the 
brain  does  not  deprive  a  ray  {Torpedo  oculata)  of  the  pow'er  of  perfect  loco- 
motion. The  same  is  true  of  the  ganoid  fish.  In  the  case  of  the  cyclostome 
fish  (Petromyzon)  the  beheaded  trunk  is,  in  the  water,  inactive,  and,  on  gentle 
mechanical  stinnilation  it  makes  inco-ordinated  responses,  but,  put  in  a  bath 
formed  by  a  3  per  cent,  solution  of  picro-sulphuric  acid,  locomotion  under  the 
influence  of  this  strong  and  extensive  dermal  stimulus  is  completely  performed. 
In  the  case  of  the  eel  the  responsiveness  even  to  the  picro-sulphuric  acid  bath 
is  evident  in  the  caudal  part  of  the  body  alone.  In  the  bony  fish  this  power 
in  the  spinal  cord  has  not  been  observed.^ 

In  these  experiments  the  central  system  is  represented  by  the  entire  spinal 
cord  with  the  associated  nerves,  or  by  some  fraction  of  it,  but  so  simple,  con- 
stant, and  independent  are  the  reactions  of  the  cord  under  normal  conditions 
that  a  strong  stimulus  is  able  to  elicit  the  characteristic  responses  from  even  a 
fragment  of  the  system.  The  higher  we  ascend  in  the  vertebrate  series  the 
less  evident  do  the  independent  powers  of  the  cord  become. 

For  the  determination  of  the  functions  of  the  several  parts  of  the  nervous 
svstem  it  is  possible  to  employ  in  animals  the  method  of  removal  as  well  as 
the  method  of  stimulation.  The  doctrine  of  localization  was  at  one  time 
crudely  expressed  by  the  statement  that  a  cortical  centre  was  one  the  stimula- 
tion of  which  produced  a  given  reaction,  and  the  removal  of  which  abolished 
this  same  reaction.  Goltz*  soon  showed  that  in  the  dog  the  removal  of  even 
an  entire  hemisphere  did  not  cause  a  ]iaralysis  of  the  muscles  on  the  opposite 
side  of  the  body,  although  others  had  shown  that  a  stinmlation  of  certain  por- 
tions of  the  cortex  of  the  hemisphere  would  cause  these  muscles  to  contract. 
It  was  argued,  therefore — and  quite  rightly — that  the  cortical  centres  of  the 
dog  did  not  completely  answer  to  the  definition. 

^  Steiner :  Die  Functionen  des  Centralnervensystems  und  ihre  Phylogenese,  2te  Ablh.,  "  Die 
Fische,"  1888.  ^  Ueber  die  Verficklungen  des  Grosshims,  1881. 


CENTRAL    NERVOUS  SYSTEM.  705 

From  the  experimental  work  of  the  strict  localizationists  like  Hitzig/ 
Munk,^  and  Fcrricr,^  and  t'roni  the  work  of  tiiose  who,  like  GoUz^  and  Loeb/ 
denied  a  strict  localization  in  the  cerebral  hemispheres,  several  important  points 
of  view  have  been  developed. 

In  the  first  instance,  anatomy  indicates  that  in  the  central  system  there  are 
but  few  localities  which  consist  only  of  one  set  of  cell-bodies,  together  with 
the  fibres  coming  to  these  bodies  and  going  from  them.  Almost  every  part 
has  both  more  than  one  set  of  connections  with  other  parts  and  also  fibres 
passing  through  it  or  by  way  of  it  to  other  localities.  Hence  in  removing  any 
part  of  the  hemispheres,  for  instance,  not  only  are  groups  of  cell-bodies  taken 
away,  but  a  number  of  extra  pathways  are  interrupted  at  the  same  time,  and 
thus  the  damage  extends  beyond  the  limits  of  the  part  removed.  Moreover, 
when  any  portion  of  the  central  system  has  been  removed  there  is  a  greater  or 
less  amount  of  disturbance  of  function  following  immediately  after  the  opera- 
tion ;  but  this  disturbance  partially  passes  away.  There  are  thus  "  temporary  " 
as  contrasted  with  "permanent"  effects  of  the  lesion,  and  these  require  to  be 
sharply  distinguished,  because  it  is  the  permanent  loss  which  is  alone  sig- 
nificant in  these  experiments.  Finally,  it  has  been  made  clear  that  neither  the 
relative  nor  the  absolute  value  of  any  division  of  the  central  system  is  fixed, 
but  depends  on  the  degree  to  which  cephalization  has  progressed,  or,  to  use  the 
more  common  measure,  the  grade  of  the  animal  in  the  zoological  series,  both 
expressions  signifying  an  increase  in  the  connections  between  the  cerebrum 


Fig.  199.— Schema  of  the  encephalon  of  a  bony  fish— embryonic  (Edinger).    The  vertical  black  line 
marks  off  the  structures  in  front  of  the  thalamus. 

and  the  lower  centres.  The  age  of  the  animal  on  which  the  operation  has 
been  made  is  also  of  no  small  importance  in  this  respect.  These  relations 
can  be  illustrated  by  reference  to  several  experiments. 

Removal  of  Cerebral  Hemispheres. — If  from  a  bony  fish  the  cerebral 

'  TTntersuchungen  iiber  das  Gehirn,  Berlin,  1874. 

*  Ueber  die  Functionen  der  Grosshirnrinde,  Berlin,  1881. 
'  The  Functions  of  the  Brain,  London,  1876. 

*  Ueber  die  Ven-ichtungen  des  Grosshim.%  Bonn,  1881. 

*  Arch.  fUr  die  gesammle  Physiologic,  Bde.  33  u.  34,  1884. 
45 


70G 


AN  AMERICAN   TEXT-HOOK    OF    PII YSIOLOC  Y. 


liemisphert's  (inclii(liii«;  the  coi-jjora  striata  as  well  as  the  iiiajitlc)  be  removed, 
the  animal  apparently  suffers  little  ineonveniencc".  The  movements  are  undis- 
turbed ;  sueh  fish  play  together  in  the  usual  manner,  discriminate  between  a 
worm  and  a  bit  of  sti'ing,  and  among  a  series  of  colored  wafers  to  which  they 
rise,  always  select  the  red  ones  first.'  In  these  fish  the  eye  is  the  controlling 
sense-organ,  and,  as  will  be  recognized  (see  Fig,  199),  the  operation  has  by  no 
means  damaged  the  primary  centres  of  vision. 

Quite  different  is  the  result  when  the  cerebrum  is  removed  from  a  shark.^ 
Tn  this  case,  although  the  eyes  are  intact,  the  animal  is  reduced  to  comj)lete 
quiescence ;  yet  on  the  whole,  the  nervous  system  of  the  shark  is  rather  less 
well  organized  and  more  simple  than  that  of  the  bony  fish.  The  astonishing 
effect  produced  is  explained  by  a  second  experiment  (see  Fig.  200).     If  the 


Fig.  'JOO.— Schema  of  the  cncephalon  of  a  cartilaginous  fish  (Edinger).    The  vertical  lilack  line  marks 
oif  the  striatum  and  pars  olfactorius,  which  lie  in  front  of  the  thalamus. 

olfactory  tract  be  severed  on  one  side,  no  marked  disturbance  in  the  reactions 
of  the  shark  is  to  be  noticed ;  when,  however,  both  tracts  are  severed,  the 
shark  acts  as  though  deprived  of  its  cerebrum.  From  this  it  appears  that 
the  removal  of  the  principal  sense-organ,  that  of  smell,  is  the  real  key  to  the 
reactions,  and  that  the  responsiveness  of  the  fish  is  reduced  in  the  first  instance, 
becau.se  in  this  case  it  has  been  deprived  of  the  impulses  coming  through  the 
principal  organs  of  sense,  and  in  the  second  the  removal  of  the  cerebrum  is 
mainly  important  because  the  cerebrum  contains  the  pathway  for  the  impulses 
from  the  olfactory  bulbs  to  the  cell-groups  which  control  the  cord. 

Passing  next  to  the  amphibia  as  represented  by  the  frog,  there  are  seveml 
series  of  observations  on  the  physiological  value  of  the  divisions  of  the  central 
system.  Schrader'^  finds  the  following:  Removal  of  the  cerebral  hemispheres 
only^  the  optic  thalami  being  uninjured,  does  not  abolish  the  spontaneous  activ- 
ity of  the  frog.  It  jumps  on  the  land  or  swims  in  the  water,  and  changes  from 
one  to  the  other  without  special  stimulation.  It  hibernates  like  a  normal  frog, 
retains  its  sexual  instincts,  and  can  feed  by  catching  passing  insect.s,  such  as  flies 

'  Steiner  :  Die  Funclionen  der  Centralnervensystems,  1888.  ^  Steiner,  loc  nt. 

'  Archiv  fur  die  gesammte  Physiologic,  1887,  Bd.  xli. 


CENTRAL    A  Eli  VO  US  SYSTEM. 


707 


(see  Fig.  201).     A  frog  without  its  hemispheres  is  therefore  capable  of  doing 
several  things  apparently  in  a  spontaneous  way.    Such  frogs  balance  themselves 


ii  \ 


Fir;  '^01  -Frog-s  brain;  the  parts  in  dotted  outline  have  been  removed:  A,  brain  intact;  B,  cerebral 
hemispheres  removed;  C,  cerebral  hemispheres  and  thalami  removed ;  i),  cerebellum  removed;  £,  two 
sections  through  the  optic  lobes  ;  F,  two  sections  through  the  right  half  of  the  bulb  (Sterner). 


when  the  support  on  which  they  rest  is  slowly  turned,  moving  forward  or  back- 
ward as  the  case  demands  in  order  to"  maintain  their  equilibrium.     In  doing 


708  AX  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

this  the  frog  tends  first  to  move  the  liead  in  the  direction  opposite  to  the  motion 
of  the  support,  and  then  to  follow  with  movements  of  the  body.  If  the  optic 
thalanii  are  removed  (Fig.  201,  C),  the  power  of  balancing  is  lost,  because, 
although  the  movements  of  the  head  still  occur,  those  of  the  body  are  abolished. 
A  frog  thus  operated  on  and  deprived  of  the  hemispheres  and  thalami  exhibits 
the  lack  of  spontaneity  which  is  usually  described  as  following  the  loss  of  the 
hemispheres  alone,  but  which  is  not  a  necessary  consequence  of  this  operation, 
as  the  preceding  experiments  show. 

A  frog  possessed  of  the  mid-brain  and  the  parts  behind  it  (Fig.  201,  C) 
will  croak  when  stroked  on  the  back.  When  the  optic  lobes  have  been 
removed  this  reaction  becomes  more  difficult  to  obtain,  but  it  is  not  necessarily 
abolished,  neither  is  the  characteristic  fling  of  the  legs  in  swimming.  At  the 
same  time,  a  frog  with  its  optic  lobes  can  direct  both  its  jumping  and  swim- 
ming movements  according  to  light  stimuli  acting  through  the  eye,  jumping 
around  and  over  obstacles  which  form  a  shadow  in  its  path,  and  climbing  out 
of  the  swimming  tank  on  the  lighter  side.  This  power  is  lost  when  the  optic 
lobes  have  been  removed. 

"When  the  anterior  end  of  the  bulb  (pars  commissuralis — Stieda)  has  been 
also  Removed,  then  the  frog  becomes  incessantly  active,  creeping  about,  and  not 
coming  to  rest  until  he  has  run  himself  into  some  corner.  Schrader  found  such 
frogs  capable  of  clambering  over  the  edge  of  a  box  18  centimeters  high.  They 
are  at  a  loss  when  the  edge  of  the  box  has  been  finally  attained,  and  vainly 
reach  into  space  from  this  position.  In  the  water  they  swim  "  dog-fashion," 
and  only  upon  special  stimulation  do  they  make  a  spring. 

If  more  of  the  bulb  is  removed,  the  bearing  of  the  frog  departs  more  and 
more  from  the  normal,  and  is  only  temporarily  regained  in  response  to  strong 
stimulation ;  nevertheless,  co-ordinated  movements  can  be  obtained  when  the 
bulb  down  to  the  calamus  scriptorius  has  been  removed,  and  only  when  the 
movements  of  the  arms  are  directly  affected  by  the  damage  of  the  upper  end 
of  the  cord  does  the  inco-ordination  become  constant. 

A  section  through  the  optic  lobes  at  a  (Fig.  201,  E)  puts  the  frog  in  a  con- 
dition similar  to  that  following  the  isolated  removal  of  the  lobes,  while  a  sec- 
tion at  b  has  the  curious  effect  of  causing  the  animal  to  move  backward  upon 
stimulation  of  the  toes. 

When  the  small  ridge  which  forms  the  cerebellum  in  the  frog  has  been 
removed,  a  slight  tremor  of  the  leg-muscles  and  a  loss  of  precision  in  jumping 
are  the  only  defects  noted  (Fig.  201,  D).  These  results  hold  for  symmetrictil 
removal  of  the  divisions  of  the  encephalon.  When  the  removal  is  unsymmet- 
rical  in  the  inter-brain,  mid-brain,  or  bulb  (Fig.  201,  F,  a  and  h),  there  is 
more  or  less  tendency  to  forced  positions  or  forced   movements. 

As  a  rule,  action  is  most  vigorous  on  the  side  of  the  body  associated  with 
the  greater  quantity  of  nerve-tissue.  This  relation  appears  as  a  natural  result 
of  the  greater  effectiveness  of  the  incoming  impulses  when  entering  a  larger 
group  of  central  cells.  Indeed,  the  removal  of  the  different  portions  of  the 
central  system  in  the  frog  is  accompanied  l)y  a  progressive  loss  in  responsive- 


CENTRAL    NERVOUS  SYSTEM.  709 

ness,  stronger  and  stronger  stimuli  being  recjuired  lo  induce  a  reaction,  Tliis 
holds  true  down  to  the  anterior  end  of"  the  bulh,  the  removal  of  wliicli,  on  the 
contrary,  sets  free  the  lower  centres,  so  that  the  frog  becomes  incessantly  active. 
Just  how  this  release  is  effected  is  not  easy  to  explain,  but  further  removal  is 
again  followed  by  the  loss  of  responsiveness. 

Passing  next  to  the  bird,  as  represented  by  the  pigeon,  the  observations  of 
Schrader  are  the  most  instructive.^  The  removal  of  the  hemispheres  from  the 
bird  (see  Fig.  202)  involves  taking  away  the  mantle  and  the  basal  ganglia,  the 


Fig.  202.— Schema  of  the  encephalon  of  a  bird  (Edinger).    The  oblique  black  line  marks  off  the 
structures  in  front  of  the  thalamus. 

chiasma  and  the  optic  nerves  being  left  intact.  For  the  first  few  days  after 
operation  the  bird  is  in  a  sleep-like  condition.  Next  the  sleep  becomes  broken 
into  shorter  and  shorter  periods,  and  then  the  bird  begins  walking  about  the 
room.  From  the  beginning  its  movements  are  directed  by  vision;  slight 
obstacles  it  surmounts  by  flying  up  to  them,  larger  ones  it  goes  around.  In 
climbing  its  movements  are  co-ordinated  by  the  sense  of  touch,  and  the  normal 
position  of  the  body  is  maintained  with  vigor.  The  birds  which  walk  about 
by  day  remain  quiet  and  asleep  during  the  night.  In  flying  from  a  high 
place  the  operated  pigeon  selects  the  point  where  it  will  alight,  and  prefers  a 
perch  or  similar  object  to  the  floor. 

A  reaction  to  sound  is  expressed  by  a  start  at  a  sudden  noise,  like  the 
explosion  of  a  percussion  cap. 

Pigeons  without  the  cerebrum  do  not  eat  voluntarily,  though  the  presence 
of  the  frontal  portions  of  the  hemispheres  is  sufficient  to  preserve  the  reaction. 

In  a  young  hawk  slight  damage  to  the  frontal  lobes  abolished  for  the  time 
the  use  of  the  feet  in  the  handling  of  food,  and  thus  abolished  in  this  way  the 
power  of  feeding  as  well  as  that  of  standing. 

With  the  loss  of  the  cerebrum  the  pigeon  does  not  lose  responsiveness  to 
the  objects  of  the  outer  world,  but  they  all  have  an  equal  value.  The  bird  is 
^  Archiv  fur  die  gesammte  Physiologie,  1888,  Bd.  xliv. 


710  AX  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

neither  attracted  nor  repelled,  save  in  so  far  as  the  selection  of  the  points  toward 
which  it  will  fly  is  an  example  of  attraction.  Sexual  and  maternal  reactions 
both  disappear,  and  neither  fear  nor  desire  is  evident. 

In  ascendini;  the  mammalian  series  the  removal  of  the  cerebrum  becomes  a 
matter  of  increasing  difficulty.  The  reasons  for  this  are  several,  and  reside  in 
the  increasing  size  of  the  blood-vessels  and  the  nutritive  complications  depend- 
ent on  the  increase  in  the  mass  of  the  cerebrum,  as  well  as  in  the  greater  physi- 
ological importance  of  this  division.  Goltz '  has  been  able  by  repeated  ope- 
rations to  remove  the  entire  cerebrum  of  a  dog,  and  still  to  keep  the  animal 
alive  and  under  observation  for  eighteen  months,  at  the  end  of  which  time  the 
animal,  though  in  good  health,  was  killed  for  further  examination.  This  dog 
was  blind,  though  he  blinked  when  a  bull's-eye  lantern  was  suddenly  flashed 
in  his  face.  He  could  be  awakened  by  a  loud  sound,  and  when  awake  re- 
sjionded  to  such  sounds  when  intense  by  shaking  the  head  or  ears.  This 
would  not,  however,  be  complete  proof  that  he  could  hear.  The  sense  of  taste 
was  so  far  present  that  meat  soaked  in  quinine  was  rejected  after  tasting. 
Tactile  stimuli  and  those  involving  the  muscle  sense,  as  in  the  case  when  the 
animal  M'as  lifted,  caused  him  to  struggle  and  to  bite  in  the  direction  of  the 
irritiition.  These  reactions  were  modified  according  to  the  locality  of  the  stim- 
ulus.    The  power  to  make  movements  expressive  of  pain  was  still  present. 

On  the  motor  side  the  dog  was  capable  of  such  highly  complicated  acts  as 
walking,  standing,  and  eating,  and  in  these  operations  was  guided  by  the  muscle 
sense  and  that  of  contact.  The  sexual  instincts  were  lost,  but  the  animal  was 
excessively  active,  and  became  more  and  more  excited  when  ready  to  defecate 
or  when  hungry. 

The  examination  of  the  brain  showed  that  all  parts  in  front  of  the  mid- 
brain had  been  removed  or  Avere  degenerated,  so  that  the  defects  were  due  to  a 
removal  of  rather  more  than  the  cerebrum  j^roper. 

Emotions,  feelings,  conscious  sensations,  or  the  capacity  to  learn  were  entirely 
wanting  in  this  dog,  and  its  reactions  were  those  of  a  very  elaborate  machine. 

If  we  compare,  now,  the  effects  of  the  removal  of  the  cerebral  hemisphere 
in  the  bony  fish,  the  pigeon,  and  the  dog,  we  see  that  the  results  of  the  operation 
are  progressively  more  disturbing  as  we  pass  up  the  series.  In  the  higher 
animals  the  effects  are  more  often  fatal,  the  disturbance  immediately  following 
is  much  more  severe,  the  return  of  function  slower,  and  the  permanent  loss 
greater.  As  a  partial  exception  to  the  above  statements  is  the  observation  that 
af^er  operation  the  general  health  of  pigeons  always  declines,  and  it  is  not 
possible  to  keep  them  alive  more  than  about  six  weeks.  On  the  contrary,  a 
dog  could  be  kept  in  good  health  for  some  eighteen  months ;  but  there  is  this 
difference,  that  the  removal  in  the  case  of  the  dog  was  made  by  several  suc- 
cessive operations. 

By  removal  of  the  cerebrum  the  higher  animal  tends  to  lose  just  those 
capacities  which  best  serve'  to  distinguish  it  from  the  lower  forms.  When, 
therefore,  the  inquiry  is  made  why  the  results  gotten  in  the  dog  are  not  obtaiu- 
'  Arehiv  fiir  die  gesammle  Physiologie,  Bd.  xli. 


CENTRAL    NERVOUS  SYSTEM.  711 

able  in  monkey  or  man,  tliero  arc  several  replies.  In  the  first  place,  no  sueii 
extensive  experiments  have  been  made  on  monkeys  of  the  right  age  and  nnder 
ecjnally  favorable  eonditions.  If  a  matnn;  animal  is  taken,  the  secondary 
degenerations  are  so  massive  that  they  certainly  cause  great  disturbance  iu  the 
remaining  part  of  the  system.  This  is  not  equivalent  to  an  assertion  that  the 
same  results  could  be  obtained  in  the  monkey  by  more  extensive  experiments, 
but  a  suggestion  of  one  difference  behind  the  results  thus  far  reported.  There 
is  no  reason  for  assuming  any  deep-seated  difference  in  the  arrangement  of  the 
central  system  of  the  highest  mammals  as  compared  with  that  in  the  lower. 
Indeed,  in  some  human  microcephalic  idiots  the  })roportion  of  sound  and 
functional  tissue  in  the  encephalon  is  less  than  one-iburth  that  found  in  a 
normal  person,  yet,  on  the  other  hand,  no  normal  adult  could  lose  anything 
like  that  amount  of  tissue  which  is  out  of  function  in  these  microcephalic  brains 
and  at  the  same  time  live. 

The  central  system,  therefore,  even  in  man,  is  to  be  looked  upon  as  possessed 
of  some  power  to  adapt  itself  when  portions  have  been  lost,  but  this  is  most 
evident  when  the  defect  begins  early  and  develops  slowly. 

Keeping  the  cerebrum  still  in  view,  it  is  possible  to  go  into  further  detail. 
In  forms  below  the  monkey  the  loss  of  portions  of  the  cerebral  cortex  from  the 
motor  area  is  accompanied  by  a  greater  or  less  paralysis  of  the  muscles  repre- 
sented. This,  however,  is  an  initial  symptom  only,  and  gradually  disappears, 
though  not  always  with  the  same  completeness.  In  man,  of  course,  the  tend- 
ency to  recover  is  least. 

The  anatomical  relations  behind  this  difference  are  the  followina :  The 
efferent  cells  iu  the  ventral  horns  are  dominated  principally  by  two  sets  of 
impulses,  those  arriving  directly  over  the  dorsal  roots  of  that  segment  in  which 
they  are  located,  and  those  coming  over  the  long  paths  by  way  of  the  cerebral 
cortex-  and  pyramidal  tracts.  In  the  lower  mammals  this  second  pathway  is 
insignificant,  and  when  interrupted,  therefore,  the  disturbance  in  the  control  of 
the  ventral-horn  cells  is  but  slight.  Passing  up  the  series,  however,  this  path- 
way tends  to  become  more  and  more  massive  and  important,  as  the  figures  pre- 
viously given  show  (see  p.  695),  until  in  man  and  the  monkey  a  damage  of  it 
such  as  is  effected  by  injury  to  the  cortex  causes  a  high  degree  of  paresis  if  not 
permanent  paralysis,  because  by  this  injury  a  greater  proportion  of  the  impulses 
is  thus  cut  off  from  the  efferent  cells. 

It  has  previously  been  shown  that  the  cortical  areas  do  not  vary  accord- 
ing to  the  mass  of  the  muscles  which  they  control.  Experiments  also  show 
that  it  is  the  fore  limbs  which  are  most  disturbed  in  their  reactions  when  the 
lesion  involves  the  cortical  centres  for  both  fore  and  hind  limbs,  and  this  falls 
under  the  law  that  the  more  highly  adaptable  movements  {i.  e.  those  of  the  fore 
limb  as  contrasted  with  the  hind  limb)  are  most  under  the  control  of  the  cortex. 
If  the  examination  be  restricted  to  the  fore  limb  alone,  it  is  found  that  the 
finger  and  hand  movements  or  those  of  the  more  distal  segments  are  in  turn 
the  ones  most  disturbed.  Thus,  in  the  limbs,  the  more  distal  groups  of  mus- 
cles are  those  best  controlled  from  the  cortex.     It  follows,  then,  that  for  the 


712        AX  amp:rican  text- hook  of  physiology. 

arm,  paralysis  of  shoulder  movements  as  the  result  of  cortieal  lesion  is  least 
eomj)lcte,  while  as  we  travel  toward  the  extremity  of  the  arm  the  liabilitv  to 
disturl)anee  of  its  function  as  the  result  of  cortical  injury  increases  steadily. 

Turniiiu',  now,  to  the  "sensory"  areas  of  the  cortex,  the  principles  under- 
lying- their  physiological  significance  and  connections  appear  to  be  similar. 
The  lower  the  animal  in  the  vertebrate  series  the  more  probable  that  its  reac- 
tions can  be  controlled  by  the  atterent  impulses  which  have  not  passed  through 
the  cerebral  cortex. 

,  None  of  the  senses  except  vision  can  be  analyzed  sufficiently  to  bring  out 
the  signiHcancf  of  subdivisions  of  the  cortical  area ;  hence  the  illustrations  are 
taken  from  that  sense  alone. 

It  has  already  been  shown  that  without  cerebral  hemispheres  a  bony  fish  can 
distinguish  the  colors  of  wafers  thrown  on  the  water  and  discriminate  between 
a  bit  of  string  and  a  worm.  In  the  same  case  a  frog  is  able  to  direct  its  move- 
ments and  to  catch  flies — i.  e.  to  detect  objects  in  motion  and  react  to  them 
normally.  A  pigeon  can  direct  its  movements  in  some  measure,  and  even  select 
a  special  object  as  a  perch,  but  it  is  not  able  to  respond  to  the  sight  of  food  or 
its  fellows  or  those  objects  which  might  be  supposed  to  excite  the  bird  to 
flight.  In  the  dog  the  vision  which  remains  permits  only  the  response  of 
blinking  when  the  eye  is  stimulated  by  the  flash  of  a  bull's-eye  lantern. 
The  progressive  diminution  in  the  response  which  follows  visual  stimuli 
in  these  animals  is  open  to  the  interpretation  that  the  path  by  which  the 
impulses  may  pass  over  to  the  cells  forming  the  primary  centres  interme- 
diate bet\Aeen  the  sense-organ  and  the  cortex  is  progressively  diminished. 
Thus  the  impulses  arriving  at  the  primary  optic  centres  are  in  a  less  and 
less  degree  reflected  toward  the  cord,  as  the  pathway  to  the  cortex  becomes 
more  permeable.  When  therefore,  the  cortex  has  been  removed  the  reac- 
tions taking  place  by  way  of  it  are  disturbed  in  proportion  to  their  normal 
importance. 

In  the  first  instance,  when  the  reflexion  occurs  in  the  primary  centres,  the 
incoming  impulses  are  distributed  toward  the  cord  by  paths  not  known, 
while  in  the  second,  they  pass  from  the  cortex  along  the  pyramidal  tracts. 

In  the  cortex  subdivisions  of  the  visual  area  have  been  made  by  Munk.* 
He  found  that  the  more  anterior  ])ortions  of  the  visual  area  were  associated 
with  the  superior  parts  of  the  retina,  and  the  more  posterior  portions  with  the 
inferior,  while  the  area  in  one  hemisphere  corresponded  with  the  nasal  portion 
of  the  contralateral  retina,  and  to  a  less  degree  M'ith  the  temporal  portion  of  the 
retina  of  the  same  side.  The  determination  of  these  relations  wns  made  by 
the  removal  of  parts  of  the  visual  area  (dogs)  and  the  subsequent  examination 
of  the  field  of  vision.  It  apj)ears,  therefore,  that  the  incoming  imjndscs  from 
certain  parts  of  the  retina  are  delivered  at  definite  points  in  the  cortex,  and 
that  when  the  j)aths  are  interrupted  in  the  dog  or  higher  mammals  these 
impulses  are  blocked.  By  stinndatioii,  it  will  be  remembered,  Schiifer  deter- 
mined similar  relations  in  the  monkey. 

'  XJiher  die  Functionen  der  Grosshirnrinde,  Herlin,  1881. 


CENTUM.    NERVOUS  SYSTEM.  713 

Before  leaving  the  eerebrul  heinisplieies,  lueiilion  ol'tlie  (iict  should  be  made 
that  still  other  functions,  control  of  the  sphincter  ani  (Fig.  189),  secretion  of 
saliva,  and  micturition  can  be  roused  by  the  stimulation  of  the  cortex  in  the 
appropriate  region — namely,  in  the  region  where  the  muscles  and  glands  con- 
cerned might  be  expected  to  have  representation  if  they  followed  the  general 
law  of  arrangement.  Changes  in  the  production  and  elimination  of  heat  from 
the  body  follow  interference  with  the  motor  region  of  the  cerebrum,  and  the 
removal  of  portions  of  the  ctn-tex  in  this  region  is  followed  by  a  rise  in  the 
temperature  of  the  muscles  aifected. 

In  the  encophalon,  the  cerebrum,  and  especially  its  outer  surface,  is  the  por- 
tion the  functions  of  which  have  been  studied.  The  significance  of  the  other 
portions  of  the  encephalon  can  be  far  less  well  determined.  The  disturbances 
caused  by  the  section  and  stimulation  of  tiie  callosum  have  been  studied  by 
Koranyi  ^  and  by  Schafer  ^  and  Mott.  It  was  found  that  comjilete  section 
of  the  corpus  callosum  was  not  followed  by  any  perceptible  loss  of  function. 
On  the  other  hand,  stimulation  of  the  uninjured  callosum  from  above  gave 
symmetrical  bilateral  movements,  while  if  the  cortex  on  one  side  was  removed 
stimulation  of  the  callosum  gave  unilateral  movements  on  the  side  controlled 
by  the  uninjured  hemisphere.  These  results  seem  to  corroborate  the  conclu- 
sion derived  froni  histological  work  to  the  effect  that  the  system  of  the  callo- 
sum is  composed  only  of  commissural  fibres  and  that  it  sends  no  fibres  directly 
into  the  internal  capsule  of  either  side.  Concerning  the  corpora  striata  and 
the  optic  thalami  very  little  is  known.  In  the  case  of  the  corpora  striata  injury 
causes  in  man  no  permanent  defect  of  sensation  or  motion,  although  both  forms 
of  disturbance  may  at  the  outset  be  present  in  the  case  of  acute  lesions.  Lesions 
of  the  corpora  striata  cause  a  rise  in  temperature.^  Following  a  puncture  of  one 
corpus  striatum  there  occurs  in  rabbits  a  rise  amounting  to  some  3°  C. :  it 
begins  a  few  minutes  after  the  operation  and  may  last  a  week,  but  the  temper- 
ature tends  to  return  to  the  normal.  The  most  striking  feature  in  these  exper- 
iments is  the  very  wide  effects  produced  by  an  extremely  small  wound,  like  the 
puncture  of  a  probe. 

In  the  cases  where  lesion  of  the  striatum  on  one  side  causes  in  man  a  rise  of 
temperature  it  appears  mainly  on  the  side  of  the  body  opposite  the  lesion.* 
A  vaso-motor  dilatation  occurs  over  the  parts  of  the  body  where  the  temper- 
ature is  high. 

In  less  degree  a  rise  of  temperature  follows  injury  of  the  optic  thalamus — 
at  least  such  is  the  result  of  experiments  on  rabbits — but  the  effect  of  the  lesion 
is  never  so  marked  as  in  the  case  of  the  striatum.  Owing  to  the  disproportion 
between  the  area  of  the  lesion  and  the  extent  of  the  effects,  it  is  difficult  to  con- 
ceive of  the  anatomical  relations  which  permit  the  reaction.  It  is  of  interest 
to  note,  however,  that  similar  relations  hold  for  the  vaso-motor  centre  in  the 

*  Archiv  fur  die  gesammte  Physiolor/ie,  Bd.  xlvii.  ^  Bram,  1890. 

'  Aronsohn  und  Sachs:  Archiv  filr  die  gesammte  Physiologie,  1885,  Bd.  xxxvii.  ;  Richet: 
Compt.  rend,  de  I' Acad,  des  Sciences,  1884  ;  Ott :  Brain,  1889,  vol.  xi, 

*  Kaiser;  Neurologische  Centralblatt,  No.  10,  1895. 


714  ^liV'  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

bull),  in  which  case  tlie  vessels  siippiyinir  a  great  area  are  controlled  by  a  small 
grou{)  of  cells. 

The  difficulty  of  an  anatomical  explanation  is  increased  by  the  fact '  that 
Ott  enumerates  in  animals  six  heat-centres  :  1.  The  cruciate,  about  the  Rolandic 
fissure;  2.  The  Sylvian,  at  the  junction  of  the  supra-  and  post-Sylvian  fis- 
sures; 3.  The  caudate  nucleus;  4.  The  tissues  about  the  striatum  ;  o.  A  point 
between  the  striatum  and  the  thalamus,  near  the  median  line;  6.  The  anterior 
mesial  end  of  the  thalanuis. 

The  only  other  division  of  the  encephalon,  the  functions  of  which  can  j)roj>- 
erly  be  described  apart,  is  the  ccrcbelhim.  This  portion  is  among  vertebrates 
almost  as  variable  in  its  development  as  the  mantle  of  the  cerebral  hemispheres, 
and  in  many  fish  and  mammals  is  asymmetrical  in  its  gross  structure. 

The  recent  work  on  this  subdivision  has  been  carried  out  in  the  first  instance 
by  Luciani,^  and  later  by  RusselP  and  by  Ferrier.* 

The  cerebellum  is  not  concerned  with  psychical  functions.  The  removal 
of  it  does  not  cause  permanently  either  paralysis  or  anaesthesia,  but  the  imme- 
diate effects  of  an  extensive  injury  are  a  paresis  and  analgesia  as  well  as  anaes- 
thesia mainly  in  the  hind  legs,  and  in  consequence  a  high  degree  of  inco- 
ordination in  locomotion.  A  distinct  series  of  symptoms,  however,  follows 
injury  to  this  organ,  and  these  are  modified  according  to  the  locality  and 
nature  of  the  lesion.  Removal  of  one  half  (cerebellar  hemisphere  plus  half 
the  vermis)  of  the  cerebellum  in  the  dog  causes  a  deviation  outward  and 
downward  of  the  optic  bulb  on  the  opposite  side,  a  proptosis  of  the  bulbs  on 
both  sides,  nystagmus  and  contracture  of  the  muscles  of  the  neck  on  the 
side  of  the  lesion,  and  an  increase  of  the  tendon  reflexes  in  the  limbs.  lu 
walking  the  dog  wheels  toward  the  side  opposite  to  the  lesion,  and  tends  to  fall 
torrard  the  side  of  the  lesion. 

The  symptoms  are  chiefly  unilateral,  and,  caudad  from  the  cerebellum,  are 
on  the  side  of  the  lesion.  The  symptoms  are  less  severe  when  only  one  hemis- 
phere, instead  of  an  entire  half  of  the  cerebellum,  has  been  removed.  The 
existing  symptoms  are  not  intensified  by  the  removal  of  the  remaining  half. 
The  permanent  condition  of  the  muscles  after  operation  is  expressed  by  an 
atoiiia,  or  lack  of  tonus,  in  the  resting  muscles  ;  an  asthenia,  or  loss  of  strength, 
which  was  measured  by  Luciani,  and  was  most  marked  in  the  hind  leg;  an 
astasia,  or  a  lack  of  steadiness  in  the  muscles  during  action ;  and  finally  an 
ataxia,  or  a  want  of  orderly  sequence,  in  the  contractions  of  a  muscle- 
group.  The  general  expression  of  these  symptoms  is  a  twist  of  the  trunk, 
the  concavity  being  toward  the  operated  side,  combined  with  a  disorderly  gait. 
At  the  same  time  there  is  no  demonstrable  permanent  disturbance  of  tactile 
or  muscular  sensibility. 

Though  the  two  halves  of  the  cerebellum  are  united  by  strong  commissural 
fibres,  the  complete  division  of  the  organ  in  the  middle  line  is  followed  by  a 
disturbance  of  the  gait  which  is  only  transitory.     Hence  it  is  inferred  that  the 

^  Ott :  loc.  cit.  ^  Archives  Italiennes  de  Bioloijic,  1891-92.  xvi. 

^  Philosophical  Transactioru  Royal  Society,  1894.  *  Brain,  1893,  vol.  xvi. 


CENTRAL    NERVOUS  SYSTEM.  715 

connections  of  the  cercbelluin  are  mainly  \vill>  the  same  side  of  the  bull)  and 
spinal  cord.  Cephalad  of  the  eerebellum  the  coimection,  however,  is  a  crossed 
one,  each  cerebellar  hemisphere  beinir  associated  with  tlu;  (contralateral  cerebral 
hemisphere.  Throughout  these  connections,  both  cephalad  and  candad  t(.  the 
cerebellum  itself,  it  appears  that  there  is  always  a  double  pathway,  and  the 
eerebellum  not  only  sends  impulses  to,  but  receives  them  from,  the  regions  with 
which  it  is  associated. 

One  eifcct  of  removal  of  one  half  of  the  cerebellum  is  to  increase  the  respon- 
siveness of  the  cortex  of  the  contralateral  cerebral  hemisphere  to  electrical  sthn- 
nlation,  therebv  making  it  possible  with  a  weaker  stimulus  to  obtain  a  reaction 
which  could  be  obtained  from  the  other  hemisphere  only  by  a  stronger  one. 
When  an  irritative  lesion  is  made,  instead  of  a  merely  destructive  one,  the  rota- 
tion and  foiling  are  away  from  the  side  of  the  lesion  instead  of  toward  it. 

The  experiments  altogether  show  the  cerebellum  to  be  closely  associated  with 
the  proper  contraction  of  the  muscles,  and  this  is  so  directly  connected  with  the 
maintenance  of  equilibrium  that  it  is  not  surprising  to  find  that  stimulation  or 
removal  of  the  cerebellar  cortex,  besides  producing  nystagmus,  may  give  rise 
to  deviations  of  the  eyes  similar  to  those  found  on  injury  to  the  semicircular 
canals  or  stimulation  of  their  nerves  in  fishes.^ 


PART  III.-PHYSIOLOGY  OF  THE  NERVOUS  SYSTEM 
TAKEN   AS  A  WHOLE. 

A.  Weight  of  the  Brain  and  Spinal  Cord. 
In  attributing  a  value  to  the  mass  of  the  nervous  system  we  assume  that 
the  elements  which  compose  it  possess  potential  energy.  This  energy  varies 
for  any  given  element  in  accordance  with  a  number  of  conditions,  but  for  the 
moment  it  will  be  sufficient  to  point  out  that  if  the  mass  of  the  entire  system 
is  sio-nificant  the  masses  of  its  respective  subdivisions  are  also  significant,  as 
showing  in  some  measure  the  relative  physiological  importance  of  the  several 

parts.  ,  .        .  , 

Changes  Dependent  upon  Age.— That  the  mass  of  the  system  varies  with 
acre  is  a  matter  of  common  observation.  The  changes  which  occur  m  the  mass, 
atthou-h  they  are  specially  evident,  are  not  the  only  changes  which  take  place  ; 
for  with  the  change  in  mass  go  hand  in  hand  changes  in  the  relations  which 
the  elements  bear  to  one  another,  and  which  result  in  making  the  organization 
of  the  svstem  different  at  the  different  periods  of  life.  Moreover,  the  special- 
ization of  the  nerve-elements,  in  the  mammals  at  least,  has  been  carried  to  such 
a  point  that  they  are  utterly  dependent  for  their  full  activity  on  the  nutritive 
system  and  the  character  and  amount  of  the  nutrient  plasma  is  a  circum- 
stance of  prime  importance.  Any  variation  in  this  factor  serves  to  com- 
pletely alter  the  activities  of  the  system,  be  it  never  so  well  organized,  and 

'  Lee:  Journal  of  Phydology,  1893,  vol.  xv.  ;  1894,  vol.  xvii. 


716  AX  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

therefore  the  discussion  of  the  general  powers  of  the  nervous  system  for  per- 
formance must  never  leave  this  factor  unconsidered. 

Constituents  of  the  Central  System. — Calculation  shows  that  the  cell- 
bodies  probably  contribute  less  than  10  per  cent,  of  the  entire  weight  of  the 
central  system,  so  that  the  remainder  must  be  made  up  of  neurons  and  other 
tissues. 

In  the  central  system  there  are  present,  besides  the  nerve-elements  proper, 
the  sustentacular  tissues  and  the  nutritive  vessels — the  channels  for  blood  and 
lymph.  Just  what  fraction  of  the  total  w^eight  of  the  central  system  is  thus 
represented  has  not  been  exactly  determined,  but  it  must  be  nearly  equal  to 
that  of  the  nerve  cell-bodies  alone. 

The  weight  of  the  brain  is  the  weight  of  these  several  constituents. 

Of  course  a  brain  congested  with  blood  would  weigh  more  than  one  from 
which  the  blood  had  been  largely  withdrawn,  but  there  is  no  way  of  controlling 
this  condition  directly.  Previous  to  weighing,  the  brain  is  sometimes  sub- 
divided and  even  cut  into  large  sections,  in  which  case  of  course  much  of  the 
blood  and  lymph  has  the  opportunity  to  drain  away.  In  some  cases  too  the 
brain  is  weighed  without,  and  in  others  with,  the  pia. 

'Weight  of  the  Pia  and  Fluid. — Broca's  table  for  the  weight  of  the  pia  in 
males  is  as  follows :  ^ 

20-30  years 45  grams. 

31^0       •'        50      " 

60  '■        60      " 

The  cast  of  the  ventricles,  as  made  by  Welcker,  displaces  26  cubic  centi- 
meters of  water,  so  that  the  fluid  filling  these  cavities  would  Aveigh  a  trifle 
over  26  grams. 

Percentag-e  ofWater. — In  man  the  percentage  of  water  in  the  gray  matter 
of  the  cerebrum  is  81.8  per  cent.,  and  in  the  -white  matter  70  per  cent.' 

Specific  Gravity. — According  to  calculation,  the  specific  gravity  of  the 
entire  encephalon  is  1036.3  in  the  male  and  1036.0  in  the  female.  Ober- 
steiner'  found  the  specific  gravity  of  the  cortex  to  gradually  increase  from 
frontal  to  the  occipital  lobe.  It  was  further  found  that  while  the  outermost 
layer  of  the  cortex  had  a  specific  gravity  of  1028,  that  of  the  middle  layers 
was  1034  and  of  the  deepest  layers  1036,  thus  indicating  a  progressive  increase 
from  the  most  suj)erficial  to  the  deepest  layers — an  increase  to  be  associated 
with  the  larger  proportion  of  medullated  fibres  in  the  deeper  layers. 

"Weight  of  the  Encephalon  and  Spinal  Cord. — As  a  result  of  the  pre- 
ceding statement  it  follows  that  when  the  weight  of  any  portion  of  the  nerv- 
ous system  is  taken,  the  final  record  represents,  in  addition  to  the  weight  of 
the  nerve-tissues  proper,  that  of  the  supporting  and  nutritive  tissues,  together 
with  the  enclosed  blood  and  lymph.  It  is,  however,  assumed  that  under 
normal  conditions  the  relation  between  the  nervous  and  non-nervous  tissues  is 

'  Broca,  quoted  bv  Topinard  :  Elements  d"  Anthropologic  ghi^nle,  1885. 

*  Halliburton  :  Journal  of  Physiology,  1894.  »  Centralblatt  fur  Nenenheilkunde,  1894. 


CENTRAL    NERVOUS  SYSTEM. 


717 


maily  a  constant  one,  and  tliat  tlio  results  of  diiforent  weighings  are  therefore 
comparable  among  tlieinselves. 

Interpretations  of  Weight.— Assuming  as  the  simplest  case  that  the  nuin- 
ber  of  the  nerve-elements  e<)mi)osing  a  given  portion  of  the  central  system  is 
constant,  then  differences  in  the  weight  of  these  portions  in^  diU'erent  individ- 
uals imply  variations  in  the  size  of  the  component  cells.  The  signifieance  of 
variations  in  the  size  of  the  nerve-elements  must  be,  primarily,  that  the  larger 
the  cells,  and  especially  the  larger  the  cell-bodies,  the  greater  the  mass  of  cell- 
substance  ready  at  any  moment  to  undergo  chemical  change  leading  to  the 
release  of  energy.  On  the  other  hand,  if  the  number  of  elements  is  variable, 
an  increase  in  the  number  must,  in  view  of  the  law  of  isolated  conduction, 
also  provide  a  larger  number  of  conducting  pathways.  Whether  this  increase 
in  the  number  of  pathways  shall  further  add  to  the  complication  of  the  sys- 
tem depends  on  the  localities  at  which  it  occurs.  Bearing  these  facts  in  mind, 
we  may  turn  to  the  records  of  the  weight  of  the  encephalon. 

-Weight  of  the  Encephalon.— The  encephalon  is  that  portion  of  the  cen- 
tral nervous  system  contained  within  the  skull.     The  accompanying  diagram 


Fig  203  -Showing  the  principal  divisions  of  the  encephalon  made  for  the  study  of  its  weight :  1, 
hemisphere  seen  from  the  side,  fissuration  according  to  Eberstaller;  2,  mid-brain,  region  of  the  quad- 
rigemina;  3,  pons;  4,  cerebellum,  or  hind-brain;  5,  bulb,  or  after-brain.  Divisions  2,  3  and  5,  taken 
together,  form  what  is  designated  the  "  stem  "  in  the  tables  of  Boyd  (modified  from  Quain  s  Anatomy). 

(Fig.  203)  shows  the  encephalon,  together  with  one  manner  of  subdividing  it. 
Its  weight  has  usually  been  taken  while  it  was  still  covered  by  the  pia,  but 
after  altowing  the  fluids  to  drain  away  for  five  minutes  or  more.  As  has 
been  stated,  sometimes  drainage  has  been  fjicilitated  by  cutting  into  the  brain ; 
hence,  when  the  brain-weight  records  by  any  observer  are  to  be  discussed,  the 
first  question  concerns  the  method  according  to  which  the  brains  were  exam- 
ined, for  the  weights  may  be  either  with  or  without  the  pia  and  with  or  with- 
out drainage. 


IS 


.liV^  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


The  anthropologists  classify  the  encephala  according  to  weight  in  tl)o  fol- 
lowing manner : 

Tlic  Xomendaiure  of  the  Encephalon  according  to  Weight.      Weight  in  Grama 

{Topinard). 

Classes.                                                                  Males.  Females. 

Macrocephalic      From  lit2o-1701  From  1743-1501 

Large "      1700-1451  "      1500-1351 

Medium "      1450-1251  "      1350-1151 

Small "      1250-1001  "      1150-  901 

Microcephalic "      1000-  300  "        900-  283 

The  brain-weight  in  the  majority  of  persons  falls  within  the  group  of 
medium  brains,  and  average  figures  are  obtained  by  combining  the  individual 
records  in  which  all  variations  from  the  medium  occur.  Of  course  races  of 
small  size,  like  the  small  people  of  India  or  the  Pygmies  of  Africa,  would  not 
be  expected  to  possess  encephala  equal  in  weights  to  those  of  the  larger  races  of 
Europe.  Any  set  of  average  figures,  therefore,  should  be  based  as  nearly  as 
possible  on  observations  made  on  a  homogeneous  population.  "Within  the 
limits  of  a  given  race  there  are  several  conditions  which  determine  differences 
in  brain-weight,  namely,  sex,  age,  stature,  and  body-weight. 

From  the  observations  by  Dr.  Boyd  on  the  weight  of  the  brain  in  England 
the  following  table  has  been  compiled  : 

Table  shoving  the  Weight  of  the  Encephalon  and  its  Subdivisions  in  Sane 
Persons,  the  Records  being  arranged  according  to  Sex,  Age,  and  Stature 
(from  3IarshaWs  tables  based  on  Boyd's  records).^ 


Males. 

Females. 

m 

bo 
< 

a 
o 

"3 

o 

S 

S 

0) 

o 

5 

1 
1 

■ 

S 
35 

a 

TO 

S 
s 

1 

1 

i 

3 

1-4 

£ 

c 
"3 

1 

1 
< 

Stature  175  cm.  and  upward. 

Stature  163  cm.  and  upward. 

20-40 

1409     .     1232            149 

28 

23 

134     I     1108     1     1265 

20-40 

41-70 

1363         1192           144 

27 

23 

131          1055          1209 

41-70 

71-90 

1330     1     1167     '       137 
Stature  172-167  cm. 

26 

24  a 

130     1     1012     1     1166 
Stature  160-155  cm. 

71-90 

20-40 

1360          1188     1       144 

28 

26  s 

137  s       1055 

1218 

20-40 

41-70 

1335         1164           144 

27 

268 

131          1055 

12128 

41-70 

71-90 

1305         1135     1      1428 

28  as 

24 

128           969  8 

1121 

71-90 

Stature  164  cm.  and  under. 

Stature  152  cm.  and  under. 

20-40 

1331          1168     1       138 

25 

24  s 

130     1     1045 

1199 

20-40 

41-70 

1297         1123     !       139  a 

25 

25a8 

129          1051  a 

1205  a 

41-70 

71-90 

1251 

1095 

131 

25 

25  as 

123 

974 

1122 

71-90 

The  method  of  weighing  the  brain  used  by  Dr.  Boyd  ^  was  as  follows :  The 
skull-cap  being  removed  and  the  pia  being  intact,  the  hemispheres  were  sliced 

'  a  indicates  that  a  record  considered  according  to  age  is  too  large;  ••<  indicates  that  a  record 
considered  according  to  stature  is  too  large. 

^  PltUomphirdl  Tranmdiom  of  the  Iioy(d  Society,  London,  1860 ;  see  also  Marshall :  Journal  of 
Anatomy  and  Physiology,  1892. 


CENTRAL    NERVOUS  SYSTEM.  719 

away  by  horizontal  sections  as  far  <l()\\ii  as  tiic  tentorium.  The  parts  of  the 
hemispheres  still  rcmainino;  were  then  removed  by  a  sec-tion  passinfr  in  front  of 
the  qiiadrigemina.  The  cerebellum  was  next  separated  from  the  stem,  this 
latter  being  represented  by  the  quadrigemina,  the  pons,  and  the  bulb.  Each 
hemisphere,  the  cerebellum,  and  the  stem  were  then  weighed  separately. 

Between  the  twentieth  year  and  old  age  there  are  here  represented  the  average 
encephalic  weights,  arranged  in  two  main  groups  according  to  sex,  and  then  in 
large  horizontal  groups  according  to  stature,  those  of  a  given  stature  being  sub- 
divided according  to  age.  This  record  is  typical  of  what  has  been  found  by 
other  observers  and  may  be  discussed  without  further  evidence. 

If  groups  of  similar  ages  and  corresponding  statures  are  compared  accord- 
ing to  sex,  it  is  at  once  seen  that  the  male  possesses  the  heavier  encephalon,  and 
that  all  the  subdivisions  of  it  are  likewise  heavier. 

When  individuals  of  the  same  sex  and  falling  within  the  same  age-limits 
are  compared  according  to  stature,  those  having  the  greater  stature  are  found  to 
have  the  greater  brain-weight,  though  in  the  case  of  the  subdivisions  of  the 
encephalon,  and  especially  among  the  females,  there  are  some  irregularities,  but 
these  would  probably  disappear  could  the  number  of  observations  be  increased. 
Finally,  within  the  groups  of  those  having  the  same  stature,  but  different  ages, 
the  weight  decreases  with  advancing  age.  The  middle  group,  forty-one  to 
seventy  years  of  age,  is  in  one  way  unfortunate,  because,  while  the  brain  is 
probably  still  growing  (see  curve  of  growth.  Fig.  204),  during  the  first  third 
of  that  period,  and  is  nearly  stationary  (males  especially)  during  the  second,  it 
begins  to  diminish  so  rapidly  during  the  last  third  that  the  average  weight  is 
lower  for  the  cases  between  sixty-one  and  seventy  years  than  for  the  twenty 
years  between  forty-one  and  sixty  years.  Between  seventy-one  and  ninety 
years  the  involutionary  changes  in  the  central  system  are  most  marked,  and 
the  decrease  in  weight  during  this  period  is  clearly  indicated. 

Body--weight. — As  regards  the  relations  between  the  weight  of  the  central 
system  and  the  weight  of  the  body  the  case  is  not  so  clear.  In  the  first  place, 
the  presence  of  fat  at  maturity  disturbs  the  results,  because  the  nervous  system 
cannot  be  expected  to  vary  with  changes  in  the  quantity  of  an  inactive  tissue 
representing  stored  food-stuff  merely.  The  taller  individuals  have  a  larger 
cranial  capacity  than  the  shorter,  and  hence  the  variation  of  brain  with  body- 
mass  can  only  be  made  fairly  when  persons  of  the  same  stature,  but  of  dif- 
ferent body-weights,  shall  have  been  carefully  compared. 

If  under  these  circumstances  it  shall  appear  that  the  bulkier  individuals 
have  the  heavier  nervous  system,  then  the  excess  in  their  favor  can  be  fairly 
correlated  with  the  excess  of  the  active  tissues. 

Before  suggesting  an  explanation  of  these  variations  according  to  age,  sex, 
and  stature,  it  is  to  be  noted  that  they  occur  in  other  mammals  as  well  as  in 
man.  As  regards  the  difference  in  the  Aveight  of  the  encephalon  due  to  sex,  it 
has  been  shown  to  obtain  among  the  apes,^  the  mate  having  the  heavier  brain  • 
and  from  the  general  relation  of  size  according  to  sex  among  the  mammalia, 
^  Keith;  Journal  of  Anatomy  and  Physiology,  1895. 


720  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

where  the  male  as  a  rule  has  the  greater  body-weight,  it  is  to  l)e  aiitit-ipated  that 
a  similar  difference  in  \\\v  weight  of  the  brain  will  be  shown  in  other  groups. 

Among  individuals  of  the  same  sj)ec'ies,  but  of  different  races  or  of  different 
lengths  and  weights,  the  law  holds  good  that  the  larger  races  have  the  heavier 
brains,  as  do  the  larger  and  heavier  individuals.  Here,  as  in  the  case  of  man, 
it  is  always  assumed  that  the  differences  in  body-weight  are  mainly  correlated 
with  the  active  tissues  like  muscle,  and  not  with  fat.  As  to  the  loss  of  the 
brain  in  weight  after  maturity,  observations  on  animals  are  scanty,  but  point 
to  decrease  in  weight  toward  the  natural  close  of  life. 

Interpretation  of  Brain-weight. — In  the  absence  of  fuller  data  the 
explanation  of  the  series  of  differences  just  mentioned  is,  in  a  very  high  degree, 
tentative.  The  loss  of  weight  in  advanced  years  appears  to  be  due  to  a  gen- 
eral atrophy  of  the  nerve-elements.  The  greater  brain-weight  associated  with 
greater  stature  appears  to  depend  on  the  variations  in  the  size  of  the  elements 
rather  than  in  their  number,  and,  so  far  as  can  be  seen,  the  distinction  accord- 
ing to  sex  is  susceptible  of  a  similar  explanation. 

The  fact  that  the  difference  in  brain-weight  between  the  two  sexes  more 
probably  depends  upon  a  difference  in  the  size  of  individual  elements  than 
upon  a  difference  in  the  number  of  these  elements  is  strongly  suggested  by 
the  following  considerations:  The  microcephalic  brains,  constituting  one  group 
which  always  appears  in  long  series  of  records,  belong  to  individuals  whose 
intelligence  is  very  limited  or  to  those  to  whom  the  functions  necessary  to  mere 
existence  are  just  possible.  In  this  latter  class  we  have  presumptively  arrived 
at  a  brain  in  which  the  functional  elements  are  reduced  to  the  lowest  number 
compatible  with  life. 

Subjoined  is  a  table  giving  the  average  weights  of  microcephalic  brains  for 
the  two  sexes,  the  observations  being  divided  into  three  groups.  In  each  of  the 
groups  taken  the  average  weight  for  the  females  is  less  than  that  for  the  males : 

Tlie  Weight  of  the  Brain  in  Microcephalics  {condensed  from  Marchand)} 

Group.  241-600  grams.    501-800  grams.    801-1015  grams. 

Males 349  651  954 

Females 299  621  912 

When  the  weight  for  the  two  sexes  is  here  compared,  it  is  seen  that  the 
average  for  the  female  is  the  closer  to  the  lower  limit  in  each  group.  As  by 
hypothesis  we  are  dealing  with  the  least  po.ssible  number  of  elements  in  either 
sex  and  as  there  is  no  reason  to  assume  that  this  minimum  number  is  materi- 
ally different  for  the  two  sexes,  the  inference  is  plausible  that  in  these  cases 
the  difference  in  weight  is  in  a  large  measure  due  to  the  difference  in  the  size 
of  the  constituent  elements.  If  this  holds  for  the  lower  limit  of  the  series,  it 
is  of  course  also  probable  that  it  holds  throughout  the  entire  series  as  well. 

As  compared  with  the  average  brain,  those  of  either  sex  forming  the  groups 
heavier  than  the  average  owe  their  greater  weight  more  often  to  an  increase  in 
the  size  of  the  constituent  elements  than  to  an  increase  in  their  number.     On 

*  Marchand:  Nova  Acta  der  Kaiserl.  Carol.  Deutseh.  Akad.  der  Naturforscher,  HaWe,  1890. 


CENTRAL    NERVOUS   SYSTEM.  721 

the  oth«-  luUKl,  in  those  gro,.ps'posse..sing  the  smallest  weight  not  only  the  si.e 
but  more  probably  also  the  n„,nber,  of  elements  may  be  r«h,ee,l  below   ha 
f,  „Kl  in  nLn,al  persons.     These  statements  are  of  eon,-.,  to  ho  aPl'l-d   "■  the 
'        n,   to  n,en,llers  of  the  sao,e  race.     We  know  ,h:,,  the  i-™™=''«  »^ 
Laller  nervous  systems  than  that  of  man  have  a  far  s.nall.r  .nnnU.r  of  ne>^e- 

"'nr;;;:X:wJ't'i::'t- the  wiOer  variations  in  the  nuntWr  of  eeUs  .»n,posing  the 
nervous  system  in  n,a,>  ocrur  among  the  different  raees,  and  that  here,  as  we  1 
rimong  the  mieroeephalies,  in  which  development  has  been  early  arrested, 
difforenoes  in  the  number  of  cells  are  most  marked.  .  , ,     f 

W^^hts  of  Different  Portions.-A  study  of  the  proport.onal  w.tghts  of 
theTevell  subdivisions  of  the  encephalon  aeeording  to  the  sex  stature,  and 
a«  4  OS  that  there  is  verv  little  difference  caused  by  vanattons  ,n  these  co,  - 
d^;^  This  too,  so  far  as  it  goes,  suggests  that  the  absolute  we.ght  ts  depend- 
en  mther  on  variations  in  the  si.e  than  in  the  number  of  the  elements,  sntee 
rl"*  nilL  variation  in  number  would  be  less  probable  than  a  harmontons 

^•"tll  y::ironr„e„t.-It  is  not  to  be  -P-^   .Hat  ^he  ^e^j'^^^^^^^^ 

brain  aM.on<.  the  least-tavored  classes  in  any  eommunity  will  be  the  same  as 

^     of  thos^  who,  during  the  yea.  of  growth,  are  -«<;;  "  -"^ "r^l 

All  extensive  series  of  observations  which  we  pos.sess  relate  to  he  lea.t  ta^or«l 

•  Tm    -es  and  hence  it  is  not  improbable  that  the  figures  in  the  foregoing 

TbTe     :^d;      e  b^^  on  data  obta'ined  mainly  at  the  Marylebone  workhouse 

Tn  Lo'uJon  are  decidedly  below  those  which  would  be  obtained  ft-om    1.  mo^ 

<-,rt„n^te  classes  in  the  same  eommunity.     We  have  a  list  of  biain-«eignts 

i  1  tn  iTthe  r  cords  for  a  number  of  men  of  acknowledged  emtnence, 

nd     IsT  or  othet.  who  attained  recognition  as  able  persons  wnthout  be.ng 

::lptionally  remarkable.     It  shows  the  men  i,,  this  list  to  have  bn.ns  on  the 

nvprao-e  heavier  than  the  usual  hospital  subject .^  .  ,       ,  i 

C:mpaHson  of  the  brain-weights  of  eminent  men  with  the  weights  taken 
frotn  Z  ksses  used  to  furnish  the  standard  has  been  made  by  Manonvrter. 
The  tible  on  p  ^e  722  gives  the  brain-weights  occurring  among  etn.nen  men 
Jompati  "th  those  fomKl  among  Parisians  of  the  lower  classes,  these  latter 
bZ  subdivided  ac«>rding  to  stature  (Manouvrier).  The  flgnr^  expre^  the 
number  of  brains  in  each  group  of  100  that  would  fall  w.tlun  the  bmtts  of 
wpio-ht  oDDO^ite  to  which  the  entries  stand. 

^t^..  wide  range  in  the  weights  given  in  these  ^tables  b«t  at  the  same 
time  their  average  is  high  as  compared  with  the  figures  of  Bo>d  and  other 
c^b^erve,"  Sinel  even  those  who  at.  undoubtedly  disttngutshed  presen 
br^hiwei^hts  havin.  a  wide  range,  and  since  any  long  series  of  observations 
wo"u  ™th  a  faFr  number  of  eases  of  high  brain-weight  without  any 
rggiiol  of  superior  mental  ability,  it  is  ,vident  that  tl^    5^     ■-■-| 

anrunnsnal  mental  capability  are  by  -  "-"^X  l^w  ve^  M;bT  'L 
sion  in  harmony  with  common  observation.     ^  hether,  However,  n  ^ 
1  Donaldson  :   The  Growth  of  the  Brain,  1895. 


46 


•22 


AA"^  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 


Aveight  is  to  be  con.sidered  more  frequent  among  men  of  tlistinetion  eannot  be 
determined  until  there  is  available  a  large  number  of  records  obtained,  not 
from  the  less-favored  social  classes,  but  from  j)ersons  accounted  as  successful 
merchants,  bankers,  and  members  pf  the  learned  j)rofessions. 


Weight  of  the  Encephaion. 
in  Grams. 

Parisians 
of  Broca. 

Adult. 

168  cm. 

Parisians 

of  Tall 

stature. 

171-185  cm. 

Eminent  Men. 

1st  Series. 

2d  SeriPR    Series  1  and 
idberies.   scombined. 

900-1000    

0.6 

0.6 

7.1 

23.3 

31.5 

23.8 

9.6 

3.5 

3.5 
15.5 
27.5 
34.6 
15.5 

3.4 

ii.i 

17.8 

33,3 

24.5 

2.2 

2.2 

2.2 

6.7 

1001-1100    

1101-1200    

2.9               1.2 

2.9              7.5 

17.2             17.5 

48.5            40.0 

22.8             23.8 

5.7               3.3 

.    .               1.6 

.    .               1.3 

.    .              3.8 

1201-1300    

1301-1400    

1401-1500    

15(»l-lti00 

11)01-1700 

1701-1800    

1801-1900    

1901-2000    

2001  and  more 

Total 

100 

100 

100 

100             100 

Brain-weight  of  Criminals. — The  observations  of  Manouvrier  have 
shown  that  among  French  murderers  the  brain-weight  is  similar  to  that  of  the 
individuals  usually  examined  in  the  Parisian  ho.spitals.  In  the  same  manner, 
the  observations  on  the  brain- weight  among  the  insane  indicate,  according  to 
the  records  of  Boyd  and  others,  that  the  insane  as  a  class  (the  microcephalics 
being  of  course  excluded)  are  not  characterized  by  a  special  brain-weight. 
AYhen,  however,  the  insane  are  grouped  according  to  the  special  diseases  from 
which  they  have  snifered,  it  is  evident  that  those  in  which  the  brain  was  con- 
gested at  death  exhibit  the  higher  weight,  while  those  in  which  the  pathological 
processes  caused  destructive  changes  exhibit  a  low^  weight.  The  differences  in 
these  cases  are  rather  the  results  of  disease  than  the  cause  of  it. 

Brain-weights  of  Different  Races. — Concerning  the  weights  of  the  brain 
in  different  races  there  are  no  extensive  observations  which  have  been  made 
directly  on  the  brain  itself.  Davi.s^  has,  however,  determined  the  cranial  capaci- 
ties of  a  series  of  skulls  belonging  to  different  races,  and  the  brain-weights  as 
calculated  from  these  are  as  follows : 


Races. 


European 

Oceanic 

American 

Asiatic  .    . 

African 

Australian 


Males. 


« 

1 

O 

299 

210 

52 

124 

53 

24 

1364—1212 
1369—1192 
1338—1209 
1397—1155 
l.fl6— 1165 
1414—1027 


1340 
1293 
1282 

1278 
1268 
1190 


1180 
1185 
1164 
1171 
1187 
1089 


Females. 


1099—1278 
1139—1239 
1087-1263 
1042—1276 
1100—1220 
966—1194 


94 
95 
31 
86 
60 
11 


'  Journal  of  the  Academy  of  Natural  Science,  Philadelphia,  1869. 


CENTRAL    NERVOUS  SYSTEM.  723 

This,  as  will  be  seen,  gives  the  largest  brain-weights  to  the  western  Europeans, 
but  for  a  proper  interpretation  of  the  results  there  are  needed  at  least  the  data 
concerning  stature  and  ag(!  of  the  cases  studied,  both  of  which  are  here  lacking. 

Weight  of  Spinal  Cord. — Comparatively  few  observations  are  available 
for  the  spinal  cord  :  Mies^  found  that  in  adults  it  weighed  24  to  33.3  grams, 
with  an  average  weight  of  26.27  grams  :  this  for  the  cord  deprived  of  the 
nerve-roots,  but  covered  by  the  pia.  The  variations  due  to  sex  and  stature 
have  not  been  determined.  It  seems  probable',  however,  that  the  cord,  like 
the  brain,  will  be  found  lighter  in  females  and  in  short  persons:  Mies  states 
that  its  decrease  in  old  age  is  proportionately  less  than  that  of  the  brain. 

Bilateral  Symmetry  as  determined  by  the  Balances. — The  central 
nervous  system  in  its  larger  features  is  bilaterally  symmetrical.  In  detail, 
however,  there  are  many  deviations.  The  question  at  once  arises  whether 
these  variations  are  normally  wide  enough  to  permit  us  to  attach  to  them  a 
distinct'  physiological  value.  While,  morphologically,  bilateral  symmetry  is 
expressed  in  the  arrangement  of  the  central  system,  common  experience  and 
clinical  observations  show  that  most  persons  are  physiologically  one-sided,  and 
the  two  sets  of  facts  are  apparently  out  of  harmony,  provided  an  anatomical 
basis  is  sought  for  the  physiological  reactions.  The  facts  bearing  on  this  ques- 
tion are  the  following  : 

The  two  cerebral  hemispheres  in  man  are  found  to  weigh  within  a  gram  of 
one  another  in  about  one-third  of  the  cases  recorded  (Franceschi).  Larger 
differences,  when  found,  are  not  distinctly  in  favor  of  either  hemisphere,  accord- 
ing to  the  observations  of  this  same  author.  The  results  of  those  observers 
who  have  found  one  side  constantly  heavier  are  discordant. 

In  individual  cases,  of  course,  wide  differences  between  the  weight  of  the  two 
hemispheres  may  occur,  but  these  are  clearly  abnormal. 

Asymmetry  Otherwise  Determined. — Other  asymmetry  has  not  been 
detected  by  the  balances.  The  human  cerebellum  has  not  been  studied  in 
reference  to  its  bilateral  symmetry,  but  in  cats  Krohn  ^  found  the  molecular 
layer  thinner  on  the  right  side,  and  the  same  is  true  in  the  case  of  the  sheep. 
In  both  these  animals  the  middle  lobe  (vermis)  is,  however,  asymmetri- 
cal, being  twisted  to  the  right,  and  it  is  just  possible  that  the  thickness  of 
the  molecular  layer  may  be  associated  with  this  arrangement.  Flechsig's 
observations  on  the  asymmetry  of  the  pyramidal  tracts  have  already  been 
noted. 

In  connection  with  these  anatomical  results  it  is  to  be  noted  that  the  blood- 
supply  to  the  anterior  portions  of  the  left  hemisphere  is  through  the  left 
carotid,  which  appears  mechanically  fitted  to  furnish  a  more  direct  supply  than 
does  the  right ;  and,  bearing  in  mind  the  dominant  influence  of  nutritive  con- 
ditions for  nervous  response,  this  arrangement  may  yet  prove  to  be  significant. 

The  few  data  which  are  available  on  the  asyinmetrv  of  the  central  system 
do  not  therefore  give  us  a  basis  sufficient  to  explain  the  asymmetry  of  function. 

^  Neurol  Off  isehe  Centralblati,  1893. 

''  Krohn  :  Journal  of  Nervous  and  Mental  Disease,  1892. 


"24 


AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


B.  Growth-changes. 

The  characters  of  the  brain  and  cord  thus  far  described  have  been  those 
found  for  the  most  part  in  tlie  adult.  Between  birth  and  the  natural  end  of 
life,  however,  great  changes  take  place,  and,  as  it  is  necessary  to  consider  the 
functions  of  the  central  system  at  all  times  in  its  history,  the  importance  of 
knowing  the  direction  in  which  the  growth-changes  are  probably  occurring  is 
obvious. 

Growth  of  Brain. — The  weight  of  the  brain  from  birth  to  the  twenty-fifth 
year  is  given  below  (Vierordt '). 

Inc7'ease  in  Brain-weight  with  Age — Encephalon  Weighed  Entire  witli  Pia 

{compiled  by  H.  Vierordt). 


Males. 

Females. 

Age. 

No.  of  Cases. 

Brain. 

Brain. 

No.  of  Cases. 

0  months 

1  year  

2  years 

3  "   

4  "   

5  "   

6  "   

7  "   

8  "   

9  "   

10  "   

11  "   

12  "   

13  "   

14  "   

15  "   

16  "   

17  "   

18  "   

19  "   

20  "   

21  "   

22  "   

23  "   

24  "   

25  "   

36 

17 

27 

19 

19 

16 

10 

14 

4 

3 

8 

7 

5 

8 

12 

3 

7 

15 

18 

21 

14 

29 

26 

22 

30 

25 

381 
945 
1025 
1108 
1330 
1263 
1359 
1348 
1377 
1425 
1408 
1360 
1416 

1487 
1289 

1490 
1435 
1-109 
1421 
1397 
1445 
1412 
1348 
1397 
1424 
14.31 

384 
872 
961 
1040 
1139 
1221 
1265 
1296 
1150 
1243 
1284 
1238 
1245 
1256 
134i> 
1238 
1273 
1237 
1325 
1234 
1228 
1320 
1283 
1278 
1249 
1224 

38 

11 

28 

23 

13 

19 

10 

8 

9 

1 

4 

1 

2 

3 

5 

8 

15 

18 

21 

15 

33 

31 

16 

26 

33 

33 

Total  number  of  cases,  415. 


Total  number  of  cases,  424. 


From  the  same  figures  the  first  part  of  the  accompanying  curve  (Fig.  204) 
has  been  formed. 

The  curve  beyond  the  twenty-fifth  year  is  continued  on  the  basis  of  the 
observations  by  Bischoff,^  and  for  comparison  the  curve  representing  the 
encephalic  Aveights  of  a  series  of  eminent  men,  forty-five  in  number,  is  drawn 
in  a  dotted  line,  the  averages  for  decennial  periods  being  alone  plotted. 

These  records  exhibit  the  fact  that  at  birth  the  weight  of  the  brain  is  about 
one-third  of  that  which  it  will  attain  at  maturity.  The  increase  is  very  rapid 
during  the  first  year,  and  vigorous  for  the  first  seven  or  eight  years,  after  which 
it  becomes  comparatively  slow.     The  maximum  weight   is  indicated   in  the 

^  Archiv  fiir  Anatomie  und  Physiologie,  1890.  *  Himgewicht  des  Menschen,  Bonn,  1880. 


CENTRAL    NERVOUS  SYSTEM. 


725 


Fig  2(M.-Curves  for  each  sex,  showing  the  weight  of  the  brain  according  to  age.  For  the  first 
twentv-five  years  the  curve  is  formed  from  annual  averages  based  on  the  figures  of  H.  Vierordt;  from 
twenty-five  years  on  the  curves  are  formed  from  decennial  averages  based  on  the  observations  of 
Bischoff.  All  the  data  are  from  observations  on  the  less  fortunate  classes.  The  dotted  curve  for  emi- 
nent men  is  formed  from  decennial  averages  based  on  forty-five  observations. 

fifth  decade  (males),  fourth  (females),  although  there  is  a  premaximum  in  the 
middle  of  the  second  decade  (at  thirteen  and  fifteen  years  for  males  and  four- 
teen vears  for  females),  in  which  the  too  early  and  too  vigorous  growth  of  the 


•20 


AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 


cncoplialon  aj>i)cars  to  be  an  important  factor  in  tho  cause  of  death  ;  hence  the 
larger  brain-weight  Ibimd  at  autopsies  during  those  years.  W'iiile,  in  general, 
the  individual  may  be  supposed  to  follow  in  the  development  of  his  eneej)halon 
the  course  here  indicated  by  the  curve,  this  premaximal  increase  must  be  ex- 
ccj)ted  tor  the  reasons  given. 

It  appears  probable,  from  varions  lines  of  research,'  that  individuals  differ 
widely  in  the  length  of  time  during  Mhich  the  brain  enlarges,  and  also  in  the 
time  at  which  the  atrophic  changes  due  to  old  age  become  evident.  The  curve 
for  the  brain-weight  of  eminent  men  also  points  in  this  direction.  In  this 
latter  group  the  atrophy  of  old  age  does  not  become  evident  until  the  sixtieth 
year.  To  explain  this,  it  must  be  remembered,  as  ha.s  been  previously  stated, 
that  the  records  of  the  weight  of  the  brain,  such  as  those  here  quoted  from 
Boyd,  Bischoff,  and  Vierordt,  are  all  based  on  hospital  autopsies  made  in 
densely-settled  communities,  and  that  the  social  status  of  the  individuals  there 
examined  was  that  of  a  class  least  vigorous  and  least  favorably  situated.  It  is 
not  surprising,  therefore,  that  when  compared  with  the  group  of  eminent  men, 
both  vigorous  and,  as  a  rule,  more  favorably  situated,  not  only  should  the 
average  weight  be  greater  in  this  group,  but,  what  is  more  important,  growth 
should  continue  for  a  longer  time  and  the  period  of  senile  atrophy  be  deferred. 

If,  as  appears  probable,  these  differences  depend  on  the  favorable  or  unfa- 
vorable conditions  existing  during  growth,  then  it  will  be  evident  that  the 
average  man  is  possessed  of  a  nervous  system  which  probably  grows  for  a 
longer  time  and  resists  decay  to  a  later  age  than  the  figures  of  Bischoff  or 
of  Boyd  would  suggest. 

"Weight  of  Brain  at  Birth. — The  older  records  gave  the  male  child  the 
heavier  brain  at  birth,  while  the  newer  records,  like  those  of  Vierordt  and 
others,  give  the  reverse.  Be  this  as  it  may,  the  weight  at  birth  is  seen  to  be 
nearly  alike  in  the  two  sexes,  and  the  difference  in  w^eight  becomes  distinct  and 
increases  during  the  period  of  most  active  growth  up  to  maturity,  from  which 
time  to  the  end  of  life  this  difference  between  the  sexes  remains  nearly  constant. 

The  proportional  weights  of  the  different  parts  according  to  the  method  of 
subdivision  practised  by  Boyd  are  here  shown.  The  figures  indicate  the  per- 
centage values  of  the  parts  of  the  encephalon  : 

Weight  of  the  Encephalon  and  its  Parts  at  Different  Ages  {Boyd). 


Males. 

No.  of  Casea. 

Age. 

Cerebrum. 

Cerebellum. 

Stem. 

45 

New-born. 

92.4 

5.8 

1.60 

22 

7  to  14   years. 

87.8 

10.3 

1.61 

99 

30   "   40       " 

87.3 

10.6 

1.98 

95 

70   "   80       " 

I 

87.0 

"EMAI.E-S. 

10.7 

2.09 

45 

New-born. 

9-2.1 

6.2 

1.50 

18 

7  to  14   veara. 

87.9 

10.5 

1.50 

80 

.30   "   40       " 

87.0 

10.8 

2.01 

128 

70   "   80       " 

86.9 

10.9 

2.15 

*  Gallon  :  Hereditary  Oeniuf,  1884;  Venn:  Nature,  1890. 


CEJSTUAL    NERVOUS   SYSTEM.  727 

Tlio  table  iiulu'iites  a  i>n.i)<)iti<)iial  relation  al  birth,  and  probably  lor  a 
short  time  alter,  dittereiit  froiu  that  (bund  at  inaliirity,  but  this  very  early 
approximates  that   tbund   in   the  adidl. 

Relation  between  Growth  of  Body  and  Encephalon.— When  the  eurve 
of  growth  Ibr  the  entire  body  is  compared  with  that  Tor  the  growth  of  the 
encephalon,  it  is  (piite  evident  that  the  growth  is  more  rapid  in  the  central 
nervous  system  than  jn  the  body  at  large,  and  that  it  is  almost  completed  in 
the  former  at  tlie  end  of  the  eighth  year,  whereas  the  body  has  reached  but 
one-third  of  the  weight  which  it  will  attain  at  maturity. 

A  causal  relation  between  a  well-developed  central  system  and  the  subse- 
quent growth  of  the  entire  body  is  thus  suggested,  aud  also  it  is  evident  that 
conditions  which  influence  growth  will  at  any  time  find  the  body  on  the  one 
liand,  and  the  central  system  on  the  other,  at  quite  different  phases  in  their 
development. 

The  long-continued  growth  of  the  body  brings  it  about  that  the  central 
system,  which  at  birth  may  form  12  per  cent,  of  the  total  weight  of  the  indi- 
vidual, is  at  maturity  about  2  per  cent,  or  less.  For  this  change  in  proportion 
the  increase  of  the  muscular  system  is  mainly  responsible. 

Further,  the  much  smaller  mass  of  the  muscular  system  in  the  female  is 
the  chief  cause  of  the  higher  percentage  value  of  the  central  system  in  the  • 
female— a  relation  which  has  been  much  emphasized,  but  which  is  really  not 
significant,  since  in  both  sexes  this  high  percentage  value  of  the  central  system 
is  most  developed  at  birth,  and  becomes  steadily  less  marked  as  maturity  is 

approached. 

Increase  in  the  Number  of  Functional  Nerve-elements.— Having 
thus  briefly  indicated  the  facts  of  growth  so  far  as  they  can  be  detected  by 
the  balances,  it  still  remains  to  mention  the  series  of  changes  which  may  be 
studied  by  other  means,  such  as  micrometric  measurements  or  enumeration. 
The  results  obtained  by  these  methods  are  somewhat  complex  and  must  be 
treated  with  great  care.  Human  embryology  indicates  that  after  the  third 
mouth  of  fetal  life  the  number  of  cells  in  the  central  system  is  not  increased. 
With  the  cessation  in  the  production  of  new  cells  the  only  remaining  means 
of  increase  in  size  is  by  enlargement  of  those  cells  already  present. 

How  this  occurs  is  well  indicated  by  the  accompanying  table  (page  728), 
which  shows  the  change  in  the  size  of  cell-bodies  in  a  given  locality  in  man. 

All  vertebrates  are  not  similar  in  respect  to  the  manner  of  this  change. 
Birge^  has  shown  that  in  frogs  there  is  a  gradual  increase  in  the  number  of 
the  fibres  forming  the  ventral  and  dorsal  spinal  roots,  and  that  this  goes  on  at 
the  rate  of  about  fifty  additional  fibres  in  the  ventral  roots  and  seventy  in  the 
dorsal,  for  each  gram  added  to  the  total  weight  of  the  frog.  The  increase  was 
still  apparent  in  a  frog  weighing  one  hundred  and  twelve  grams.  In  the  case 
of  the  ventral  root-fibres  it  was  also  determined  that  the  cells  of  origin  in  the 
ventral  horns  of  the  spinal  cord  increased  in  number  in  a  similar  manner. 
Here  is  exemplified  an  instance  of  long-continued  enlargement  of  the  nervous 
1  Birge:  Archivfur  Anaiamie  und  Pkysiolocjie,  Supplem.,  1882. 


728 


AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 


system  by  tlie  regular  developiuuiit  ol"  iiiiinuturc  cells,  a  inetliod  of"  growth 
most  marked  probably  in  those  animals  which  increase  in  size  so  long  as  they 
live. 

Volumes  of  the  Largest  Cell-bodies  in  the  Ventral  Horn  of  the  Cervical  Cord  of 

Man  [based  on  Kaiser* s  records  of  the  mean  diameters). 

The  volume  TOOjW^  in  tlie  fetus  of  four  weeks,  is  taken  from  His,  and  the  figures  represent 
multiples  of  that  volume. 


Fetus 


Child  at  birth 
Boy  at  fifteen  years 
Man,  adult  .... 


It  is  believed  that  in  this  case  the  new  cells  and  new  fibres  are  not,  strictly 
sjieaking,  new  morphological  elements,  but  are  the  result  of  developmental 
changes  taking  place  in  the  cells  present  in  the  system  from  an  early  period. 

A  distinction  is  thus  to  be  made  between  cell-elements  which,  because  they 
are  not  developed,  are  therefore  not  a  part  of  the  system  already  physiologi- 
cally active,  and  those  cells  already  organized  together  and  which  are  fully 
functional.  When,  therefore,  it  is  said  that  the  cells  of  origin  for  the  ventral 
root-fibres  increase  in  number,  the  increase  refers  to  the  latter  group,  and  not 
to  the  total  number  of  elements  of  both  kinds  present  in  the  cord.  In  other 
^vords,  the  number  of  cells  appears  to  increase  because  the  number  of  devel- 
oped cells  become  greater. 

On  the  other  hand,  Schiller  ^  counted  the  number  of  nerve-fibres  in  the 
oculo-motor  nerves  of  cats,  and  found  but  a  very  slight  difference  in  this  num- 
ber between  birth  and  maturity.  So  far,  then,  as  this  nerve  is  concerned,  it  is 
found  in  the  cat  to  be  nearly  complete  at  the  time  of  birth. 

In  man  there  are  very  few  observations  on  the  increase  in  the  number  of 
functional  nerve-cells  with  age.  Kaiser,^  as  is  shown  in  the  accompanying 
table,  found  in  man  increasing  numbers  of  large  nerve-cells  in  the  ventral 
horns  of  the  spinal  cord  at  the  ages  named  : 

Number  of  Developed  Cells  in  the  Cervical  Enlargement  of  Man  ai 
Different  Ages  (Kaiser). 

Age.  Number  of  Nerve-cells. 

Fetus,  16  weeks 50,500 

"      32      "        118,330 

New-born  child      104,270 

Boy,  fifteen  years 211,800 

Male,  adult 221,200 

'  Schiller:  Compter  rendus  de  P Academic  dcs  Sciences,  Paris,  1889. 
*  Die  Functionen  der  Gangliemellen  des  Halsmarkes,  Haag,  1891. 


CENTRAL    NERVOUS  SYSTEM. 


729 


Here,  as  in  the  frog,  the  apparent  increase  must  be  looked  upon  as  due  to 
the  gradual  development  of  elements  present  from  an  early  date. 

Increase  in  the  Fibres  of  the  Cortex. — The  area  of  the  cerebral  cortex 
(see  Fig.  205)  varies  according  to  several  conditions,  but  in  general  the  more 
voluminous  the  cerebral  hemispheres  the  greater  its  extent.  That  which  cov- 
ers the  walls  of  the  sulci  has  in  man  about  twice  the  extent  of  that  directly 
exposed  on  the  surface  of  the  hemispheres. 


Fig.  205.— Diagram  illustrating  the  extent  of  the  cerebral  cortex.  The  outer  square  {E)  shows  a  sur- 
face approximately  ^V  of  2352  sq.  cm.  in  extent ;  the  inner  square  (A)  has  two-thirds  of  this  area,  and  is 
the  proportion  of  the  cortex  sunken  in  the  fissures.  2352  sq.  cm.  is  approximately  the  area  of  the  entire 
cortex  in  a  male  brain  weighing  1360  grams. 

In  the  cortex  of  the  human  cerebral  hemispheres  it  has  been  shown  by 
Vulpius'  that  the  number  of  fibres  in  the  different  layers  is  greater  at  the 
thirty-third  year  than  at  earlier  periods,  and  in  old  age  the  number  is  again 
decreased.  At  exactly  what  age  decrease  sets  in  is  not  to  be  determined  from 
these  observations.  They  show,  simply,  that  in  general  the  number  of  fibres 
was  less  at  seventy-nine  years  than  at  thirty-three  years. 

In  a  similar  way  Kaes^  has  compared  the  development  of  the  thickness  of 
the  cortical  fibre-layers  in  a  youth  of  eighteen  years  as  contrasted  with  a  man 
of  thirty-eight  years,  and  found  them  thicker  in  the  latter. 

The  relation  of  the  cell-bodies  in  the  cerebral  cortex  at  different  ages  is 
illustrated  by  Figure  206. 

Significance  of  Medullation. — Two  sorts  of  nerve-fibres  are  described — 
those  with  and  those  without  a  medullary  sheath.  Both  have  the  power  of 
isolated  conduction,  but  in  the  peripheral  system  the  non-medullated  fibres  are 
found  in  connection  with  the  sympathetic  system,  where  less  specialized  func- 
tions are  carried  on,  and  also  in  a  large  but  varying  degree  in  the  central  sys- 

^  Vulpins:  Archivfur  Psychiatric  und  Nervenkrankheiten,  1892. 
^  Neurologische  CkntralblaU,  1891. 


730 


AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 


tern.     The    wider    significance    of"  this   difference    in    medullatiou    is   at   the 
moment  quite  obscure. 

The  first  suggestion,  tliat  absence  of  the  medullary  sheath  is  an  immature 
condition  which  persists  in  various  parts  of  the  nervous  system,  brings  us  at 


ol 


D 


Fig.  206.— To  show  in  the  developing  human  cortex  the  increase  in  the  number  and  size  of  the 
mature  ceU-bodies,  as  well  as  the  separation  of  them  from  one  another  (Vignal) :  A,  fetus  of  twenty- 
eight  weeks;  JS,  fetus  of  thirty-two  weeks:  C,  child  at  birth;  A  man  at  maturity;  I-V,  layers  of  the 
cortex  according  to  the  enumeration  of  Meynert. 

once  to  the  question  of  the  physiological   difference  thus  implied   but  not 
explained. 

It  is  known  that  the  central  system  is  at  birth  very  imperfectly  medullated, 
and  the  growth  of  these  medullary  sheaths  must  form  a  large  part  of  the  total 
increase  in  its  bulk.  In  the  mature  fibre  the  axis-cylinder  and  the  medullary 
sheath  have  nearly  equal  volumes,  and  therefore  approximately  equal  weights. 
The  medullated  fibres  form  probably  not  less  than  90  per  cent,  of  the  total 


CENTRAL    NERVOUS  SYSTEM. 


731 


weight  of  tlie   norvo-tissiies  composing  the  encephaloii,  and  of  this  one-half 
would    he  medullary  substance. 

Increase  in  the  Mass  of  Nerve-cells. — The  amount  of  this  increase  under 
various  conditions  has  ali'cady  l)een  discussed,  and  heen  found  to  range  between 
zero  and  fifty-thousand-fold. 

Number  of  Cells. — A  conservative  estimate  of  the  number  of  cells  in  the 
entire  central  system  is  3,000,000,000.  Giving  each  cell  of  this  number  a  vol- 
ume of  at  least  700//'  (His'  measurements  give  697;/'),  then  this  entire  number 
could  easily  be  placed  in  2.25  cu.cm.  We  assume  that  about  three-quarters 
of  the  total  volume  of  the  central  system  is  nerve-tissue  proper,  while 
the  remaining  quarter  is  composed  of  the  supporting  tissues  and  blood- 
vessels. 

Volume  of  Central  System. — The  volume  of  the  entire  system  contain- 
ing cells  of  the  number  and  size  chosen,  as  well  as  the  supporting  tissues,  would 
then,  on  the  supposition  made,  be  about  3  cu.cm.,  which  is  approximately  that 
found  in  the  human  fetus  at  the  end  of  the  twelfth  week  (see  Fig.  207).  The 
enlargement  occurring  between  this  time  and  maturity  is  that  between  3  cu.cm. 
and  1340  cu.cm.,  the  latter  figure  being  the  volume  of  the  encephalon  and  cord, 


Maturity 


/ 

Birth 

/ 

/ 

/Fet''B 

A 

/                   1 

12  wks. 

/ 

/ 

Fig.  207.— Cubes  illustrating  the  relative  volumes  of  the  central  nervous  system  at  the  twelfth  week 
of  fetal  life,  at  birth,  and  at  maturity.  The  cubes  as  shown  have  exactly  one-eighth  of  their  true 
volumes. 


weighing  1386  grams  (encephalon  1360  grams,  and  spinal  cord  26  grams), 
and  having  together  a  specific  gravity  of  1036.  This  change  demands  an 
average  enlargement  in  the  nerve-elements  of  four  hundred  and  forty- 
seven-fold,  which,  it  is  seen,  is  well  within  the  limits  of  that  found  for 
a  cortical  cell  of  medium  size  which  had  enlarged  six  hundred  and  sixty 
times  (pages  608,  609). 


732 


AN  AMERICAN   TEXT- BO  OK   OF  PHYSIOLOGY. 


Estimates  of  the  Volume  of  the  Central  No'vous  St/stem.     Encephalon  and  Spinal 

Cord  at  Different  Ages. 

Three-quarters  of  this  volume  is  assumed  to  represent  the  nerve-elements  i)roper.     For  the 
first  two  records  I  am  indebted  to  Professor  F.  P.  Mall.     The  third  is  estimated. 


Subject. 


Fetus 

(( 

(( 
Child 

•Man  . 


Age. 


2  weeks. 

4  " 
12  " 
At  birth. 

Adult. 


Weight. 


Grams. 


Volume  of  Nervous  SyBtem— 
Encephalon  and  Cord. 


Vol., 
cu.cm. 


%  of  this  in 
cu.cm. 


381-f4 

385 

1360+26 

1386 


0.04 
0.2 
3.0 
376 

1340 


0.03 
0.15 
2.25 

282 

1005 


From  the  foregoing  facts,  together  with  those  bearing  on  the  cell-elements, 
it  is  possible  to  get  some  conception  of  the  growth-processes  in  the  central 
system,  and  to  see  how  they  are  due  to  an  enlargement  of  the  nerve-elements 
which  have  been  formed  at  a  very  early  stage  in  the  life-history  of  the 
individual.  In  such  enlargements  the  chief  inci-ease  is  due  to  the  formation 
of  the  neurons,  and  in  them,  in  turn,  about  half  the  substance  is  represented 
by  the  medullary  sheaths. 

In  all  probability  these  sheaths  are  no  exception  to  the  rule  according  to 
which  all  parts  of  the  body  are  variable,  not  only  in  their  absolute  but  also  in 
their  relative  size,  and  therefore  it  is  possible  that  the  quantitative  variation  in 
this  constituent  is  a  very  important  factor  in  modifying  the  weight  of  the  cen- 
tral system. 

Change  in  Specific  Gravity  with  Age. — During  fetal  life  and  at  birth  the 
specific  gravity  of  the  nerve-tissues  is  low,  but  becomes  higher  at  maturity. 
This  change  is  correlated  in  some  measure  with  the  development  of  the  medul- 
lary substance. 

For  the  gross  physical  changes  which  have  thus  been  indicated  as  occurring 
during  growth  an  explanation  is  to  be  found  in  the  changes  affecting  the  con- 
stituent elements,  and  these  have  been  set  forth  when  describing  the  growth 
of  the  individual  cells. 


C.  Organization  and  Nutrition  of  the  Central  Nervous 

System. 

What  is  here  meant  by  organization  may  be  easily  illustrated.  When,  for 
example,  by  later  growth  new  tissue  is  added  to  the  liver  or  the  skin  is  in- 
creased in  area  or  a  muscle  enlarged,  there  is  caused  by  the  addition  of  new 
substance  a  change  in  the  powers  of  these  tissues,  which  is  mainly  quantitative. 
The  larger  organ  exhibits  the  same  capabilities  that  the  smaller  organ  exhibited, 
but  does  so  in  a  greater  degree. 

In  the  central  nervous  system,  on  the  other  hand,  it  appears  that  with 


CENTRAL    NERVOUS  SYSTEM.  733 

growth  the  system  becomes  capable  of  new  reactions  iu  the  sense  that  its 
various  responses  are  controlled  and  directed  by  a  larger  number  of  incoming 
impulses,  and  thus  the  number,  complexity,  and  refinement  of  the  reactions 
is  iucreaseil,  and   in  this  sense  it  really  attains  new  powers. 

AVith  the  change  in  the  age  of  the  central  system  there  occurs  from 
birth  to  matnritv,  if  we  may  ju(l<r('  from  general  reactions,  an  increase  in 
this  organization  which  is  maintained  during  the  prime  of  life,  and  then 
in  old  age  this  breaks  down,  at  first  gradually,  and  later  rapidly.  It 
becomes  important,  therefore,  to  examine  the  manner  in  which  this  organ- 
ization is  accomplished. 

Organization  in  the  Central  System. — When  first  formed  the  cells  com- 
posing the  central  system  are  completely  separated  from  one  another.  In  the 
mature  nervous  system  the  impulses,  as  has  been  pointed  out,  probably  travel 
for  the  most  part  from  the  neurons  of  one  unit  to  the  dendrons  of  another. 
From  the  original  position  in  which  the  young  cells,  the  neuroblasts,  are 
produced,  they  plainly  migrate,  and  often  these  migrations  involve  groups  of 
cells,  as  in  the  case  of  those  forming  the  olivary  bodies  (His). 

For  organization  the  most  important  changes,  however,  are  those  affecting 
the  branches,  both  dendrons  and  neuron.  During  growth  both  of  these  in- 
crease in  the  length  of  their  main  stem  and  of  their  respective  branches.  In 
picturing  the  approach  of  two  elements  within  the  central  system  the  process 
is  usually  described  as  that  of  the  outgrowth  of  the  neuron  toward  the  den- 
drons or  bodies  of  those  cells  which  are  destined  to  receive  the  impulse,  but  it 
must  by  no  means  be  forgotten  that  the  dendrons  are  also  growing,  and  the 
question  of  the  approximation  of  the  branches  of  these  latter  to  those  of  the 
neurons  depends  on  their  own  activities  as  well. 

The  conditions  modifying  this  process  are,  however,  obscure.  It  is  evident 
that  medullation  outside  of  the  central  system  is  not  necessary  to  the  functional 
activity  of  a  fibre,  and  therefore  probably  in  the  central  system  unmeduUatetl 
fibres  are  also  in  many  cases  functional.  Whatever  may  be  the  relation  of 
the  establishment  of  new  pathways  to  the  acquisition  of  medullary  sheaths  by 
the  neuron  and  its  branches,  it  is  also  clear  that  all  fibres  which  when  mature 
are  medullated  begin  as  unmedullated  fibres,  that  the  increase  in  medullation 
throughout  the  central  system  is  an  index  of  the  increase  in  organization.  A 
consideration  of  the  facts  of  growth  iu  the  layers  of  the  cortex,  for  instance, 
will  show  them  to  be  open  to  this  interpretation. 

Applying  these  ideas  concerning  organization  to  the  three  classes  of  cells, 
afferent,  central,  and  efferent,  composing  the  nervous  system,  we  find  the  fol- 
lowing :  In  the  central  system  the  afferent  cells  contribute  to  organization  by 
the  multiplication  of  the  collaterals.  At  the  periphery  the  division  of  the 
branches  of  the  neuron  increases  the  number  of  opportunities  for  excitation 
which  such  an  element  offers.  These  cells  are  without  dendrons.  Among 
the  central  cells  all  possible  modes  of  growth  are  contributory;  that  is, 
the  branches  of  both  kinds  add  directly  to  the  complexity  of  the  central 
pathways.     On  the  other  hand,  the  efferent  grouj)  contributes  to  this  com.- 


734  AX  AMERICAN    TEXT- HOOK    OF  PHYSIOLOGY. 

plcxity  almost  solelv  by  the  furination  of  dcndroiis,  the  collaterals  which  come 
from  the  neurons  of  these  cells  forming  but  an  insignificant  contribution.  Not 
onlv,  tiierefore,  is  organization  in  large  ])art  dependent  on  changes  in  the  cen- 
tral cells  bv  reason  of  their  numerical  preponderance,  l)ut  also  by  reason  of  the 
fact  that  to  them  a  multiplication  of  pathways  both  by  elaboration  of  the 
neurons  and  the  dendrons  is  alone  possible. 

Defective  Development. — In  view  of  these  facts,  defective  development 
in  the  nervous  system  may  depend  on  failure  in  one  or  more  of  these  several 
processes  by  which  the  system  is  organized,  and  it  should  be  possible  to  correlate 
defective  development  involving  mainly  one  set  of  elements  with  a  distinct 
clinical  picture.  The  results  of  defective  development  are  not  merely  an 
absence  of  certain  powers,  but  in  some  measure  a  diminution  in  the  strength 
and  range  of  thos(;  that  remain. 

Laboratory  Animals. — The  bearing  of  these  facts  on  the  conception  which 
we  form  of  the  nervous  systems  of  those  animals  commonly  employed  for 
laboratory  experiments  may  be  here  mentioned.  The  frog,  pigeon,  rabbit, 
cat,  and  dog  form  a  series  in  which  the  total  mass  of  the  central  system 
increases  from  the  beginning  to  the  end  of  the  series. 

The  number  of  cells  in  the  largest  system,  that  of  the  dog,  is  many  times 
greater  than  that  in  the  smallest,  the  frog,  and  it  is  probable  that  the  others  are 
in  this  respect  intermediate.  Organization  is  apparently  more  rapidly  completed 
and  more  nearly  simultaneous  throughout  the  entire  system  in  forms  like  the 
froo;  and  pigeon,  and  also  in  these  latter  the  organization  is  least  elaborate  at  the 
cephalic  end.  While  the  educability  of  the  nervous  system  of  the  dog  may 
depend  on  several  conditions,  the  comparative  slowness  of  organization  is 
undoubtedly  one  of  them,  and  a  very  important  one.  Where  the  organ- 
ization is  early  established  it  is  found  that  the  parts  organized  have  a 
greater  independence  than  under  the  reverse  conditions.  In  selecting  an 
animal,  therefore,  on  which  to  make  a  series  of  experiments,  these  several 
facts  must  be  kept  in  view,  for  the  choice  is  by  no  means  a  matter  of 
indifference. 

Blood-supply. — For  the  general  distribution  of  the  blood-vessels  in  rela- 
tion to  the  gross  subdivision  of  the  brain  the  student  is  referred  to  the  works 
on  anatomy.  The  finest  network  of  vessels  is,  however,  to  be  found  where 
the  cell-bodies  are  most  densely  congregated,  and  indeed  the  distinction 
between  the  masses  of  gray  and  white  matter  in  the  central  system  is  as 
clearly  marked  by  the  relative  closeness  of  the  capillary  network  as  in  any 
other  way.  One  result  of  this  relation  between  the  blood-supply  and  tiie  cell- 
bodies  which  form  the  gray  matter  is  a  general  arrangement  of  the  vessels  along 
the  radii  of  the  larger  subdivisions  of  the  brain,  as  the  cerebral  hemispheres 
and  the  cerebellum. 

The  conditions  which  control  the  circulation  within  the  cranium  and  spinal 
canal  are  not  exactly  the  same  at  all  periods  of  life,  but  the  variations  occur 
in  minor  points  only. 

The  general  conditions  are  the  following  :  The  evidence,  physiological  and 


CENTRAL   NERVOUS  SYSTEM.  735 

histological,  is  against  the  existence  of  vaso-motor  nerves  in  the  vessels  of  the 
pia  or  of  the  enccphalon  and  cord  (see  Circnlation).' 

The  circulation  in  these  regions,  therefore,  is  not  modified  by  any  rcjicx  varia- 
tions in  the  calibre  of  the  vessels.  The  authors  just  cited  do  not  find  any  evi- 
dence for  a  local  control  of  the  arterioles  whereby  the  products  of  nerve-cell 
activity  cause  an  increase  iu  the  diameter  of  the  vessels  affected  by  these  sub- 
stances. The  reactions  of  the  central  vessels  are  broadly  those  of  a  system  of 
elastic  tubes  in  a  closed  cavity.  As  a  result,  it  is  found  that  the  quantity 
of  blood  in  the  central  system  is  subject  to  very  slight  variations  only.  A  rise 
in  the  arterial  pressure  causes  a  more  rapid  flow  of  the  blood  through  the 
encephalon.  It  also  causes  a  rise  in  the  venous  j)ressure,  and  with  this  a 
corresponding  rise  in  the  intracranial  pressure,  the  last  two  varying  in  the 
same  sense  and  to  the  same  extent. 

The  flow  through  the  central  system  is  subject  to  the  influence  of  gravity, 
and  takes  place  the. more  readily  the  more  the  resistance  is  diminished.^  The 
principal  controlling  mechanism  is  in  the  splanchnic  area.  According  to  the 
condition  of  the  vessels  in  this  area  the  intracranial  blood-pressure  varies. 

It  is  to  be  noted  in  passing  that  when  a  person  lying  on  a  table  is  balanced 
on  a  transverse  axis,  this  axis  is  about  8.77  centimeters  to  the  cephalic  side  of 
the  line  which  joins  the  heads  of  the  femurs.^  This  leaves,  of  course,  the 
splanchnic  area  mainly  on  tiie  cephalic  side  of  this  axis,  and  hence  any  inflow 
of  blood  from  the  extremities  would  tend  to  make  the  head  end  of  the  person 
thus  balanced  dip  down.  This  dip  will  occur  even  when  the  splanchnic  area 
alone  is  filled,  and  hence  the  dipping  as  such  would  not  necessarily  indicate  an 
increase  in  the  quantity  of  blood  in  the  encephalon. 

In  the  adult  the  cranial  cavity  is  almost  rigidly  closed.  There  is  an  oppor- 
tunity for  the  escape  of  a  small  quantity  of  fluid  through  the  foramen  magnum 
into  the  vertebral  canal.  When,  as  the  result  of  increased  arterial  pressure, 
the  brain  has  increased  so  as  to  drive  out  the  subdural  fluid,  the  brain  is  forced 
against  the  walls  of  the  cranium  and  blocks  the  outflow  into  the  spinal  canal. 
In  the  same  way  it  has  been  found  that  if  a  mass  displacing  from  2-3  cu.cra. 
be  introduced  into  the  subdural  space  of  a  dog  the  brain  will  adjust  itself  with- 
out rise  of  intracranial  pressure.  If  in  this  case  the  volume  of  the  mass  intro- 
duced is  increased,  there  follows  a  rise  of  intracranial  pressure,  and  this  rise  in 
every  instance  tends  to  impede  the  circulation  through  the  brain.  While  the 
fontanelles  are  open  the  brain  normally  pulsates,  and  we  recognize  in  its  varia- 
tions in  volume  all  the  different  variations  in  blood-pressure  with  which  we  are 
familiar.  The  pulsation  of  the  brain  is  doubtless  an  important  aid  to  the 
movements  of  the  fluids  within  and  hence  tends  to  facilitate  nutrition  during 
the  earlier  periods  of  growth. 

In  pathological  cases  where  the  cranial  wall  has  been  destroyed,  there  is 
a  similar  variation  in  volume  to  be  observ^ed  in  the  adult,  and  it  is  possible 

'  Bayliss,  Hill,  and  Gulland :  Journal  of  Physiology,  1895,  vol.  xviii. 

'  Hill  :  Jownal  nf  Phyniolof/y,  1895,  vol.  xviii. 

*  W.  und  Ed.  Weber:  Mechanik  der  menschlichen  Gehwerkzewje,  1836. 


736  JN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

that  the  beneficial  effects  which  in  .so  many  instances  follow  trc})hinin<^  of  the 
sknll  may  depend  upon  this  mechanical  release.  Of  course  in  cases  with  a 
defective  skull-wall  an  increase  in  arterial  pressure  causes  a  more  decided 
increase  in  the  volume  of  blood  in  the  brain  ;  this,  however,  is  much  more 
marked  than  it  would  be  under  ordinary  conditions,  and  is  not  to  be  regarded 
as  the  main  effect,  which  is  an  increase  in  the  quantity  of  the  blood  passed 
through  the  central  system  in  a  unit  of  time.  Mosso  ^  has  found  the  tempera- 
ture of  the  blood  coming  from  the  brain  (dogs)  slightly  higher  than  tiiat  of 
the  rectum  and  of  the  arterial  blood.  The  differences  are  very  small,  but 
he  draws  the  conclusion  that  the  metabolic  processes  in  the  brain  are  suffi- 
ciently intense  to  raise  the  temperature  of  the  blood  passing  through  it. 

As  against  the  intensity  of  the  metabolism  in  the  central  system,  it  has 
been  observed  that  blood  taken  from  the  torcular  Herophili  of  the  dog  was 
intermediate  between  arterial  blood  and  that  taken  from  the  femoral  vein,  thus 
indicating  that  the  arterial  exchange  was  less  intense  in  the  brain  than  in  the 
muscles  of  the  leg.     The  following  is  a  condensed  statement  of  the  figures : 

Percentages  of  Oxygen  and  Carbonic  Acid  in  various  Samples  of  Dogs' 

Blood  {Hiliy 

.  r  CO     .    •  1  1  ^  CO.,        37.64  per  cent. 

Average  of  52  arterial  samples ■,  ^  „  „,       „ 

t.  O  18.25       " 

Average  of  42  torcular  samples 1r»*         iq'^q       « 

A               r  OQ  <•          1      •  f  CO2        45.75       " 

Average  of  28  femoral  vein 1  rk  «  Q/I        « 

The  absolute  quantity  of  blood  in  the  brain  and  cord  is  certainly  small ; 
if  we  nuiy  judge  from  the  observations  on  animals,  it  is  not  more  than  1  per 
cent,  of  the  entire  blood  in  the  body.  It  is  to  be  remembered,  however,  that 
the  cell-bodies,  which  alone  are  well  supplied  with  blood,  probably  represent 
less  than  one-tenth  of  the  entire  encephalic  mass. 

With  general  rise  and  fall  of  pressure  elsewhere  there  is  a  rise  and  fall  of 
pressure  within  the  central  system.  During  the  first  phases  of  mental  activity 
blood  is  withdrawn  from  the  limbs ;  the  blood  thus  withdrawn  can  be  shown 
to  pass  toward  the  trunk,  for  when  a  pei-son  lying  on  a  horizontal  table  sup- 
ported at  the  centre  on  a  transverse  knife-edge  is  just  balanced,  then  increased 
activity  of  the  cerebral  centres  causes  the  head  end  to  dip  down  (Mosso),  and 
if  the  skull  wall  is  defective  the  brain  is  seen  to  swell. 

In  the  latter  stages  of  fatigue  the  blood-supj)ly  to  the  nerve-centres  dimin- 
ishes owing  to  a  decrease  in  force  of  the  heart-beat  and  the  tonicity  of  the 
splanchnic  vessels,  .so  that  the  brain  in  birds  exhau.sted  by  a  long  flight  has 
been  found  by  Mosso  to  be  in  a  high  degree  anaemic.  There  is  much  rea.sou  to 
think  that  in  man  a  similar  reaction  occurs. 

The  study  of  the  cerebral  circulation  in  the  case  of  those  in  whom  the 
skull-wall  is  at  some  point  deficient  shows  a  bulging  of  the  skin  over  the  open- 
ing into  the  cranial  cavity  as  a  result  of  mental  effort  or  emotion.     In  the 

^  Die  Temperatur  des  Gehims,  1894,  Leipzig.         *  Journal  of  Physiology,  vol.  xviii.,  1895. 


CENTRAL    NERVOUS  SYSTEM. 


737 


nonnal  adult  this  bultring  cannot  of  course  occur  to  anything  like  such  an 
extent,  and  the  s|)ace  for  the  arterial  blood  must  he  gained  in  the  first  instance 
by  driving-  out  the  blood  from  the  venous  simises  within  the  erauimn  and 
througli  the  removal  of  the  subduial   Ihiid. 

Influence  of  Glands. —  In  the  growth  of  the  nervous  system  it  is  not  only 
the  quantity,  but  the  })eeuliar  qualities,  of  the  blood  that  are  important,  and 
among  the  various  glauds  the  activity  of  which  is  necessary  for  the  growth 
of  the  nervous,  as  well  as  the  other  systems,  and  also  needed  for  its  full 
maintenance,  the  thyroid  appears  as  very  important.  In  sporadic  cretinism, 
associated  as  it  is  with  atrophy  of  the  thyroid,  the  feeding  of  sheep's  thyroids 
has  produced  remarkable  growth-changes  in  all  parts  of  the  body — the  nervous 
system  included. 

At  the  same  time,  experimental  extirpation  of  the  thyroid  is  followed  by  de- 
structive changes  in  the  central  system,  caused  by  disturbances  in  its  nutrition. 

Starvation. — In  starving  animals  the  nervous  system  loses  but  very  little 
in  weight.'  This  small  loss  is  most  striking,  and  would  seem  to  be  best 
explained  on  the  assumption  that  the  other  tissues  are  used  to  keep  up  the 
central  system,  which,  when  even  slightly  reduced  in  weight,  ceases  to  act. 

Fatig-ue. — The  histological  basis  of  fatigue,  as  expressed  by  the  changes 
in  the  individual  cells,  has  already  been  discussed.  The  fatigue  of  the 
system  as  a  whole  is  but  the  expression  of  fatigue  in  large  numbers  of  its 
elements,  but  the  manner  in  which  the  changes  show  themselves  is  somewhat 
complicated. 

When  the  attempt  is  made  to  raise  a  weight  by  the  voluntary  contractions 
of  the  muscles  of  the  index  finger  at  regular  intervals,  say  once  a  second,  it  is 
found  that  if  the  weight  be  heavy  the  power  of  the  finger  decreases,  and  the 


lllililll  I  I  I  lllllllll  III!  I  II  I  I  I 

Fig.  208.— a  record  of  the  extent  of  the  flexions  of  the  forefinger  lifting  a  weight  at  regular  intervals. 
The  light  lines  are  those  for  the  voluntary  contractions;  the  heavy  lines,  those  for  contractions  follow- 
ing the  direct  stimulation  of  the  flexor  muscles  by  electricity.  In  the  former  there  are  periods,  in  the 
latter  none.    The  arrow  shows  the  direction  in  which  the  record  is  to  be  read  (Lombard). 

weight  soon  ceases  to  be  lifted  as  high  as  at  first.  Finally,  a  point  is  reached 
when  the  voluntary  effort  produces  little  or  no  elevation  of  the  weight.  If, 
however,  despite  this  failure,  the  effort  is  still  made  at  regular  intervals,  it 
occurs  in  some  persons  that  this  power  returns  gradually,  and  a  few  seconds 
later  the  contractions  are  very  nearly  as  high  as  at  the  beginning  of  the  ex- 
periment (Mosso).  This  phenomenon  may  repeat  itself  many  times,  giving  a 
record  formed  by  groups  of  contractions  most  extensive  near  the  centre  of 
*  Voit :  Zeitschrift  fur  Biolofjie,  Bd.  xxx.,  1894. 
47 


738 


AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 


each  grouji,  these  latter  being  separateil  by  jwrtions  of  tlie  curve  in  whieh  the 
contractions  are  very  small  or  \vanting(see  Fig.  208).  (See  General  Physiology 
of  Nerve  and  ^rusclc,  p.  120.) 

Daily  Rhythms. — Within  the  cycle  of  the  astronomiciil  day  the  progress 
of  events  leading  to  fatigue  is  not  a  steady  one.  Lombard '  found  that  if  the 
cajiacity  for  voluntary  effoi-t  was  measured  by  the  amount  of  work  which  could 
be  done  by  voluntarily  contracting  the  flexor  muscles  of  the  index  finger  before 
the  first  failure  to  respond  to  a  voluntary  stimulus  appeared,  then  the  curve 


Fig.  209.— Showing  at  each  hour  of  the  day  and  night  how  many  centimeters  a  weight  of  3000  grams 
could  be  raised  by  repeated  voluntary  contractions  of  the  forefinger  before  fatigue  set  in.  The  curve  is 
highest  at  10  to  11  a.  m.  and  10  to  11  p.  .m.  ;  lowest,  3  to  4  p.  m.  and  3  to  4  a.  m.  Circle  with  dot,  observation 
made  just  after  taking  food;  sqiiare  with  dot,  smoking;  *,  work  done  eight  minutes  after  drinking  15 
cubic  centimeters  of  whisky  (Lombard;. 

expressing  this  capacity  for  voluntary  work  throughout  the  day  was  repre- 
sented as  in  Fig.  209.  Briefly,  the  curve  shows  two  maxima,  at  10  p.  m.  and 
10  A.  M.,  with  two  minima  midway  between  them.  In  general  the  immediate 
effect  of  taking  food  i.s  to  increa.se  the  work  done  by  the  subject.  Alcohol  has 
the  same  effect,  while  smoking  produces  a  decrease. 

Further,  from  day  to  day  this  capacity  for  w(jrk  was  influenced  by  a  num- 
ber of  external  conditions — temperature,  barometric  pressure,  etc. 

Time  taken  in  Central  Processes. — All  processes  in  the  nervous  system 
take  time,  and  are  for  the  most  part  easy  to  measure.  The  rate  of  the  nerve- 
impulse  has  already  been  given.  It  has  also  been  noted  that  in  passing  through 
the  body  of  a  spinal  ganglion-cell  the  impulse  suffers  some  delay.  When, 
'  Journal  of  Physiology,  vol.  xiii.,  1892. 


CENTRAL    NERVOUS  SYSTEM.  739 

however,  it  passes  fVoiu  uiic  clement  t<t  anotlier  the  delay  is  even  more  marked, 
and  it  is  [)lansil)le  to  assume  that  this  detention  oc(.'urs  at  the  juncture  of  the 
elemcuts.  Thus  in  those  parts  of"  the  central  system  where  the  cell-eleraents 
and  also  the  cell-junctions  are  most  numerous,  the  time  taken  is  longest. 


0.5  S^ec. 


^ 


Fig.  210.— To  show  the  rate  at  wliich  impulses  pass  through  the  nervous  system  of  a  frog.  At  the 
extreme  left  the  vertical  has  the  value  of  0.5  second  and  the  other  verticals  arc  compared  with  it;  thus 
between  the  cerebrum  and  the  optic  lobe  requires  about  0.25  second ;  between  the  bulb  and  the  lumbar 
enlargement  a  greater  distance— only  about  half  the  time;  and  for  the  still  greater  distance  represented 
by  the  length  of  the  sciatic  nerve  even  less  time  is  needed  (Exner). 

Figure  210  shows  this  very  well.  Between  the  middle  of  the  cerebral 
hemisphere  and  the  optic  lobe,  although  the  distance  is  short,  the  impulse  takes 
twice  as  long  to  travel  as  between  the  bulb  and  the  lumbar  enlargement.  When 
this  time  is  measured  in  the  conscious  individual  it  is  of  coiir.se  open  to  a  long 
series  of  modifying  conditions,  and  these  appear  to  be  in  part  the  same  condi- 
tions which  modify  the  muscular  endurance  of  the  individual  at  different  por- 
tions of  the  day.  Thus  it  has  been  determined  that  the  speed  with  which 
reactions  can  be  made,  as  indicated  by  the  reaction  time,  is  subject  to  varia- 
tions, and  does  not  steadily  decrease  from  the  morning  to  the  evening. 

It  has  been  the  purpose  of  the  paragraphs  just  preceding  to  indicate  that 
through  the  day  it  is  not  possible  to  demonstrate  a  steady  decline  of  power  in 
the  nervous  system.  We  begin  the  morning,  to  be  sure,  feeling  fresh,  and  are 
fagged  in  the  evening,  but  the  course  by  which  this  condition  has  been  attained 
is  not  a  simple  or  direct  one. 

D.  Sleep. 

Conditions  Favoring  Sleep. — To  recover  from  fatigue  sleep  is  required. 
The  prime  condition  favoring  sleep  is  the  diminution  of  nerve-impulses  pass- 
ing through  the  central  system.  This  is  accomplished  in  two  ways.  In  the 
first  instance  it  is  usual  to  reduce  all  incoming  stimuli  to  a  minimum.  This  is 
most  directly  under  our  own  control.  On  the  other  hand,  the  permeability  of 
the  nervous  system  and  the  intensity  with  which  it  responds  are  decreased  as 
the  result  of  the  beginning  fatigue.  How  these  conditions  are  brought  about 
has  been  a  matter  of  much  speculation  and  some  experiment. 

The  parts  played  by  the  sensory  and  that  by  the  central  cells  vary  some- 
what at  different  times  of  life,  for  impulses  are  much  less  widely  diffu.sed  in 
the  early  years  than  at  maturity.  Moreover,  in  childhood  the  amount  of 
stored  material  is  small,  large  at  maturity,  and  small  again  in  old  age,  and 
this  holds  true  for  all  the  groups  of  cells.  Hence  the  cells  would,  by  reason 
of  this    fact,  have    the  greatest  ca])ability  for  work    in   the   middle    period. 


740  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

Between  cliildliood  and  old  a^e  there  i.s,  huvvever,  this  dillerenee — tliut  wliile 
iu  the  former  tlie  noii-uvaihible  substances  in  the  cell  are  developing,  not  yet 
having  matured,  those  in  the  latter  have  in  some  way  become  permanently 
useless.  The  degree  to  which  the  blood-su[)pIy  can  be  controlled  varies  with 
age,  and  the  amounts  of  substance  capable  of  yielding  energy  at  various  periods 
of  life  are  different ;  so  that,  considering  these  factors  alone,  though  there  are 
jn-obably  others,  it  may  be  easily  appreciated  that  the  sleep  of  childhood, 
maturity,  and  old  age  should  be  quite  distinguishable. 

Cause  of  Sleep. — It  is  recognized  that  local  exercise  is  capable  of  producing 
general  fatigue,  and  the  fatigued  portions  give  rise  to  afferent  imi)ulses  which, 
reaching  the  central  system,  cause  some  of  the  sensations  of  fatigue  ;  moreover, 
the  active  tissues  (nerve-cells  aud  muscles)  yield  as  the  result  of  their  activity 
some  by-product  which  is  carried  by  the  blood  through  the  central  system  and 
becomes  the  chief  cause  of  sleep.  It  has  been  shown  by  Mosso  that  if  a  dog 
be  thoroughly  fatigued,  giving  all  the  signs  of  exhaustion,  and  the  blood  from 
this  dog  be  transfused  to  one  that  has  been  at  rest,  after  the  transfusion  the 
dog  which  has  received  the  blood  from  the  exhausted  animal  will  exhibit 
the  symptoms  of  fatigue  in  full  force.  The  inference  is  that  from  the  tired 
animal  certain  by-products  have  thus  been  transferred,  and  that  these  are 
responsible  for  the  reactions.  AVe  know,  further,  that  we  can  distinguish  in 
ourselves  different  forms  of  the  feeling  of  fatigue,  and  that  the  sensations  which 
follow  the  prolonged  exercise  of  the  muscular  system  differ  from  those  follow- 
ing the  exercise  of  the  higher  nerve-centres. 

Cessation  of  stimuli,  decreased  responsiveness  of  the  active  tissues,  and  a 
change  in  the  composition  of  the  blood  are  the  preliminaries  to  sleep.  To 
these  should   be  added  the  diminiition  of  the  blood-supply  to  the  head. 

A  condition  superficially  resembling  sleep  can  be  induced  in  various  ways. 
Removal  of  all  external  stimuli,  extreme  cold,  anaesthetics,  hypnotic  suggestion, 
compression  of  the  carotids,  a  blow  on  the  head,  loss  of  blood,  all  produce  a 
state  of  unconsciousness  which,  in  so  far,  has  a  similitude  with  sleep.  These 
conditions  produce  this  state,  however,  by  mechanically  decreasing  the  blood- 
supply  or  cutting  off  the  peripheral  stimuli. 

Normal  sleep  is  tested  by  the  fact  that  during  its  progress  the  changes  that 
occur  in  the  central  system  are  recuperative,  whereas  this  feature  may  be  more 
or  less  absent  from  the  states  which  merely  resemble  it. 

Condition  of  the  System  during  Sleep. — It  apjiears  that  during  sleep 
the  ca])acity  of  the  central  system  to  react  is  never  lost.  Were  such  the  case 
it  would  not  be  possible  to  awaken  the  sleeper.  Moreover,  the  sleeping  per- 
son is  far  more  responsive  to  stimuli  from  without  than  at  first  might  be 
thought.  The  close  i*elations  between  dreams  and  external  stimuli  has  been 
recognized,  and  plethysmographic  studies  show  still  more  clearly  how  the  matter 
stands. 

It  was  found  that  when  a  subject  fell  asleep  with  the  arm  in  a  plethysmo- 
graph  various  stimuli  which  did  not  waken  the  sleeper  still  served  to  cause  a 
diminution  in  the  volume  of  the  arm,  which  was  certainly  due  to  the  with- 


CENTRAL    NERVOUS   SYSTEM. 


741 


drawal  of  blood  IVoin  it,  the  blood-supply  to  the  brain  being  probably  at  the 
same  time  increased  (see  Fig.  211). 


1 

..il'iil, 


1,1' 


.III 


,.|'"'"|ill|l"  ''III 


''''""'",l|i„(ii|i"l''i"" 


ii'ii' 


I'l' 


I"' 


'"'•I, ,i,i>""' 

Fig  "U  -ricthysinosraphif  record  taken  from  the  arm  of  a  person  sleeping  in  the  laboratory.  A  fall 
in  the  curve  indicates  a  decrease  in  the  volume  of  the  arm.  The  curve  is  to  be  read  in  the  direction  of 
the  arrow  1  the  night  watchman  entering  the  laboratory,  waking  the  subject,  who  shortly  fell  asleep 
again-  2  the  watchman  spoke ;  3,  watchman  went  out;  these  changes  {2  and  3)  occurred  without  awak- 
ening the  subject  (from  experiments  made  by  Messrs.  Bardeen  and  Nichols,  Johns  Hopkins  Medical 
School). 

This  oxi>erinient  shows  that  during  sleep  the  nervous  sy.stem  is  capable  of 
reactions  which  are  not  reuierabered  in  any  way,  but  which  naturally  form  a 
feature  of  the  condition  intermediate  between  waking  and  deep  slumber.  The 
depth  of  sleep  as  determined  by  the  strength  of  the  stimulus  necessary  to  elicit 
an  efficient  response  has  been  measured.  The  stimulus  in  these  experiments 
was  the  sound  caused  by  the  fall  of  a  ball  upon  a  plate,  and  the  measure  was 


r 

80U 

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600 

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500 

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4U0 

- 

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300 

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' — 

c    na 

Hours     0.5     1.0      1.5    2.0     2.5    3.0    3.b     4.U    4.i     ^.u    o.o    txu     o-a     /.w     /.^    /.- 

Fig  •'12  -Curve  illustrating  the  strength  of  an  auditory  stimulus  (a  ball  falling  from  a  height)  neces- 
sary to  waken  a  sleeping  person.  The  hours  marked  below.  The  tests  were  made  at  half-hour  intervals. 
The  curve  indicates  that  the  distance  through  which  the  ball  required  to  be  dropped  increased  during  the 
first  hour,  and  then  diminished,  at  first  very  rapidly,  then  slowly  (Kohlschutter). 

the  height  from  which  the  ball  must  fall  in  order  to  produce  a  sound  loud 
enough  to  awaken  a  sleeping  person.  The  results  of  the  observations  are  shown 
in  Figure  212. 


742  AN  AMERICAN    TEXT- HOOK    OF  PJIYiSIOLOGY. 

It  is  seen  fntiii  this  tJiat  tlio  jK-riod  of  dcop  slumber  is  short,  loss  than  two 
hours,  and  is  i'oliowed  by  a  long  period,  that  of  an  average  night's  rest,  during 
which  a  comparatively  slight  stimulus  is  sufficient  to  awaken.  Almost  the 
same  results  have  been  more  recently  obtained  by  Monninghoff  and  Pies- 
bergen.' 

It  is  evident  that  the  effectiveness  of  such  a  stimulus  is,  however,  no  measure 
of  the  recupci-ative  processes  in  the  central  system.  Repair  is  by  no  means 
accomplished  during  the  interval  of  deep  sleep,  and  experience  has  shown,  as 
in  the  case  of  persons  undertaking  to  walk  a  thousand  miles  in  one  thousand 
hours,  that  although  such  an  arrangement  left  the  subject  with  two-thirds  of 
the  total  time  for  rest  and  refreshment,  yet  the  feat  was  most  difficult  to  accom- 
plish by  reason  of  the  discontinuity  in  the  sleep.  The  changes  leading  to 
recuperation  needed  longer  periods  than  those  permitted  by  the  conditions  of 
the  experiment. 

Loss  of  Sleep. — Loss  of  sleep  is  more  damaging  to  the  organism  as  a 
whole  than  is  starvation.  It  has  been  found  (Maniiceine)  that  in  young  dogs 
which  can  recover  from  starvation  extending  over  twenty  davs,  loss  of  sleep  for 
five  days  or  more  was  fatal.  Toward  the  end  of  such  a  period  the  body-tem- 
perature may  fall  as  much  as  8°  C.  below  the  normal  and  the  reflexes  disap- 
pear. The  red  blood-corpuscles  are  first  diminished  in  number,  to  be  finally 
increased  during  the  last  two  days,  when  the  animal  refuses  food.  The  most 
widespread  change  in  the  tissues  is  a  fatty  degeneration,  and  in  the  nervous 
system  there  were  found  capillary  hemorrhages  in  the  cerebral  hemispheres,  the 
spinal  cord  appearing  abnormally  dry  and  ancTcmie. 

E.  Old  Age  op  the  Central  System. 

Metabolism  in  the  Nerve-cells. — Connected  closely  with  fatigue  are  those 
alterations  both  of  the  constituent  nerve-cells  and  of  the  entire  system  found  in 
old  age.  The  picture  of  the  changes  in  the  living  cells  is  that  of  anabolic  and 
katabolic  processes  always  going  on,  but  varying  in  their  absolute  and  relative 
intensity  according  to  several  conditions.  Of  these  conditions  one  of  the  most 
important  is  the  age  of  the  individual.  In  youth  and  during  the  growing 
period  of  life  the  anabolic  changes  appear  within  the  daily  cycle  of  activity  and 
repose  to  overbalance  the  katabolic,  the  total  expenditure  of  energy  increasing 
toward  maturity.  During  middle  life  the  two  processes  are  more  nearly  in 
equilibrium,  though  the  total  expenditure  of  energy  is  probably  greatest 
then,  and  finally  in  old  age  the  total  expenditure  diminishes,  while  at  the  same 
time  the  anabolic  processes  become  less  and  less  competent  to  repair  the  waste. 
The  question  why  in  the  nervous  system  the  energies  wane  with  advanced  age 
is  but  the  obverse  of  the  question  why  they  wax  during  the  growing  period. 
The  essential  nature  of  these  changes  is  in  both  instances  equally  obscure. 

Decrease  in  Weight  of  Brain. — The  weight  of  the  brain  in  advanced 
life  shows  that  between  fifty  and  sixty  years  there  is  a  decrease  in  the  bulk  of 
the  encephalon  in  those  persons  belonging  to  the  classes  from  which  the  greater 
'  Zeitschri/t  Jur  Bioloyie,  1893,  Bd.  xix. 


CENTRAL    NERVOUS  SYSTEM.  743 

number  of  the  records  have  been  obtained.  So  far  as  can  be  seen,  there  is  no 
marked  change  in  the  proportional  development  of  the  encephalon  in  old  age, 
save  that  the  waste  appears  to  be  slightly  greiiter  in  the  cerebral  hemispheres 
than  in  the  other  portions. 

Changes  in  Encephalon. — The  thickness  of  the  cerebral  cortex  diminishes 
in  harmony  witii  tlie  shrinkage  of  the  entire  system.  In  large  measure  this 
must  depend  on  tiie  loss  of  volume  in  the  various  fibre-systems,  which,  accord- 
ing to  the  observations  of  Vulpius,  show  a  senile  decrease  in  the  number  of 
fibres  composing  them.  This  decrease  is  more  marked  in  the  motor  than  in 
the  sensory  areas.  The  time  at  which  it  commences  cannot,  however,  be  well 
judged,  owing  to  the  small  number  of  records  after  the  thirty-third  year. 
Where  records  are  made  between  this  and  the  seventy-ninth  year  it  appears 
that  there  is  no  decided  diminution  until  after  the  fiftieth  year,  though  at  the 
seventy-ninth  the  decrease  is  clearly  shown.  Engel  has  shown  that  tiie 
branches  of  the  arbor  vitae  of  the  human  cerebellum  decrease  in  size  and 
number  in  old  age.^ 

To  the  anatomy  of  the  human  nervous  system  in  old  age  contributions  have 
been  made  by  studies  on  the  pathological  anatomy  of  paralysis  agitans.^ 

In  subjects  suffering  from  this  affection  the  bodies  of  the  uerve-cells  are 
shrunken,  pigmented,  and  show  in  some  cases  a  granular  degeneration ;  the 
fibres  in  part  are  atrophied  and  degenerated ;  the  supporting  tissues  increase, 
and  the  walls  of  the  small  blood-vessels  are  thickened.  These  changes  have 
been  found  principally  in  the  spinal  cord,  being  most  marked  in  the  lumbar 
region.  But  the  cords  of  the  aged  persons  who  do  not  exhibit  the  symptoms 
of  paralysis  agitans  show  similar  changes,  though  usually  they  are  not  so 
evident,  and  hence  the  pathological  anatomy  of  this  disease  resolves  itself  into 
a  somewhat  premature  and  excessive  senility  of  the  central  system. 

Changes  in  the  Cerebellum. — From  the  examination  of  the  cerebral  cor- 
tex in  the  case  of  a  man  dying  of  old  age  (Hodge)  no  peculiarities  were  deter- 
mined, but  in  the  cerebellum  some  cells  were  shrunken  and  others  (cells  of 
Purkinje)  had  completely  disappeared.  In  the  antennary  ganglion  of  bees  a 
very  striking  difference  ajDpears  between  those  dying  of  old  age  and  the  adult 
just  emerged  from  its  larval  skin.  These  changes  are  comparable  with  those 
described  in  mammals,  and  it  further  appears  that  in  passing  from  the  youngest 
to  the  oldest  forms  cells  have  disappeared  from  the  ganglia,  and  that  in  the  young 
form  of  the  bee  there  are  some  twenty-nine  cells  present  for  each  one  found  at 
a  later  period.  Shrinkage,  decay,  and  destruction  mark  the  progress  of  senes- 
cence, and  the  nervous  system  as  a  whole  becomes  less  vigorous  in  its  responses, 
less  capable  of  repair  or  extra  ^strain,  and  less  permeable  to  the  nervous 
impulses  that  fall  upon  it ;  and  it  thus  breaks  down,  not  into  the  disconnected 
elements  of  the  fetus,  but  into  groups  of  elements,  so  that  its  capacities  are  lost 
in  a  fragmentary  and  uneven  way. 

'  Engel :  Wiener  medicinische  Wochenschrift,  1863. 

■^  Ketcber:  Zeiischrift  fiir  Heilkunde,  1892;  Eedlich  :  Jahrbuch  j'iir  Psychiatrie,  1893. 


XI.  THE  SPECIAL  SENSES. 


A.   Vision. 


The  Physiology  of  Vision. — Tlie  eye  i.s  the  organ  by  means  of  which 
certain  vibration.s  of  the  luminiferous  ether  are  enabled  to  aifect  our  conscious- 
ness, producing  the  sensation  which  we  call  "  light,"  Hence  the  es.-ential  part 
of  an  organ  of  vision  is  a  substance  or  an  apparatus  which,  on  the  one  hand, 
is  of  a  nature  to  be  stimulated  by  waves  of  light,  and,  on  the  other,  is  so  con- 
nected with  a  nerve  that  its  activity  causes  nerve-impul.ses  to  be  transmitted  to 
the  nerve-centres.  Any  animal  in  which  a  portion  of  the  ectoderm  is  thus 
differentiated  and  connected  may  be  said  to  possess  an  eye — i.  e.  an  organ 
through  which  the  animal  may  consciously  or  unconsciously  react  to  the  exi.st- 
ence  of  light  around  it.*  But  the  human  eye,  as  well  as  that  of  all  the  higher 
animals,  not  only  informs  us  of  the  existence  of  light,  but  enables  us  to  form 
correct  ideas  of  the  direction  from  which  the  light  comes  and  of  the  form,  color, 
and  distance  of  the  luminous  body.  To  accomplish  this  result  the  substance 
sensitive  to  light  must  form  a  part  of  a  complicated  piece  of  apparatus  capable 
of  very  varied  adjustments.  The  eye  is,  in  other  w^ords,  an  optical  instrument, 
and  its  description,  like  that  of  all  oj)tical  instruments,  includes  a  consideration 
of  its  mechanical  adjustments  and  of  its  refracting  media. 

Mechanical  Movements. — The  first  point  to  be  observed  in  studying  the 
movements  of  the  eye  is  that  they  are  essentially  those  of  a  ball-and-.socket 
joint,  the  globe  of  the  eye  revolving  freely  in  the  socket  formed  by  the  capsule 
of  Tenon  through  a  horizontal  angle  of  almost  88°  and  a  vertical  angle  of  about 
80°.  The  centre  of  rotation  of  the  eye  (which  is  not,  however,  an  absolutely 
fixed  point)  does  not  coincide  with  the  centre  of  the  eyeball,  but  lies  a  little 
behind  it.  It  is  rather  farther  forward  in  hypermetropic  than  in  myopic  eyes. 
The  movements  of  the  eye,  especially  those  in  a  horizontal  direction,  are  sup- 
plemented by  the  movements  of  the  head  upon  the  shoulders.  The  combined 
eye  and  head  movements  are  in  mo.st  persons  sufficiently  extensive  to  enable 
the  individual,  without  any  movement  of  the  body,  to  receive  upon  the  lateral 
portion  of  the  retina  the  image  of  an  object  directly  behind  his  back.  The 
rotation  of  the  eye  in  the  socket  is  of  course  easiest  and  most  extensive  when 
the  eyeball  has  an  a])pr()ximately  spherical  shape,  as  in  the  normal  or  emme- 
tropic eye.    When  the  antero-posterior  diameter  is  very  much  longer  than  those 

'  In  certain  of  the  lower  orders  of  animals  no  local  cliflTerentiations  seem  to  have  occurred, 
and  the  whole  surface  of  the  body  appears  to  be  obscurely  sen.'iitive  to  light.     See  Nagel :  Der 
Lichtginn  augenloser  Thiere,  Jena,  1896. 
744 


THE  SENSE    OF    VISION.  745 

at  riglit  angles  to  it,  as  iu  extroinoly  inyo})ic  or  short-sighted  eyes,  the  rotation 
of  the  eyeball  niav  he  considerably  limited  iu  its  extent.     In  addition  to  the 
movements  of  rotation  round  a  centre  situated  in  the  axis  of  vision,  the  eye- 
ball may  be  uioved  Ibrward  and  backward  in  the  socket  to  the  extent  of  about 
one  millimeter.     This  movement  may  be  observed  whenever  the  eyelids  are 
widelv  opened,  and  is  supposed  to  be  effected  by  the  simultaneous  contraction  of 
both  the  oblique  muscles.     A  slight  lateral  uiovement  has  also  been  described. 
The  movements  of  the  eye  will   be  best  understood  when  considered  as 
referred  to  three  axes  at  right  angles  to  each  other  and  passing  through  the 
centre  of  rotation  of  the  eye.     The  first  of  these  axes,  which  may  be  called 
the  longitudinal  axis,  is  best  described  as  coinciding  with  the  axis  of  vision 
when,  with  head  erect,  we  look  straight  forward   to  the  distant  horizon ;   the 
second,  or  transverse,  axis  is  defined  as  a  line  passing  through  the  centres  of 
rotation  of  the  two  eyes ;  and  the  third,  or  vertical,  axis  is  a  vertical  line  nec- 
essarily perpendicular  to  the  other  two  and  also  passing  through  the  centre  of 
rotation.     When  the  axis  of  vision  coincides  with  the  longitudinal  axis,  the  eye 
is  said  to  be  in  the  primary  position.     When  it  moves  from  the  primary  posi- 
tion by  revolving  around  ehher  the  transverse  or  the  vertical  axis,  it  is  said  to 
assume  secondary  positions.     All  other  ])ositions  are  called  tertiary  positions, 
and  are  reached  from  the  primary  position  by  rotation  round  an  axis  which 
lies  in  the  same  plane  as  the  vertical  and  horizontal  axis — i.  e.  in  the  "  equato- 
rial plane  "  of  the  eye.     AVhen  the  eye  passes  from  a  secondary  to  a  tertiary 
position,  or  from  one  tertiary  position  to  another,  the  position  assumed  by  the 
eve  is  identical  with  that  which  it  would  have  had  if  it  had  reached  it  from 
the  primary  position  by  rotation  round  an  axis  in  the  equatorial  plane.     In 
other  words,  every  direction  of  the  axis  of  vision   is  associated  with  a  fixed 
position  of  the  whole  eye — a  condition  of  the  greatest  importance  for  the  easy 
and  correct  use  of  the  eyes.     A  rotation  of  the  eye  round  its  antero-posterior 
axis  takes  place  in  connection  wuth  certain  movements,  but  authorities  differ 
■with  regard  to  the  direction  and  amount  of  this  rotation. 

Muscles  of  the  Eye. — The  muscles  of  the  eye  are  six  in  number — viz : 
the  superior,  inferior,  internal  and  external  recti,  and  the  superior  and  inferior 
oblique.  This  apparent  superfluity  of  muscles  (for  four  muscles  would  suffice 
to  turn  the  eye  in  any  desired  direction)  is  probably  of  advantage  in  reducing 
the  amount  of  muscular  exertion  required  to  put  the  eye  into  any  given  posi- 
tion, and  thus  facilitating  the  recognition  of  slight  differences  of  direction,  for, 
according  to  Fechner's  psycho-physic  law  the  smallest  perceptible  difference  in 
a  sensation  is  proportionate  to  the  total  amount  of  the  sensation.  Hence  if  the 
eye  can  be  brought  into  a  given  position  by  a  slight  muscular  effort,  a  change 
from  that  position  will  be  more  easily  perceived  than  if  a  powerful  effort  were 
necessary. 

Each  of  the  eye-muscles,  acting  singly,  tends  to  rotate  the  eye  round  an  axis 
which  may  be  called  the  axis  of  rotation  of  that  muscle.  Now,  none  of  the 
muscles  have  axes  of  rotation  lying  exactly  in  the  equator  of  the  eye — i.  e. 
in  a  plane  passing  through  the  centre  of  rotation  perpendicular  to  the  axis 


746  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

of  vision.'  But  all  movements  of  the  eye  from  the  primary  position  take  place, 
as  we  have  seen,  round  an  axis  lying  in  this  plane.  Hence  all  such  movements 
must  be  produced  by  more  than  one  muscle,  and  this  circumstance  also  is  prob- 
ablv  of  advantai^e  in  estimating  the  extent  and  direction  of  the  movement.  In 
this  connection  it  is  interesting  to  note  that  the  eye-muscles  have  an  exception- 
ally abundant  nerve-supply — a  fact  which  it  is  natural  to  associate  with  their 
power  of  extremely  delicate  adjustment.  It  has  been  found  by  actual  count 
that  in  the  muscles  of  the  human  eye  each  nerve-fibre  supplies  only  two  or  three 
muscle-fibres,  while  in  the  muscles  of  the  limbs  the  ratio  is  as  high  as  1  to 
40-125.2 

Although  each  eye  has  its  own  supply  of  muscles  and  nerves,  yet  the  two 
eyes  are  not  independent  of  each  other  in  their  movements.  The  nature  of 
their  connections  with  the  nerve-centres  is  such  that  only  those  movements  are, 
as  a  rule,  possible  in  which  both  axes  of  vision  remain  in  the  same  plane.  This 
condition  being  fulfilled,  the  eyes  may  be  together  directed  to  any  desired  point 
above,  below,  or  at  either  side  of  the  observer.  The  axes  may  also  be  con- 
verged, as  is  indeed  necessary  in  looking  at  near  objects,  and  to  facilitate  this 
convergence  the  internal  recti  muscles  are  inserted  nearer  to  the  cornea  than  the 
other  muscles  of  the  eye.  Though  in  the  ordinary  use  of  the  eyes  there  is  never 
anv  occasion  to  diverge  the  axes  of  vision,  yet  most  persons  are  able  to  effect  a 
divergence  of  about  four  degrees,  as  shown  by  their  power  to  overcome  the  ten- 
dency to  double  vision  produced  by  holding  a  prism  in  front  of  one  of  the  eyes. 
The  nervous  mechanism  through  which  this  remarkable  co-ordination  of  the 
muscles  of  the  two  eyes  is  effected,  and  their  motions  limited  to  those  which 
are  useful  in  binocular  vision,  is  not  completely  understood,  but  it  is  supposed 
to  have  its  seat  in  part  in  the  tubercula  quadrigemina,  in  connection  with  the 
nuclei  of  origin  of  the  third,  fourth,  and  sixth  cranial  nerves.  Its  disturbance 
by  disease,  alcoholic  intoxication,  etc.  causes  strabismus,  confusion,  dizziness, 
and  double  vision. 

A  nerve  termination  sensitive  to  light,  and  so  arranged  that  it  can  be  turned 
in  different  directions,  is  sufficient  to  give  information  of  the  direction  from 
which  the  light  comes,  for  the  contraction  of  the  various  eye-muscles  indicates, 
through  the  nerves  of  muscular  sense,  the  position  into  which  the  eye  is  nor- 
mally brought  in  order  to  best  receive  the  luminous  rays,  or,  in  other  words, 
the  direction  of  the  luminous  body.  The  eye,  however,  informs  us  not  only  of 
the  direction,  but  of  the  form  of  the  object  from  which  the  light  proceeds ;  and 
to  understand  how  this  is  effected  it  will  be  necessary  to  consider  the  refracting 
media  of  the  eye  by  means  of  which  an  optical  image  of  the  luminous  object 
is  thrown  upon  the  expanded  termination  of  the  optic  nerve — viz.  the  retina. 

Dioptric  Apparatus  of  the  Eye. — For  the  better  comprehension  of  this 
portion  of  the  subject  a  few  definitions  in  elementary  optics  may  be  given.     A 

'  The  axes  of  rotation  of  the  internal  and  external  recti,  however,  deviate  but  sli<,'htly  from 
the  equatorial  plane. 

-  P.  Tergast :  '"  Ueber  das  Verhiiltniss  von  Nerven  und  Muskehi,"  Archie  fur  tuikr.  Anut.. 
ix.  36-46. 


THE   SENSE    OF    VISION. 


•-47 


dioptric  system  in  its  simplest  form  consists  of  two  adjacent  media  which  have 
different  indices  of  refraction  and  whose  surface  of  separation  is  the  segment 
of  a  sphere.  A  line  joining  the  middle  of  the  segment  with  the  centre  of  the 
sphere  and  prolonged  in  either  direction  is  called  the  axis  of  the  svstem.  Let 
the  line  .1  P  B  in  Figure  213  represent  in  section  such  a  spherical  surface  the 


M'^  B 

Fig.  213.— Diagram  of  simple  optical  system  (after  Foster). 

centre  of  which  is  at  iV,  the  rarer  medium  being  to  the  left  and  the  denser  me- 
dium to  the  right  of  the  line.  Any  ray  of  light  which,  in  passing  from  the 
rarer  to  the  denser  medium,  is  normal  to  the  spherical  surface  will  be  unchanged 
in  its  direction — i.  e.  will  undergo  no  refraction.  Such  rays  are  represented  bv 
the  lines  0  F,  31 D,  and  31'  E.  If  a  pencil  of  rays  having  its  origin  in  the  rarer 
medium  at  any  point  in  the  axis  falls  upon  the  spherical  surface,  there  will  be 
one  ray — viz.  the  one.  which  coincides  with  the  axis  of  the  system,  which  will 
pass  into  the  second  medium  unchanged  in  its  direction.  This  ray  is  called 
the  principal  ray  {OP),  and  its  point  of  intersection  (P)  with  the  spherical 
surface  is  called  the  principal  point.  The  centre  of  the  sphere  (jV)  through 
which  the  principal  ray  necessarily  passes  is  called  the  nodal  jjoint.  All  the 
other  rays  in  the  pencil  are  refracted  toward  the  principal  ray  by  an  amount 


F' 


P' 

r~~^v: 

^' 

p 

0' 

t 

^^^ 

0 

^--^^^^ 

A 

y 

^^"^^~~^~^^ 

Fig.  214.— Diagram  to  show  method  of  finding  principal  foci  (Neumann). 

which  depends,  for  a  given  radius  of  curvature,  upon  the  difference  in  the 
refractive  power  of  the  media,  or,  in  other  words,  upon  the  retardation  of  light 
in  passing  from  one  medium  to  the  other.  If  the  incident  rays  have  their 
origin  at  a  point  infinitely  di.stant  on  the  axi.s — /.  e.  if  they  are  parallel  to  each 
other — they  will  all  be  refracted  to  a  point  behind  the  spherical  surface  known 


748  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOdY. 

as  the  principal  focus,  F.  There  is  aiwther  principal  focu.s  {F')  in  front  of  tlie 
spherical  surface — viz.  the  point  from  which  divergin<^  incident  rays  will  l>e 
refracted  into  parallelism  on  passing  the  spherical  surface,  or,  in  other  words, 
the  point  at  which  parallel  rays  coining  Ironi  the  opjxtsite  direction  will  l)e 
brought  to  a  focus.  The  position  of  these  two  principal  foci  may  be  deter- 
mined by  the  construction  .shown  in  Figure  214.  Let  CA  C  represent  a  sec- 
tion of  a  sj)hcrical  refracting  surface  with  the  axis  A  K,  the  nodal  point  -V,  and 
the  principal  point  A.  The  problem  is  to  find  the  foci  of  rays  parallel  to  the 
axis.  Erect  perpendiculars  at  A  and  N.  Set  off  on  each  perpendicular  dis- 
tances No,  Xp,  Ao',  Ap'  proportionate  to  the  rapidity  of  light  in  the  two  media 
{e.  rj.  2:3).  The  points  where  the  lines  p'o  and  po'  prolonged  will  cut  the 
axis  are  the  two  principal  foci  i^and  F' — i.  e.  the  points  at  which  parallel  rays 
coming  from  either  direction  are  brought  to  a  focus  after  passing  the  .spherical 
refracting  surface.  If  the  rays  are  not  parallel,  but  diverging — /.  e.  coming 
from  an  object  at  a  finite  distance — the  point  where  the  rays  will  be  brought  to 
a  focus,  or,  in  other  words,  the  point  where  the  optical  image  of  the  luminou-s 
object  will  be  formed,  may  be  determined  by  a  construction  which  combines 
any  two  of  the  three  rays  whose  course  is  given  in  the  manner  above  described. 
Thus  in  Figure  215  let  A  Nhe  the  axis,  and  F  and  F'  the  principal  foci  of 


Fig.  215.— Diagram  to  show  method  of  finding  conjugate  foci. 

the  spherical  refracting  surface  CA  C,  with  a  nodal  point  at  y.  Let  B  be 
the  origin  of  a  pencil  of  rays  the  focus  of  which  is  to  be  determined.  Draw 
the  line  B  C  representing  the  course  of  an  incident  ray  parallel  to  the  axis. 
This  ray  will  necessarily  be  refracted  through  the  focus  F,  its  couree  being 
represented  by  the  line  C F  and  its  prolongation.  Similarly,  the  incident  ray 
passing  through  the  focus  F'  and  striking  the  spherical  surface  at  C  will,  after 
refraction,  be  parallel  to  the  axis — i.  e.  it  will  have  the  direction  C  b.  The 
principal  ray  of  the  pencil  will  of  course  pass  through  the  spherical  surface  and 
the  nodal  point  ^V  without  change  of  direction.  These  three  rays  will  come 
together  at  the  same  point  6,  the  position  of  which  may  be  determined  by  con- 
structing the  course  of  any  two  of  the  three.  The  ])oints  B  and  6  are  called 
conjugate  foci,  and  are  related  to  each  other  in  such  a  way  that  an  optical  image 
is  formed  at  one  point  of  a  luminous  object  situated  at  the  other.  When  the 
rays  of  light  pass  through  several  refracting  surfaces  in  succession  their  course 
may  be  determined  by  se])arate  calculations  for  each  surface,  a  process  which 
is  much  simplified  when  the  surfaces  are  "centred" — i.  e.  have  their  centres 
of  curvature  lying  in  the  same  axis,  as  is  approximately  the  ca.se  in  the  eye. 

Refracting  Media  of  the  Eye. — Rays  of  light  in  passing  through  the  eye 
penetrate  seven  different  media  and  are  refracted  at  .seven  surfaces.    The  media 


THE  SENSE    OF    VISION.  749 

are  as  follows :  layer  of  tears,  cornea,  aqueous  humor,  anterior  capsule  of  lens, 
lens,  posterior  capsule  of  lens,  vitreous  humor.  The  surfaces  are  those  which 
separate  the  successive  media  from  each  other  and  that  which  separates  the  tear 
layer  from  the  air.  For  purposes  of  practical  calculation  the  number  of  sur- 
faces and  media  may  be  reduced  to  three.  In  the  first  place,  the  layer  of  tears 
which  moistens  the  surface  of  the  cornea  has  the  same  index  of  refraction  as 
the  aqueous  humor.  Hence  the  index  of  refraction  of  the  cornea  may  be  left 
out  of  account,  since,  having  practically  parallel  surfaces  and  being  bounded 
on  both  sides  by  substances  having  the  same  index  of  refraction,  it  does  not 
influence  the  direction  of  rays  of  light  passing  through  it.  For  this  same 
reason  objects  seen  obliquely  through  a  window  appear  in  their  true  direction, 
the  refraction  of  the  rays  of  light  on  entering  the  glass  being  equal  in  amount 
and  opposite  in  direction  to  that  which  occurs  in  leaving  it.  For  purposes  of 
optical  calculation  we  may,  therefore,  disregard  the  refraction  of  the  cornea 
(which,  moreover,  does  not  differ  materially  from  that  of  the  aqueous  humor), 
and  imagine  the  aqueous  humor  extending  forward  to  the  anterior  surface  of 
the  layer  of  tears  which  bathes  the  corneal  epithelium.  Furthermore,  the  cap- 
sule of  the  lens  has  the  same  index  of  refraction  as  the  outer  layer  of  the  lens 
itself,  and  for  optical  purposes  may  be  regarded  as  replaced  by  it.  Hence 
the  optical  apparatus  of  the  eye  may  be  regarded  as  consisting  of  the  fol- 
lowing three  refracting  media:  Aqueous  humor,  index  of  refraction  1.33; 
lens,  average  index  of  refraction  1.45 ;  vitreous  humor,  index  of  refraction 
1.33.  The  surfaces  at  which  refraction  occurs  are  also  three  in  number  :  An- 
terior surface  of  cornea,  radius  of  curvature  8  millimeters ;  anterior  surface 
of  lens,  radius  of  curvature  10  millimeters;  posterior  surface  of  lens,  radius  of 
curvature  6  millimeters.  It  will  thus  be  seen  that  the  anterior  surface  of  the 
lens  is  less  and  the  posterior  surface  more  convex  than  the  cornea. 

To  the  values  of  the  optical  constants  of  the  eye  as  above  given  may  be 
added  the  following :  Distance  from  the  anterior  surface  of  the  cornea  to  the 
anterior  surface  of  the  lens,  3.6  millimeters ;  distance  from  the  posterior  sur- 
face of  the  lens  to  the  retina,  15.  millimeters ;  thickness  of  lens,  3.6  millimeters. 

The  methods  usually  employed  for  determining  these  constants  are  the  fol- 
lowing :  The  indices  of  refraction  of  the  aqueous  and  vitreous  humor  are 
determined  by  filling  the  space  between  a  glass  lens  and  a  glass  plate  with  the 
fresh  humor.  The  aqueous  or  vitreous  humor  thus  forms  a  convex  or  concave 
lens,  from  the  form  and  focal  distance  of  which  the  index  can  be  calculated. 
Another  method  consists  in  placing  a  thin  layer  of  the  medium  between  the 
hypothenuse  surfaces  of  two  right-angled  prisms  and  determining  the  angle  at 
which  total  internal  reflection  takes  place.  In  the  case  of  the  crystalline  lens 
the  index  is  found  by  determining  its  focal  distance  as  for  an  ordinary  lens, 
and  solving  the  equation  which  expresses  the  value  of  the  index  in  terms  of 
radius  of  curvature  and  focal  distance,  thickness,  and  focal  length.  The 
refractive  index  of  the  lens  increases  from  the  surface  toward  the  centre,  a 
peculiarity  which  tends  to  correct  the  disturbances  due  to  spherical  aberration, 
as  well  as  to  increase  the  refractive  power  of  the  lens  as  a  whole. 


750 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


The  curvature  of  the  retracting  surfaces  of  the  eye  is  determined  by  an 
instrument  known  as  an  ophthalmometer,  which  measures  tlie  size  of  the 
reflected  image  of  a  known  object  in  the  various  curved  surfaces.  The 
radius  of  curvature  of  the  surface  is  determined  by  the  following  formula : 
r  2Ab 


B:b  =  A 


,  or  r     ----- 
2'  B 


in  which  B  =  the  size  of  the  object,  6  =  the  size  of 


the  image,  ^  =  distance  between  the  object  and  the  reflecting  surface,  and 
r  =  the  radius  of  the  reflecting  surface.  The  distances  between  the  various 
surfaces  of  the  eye  are  measured  on  frozen  sections  of  the  organ,  or  can  be 
determined  upon  the  living  eye  by  optical  methods  too  complicated  to  be  here 
described.  It  should  bo  borne  in  mind  that  the  above  values  of  the  so-called 
"optical  constants"  of  the  eye  are  subject  to  considerable  individual  variation, 
and  that  the  statements  of  authors  concerning  them  are  not  always  consistent. 
The  refracting  surfaces  of  the  eye  may  be  regarded  as  still  further  sim- 
plified, and  a  so-called  "  reduced  eye "  constructed  which  is  very  useful  for 
purposes  of  optical  calculation.  This  reduced  eye,  which  for  optical  purposes 
is  the  equivalent  of  the  actual  eye,  is  regarded  as  consisting  of  a  single  refract- 
ing medium  having  an  index  of  1.33,  a  radius  of  curvature  of  5.017  milli- 
meters, its  principal  point  2.148  millimeters  behind  the  anterior  surface  of  the 
cornea,  and  its  nodal  point  0.04  millimeter  in  front  of  the  posterior  surface 
of  the  lens.^  The  principal  foci  of  the  reduced  eye  are  respectively  12.918 
millimeters  in  front  of  and  22.231  millimeters  behind  the  anterior  surface  of 
the  cornea.  Its  optical  power  is  equal  to  50.8  dioptrics.^  The  position  of  this 
imaginary  refracting  surface  is  indicated  by  the  dotted  line  in  figure  216.    The 


Fig.  216.— Diagram  of  the  formation  of  a  retinal  image  (after  Foster). 

nodal  point,  n,  in  this  construction  may  be  regarded  as  the  crossing-point  of  all 
the  j)rincipal  rays  which  enter  the  eye,  and,  as  these  rays  are  unchanged  in  their 
direction  by  refraction,  it  is  evident  that  the  image  of  the  point  whence  they 
proceed  will  be  formed  at  the  point  where  they  strike  the  retina.  Hence  to 
determine  the  size  and  position  of  the  retinal  image  of  any  external  object — 
e.  q.  the  arrow  in  Figure  216 — it  is  only  necessary  to  draw  lines  from  various 

1  Strictly  speaking,  there  are  in  this  imaginary  refracting  apparatus  which  is  regarded  as 
equivalent  to  the  actual  eye  two  principal  and  two  nodal  points,  each  pair  about  0.4  millimeter 
apart.  The  distance  is  so  small  that  the  two  points  may,  for  all  ordinary  constructions,  be 
regarded  as  coincident. 

^  The  optical  power  of  a  lens  is  the  reciprocal  of  its  focal  length.  The  dioptry  or  unit  of 
optical  power  is  the  power  of  a  lens  with  a  focal  length  of  1  meter. 


THE  SENSE    OF    VISION. 


751 


points  of  the  object  through  the  above-mentioned  nodal  point  and  to  prolong 
tiicm  till  they  strike  the  retina.  It  is  evident  that  the  size  of  the  retinal  image 
will  be  as  nuich  smaller  than  that  of  the  object  as  the  di.stau(;e  of  the  nodal 
point  from  the  retina  is  smaller  than  its  distance  from  the  object. 

According  to  the  figures  above  given,  the  nodal  point  is  about  7.2  milli- 
meters behind  the  anterior  surface  of  the  cornea  and  about  15.0  millimeters  in 
front  of  the  retina.  Hence  the  size  of  the  retinal  image  of  an  object  of  known 
size  and  distance  can  be  readily  calculated — a  problem  which  has  frequently  to  be 
solved  in  the  study  of  physiological  optics.  The  construction  given  in  Figure 
216  shows  that  from  all  external  objects  in y(?We(Z  images  are  projected  upon  the 
retina,  and  such  inverted  images  can  actually  be  seen  under  favorable  condi- 
tions. If,  for  instance,  the  eye  of  a  white  rabbit,  which  contains  no  choroidal 
pigment,  be  excised  and  held  with  the  cornea  directed  toward  a  window  or 
other  source  of  light,  an  inverted  image  of  the  luminous  object  will  be  seen 
through  the  transparent  sclerotic  in  the  same  way  that  one  sees  an  inverted 
image  of  a  landscape  on  the  ground-glass  plate  of  a  photographic  camera. 
The  question  is  often  asked,  "  ^^  liy,  if  the  images  are  inverted  in  the  retina, 
do  we  not  see  objects  upside  down  ?"  The  only  answer  to  such  a  question  is 
that  it  is  precisely  because  images  are  inverted  on  the  retina  that  we  do  not  see 
objects  upside  down,  for  the  eye  has  learned  through  lifelong  practice  to  asso- 
ciate an  impression  made  upon  any  portion  of  the  retina  with  light  coming 
from  the  opposite  portion  of  the  field  of  vision.  Thus  if  an  image  falls  upon 
the  lower  portion  of  the  retina,  our  experience,  gained  chiefly  through  mus- 
cular movements  and  tactile  sensations,  has  taught  us  that  this  image  must  cor- 
respond to  an  object  in  the  upper  portion  of  our  field  of  vision.  In  whatever 
M'ay  the  retina  is  stimulated  the  same  eflPect  is  produced.  If,  for  instance, 
gentle  pressure  is  made  with  the  finger  on  the  lateral  portion  of  the  eyeball 
through  the  closed  lids  a  circle  of  light  known  as  a  phosphene  immediately 
appears  on  the  opposite  side  of  the  eye.  Another  good  illustration  of  the 
same  general  rule  is  found  in  the  effect  of  throwing  a  shadow  upon  the  retina 
from  an  object  as  close  as  possible  to  the  eye.     For  this  purpose  place  a  card 


B 

Fig.  217.— Diagram  illustrating  the  projection  of  a  shadow  on  the  retina. 

with  a  small  pin-hole  in  it  in  front  of  a  source  of  light,  and  three  or  four 
centimeters  distant  from  the  eye.  Then  hold  some  object  smaller  than  the 
pupil — e.  g.  the  head  of  a  pin — as  close  as  possible  to  the  cornea.  Under  these 
conditions  neither  the  pin-hole  nor  the  pin-head  can  be  really  seen — i.  e.  they 


752  ^.V   AMERICA X    TEXT-BOOK    OF  PJIVSIOLOGY. 

are  both  too  near  to  have  their  image  focusscd  upon  the  retina.  The  pin-hole 
beroraes  itself  a  source  of  light,  and  appears  as  a  luminous  circle  bounded  by 
the  shadow  thrown  by  the  edge  of  the  iris.  Within  tliis  circle  of  light  is  seen 
the  shadow  of  the  pin-head,  but  the  pin-head  appears  inrcrted,  for  the  obvious 
reason  that  the  eye,  being  accustomed  to  interpret  all  retinal  impressions  as 
corresponding  to  objects  in  the  opposite  portion  of  the  field  of  vision,  regards 
the  upright  shadow  of  the  pin-head  as  the  representation  of  an  inverted  object. 
The  course  of  the  rays  in  this  experiment  is  shown  in  Figure  217,  in  wiiieh 
.1  B  represents  the  card  with  a  pin-hole  in  it,  P  the  pin,  and  P'  its  upright 
shadow  thrown  on  the  retina. 

Accoramodation. — From  what  has  been  said  ot"  conjugate  foci  and  their 
relation  to  each  other  it  is  evident  that  any  change  in  the  distance  of  the  object 
from  the  refracting  media  will  involve  a  corresponding  change  in  the  position 
of  the  image,  or,  in  other  words,  only  objects  at  a  given  distance  can  be 
focussed  upon  a  plane  which  has  a  fixed  position  with  regard  to  the  refracting 
surface  or  surfaces.  Hence  all  optical  instruments  in  which  the  principle  of 
conjugate  foci  finds  its  application  have  adjustments  for  distance.  In  the 
telescope  and  opera-glass  the  adjustment  is  effected  by  changes  in  the  distance 
between  the  lenses,  and  in  the  photographic  camera  by  a  change  in  the  posi- 
tion of  the  ground-glass  plate  representing  the  focal  plane.  In  the  microscope 
the  adjustment  is  effected  by  changing  the  distance  of  the  object  to  suit  the 
lenses,  the  higher  powers  having  a  shorter  "  working  distance." 

We  must  now  consider  in  what  way  the  eye  adapts  itself  to  see  objects  dis- 
tinctly at  different  distances.  That  this  power  of  adaptation,  or  "accommo- 
dation," really  exists  we  can  easily  convince  ourselves  by  looking  at  different 
objects  through  a  network  of  fine  wire  held  near  the  eyes.  When  with  normal 
vision  the  eyes  are  directed  to  the  distant  objects  the  network  nearly  disappears, 
and  if  we  attempt  to  see  the  network  distinctly  the  outlines  of  the  distant 
objects  become  obscure.  In  other  words,  it  is  impossible  to  see  both  the 
network  and  the  distant  objects  distinctly  at  the  same  time.  It  is  also  evident 
that  in  accommodation  for  distant  objects  the  eyes  are  at  rest,  for  when  they 
are  suddenly  opened  after  having  been  closed  for  a  short  time  they  are  found 
to  be  accommodated  for  distant  objects,  and  we  are  conscious  of  a  distinct 
effort  in  directing  them  to  any  near  object.* 

From  the  optical  principles  above  described  it  is  clear  that  the  accommo- 
dation of  the  eve  for  near  objects  may  be  conceived  of  as  taking  place  in  three 
different  ways :  1st,  By  an  increase  of  the  distance  between  the  refracting  sur- 
faces of  the  eye  and  the  retina;  2d,  By  an  increase  of  the  index  of  refraction 
of  one  or  more  of  the  media;  3d,  By  a  diminution  of  the  radius  of  curvature 
of  one  or  more  of  the  surfaces.  The  firet  of  these  methods  was  formerly  sup- 
posed to  be  the  one  actually  in  use,  a  lengthening  of  the  eyeball  under  a  pres- 

'  It  has  been  shown  by  Beer  (Archivfiir  die  gesammte  Phymohgie,  Iviii.  o23)  that  in  fishes 
the  eyes  when  at  rest  are  accommodated  for  near  objects,  and  tliat  accommodation  for  distant 
objects  is  effected  by  the  contraction  of  a  muscle  for  which  the  name  "  retractor  lentis  "  is  pro- 
posed. 


TJIK  SENi^E    OF    VISION.  753 

sure  produoed  by  the  eye-niusdes  beinjj;;  assumed  to  occur.  This  lengthening 
would,  in  the  ease  of  a  normal  eye  accommodating  itself  for  an  object  at  a 
distance  of  15  centimeters,  amount  to  not  less  than  2  millimeters — a  change 
which  could  hardly  be  brought  about  by  the  action  of  any  muscles  connected 
with  the  eye.  Moreover,  accommodation  changes  can  be  observed  upon  elec- 
trical stimulation  of  the  excised  eye.  Its  mechanism  must,  therefore,  lie  within 
the  eye  itself.  As  for  the  second  of  these  methods,  there  is  no  conceivable  way 
by  which  a  change  in  the  index  of  refraction  of  the  media  can  be  effected,  and 
we  are  thus  forced  to  the  conclusion  that  accommodation  is  brought  about  by 
a  change  in  the  curvature  of  the  refracting  surfaces — i.  e.  by  a  method  quite 
different  from  auy  which  is  employed  in  optical  instruments  of  human  con- 
struction. Now,  by  measuring  the  curvature  of  the  cornea  of  a  person  who 
looks  alternately  at  near  and  distant  objects  it  has  been  shown  that  the  cornea 
undergoes  no  change  of  form  in  the  act  of  accommodation.  By  a  process  of 
exclusion,  therefore,  the  lens  is  indicated  as  the  essential  organ  in  this  function 
of  the  eye,  and,  in  fact,  the  complicated  structure  and  connections  of  the  lens 
at  once  suggest  the  thought  that  it  is  in  the  surfaces  of  this  portion  of  the  eye 
that  the  necessary  changes  take  place.  Indeed,  from  a  teleological  point  of 
view  the  lens  would  seem  somewhat  superfluous  if  it  were  not  important  to 
have  a  transparent  refracting  body  of  variable  form  in  the  eye,  for  the  amount 
of  refraction  which  takes  place  in  the  lens  could  be  produced  by  a  slightly 
increased  curvature  of  the  cornea.  Now,  the  changes  of  curvature  which  occur 
in  the  surfaces  of  the  lens  when  the  eye  is  directed  to  distant  and  near  objects 
alternately  can  be  actually  observed  and  measured,  with  considerable  accuracy. 
For  this  purpose  the  changes  in  the  form,  size,  and  position  of  the  images  of 
brilliant  objects  reflected  in  these  two  surfaces  are  studied.  If  a  candle  is  held 
in  a  dark  room  on  a  level  with  and  about  50  centimeters  away  from  the  eye  in 
which  the  accommodation  is  to  be  studied,  an  observer,  so  placed  that  his  own 
axis  of  vision  makes  about  the  same  angle  (15°— 20°)  with  that  of  the  ob- 
served eye  that  is  made  by  a  line  joining  the  observed  eye  and  the  candle,  will 
readily  see  a  small  upright  image  of  the  candle  reflected  in  the  cornea  of  the 
observed  eye.  Near  this  and  within  the  outline  of  the  pupil  are  two  other 
images  of  the  candle,  which,  though  much  less  easily  seen  than  the  corneal 
image,  can  usually  be  made  out  by  a  proper  adjustment  of  the  light.  The 
first  of  these  is  a  large  faint  upright  image  reflected  from  the  anterior  surface 
of  the  lens,  and  the  second  is  a  small  inverted  image  reflected  from  the  pos- 
terior surface  of  the  lens.  It  will  be  observed  that  the  size  of  these  images 
varies  with  the  radius  of  curvature  of  the  three  reflecting  surfaces  as  given  on 
p.  749.  The  relative  size  and  position  of  these  images  having  been  recog- 
nized while  the  eye  is  at  rest — i.  e.  is  accommodated  for  distance — let  the 
person  who  is  under  observation  be  now  requested  to  direct  his  eye  to  a  near 
object  lying  in  the  same  direction.  When  this  is  done  the  corneal  image  and 
that  reflected  from  the  posterior  surface  of  the  lens  will  remain  unchanged,^ 

'  A  very  slight  diminution  in  size  may  sometimes  be  observed  in  the  image  reflected  from 
the  posterior  surface  of  the  lens. 
48 


754 


AN  AMKincAX    TEXT-JiOOK    OF    PHYSIOLOaY 


while  tliat  reflected  from  the  anterior  surface  of  the  lens  will  lu'conie  smaller 
and  move  toward  the  corneal  image.  This  change  in  the  size  and  j)osition  of 
the  reflected  image  can  only  mean  that  the  surface  from  which  the  reflection 
takes  })lace  has  become  more  convex  and  has  moved  forward.  Coincident 
with  this  change  a  contraction  of  the  puj)il  will  be  observed. 

An  apparatus  for  making  observations  of  this  sort  is  known  as  the  phako- 
scope  of  H^lmholtz  (Fig.  218).     The  eye  in  which  the  changes  due  to  accom- 
modation are  to  be  observed  is  placed  at  an  opening 
in  the  back  of  the  instrument  at  C,  and  directed  al- 
ternately to  a  needle  placed  in  the  opening  D  and 
to  a  distant  ol)ject  lying  in  the  same  direction.   Two 
prisms  at  B  and  B'  serve  to  throw  the  light  of  a 
candle  on  to  the  observed  eye,  and  the  eye  of  an 
observer  at  A  sees  the  three  reflected  images,  each 
as  two  small  square  spots  of  light.     The  movement 
and  the  change  of  size  of  the  image  reflected  from 
the  anterior  surface  of  the  lens  can  be  thus  much 
better  observed  than  when  a  candle-flame  is  used. 
The  course  of  the  rays  of  light  in  this  experi- 
ment is  shown  diagrammatically  in  Figure  219. 
The  observed  eye  is  directed  to  the  point  A,  while 
the  candle  and  the  eye  of  the  observer  are  placed 
symmetrically  on  either  side.  The  images  of  the  candle  reflected  from  the  various 
surfaces  of  the  eye  will  be  seen  projected  on  the  dark  background  of  the  pupil 


Fig. 


^8.— Phakoscope  of 
Helmholtz. 


Fig.  219.~Diagram  explaining  the  change  in  the  position  of  the  image  reflected  from  the  anterior  surface 
of  the  crystalline  lens  (Williams,  after  Bonders). 


in  the  directions  indicated  by  the  dotted  lines  ending  at  a,  6,  and  c.  When  the 
eye  is  accommodated  for  a  near  object  the  middle  one  of  the  three  images  moves 
nearer  the  corneal  image — i.  e.  it  changes  in  its  direction  from  h  to  h' ,  showing 
that  the  anterior  surface  of  the  lens  has  bulged  forward  into  the  position  indi- 


THE  SENSE    OF    VISION.  755 

catod  1)V  the  (lolled  line.  The  chiinge  in  tlie  appeariince  of  the  images  is 
vepreseiiteil  diaurainniat ieally  in  Figure  220.  ( )n  the  left  is  shown  the  appear- 
ance of  the  images  as  seen  when  the  eye  is  at  rest,  a  representing  the  corneal 
image,  b  that  reflected  from  the  anterior,  and  c  that  from  the  posterior  surface 
of  the  lens  when  the  observing  eye  and  the  candle  are  in  the  position  repre- 


FiG.  220.-Rcflcctcd  images  of  a  candle-flame  as  seen  in  the  pupil  of  an  eye  at  rest  and  accommodated 

for  near  objects  (Williams). 

sented  in  Figure  219.  The  images  arc  represented  as  they  appear  in  the  dark 
background  of  the  pupil,  though  of  course  the  corneal  image  may,  in  certain 
positions  of  the  light,  appear  outside  of  the  pupillary  region.  When  the  eye 
is  accommodated  for  near  objects  the  images  appear  as  shown  in  the  circle  on 
the  right,  the  image  b  becoming  smaller  and  brighter  and  moving  toward  the 
corneal  image,  while  the  pupil  contracts  as  indicated  by  the  circle  drawn  round 

the  images. 

The  changes  produced  in  the  eye  by  an  effort  of  accommodation  are  indi- 
cated in  Figure  221,  the  left-hand  side  of  the  diagram  showing  the  condition 


Fig.  221.-Showing  changes  in  the  eye  produced  by  the  act  of  accommodation  (Helmholtz). 

of  the  eye  at  rest,  and  the  right-hand  side  that  in  extreme  accommodation  for 
near  objects. 

It  will  be  observed  that  the  iris  is  pushed  forward  by  the  bulging  lens  and 
that  its  free  border  approaches  the  median  line.  In  other  words,  the  pupil  is 
contracted  in  accommodation  for  near  objects.  The  following  explanation  of 
the  mechanism  by  which  this  change  in  the  shape  of  the  lens  is  effected  has 
been  proposed  by  Helmholtz,  and  is  still  generally  accepted.  The  structure 
of  the  lens  is  such  that  by  its  own  elasticity  it  tends  constantly  to  assume  a 
more  convex  form  than  the  pressure  of  the  capsule  and  the  tension  of  the  sus- 
pensory ligaments  (s,  s,  Fig.  221)  allow.  This  pressure  and  tension  are  dimin- 
ished when  the  eye  is  accommodated  for  near  vision  by  the  contraction  of  the 
ciliary  muscles  (c,  o.  Fig.  221),  most  of  whose  fibres,  having  their  origin  at  the 


756 


AN   ANJJlilCAN    TKXT-liOOK    OF   J'JIYSJOLOGY 


point  of  union  of  the  cornoa  and  sclerotic,  extend  radially  outward  in  every 
direction  and  are  attached  to  the  front  part  of  the  choroid.  The  contrac- 
tion of  the  ciliary  nuiscle,  drawing;;  forward  the  niembruue.s  of  the  eye,  will 
relax  the  tension  of  the  suspensory  ligament  and  allow  the  lens  to  take 
the  form  determined  by  its  own  elastic  structure.  According  to  another 
theory  of  accommodation  proposed  by  Tscherning,^  the  suspensory  liga- 
ment is  stretched  and  not  relaxed  by  the  contraction  of  the  ciliary  muscle. 
In  consequence  of  the  pressure  thus  produced  upon  the 
lens,  the  soft  external  })ortions  are  moulded  upon  the 
harder  nuclear  portion  in  such  a  way  as  to  give  to  the 
anterior  (and  to  some  extent  to  the  posterior)  surface  a 
hyperboloid  instead  of  a  spherical  form.  A  similar  theory 
has  been  recently  brought  forward  by  Schoeu,^  who  com- 
jxires  the  action  of  the  ciliary  muscle  u|)on  the  lens  to  that 
of  the  fingers  compressing  a  rubber  ball,  as  shown  in  Fig- 
ure 222.  These  theories  have  an  advantage  over  that 
offered  by  Helniholtz,  inasmuch  as  they  afford  an  expla- 
nation of  the  presence  in  the  ciliary  muscle  of  circular 
fibres,  which,  on  the  theory  of  Helmholtz,  seem  to  be  su- 
perfluous. They  also  make  the  fact  of  so-called  "  astig- 
matic accommodation "  comprehensible.  This  term  is 
applied  to  the  power  said  to  be  sometimes  gradually 
acquired  by  persons  with  astigmatic^  eyes  of  correcting 
this  defect  of  vision  by  accommodating  the  eye  more  strongly  in  one  meridian 
than  another.'' 

Whatever  views  may  be  entertained  as  to  the  exact  mechanism  by  which  its 
change  of  shape  is  brought  about,  there  can  be  no  doubt  that  the  lens  is  the 
portion  of  the  eye  chiefly  or  wholly  concerned  in  accommodation,  and  it  is 
accordingly  found  that  the  removal  of  the  lens  in  the  operation  for  cataract 
destroys  the  power  of  accommodation,  and  the  patient  is  compelled  to  use 
convex  lenses  for  distant  and  still  stronger  ones  for  near  objects. 

It  is  interesting  to  notice  that  the  act  of  accommodation,  though  distinctly 
voluntary,  is  performed  by  the  agency  of  the  unsiriped  fibres  of  the  ciliary 
muscles.  It  is  evident,  therefore,  that  the  term  "  involuntary "  sometimes 
applied  to  muscular  fibres  of  this  sort  may  be  misleading.  The  voluntary 
character  of  the  act  of  accommodation  is  not  affected  by  the  circumstance  that 
the  will  needs,  as  a  rule,  to  be  assisted  by  visual  sensations.  The  fact  that 
most  persons  cannot  affect  the  necessary  change  in  the  eye  unless  they  direct 
their  attention  to  some  near  or  far  object  is  only  an  instance  of  the  close  rela- 
tion between  sensory  imjiressions  and  motor  impulses,  which   is  further  exem- 


FiG.  222. — To  illustrate 
Schoen's  theory  of  ac- 
commodation. 


1  Archives  de  Physiologic,  1894,  j).  40.  '  Archiv  fiir  die  rjesmninlc  Phi/s.,  lix.  427. 

«  See  p.  763. 

*  Recent  observations  by  Hess  {Archiv f.  Ophthalmologie,  xlii.  288)  tend  to  confirm  the  Helm- 
holtz theory  by  showing  that  the  suspensory  ligament  is  relaxed  and  not  stretched  in  accommo- 
dation for  near  objects. 


THE   SENSE    OF    VISION.  757 

plified  l)v  siicli  plK'iioiiK'iia  as  the  paralysis  of  the  lip  of  a  horse  caused  by  the 
division  of  tlu;  trifacial  nerve.  It  is  found,  moreover,  that  by  practice  the 
power  of  acconiniodating  tiie  eye  without  directino;  it  to  near  and  distant 
objects  can  be  ac(juircd.  The  nerve-channels  through  which  accommodation 
is  aftectcd  arc  tlic  anteiior  part  of  the  imcleus  of  the  third  j)air  of  nerves 
lying  in  the  extn!ni(>  hind  j)art  of  the  floor  of  the  third  ventricle,  the  most 
anterior  bundle  of  the  nerve-root,  the  third  nerve  itself,  the  lenticular  ganglion, 
and  the  short  ciliary  nerves  (see  diagram  p.  769). 

The  mechanism  of  accommodation  is  affected  in  a  remarkable  way  by  drugs, 
the  most  important  of  which  are  atropia  and  physostigmin,  the  former  para- 
lyzing and  the  latter  stimulating  the  ciliary  muscle.  As  these  drugs  exert  a 
corresponding  effect  upon  the  iris,  it  will  be  convenient  to  discuss  their  action 
in  connection  with  the  physiology  of  that  organ. 

The  changes  occurring  in  the  eye  during  the  act  of  accommodation  are 
indicated  in  the  following  table,  which  shows,  both  for  the  actual  and  the 
reduced  eye,  the  extent  to  which  the  refracting  media  change  their  form  and 
position,  and  the  consequent  changes  in  the  position  of  the  foci  : 

Accommodation  for 
Actual  Eye.  distant  objects.  near  objects. 

Radius  of  cornea 8  mm.  8  mm. 

Radius  of  anterior  surface  of  lens 10  "  6  " 

Radius  of  posterior  surface  of  lens 6  "  5.5        " 

Distance  from  cornea  to  anterior  surface  of  lens    .    .    3.6        "  3.2        " 

Distance  from  cornea  to  posterior  surface  of  lens      .    7.2        "  7.2        " 

Reduced  Eye. 

Radius  of  curvature 5.02  "  4.48  " 

Distance  from  cornea  to  principal  point 2.15  "  2.26  " 

Distance  from  cornea  to  nodal  point 7.16  "  6.74  " 

Distance  from  cornea  to  anterior  focus 12.918  "  11.241  " 

Distance  from  cornea  to  posterior  focus 22.231  "  20.248  " 

It  will  be  noticed  that  no  change  occurs  in  the  curvature  of  the  cornea,  and 
next  to  none  in  the  posterior  surface  of  the  lens,  while  the  anterior  surface  of 
the  lens  undergoes  material  alterations  both  in  its  shape  and  position. 

Associated  with  the  accommodative  movements  above  described,  two  other 
changes  take  place  in  the  eyes  to  adapt  them  for  near  vision.  In  the  first 
place,  the  axes  of  the  eyes  are  converged  upon  the  near  object,  so  that  the 
images  formed  in  the  two  eyes  shall  fall  upon  corresponding  points  of  the 
retinas,  as  will  be  more  fully  explained  in  connection  with  the  subject  of 
binocular  vision.  In  the  second  place,  the  pupil  becomes  contracted,  thus 
reducing  the  size  of  the  pencil  of  rays  that  enters  the  eye.  The  importance 
of  this  movement  of  the  pupil  will  be  better  understood  after  the  subject  of 
spherical  aberration  of  light  has  been  explained.  These  three  adjustments, 
focal,  axial,  and  pupillary,  are  so  habitually  associated  in  looking  at  near  objects 
that  the  axial  can  only  by  an  effort  be  dissociated  from  the  other  two,  while 
these  two  are  quite  inseparable  from  one  another.  This  may  be  illustrated 
by  a  simple  experiment.     On  a  sheet  of  paper  about  40  centimeters  distant 


758  .l.Y  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

from  the  eyes  draw  two  lettere  or  figures  precisely  alike  and  about  3  centimeters 
apart.  (Two  letters  cut  from  a  ncwsjjaper  and  fastened  to  the  sheet  will  answer 
the  same  purj)ose.)  Hold  a  small  object  like  the  head  of  a  pin  between  the 
eves  ami  the  ])apcr  at  the  point  of  intersection  of  a  line  joining  the  right  eye 
and  the  left  letter  with  a  line  joining  the  left  eye  and  the  right  letter.  If  the 
axes  of  vision  are  converged  upon  the  pin-head,  that  object  will  be  seen  dis- 
tinctlv,  and  beyond  it  will  be  seen  indistinctly  tlirce  images  of  the  letter,  the 
centi'al  one  being  formed  by  the  blending  of  the  inner  one  of  each  pair  of 
images  formed  on  the  two  retinas.  If  now  the  attention  be  directed  to  the 
middle  image,  it  will  gradually  become  perfectly  distinct  as  the  eye  accommo- 
dates itself  for  that  distance.  We  have  thus  an  axial  adjustment  for  a  very 
near  object  and  a  focal  adjustment  for  a  more  distant  one.  If  the  pupil  of  the 
individual  making  this  observation  be  watched  by  another  person,  it  will  be 
found  that  at  the  moment  when  the  middle  image  of  the  letter  becomes  distinct 
the  pupil,  which  had  been  contracted  in  viewing  the  pin-head,  suddenly  dilates. 
It  is  thus  seen  that  when  the  axial  and  focal  adjustments  are  dissociated  from 
each  other  the  pupillary  adjustment  allies  itself  with  the  latter. 

The  opposite  form  of  dissociation — viz.  the  axial  adjustment  for  distance 
and  the  focal  adjustment  for  near  vision — is  less  easy  to  bring  about.  It  may 
perhaps  be  best  accomplished  by  holding  a  pair  of  stereoscopic  pictures  before 
the  eyes  and  endeavoring  to  direct  the  right  eye  to  the  right  and  the  left  eye  to 
the  left  picture — /.  e.  to  keep  the  axes  of  vision  parallel  while  the  eyes  are 
accommodated  for  near  objects.  One  who  is  successful  in  this  species  of  ocular 
gymnastics  sees  the  two  pictures  blend  into  one  having  all  the  appearance  of 
a  solid  object.  The  power  of  thus  studying  stereoscopic  pictures  without  a 
stereoscope  is  often  a  great  convenience  to  the  possessor,  but  individuals  differ 
very  much  in  their  ability  to  acquire  it. 

Range  of  Accommodation. — By  means  of  the  mechanism  above  described 
it  is  possible  for  the  eye  to  produce  a  distinct  image  upon  the  retina  of  objects 
lying  at  various  distances  from  the  cornea.  The  point  farthest  from  the  eye 
at  which  an  object  can  be  distinctly  seen  is  called  tha  far-point,  and  the  nearest 
point  of  distinct  vision  is  called  the  near-point  of  the  eye,  and  the  distance 
between  the  near-point  and  the  far-point  is  called  the  range  of  distinct  vision 
or  the  range  of  accommodation.  As  the  normal  emmetropic  eye  is  adapted, 
when  at  rest,  to  bring  parallel  rays  of  light  to  a  focus  upon  the  retina,  its  far- 
point  may  be  regarded  as  at  an  infinite  distance.  Its  near-point  varies  with  age, 
as  will  be  described  under  Presbyopia.  In  early  adult  life  it  is  from  10  to 
13  centimeters  from  the  eye.  For  every  point  within  this  range  there  will  be 
theoretically  a  corresponding  condition  of  the  lens  adapted  to  bring  rays  pro- 
ceeding from  that  point  to  a  focus  on  the  retina,  but  as  rays  reaching  the  eye 
from  a  point  175  to  200  centimeters  distant  do  not,  owing  to  the  small  size  of 
the  pupil,  differ  sensibly  from  parallel  rays,  there  is  no  appreciable  change  in 
the  lens  unless  the  object  looked  at  lies  within  that  distance.  It  is  also  evi- 
dent that  as  an  object  approaches  the  eye  a  given  change  of  distance  will 
cause  a  constantly  increasing  amount  of  divergence  o{'  the  rays  proceeding  from 


THE   SENSE    OF    VISION. 


759 


it,  and  will  therefore  ucce-ssitate  a  constantly  increasing  amount  of  change  in 
the  lens  to  enable  it  to  focus  the  rays  on  the  retina.  We  find,  accordingly,  that 
all  objects  more  than  two  meters  distant  from  the  eye  can  be  seen  distinctly  at 
the  same  time — /.  e.  without  any  change  in  the  accommodative  mechanism — 
but  for  objects  within  that  distance  we  are  conscious  of  a  special  etfort  of 
accommodation  which  becomes  more  and  more  distinct  the  shorter  the  distance 
between  the  eye  and  the  object. 

Myopia  and  Hypermetropia. — There  are  two  conditions  of  the  eye  in 
which  the  range  of  accommodation  may  differ  from  that  which  has  just  been 
described  as  normal.  These  conditions,  which  are  too  frequent  to  be  regarded 
(except  in  extreme  cases)  as  pathological,  are  generally  dependent  upon  the 
eyeball  being  unduly  lengthened  or 
shortened.  In  Fig.  223  are  shown 
diagrammatically  the  three  conditions 
known  as  emmetropia,  myopia,  and 
hypermetropia.  In  the  normal  or 
emmetropic  eye,  A,  parallel  rays  are 
represented  as  brought  to  a  focus  on 
the  retina ;  in  the  short-sighted,  or 
myopic,  eye,  B,  similar  rays  are 
focussed  in  front  of  the  retina,  since 
the  latter  is  abnormally  distant;  while 
in  the  over-sighted,  or  hypermetropic, 
eye,  C,  they  are  focussed  behind  the 
retina,  since  it  is  abnormally  near. 

It  is  evident  that  when  the  eye  is 
at  rest  both  the  myopic  and  the  hy- 
permetropic eye  will  see  distant  ob- 
jects indistinctly,  but  there  is  this 
important  difference :  that  in  hyper- 
metropia the  difficulty  can  be  cor- 
rected by  an  effort  of  accommodation, 
while  in  myopia  this  is  impossible, 
since  there  is  no  mechanism  by  M'hich 
the  radius  of  the  lenticular  surfaces  can  be  increased.  Hence  an  individual 
affected  with  myopia  is  always  aware  of  the  infirmity,  while  a  person  with 
hypermetropic  eyes  often  goes  through  life  unconscious  of  the  defect.  In  this 
case  the  accomodation  is  constantly  called  into  play  even  for  distant  objects,  and 
if  the  hypermetropia  is  excessive,  any  prolonged  use  of  the  eyes  is  apt  to  be 
attended  by  a  feeling  of  fatigue,  headache,  and  a  train  of  nervous  symptoms 
familiar  to  the  ophthalmic  surgeon.  Hence  it  is  important  to  discover  this  defect 
where  it  exists  and  to  apply  the  appropriate  remedy — viz.  convex  lenses  placed 
in  front  of  the  eyes  in  order  to  make  the  rays  slightly  convergent  when  they 
enter  the  eye.  Thus  aided,  the  refractive  power  of  the  eye  at  rest  is  sufficient 
to  bring  the  rays  to  a  focus  upon  the  retina  and  thus  relieve  the  accommoda- 


FiG.  223.— Diagram  showing  the  difference  between 
normal,  myopic,  and  hypermetropic  eyes. 


760  AX  AMERICAN    TEXT- HOOK    OF   PlIYSIOLOaV. 

tion.  This  action  of  a  convex  lens  in  hypcrmetropia  is  indicated  by  tlie  dotted 
lines  in  Fig.  222,  C,  and  the  corresponding  use  of  a  concave  lens  in  myopia  is 
shown  in  Fi'g.  222,  B. 

The  detection  and  (juantitative  determination  of  iiypermetropia  are  best 
made  after  the  accommodation  has  been  paralyzed  by  the  use  of  atropia,  l>y 
ascertaining  how  strong  a  convex  lens  must  be  placed  before  the  eye  to  pro- 
duce distinct  vision  of  distant  objects. 

The  range  of  accommodation  varies  very  much  from  the  normal  in  myopic 
and  hypermetropic  eyes.  In  myopia  the  near-point  is  often  5  or  6  centimeters 
from  the  cornea,  while  the  far-point,  instead  of  being  infinitely  far  off,  is  at  a 
variable  but  no  veiy  great  distance  from  the  eye.  The  range  of  accommoda- 
tion is  therefore  very  limited.  In  Iiypermetropia  the  near-point  is  slightly 
farther  than  normal  from  the  eye,  and  the  far-point  cannot  be  said  to  exist, 
for  the  eye  at  rest  is  adapted  to  bring  converging  rays  to  a  focus  on  the  retina, 
and  such  pencils  of  rays  do  not  exist  in  nature.  Mathematically,  the  far-point 
may  be  said  to  be  at  more  than  an  infinite  distance  from  the  eye.  The  range 
of  effective  accommodation  is  therefore  reduced,  for  a  portion  of  the  accommo- 
dative power  is  used  up  in  adapting  the  eye  to  receive  parallel  rays. 

Presbyopia. — The  power  of  accommodation  diminishes  with  age,  owing 
apparently  to  a  loss  of  elasticity  of  the  lens.  The  change  is  regularly  pro- 
gressive, and  can  be  detected  as  early  as  the  fifteenth  year,  though  in  normal 
eyes  it  does  not  usually  attract  attention  until  the  individual  is  between  forty 
and  forty-five  years  of  age.  At  this  period  of  life  a  difficulty  is  commonly 
experienced  in  reading  ordinary  type  held  at  a  convenient  distance  from  the 
eve,  and  the  individual  becomes  old-sighted  or  j)reshyoj)ic — a  condition  which 
can,  of  course,  be  remedied  by  the  use  of  convex  glasses.  Cases  are  occasion- 
ally reported  of  persons  recovering  their  power  of  near  vision  in  extreme  old 
age  and  discontinuing  the  use  of  the  glasses  previously  employed  for  reading. 
In  these  cases  there  is  apparently  not  a  restoration  of  the  power  of  accommo- 
dation, but  an  increase  in  the  refractive  power  of  the  lens  through  local  changes 
in  its  tissue.  A  diminution  in  the  size  of  the  pupil,  sometimes  noticed  in  old 
age,  may  also  contribute  to  the  distinctness  of  the  retinal  image,  as  will  be 
described  in  connection  with  spherical  aberration. 

Defects  of  the  Dioptric  Apparatus. — The  above-described  imperfections 
of  the  eye — viz.  mvopia  and  hypermetrojiia — being  generally  (though  not 
invariably)  due  to  an  abnormal  length  of  the  longitudinal  axis,  are  to  be 
regarded  as  defects  of  construction  affecting  only  a  comparatively  small 
number  of  eyes.  There  are,  however,  a  number  of  imperfections  of  the  diop- 
tric apparatus,  many  of  which  affect  all  eyes  alike.  Of  these  imperfections 
some  affect  the  eye  in  common  with  all  optical  instruments,  while  others  are 
jieculiar  to  the  eve  and  are  not  found  in  instruments  of  human  construction. 
The  former  class  will  be  first  considered. 

Spherical  Aberration. — It  has  been  stated  that  a  ]iencil  of  rays  falling 
ui)on  a  spherical  refra»-ting  surface  will  be  refracted  to  a  common  focus. 
Strictlv  sjxiaking,  however,  the  outer  rays  of  the  pencil — i.  e.  those  which  fall 


THE   SENSE    OF    VISION. 


761 


near  the  periphery  <>f  the  refracting  snrface— will  be  reiracted  more  than  those 
\\\\\A\  lie  near  the  axis  and  will  come  to  a  focus  sooner.  This  phenomenon, 
which  is  called  spherical  aberration,  is  more  marked  with  diverging  tlian  with 
parallel  rays,  and  tends,  of  course,  to  produce  an  indistinctness  of  the  image 
which  wili  increase  with  the  extent  of  the  surlace  through  whicli  the  rays 
pass.  The  effect  of  a  diaphragm  used  in  many  optical  instruments  to  reduce 
the  amount  of  spherical  aberration  by  cutting  oil'  the  side  rays  is  shown  dia- 
grammatically  in  Fig.  224. 


Fig.  224.-Diagram  showing  the  effect  of  a  diaphragm  in  reducing  the  amount  of  spherical 

aberration. 

The  r6le  of  the  iris  in  the  vision  of  near  objects  is  now  evident,  for  when 
the  eye  is  directed  to  a  near  object  the  spherical  aberration  is  increased  in  con- 
sequence of  the  rays  becoming  more  divergent,  but  the  contraction  of  the 
pupil  which  accompanies  accommodation  tends,  by  cutting  off  the  side  rays,  to 
prevent  a  blurring  of  the  image  which  otherwise  would  be  produced.  It  must, 
however,  be  remembered  that  the  crystalline  lens,  unlike  any  lens  of  human 
construction,  has  a  greater  index  of  refraction  at  the  centre  than  at  the  periph- 
ery. This,  of  course,  tends  to  correct  spherical  aberration,  and,  in  so  far  as  it 
does  so,  to' render  the  cutting  off  of  the  side  rays  unnecessary.  Indeed,  the 
total  amount  of  possible  spherical  aberration  in  the  eye  is  so  small  that  its 
effect  on  vision  may  be  regarded  as  insignificant  in  comparison  with  that  caused 
by  the  other  optical  imperfections  of  the  eye. 

Chromatic  Aberration.— In  the  above  account  of  the  dioptric  apparatus 
of  the  eye  the  phenomena  have  been  described  as  they  would  occur  with  mono- 
chromatic light— i.  e.  with  light  having  but  one  degree  of  refrangibility.  But 
the  light  of  the  sun  is  composed  of  an  infinite  number  of  rays  of  different 
degrees  of  refrangibility.  Hence  when  an  image  is  formed  by  a  simple  lens 
the  more  refrangible  ravs— i.  e.  the  violet  rays  of  the  spectrum— are  brought 
to  a  focus  sooner  than  the  less  refrangible  red  rays.     The  image  therefore 


762  .l.V    AMEIilCAX    TEXT-BOOK    OF   Pll  YSlOLOd  Y. 

apjx-ars  bordereil  by  fringes  of  coKux'd  light.  This  phenoiueiioii  of  chromatic 
aberration  cau  be  well  observed  by  looking  at  objects  throngh  the  lateral  por- 
tion of  a  simple  lens,  or,  still  better,  by  observing  them  through  two  simple 
lenses  held  at  a  distance  apart  equal  to  the  sum  of  their  fbeal  distances.  The 
objects  will  appear  inverted  (as  through  an  astronomical  telescope)  and  sur- 
rounded with  borders  of  colored  light.  Xow,  the  chromatic  aberration  of  the 
eye  is  so  slight  that  it  is  not  easily  detected,  and  the  physicists  of  the  eighteenth 
century,  in  their  etforts  to  produce  an  achromatic  lens,  seem  to  have  been 
impressed  by  the  fact  that  in  the  eye  a  combination  of  media  of  different 
refractive  powers  is  employed,  and  to  have  sought  in  this  circumstance  an 
explanation  of  the  supposed  achromatism  of  the  eye.  AVork  directed  on  this 
line  was  crowned  with  brilliant  success,  for  by  combining  two  sorts  of  glass  of 
different  refractive  and  dispersive  powers  it  was  found  possible  to  refract  a  ray 
of  light  without  dispersing  it  into  its  different  colored  rays,  and  the  achromatic 
lens,  thus  constructed,  became  at  once  an  essential  part  of  every  first-class  opti- 
cal instrument.  Xow,  as  there  is  not  only  no  evidence  that  the  principle  of 
the  achromatic  lens  is  employed  in  the  eye,  but  distinct  evidence  that  the  eye 
is  uncorrected  for  chromatic  aberration,  we  have  here  a  remarkable  instance  of 
a  misconception  of  a  physical  fact  leading  to  an  important  discovery  in  physics. 
The  chromatic  aberration  of  the  eye,  though  so  slight  as  not  to  interfere  at  all 
with  ordinary  vision,  can  be  readily  shown  to  exist  by  the  simple  experiment 
of  covering  up  one  half  of  the  ])upil  and  looking  at  a  bright  source  of  light 
e.  g.  a  window.     If  the  lower  half  of  the  pupil  be  covered,  the  cross-bars  of 


Fig.  225.— Diagram  to  illustrate  chromatic  aberration. 

the  window  will  appear  bordered  with  a  fringe  of  blue  light  on  the  lower  and 
reddish  light  on  the  upper  side.  The  explanation  usually  given  of  the  way  in 
which  this  result  is  produced  is  illustrated  in  Fig.  225.  Owing  to  the  chromatic 
aberration  of  the  eye  all  the  rays  emanating  from  an  object  at  A  are  not 
focussed  accurately  on  the  retina,  but  if  the  eye  is  accommodated  for  a  ray  of 
medium  refrangibility,  the  violet  rays  will  be  brought  to  a  focus  in  front  of 
the  retina  at  T^,  while  the  red  rays  will  be  focussed  behind  the  retina  at  R. 
On  the  retina  itself  will  be  formed  not  an  accurate  optical  image  of  the  point 
A,  but  a  small  circle  of  dispersion  in  which  the  various  colored  rays  are  mixed 
together,  the  violet  rays  after  crossing  falling  upon  the  same  part  of  the  retina 
as  the  red  rays  before  crossing.  Thus  by  a  sort  of  compensation,  which,  how- 
ever, cannot  be  equivalent  to  the  synthetic  reproduction  of  white  light  by  the 
union  of  the  spectral  colors,  the  disturbing  effect  of  chromatic  aberration  is 


THE   SENSE    OF    VISION. 


763 


diiiiiuished.  WIrii  tlu-  lower  half"  of  the  pupil  is  eovered  by  the  edge  of  a 
card  held  in  front  of  the  cornea  at  I),  the  aberration  produced  in  the  upper 
half  of  tlie  eye  is  not  compensated  by  that  of  the  lower  half.  Hence  the 
image  of  a  point  of  white  light  at  .1  will  appear  as  a  row  of  spectral  colors 
on  the  retina,  and  all  objects  will  appear  bordered  by  colored  fringes.  Another 
good  illustration  of  the  chromatic  aberration  of  the  eye  is  oljtained  by  cutting 
two  holes  of  any  convenient  shape  in  a  piece  of  black  cardboard  and  placing 
behind  one  of  them  a  piece  of  blue  and  behind  the  other  a  piece  of  red  glass. 
If  the  card  is  placed  in  a  window  some  distance  (10  meters)  from  the  observer, 
in  such  a  position  that  the  white  light  of  the  sky  may  be  seen  through  the  col- 
ored glasses,  it  will  be  found  that  the  outlines  of  the  two  holes  will  generally 
be  seen  with  unequal  distinctness.  To  most  eyes  the  red  outline  will  appear 
quite  distinct,  while  the  blue  figure  will  seem  much  blurred.  To  a  few  indi- 
viduals the  blue  figure  appears  the  more  distinct,  and  these  will  generally  be 
found  to  be  hypermetropic. 

Astigmatism. — The  defect  known  as  astigmatism  is  due  to  irregularities 
of  curvature  of  the  refracting  surfaces,  in  consequence  of  which  all  the  rays 
proceeding  from  a  single  point  cannot  be  brought  to  a  single  focus  on  the 
retina. 

Astigmatism  is  said  to  be  regular  when  one  of  the  surfaces,  generally  the 
cornea,  is  not  spherical,  but  ellipsoidal — i.  e.  having  meridians  of  maximum 


Fig.  226.— Model  to  illustrate  astigmatism. 


and  minimum  curvature  at  right  angles  to  each  other,  though  in  each  meridian 
the  curvature  is  regular.  When  this  is  the  case  the  rays  proceeding  from  a 
single  luminous  point  are  brought  to  a  focus  earliest  when  they  lie  in  the 
meridian  in  which  the  surface  is  most  convex.     Hence  the  pencil  of  rays  will 


7G4 


AN  AMUR/CAN   TEXT- BO  OK    OF  PHYSIOLOGY. 


have  two  linear  foci,  at  right  augles  to  the  nieridiaus  of  greatest  and  least 
curvature  separated  by  a  space  in  which  a  section  of  the  cone  of  rays  will  be 
first  elliptical,  then  circular,  and  then  again  elliptical.  This  defect  exists  to  a 
certain  extent  in  nearly  all  eyes,  and  is,  in  some  cases,  u  serious  obstacle  to  dis- 
tinct vision.  The  course  of  the  rays  when  thus  refracted  is  illustrated  in  Fig.  226, 
which  represents  the  interior  of  a  box  through  which  black  threads  are  drawn 
to  indicate  the  course  of  the  rays  of  light.  The  threads  start  at  one  end  of  the 
box  from  a  circle  representing  the  cornea,  and  converge  with  different  degrees 
of  rapidity  in  different  meridians,  so  that  a  section  of  the  cone  of  rays  will  be 
successively  an  ellipse,  a  straight  line,  an  ellipse,  a  circle,  etc.,  as  shown  by  the 
model  represented  in  Fig.  227.     It  will  be  noticed  that  this  and  the  preced- 


FiG.  227.— Model  to  illustrate  astigmatism. 

ing  figure  are  drawn  in  duplicate,  but  that  the  lines  are  not  precisely  alike  on 
the  two  sides.  In  fact,  the  lines  on  the  left  represent  the  model  as  it  would 
be  seen  with  the  right  eye,  and  those  on  the  right  as  it  would  ai)pear  to 
the  left  eye,  which  is  just  the  opposite  from  an  ordinary  stereoscopic  slide. 
The  figures  are  drawn  in  this  way  because  they  are  intended  to  j)roduce  a 
"  pseudoscopic  "  effect  in  a  way  which  will  be  explained  in  connection  with 
the  subject  of  binocular  vision.  For  this  purpose  it  is  only  necessary  to  cross 
the  axes  of  vision  in  front  of  the  page,  as  in  the  experiment  described  on  page 
758,  for  studying  the  relation  between  the  focal,  axial,  and  pupillary  adju.st- 
ments  of  the  eye.  As  soon  as  the  middle  image  becomes  di.stinct  it  as.sumes  a 
stereoscopic  appearance,  and  the  correct  relations  between  the  different  parts  of 
the  model  are  at  once  obvious. 

This  imperfection  of  the  eye  may  be  detected  by  looking  at  lines  such  as  are 
shown  in  Figure  228,  and  testing  each  eye  separately.     If  the  straight  lines 


77//';   SENSE    OF    VISION.  765 

drawn  in  various  directions  through  a  coninioii  point  cannot  be  seen  with  equal 
distinctness  at  the  same  time,  it  is  evident  that  the  eye  is  better  adapted  to  focus 
rays  in  one  meridian  than  in  anotlier — /.  c.  it  is  astigmatic.     The  concentric 


Fig.  228.— Lines  for  the  detection  of  astigmatism. 


circles  are  a  still  more  delicate  test.  Few  persons  can  look  at  this  figure  attentively 
without  noticing  that  the  lines  are  not  everywhere  equally  distinct,  but  that  in 
certain  sectors  the  circles  present  a  blurred  appearance.  Xot  infrequently  it 
will  be  found  that  the  blurred  sectors  do  not  occupy  a  constant  position,  but 
oscillate  rapidly  from  one  part  of  the  series  of  circles  to  another.  This  phe- 
nomenon seems  to  be  due  to  slight  involuntary  contractions  of  the  ciliary 
muscle  causing  changes  in  accommodation. 

The  direction  of  the  meridians  of  greatest  and  least  curvature  of  the  cornea 
of  a  regularly  astigmatic  eye,  and  the  difference  in  the  amount  of  this  curvature, 
can  be  very  accurately  measured  by  means  of  the  ophthalmometer  (see  p.  750). 
These  points  being  determined,  the  defect  of  the  eye  can  be  perfectly  corrected 
by  cylindrical  glasses  adapted  to  compensate  for  the  excessive  or  deficient 
refraction  of  the  eye  in  certain  meridians. 

By  another  method  known  as  "  skiascopy,"  which  consists  in  studying  the 
light  reflected  from  the  fundus  of  the  eye  when  the  ophthalmoscopic  mirrol'  is 
moved  in  various  directions,  the  amount  and  direction  of  the  astigmatism  of 
the  eye  as  a  whole  (and  not  that  of  the  cornea  alone)  may  be  ascertained. 

Astigmatism  is  said  to  be  irregular  when  in  certain  meridians  the  curvatures 
of  the  refracting  surfaces  are  not  arcs  of  circles  or  ellipses,  or  when  there  is  a 
lack  of  homogeneousness  in  the  refracting  media.  This  imperfection  exists  to 
a  greater  or  less  extent  in  all  eyes,  and,  unlike  regular  astigmatism,  is  incapable 
of  correction.  It  manifests  itself  by  causing  the  outlines  of  all  brilliant  objects 
to  appear  irregular.  It  is  on  this  account  that  the  fixed  stars  do  not  appear  to 
us  like  points  of  light,  but  as  luminous  bodies  with  irregular  "  star  "-si i aped 
outlines.  The  phenomenon  can  be  conveniently  studied  by  looking  at  a  pin- 
hole in  a  large  black  card  held  at  a  convenient  distance  between  the  eye  and  a 
strong  light.  The  hole  will  appear  to  have  an  irregular  outline,  and  to  some 
eyes  will  appear  double  or  treble. 

Intraocular  Images. — Light  entering  the  eye  makes  visible,  under  certain 
circumstances,  a  number  of  objects  which  lie  within  the  eye  itself.  These 
objects  are  usually  opacities  in  the  media  of  the  eye  which  are  ordinarily  invisi- 


766  ^l.Y  AMERICAN    TEX  I- HOOK    OF  PHYSIOLOGY. 

ble,  because  the  retina  i.s  illuuiinuted  bv  light  coiuiiij^  I'roni  all  parts  ol"  the 
pupil,  and  witli  such  a  broad  source  of  light  no  object,  unless  it  is  a  very  large 
one  or  one  lying  very  near  the  back  of  the  eye,  can  cast  a  shadow  on  the  retina. 
Such  shadows  can,  however,  be  made  apparent  l)y  allowing  the  media  of  the 
eve  to  be  traversed  by  parallel  rays  of  light.  This  can  be  accomplished  by 
holding  a  small  polished  sphere — e.g.  the  steel  head  of  a  shawl-])in  illuminated 
bv  sunlight  or  strong  artificial  light — in  the  anterior  focus  of  the  eye — /.  e. 
about  22  millimeters  iu  front  of  the  cornea,  or  by  placing  a  dark  screen  with  a 
pin-hole  in  it  iu  the  same  position  between  the  eye  and  a  source  of  uniform 
diffused  light,  such  as  the  sky  or  the  porcelain  shade  of  a  student  lamj).  In 
either  case  the  rays  of  light  diverging  from  the  minute  source  will  be  refracted 
into  parallelism  by  the  media  of  the  eye,  and  will  ])roduce  the  sensation  of  a 
circle  of  diffused  light,  the  size  of  which  will  depend  up(jn  the  amount  of  dila- 
tation of  the  pu])il.  Within  this  circle  of  light  will  be  seen  the  shadows  of  any 
opaque  substances  that  may  be  present  in  the  media  of  the  eye.  These  shadows, 
being  cast  by  parallel  rays,  will  be  of  the  same  size  as  the  objects  themselves, 
as  is  shown  diagrammatically  in  Figure  229,  in  which  .4  represents  a  source 


Fig.  229.— Showing  the  method  of  studying  intraocular  images  (Helmholtz). 

of  light  at  the  anterior  focus  of  the  eye,  and  b  an  opacity  iu  the  vitreous  humor 
casting  a  shadow  B  of  the  same  size  as  itself  upon  the  retina.  It  is  evident  that 
if  the  source  of  light  A  is  moved  from  side  to  side  the  various  opacities  will  be 
displaced  relatively  to  the  circle  of  light  surrounding  them  by  an  amount  de- 
pending upon  the  distance  of  the  opacities  from  the  retina.  A  study  of  these 
displacements  will  therefore  afford  a  means  of  determining  the  position  of  the 
opacities  within  the  media  of  the  eye. 

Muscffi  Volitantes. — Among  the  objects  to  be  seen  in  thus  examining  the 
eye  the  most  conspicuous  are  those  known  as  the  muscce  volitantes.  These  pre- 
sent themselves  in  the  form  of  beads,  either  singly  or  in  groups,  or  of  streaks, 
patches,  and  granules.  They  have  an  almost  constant  floating  motion,  which 
is  increased  by  the  movements  of  the  eye  and  head.  They  usually  avoid  the 
line  of  vision,  floating  away  when  an  attempt  is  made  to  fix  the  sight  upon 
them.  When  the  eye  is  directed  vertically,  however,  they  sometimes  place 
themselves  directly  in  line  with  the  object  looked  at.  If  the  intraocular  object 
is  at  the  .same  time  sufficiently  near  the  back  of  the  eye  to  ca.st  a  shadow  which 
is  visible  without  the  use  of  the  focal  illumination,  some  inconvenience  may 
thus  be  caused  in  using  a  vertical  microscope. 
•     A  studv  of  the  motions  of  the  musca:  volitantes  makes  it  evident  that  the 


THE  SENSE    OF    VISION.  767 

phenomenon  is  due  to  small  bodies  floating  in  a  liquid  medium  of  a  little 
greater  specific  gravity  than  thcni.sclves.  Their  movements  are  chicifly  in 
planes  perpendicular  to  the  axis  of  vision,  for  when  the  eye  is  directed  verti- 
cally upward  they  move  as  usual  through  the  field  of  vision  without  increasing 
the  distance  from  the  retina.  They  are  generally  supposed  to  be  the  remains 
of  the  embyronic  structure  of  the  vitreous  body — i.  e.  portions  of  the  cells  and 
fibres  which  have  not  undergone  complete  raucous  transformation. 

In  addition  to  these  floating  opacities  in  the  vitreous  body  various  other 
defects  in  the  transparent  media  of  the  eye  may  be  revealed  by  the  method  of 
focal  illumination.  Among  these  may  be  mentioned  spots  and  stripes  due  to 
irregularities  in  the  lens  or  its  capsule,  and  radiating  lines  indicating  the  stel- 
late structure  of  the  lens. 

Retinal  Vessels.— Owing  to  the  fact  that  the  blood-vessels  ramify  near  the 
anterior  surface  of  the  retina,  while  those  structures  which  are  sensitive  to  light 
constitute  the  posterior  layer  of  that  organ,  it  is  evident  that  light  entering  the 
eye  will  cast  a  shadow  of  the  vessels  on  the  light-perceiving  elements  of  the 
retina.  Since,  however,  the  diameter  of  the  largest  blood-vessels  is  not  more 
than  one-sixth  of  the  thickness  of  the  retina,  and  the  diameter  of  the  pupil  is 
one-fourth  or  one-fifth  of  the  distance  from  the  iris  to  the  retina,  it  is  evident 
that  when  the  eye  is  directed  to  the  sky  or  other  broad  illuminated  surfaces  it 
is  only  the  penumbra  of  the  vessels  that  will  reach  the  rods  and  cones,  the  umbra 
terminating  conically  somewhere  in  the  thickness  of  the  retina.  But  if  light 
is  allowed  to  enter  the  eye  through  a  pin-hole  in  a  card  held  a  short  distance 
from  the  cornea,  as  in  the  above-described  method  of  focal  illumination,  a 
sharply  defined  shadow  of  the  vessels  will  be  thrown  on  the  rods  and  cones. 
Yet  under  these  conditions  the  retinal  vessels  are  not  rendered  visible  unless 
the  perforated  card  is  moved  rapidly  to  and  fro,  so  as  to  throw  the  shadow 
continually  on  to  fresh  portions  of  the  retinal  surface.  When  this  is  done  the 
vessels  appear,  ramifying  usually  as  dark  lines  on  a  lighter  background,  but 
the  dark  lines  are  sometimes  bordered  by  bright  edges.  It  will  be  observed 
that  those  vessels  appear  most  distinctly  the  course  of  which  is  at  right  angles 
to  the  direction  in  which  the  card  is  moved.  Hence  in  order  to  see  all  the 
vessels  with  equal  distinctness  it  is  best  to  move  the  card  rapidly  in  a  circle 
the  diameter  of  which  should  not  exceed  that  of  the  pupil.  In  this  manner 
the  distribution  of  the  vessels  in  one's  own  retina  may  be  accurately  observed, 
and  in  many  cases  the  position  of  the  fovea  centralis  may  be  determined  by  the 
absence  of  vessels  from  that  portion  of  the  macula  lutea. 

The  retinal  vessels  may  also  be  made  visible  in  several  other  ways — e.  g., 
1.  By  directing  the  eye  toward  a  dark  background  and  moving  a  candle  to  and 
fro  in  front  of  the  eye,  but  below  or  to  one  side  of  the  line  of  vision.  2.  By 
concentrating  a  strong  light  by  means  of  a  lens  of  short  focus  upon  a  point 
of  the  sclerotic  as  distant  as  possible  from  the  cornea.  By  either  of  these 
methods  a  small  image  of  the  external  source  of  light  is  formed  upon  the 
lateral  portion  of  the  eye,  and  this  image  is  the  source  of  light  which  throws 
shadows  of  the  retinal  vessels  on  to  the  rods  and  cones. 


768  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

Circiilation  of  Blood  in  the  Retina. — W'ljen  the  eye  is  directed  toward  a 
surface  which  is  uniformly  aud  brightly  illuniinated — e.  g.  the  sky  or  a  sheet 
of  white  paper  on  which  the  sun  is  shinintr — the  Held  of  vision  is  soon  seen  to 
be  filled  with  small  brij^ht  bodies  moving;  with  considerable  raj)idity  in  irregu- 
lar turved  lines,  but  with  a  certain  uniformity  which  suggests  that  their 
movements  are  confined  to  definite  channels.  They  are  usually  better  seen 
Avhen  one  or  more  sheets  of  cobalt  glass  are  held  before  the  face,  so  tiiat  the 
eyes  are  bathed  in  blue  light.  That  the  phenomenon  depends  upon  the  circu- 
lation of  the  blood  globules  in  the  retina  is  evident  from  the  fact  that  tiie 
moving  bodies  follow  paths  which  correspond  with  the  form  of  the  retinal 
capillaries  as  seen  by  the  methods  above  described,  and  also  from  the  corre- 
spondence between  the  rate  of  movement  of  the  intraocular  image  and  the 
rapidity  of  the  capillary  circulation  in  those  organs  in  which  it  can  be  di- 
rectly measured  under  the  microscope.  The  exact  way  in  which  the  moving 
globules  stimulate  the  retina  so  as  to  produce  the  observed  phenomenon  must 
be  regarded  as  an  unsettled  question. 

We  have  thus  seen  that  the  eye,  regarded  from  the  optician's  point  of  view, 
has  not  only  all  the  faults  inherent  in  optical  instruments  generally,  but  many 
others  w'hich  Avould  not  be  tolerated  in  an  instrument  of  human  construction. 
Yet  with  all  its  imperfections  the  eye  is  perhaps  the  most  wonderful  instance 
in  nature  of  the  development  of  a  highly  specialized  organ  to  fulfil  a  definite 
purpose.  In  the  accomplishment  of  this  object  the  various  parts  of  the  eye 
have  been  perfected  to  a  degree  sufficient  to  enable  it  to  meet  the  requirements 
of  the  nervous  system  with  which  it  is  connected,  and  no  farther.  In  the 
ordinary  use  of  the  eye  we  are  unconscious  of  its  various  irregularities,  shadows, 
opacities,  etc.,  for  these  imperfections  are  all  so  slight  that  the  resulting  inac- 
curacy of  the  image  does  not  much  exceed  the  limit  which  tiie  size  of  the 
light-perceiving  elements  of  the  retina  imposes  upon  the  delicacy  of  our  visual 
perceptions,  and  it  is  only  by  illuminating  the  eye  in*  some  unusual  way  that 
the  existence  of  these  imperfections  can  be  detected.  In  other  words,  the  eye 
is  as  good  an  optical  instrument  as  the  nervous  system  can  appreciate  and 
make  use  of.  Moreover,  when  we  reflect  upon  the  difficulty  of  the  problem 
which  nature  has  solved,  of  constructing  an  optical  instrument  out  of  living 
and  growing  animal  tissue,  we  cannot  fail  to  be  struck  by  the  perfection  of  the 
dioptric  apparatus  of  the  eye  as  well  as  by  its  adaptation  to  the  needs  of  the 
organism  of  which  it  forms  a  part. 

Iris. — The  importance  of  the  iris  as  an  adjustable  diaphragm  for  cutting 
offside  rays  and  thus  securing  good  definition  in  near  vision  has  been  described 
in  connection  with  the  act  of  accommodation.  Its  other  function  of  protecting 
the  retina  from  an  excess  of  light  is  no  less  important,  and  we  must  now  con- 
sider how  this  pupillary  adjustment  may  be  studied  and  by  what  mechanism 
it  is  effected.  The  changes  in  the  size  of  the  pupil  may  be  conveniently  ob- 
served in  man  and  animals  by  holding  a  millimeter  scale  in  front  of  the  eye 
aud  noticing  the  variations  in  the  diameter  of  the  pupil.  It  should  be  borne 
in  mind  that  the  iris,  seen  in  this  way,  does  not  appear  in  its  natural  size  and 


THE   SENSE    OF    VISION. 


7G9 


position,  but  soincwhnt  eiilari^ctl  and  bulged  forward  by  the  magnifying  effect 
of  i\w  coriK'a  aiul  the  acjueous  humor.  The  changes  in  one's  own  pupil  may 
be  readily  observed  by  noticing  the  varying  size  of  the  circle  of  light  thrown 
upon  the  retina  when  the  eye  is  illuniinateil  by  ti  point  of  light  held  at  the 
anterior  ftK-us,  as  in  the  method  above  described  for  the  .study  of  intraocular 
images. 

The  muscles  of  the  iris  are,  except  in  birds,  of  the  unstriped  variety,  and 
are  arranged  concentrically  around  the  pupil.  Radiating  fibres  are  also  recog- 
nized by  many  observers,  though  their  existence  has  been  called  in  question 
by  others.  The  circular  or  constricting  muscles  of  the  iris  are  under  the  con- 
trol of  the  third  pair  of  cranial  nerves, 
and  are  normally  brought  into  activity 
in  consequence  of  light  falling  upon 
the  retina.  Tliis  is  a  reflex  phenom- 
enon, the  optic  nerve  being  the  affer- 
ent, and  the  third  pair,  the  ciliary 
ganglion,  and  the  short  ciliary  nerves 
the  efferent,  channel,  as  indicated  in 
Figure  230.  This  reflex  is  in  man 
and  many  of  the  higher  animals  bi- 
lateral— i.  e.  light  falling  upon  one 
retina  will  cause  a  contraction  of  both 
pupils.  This  may  readily  be  observed 
in  one's  own  eye  when  focally  illumi- 
nated in  the  manner  above  described. 
Opening  the  other  eye  will,  under 
these  conditions,  cause  a  diminution, 
and  closing  it  an  increase,  in  the  size 
of  the  circle  of  light.  This  bilateral 
character  is  found  to  be  dependent 
upon  the  nature  of  the  decussation  of 
the  optic  nerves,  for  in  animals  in 
which  the  crossing  is  complete  the 
reflex  is  confined  to  the  illuminated 
eve.     The  arrangement  of  the  fibres 


Course  of  constrictor  nerve-fibres  • 
"        dilator  " 


Fig.  230.— Diagrammatic   representation  of  the 
nerves  governing  the  pupil  (after  Foster) :  II,  optic 
nerve ;  l.  g,  ciliary  ganglion ;  r.  b,  its  short  root  from 
III,  motor-oculi  nerve  ;  ^ym,  its  sympathetic  root ;  r.  I, 
in    the    optic   commissure  is  in  general     its  long  root  from  F.ophthalmo-nasal  branch  of  oph- 

associated    with    the   position  of   the 
the   head.     When    the 


thalmic  division  of  fifth  nerve;  8. c.  short  ciliary 
nerves ;  I.  c,  long  ciliary  nerves. 

eyes  in  the  head.  When  the  eyes 
are  so  placed  that  they  can  both  be  directed  to  the  same  object,  as  in  man 
and  many  of  the  higher  animals,  the  fibres  of  each  optic  nerve  are  usually 
found  to  be  distributed  to  bo^h  optic  tracts,  while  in  animals  whose  eyes 
are  in  opposite  sides  of  the  head  there  is  complete  crossing  of  the  optic  nerves. 
Hence  it  may  be  said  that  animals  having  binocular  vision  have  in  general 
a  bilateral  pupillary  reflex.  The  rule  is,  however,  not  without  exceptions, 
for  owls,  though  their  visual  axes  are  parallel,  have,  like  other  birds,  a  com- 

49 


770  AN  AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 

plete  crossing  of  the   optic;   uorvcs,  and    coiisinjueiitiy  a    unilateral    pupillary 
reflex.' 

A  direct  as  well  as  a  reflex  constri<^tion  of  the  pupil  under  the  influence  of 
light  has  been  observed  in  the  excised  eyes  of  eels,  frogs,  and  some  other  ani- 
mals. As  the  phenomenon  can  be  seen  in  preparations  ccnisisting  of  the  iris 
alone  or  of  the  iris  and  cornea  together,  it  is  evident  that  the  light  exerts  its 
influence  directlv  upon  the  tissues  of  the  iris  and  not  through  an  intraocular 
connection  with  the  retina.  The  maximum  effect  is  produced  l)y  the  yellowish- 
green  portion  of  the  spectrum. 

Autatroniziuir  the  motor  oculi  nerve  in  its  constricting  influence  on  the 
pupil  is  a  set  of  nerve-fibres  the  function  of  which  is  to  increase  the  size  of 
the  pupil.  Most  of  these  fibres  seem  to  run  their  course  from  a  centre  which 
lies  in  the  floor  of  the  third  ventricle  not  far  from  the  origin  of  the  third  pair, 
through  the  bulb,  the  cervical  cord,  the  anterior  roots  of  the  upper  dorsal 
nerves,  the  upper  thoracic  ganglion,  the  cervical  sympathetic  nerve  as  far  as 
the  upper  cervical  ganglion ;  then  through  a  branch  which  accompanies  the 
internal  carotid  artery,  passes  over  the  Gasserian  ganglion  and  joins  the  oph- 
thalmic branch  of  the  fifth  pair ;  then  through  the  nasal  branch  of  the  latter 
nerve  and  the  long  ciliary  nerves  to  the  eye  ^  (see  diagram,  p.  769).  These 
fibres  ap})ear  to  be  in  a  state  of  tonic  activity,  for  section  of  them  in  any  part 
t)f  their  course  (most  conveniently  in  the  cervical  sympathetic)  causes  a  con- 
traction of  the  pupil  which,  on  stimulation  of  the  peripheral  end  of  the  divided 
nerve,  gives  place  to  a  marked  dilatation.  Their  activity  can  be  increased  ia 
various  ways.  Thus  dilatation  of  the  pupil  may  be  caused  by  dyspnea,  vio- 
lent muscular  efforts,  etc.  Stimulation  of  various  sensory  nerves  may  also 
cause  reflex  dilatation  of  the  pupil,  and  this  phenomenon  may  be  observed, 
though  greatly  diminished  in  intensity,  after  extirpation  of  the  superior  cervi- 
cal sympathetic  ganglion.  It  is  therefore  evident  that  the  dilator  nerves  of  the 
pupil  do  not  have  their  course  exclusively  in  the  cervical  sympathetic  nerve. 

Since  the  cervical  sympatlietic;  nerve  contains  vaso-constrictor  fibres  for  the 
head  and  neck,  it  has  been  thought  that  its  dilating  effect  upon  the  pupil  might 
be  explained  by  its  power  of  causing  changes  in  the  amount  of  blood  in  the 
vessels  of  the  iris.  There  is  no  doubt  that  a  condition  of  vascular  turgescence 
or  depletion  will  tend  to  produce  contraction  or  dilatation  of  the  pupil,  but  it  is 
impossible  to  explain  the  observed  phenomena  in  this  way,  since  the  pupillary 
are  more  prompt  than  the  vascular  changes,  and  may  be  observed  on  a  bloodless 
eye.  Moreover,  the  nerve-fibres  producing  them  are  said  to  have  a  somewhat 
different  coui*se.  Another  explanation  of  the  influence  of  the  sympathetic  on 
the  pupil  is  that  it  acts  by  inhibiting  the  contraction  of  the  sphincter  muscles, 
and  that  the  dilatation  is  simply  an  elastic  reaction.  But  since  it  is  posssible  to 
produce  local  dilatation  of  the  pupil  by  circumscribal  stimulation  at  or  near 

'  Steinach  :   Archir  fur  die  (/esummte  PhymAogiv,  xlvii.  31i). 

'^  Langley  :  Journal  of  Physiology,  xiii.  p.  575.  For  the  evidence  of  the  existence  of  a 
"  cilio-spinal "  centre  in  the  cord,  see  Steil  and  Langendorff:  Archiv  fiir  die  gesammte  Phys- 
iologie,  Iviii.  p.  155;  also  Scheuck :   Ibid.,  Ixii.  p.  494. 


THE   SENSE    OF    VISION.  Ill 

the  outer  border  of  the  iris,  it  seems  more  reasonable  to  conclude  that  the 
dilator  nerves  of  the  puj)il  act  upon  radial  muscular  fibres  in  the  substance  of 
the  iris,  in  spite  of  the  fact  that  the  existence  of  such  fibres  has  not  been  uni- 
versally admitted. 

Whatever  view  may  be  taken  of  the  mechanism  by  which  the  sympathetic 
nerves  influence  the  pupil,  there  is  no  doubt  that  the  iris  is  under  the  control 
of  two  antagonistic  sets  of  nerve-fibres,  both  of  which  are,  under  normal  cir- 
cumstances, in  a  state  of  tonic  activity.  Therefore,  when  the  sympathetic 
nerve  is  divided  the  pu])il  contracts  under  the  influence  of  the  motor  oculi,  and 
section  of  the  motor  oculi  causes  dilatation  through  the  unopposed  influence  of 
the  sympathetic. 

The  movements  of  the  iris,  though  performed  by  smooth  muscles,  are  more 
rapiil  than  those  of  smooth  muscles  found  elsewhere— e.  g.  in  the  intestines 
and  the  arteries.  The  contraction  of  the  pupil  when  the  retina  of  the  oppo- 
site eye  is  illuminated  occupies  about  0.3" ;  the  dilatation  when  the  light  is  cut 
off  from  the  eye,  about  3"  or  4".  The  latter  determination  is,  however,  diffi- 
cult to  make  with  precision,  since  dilatation  of  the  pupil  takes  place  at  first 
rapidly  and  then  more  slowly,  so  that  the  moment  when  the  process  is  at  an 
end  is  not  easily  determined.  After  remaining  a  considerable  time  in  absolute 
darkness  the  pupils  become  enormously  dilated,  as  has  been  shown  by  flash- 
light photographs  taken  under  these  conditions.  In  sleep,  though  the  eyes  are 
protected  from  the  light,  the  pupils  are  strongly  contracted,  but  dilate  on 
stimulation  of  sensory  nerves,  even  though  the  stimulation  may  be  insufficient 
to  rouse  the  sleeper. 

Many  drugs  when  introduced  into  the  system  or  applied  locally  to  the  con- 
junctiva produce  effects  upon  the  pupil.  Those  which  dilate  it  are  known  as 
mydriatics,  those  which  contract  it  as  myotics.  Of  the  former  class  the  most 
important  is  atropin,  the  alkaloid  of  the  Atropa  belladonna,  and  of  the  latter 
physostigmin,  the  alkaloid  of  the  Calabar  bean.  In  addition  to  their  action 
upon  the  pupil,  mydriatics  paralyze  the  accommodation,  thus  focussing  the  eye 
for  distant  objects,  while  myotics,  by  producing  a  cramp  of  the  ciliary  muscle, 
adjust  the  eye  for  near  vision.  The  effect  on  the  accommodation  usually 
begins  later  and  passes  off  sooner  than  the  affection  of  the  pupil.  Atropin 
seems  to  act  by  producing  local  paralysis  of  the  terminations  of  the  third  pair 
of  cranial  nerves  in  the  sphincter  iridis  and  the  ciliary  muscle.  In  large 
doses  it  may  also  paralyze  the  muscle-fibres  of  the  sphincter.  With  this  para- 
lyzing action  there  .appears  to  be  combined  a  stimulating  effect  upon  the  dilator 
muscles  of  the  iris.  The  myotic  action  of  physostigmin  seems  to  be  due  to  a 
local  stimulation  of  the  fibres  of  the  sphincter  of  the  iris. 

Although  in  going  from  a  dark  room  to  a  lighter  one  the  pupil  at  first  con- 
tracts, this  contraction  soon  gives  place  to  a  dilatation,  and  in  about  three  or 
four  minutes  the  pupil  usually  regains  its  former  size.  In  a  similar  manner 
the  primary  dilatation  of  the  pupil  caused  by  entering  a  dark  room  from  a 
lighter  one  is  followed  by  a  contraction  which  usually  restores  the  pupil  to  its 
original  size  within   fifteen  or  twenty  minutes.     It   is  thus  evident  that  the 


772 


AN  AMERICAN   TEXT-BOOK    OF   J'JIYSIOLOGY. 


amount  of  light  lulling  u])on  the  retina  is  uot  the  only  taet<;r  in  determining 
the  size  of  the  pupil.  In  fact,  if  the  light  aets  for  a  sufficient  length  of  time 
the  pupil  may  have  the  same  size  under  the  influence  of  widely  difl'erent 
degrees  of  illumination.' 

This  so-cidled  "  adaptation  "  of  the  eye  to  various  amounts  of  light  seems 
to  be  connected  w  ilh  the  movements  of  the  retinal  pigment-granules  and  with 
the  chemical  changes  of  the  visual  purple,  to  be  more  fully  described  in  c<jn- 
nection  with  the  physiology  of  the  retina. 

The  Ophthalmoscope. — Under  normal  conditions  the  pupil  of  the  eye 
appears  as  a  black  spot  in  the  middle  of  the  colored  iris.  The  cause  of  this 
dark  appearance  of  the  pupil  is  to  be  found  in  the  fact  that  a  source  of  light 
and  the  retina  lie  in  the  conjugate  foci  of  the  dioptric  apparatus  of  the  eye. 
Hence  any  light  entering  the  eye  that  escapes  absorption  by  the  retinal  pig- 
ment and  is  reflected  from  the  fundus  must  be  refracted  back  to  the  source 
from  which  it  came.  The  eye  of  an  observer  who  looks  at  the  pupil  from 
another  direction  will  see  no  light  coming  from  it,  and  it  will  therefore  appear 
to  him  black.  It  is  therefore  evident  that  the  essential  condition  for  perceiving 
light  coming  from  the  fundus  of  the  eye  is  that  the  line  of  vision  of  the 
observing  eye  shall  be  in  the  line  of  illumination.  This  condition  is  fulfilled 
by  means  of  instruments  known  as  ophthalmoscopes.  The  principles  involved 
in  the  construction  of  the  most  common  form  of  ophthalmoscope  are  illustrated 
diagrammatically  in  Figure  231. 


Fig.  2.31.— Diagram  to  illustrate  the  principles  of  a  simple  ophthalmoscope  (after  Foster). 

The  rays  from  a  source  of  light  L,  after  being  brought  to  a  focus  at  a  by 
the  concave  perforated  mirror  M  M,  pass  on  and  are  rendered  parallel  by  the 
lens  /.  Then,  entering  the  observed  eye  B,  they  are  brought  to  a  focus  on  the 
retina  at  a'.  Any  rays  which  are  reflected  back  from  the  part  of  the  retina 
thus  illuminated  will  follow  the  course  of  the  entering  rays  and  be  brought  to 
a  focus  at  a.  The  eye  of  an  observer  at  A,  looking  through  the  hole  in  the 
mirror,  will  therefore  see  at  a  an  inverted  image  of  the  retina,  the  observation 
of  which  may  be  facilitated  by  a  convex  lens  placed  immediately  in  front  of 
the  observer's  eye. 

*  Schirmer :  Archiv/iir  Ophlhalmologie,  xi.  5. 


THE   SENSE    OF    VISION. 


773 


The  fundus  of  the  eye  thus  observed  presents  a  reddish  background  on 
wliich  the  retinal  vessels  are  distinctly  visible. 

Retina. — ITavin<!;  considered  the  mechanism  by  which  optical  images  of 
objects  at  various  distances  from  the  eye  are  formed  upon  the  retina,  we  nmst 
next  inquire  what  part  of  the  retina  is  affected  by  the  rays  of  light,  and  in 
what  this  affection  consists.  To  the  former  of  these  questions  it  will  be  found 
possible  to  give  a  fairly  satisfactory  answer.  Witli  regard  to  the  latter  nothing 
positive  is  known. 

The  structure  of  the  retina  is  exceedingly  complicated,  but,  as  very  little 
is  known  of  the  functions  of  the  ganglion  cells  and  of  the  molecular  and 
nuclear  layers,  it  will  suffice  for  the  present  purpose  of  physiological  descrip- 
tion to  regard  the  retina  as  consisting  of  fibres  of  the  optic  nerve  which  are 
connected  through  various  intermediate  structures  with  the  layer  of  rods  and 
cones. 


A 

Fig.  232 


-Diagrammatic  representation  of  the  retina. 

Figure  232  is  intended  to  show,  diagrammatically,  the  mutual  relation  of 
these  various  portions  of  the  retina  in  different  parts  of  the  eye,  and  is  not 
drawn  to  scale.  It  will  be  observed  that  the  optic  nerve  0,  wdiere  it  enters  the 
eye,  interrupts  the  continuity  of  the  layer  of  rods  and  cones  R  and  of  the 
intermediate  structures  /.  Its  fibres  spread  themselves  out  in  all  directions, 
forming  the  internal  layer  of  the  retina  N.  The  central  artery  of  the  retina 
A  accompanying  the  optic  nerve  ramifies  in  the  layer  of  nerve-fibres  and  in 
the  immediately  adjacent  layers  of  the  retina,  forming  a  vascular  layer  V.  In 
the  fovea  centralis  F  of  the  macula  lutea  (the  centre  of  distinct  vision)  the 
layer  of  rods  and  cones  becomes  more  highly  developed,  while  the  other  layers 
of  the  retina  are  much  reduced  in  thickness  and  the  blood-vessels  entirely  dis- 
appear. This  histological  observation  points  strongly  to  the  conclusion  that 
the  rods  and  cones  are  the  structures  which  are  essential  to  vision,  and  that  in 
them  are  found  the  conditions  for  the  conversion  of  the  vibrations  of  the 
luminiferous  ether  into  a  stimulus  for  a  nerve-fibre.  This  view  derives  con- 
firmation from  the  observations  on  the  retinal  blood-vessels,  for  it  is  found 
that  the  distance  between  the  vascular  layer  of  the  retina  and  the  layer 
of  rods  and  cones  determined  by  histological  methods  corresponds  with  that 
which  must  exist  between  the  vessels  and  the  light-perceiving  elements  of  the 
retina,  as  calculated  from  the  apparent  displacement  of  the  shadow  caused  by 
given  movements  of  the  source  of  light  used  in  studying  intraocular  images^  as 

1  "  Dimmer  Verb.  d.  phys.  Clubs  zu  Wien,  24  April,  1894,"  CentrcJbl.  fur  Physiologie,  1894, 159. 


774 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


described  on  p.  767,  Another  argument  in  favor  of  this  view  is  fcjiind  in  the 
correspondence  between  the  size  of  the  smallest  visible  images  on  the  retina  and 
the  diameter  of  the  rods  and  cones.  A  double  star  can  be  recognized  as  double 
by  the  normal  eye  when  the  distance  between  the  components  corresponds  to 
a  visual  angle  of  60".  Two  white  lines  on  a  black  ground  are  seen  to  be  dis- 
tinct when  the  distance  between  them  subtends  a  visual  angle  of  64"-73". 
These  angles  correspond  to  a  retinal  image  of  0.0044,  0.0046,  and  0.0053  mil- 
limeter. Now,  the  diameter  of  the  cones  in  the  macula  lutea,  as  determined 
by  Kolliker,  is  0.0045-0.0055  millimeter,  a  size  which  agrees  well  with  the 
hypothesis  that  each  cone  when  stimulated  can  produce  a  special  sensation  of 
light  distinguishable  from  those  caused  by  the  stimulation  of  the  neighboring 
cones.  The  existence  of  the  so-called  blind  spot  in  the  retina  at  the  point  of 
entrance  of  the  optic  nerve  is  sometimes  regarded  as  evidence  of  the  light- 
perceiving  function  of  the  rods  and  cones,  but  as  the  other  layers  of  the  retina, 
as  well  as  the  rods  and  cones,  are  absent  at  this  point,  and  the  retina  here 
consists  solely  of  nerve-fibres,  it  is  evident  that  the  presence  of  the  blind  spot 


Fig.  233.— To  demonstrate  the  blind  spot. 

only  proves  that  the  optic  nerve-fibres  are  insensible  to  light.  Figure  233  is 
intended  to  demonstrate  this  insensibility.  For  this  purpo.se  it  should  be  held 
at  a  distance  of  about  23  centimeters  from  the  eyes  [i.  e.  about  3.5  times  the  dis- 
tance between  the  cross  and  the  round  spot).  If  the  left  eye  be  closed  and  the 
right  eye  fixed  upon  the  cross,  the  round  spot  will  disappear  from  view,  though 
it  will  become  visible  if  the  eye  be  directed  either  to  the  right  or  to  the  left  of 
the  cross,  or  if  the  figure  be  held  either  a  greater  or  a  less  distance  from  the 
eye.  The  size  and  shape  of  the  blind  spot  may  readily  be  determined  as 
follows  :  Fix  the  eye  upon  a  definite  point  marked  upon  a  sheet  of  white 
paper.  Bring  the  black  point  of  a  lead  pencil  (which,  except  the  point,  has 
been  painted  white  or  covered  with  white  paper)  into  the  invisible  portion  of 
the  field  of  vision  and  carry  it  outward  in  any  direction  until  it  becomes  vis- 
ible. Mark  upon  the  paper  the  point 
at  which  it  just  begins  to  be  seen,  and 
by  repeating  the  process  in  as  many 
different  directions  as  po.ssible  the  out- 
line of  the  blind  spot  may  be  marked 
out.  Figure  234  shows  the  shape  of 
the  blind  spot  determined  by  Helni- 
holtz  in  his  own  right  eye,  a  being 
^*Z~~T.    Z        7irTr~i      ,  ,„  ,   .   ,»  /       the  i)oint  of  fixation  of  the  eye,  and 

Fig.  234.— Form  of  the  blind  spot  (Helmholtz).  J  _  . 

the  line  .1  B  being  one-third  of  the 
distance  between  the  eye  and  the  paper.     The  irregularities  of  outline,  as  at 


TIIK   SENSE    OF    VISION. 


lib 


d  are  cl.>e  to  shadows  of  tin-  large  retinal  vessels.     During  this  determination 
it'  is  of  course  necessary  that  the  head  should  occ-upy  a  fixed   position  with 
rec^ard  to  the  paper.     This  condition  can  be  secured  by  holding  fu.nly  between 
the  teeth  a  piece  of  wood  that  is  clamped  in  a  suitable  position  to  the  edge  of 
the  table.    The  diameter  of  the  blind  spot,  as  thus  determined,  has  been  found 
to  correspond  to  a  visual  angle  varying  from  3°  39'  to  9°  47  ,  the  average 
measurement  being  6°  10'.     This  is  about  the  angle  that  is  subtended  by  the 
human  face  seen  at  a  distance  of  two  meters.     Although  a  considerable  por- 
tion of  the  retina  is  thus  insensible  to  light,  we  are,  in  the  ordinary  us^  of  the 
eyes,  conscious  of  no  corresponding  blank   in  the  field  of  visioiu     By  what 
psvchieal  operation  we  "fill  up"  the  gap  in  our  subjective  field  of  vision 
caused  by  the  blind  spot  of  the  retina  is  a  question  that  has  been  much  dis- 
cussed without  being  definitely  settled.  ,.     r  i  f 
The  above-mentioned  reasons  for  regarding  the  rods  and  cones  as  the  light- 
perceiving  elements  of  the  retina  seem  sufficiently  conclusive.     Whether  there 
is  anv  difference  between  the  rods  and  the  cones  with  regard  to  their  bght- 
perceivinc  function  is  a  question  which  may  be  best  considered  m  connection 
with  a  description  of  the  qualitative  modifications  of  light 

The  histological  relation  between  the  various  layers  of  the  retina  is  still 
under  discussion.     According  to  recent  observations  of  Cajal,^  the  connection 
between  the  rods  and  cones  on  the  one 
side  and  the  fibres  of  the  optic  nerve 
on  the  other  is  established  in  a  man- 
ner   which     is     represented    diagram- 
matically   in   Figure   235.     The   pro- 
longations of  the  bipolar  cells  of  the 
internal  nuclear  layer  E  break  up  into 
fine  fibres   in   the   external   molecular 
(or  plexiform)  layer  C.     Here  they  are 
brought  into  contact,  though   not  into 
anatomical  continuity,  with  the  termi- 
nal fibres  of  the  rods  and  cones.     The 
inner  prolongations  of  the  same  bipolar 
cells  penetrate  into  the  internal  molec- 
ular (or  plexiform)  layer  F,  and  there 
come  into  contact   with   the   dendrites 
coming  from  the  layer  of  ganglion-cells 
G.     These  cells  are,  in  their  turn,  con- 
nected by  their  axis-cylinder  processes 
Avith  the  fibres  of  the  optic  nerve.   The 


Rods. 


Cones. 


Fig.  235.-Diagrammatic  representation  of  the 

xvWh  the  fibres  Ol    tne  OpUC  neive.     -lh^  structure  of  the  retina  (Cajal):  A,  layer  of  rods 

AVltn  tne  noieb  ui    u          ^  and  cones-  B  external  nuclearlayer;  C.  external 

bipolar  cells  which  serve  as  connective  ^°^^j;^"i^; (^;  plexiform)  layer;  e,  internal  un- 
links between  the  rods  and  the  optic  J-r:ay^er;^..int.^^^^^^^^^ 
nerve-fibres    are    anatomically    distin-  ^^-^^^^.g^,;,. 
guishable  (as  indicated  in  the  diagram) 


Die  Retina  der  Wirbeltkiere,  Wiesbaden,  1894. 


776  AX  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

from  those  wliicli  perl'onn  the  same  t'unetion  lor  the  cones.  Whatever  be  tlie 
precise  mode  of  connection  between  the  rods  and  cones  and  the  fibres  of  tlie 
optic  nerve,  it  is  evident  that  each  retinal  element  cannot  be  counectod  with 
the  nerve-centres  by  a  separate  independent  nerve-channel,  since  the  retina 
contains  many  millions  of  rods  and  cones,  while  the  optic  nerve  has  only 
about  438,000  nerve-fibres,'  though  of  course  such  a  connection  may  exist  in 
the  fovea  centralis,  as  Cajal  has  shown  is  probably  the  case  in  reptiles  and  birds. 
Changes  Produced  in  the  Retina  by  Light. — We  must  now  inquire 
what  changes  can  be  supposed  to  occur  in  the  rods  and  cones  under  the  influ- 
ence of  light  by  means  of  which  they  are  able  to  transform  the  energy  of  the 
ether  vibrations  into  a  stimulus  for  the  fibres  of  the  optic  nerve.  Though  in 
the  present  state  of  our  knowledge  no  satisfactory  answer  can  be  given  to  this 
question,  yet  certain  direct  effects  of  light  upon  the  retina  have  been  observed 
which  are  doubtless  associated  in  some  way  with  the  transformation  in 
question. 

The  retina  of  an  eye  which  has  been  protected  from  light  for  a  considerable 
length  of  time  has  a  purplish-red  color,  which  upon  exposure  to  light  changes 
to  yellow  and  then  fades  away.  This  bleaching  occurs  also  in  monochromatic 
light,  the  most  powerful  rays  being  those  of  the  greenish-yellow  portion  of 
the  spectrum — /.  e.  those  rays  which  are  most  completely  absorbed  by  the  pur- 
plish-red coloring  matter.  A  microscopic  examination  of  the  retina  shows 
that  this  coloring  matter,  which  has  been  termed  visual  purple,  is  entirely  con- 
fined to  the  outer  portion  of  the  retinal  rods  and  does  not  occur  at  all  in  the 
cones.  After  being  bleached  by  light  it  is,  during  life,  restored  through  the 
agency  of  the  pigment  epithelium,  the  cells  of  which,  under  the  influence  of 
light,  send  their  prolongations  inward  to  envelop  the  outer  limbs  of  the  rods 
and  cones  with  pigment.  If  an  eye,  either  excised  or  in  its  natural  position, 
is  protected  from  light  for  a  time,  and  then  placed  in  such  a  position  that  the 
image  of  a  lamp  or  a  window  is  thrown  upon  the  retina  for  a  time  which  may 
vary  with  the  amount-of  light  from  seven  seconds  to  ten  minutes,  it  will  be 
found  that  the  retina,  if  removed  and  examined  under  red  light,  will  show  the 
image  of  the  luminous  object  impressed  ujion  it  by  the 
bleaching  of  the  visual  purple. 

If  the  retina  be  treated  with  a  4  per  cent,  solution  of 
alum,  the  restoration  of  the  visual  purple  will  be  pre- 
vented, and  the  so-called  '^  optogram"  will  be,  as  pho- 
tographers say,  "  fixed."  ^ 
Fig.  236.-optoKram  in  eye  Figure  236  shows  the  ai)iiearance  of  a  rabbit's  retina 

of  rabbit  (Kiihne).  ,  •    ,       ,  />  •     i         i         i  •  i 

on  whicli  the  optogram  oi  a  wnidow  has  been  nupressed. 

Although  the  chemical  changes  in  the  visual  purple  under  the  influence  of 

light  seem,  at  first  sight,  to  afford  an  cxjilanation  of  the  transformation  of  the 

vibrations  of  the  luminiferous  ether  into  a  stimulation  for  the  optic  nerve,  yet 

the  fact  that  vision  is  most  distinct  in  the  fovea  centralis  of  the  retina,  which, 

^  Salzer:  Wiener  Sitzungsberichle,  1880.  Bd.  Ixxxi.  S.  3. 

'  Kiihne :  Unlersuchungen  a.  d.  phys.  Inst.  d.  UniversUdt  Heidelbeig,  i.  1. 


THE   SENSE    OF    VISION.  Ill 

as  it  contains  lU)  rods,  is  destitute  ol"  visual  purple,  makes  it  impossible  to 
rejiard  this  colorinj>;  matter  as  essential  to  vision.  The  most  probable  theory 
of  its  tunotion  is  perhaps  that  which  connects  it  with  the  adaptation  of"  the 
eye  to  varying  amounts  of  ligiit,  as  described  on  p.  772. 

In  addition  to  the  above-mentioned  movements  of  the  ])igment  epithelium 
cells  under  the  influence  of  light,  certain  changes  in  the  retinal  cones  of  frogs 
and  fishes  have  been  observed.^  The  change  consists  in  a  shortening  and  thick- 
ening of  the  inner  portion  of  the  cones  when  illuminated,  but  the  relation  of 
the  ])henomenon  to  vision  has  not  been  explained. 

Like  most  of  the  living  tissues  of  the  body,  the  retina  is  the  seat  of  electri- 
cal currents.  In  repose  the  fibres  of  the  optic  nerve  are  said  to  be  positive  in 
relation  to  the  layer  of  rods  and  cones.  When  light  falls  upon  the  retina  this 
current  is  at  first  increased  and  then  diminished  in  intensity. 

Sensation  of  Light. — Whatever  view  may  be  adopted  with  regard  to  the 
mechanism  by  which  light  is  enabled  to  become  a  stimulus  for  the  optic  nerve, 
the  fundamental  fact  remains  that  the  retina  (and  in  all  probability  the  layer 
of  rods  and  cones  in  the  retina)  alone  supplies  the  conditions  under  which  this 
transformation  of  energy  is  possible.  But  in  accordance  with  the  "  law  of 
specific  energy  "  a  sensation  of  light  may  be  produced  in  whatever  way  the 
optic  nerve  be  stimulated,  for  a  stimulus  reaching  the  visual  centres  through 
the  optic  nerve  is  interpreted  as  a  visual  sensation,  in  the  same  way  that 
pressure  on  a  nerve  caused  by  the  contracting  cicatrix  of  an  amputated  leg 
often  causes  a  painful  sensation  which  is  referred  to  the  lost  toes  to  which  the 
nerve  was  formerly  distributed.  Thus  local  pressure  on  the  eyeball  by  stimu- 
lating the  underlying  retina  causes  luminous  sensations,  already  described  as 
*'  phosphenes,"  and  electrical  stimulation  of  the  eye  as  a  whole  or  of  the  stump 
of  the  optic  nerve  after  the  remos'al  of  the  eye  is  found  to  give  rise  to  sensa- 
tions of  light. 

Vibrations  of  the  luminiferous  ether  constitute,  however,  the  normal  stim- 
ulus of  the  retina,  and  we  must  now  endeavor  to  analyze  the  sensation  thus 
produced.  In  the  first  place,  it  must  be  borne  in  mind  that  the  so-called  ether 
waves  differ  among  themselves  very  widely  in  regard  to  their  rate  of  oscilla- 
tion. The  slowest  known  vibrations  of  the  ether  molecules  have  a  frequency 
of  about  107,000,000,000,000  in  a  second,  and  the  fastest  a  rate  of  about 
40,000,000,000,000,000  in  a  second — a  range,  expressed  in  musical  terms,  of 
about  eight  and  one-half  octaves.  All  these  ether  waves  are  capable  of  warm- 
ing bodies  upon  which  they  strike  and  of  breaking  up  certain  chemical  com- 
binations, the  slowly  vibrating  waves  being  especially  adapted  to  produce  the 
former  and  the  rapidly  vibrating  ones  the  latter  effect.  Certain  waves  of 
intermediate  rates  of  oscillation — viz.  those  ranging  between  392,000,000,- 
000,000  and  757,000,000,000,000  in  a  second— not  only  produce  thermic  and 
chemical  effects,  but  have  the  power,  when  they  strike  the  retina,  of  causing 
changes  in  the  layer  of  rods  and  cones,  which,  in  their  turn,  act  as  a  stimulus 
to  the  optic  nerve.     The  ether  waves  which  produce  these  various  phenomena 

^  Engelniann  :  Archivfiir  die  gesammte  PhysMogie,  xxxv.  498. 


778  A^'  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

are  often  spoken  of  as  heat  rays,  light  rays,  and  actinic  or  chemical  rays,  but 
it  must  be  remembered  that  the  same  wave  may  produce  all  three  classes  of 
phenomena,  the  effect  dependincr  upon  the  nature  of  the  sub.<tance  upon  which 
it  strikes.  It  will  be  observed  that  the  range  of  vibrations  capable  of  affecting 
the  retina  is  rather  less  than  one  octave,  a  limitation  which  obviously  tends  to 
reduce  the  amount  of  chromatic  aberration. 

In  this  connection  it  is  interesting  to  notice  that  the  highest  audible  note  is 
produced  by  about  40,000  sonorous  impulses  in  a  second.  Between  the  high- 
est audible  note  and  the  lowest  visible  color  there  is  a  gap  of  nearly  thirty-four 
octaves  in  which  neither  the  vibrations  of  the  air  nor  those  of  the  luminifer- 
ous  ether  affect  our  senses.  Even  if  the  slowly  vibrating  heat-rays  which 
affect  our  cutaneous  nerves  are  taken  into  account,  there  still  remain  over 
thirty-one  octaves  of  vibrations,  either  of  the  air  or  of  the  luminiferous  ether, 
which  may  be,  and  very  likely  are,  filling  the  universe  around  us  without  in 
any  way  impressing  themselves  upon  our  consciousness. 

Qualitative  Modifications  of  Light. — All  the  ethereal  vibrations  which 
are  capable  of  affecting  the  retina  are  transmitted  with  very  nearly  the  same 
rapidity  through  air,  but  when  they  enter  a  denser  medium  the  waves  having 
a  rapid  vibration  are  retarded  more  than  those  vibrating  more  slowly.  Hence 
Avhen  a  ray  of  sunlight  composed  of  all  the  visible  ether  waves  strikes  upon  a 

plane  surface  of  glass,  the  greater 
1^'  retardation  of  the  waves  of  rapid 
vibration  causes  them  to  be  more 
refracted  than  those  of  slower  vibra- 
tion, and  if  the  glass  has  the  form 
of  a  prism,  as  shown  in  Figure  237, 
this  so-called  *'  dispersion  "  of  the 
rays  is  still  further  increased  when 
the  rays  leave  the  glass,  .so  that  the 
emerging  beam,  if  received  upon  a 

Fig.  237.-Diagrain  iUustrating  the  dispersion  of  light      ^.j^j^^  surface,  instead  of  forming  a 
by  a  prism.  '  » 

spot  of  white  light,  produces  a  band 
of  color  known  as  the  solar  spectrum.  The  colors  of  the  spectrum,  though 
commonly  spoken  of  as  seven  in  number,  really  form  a  continuous  series  from 
the  extreme  red  to  the  extreme  violet,  these  colors  corresponding  to  ether  vibra- 
tions have  rates  of  392,000.000,000,000  and  757,000,000,000,000  in  1  second, 
and  wave  lengths  of  0.7G67  and  0.3970  microniilliraeters*  respectively. 

Colors,  therefore,  are  sensations  caused  by  the  impact  upon  the  retina  of 
certain  ether  waves  having  definite  frequencies  and  wave-lengths,  but  these 
are  not  the  only  peculiarities  of  the  ether  vibration  which  influence  the  retinal 
sensation.  The  energy  of  the  vibration,  or  the  vis  viva  of  the  vibrating  mole- 
cule, determines  the  "  intensity  "  of  the  .sensation  or  the  brilliancy  of  the  light.* 

'One  micromillimeter^  0.001  millimeter  =  one  ,". 

^  The  energy  of  vibration  capable  of  producing  a  given  subjective  sensation  of  intensity 
varies  with  the  color  of  the  light,  as  will  be  later  explained  (see  p.  786). 


THE  SENSE    OF    VISION.  779 

Furthermore,  the  sensation  produced  by  the  impact  of  ether  waves  of  a  definite 
length  will  vary  according  as  the  eye  is  simultaneously  affected  by  a  greater  or 
less  amount  of  wliite  light.  This  modification  of  the  sensation  is  termed  its 
degree  of  'Saturation,"  light  being  said  to  be  completely  saturated  when  it  is 
"  monochromatic  "  or  produced  by  ether  vibrations  of  a  single  wave-length. 

The  modifications  of  light  which  taken  together  determine  completely  the 
character  of  the  sensation  are,  then,  three  in  number — viz.  :  1.  Color,  depend- 
ent upon  rate  of  vibration  or  length  of  the  other  wave  ;  2.  Intensity,  dependent 
upon  the  energy  of  the  vibration  ;  3.  Saturation,  dependent  upon  the  amount 
of  white  light  mingled  with  the  monochromatic  light.  These  three  qualitative 
modifications  of  light  must  now  be  considered  in  detail. 

Color. — In  our  profound  ignorance  of  the  nature  of  the  process  by  which, 
in  the  rods  and  cones,  the  movements  of  the  ether  waves  are  converted  into  a 
stimulus  for  the  optic  nerve-fibres,  all  that  can  be  reasonably  demanded  of  a 
color  theory  is  that  it  shall  present  a  logically  consistent  hypothesis  to  account 
for  the  sensations  actually  produced  by  the  impact  of  ether  waves  of  varying 
rates,  either  singly  or  combined,  upon  different  parts  of  the  retina.  Some  of 
the  important  phenomena  of  color  sensation  of  which  every  color  theory  must 
take  account  may  be  enumerated  as  follows  : 

1.  Luminosity  is  more  readily  recognized  than  color.  This  is  shown  by 
the  fact  that  a  colored  object  appears  colorless  when  it  is  too  feebly  illuminated, 
and  that  a  spectrum  produced  by  a  very  feeble  light  shows  variations  of  inten- 
sity with  a  maximum  nearer  than  normal  to  the  blue  end,  but  no  gradations 
of  color.  A  similar  lack  of  color  is  noticed  when  a  colored  object  is  observed 
for  too  short  a  time  or  when  it  is  of  insufficient  size.  In  all  these  respects  the 
various  colors  present  important  individual  differences  which  will  be  considered 
later, 

2.  Colored  objects  seen  with  increasing  intensity  of  illumination  appear 
more  and  more  colorless,  and  finally  present  the  appearance  of  pure  white. 
Yellow  passes  into  white  more  readily  than  the  other  colors, 

3.  The  power  of  the  retina  to  distinguish  colors  diminishes  from  the  centre 
toward  the  periphery,  the  various  colors,  in  this  respect  also,  differing  mate- 
rially from  each  other.  Sensibility  to  red  is  lost  at  a  short  distance  from  the 
macula  lutea,  while  the  sensation  of  blue  is  lost  only  on  the  extreme  lateral 
portions  of  the  retina.  The  relation  of  this  phenomenon  to  the  distribution 
of  the  rods  and  cones  in  the  retina  will  be  considered  in  connection  with  the 
perception  of  the  intensity  of  light. 

Color-mixture. — Since  the  various  spectral  colors  are  produced  by  the  dis- 
persion of  the  white  light  of  the  sun,  it  is  evident  that  white  light  may  be 
reproduced  by  the  reunion  of  the  rays  corresponding  to  the  different  colors,  and 
it  is  accordingly  found  that  if  the  colored  rays  emerging  from  a  prism,  as  in 
Fig.  237,  are  reunited  by  suitable  refracting  surfaces,  a  spot  of  white  light  will  be 
produced  similar  to  that  which  would  have  been  caused  by  the  original  beam 
of  sunlight.  But  white  light  may  be  produced  not  only  by  the  union  of  all 
the  spectral  colors,  but  by  the  union  of  certain  selected  colors  in  twos,  threes. 


780  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

fours,  etc.  Any  tw(3  spectral  colors  which  by  their  union  produce  white  are 
said  to  be  "  complementary  "  colors.  The  relation  of  these  pairs  of  comple- 
mentary colors  to  each  otlier  may  be  best  mulerstood  by  reference  to  Figure  238. 


p 

Fig.  238.— Color  diagram. 

Here  the  spectral  colors  are  supposed  to  be  disposed  around  a  curved  line, 
as  indicated  by  their  initial  letters,  and  the  two  ends  of  the  curve  are  united 
by  a  straight  line,  thus  enclosing  a  surface  having  somewhat  the  form  of  a  tri- 
angle with  a  rounded  apex.  If  the  curved  edge  of  this  surface  be  supposed  to 
be  loaded  with  weights  proportionate  to  the  luminosity  of  the  different  colors, 
the  centre  of  gravity  of  the  surface  will  be  near  the  point  W.  Now,  if  a 
straight  line  be  drawn  from  any  point  on  the  curved  line  through  the  point 
IF  and  prolonged  till  it  cuts  the  curve  again,  the  colors  corresponding  to  the 
two  ends  of  this  straight  line  will  be  complementary  colors.  Thus  in  Figure 
238  it  will  be  seen  that  the  complementary  color  of  red  is  blui.sh -green,  and 
that  of  yellow  lies  near  the  indigo.  It  is  also  evident  that  the  complementary 
color  of  green  is  purple,  which  is  not  a  spectral  color  at  all,  but  a  color 
obtained  by  the  union  of  violet  and  red.  The  union  of  a  pair  of  colors 
lying  nearer  together  than  complementary  colors  produces  an  intermediate  color 
mixed  with  an  amount  of  white  which  is  proportionate  to  the  nearness  of  the 
colors  to  the  complementary.  Thus  the  union  of  red  and  yellow  produces 
orange,  but  a  less  saturated  orange  than  the  spectral  color.  The  union  of  two 
colors  lying  farther  apart  than  complementary  colors  produces  a  color  which 
borders  more  or  less  upon  purple. 

The  mixing  of  colors  to  demonstrate  the  above-mentioned  effects  may  be 
accomplished  in  three  different  ways  : 

1.  By  employing  two  prisms  to  produce  two  independent  spectra,  and  then 
directing  the  colored  rays  which  are  to  be  united  so  that  they  will  illuminate 
the  same  white  surface. 

2.  By  looking  ol)liquely  through  a  glass  plate  at  a  colored  object  placed 
behind  it,  while  at  the  same  time  light  from  another  colored  object,  placed  in 
front  of  the  glass,  is  reflected  into  the  eye  of  the  observer,  as  shown  in  Figure 
239.  Here  the  transmitted  light  from  the  colored  object  A  and  the  reflected 
light  from  the  colored  object  B  enter  the  eye  at  C  from  the  same  direction, 
and  are  therefore  united  upon  the  retina. 

3.  By  rotating  before  the  eye  a  disk  on  which  the  colors  to  be  united  are 


THE  SENSE    OF    VISION.  781 

painted  upon  different  sectors.  Tliis  is  most  readily  accomplislied  by  using 
a  number  of  disks,  each  painted  with  one  of  the  colors  to  be  experimented 
with,  and  each  divided  radially  by  a  cut  running  from  the  centre  to  the  circum- 
ference. The  disks  can  then  l)e  lapped  over  each  other  and  rotated  together,  and 
in  this  way  two  or  more  colors  can  be  mixed  in  any  desired  proportions.  Tiiis 
method  of  mixing  colors  depends  upon 
the  property  of  the  retina  to  retain  an 

impression  after  the  stimulus  causing  / 

it  has  ceased  to  act — a  phenomenon  of  / 


\ 
and  one  which  will  be  further  discussed  / 


great  importance  in  physiological  optics,  y  \ 


in  connection  with  the  subject  of  "  after-  /  \ 

images."  jj/  \^ 


The    physiological    mixing  of  colors      Fig.  239.— Diagram  to  illustrate  color  mixture  by 

cannot  be  accomplished  by  the  mixture  '^^^''^^^  ^""^  transmitted  light  (Heimhoitz). 
of  pigments  or  by  allowing  sunlight  to  pass  successively  through  glasses  of 
different  colors,  for  in  these  cases  rays  corresponding  to  certain  colors  are 
absorbed  by  the  medium  through  which  the  white  light  passes,  and  the  phe- 
nomenon is  the  result  of  a  process  of  subtraction  and  not  addition.  Light 
reaching  the  eye  through  red  glass,  for  instance,  looks  red  because  all  the  rays 
except  the  red  rays  are  absorbed,  and  light  coming  through  green  glass  appears 
green  for  a  similar  reason.  Now,  when  light  is  allowed  to  pass  successively 
through  red  and  green  glass  the  only  rays  which  pass  through  the  red  glass 
wall  be  absorbed  by  the  green.  Hence  no  light  will  pass  through  the  combi- 
nation of  red  and  green  glass,  and  darkness  results.  But  when  red  and  green 
rays  are  mixed  by  any  of  the  three  methods  above  described  the  result  of  this 
process  of  addition  is  not  darkness,  but  a  yellow  color,  as  will  be  understood 
by  reference  to  the  color  diagram  on  p.  780.  In  the  case  of  colored  pigments 
similar  phenomena  occur,  for  here  too  light  reaches  the  eye  after  rays  of  cer- 
tain wave-lengths  have  been  absorbed  by  the  medium.  This  subject  will  be 
further  considered  in  connection  with  color-theories. 

Color-theories. — From  what  has  been  said  of  color-mixtures  it  is  evident 
that  every  color  sensation  may  be  produced  by  the  mixture  of  a  number  of 
other  color  sensations,  and  that  certain  color  sensations — viz.  the  purples — can 
be  produced  only  by  the  mixture  of  other  sensations,  since  there  is  no  single 
wave-length  corresponding  to  them.  Hence  the  hypothesis  is  a  natural  one 
that  all  colors  are  produced  by  the  mixture  in  varying  proportions  of  a  certain 
number  of  fundamental  colors,  each  of  which  depends  for  its  production  upon 
the  presence  in  the  retina  of  a  certain  substance  capable  of  being  affected 
(probably  through  some  sort  of  a  photo-chemical  process)  by  light  of  a  certain 
definite  wave-length.  A  hypothesis  of  this  sort  lies  at  the  basis  of  both  the 
Young-Helmholtz  and  the  Hering  theories  of  color  sensation. 

The  former  theory  postulates  the  existence  in  the  retina  of  three  substances 
capable  of  being  affected  by  red,  green,  and  violet  rays,  respectively — i.  e.  by 
the  three  colors  lying  at  the  three  angles  of  the  color  diagram  given  on  p.  780 


782  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

— and  regards  all  other  color  sensations  as  pro<lucetl  by  the  simultaneous  affec- 
tion of  two  of  these  substances  in  varying  proportions.  Thus  when  a  rav  of 
blue  light  fall^^  on  the  retina  it  stimulates  the  violet-  and  green-perceiving  suIh 
stances,  and  produces  a  sensation  intermediate  between  the  two,  while  simul- 
taneous stimulation  of  the  red-  and  green-perceiving  substances  produces  the 
sensations  corresponding  to  yellow  and  orange ;  and  when  the  violet-  and  red- 
jierceiving  substances  are  affected  at  the  same  time,  the  various  shades  of 
purple  are  produced.  Each  of  these  three  substances  is,  however,  supposed  to 
be  affected  to  a  slight  extent  by  all  the  rays  of  the  visible  spectrum,  a  supj)o- 
sition  which  is  rendered  necessary  by  the  fact  that  even  the  pure  spectral 
colors  do  not  appear  to  be  perfectly  saturated,  as  will  be  explained  in  connec- 
tion with  the  subject  of  saturation.  Furthermore,  the  disappearance  of  color 
when  objects  are  very  feebly  or  very  brightly  illuminated  or  when  they  are 
seen  with  the  lateral  portions  of  the  retina  (as  described  on  p.  770)  necessitates 
the  additional  hypotheses  that  these  three  substances  are  all  equally  affected  by 
all  kinds  of  rays  when  the  light  is  of  either  very  small  or  v^ery  great  intensity 
or  when  it  falls  on  the  extreme  lateral  portions  of  the  retina,  and  that  they 
manifest  their  specific  irritability  for  red,  green,  and  violet  rays  respectively 
only  in  light  of  moderate  intensity  falling  not  too  far  from  the  fovea  centralis 
of  the  retina. 

The  modifications  of  the  Young-Hemholtz  theory  introduced  by  these  sub- 
sidiary hypotheses  greatly  diminish  the  simplicity  which  was  its  chief  claim  to 
acceptance  when  originally  proposed.  Moreover,  there  will  always  remain  a 
psychological  difficulty  in  supposing  that  three  sensations  so  different  from  each 
other  as  those  of  red,  green,  and  violet  can  by  their  union  produce  a  fourth 
sensation  absolutely  distinct  from  any  of  them — viz.  white. 

The  fact  that  in  the  Heriug  theory  this  difficulty  is  obviated  has  contributed 
greatly  to  its  acceptance  by  physiologists.  In  this  theory  the  retina  is  supposed 
to  contain  three  substances  in  which  chemical  changes  may  be  produced  by  ether 
vibrations,  but  each  of  these  substances  is  supposed  to  be  affected  in  two  oppo- 
site ways  by  rays  of  light  which  correspond  to  complementary  color  sensa- 
tions. Thus  in  one  substance — viz.  the  white-black  visual  substance — kata- 
bolic  or  destructive  changes  are  supposed  to  be  producetl  by  all  the  rays  of  the 
visible  spectrum,  the  maximum  effect  being  caused  by  the  yellow  rays,  while 
anabolic  or  constructive  changes  occur  when  no  light  at  all  falls  upon  the 
retina.  The  chemical  changes  of  this  substance  correspond,  therefore,  to  the 
sensation  of  luminosity  as  distinguished  from  color.  In  a  second  substance  red 
rays  are  supposed  to  produce  katabolic,  and  green  rays  anabolic  changes,  while 
a  third  substance  is  similarly  affected  by  yellow  and  blue  rays.  These  two 
substances  are  therefore  spoken  of  as  red-green  and  yellow-blue  visual  sub- 
stances re.spectively. 

It  has  been  sometimes  urged  as  an  objection  to  this  theory  that  the  effect  of 
a  stimulus  is  usually  katabolic  and  not  anabolic.  This  is  true  with  regard  to 
muscular  contraction,  from  the  study  of  which  phenomenon  most  of  our  know- 
ledge of  the  effect  of  stimulation  has  been  obtained,  but  it  should  be  remem- 


THE  SENSE    OF    VISION.  783 

bered  tliat  observations  on  tlie  auj^intMitor  and  inhibitory  cardiac  nerves  have 
shown  ns  that  norve-stimnhition  may  produce  very  contrary  effects.  There 
seems  to  be,  therelbro,  no  serious  theoretieal  difficulty  in  su|)j>osing  that  light 
rays  oi'ditrcrent  wave-lengths  may  produce  opposite  metabolic  effects  upon  the 
substances  in  which  changes  are  associated  with  visual  sensations. 

A  more  serious  objection  lies  in  the  difficulty  of  distinguishing  between  the 
sensation  of  blackness,  which,  on  Hering's  hypothesis,  must  correspond  to  active 
anabolism  of  the  white-black  substance,  and  the  sensation  of  darkness  (such  as 
we  experience  when  the  eyes  have  been  withdrawn  for  some  time  from  the 
influence  of  light),  which  must  correspond  to  a  condition  of  equilibrium  of 
the  white-black  substance  in  which  neither  anabolism  nor  katabolism  is 
occurring. 

Another  objection  to  the  Hering  theory  is  to  be  found  in  the  results  of 
experiments  in  comparing  grays  or  whites  produced  by  mixing  different  colored 
rays  under  varying  intensities  of  light.  The  explanation  given  by  Hering  of 
the  production  of  white  through  the  mixture  of  blue  and  yellow  or  of  red  and 
green  is  that  when  either  of  these  pairs  of  complementary  colors  is  mixed 
the  anabolic  and  the  katabolic  processes  balance  each  other,  leaving  the  corre- 
sponding visual  substance  in  a  condition  of  equilibrium.  Hence,  the  white- 
black  substance  being  alone  stimulated,  the  result  will  be  a  sensation  of  white 
corresponding  to  the  intensity  of  the  katabolic  process  caused  by  the  mixed 
rays.  Now,  it  is  found  that  when  blue  and  yellow  are  mixed  in  certain  pro- 
portions on  a  revolving  disk  a  white  can  be  produced  which  will,  with  a  certain 
intensity  of  illumination,  be  undistinguishable  from  a  white  produced  by  mix- 
ing red  and  green.  If,  however,  the  intensity  of  the  illumination  is  changed, 
it  will  be  found  necessary  to  add  a  certain  amount  of  white  to  one  of  the  mix- 
tures in  order  to  bring  them  to  equality.  On  the  theory  that  complementary 
colors  produce  antagonistic  processes  in  the  retina  it  is  difficult  to  understand 
why  this  should  be  the  case. 

A  color  theory  which  is  in  some  respects  more  in  harmony  with  recent 
observations  in  the  physiology  of  vision  has  been  proposed  by  Mrs.  C.  L. 
Franklin.  In  this  theory  it  is  supposed  that,  in  its  earlier  periods  of  de- 
velopment, the  eye  is  sensitive  only  to  luminosity  and  not  to  color — i.  e.  it 
possesses  only  a  white-black  or  (to  use  a  single  word)  a  ^ra2/-perceiving  sub- 
stance which  is  affected  by  all  visible  light  rays,  but  most  powerfully  by  those 
lying  near  the  middle  of  the  spectrum.  The  sensation  of  gray  is  supposed  to 
be  dependent  upon  the  chemical  stimulation  of  the  optic  nerve-terminations  by 
some  product  of  decomposition  of  this  substance.- 

In  the  course  of  development  a  portion  of  this  gray  visual  substance  becomes 
differentiated  into  three  different  substances,  each  of  which  is  affected  by  rays 
of  light  corresponding  to  one  of  the  three  fundamental  colors  of  the  spectrum 
— viz.  red,  green,  and  blue.  AVhen  a  ray  of  light  intermediate  between  two 
of  the  fundamental  colors  falls  upon  the  retina,  the  visual  substances  corre- 
sponding to  these  two  colors  will  be  affected  to  a  degree  proportionate  to  the 
proximity  of  these  two  colors  to  that  of  the  incident  ray^     Since  this  effect  is 


784  AN  AMERICAN    TEXT- HOOK    OF  PHYSIOLOGY. 

exactly  the  satnc  as  tlmt  which  is  produced  when  the  retina  is  acted  iij)()n  siinnl- 
taneoiislv  by  light  of  two  fundamental  colors,  we  are  incapable  of  distinguish- 
ing in  sensation  between  an  intermediate  wave-length  and  a  mixture  in  proper 
amounts  of  two  fundamental  wave-lengths. 

When  the  retina  is  ailccted  by  two  or  more  rays  of  such  wave-lengths  that 
all  three  of  the  color  visual  substances  are  equally  aifected,  the  resulting  decom- 
position will  be  the  same  as  that  produced  by  the  stimulation  of  tiie  gray  visual 
substance  out  of  which  the  color  visual  substances  were  differentiated,  and  the 
corresponding  sensation  will  therefore  be  that  of  gray  or  white. 

It  will  be  noticed  that  the  important  feature  of  this  theory  is  that  it  pro- 
vides for  the  independent  existence  of  the  gray  visual  substance,  while  at  the 
same  time  the  stimulation  of  this  substance  is  made  a  necessary  result  of  the 
mixture  of  certain  color  sensations. 

Color-blindness. — The  fact  that  many  individuals  are  incapable  of  distin- 
guishing between  certain  colors — i.  e.  are  more  or  less  '*  color-blind  " — is  one 
of  fundamental  importance  in  the  discussion  of  theories  of  color  vision.  By 
far  the  most  common  kind  of  color-blindness  is  that  in  which  certain  shades 
of  red  and  green  are  not  recognized  as  different  colors.  The  advocates  of  the 
Young-Helmholtz  theory  explain  such  cases  by  supposing  that  either  the  red 
or  the  green  perceiving  elements  of  the  retina  are  deficient,  or,  if  present,  are 
irritable,  not  by  rays  of  a  particular  wave-length,  but  by  all  the  rays  of  the 
visible  spectrum.  In  accordance  with  this  view  these  cases  of  color-blindness 
are  divided  into  two  classes — viz.  the  red-blind  and  the  green-blind — the  basis 
for  the  classification  being  furnished  by  more  or  less  characteristic  curves  repre- 
senting the  variations  in  the  luminosity  of  the  visible  spectrum  as  it  appears 
to  the  diiferent  eyes.  There  are,  however,  cases  which  cannot  easily  be  brought 
under  either  of  these  two  classes.  Moreover,  it  has  been  proved  in  cases  of 
monocular  color-blindness,  and  is  admitted  even  by  the  defenders  of  the  Helm- 
holtz  theory,  that  such  persons  see  really  only  two  colors — viz.  blue  and  yellow. 
To  such  persons  the  red  end  of  the  spectrum  appears  a  dark  yellow,  and  the 
green  portion  of  the  spectrum  has  luminosity  without  color. 

A  better  explanation  of  this  sort  of  color-blindness  is  given  in  the  Hering 
theory  by  simply  supposing  that  in  such  eyes  the  red-green  visual  substance  is 
deficient  or  wholly  wanting,  but  the  theory  of  Mrs.  Franklin  accounts  for  the 
phenomena  in  a  still  more  satisfactory  way ;  for,  by  supposing  that  the  differ- 
entiation of  the  primary  gray  visual  substance  has  first  led  to  the  formation 
of  a  blue  and  a  yellow  visual  substance,  and  that  the  latter  has  subsequently 
been  differentiated  into  a  red  and  a  green  visual  substance,  color-blindness  is 
readily  explained  by  supposing  that  this  second  differentiation  has  either  not 
occurred  at  all  or  has  taken  place  in  an  imperfect  manner.  It  is,  in  other 
words,  an  arrest  of  development. 

Cases  of  absolute  color-blindness  are  said  to  occasionally  occur.  To  such 
persons  nature  is  colorless,  all  objects  presenting  simply  differences  of  light 
and  shade. 

In  whatever  way- color-blindness  is  to  be  explained,  the  defect  is  one  of 


THE   SENSE    (>!■•    VISION.  ''^^ 

considerable  ,,™ctical  inM.u,-.a„..o,  since  it  .cde,.  t.,„se  affected  by  it  incapable 
of  distinguishing  tl,e  .vd  and  (.rcen  lights  ordinardy  nscd  lor  signals,  bnch 
;  ,tl  L,  .ho'r„.e,  unsuitable  Ibr  e„.,,h,y,ncnt  as  pilote,  ra,  way  c„gn,c*rs 

te.,  and  it  is  now  eusl y  to  test  the  vision  of  all  candidates  for  e,„pUo^    en^ 

in     ueh  situations.     It  has  been   found  that  no  sat.slae  ory  results     a     be 
reached  bv  re,niring  persons  to  nan,e  colors  winch  are  «''-;/hcnr^    ml 
ehrotua.ie'sen«.  is  now  eomuKady  tested  by  what  .s  known  as  the     Holmg.en 
n>     ,od,"  which  consists  in  requiring  the  individual  examu.ed  to  se  ect  from  a 
pi     rf  borstals  of  various  eolo,-s  those  shades  which  seem  to  h,m  to  resemble 
S  uhrd  skeins  of  green  and  pink.     When  e.xandned  n,  tins  way  about  4  p^ 
I      of  the  n.ale  a.tl  one-quar.er  of  1  per  cent,  of  the  female  sex  are  found  to 
Te  mire  or  less  color-blind.    The  defect  may  be  inherited,  and  the  relatives 
rf  rilor-blind  person  are  therefore  to  be  tested  with  spcc.al  care      S.nee 
females  are  less  Lble  to  be  affectcl  than  n.ales,  it  often  happen    that  the 
toghters  of  a  color-blind  person,  themselves  with  normal  v.s,on,  have  sons 
who  inherit  their  grandfather's  infirmity. 

A  hough  in  alltheories  of  color  vision  the  diiferent  sensat.ons  are  suppose! 
to  depend  upon  changes  produced  by  the  ether  vibrations  of  varyn,g  rates 
litrupon 'different  subLces  in  the  retina,  yet  it  should  be  borne  m  mnul 
It  we  Lve  at  present  no  proof  of  the  existence  of  any  sneh  -bs tanees  The 
visual  pnrple-or,  to  adopt  Mrs.  Franklin's  more  appropriate  te.m  the  rod 
;r™er'-was  a;  one  tiie  thought  to  be  such  a  substance,  but  for  the  reasons 
above  o-iven  cannot  be  regarded  as  essential  to  vision.  .  »    • ,  tu„ 

Th^t  a  centre  for  cote  vision,  distinct  from  the  visual  centre  exists  in  the 
cereb  a  eort  x  is  rendered  probable  by  the  occurrence  of  cases  of  hemianopsia 
Trttrand  also  by  the  Experiments  of  Heidenhain  and  Cohn  on  the  inHu- 
Mice  of  the  hypnotic  trance  upon  color-blindness. 

/lUiThe  second  of  the  above-mentioned  qualitative  modifications  of 
Ugh"s'i„te„sity,  which  is  dependent  upon  the  energy  of  v^— ^    - 
molecules  of  the  luminiferons  ether.     The  sensation  of  luminosity  is  not,  how 
Tvr  proportionate  to  the  intensity  of  the  stimulus  but  varies  in  such  aw  y 
hit  a  given  inc-ema.t  of  intensity  causes  a  greater  difference  ,„  --  ""J  "^^ 
feeble  fhan  with  strong  illuminations.     This  phenomenon  ,s  illustrated  by  the 
Sappea  le  of  a  sh^Tlow  thrown  by  a  candle  in  a  darkened  room  on  a  she  t 
oTite  paper  when  sunlight  is  allowed  to  fall  on  the  paper  from  the  opposite 
drectit      In  this  ease  L  absolute  difference  in  lumiuos,^-  between   the 
iiadov^  and  unshadowed  portions  of  the  paper  reman^  the  same,  but  it 
teeomes  imperceptible  in  consequence  of  the  increased  total  dlinninatron. 

"hough  our  power  of  distinguishing  cto^.*  differences  in  huninosi  y 
dimin   hes  as  the  intensitv  of  the  illumination  increases,  yet  with  regard  to 

substance  in  connection  with  other  substances  of  a  hypotlietual  character. 


50 


786 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


it  must  be  increased  by  a  certain  constant  fraction  of"  its  total  amount  in  order 
to  produce  a  perceptible  difference  in  sensation.  This  is  only  a  special  case  of 
a  general  law  of  sensation  known  as  Weber's  law,  which  has  been  formulated 
by  Foster  as  follows:  "The  smallest  change  in  the  magnitude  of  a  stimulus 
which  we  can  a])preciate  through  a  change  in  our  sensation  always  bears  the 
same  proportion  to  the  whole  magnitude  of  the  stimulus." 

Luminos'dy  of  Different  Colors. — When  two  sources  of  light  having  the 
same  color  are  compared,  it  is  possible  to  estimate  their  relative  luminosity 
with  considerable  accuracy,  a  difference  of  about  1  per  cent,  of  the  total 
luminosity  being  appreciated  by  the  eye.  W^iien  the  sources  of  light  have 
different  colors,  much  less  accuracy  is  attainable,  but  there  is  still  a  great  differ- 
ence in  the  intensity  with  which  rays  of  light  of  different  wave-lengths  affect 
the  retina.  We  do  not  hesitate  to  say,  for  instance,  that  the  maximum 
intensity  of  the  solar  spectrum  is  found  in  the  yellow  portion,  but  it  is  import- 
ant to  observe  that  the  position  of  this  maximum  varies  with  the  illumina- 
tion. In  a  very  brilliant  spectrum  the  maximum  shifts  toward  the  orange, 
and  in  a  feeble  spectrum  (such  as  may  be  obtained  by  narrowing  the  slit  of 
the  spectroscope)  it  moves  toward  the  green.     The  curves  in  Figure  240  illus- 


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G70  650  025  605 .590  575  555  535   520  505   490 
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Fig.  240.— Diagram  showing  the  distribution  of  the  intensity  of  the  spectrum  as  dependent  upon  the 

degree  of  illumination  (Konig). 


trate  this  shifting  of  the  maximum  of  luminosity  of  the  spectrum  with  vary- 
ing inten.sities  of  illumination.  The  ab.scissas  represent  wave-lengths  in 
millionths  of  a  millimeter,  and  the  ordinates  the  luminosity  of  the  different 
colors  as  expressed  by  the  reciprocal  values  of  the  width  of  the  slit  necessary 
to  give  to  the  color  under  observation  a  luminosity  equal  to  that  of  an  arbi- 


THE  SENSE    OF    VISION.  787 

trarily  chosen  standard.  The  curves  from  A  to  H  represent  tlie  distribution 
of  the  intensity  of  light  in  the  spectrum  witli  eight  different  grades  of  ilhimi- 
nation.  This  shifting  of  tiie  maximum  of  himinosity  in  the  spectrum 
explains  the  so-called  "  Purkinje's  ])henoraenon " — viz.  the  changing  rela- 
tive values  of  colors  in  varying  illumination.  This  can  be  best  observed 
at  nightfall,  the  attention  being  directed  to  a  carpet  or  a  wall-paper 
the  pattern  of  which  is  made  up  of  a  number  of  different  colors.  As 
the  daylight  fades  away  the  red  colors,  which  in  full  illumination  are 
the  most  intense,  become  gradually  darker,  and  are  scarcely  to  be  distin- 
guished from  black  at  a  time  when  the  blue  colors  are  still  very  readily 
distinguished. 

Function  of  Bods  and  Cones. — The  layer  of  rods  and  cones  has  thus  far 
been  spoken  of  as  if  all  its  elements  had  one  and  the  same  function.     There 
is,  however,  some  reason  to  suppose  that  the  rods  and  cones  have  different 
functions.     That  color  sensation  and  accuracy  of  definition  are  most  perfect 
in  the  central  portion  of  the  retina  is  shown  by  the  fact  that  when  we  desire 
to  obtain  the  best  possible  idea  of  the  form  and  color  of  an  object  we  direct 
our  eyes  in  such  a  way  that  the  image  falls  upon  the  fovea  centralis  of  the 
retina.     The  luminosity  of  a  faint  object,  however,  seems  greatest  when  we 
look   not  directly  at  it,  but  a  little  to  one  side  of  it.     This  can  be  readily 
observed  when  we  look  at  a  group  of  stars,  as,  for  example,  the  Pleiades. 
When  the  eyes  are  accurately  directed  to  the  stars  so  as  to  enable  us  to  count 
them,  the  total  luminosity  of  the  constellation  appears  much  less  than  when 
the  eyes  are  directed  to  a  point  a  few  degrees  to  one  side  of  the  object.     Now, 
an  examination  of  the  retina  shows  only  cones  in  the  fovea  centralis.     In  the 
immediately  adjacent  parts  a  small  number  of  rods  are  found  mingled  with 
the  cones.     In  the  lateral  portions  of  the  retina  the  rods  are  relatively  more 
numerous  than  the  cones,  and  in  the  extreme  peripheral  portions  the  rods  alone 
exist.      Hence  this  phenomenon  is  readily  explained  on  the  supposition  that 
the  rods  are  a  comparatively  rudimentary  form  of  visual  apparatus  taking 
cognizance  of  the  existence  of  light  with  special  reference  to  its  varying 
intensity,  and  that  the  cones  are  organs  specially  modified  for  the  localization 
of  stimuli  and  for  the  perception  of  differences  of  wave-lengths.     The  view 
that  the  rods  are  specially  adapted  for  the  perception  of  luminosity  and  the 
cones  for  that  of  color  derives  support  from  the  fact  that  in  the  retina  of  cer- 
tain nocturnal  animals — e.  g.  bats  and  owls — rods  alone  are  present.     This 
theory  has  been  further  developed  by  Von  Kries,^  who  in  a  recent  article 
describes  the  rods  as  differing  from  the  cones  in  the  following  respects :    (1) 
They  are  color-blind — i.  e.  they  produce  a  sensation  of  simple  luminosity 
whatever  be  the  wave-length  of  the  light-ray  falling  on  them  ;  (2)  they  are 
more  easily  stimulated  than  the  cones,  and  are  particularly  responsive  to  light- 
waves of  short  wave-lengths  ;  (3)  they  have  the  power  of  adapting  themselves 
to  light  of  varying  intensity. 

On  this  theory  it  is  evident  that  we  must  get  the  sensation  of  white  or 
'  Zeitschrifi  fur  Psychologie  und  Physiologie  der  Sinnesorgane,  ix.  81. 


788  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

colorless  light  in  two  different  ways  :  (1)  In  consequence  of  the  stimulation 
of  the  rods  by  any  sort  of  light-rays,  and  (2)  in  consequence  of  the  stimula- 
tion of  the  cones  by  certain  combinations  of  light-rays — i.  e.  complementary 
colors.  In  this  double  mode  of  white  perception  lies  perhaps  the  explanation 
of  the  effect  of  varying  intensity  of  illumination  upon  the  residts  of  color- 
mixtures  which  has  been  above  alluded  to  (see  p.  783)  as  an  objection  to  the 
Hering  theory.  The  so-called  "  Purkinje's  phenomenon,"  described  on  p.  787, 
is  readily  explained  in  accordance  with  this  theory,  for,  owing  to  the  greater 
irritability  of  the  rods,  the  importance  of  these  organs,  as  compared  with  the 
cones,  in  the  production  of  the  total  visual  sensation  is  greater  with  feeble 
than  with  strong  illumination  of  the  field  of  vision.  At  the  same  time,  the 
power  of  the  rods  to  respond  particularly  to  light-rays  of  short  wave-length 
will  cause  a  greater  apparent  intensity  of  the  colors  at  the  blue  than  at  the  red 
end  of  the  spectrum.  In  this  connection  it  is  interesting  to  note  that  the  phe- 
nomenon is  said  not  to  occur  wlien  the  observation  is  limited  to  the  fovea 
centralis,  where  cones  alone  are  found.^ 

Saturation. — The  degree  of  saturation  of  light  of  a  given  color  depends,  as 
above  stated,  upon  the  amount  of  white  light  mixed  with  it.  The  quality  of 
light  thus  designated  is  best  studied  and  appreciated  by  means  of  experiments 
with  rotating  disks.  If,  for  instance,  a  disk  consisting  of  a  large  white  and  a 
small  red  sector  be  rapidly  rotated,  the  effect  produced  is  that  of  a  pale  pink 
color.  By  gradually  increasing  the  relative  size  of  the  red  sector  the  pink 
color  becomes  more  and  more  saturated,  and  finally  when  the  white  sector  is 
reduced  to  zero  the  maximum  of  saturation  is  produced.  It  must  be  borne 
in  mind,  however,  that  no  pigments  represent  completely  saturated  colors. 
Even  the  colors  of  the  spectrum  do  not  produce  a  sensation  of  absolute 
saturation,  for,  whatever  theory  of  color  vision  be  adopted,  it  is  evident  that 
all  the  color-perceiving  elements  of  the  retina  are  affected  more  or  less  by  all 
the  rays  of  light.  Thus  when  rays  of  red  light  fall  upon  the  retina  they  will 
stimulate  not  only  the  red-perceiving  elements,  but  to  a  slight  extent  also  (to 
use  the  language  of  the  Helmholtz  theory)  the  green-  and  violet-perceiving 
elements  of  the  retina.  The  effect  of  this  will  be  that  of  mixing  a  small 
amount  of  white  with  a  large  amount  of  red  light — /.  e.  it  will  produce  the 
sensation  of  incompletely  saturated  red  light.  This  dilution  of  the  sensation 
can  be  avoided  only  by  previously  exhausting  the  blue-  and  green-perceiving 
elements  of  the  retina  in  a  manner  which  will  be  explained  in  connection  with 
the  phenomena  of  after-images. 

Retinal  Stimulation. — Whenever  by  a  stimulus  applied  to  an  irritable 
substance  the  potential  energy  there  stored  up  is  liberated  the  following  phe- 
nomena may  be  observed  :  1.  A  so-called  latent  period  of  variable  duration 
during  which  no  effects  of  stimulation  are  manifest ;  2.  A  very  brief  period 
during  which  the  effect  of  the  stimulation  reaches  a  maximum  ;  3.  A  period 
of  continued  stimulation  during  which  the  effect  diminishes  in  consequence  of 
the  using  up  of  the  substance  containing  the  potential  energy — i.  e.  a  period 
'  Von  Kries  :   Centralblalt  Jiir  Physiologic,  1896,  i. 


THE  SENSE    OF    VISION.  789 

of  fatigue ;  4.  A  j)criod  after  tlie  stimulation  has  ceased  in  which  the  effect 
slowly  passes  away. 


Fig.  241.— Diagram  showing  the  effect  of  stimulation  of  an  irritable  substance. 

The  curve  drawn  by  a  muscle  iu  tetanic  contraction,  as  shown  in  Figure 

241,  illustrates  this  phenomenon.  Thus,  MAD  represents  the  duration  of  the 
stimulation,  A  B  indicates  the  latent  period,  B  C  the  period  of  contraction, 
C  1)  the  period  of  fatigue  under  stimulation,  and  D  E  the  after-effect  of 
stinndation  showing  itself  as  a  slow  relaxation.  When  light  falls  upon  the 
retina  corresponding  phenomena  are  to  be  observed. 

Latent  Period. — That  there  is  a  period  of  latent  sensation  in  the  retina 
{i.  e.  an  interval  between  the  falling  of  light  on  the  retina  and  the  beginning 
of  the  sensation)  is,  judging  from  the  analogy  of  other  parts  of  the  nervous 
system,  quite  probable,  though  its  existence  has  not  been  demonstrated. 

Rise  to  Maximum  of  Sensation. — The  rapidity  with  which  the  sensation  of 
light  reaches  its  maximum  increases  with  the  intensity  of  the  light  and  varies 
with  its  color,  red  light  producing  its  maximum  sensation  sooner  than  green 
and  blue.  Consequently,  when  the  image  of  a  white  object  is  moved  across 
the  retina  it  will  appear  bordered  by  colored  fringes,  since  the  various  con- 
stituents of  white  light  do  not  produce  their  maximum  effects  at  the  same 
time.  This  phenomena  can  be  readily  observed  when  a  disk  on  which  a 
black  and  a  white  spiral  band  alternate  with  each  other  (as  shown  in  Figure 

242,  A)  is  rotated  before  the  eyes.     The  white  band  as  its  image  moves  out- 


A  B 

Fig.  242.— Disks  to  illustrate  the  varying  rate  at  which  colors  rise  to  their  maximum  of  sensation. 

ward  or  inward  over  the  retinal  surface  appears  bordered  with  colors  which 
vary  with  the  rate  of  rotation  of  the  disk  and  with  the  amount  of  exhaustion 
of  the  retina.  Chromatic  effects  due  to  a  similar  cause  are  also  to  be  seen 
when  a  disk,  such  as  is  shown  in  Figure  242,  B  (known  as  Benham's  spectrum 


790  AX  AMEIUCAX    TEXT-BOOK    01     J'JI YSJOLOG  Y. 

top),  is  rotated  with  moderate  rapidity.  The  eoncentric  bands  of  color  appear 
in  reverse  order  Aviien  the  direction  of  rotation  is  reversetl.  The  ap])arent 
movement  of  colored  figures  on  a  background  of  a  different  color  when  the 
eve  moves  rapidly  over  the  object  or  the  object  is  moved  rapidly  bef<jre  the 
eve  seems  to  depend  upon  this  same  retinal  peculiarity.  The  phenomenon 
mav  be  best  observed  when  small  pieces  of  bright-red  paper  are  fastened  u|X)n 
a  bright-blue  sheet  and  the  sheet  gently  shaken  i>efore  the  eyes.  The  red 
figures  will  appear  to  move  upon  the  blue  background.  The  effect  may  be 
best  observed  in  a  dimly-lighted  room. 

In  this  connection  should  be  mentioned  the  phenomenon  of  "  recurrent 
images"  or  "  oscillatory  activity  of  the  retina."  ^  This  may  be  best  observed 
when  a  black  disk  containing  a  white  sector  is  rotated  at  a  rate  of  about  one 
revolution  in  two  seconds.     If  the  disk  is  brightly  illuminated,  as  by  sunlight, 

and  the  eye  fixed  steadily  upon  the  axis  of  rota- 
tion, the  moving  white  sec-tor  seems  to  have  a 
shadow  upon  it  a  short  distance  behind  its  ad- 
vancing border,  and  this  shadow  may  be  fijllowed 
by  a  second  fainter,  and  even  by  a  third  still 
fainter  shadow,  as  shown  in  Figure  243.  The 
distance  of  the  shadows  from  each  other  and 
from  the  edge  of  the  sector  increases  with  the  rate 
of  rotation  of  the  disk  and  corresponds  to  a  time 
Fig.  243.-TO  illustrate  the  oscniatorj-  interval  of  about  0.015".     It  thus  appears  that 

activity  of  the  retina  (Charpentier).  ,.    ,        .  ii      i        i 

when  light  is  suddenly  thrown  upon  the  retina 
the  sensation  does  not  at  once  rise  to  its  maximum,  but  reaches  this  point  by 
a  sort  of  vibratory  movement.  The  apparent  duplication  of  a  single  very 
brief  retinal  stimulation,  as  that  caused  by  a  flash  of  lightning,  may  perhaps 
be  a  phenomenon  of  the  same  sort. 

Fatigue  of  Hetina. — When  the  eye  rests  steadily  upon  a  uniformly  illu- 
minated white  surface  (e.g.  a  sheet  of  white  paper),  we  are  usually  unconscious 
of  any  diminution  in  the  intensity  of  the  sensation,  but  it  can  be  shown  that 
the  longer  we  look  at  the  paper  the  less  brilliant  it  appears,  or,  in  other  words, 
that  the  retina  really  becomes  fatigued.  To  do  this  it  is  only  necessary  to  place 
a  disk  of  black  paper  on  the  white  surface  and  to  keep  the  eyes  steadily  fixed 
for  about  half  a  minute  upon  the  centre  of  the  disk.  Upon  removing  the  disk 
without  changing  the  direction  of  the  eyes  a  round  spot  will  be  seen  on  the 
white  paper  in  the  place  previously  occupied  by  the  disk.  On  this  spot  the 
whiteness  of  the  paper  will  appear  much  more  intense  than  on  the  neighboring 
portion  of  the  sheet,  because  we  are  able  in  this  experiment  to  bring  into  direct 
contrast  the  sensations  produced  by  a  given  amount  of  light  upon  a  fresh  and 
a  fatigued  portion  of  the  retina.^ 

*  Charpentier:  Archives  de  Physiologie,  1892,  pp.  .541,  629;  and  1896,  p.  677. 

^  Although  the  retina  is  here  spoken  of  as  the  pf)rtion  of  tlie  visual  apparatus  subject  to 
fatigue,  it  should  Ije  borne  in  mind  that  we  cannot,  in  the  present  state  of  our  knowledge,  dis- 
criminate between  retinal  fatigue  and  exhaustion  of  the  visual  nerve-centres. 


THE   SENSK    OF    VISION.  791 

The  rapidity  with  which  the  retina  becomes  fatiirued  varies  witli  the  color 
of  the  liglit.  Hence  when  intense  white  light  falls  upon  the  retina,  as  when 
we  look  at  the  setting  sun,  its  disk  seems  to  undergo  changes  of  color  as  one 
or  another  of  the  constituents  of  its  light  becomes,  through  fatigue,  less  and 
less  conspicuous  in  the  combination  of  rays  whi(-h  produces  the  sensation  of 
white. 

Tlie  After-effect  of  Stimulalion. — The  persistence  of  the  sensation  after  the 
stimulus  has  ceased  causes  very  brief  illuminations  (e.  g.  by  an  electric  spark)  to 
produce  distinct  effects.  On  this  phenomenon  depends  also  the  above-described 
method  of  mixing  colors  on  a  revolving  disk,  since  a  second  color  is  thrown 
upon  the  retina  before  the  impression  produced  by  the  first  color  has  had  time 
enough  to  become  sensibly  diminished.  The  interval  at  which  successive  stim- 
ulations must  follow  each  other  in  order  to  pro- 
duce a  uniform  sensation  (a  process  analogous 
to  the  tetanic  stimulation  of  a  muscle)  may  be 
determined  by  rotating  a  disk,  such  as  repre- 
sented in  Figure  244,  and  ascertaining  at  what 
speed  the  various  rings  produce  a  uniform  sen- 
sation of  gray.  The  interval  varies  with  the 
intensity  of  the  illumination  from  0.1"  to 
0.033".  The  duration  of  the  after-effect  de- 
pends also  upon  the  length  of  the  stimulation 
and  upon  the  color  of  the  light  prodqcing  it, 
the  most  persistent  effect  being  prodnced  by  the  ''-^-fi^J^rS'CmSr" 
red  rays.    In  this  connection  it  is  interesting  to 

note  that  while  with  the  rapidly  vibrating  blue  rays  a  less  intense  illumination 
suffices  to  stimulate  the  eye,  the  slowly  vibrating  red  rays  produce  the  more 
permanent  impression. 

After-images. — When  the  object  looked  at  is  very  brightly  illuminated  the 
impression  upon  the  retina  may  be  so  persistent  that  the  form  and  color  of  the 
object  are  distinctly  visible  for  a  considerable  time  after  the  stimulus  has  ceased 
to  act.  This  appearance  is  known  as  a  "  positive  after-image,"  and  can  be  best 
observed  when  we  close  the  eyes  after  looking  at  the  sun  or  other  bright  source 
of  light.  Under  these  circumstances  we  perceive  a  brilliant  spot  of  light  which, 
owing  to  the  above-mentioned  difference  in  the  persistence  of  the  impressions 
produced  by  the  various  colored  rays,  rapidly  changes  its  color,  passing  gen- 
erally through  bluish  green,  blue,  violet,  purple,  and  red,  and  then  disappear- 
ing. This  phenomenon  is  apt  to  be  associated  with  or  followed  by  another 
effect  known  as  a  "  negative  after-image."  This  form  of  after-image  is  much 
more  readily  observed  than  the  ])ositive  variety,  and  seems  to  depend  upon  the 
fatigue  of  the  retina.  It  is  distinguished  from  the  positive  after-image  by  the 
fact  that  its  color  is  always  complementary  to  that  of  the  object  causing  it.  In 
the  experiment  to  demonstrate  the  fatigue  of  the  retina,  described  on  p.  790, 
the  white  spot  which  appears  after  the  black  disk  is  withdrawn  is  the  "  nega- 
tive after-image"  of  the  disk,  white  being  complementary  to  black.     If  a 


792  AX  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

colored  disk  be  placed  upon  a  sheet  of  white  paper,  hioketl  at  attentively  for  a 
few  seconds,  and  then  withdrawn,  the  eye  will  perceive  in  its  place  a  spot  of 
light  of  a  color  complementary  to  that  of  the  disk.  If,  for  example,  the  disk 
be  vellow,  the  vellow-perceiving  elements  of  the  retina  become  fatigued  in 
looking  at  it.  Therefore  when  the  mixed  rays  constituting  white  light  are 
thrown  upon  the  portion  of  the  retina  which  is  thus  fatigued,  those  rays  which 
produce  the  sensation  of  yellow  will  produce  less  effect  than  the  other  rays  for 
which  the  eye  has  not  been  fatigued.  Hence  white  light  to  an  eye  fatigued  for 
yellow  will  appear  blue. 

If  the  experiment  be  made  with  a  yellow  disk  resting  on  a  sheet  of  blue 
paper,  the  negative  after-image  will  be  a  spot  on  which  the  blue  color  will 
appear  (1)  more  intense  than  on  the  neighboring  portions  of  the  sheet,  owing 
to  the  blue-perceiving  elements  of  that  portion  of  the  retina  not  being  fatigued  ; 
(2)  more  saturated,  owing  to  the  yellow-perceiving  elements  being  so  far 
exhausted  that  they  no  longer  respond  to  the  slight  stimulation  which  is  pro- 
duced when  light  of  a  complementary  color  is  thrown  upon  them,  as  has  been 
explained  in  connection  with  the  subject  of  saturation. 

Contrast. — As  the  eye  wanders  from  one  part  of  the  field  of  vision  to 
another  it  is  evident  that  the  sensation  produced  by  a  given  portion  of  the 
field  will  be  modified  by  the  amount  of  fatigue  produced  by  that  portion  on 
which  the  eye  has  last  rested,  or,  other  w'ords,  the  sensation  will  be  the  result 


Fig.  245.— To  illustrate  the  phenomenon  of  contrast. 

of  the  stimulation  by  the  object  looked  at  combined  with  the  negative  after- 
image of  the  object  previously  observed.  The  effect  of  this  combination  is  to 
produce  the  phenomenon  of  successive  contrast,  the  ])rinciple  of  which  may  be 
thus  stated  :  Every  part  of  the  field  of  vision  appears  lighter  near  a  darker 


THE  SENSE    OF    VISION.  793 

part  and  darker  near  a  lighter  part,  and  its  color  seen  near  another  color 
approaches  the  complementary  color  of  the  latter.  A  contrast  phenomenon 
similar  in  its  effects  to  that  above  described  may  be  produced  under  conditions 
in  which  negative  after-images  can  play  no  part.  This  kind  of  contrast  is 
known  as  simnltaneous  contrast,  and  may  perhaps  be  explained  on  the  theory 
that  a  stimulation  of  a  given  portion  of  the  retina  produces  in  the  neighboring 
portions  an  effect  to  some  extent  antagonistic  to  that  caused  by  direct  stimulation. 
A  good  illustration  of  the  phenomenon  of  contrast  is  given  in  Figure  245, 
in  which  black  squares  are  separated  by  white  bands  which  at  their  points  of 
intersection  appear  darker  than  where  they  are  bordered  on  either  side  by  the 
black  squares. 

A  black  disk  on  a  yellow  background  seen  through  white  tissue-paper 
appears  blue,  since  the  white  paper  makes  the  black  disk  look  gray  and  the 
yellow  background  pale  yellow.  The  gray  disk  in  contrast  to  the  pale  yellow 
around  it  appears  blue. 

The  phenomenon  of  colored  shadows  also  illustrates  the  principle  of  con- 
trast. These  may  be  observed  whenever  an  object  of  suitable  size  and  shape 
is  placed  upon  a  sheet  of  white  paper  and  illuminated  from  one  direction  by 
daylight  and  from  another  by  gaslight.  Two  shadows  will  be  produced,  one 
of  which  will  appear  yellow,  since  it  is  illuminated  only  by  the  yellowish  gas- 
light, while  the  other,  though  illuminated  by  the  white  light  of  day,  will 
appear  blue  in  contrast  to  the  yellowish  light  around  it. 

Space-perception. — Rays  of  light  proceeding  from  every  point  in  the 
field  of  vision  are  refracted  to  and  stimulate  a  definite  point  on  the  sur- 
face of  the  retina,  thus  furnishing  us  with  a  local  sign  by  which  we  can 
recognize  the  position  of  the  point  from  which  the  light  proceeds. 
Hence  the  size  and  shape  of  an  optical  image  upon  the  retina  enable  us  to 
judge  of  the  size  of  the  corresponding  object  in  the  same  way  that  the  cutane- 
ous terminations  of  the  nerves  of  touch  enable  us  to  judge  of  the  size  and 
shape  of  an  object  brought  in  contact  with  the  skin.  This  spatial  perception 
is  materially  aided  by  the  muscular  sense  of  the  muscles  moving  the  eyeball, 
for  we  can  obtain  a  much  more  accurate  idea  of  the  size  of  an  object  if 
we  let  the  eye  rest  in  succession  upon  its  different  parts  than  if  we  gaze  fixedly 
at  a  given  point  upon  its  surface.  The  conscious  effort  associated  with  a  given 
amount  of  muscular  motion  gives,  in  the  case  of  the  eye,  a  measure  of  distance 
similar  to  that  secured  by  the  hand  when  we  move  the  fingers  over  the  surface 
of  an  object  to  obtain  an  idea  of  its  size  and  shape. 

The  perception  of  space  by  the  retina  is  limited  to  space  in  two  dimensions 
— i.  e.  in  a  plane  perpendicular  to  the  axis  of  vision.  Of  the  third  dimension 
in  space — i.  e.  of  distance  from  the  eye — the  retinal  image  gives  us  no  know- 
ledge, as  may  be  proved  by  the  study  of  after-images.  If  an  after-image  of 
any  bright  object — e.  g.  a  window — be  produced  upon  the  retina  in  the  man- 
ner above  described  and  the  eye  be  then  directed  to  a  sheet  of  paper  held  in 
the  hand,  the  object  will  appear  outlined  in  miniature  upon  the  surface  of  the 
paper.     If,  however,  the  eye  be  directed  to  the  ceiling  of  the  room,  the  object 


794  AX  AMERICAN    IKXT-BOOK    OF  PHYSIOLOGY. 

will  appear  enlarged  and  at  a  distance  corresponding  to  that  of  the  surface 
looked  at.  Hence  one  and  the  same  retinal  image  may,  under  tlitferent  cir- 
cumstances, o-ive  rise  to  the  impression  of  objects  at  different  distances.  We 
must  therefore  regard  the  jierception  of  distance  not  as  a  direct  datum  of  vision, 
but,  as  will  be  later  explained,  a  matter  of  visual  judgment. 

When  objects  are  of  such  a  shape  that  their  images  may  be  thrown  suc- 
cessively upon  the  same  part  of  the  retina,  it  is  possible  to  judge  of  their  rela- 
tive size  with  considerable  accuracy,  the  retinal  surface  serving  as  a  scale  to 
which  the  images  are  successively  applied.  When  this  is  not  the  case,  the 
error  of  judgment  is  much  greater.  We  can  compare,  for  instance,  the  relative 
length  of  two  vertical  or  of  two  horizontal  lines  with  a  good  deal  of  precision, 
but  in  comparing  a  vertical  with  a  horizontal  line  we  are  liable  to  make  a  con- 
siderable error.  Thus  it  is  difficult  to  realize  that  the  vertical  and  the  hori- 
zontal lines  in  Figure  246  are  of  the  same  length.     The  error  consists  in  an 

over-estimation  of  the  length  of  the  vertical 
lines  relatively  to  horizontal  ones,  and  appears  to 
depend,  in  part  at  any  rate,  upon  the  small  size 
of  the  superior  rectus  muscle  relatively  to  the 
other  muscles  of  the  eye.  The  difference  amounts 
to  30-45  per  cent,  in  weight  and  40-53  per  cent, 
in  area  of  cross  section.  It  is  evident,  therefore, 
that  a  given  motion  of  the  eye  in  the  upward 
direction  will  require  a  more  powerful  contraction 
of  the  weaker  muscle  concerned  in  the  movement 


Fig.  246.— To  illustrate  the  over-esti-    than  will  be  demanded  of  the  stronger  muscles 

mation  of  vertical  lines.  .  ,  i    ^        ii       .  i  a 

moving  the  eye  laterally  to  an  equal  amount. 
Hence  we  judge  the  upward  motion  of  the  eye  to  be  greater  because  to  accom- 
plish it  we  make  a  greater  effort  than  is  required 
for  a  horizontal  movement  of  equal  extent. 

The  position  of  the  vertical  line  bisecting  the 
horizontal  one  (in  Fig.  246)  aids  the  illusion,  as 
may  be  seen  by  turning  the  page  through  90°,  so 
as  to  bring  the  bisected  line  into  a  vertical  posi- 
tion, or  by  looking  at  the  lines  in  Figure  247,  in 
which  the  illusion  is  much  less  marked  than  in 
Figure  246. 

The  tendency  to  over-estimate  the  length  of 

vertical   lines   is  also  illustrated   by  the  error 

commonly  made  in  supposing  the  height  of  the 

crown  of  an  ordinarv  silk  hat   to   be  greater  ~  ~" 

"  Fi<i. '247.— To  illustrate  the  over-estima- 

than   its   breadth.  tion  of  vertical  lines. 

Irradiation.  —  Many    other    circumstances 
affect  the  accuracy  of  the  spatial  perception  of  the  retina.     One  of  the  most 
important  of  these  is  the  intensity  of  the  illumination.     All  brilliantly  illumi- 
nated objects  appear  larger  than  feebly  illuminated  ones  of  the  same  size,  as  is 


THE  SENSE    OF    VISION.  795 

well  shown  by  the  ordinary  incandescent  electric  lamp,  the  delicate  filament  of 
which  is  scarcely  visible  when  cold,  but  when  intensely  heated  by  the  electric 
current  glows  as  a  broad  band  of  light.  The  phenomenon  is  known  as  "  irra- 
diation," and  seems  to  depend  chiefly  upon  the  above-described  imperfections 
in  the  dioptric  apparatus  of  the  eye,  in  consequence  of  which  points  of  light 
produce  small  circles  of  dispersion  on  the  retina  and  bright  objects  produce 


Fig.  248.— To  illustrate  the  phenomenon  of  irradiation. 

images  with  imperfectly  defined  outlines.  The  white  square  surrounded  by 
black  and  the  black  square  surrounded  by  white  (Figure  248),  being  of  the 
same  size,  would  in  an  ideally  perfect  eye  produce  images  of  the  same  size  on 
the  retina,  but  owing  to  the  imperfections  of  the  eye  the  images  are  not  sharply 


Fig.  249.— To  illustrate  the  phenomenon  of  irradiation. 

defined,  and  the  white  surfaces  consequently  appear  to  encroach  upon  the  darker 
portions  of  the  field  of  vision.  Hence  the  white  square  looks  larger  than  the 
black  one,  the  difference  in  the  apparent  size  depending  upon  the  intensity  of 
the  illumination  and  upon  the  accuracy  with  which  the  eye  can  be  accommo- 


796 


A^'  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY . 


dated  for  tlio  distance  at  which  tlie  ubjects  are  viewed.  The  ellect  of  irradi- 
ation is  most  manifest  when  the  dark  portion  of  the  field  of  vision  over  which 
the  irradiation  takes  phice  lias  a  considerable  breadth.  Thus  the  circidar  white 
spots  in  Figure  249,  when  viewed  from  a  distance  of  three  or  four  meters, 
appear  hexagonal,  since  the  irradiation  is  most  marked  into  the  triangular  dark 
space  between  three  adjacent  circles.  A  familiar  example  of  the  effect  of  irra- 
diation is  afforded  by  the  a])poarance  of  the  new  moon,  whose  sun-illuminated 
crescent  seems  to  be  part  of  a  much  larger  circle  than  the  remainder  of  tiie 
disk,  which  shines  only  by  the  light  reflected  upon  it  from  the  surface  of  the 
earth. 

Subdivided  Space. — A  space  subdivided  into  smaller  portions  by  inter- 
mediate objects  seems  more  extensive  than  a  space  of  the  same  size  not  so  sub- 
divided.   Thus  the  distance  from  Aio  B  (Fig.  250)  seems  longer  than  that  from 


D  E 

Fig.  250.— To  illustrate  the  illusion  of  subdivided  space. 


B  to  C,  though  both  are  of  the  same  length,  and  for  the  same  reason  the  square 
D  seems  higher  than  it  is  broad,  and  the  .square  E  broader  than  it  is  high,  the 
illusion  being  more  marked  in  the  case  of  D  than  in  the  case  of  E,  because,  as 
above  explained,  vertical  distances  are,  as  a  rule,  over-estimated. 

The  explanation  of  this  illasion  .seems  to  be  that  the  eye  in  passing  over  a 
subdivided  line  or  area  recognizes  the  number  and  size  of  the  subdivision.s, 
and  thus  gets  an  impression  of  greater  total  size  than  when  no  subdivisions 
are  present. 

A  good  example  of  this  phenomenon  is  afforded  by  the  apparently  increased 
extent  of  a  meadow  when  the  grass  growing  on  it  is  cut  and  arranged  in  hay- 
cocks.^ 

The  relations  of  lines  to  each  other  gives  rise  to  numerous  illusions  of 
spatial  perception,  among  the  mo.st  striking  of  which  are  those  afforded  by  the 
so-called  "  Zollner's  lines,"  an  example  of  which  is  given  in  Figure  251.    Here 

^  It  is  interesting  to  note  tliat  a  similar  illusion  has  been  observed  when  an  interval  of  time 
subdivided  by  audible  signals  is  compared  with  an  equal  interval  not  so  subdivided  (Hall  and 
Jastrow  :  Mind,  xi.  62). 


THE  SENSE   OF    VISION.  797 

the  horizontal  lines,  though  strictly  parallel  to  each  other,  seem  to  diverge  and 
converge  alternately,  their  apparent  direction  being  changed  toward  greater  per- 

/////// 


/////////// 

Fig.  251.— ZoUner's  lines. 

pendicularity  to  the  short  oblique  lines  crossing  them.  This  illusion  is  to  be  ex- 
plained in  part  by  the  tendency  of  the  eye  to  over-estimate  the  size  of  acute  and  to 
under-estimate  that  of  obtuse  angles — a  tendency  which 
also  affords  a  partial  explanation  of  the  illusion  in 
Figure  252,  where  the  line  d  is  the  real  and  the  line/ 
the  apparent  continuation  of  the  line  a.  The  illusion 
in  Zollner's  figures  is  more  marked  when  the  figure  is 
so  held  that  the  long  parallel  lines  make  an  angle  of 
about  45°  with  the  horizon,  since  in  this  position  the 
eye  appreciates  their  real  position  less  accurately  than 
when  they  are  vertical  or  horizontal.  It  is  dimin- 
ished, but  does  not  disappear,  when  the  eye,  instead 
of  being  allowed  to  wander  over  the  figure,  is  fixed 

upon  any  one  point  of  the  field  of  vision.     Hence  the  ^^^  ^^^  _^^  _^^^^^^^^^  .^^^^.^^ 
motions  of  the  eye  must  be  regarded  as  a  factor  in,  but  of  space-perception. 

not  the  sole  cause  of,  the  illusion. 

Our  estimate  of  the  size  of  given  lines,  angles,  and  areas  is  influenced  by 
neighboring  lines,  angles,  and  areas  with  which  they  are  compared.  This 
influence  is  sometimes  exerted  in  accordance  with  the  principle  of  contrast, 
and  tends  to  make  a  given  extension  appear  larger  in  presence  of  a  smaller. 


Fig.  253.— To  illustrate  contrast  in  space-perception  (Miiller-Lyer). 

and  smaller  in  presence  of  a  larger  extension.  This  effect  is  illustrated  in 
Figure  253,  in  which  the  middle  portion  of  the  shorter  line  appears  larger 
than  the  corresponding  portion  of  the  longer  line,  in  Figure  254,  in  which  a 
similar  effect  is  observed  in  the  case  of  angles,  and  in  Figure  255,  in  which 


798  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

the  space  between  the  two  squares  seems  smaller  than  that  between  the  two 
oblong  figures. 

In  some  case,  however,  an   influence  of  the  opposite  sort'  seems  to   be 


Fig.  254.— To  illustrate  contrast  in  space-perception  (Miiller-Lyer). 

exerted,  as  is  shown  in  Figure  256,  in  which  the  middle  one  of  three  parallel 
lines  seems  longer  when  the  outside  lines  are  longer,  and  shorter  when  they 
are  shorter  than  it  is  itself,  and  in  Figure  257,  where  a  circle  appears  larger 


Fig.  255.— To  illustrate  contrast  in  space-perception  (Miiller-Lyer). 

if  surrounded  by  a  circle  larger  than  itself,  and  smaller  if  a  smaller  circle  is 
shown  concentrically  within  it. 

Lines  meeting  at  an  angle  appear  longer  when  the  included  angle  is  large 


Fig.  256.— To  illustrate  so-called  "  confluxion  "  in  space-perception  (Miiller-Lyer). 

than  when  it  is  small,  as  is  shown  in  Figure  258.  This  influence  of  the 
included  angle  aflx)rds  a  partial  explanation  of  the  illusion  shown  in  Figure 
259,  where  the  horizontal  line  at  B  seems  longer  than  at  A  ;  but  the  distance 

^  For  this  influence  the  name  "confluxion"  has  been  proposed  by  Miiller-Lyer,  from  whose 
article  in  the  Archivfiir  Phyaiologie,  1889,  Sup.  Bd.,  the  above  examples  are  taken. 


THE   SENSE    OF    VISION. 


799 


between  the  extremities  of  the  oblique  lines  seems  also  to  aifect  our  estimate 
of  the  horizontal  line  in  the  same  way  as  the  outside  lines  in  Figure  256 
influence  our  judiruKMit  of  the  length  of  the  line  between  them. 

Perception  of  Distance. — The  retinal  image  gives  us,  as  we  have  seen, 
no  direct  infornintion   as  to  the  distance  of  the  object  from  the  eye.     This 


Fig.  257.— To  illustrate  so-called  "  confluxion  "  in  space-perception  (Muller-Lyer). 

knowledge  is,  however,  quite  as  important  as  that  of  position  in  a  plane  per- 
pendicular to  the  line  of  vision,  and  we  must  now  consider  in  what  way  it  is 
obtained.  The  first  fact  to  be  noted  is  that  there  is  a  close  connection  between 
the  judgments  of  distance  and  of  actual  size.  A  retinal  image  of  a  given 
size  may  be  produced  by  a  small  object  near  the  eye  or  by  a  large  one  at  a 


Fig.  258.— To  illustrate  the  influence  of  angles  upon  the  apparent  length  of  lines  (Muller-Lyer). 

distance  from  it.  Hence  when  we  know  the  actual  size  of  any  object  (as,  for 
example,  a  human  figure)  we  judge  of  its  distance  by  the  size  of  its  image  on 
the  retina.  Conversely,  our  estimate  of  the  actual  size  of  an  object  will 
depend  upon  our  judgment  of  its  distance.  The  fact  that  children  constantly 
misjudge  both  the  size  and  distance  of  objects  shows  that  the  knowledge  of 


Fig.  259.— Illusion  of  space-perception. 


US 


this  relation  is  acquired  only  by  experience.  If  circumstances  mislead 
with  regard  to  the  distance  of  an  object,  we  necessarily  make  a  corresponding 
error  with  regard  to  its  size.  Thus,  objects  seen  indistinctly,  as  through  a  fog, 
are  judged  to  be  larger,  because  we  suppose  them  to  be  farther  off,  than  they 
really  are.  The  familiar  fact  that  the  moon  seems  to  be  larger  when  near  the 
horizon  than  when  near  the  zenith  is  also  an  illustration  of  this  form  of  illu- 


800  ^^V   AMERICAN    TEXT-BOOK    OF   PHY'SIOLOGY. 

sion.  When  the  moon  is  higli  above  our  heads  we  have  no  means  of  esti- 
mating its  distance  from  us,  since  there  are  no  intervening  objects  with  which 
we  can  compare  it.  Hence  we  judge  it  to  be  nearer  than  when,  seen  on  the 
horizon,  it  is  obviously  farther  oif  than  all  terrestrial  objects.  Since  the  size 
of  the  retinal  image  of  the  moon  is  the  same  in  the  two  cases,  we  reconcile 
the  sensation  with  its  appaient  greater  distance  when  seen  on  the  horizon  by 
attributing  to  the  moon  in  this  position  a  greater  actual  size. 

If  the  retinal  image  have  the  form  of  a  familiar  object  of  regular  siiape — 
e.  r/.  a  house  or  a  table — we  interpret  its  outlines  in  the  light  of  experience 
and  distinguish  without  difficulty  between  the  nearer  and  more  remote  parts  of 
the  object.  Even  the  projection  of  the  outlines  of  such  an  object  on  to  a  plane 
surface  (/.  e.  a  perspective  drawing)  suggests  the  real  relations  of  the  different 
parts  of  the  picture  so  strongly  that  we  recognize  at  once  the  relative  distances 
of  the  various  portions  of  the  object  represented.  How  powerfully  a  familiar 
outline  can  susrirest  the  form  and  relief  usuallv  associated  with  it  is  well  illus- 
trated  by  the  experiment  of  looking  into  a  mask  painted  on  its  interior  to 
resemble  a  human  face.  In  this  case  the  familiar  outlines  of  a  human  face 
are  brought  into  unfamiliar  association  with  a  receding  instead  of  a  projecting 
form,  but  the  ordinary  association  of  these  outlines  is  strong  enough  to  force 
the  eye  to  see  the  hollow  mask  as  a  projecting  face.*  The  fact  that  the  pro- 
jecting portions  of  an  object  are  usually  more  brightly  illuminated  than  the 
receding  or  depressed  portions  is  of  great  assistance  in  determining  their  rela- 
tive distance.  This  use  of  shadows  as  an  aid  to  the  perception  of  relief  pre- 
supposes a  knowledge  of  the  direction  from  which  the  light  falls  on  an  object, 
and  if  we  are  deceived  on  the  latter  we  draw  erroneous  conclusions  with 
regard  to  the  former  point.  Thus,  if  we  look  at  an  embossed  letter  or  figure 
through  a  lens  which  makes  it  appear  inverted  the  accompanying  reversal  of 
the  shadows  will  cause  the  letter  to  appear  depressed.  The  influence  of 
shadows  on  our  judgment  of  relief  is,  however,  not  so  strong  as  that  of  the 
outline  of  a  iamiliar  object.  In  a  case  of  conflicting  testimony  the  latter 
usually  prevails,  as,  for  example,  in  the  above-mentioned  experiment  with  the 
mask. 

Aided  by  these  peculiarities  of  the  retinal  picture,  the  mind  interprets  it  as 
corresponding  in  its  different  parts  to  points  at  different  distances  from  the  eye, 
and  it  is  interesting  to  notice  that  painters,  whose  work,  being  on  a  plane  sur- 
face, is  necessarily  in  all  its  parts  at  the  same  distance  from  the  eye,  use  similar 
devices  in  order  to  give  depth  to  their  pictures.  Distant  hills  are  painted  with 
indistinct  outlines  to  secure  what  is  called  "  aerial  perspective."  Figures  of 
men  and  animals  are  introduced  in  appropriate  dimensions  to  suggest  the  dis- 
tance between  the  foreground  and  the  background  of  the  picture.  Landscapes 
are  painted  preferably  by  morning  and  evening  light,  since  at  these  liours  the 
marked  shadows  aid  materially  in  the  suggestion  of  distance. 

^  In  the  experiment  the  mask  should  be  placed  at  a  distance  of  about  two  meters  and  one 
eye  closed.  Even  with  both  eyes  open  the  illusion  often  persists  if  the  distance  is  increased  to 
five  or  six  meters. 


THE   SENSE    OE    VISION.  801 

The  eve,  however,  can  aid  itself  in  the  perception  of  depth  in  ways  which 
the  painter  has  not  at  his  disposal.  By  the  sense  of  effort  associated  with  the 
act  of  accommodation  we  are  able  to  estimate  roughly  the  relative  distance  of 
objects  before  us.  This  aid  to  our  judg!;ment  can,  of  course,  be  employed  only 
in  the  case  of  objects  comparatively  near  the  eye.  Its  effectiveness  is  greater 
for  objects  not  far  from  the  near-point  of  vision,  and  diminishes  rapidly  as  the 
distance  is  increased,  and  disappears  for  distances  more  than  two  or  three  meters 
from  the  eye. 

When  the  head  is  moved  from  side  to  side  an  apparent  change  in  the  rela- 
tive position  of  objects  at  different  distances  is  produced,  and,  as  the  extent  of 
this  change  is  inversely  proportional  to  the  distance  of  the  objects,  it  serv^es  as 
a  measure  of  distance.  This  method  of  obtaining  the  "parallax"  of  objects 
by  a  motion  of  the  head  is  often  noticeable  in  persons  whose  vision  in  one 
eye  is  absent  or  defective. 

Binocular  Vision. — The  same  result  which  is  secured  by  the  comparison 
of  retinal  images  seen  successively  from  slightly  different  points  of  view  is 
obtained  by  the  comparison  of  the  images  formed  simultaneously  by  any  object 
in  the  two  eyes.  In  binocular  vision  we  obtain  a  much  more  accurate  idea  of 
the  shape  and  distance  of  objects  around  us  than  is  possible  with  monocular 
vision,  as  may  be  proved  by  trying  to  touch  objects  in  our  neighborhood  with 
a  crooked  stick,  first  with  both  eyes  open  and  then  with  one  eye  shut.  When- 
ever we  look  at  a  near  solid  object  with  two  eyes,  the  right  eye  sees  farther 
round  the  object  on  the  right  side  and  the  left  eye  farther  round  on  the  left. 
The  mental  comparison  of  these  two  slightly  different  images  produces  the 
perception  of  solidity  or  depth,  since  experience  has  taught  us  that  those  objects 
only  which  have  depth  or  solidity  can  affect  the  eyes  in  this  way.  Conversely, 
if  two  drawings  or  photographs  differing  from  each  other  in  the  same  way  that 
the  two  retinal  images  of  a  solid  object  differ  from  each  other  are  presented, 
one  to  the  right  and  the  other  to  the  left  eye,  the  two  images  will  become 
blended  in  the  mind  and  the  perception  of  solidity  will  result.  Upon  this  fact 
depends  the  effect  of  the  instrument  known  as  the  stereoscope,  the  slides  of 
which  are  generally  pairs  of  photographs  of  natural  objects  taken  simultaneous- 


FiG.  260.— To  illustrate  stereoscopic  vision. 

ly  with  a  double  camera,  of  which  the  lenses  are  at  a  distance  from  each  other 
equal  to  or  slightly  exceeding  that  between  the  two  axes  of  vision.  The  prin- 
ciple of  the  stereoscope  can  be  illustrated  in  a  very  .simple  manner  by  drawing 
circles  such  as  are  represented  in  Figure  260  on  thin  paper,  and  fastening  each 

51 


802 


^iV^  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


pair  across  the  end  of  a  piece  of  brass  tube  about  one  inch  or  more  in  diameter 
and  ten  inches  long.  Let  the  tubes  be  held  one  in  front  of  each  eye  with  the 
distant  ends  nearly  in  contact  with  each  other,  as  shown  in  Figure  261.  If 
the  tubes  are  in  such  a  position  that  the  small  circles  are  brought  as  near  to 
each  other  as  possible,  as  shown  in  Figure  260,  the  retinal  images  will  blend, 

the  smaller  circle  will  seem  to  be  much 
nearer  than  the  larger  one,  and  the  eyes  will 
appear  to  be  looking  down  upon  a  truncated 
cone,  such  as  is  shown  in  Figure  262,  since 
a  solid  body  of  this  form  is  the  only  one 


Fig.  261. — To  illustrate  stereoscopic  vision. 


Fig.  262.— To  illustrate  stereoscopic  vision. 


bounded  by  circles  related  to  each  other  as  those  shown  in  this  experiment. 

Stereoscopic  slides  often  serve  well  to  illustrate  the  superiority  of  binocular 
over  monocular  vision.  If  the  slide  represents  an  irregular  mass  of  rocks  or 
ice,  it  is  often  very  difficult  by  looking  at  either  of  the  pictures  by  it.self  to 
detei-mine  the  relative  distance  of  the  various  objects  represented,  but  if  the 
slide  is  placed  in  the  stereoscope  the  true  relation  of  the  different  parts  of  the 
picture  becomes  at  once  apparent. 

Since  the  comparison  of  two  slightly  dissimilar  images  received  on  the  two 
retinas  is  the  essential  condition  of  stereoscopic  vision,  it  is  evident  that  if  the 
two  pictures  are  identical  no  sensation  of  relief  can  be  produced.  Thus,  when 
two  pages  printed  from  the  same  type  or  two  engravings  printed  from  the  same 
plate  are  united  in  a  stereoscope,  the  combined  picture  appears  as  flat  as  either 
of  its  components.  If,  however,  one  of  the  pictures  is  copied  from  the  other, 
even  if  the  copy  be  carefully  executed,  there  will  be  slight  differences  in  the 
distances  between  the  lines  or  in  the  spacing  of  the  letters  which  will  cause 
apparent  irregularities  of  level  in  the  different  portions  of  the  combined  pic- 
ture. Thus,  a  suspected  banknote  may  be  proved  to  be  a  counterfeit  if,  when 
placed  in  a  stereoscope  by  the  side  of  a  genuine  note,  the  resulting  combined 
picture  shows  certain  letters  lying  apparently  on  different  planes  from  the  rest. 

Pseudoscopic  Vision. — If  the  pictures  of  an  ordinary  stereoscopic  slide  be 
reversed,  so  that  tiie  picture  belonging  in  front  of  the  right  eye  is  presented  to 
the  left  eye,  and  ince  versd,  the  stereoscopic  gives  place  to  what  is  called  a  pseudo- 
scopic effect — i.  e.  we  perceive  not  a  solid  but  a  hollow  body.    The  effect  is  best 


THE  SENSE    OF    VISION.  803 

obtained  with  the  outlines  of  geometrical  solids,  photographs  of  coins  or  medals 
or  of  objects  which  may  readily  exist  in  an  inverted  form.  Where  the  photo- 
graphs represent  objects  which  cannot  be  thus  inverted,  such  as  buildings  and 
landscapes,  the  pseudoscopic  effect  is  not  readily  produced — another  example 
of  the  power  (see  p.  800)  of  the  outline  of  a  familiar  object  to  outweigh  other 
sorts  of  testimony. 

A  pseudoscopic  effect  may  be  readily  obtained  without  the  use  of  a  stereo- 
scope by  simply  converging  the  visual  axes  so  that  the  right  eye  looks  at  the 
left  and  the  left  eye  at  the  right  picture  of  a  stereoscopic  slide.  The  eyes  mav 
be  aided  in  assuming  the  right  degree  of  convergence  by  looking  at  a  small 
object  like  the  head  of  a  pin  held  between  the  eyes  and  the  slide  in  the  manner 
described  on  p.  758.  Figure  260,  viewed  in  this  way,  will  present  the  appear- 
ance of  a  hollow  truncated  cone  with  the  base  turned  toward  the  observer.  A 
stereoscopic  slide  with  its  pictures  reversed  will,  of  course,  when  viewed  in  this 
way,  present  not  a  pseudoscopic,  but  a  true  stereoscopic,  appearance,  as  shown 
by  Figures  226  and  227. 

Binocular  Combination  of  Colors. — The  effect  of  binocnlarly  combin- 
ing two  different  colors  varies  Avith  the  difference  in  wave-length  of  the  colors. 
Colors  lying  near  each  other  in  the  spectrum  will  generally  blend  together 
and  produce  the  sensation  of  a  mixed  color,  such  as  would  result  from  the 
union  of  colors  by  means  of  the  revolving  disk  or  by  the  method  of  reflected 
and  transmitted  light,  as  above  described.  Thus  a  red  and  a  yellow  disk 
placed  in  a  stereoscope  may  be  generally  combined  to  produce  the  sensation 
of  orange.  If,  however,  the  colors  are  complementary  to  each  other,  as  blue 
and  yellow,  no  such  mixing  occurs,  but  the  field  of  vision  seems  to  be  occupied 
alternately  by  a  blue  and  by  a  yellow  color.  This  so-called  "  rivalry  of  the 
fields  of  vision  "  seems  to  depend,  to  a  certain  extent,  upon  the  fact  that  in 
order  to  see  the  different  colors  with  equal  distinctness  the  eyes  must  be  dif- 
ferently accommodated,  for  it  is  found  that  if  the  colors  are  placed  at  different 
distances  from  the  eyes  (the  colors  with  the  less  refrangible  rays  being  at  the 
greater  distance),  the  rivalry  tends  to  disappear  and  the  mixed  color  is  more 
easily  produced. 

An  interesting  effect  of  the  stereoscopic  combination  of  a  black  and  a 
white  object  is  the  production  of  the  appearance  of  a  metallic  lustre  or  polish. 
If,  for  instance,  the  two  pictures  of  a  stereoscopic  slide  represent  the  slightly 
different  outlines  of  a  geometrical  solid,  one  in  black  upon  white  ground  and 
the  other  in  white  upon  black  ground,  their  combination  in  the  stereoscope 
will  produce  the  effect  of  a  solid  body  having  a  smooth  lustrous  surface. 
The  explanation  of  this  effect  is  to  be  found  in  the  fact  that  a  polished  surface 
reflects  the  light  differently  to  the  two  eyes,  a  given  point  appearing  bril- 
liantly illuminated  to  one  eye  and  dark  to  the  other.  Hence  the  stereoscopic 
combination  of  black  and  white  is  interpreted  as  indicating  a  polished  surface, 
since  it  is  by  means  of  a  polished  surface  that  this  effect  is  usually  produced. 

Corresponding-  Points. — When  the  visual  axes  of  both  eyes  are  directed 
to  the  same  object  two  distinct  images  of  that  object  are  formed  upon  widely 


804  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

separated  parts  of  the  nervous  system.  Yet  but  a  sinfjle  object  is  perceived. 
The  phencnnenon  is  the  same  as  that  which  occurs  when  a  grain  of  sand  is 
held  between  the  thuiiil)  and  finger.  In  both  cases  we  have  learned  (chiefly 
through  the  agency  of  muscular  movements  and  the  nerves  of  muscular  sense) 
to  interpret  the  double  sensation  as  produced  by  a  single  object. 

Any  two  points,  lying  one  in  each  retina,  the  stimulation  of  which  by  rays 
of  light  gives  rise  to  the  sensation  of  light  proceeding  from  a  single  object  are 
said  to  be  "  corresponding  points."  Now,  it  is  evident  that  ih^fovece  centrnleft 
of  the  two  eyes  must  be  corresponding  points,  for  an  object  always  appears 
single  when  both  eyes  are  fixed  upon  it.  That  double  vision  results  when  the 
images  are  formed  on  points  which  are  not  corresponding  may  be  best  illus- 
trate<:l  by  looking  at  three  pins  stuck  in  a  straight  rod  at  distances  of  35,  45, 
and  55  centimeters  from  the  end.  If  the  end  of  the  rod  is  held  against  the 
nose  and  the  eyes  directed  to  each  of  the  three  pins  in  succession,  it  will  be 
found  that,  while  the  pin  looked  at  appears  single,  each  of  the  others  appears 
double,  and  that  the  three  pins  therefore  look  like  five. 

The  two  fovece  centrales  are  not,  of  course,  the  only  corresponding  points. 
In  fact,  it  may  be  said  that  the  two  retinas  correspond  to  each  other,  point  for 
point,  almost  as  if  they  were  superposed  one  upon  the  other  with  the  foveae 
together.  The  exact  position  of  the  points  in  space  which  are  projected  on  to 
corresponding  points  of  the  two  retinas  varies  with  the  position  of  the  eyes. 
The  line  or  surface  in  which  such  points  lie  is  known  as  the  "  horopter."  A 
full  discussion  of  the  horopter  would  be  out  of  place  in  this  connection,  but 
one  interesting  result  of  its  study  may  be  pointed  out — viz.  the  demonstration 
that  when,  standing  upright,  we  direct  our  eyes  to  the  horizon  the  horopter  is 
approximately  a  plane  coinciding  with  the  ground  on  which  we  stand.  It  is 
of  course  important  for  security  in  walking  that  all  objects  on  the  ground 
should  appear  single,  and,  as  they  are  known  by  experience  to  be  single,  the 
eye  has  apparently  learned  to  see  them  so. 

Since  the  vertical  meridians  of  the  two  eyes  represent  approximately  rows 
of  corresponding  points,  it  is  evident  that  when  two  lines  are  so  situated  that 
their  images  are  formed  each  upon  a  vertical  meridian  of  one  of  the  eyes,  the 
impression  of  a  single  vertical  line  will  be  produced,  for  such  a  line  seen  bin- 
ocularly  is  the  most  frequent  cause  of  this  sort  of  retinal  stimulation.  This 
is  the  explanation  commonly  given  of  the  singular  optical  illusion  which  is 
produced  when  lines  drawn  as  in  Figure  263  are  looked  at  with  both  eyes  fixed 
upon  the  })oint  of  intersection  of  the  lines  and  with  the  plane  in  which  the 
visual  axes  lie  forming  an  angle  of  about  20°  with  that  of  the  paper,  the  dis- 
tance of  the  lines  from  the  eyes  being  such  that  each  line  will  lie  approximately 
in  the  same  vertical  plane  with  one  of  the  visual  axes.  Under  these  circum- 
stances each  line  will  form  its  image  on  a  vertical  meridian  of  one  of  the  eyes, 
and  the  combination  of  these  images  results  in  the  perception  of  a  third  line, 
not  lying  in  the  plane  of  the  paper,  but  apparently  passing  through  it  more  or 
less  vertically,  and  swinging  round  its  middle  point  with  every  movement  of 
the  head  or  the  paper.     In  this  experiment  it  will  be  found  that  the  illusion 


THE   SENSE    OF    VISION. 


805 


of  a  lino  placed  vertically  to  the  plane  of  the  paper  does  not  entirely  dis- 
appear when  one  eye  is  closed.     Hence  it  is  evident  that  there  is,  as  Mrs, 


Fig.  264.— Monocular  illusion  of  vertical  lines. 

C.  L.  Franklin  has  pointed  out,^  a  strong  tendency  to  regard 
lines  which  form  their  images  approximately  on  the  vertical 
meridian  of  the  eye  as  themselves  vertical.  This  tendency 
is  well  shown  when  a  number  of  short  lines  converging 
toward  a  point  outside  of  the  paper  on  which  they  are 
drawn,  as  in  Figure  264,  are  looked  at  with  one  eye  held 
a  short  distance  above  the  point  of  convergence.  Even 
when  the  lines  are  not  convergent,  but  parallel,  so  that  their 
images  cannot  fall  upon  the  vertical  meridian  of  the  eye,  the 
illusion  is  not  entirely  lost.  It  will  be  found,  for  instance, 
that  when  the  Zollner  lines,  as  given  in  Figure  251,  are 
looked  at  obliquely  with  one  eye  from  one  corner  of  the 
figure,  the  short  lines  which  lie  nearly  in  a  plane  with  the 
visual  axis  appear  to  stand  vertically  to  the  plane  of  the 
paper. 
In  this  connection  it  may  be  well  to  allude  to  the  optical  illusion  in  conse- 
quence of  which  certain  portraits  seem  to  follow  the  beholder  with  the  eyes. 
This  depends  upon  the  fact  that  the  face  is  painted  looking  straight  out  from 
the  canvas  —i.  e.  with  the  pupil  in  the  middle  of  the  eye.  The  painting  being 
upon  a  flat  surface,  it  is  evident  that,  from  whatever  direction  the  picture  is 
viewed,  the  pupil  will  always  seem  to  be  in  the  middle  of  the  eye,  and  the 
eye  will  consequently  appear  to  be  directed  upon  the  observer.  The  phenom- 
enon is  still  more  striking  in  the  case  of  pictures  of  which  the  one  repre- 
sented in  Figure  265  may  be  taken  as  an  example.     Here  the  soldier's  rifle 

'  Am.  Journal  of  Psychology,  vol.  i.  p.  99. 


Fig.  263,— Binocu 
Jar  illusion  of  a  ver 
tical  line. 


806 


AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


Fig.  265.— Illusion  of  lines  always  pointing 
toward  observer. 


is  dnnvn  as  it  appears  to  an  eye  looking  straight  down  tlie  barrel,  ami,  as  this 
foreshortening  is  the  same  in  all  positions  of  the  observer,  it  is  evident  that 

when  such  a  picture  is  hung  upon  tlie  wall 
of  a  room  tlie  .'^oldier  will  appear  to  be 
aiming  directly  at  tlie  head  of  every  person 
present. 

In  concluding  this  brief  survey  of  some 
of  the  most  important  subjects  connected 
with  the  physiology  of  vision  it  is  well  to 
utter  a  word  of  caution  with  regard  to  a 
danger  connected  with  the  study  of  the  sub- 
ject. This  danger  arises  in  part  from  the 
fact  that  in  the  scientific  study  of  vision  it 
is  often  necessary  to  use  the  eyes  in  a  way 
quite  different  from  that  in  which  they  are 
habitually  employed,  and  more  likely,  there- 
fore, to  cause  nervous  and  muscular  fatigue. 
We  have  seen  that  in  any  given  position  of 
the  eye  distinct  definition  is  limited  to  an 
area  which  bears  a  very  small  proportion  to 
the  whole  field  of  vision.  Hence  in  order  to  obtain  an  accurate  idea  of  the 
appearance  of  any  large  object  our  eyes  must  wander  rapidly  over  its  whole 
surface,  and  we  use  our  eyes  so  instinctively  and  unconsciously  in  this  way 
that,  unless  our  attention  is  specially  directed  to  the  subject,  we  find  it  diffi- 
cult to  believe  that  the  power  of  distinct  vision  is  limited  to  such  a  small 
portion  of  the  retina.  In  most  of  the  experiments  in  physiological  optics, 
however,  this  rapid  change  of  direction  of  the  axis  of  vision  must  be  carefully 
avoided,  and  the  eye-muscles  held  immovable  in  tonic  contraction. 

Our  eyes,  moreover,  like  most  of  our  organs,  serve  us  best  when  we  do  not 
pay  too  much  attention  to  the  mechanism  by  which  their  results  are  brought 
about.  In  the  ordinary  use  of  the  eyes  we  are  accustomed  to  neglect  after- 
images, intraocular  images,  and  all  the  other  imperfections  of  our  visual  appa- 
ratus, and  the  usefulness  of  our  eyes  depends  very  much  upon  our  ability  thus 
to  neglect  their  defects.  Now,  the  habit  of  observing  and  examining  these 
defects  that  is  involved  in  the  scientific  study  of  the  eye  is  found  to  interfere 
with  our  ability  to  disregard  them.  A  student  of  the  physiology  of  vision 
who  devotes  too  much  attention  to  the  study  of  after-images,  for  instance,  may 
render  his  eyes  so  sensitive  to  these  phenomena  that  they  become  a  decided 
obstacle  to  ordinary  vision. 


THE  SENSE    OF   HEARING. 


807 


B.  The  Ear  and  Hearing. 
Anatomy  and  Histology  of  the  Ear.— The  organ  of  hearing  may  con- 
veuiently  be  divided  into  three  parts  :  (1)  The  external  ear,  including  the 
pinna  or  auride  and  the  external  auditory  meatus;  (2)  the  middle  ear,  called 
the  "  tympanic  cavity  "  or  ti/mpamim  ;  and  (3)  the  internal  ear,  or  labyrinth. 
The  labyrinth  is  situated  in  the  dense  petrous  bone,  and  it  contains  a  mem- 
branous sac  of  complex  form  which  receives  the  peripheral  terminations  of  the 
auditory  nerve.  This  sac,  therefore,  is  to  the  ear  what  the  retina  is  to  the  eye ; 
as  the  lens,  cornea,  etc.  of  the  eye  are  simply  physical  media  for  the  production 
of  sharp  images  on  the  retina,  so  all  parts  of  the  organ  of  hearing  are  devoted 
solely  to  the  accurate  transmission  of  the  energy  of  air-waves  to  the  internal 

ear. 

The  External  Ear. — The  pinna  or  auride,  commonly  known  simply  as 
the  "  ear  "  (Fig.  2(36),  is  a  peculiarly  wrinkled  sheet  of  tissue,  consisting  es.sen- 


FiG.  266.-Diagram  of  organ  of  hearing  of  left  side  (Quain,  after  Arnold) :  1,  the  pinna;  2,  bottom  of 
concha ;  2-2'.  meatus  externus ;  3,  tympanum ;  above  3,  the  chain  of  ossicles ;  3',  opening  into  the  mastoid 
cells-  4,  Eustachian  tube;  5,  meatus  internus,  containing  the  facial  (uppermost)  and  auditory  nerves; 
6  placed  on  the  vestibule  of  the  labyrinth  above  the  fenestra  ovalis ;  a,  apex  of  the  petrous  bone ;  6, 
internal  carotid  artery;  c,  styloid  process;  d,  facial  nerve,  issuing  from  the  stylo-mastoid  foramen;  e, 
mastoid  process  ;  /,  squamous  part  of  the  bone. 

tially  of  yellow  elastic  cartilage  covered  with  skin,  and  forming  at  the  entrance 
of  the  auditory  meatus  a  cup-shaped  depression  called  the  "  concha." 

17? e  concha,  and  to  some  extent  the  whole  auricle,  serves  a  useful  purpose 
in  collecting,  like  the  mouth  of  a  speaking-trumpet,  the  waves  of  sound  falling 
upon  it ;  but  in  many  of  the  lower  animals  the  concha  is  relatively  larger  than 
in  man,  and,  their  ears  being  freely  movable,  the  auricle  becomes  of  greater 
physiological  importance. 

External  Auditory  Meatus.— In  man  the  external  auditory  meatus  or  audi- 
tory canal  is  about  one  and  a  quarter  inches  in  length,  and  it  extends  from 


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AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


the  bottom  and  anterior  edge  of  the  concha  to  tlie  membrana  tympani,  or 

tympanic  membrane.  Starting 
from  the  bottom  of  the  conclia, 
the  general  direction  of  the  audi- 
tory canal  is  first  obliquely  up- 
ward and  backward  for  about 
half  an  inch,  and  then  inward 
and  forward.  Therefore,  to  look 
into  the  ear  or  to  introduce  the 
aural  speculum  the  canal  must  be 
straightened  by  pulling  the  pinna 
upward  and  backward.  The 
canal-wall  is  cartilaginous  and 
movable  for  about  half  an  inch 
from  the  exterior,  but  is  osseous 
for  the  rest  of  its  extent ;  it  is 
lined  by  a  reflexion  of  thin  skin, 
on  whose  surface,  in  the  cartilag- 
inous part  of  the  canal,  open  the 
ducts  of  numerous  sebaceous  and 
ceruminous  glands. 

Tympanum. — The  middle  ear, 
or  tympanum  (Figs.  2G6,  267),  is 
shut  oif  from  the  auditory  canal 
by  the  tympanic  membrane.     It 

is  an  air-holding  cavity  of  irregular  shape  in  the  petrous  bone,  and  it  is  broader 

behind  and   above  than   it   is  below  and 

in  front.     Posteriorly  it  is  in  open  com- 
munication  with   the  comj)lcx  system  of" 

air-cavities  in  the  mastoid   bone  known 

as  the   mastoid   antrum  and  the  mastoid 

cells.    Anteriorly  it  is  continuous  with  the 

pharynx    through   the   Eustachian    tube. 

The  inner  wall  slants  somewhat  outward 

from    top   to    bottom,  and    it    is  formed 

chiefly  by  part  of  the  bony  envelope  of 

the  internal  ear.    The  surface  of  this  wall 

is  pierced  by  two  apertures,  the  fenestra 

ovalis,  or  oval  window,  and   the  fenestra 

rotunda,  or  round  window,   leading  into 

the  cavity  of  the  bony  labyrinth ;  in  life 

each  fenestra  is  covered  by  a  thin   sheet 

of  membrane,  and  the  foot  of  the  stapes 

h  fastened  by  a  ligamentous  fringe  in  the 

oval  window.     The  outer  wall  of  the  middle  ear  is  made  up  of  the  tymj>anic 


Fig.  267.— Tympanum  of  left  ear,  with  ossicles  m  situ 
(after  Morris) :  1,  suspensory  ligament  of  malleus  ;  2,  head 
of  malleus  ;  3,  epitympanic  region;  4,  external  ligament 
of  malleus  ;  5,  processus  longus  of  incus ;  6,  base  of  stapes ; 
7,  processus  brevis  of  malleus;  8,  head  of  stapes;  9,  o>! 
orbicnlare;  10,  manubrium  ;  11,  Eustachian  tube  ;  12,  exter- 
nal auditory  meatus:  13,  membrana  tympani;  14,  lower 
part  of  tympanum. 


Fig.  268.— ()tosco|iic  view  of  left  membrana 
tympani  (Morris):  1,  viembrana  flaccida ;  2,2', 
folds  bounding  the  former ;  3,  reflection  from 
processus  brevis  of  malleus ;  4,  processus  lon- 
gus of  incus  (occasionally  seen) :  .'>,  mem- 
brana tympani ;  6,  umbo  and  end  of  manu- 
brium ;  7,  pyramid  of  light. 


THE  SENSE    OF  HEARING. 


809 


membrane  and  tlie  ring  of  bone  into  which  tliis  membrane  is  inserted. 
The  roof  is  formed  by  a  thin  plate  of  bone,  the  tegrnen,  which  separates  it 
from  the  cranial  cavity,  and  the  narrow  floor,  concave  upward,  is  just  above 
the  jugular  fossa.  The  cavity  is  lined  by  mucous  membrane  continuous  with 
that  of  the  Eustachian  tube  and  the  pharynx,  and  the  membrane,  like  that 
of  the  Eustachian  tube,  is  ciliated  except  over  the  surfaces  of  the  ossicles  ahd 
the  tympanic  membrane.  Suppurative  inflammation  of  the  middle  ear  may 
not  only  involve  the  mastoid  cells,  but  may  also  cause  absorption  of  the  tiiin 
plate  of  bone  forming  the  roof  of  the  tympanic  cavity  and  the  mastoid 
antrum.  In  this  and  in  other  ways  inflammation  may  extend  from  the  tym- 
panic to  the  cranial  cavity,  making  otitk  media,  or  inflammation  of  the  middle 
ear,  the  commonest  source  of  pyogenic  atfections  of  the  brain.* 

Tympanic  Membrane,  or  Drum-skin. — The  membrana  tympani  (Figs,  268, 
269)  is  a  somewhat  oval  disk  whose  longer  axis  is  directed  from  behind  and  above 

downward  and  forward,  and 
whose  length  is  about  nine 
millimeters.  The  membrane 
is  inserted  obliquely  to  the 
axis  of  the  .  auditory  canal, 
so  that  the  floor  of  the  canal 
is  longer  than  its  roof.  The 
membrana  tympani,  though 
so  thin  as  to  be  semi-trans- 
parent, is  composed  of  three 
layers  of  tissue.  Externally 
it  is  covered  by  a  thin  plate 
of  skin ;  internally,  by  mu- 
cous membrane;  and  between 
these   lies  the   proper   sub- 


FiG.  2692— Tympanum  of  right  side  with  ossicles  in  place,  viewed 
from  within  (after  Morris) :  1,  body  of  incus  ;  2,  suspensory  ligament 
of  malleus ;  3,  ligament  of  incus ;  4,  head  of  malleus ;  5,  epityra- 
panic  cavity ;  6,  chorda  tijmpani  nerve ;  7,  tendon  of  tensor  tympani 
muscle;  8,  foot-piece  of  stirrup;  9,  of  orbiculare ;  10,  manubrium: 
11,  tensor  tympani  muscle;  12,  membrana  tympani;  13,  Eustachian 
tube. 


Fig.  270.— The  chain  of  auditory 
ossicles,  anterior  view  (after  Tes- 
tut) :  1,  head  of  malleus;  2,  long 
process  of  incus ;  3,  stapes. 


Stance  (membrana  propria)  of  the  membrane,  made  up  chiefly  of  fibrous  tissue. 
The  greater  number  of  the  fibres  of  the  membrana  propria  radiate  from  near 
the  centre  to  the  periphery  of  the  membrane ;  but  there  are  also  circular  filjres 
of  elastic  tissue  which  are  most  numerous  in  a  ring  near  the  attached  margin 
of  the  membrane.  The  surface  of  the  tympanic  membrane  is' not  flat,  but  is 
funnel-shaped,  with  the  apex  of  the  funnel  pointing  inward.     Moreover,  lines 

^  Macewen  :  Pyogenic  Diseases  of  the  Brain  and  Spinal  Cord,  1893. 

'  Figs.  267,  268,  and  269  are  taken  by  permission  from  Morris's  Text-Book  of  Anatomy,  Phila.,  1893. 


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AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


drawn  from  the  centre  to  the  margin  of  the  membrane  would  not  be  straight, 
but  would  be  curved  slightly,  with  the  convexity  outward,  this  shape  being 
due  to  the  tension  of  the  clastic  circular  fibres  of  the  meml)rane.  The  mem- 
brane, throughout  the  greater  part  of  its  circumlerence,  is  inserted  in  a  groove 
in  a  bony  ring  set  in  the  wall  of  the  auditory  canal,  but  a  small  arc  at  its 
superior  portion  is  attached  directly  to  the  wall  of  the  canal.  The  segment  of 
membrane  corresponding  to  this  arc,  known  as  the  membrnna  Jlaccida,  lacks 
the  tenseness  of  the  rest  of  the  drum-skin. 

Viewed  through  the  aural  speculum,  the  normal  tympanic  membrane  has 
a  pearly  lustre  (Fig.  268).  The  handle  of  the  malleus,  or  manubrium,  inserted 
within  its  fibrous  layer,  can  be  seen  as  an  opaque  ridge  running  from  near  the 
upper  anterior  margin  downward  and  backward  and  ending  in  the  umbo,  or 
central  depression,  where  the  membrane  is  drawn  considerably  inward  by  the 
tip  of  the  manubrium.  It  is  from  this  point  that  the  radial  fibres  of  the  mem- 
brana  prop-ia  diverge. 

At  the  top  of  the  manubrium  is  a  shining  spot  which  is  the  reflection 
from  the  short  process  of  the  malleus  where  it  presses  against  the  membrane. 
From  this  point  two  delicate  folds  of  the  membrane  run  to  the  periphery — 
one  forward  and  the  other  backward.  They  form  the  lower  border  of  the 
membrana  jlaccida,  or  ShrapneU's  membrane,  in  which  there  is  less  fibrous  tissue 
than  in  the  remaining  part  of  the  membrane,  and  the  cutaneous  and  mucous 
layers  are  also  less  tense  than  elsewhere.  A  bright  reflection  of  triangular 
shape,  known  as  the  "  pyramid  of  light,"  is  seen  in  the  lower  quadrant  of  tiie 

tympanic  membrane.  The  apex  of  this 
bright  triangle  is  at  the  tip  of  the  manu- 
brium, and  its  base  is  on  or  near  the 
peripheiy  of  the  membrane. 

Auditory  Ossicles.  —  The  tympanic 
membrane  is  put  into  relation  with  the 
internal  ear  by  a  chain  of  bone,  the 
auditory  ossicles,  known  as  the  malleus, 
the  incus,  and  the  stapes,  so  called  from 
their  fancied  resemblance  to  a  hammer,  an 
anvil,  and  a  stirrup  (Figs.  267,  269,  270). 
The  malleus  (Fig.  271)  is  18  to  19  milli- 
meters long ;  it  presents  a  rounded  head, 
grooved  on  one  side  for  articulation  with 
the  incus,  a  short  neck,  and  a  long  handle 
or  manubrium,  which  is  inserted  in  the 
tissue  of  the  tympanic  membrane  from 
a  point  on  its  upper  periphery  to  a  little  below  its  centre.  The  processus 
bi-evis  of  the  malleus  is  a  low  conical  projection  which  springs  from  the  top 
of  the  manubrium  and  presses  directly  against  that  segment  of  the  tympanic 
membrane  known  as  the  membrana  Jlaccida,  through  which  it  can  be  seen 
shining  on  inspection  with  the  ear-speculum.     The  processus  gracilis,  or  pj-o- 


FiG.  271.— Malleus  of  the  right  side :  a,  anterior 
face;  b,  internal  face  (after  Testut):  1,  capitu- 
lum  or  head  of  malleus ;  2,  cervix  or  neck ;  3, 
processus  brevis ;  4,  processus  gracilis ;  5,  manu- 
brium ;  6,  grooved  articular  surface  for  incus ; 
7,  tendon  of  m.  tensor  tympani. 


THE  SENSE    OF  HEARING. 


811 


cessus  Folianus,  long  and  slender,  arises  from  an  eminence  just  below  the 
neck  of  the  malleus,  and,  passing  forward  and  outward,  is  inserted  in  the 
Glaserian  fissure  in  the  wall  of  the  tympanum.  The  malleus  is  held  in  posi- 
tion ])artly  by  ligaments;  the  suspensory  or  superior  ligament  passes  downward 
and  outward  from  the  roof  of  the  tympanum  to  be  inserted  into  the  head  of 
the  malleus.  The  main  portion  of  the  anterior  ligament  is  attached  to  the 
neck  of  the  malleus  just  above  the  processus  gracilis ;  it  embraces  the  latter, 
and,  passing  forward,  finds  its  origin 
in  the  anterior  wall  of  the  tympanum 
attd  in  the  Glaserian  fissure.  Another 
division  of  this  ligament,  the  external 
ligament,  arises  and  is  attached  more 
externally  than  that  just  described. 
The  lig-aments  of  the  malleus  serve  to 
keep  its  head  in  position.  The  exter- 
nal ligament,  being  attached  above  the 
axis  of  rotation  of  the  hammer,  pre- 
vents the  head  of  this  bone  from 
moving  too  far  inward,  and  the  manu- 
brium from  being  pushed  too  far  outward.  The  superior  ligament,  owing  to 
its  oblique  course,  restrains  the  head  of  the  hammer  from  moving  too  far 
outward. 

The  incus,  umbos,  or  anvil-bone  (Fig.  273)  is  shaped  somewhat  like  a  bicus- 
pid tooth.     Its  thicker  portion  is  hollowed  on  the  surface  and  is  covered  with 

cartilage  for  articulation  with  the 
^  ^  head  of  the  malleus.     It  has  two 

processes,   a    long    and   a  short, 
which  project  at  right  angles  to 


Fig.  272.— Ligaments  of  the  ossicles  and  their  axis 
of  rotation  (from  Foster,  after  Hensen).  The  figure 
represents  a  nearly  horizontal  section  of  the  tym- 
panum, carried  through  the  heads  of  the  malleus 
and  incus :  M,  malleus  ;  1,  incus ;  t,  articular  tooth 
of  incus ;  Ig.a  and  Ig.e,  external  ligament  of  mal- 
leus ;  Ig.inc,  ligament  of  the  incus  ;  the  line  a-x  rep- 
resents the  axis  of  rotation  of  the  two  ossicles. 


Fig.  273.— The  incus  of  the  right  side :  a,  anterior  face;  B, 
internal  face  (after  Testut) :  1,  body  of  incus ;  2,  processus 
brevis ;  3,  processus  longus  ;  4,  articular  surface  for  the  mal- 
leus ;  5,  a  convex  tubercle,  processus  lenticularis,  for  articu- 
lation with  stapes ;  6,  rough  surface  for  attachment  of  the 
ligament  of  the  incus. 


Fig.  274.— The  stapes  (after  Testut) :  1, 
base ;  2,  anterior  crus ;  3,  posterior  eras ; 
4,  articulating  surface  of  head  of  the 
bone ;  5,  cervix  or  neck. 


each  other ;  the  former  has  a  length  of  4^  millimeters,  and  the  latter  a  length 
of  3  to  ^  millimeters.  When  in  position  the  long  process  descends  nearly 
parallel  with  the  manubrium,  but  it  has  less  than  three-fourths  the  length  of 
the  latter.  The  free  end  of  the  long  process  is  turned  sharply  inward  at  right 
angles,  and  terminates  in  a  round  projection,  the  os  orbiculare,  which  is  provided 
with  cartilage  for  articulation  with  the  head  of  the  stapes.     The  short  process  is 


812  .i;V'   AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

coniciil  ill  -sliape  and  is  thicker  thau  the  long  process.  It  lias  a  horizontal  ])()si- 
tion,  and  is  attached  by  a  thick  ligament  to  the  posterior  wall  of  the  tympanum. 

The  stapes  (Fig.  274)  articulates  with  the  end  of  the  long  process  of  the 
incus ;  its  plane  is  horizontal  and  about  at  right  angles  to  that  process.  It 
measures  3  to  4  millimeters  in  length  and  about  2J  millimeters  in  breadth. 
The  base  of  the  stapes  is  somewhat  oval  in  shape,  the  superior  margin  being 
convex  and  the  inferior  being  slightly  concave.  It  is  set  in  the  fenestra  ovalis, 
an  aperture  measuring  about  3  millimeters  by  1^  millimeters,  and  is  held  in 
place  by  a  narrow  membrane  made  up  of  radial  fibres  of  connective  tissue. 
When  in  position,  the  inner  face  of  the  base  of  the  stirrup  is  covered  with 
lymphatic  endothelium  and  is  washed  by  the  perilymph  of  the  internal  ear; 
the  outer  face,  like  the  other  tympanic  bones  and  the  wall  of  the  cavity,  is 
covered  by  thin  mucous  membrane. 

Movement  of  the  Ossicles. — The  malleus-incus  articulation  is  so  arranged 
that  with  outward  movements  of  the  manubrium  the  head  of  the  malleus 
glides  freely  in  the  joint;  but  the  lower  margins  of  the  articulating  surfaces 
project  in  such  a  way  that  the  prominences  lock  together  when  the  manubrium 
moves  inward.  Thus,  in  inward  movements  of  the  tympanic  membrane  and 
its  attached  manubrium,  the  malleus  and  the  incus  move  together  like  one 
rigid  piece  of  bone,  the  motions  of  the  manubrium  and  the  long  process  of  the 
incus  being  parallel.  Of  the  malleus-incus  articulation  Helmholtz'  says: 
"  In  its  action  it  may  be  cora])ared  with  the  joints  of  the  well-known  Breguet 
watch-keys,  which  have  rows  of  interlocking  teeth,  oifering  scarcely  any  resist- 
ance to  revolution  in  one  direction,  but  allowing  no  revolution  whatever  in  the 
other."  In  the  outward  movements  the  locking  teeth  or  projections  are  prob- 
ably still  kej)t  in  apposition,  under  ordinary  circumstances,  through  the  elastic 
reaction  of  the  ligament  and  the  stapedial  attachment  of  the  incus.  Should, 
however,  the  tympanic  membrane  be  forced  unduly  outward,  as  by  increase  of 
pressure  within  the  tympanum  or  by  rarefaction  of  air  in  the  auditory  meatus, 
the  incus  only  follows  the  malleus  for  a  certain  distance,  the  latter  completing 
its  motion  by  gliding  in  the  joint.  Tiiere  is  thus  no  danger  of  the  stapes  being 
torn  out  of  the  oval  window.  The  hammer  and  the  anvil,  suspended  by  their 
ligaments,  move  freely  about  an  axis  one  end  of  which  is  found  at  the  origin  of 
the  anterior  part  of  the  anterior  ligament  of  the  malleus,  and  the  other  end  in 
the  origin  of  the  ligament  which  is  continuous  with  the  short  process  of  the  incus 
(Fig.  272).  In  inward  motions  of  the  tympanic  meml)rane  the  ossicles  move  like 
a  single  bone  around  the  axis  of  suspension  ;  and  as  the  distance  measured  from 
the  axis  of  rotation  to  the  tip  of  the  manubrium,  where  the  power  is  applied,  is 
about  one  and  one-half  times  the  distance  to  the  end  of  the  long  process  of  tlie 
incus,  where  the  effect  is  produced,  the  motions  transmitted  to  the  stapes  can  have 
but  two-thirds  the  am])litude  of  the  movements  of  the  tip  of  the  manubrium,  but 
have  one  and  one-half  times  their  force.  It  will  be  noticed  that  a  large  ])ro- 
portion  of  the  mass  of  both  anvil  and  hammer  is  found  above  their  axis  of  rota- 
tion ;  this  upper  portion  acts  as  a  counterjwise  to  the  parts  below  which  are  directly 
'  Sensations  of  Tone,  trans,  by  Ellis,  1885,  p.  133. 


THE  SENSE    OF   HEARING.  813 

concerned  in  the  lever  action.  The  bony  lever  being  thus  balanced,  it  is  less 
diHicult  to  understand  its  known  sensitiveness  to  impulses  that  are  inconceivably 
weak.  The  tense  tympanic  membrane,  by  reason  of  its  funnel  shape,  resists 
strong  inward  compression ;  hence  the  stapes  is  prevented  from  being  pressed 
too  far  inward.  The  maximum  amplitude  of  motion  of  the  stapes  in  the 
fenestra  is  very  small,  being  only  about  -jlg-  millimeter  to  -^  millimeter,  while 
that  of  the  centre  of  the  tympanic  membrane  is  about  -^  millimeter  to  ^ 
millimeter. 

The  functional  movements  of  the  auditory  ossicles  are  not  molecular  but 
are  molar  vibrations,  the  chain  of  bones  moving  in  a  body.  The  sole  purpose 
of  this  apparatus  of  the  middle  ear  is  to  transmit  exactly  the  variations  of 
pressure  in  the  air  of  the  external  auditory  meatus  to  the  perilymph  which 
bathes  the  foot  of  the  stapes — in  other  words,  to  convert  air- waves  into  a 
similar  series  of  water-waves.  In  the  words  of  Helmholtz,^  "  The  mechanical 
problem  which  the  apparatus  within  the  drum  of  the  ear  had  to  solve  was  to 
transform  a  motion  of  great  amplitude  and  little  force,  such  as  impinges  on 
tiie  drum-skin,  into  a  motion  of  small  amplitude  and  great  force,  such  as  had 
to  be  communicated  to  the  fluid  in  the  labyrinth." 

The  adaptation  of  the  apparatus  of  the  middle  ear  to  this  end  is  worthy 
of  careful  consideration.  In  the  first  place,  it  will  be  noticed  that  the  area 
of  the  fenestra  ovalis  which  receives  the  impulses  of  the  stapes  is  but  a  small 
fraction  of  the  surface  of  the  tympanic  membrane  on  which  the  air-waves 
impinge,  the  latter  area  being  some  fifteen  to  twenty  times  greater  than  the 
former,  so  that  the  energy  of  air-motion  is,  in  a  fashion,  concentrated.  In  the 
second  place,  as  previously  observed,  the  lever  mechanism  of  the  auditory 
ossicles  is  such  that  the  movements  of  the  end  of  the  long  process  of  the  incus 
have  two-thirds  the  amplitude  of  those  of  the  tip  of  the  manubrium,  but 
about  one  and  one-half  times  their  force.  It  should  also  be  noticed  that  the 
membrane  fastening  the  foot  of  the  stapes  in  the  fenestra  is  somewhat  less 
tense  on  the  upper  side,  so  that  the  top  of  the  oval  foot-piece  has  a  freer 
motion  than  the  bottom,  and  the  head  of  the  stirrup  rises  slightly  with  inward 
motions.  In  the  third  place,  it  has  been  demonstrated  by  Helmholtz^  that  the 
shape  of  the  tympanic  membrane  peculiarly  adapts  it  for  transforming  weak 
movements  of  wide  amplitude  into  strong  ones  of  small  compass.  For  this 
membrane  is  not  a  simple  funnel  depressed  inwardly,  but  the  radii  are  slightly 
curved  with  the  convexity  outward,  a  shape  chiefly  due  to  the  tension  of  the 
elastic  circular  fibres  of  the  membrane  on  its  inner  face,  these  being  most 
numerous  toward  the  circumference.  Air-waves  beating  upon  this  convexity 
flatten  the  curve  somewhat,  and  their  whole  energy  must  be  concentrated,  witli 
increased  intensity  but  loss  of  motion,  at  the  central  point  of  the  membrane. 
This  effect  may  be  illustrated  by  holding  a  slightly-curved  brass  wire,  several 
inches  in  length,  with  its  plane  perpendicular  to  the  surface  of  a  table  and 
supported  on  its  ends.  When  one  end  of  the  wire  is  held  immovable,  up-and- 
down  motions  of  the  arch  are  transferred  to  the  free  end  with  diminished 
'  Op.  cit.,  p.  134.  ^  Op.  cit. 


814  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

amplitude.  The  wire  represents  a  single  radial  fibre  of  the  tympanic  mem- 
brane, and  the  tunnel  shape  of  this  membrane  is  adapted  to  concentrating  this 
motion  of  the  radial  fibres  upon  the  manubrium.  The  same  effect  is  illus- 
trated by  the  fact  that  when  a  string  or  a  rope  is  stretched  between  two  })oints, 
no  matter  how  tightly,  it  always  sags  at  its  middle ;  the  weight  of  the  cord, 
however  slight,  is  sufficient  to  give  it  a  curved  course,  and  produces  a  corre- 
sponding traction  on  the  points  of  support. 

Eustachian  Tube. — That  the  tympanic  membrane  may  maintain  its 
freedom  of  motion,  it  is  obviously  necessary  that  the  averacje  atmospheric 
pressure  on  each  side  of  it  should  remain  the  same.  This  equalitv  of  pressure 
is  maintained  through  the  medium  of  the  Eustachian  tube,  a  somewhat  trumpet- 
shaped  canal  which,  beginning  in  the  lower  anterior  walls  of  the  tympanum, 
runs  downward,  forward,  and  inward,  and  terminates  in  a  slit  in  the  side  of 
the  upper  i)art  of  the  pharynx.  The  Eustachian  tube  is  lined,  like  the  walls 
of  the  tympanum,  with  ciliated  epithelium,  the  cilia  working  in  such  a  way 
as  to  carry  into  the  pharynx  such  secretions  as  may  arise  from  the  mucous 
membrane  of  the  middle  ear.  The  pharyngeal  opening  of  the  Eustachian  tube 
is  probably  normally  closed,  but  it  may  easily  be  made  to  open  by  increase  or 
decrease  of  air-pressure  within  the  pharynx,  as  may  be  produced  by  closing 
the  nose  and  mouth  and  either  forcing  air  into  the  pharynx  by  strong  expiration 
or  rarefying  it  by  suction.  In  the  former  case  the  air-pressure  within  the 
tympanum  is  increased,  and  in  the  latter  it  is  diminished.  When  air  is  thus 
made  to  enter  or  to  leave  the  tympanum,  a  sensation  of  a  sudden  snap  and 
a  dull  crackling  noise  in  the  ear  is  experienced.  The  lower  end  of  the  tube 
is  normally  opened  during  the  act  of  swallowing,  and  it  is  at  this  moment  that 
the  intra-  and  extra-tympanic  air-pressures  are  equalized. 

Muscles  of  the  Middle  Ear. — Two  muscles  are  devoted  to  adjusting  the 
tension  of  the  auditory  mechanism  of  the  middle  ear.  The  tensor  tympani  is 
lodged  within  a  groove  which  is  just  above  and  about  parallel  with  the  Eusta- 
chian tube.  It  terminates  externally  in  a  long  tendon  which  bends  nearly  at 
right  angles  round  the  outer  edge  of  the  groove  and  is  inserted  into  the 
handle  of  the  malleus  near  the  neck.  Contraction  of  the  tensor  tympani  thus 
results  in  pulling  the  tympanic  membrane  inward  and  rendering  it  more  tense 
(PI.  2,  Fig.  1).  This  increase  of  tension  of  the  membrane  seems  to  adapt  it 
better  to  the  more  rapid  vibrations  of  high  musical  notes,  but  allows  less  ready 
response  to  lower  notes.  It  is  said  that  the  tensor  tympani  comes  normally 
into  action  at  the  beginning  of  a  sound,  thus  tuning  the  membrane  for  the 
note  that  is  to  follow,  and  then  relaxes.  One  of  its  effects  is  probably  to  bring 
closely  together  the  toothed  processes  of  malleus  and  incus  at  the  beginning 
of  a  sound,  so  that  there  shall  be  no  loss  of  motion  during  the  vibrations 
of  the  membrane.  The  stapedius  is  a  small  muscle  imbedded  in  the  inner 
wall  of  the  tympanum  near  the  fenestra  ovalis.  Its  tendon,  ])assing  forward, 
is  inserted  into  the  neck  of  the  stapes.  Contraction  of  the  muscle  would  cause 
a  slight  rotation  of  the  stapes  round  a  vertical  axis,  so  that  the  hinder  part 
of  the  foot  of  the  ossicle  would  be  pressed  more  deeply  into  the  fenestra,  while 


THE  SENSE   OF  HEARING.  815 

the  retnainiug  portion  would  be  drawn  out  of  it.  Its  action  probably  reduces 
tiie  pressure  in  the  cavity  of  the  perilymph,  and  thus  is  antagonistic  to  that 
of  the  tensor  tynipani  (PI.  2,  Fig.  2,  a,  b). 

Vibrations  of  the  Tympanic  Membrane. — It  is  a  general  physical  law 
that  every  elastic  body  can  be  made  to  vibrate  more  easily  at  one  definite  rate 
than  at  any  other.  The  musical  tone  represented  by  this  rate  of  vibration  is 
known  as  the  prime  or  fundamental  tone  of  the  body.  Membranes  have  funda- 
mental tones  (see  p.  827),  whose  pitch  is  determined  by  their  area,  thickness, 
and  tension,  but  they  differ  from  rods  and  strings  in  being  less  strictly  confined 
to  a  single  fundamental  tone  in  their  vibration.  The  tympanic  membrane  is 
quite  peculiar  in  that  it  can  hardly  be  said  to  have  a  definite  fundamental  tone. 
It  would  obviously  be  a  great  imperfection  in  an  organ  of  hearing  were  cer- 
tain sounds  intensified  by  it  out  of  proportion  to  others,  as  would  be  the  case 
if  the  tvmpanic  membrane  had  a  marked  fundamental  tone  of  its  own.  This 
is  prevented  in  the  case  of  the  membrana  tympani  probably  both  by  reason  of 
the  peculiar  form  of  its  surface  and  its  structure,  and  also  because  its  oscilla- 
tions are  damped  by  the  pressure  of  the  malleus  held  in  position  by  tlie  other 
mechanisms  of  the  tympanum.  When  the  tympanic  membrane  is  perforated 
or  is  wholly  removed,  without  destructive  inflammatory  changes  in  the  middle 
ear,  sounds  are  still  heard,  though  usually  with  diminished  loudness.  A 
musician  who  had  suffered  this  accident  was  no  longer  able  to  play  his  violin, 
probably  because  sounds  of  different  pitch  ceased  to  be  perceived  in  their  true 
relations  of  loudness.  We  may  thus  conclude  that  the  function  of  the  tym- 
panic membrane  is  not  only  to  guard  against  injury  to  the  delicate  mem- 
branes of  the  fenestrse  and  the  internal  ear,  but  also  to  transmit  to  the  ossicles 
sonorous  vibrations  with  their  true  proportion  of  intensity.  The  membranes 
covering  the  round  and  oval  windows  of  the  internal  ear  have  no  means  of 
damping  sympathetic  vibrations  (see  p.  829),  and,  should  complex  air-waves 
strike  directly  upon  them,  they  would,  probably,  by  sympathetic  resonance, 
respond  more  powerfully  to  tones  of  certain  pitch  than  to  any  others. 

The  sensation  of  sound  may  be  excited  by  conduction  through  the  bones 
of  the  skull  as  well  as  in  the  ordinary  way.  Thus,  a  tuning-fork  set  vibrating 
and  held  between  the  teeth  or  on  the  forehead  is  heard  perfectly,  and  more 
loudly  when  the  ears  are  closed  than  when  open.  The  vibrations  thus  con- 
ducted probably  partly  affect  the  internal  ear  directly,  and  partly  indirectly  by 
setting  in  oscillation  the  tympanic  membrane.  When  a  sounding  tuning-fork 
is  held  between  the  teeth  until  the  sound  dies  away,  it  may  still  be  heard  if 
held  in  front  of  the  ear,  though  the  contrary  statement  is  frequently  erroneously 
made.  When  the  sound  of  the  fork  held  between  the  teeth  has  failed,  it  may 
again  be  heard  by  stopping  the  ears. 

The  Internal  Ear,  or  Labyrinth. — The  internal  ear  is  the  site  of  the  true 
organ  of  hearing.  The  membranous  labyrinth  (PI.  2,  Fig.  4 ;  Fig.  278)  is  a  com- 
plicated system  of  membranous  tubes  and  sacs,  in  which  terminate  at  particular 
points  the  filaments  of  the  auditoiy  nerve ;  it  is  contained  within  a  chamber, 
the  bony  labyrinth,  hollowed  out  in  the  petrous  bone.    The  cavity  of  the  bony 


81(5 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


lal)yrintli(Fig.s.  275,  270)  consists  of  a  median  part,  the  vestibule,  which  is  pro- 
lougt'd  posteriorly  in  the  system  of  semicircular  canals  and  anteriorly  in  the 
cochlea.  The  vestibule  is  a  space  which  measures  about  one-fifth  of  an  inch 
in  diameter,  and  it  is  perforated  in  its  outer  wall  by  an  oval  opening  known 
as  the  Jenesira  ovalis.     The  semicircular  canals  are  three  tubes  of  ciroular 


Fig.  275.— Right  bony  labyrinth,  viewed  from 
outer  side  :  the  figure  represents  the  appearance 
produced  by  removing  the  petrous  bone  down  to 
tlie  denser  layer  immediately  surrounding  the 
labyrinth  (from  Quain,  after  Sommering):  1,  2,3, 
the  superior,  posterior,  and  horizontal  semicir- 
cular canals;  4,  5,  6,  the  ampullae  of  the  same; 
7,  the  vestibule ;  8,  the  fenestra  ovalis ;  9,  fenestra 
rotunda  ;  10,  first  turn  of  the  cochlea ;  11,  second 
turn ;  12,  apex. 


Fig.  276.— Interior  view  of  left  bony  labyrinth  after 
removal  of  the  superior  and  external  walls  (from 
Quain,  after  Sommering) :  1,  2,  3,  the  superior,  pos- 
terior, and  horizontal  semicircular  canals ;  4,  fovea 
hemi-elliptica;  o,  fovea  hemisphcrica;  6,  common 
opening  of  the  superior  and  jioRterior  semicircular 
canals  ;  7,  opening  of  the  aqueduct  of  the  vestibule  ; 
8,  opening  of  the  aqueduct  of  tlie  cochlea;  9,  the 
scala  vestibuli ;  10,  scala  tympani ;  the  lamina  spiralis 
separating  9  and  10. 


section,  known  respectively  as  the  anterior  or  superior,  the  posterior,  and  the 
external  or  horizontal  semicircular  canal.  Their  planes  are  at  right  angles  to 
one  another,  so  that  they  occupy  the  three  possible  dimensions  of  space.  The 
external  canal  lies  in  a  nearly  horizontal  plane,  while  the  other  two  approach 
the  vertical.     Each    canal   is  dilated  at  one  extremity  into  a  globular  cavity 

which  is  more  than  twice  the  diameter  of  the 
canal  itself,  and  which  is  known  as  the  am- 
pulla. The  anterior  and  posterior  canals 
unite  near  the  ends  not  provided  with  am- 
pull?e,  and  they  enter  the  vestibule  as  a  com- 
mon tube.  Anteriorly  the  cavity  of  the 
vestibule  is  continued  as  a  tube  of  complex 
internal  structure  which  is  coiled  upon  itself 
two  and  one-half  times,  and  which,  from  its 
resemblance  to  the  shell  of  a  snail,  is  known 
as  the  cochlea  (PI.  2,  Fig.  3).  The  osseous 
cochlea  may  be  conceived  as  formed  by  a  bony  tube  turned  about  a  bony  central 
pillar,  the  modiolus,  which  diminishes  in  diameter  from  the  base  to  the  apex 
of  the  cochlea.  From  the  modiolus  a  bony  shelf  stretches  into  the  cavity  of 
the  tube,  incompletely  dividing  it  into  two  tubular  chambers,  winding  round 
the  modiolus  like  a  circular  staircase,  the  upper  of  which  chambers  we  shall 


Fig.  277.— Diagram  of  the  osseous  cochlea 
laid  open  (after  Quain) :  1,  scala  vestibuli ; 
2.  lamina  spiralis  ;  3,  scala  tympani ;  l,  cen- 
tral pillar  or  modiolus. 


Explanation  of  Plate  2. 

Fig.  1. — Schematic  representation  of  displacement  of  the  auditor)'  ossicles  due  to  contraction  of  the 
tensor  tympani  muscle  (.Testut) :  ((.external  auditory  meatus;  ti,  tympanic  cavity;  c,  vestibule  of  the 
bony  labyrinth  ;  d,  fenestra  ovalis  ;  1,  membrana  tympani  ;  2,  handle  of  malleus  ;  3,  head  of  malleus  ;  4, 
insertion  of  tendon  of  tensor  tympani ;  5,  long  or  vertical  process  of  incus  ;  6,  head  of  incus;  7,  stapes. 
(The  arrow  indicates  the  direction  of  traction  of  the  tensor  tympani  muscle ;  and  the  lines  in  red  indi- 
cate the  change  in  the  position  of  the  parts  produced  by  it.) 

Fig.  2.— Schematic  representation  of  the  displacement  of  the  stapes  due  to  contraction  of  the  stape- 
dius muscle  (Testut) :  A,  the  stapes  in  repose;  B,  stapes^  during  contraction  of  stapedius  muscle;  1,  base 
of  stapes;  2,  anterior  border  of  fenestra  ovalis  ;  3,  the  pyramid  ;  4,  tendon  of  stapedius  muscle  ;  a,  anterior 
portion  of  annular  ligament  of  stapes,  longer  than  b,  posterior  portion  of  same  ligament ;  x,  x,  antero- 
posterior diameter  of  fenestra  ovalis,  passing  through  the  base  of  the  resting  stapes;  y,  point  of  passage 
of  the  vertical  line  which  represents  the  axis  of  rotation  of  the  stapes. 

Fig.  3.— The  three  parts  making  up  the  bony  cochlea  (schematic,  from  Ttstut) :  A.  the  columella;  B, 
spiral  tube  containing  the  scalae ;  C,  lamina  spiralis ;  J>.  the  three  parts  in  their  normal  relations. 

Fig.  4.— Schematic  representation  of  the  perilymphatic  and  endolymphatic  sfiaces.  The  former 
apfjear  in  black,  and  the  latter  are  colored  blue  (Testut  i :  1,  utricle  ;  2,  saccule  ;  3,  semicircular  canal ;  4, 
caualis  cochlearis  ;  5,  ductus  endolymphaticus  with  its  two  branches  of  origin  ;  6,  saccus  endolymph- 
aticus  ;  7,  canalis  reuniens,  or  canal  of  Ilensen  ;  8,  scala  tympani ;  9,  scala  vestibuli ;  10,  their  communi- 
cation at  the  helieotrema  ;  11,  aqua-ductus  vestibuli  ;  12,  aqua^ductus  cochlearis  :  13,  periosteum ;  14,  dura 
mater;  15,  stapes  in  the  fenestra  ovalis ;  16,  fenestra  rotunda  with  its  membrane. 


77//;  s/:.\s/':  or  u earing. 


I'LATK    ± 


Fif!.    1. 


Fig.  2. 


THE  SENSE    OF  HEARING. 


817 


soon  learn  to  know  as  the  .sm/a  vesfibull,  and  the  lower  chamber  as  the  scala 
tympani  (Fig.  277 ;  PI.  2,  Fig.  3).  The  bony  shelf  mentioned  above  as  partly 
bisecting  the  cochlear  tube  has,  of  course,  like  the  latter,  a  spiral  course,  and  is 
known  as  the  lamina  spiralis;  its  importance  as  a  supporter  of  the  auditory- 
nerve  filaments  will  soon  be  seen. 

Contained  within  the  cavity  of  the  bony  labyrinth,  and  parallel  with  its  walls, 
is  the  manhranom  labijrinth,  in  which  are  found  the  essential  structures  of  the 
organ  of  hearing  (PI.  2,  Fig.  4  ;  Fig.  278).  The  membranous  labyrinth  is  filled 
with  a  somewhat  watery,  mucin-holding  fluid,  the  endolymph,  while  a  similar 
fluid,  the  perilymph,  is  found  outside  it  and  within  the  osseous  labyrinth.  The 
perilymph  space,  which  is  lined  by  lymphafic  epithelium,  is  in  communication, 
along  the  sheath  of  the  auditory  nerve,  with  the  subdural  and  subarachnoid 
lymph-areas  of  the  brain.  Numerous  sheets  and  bars  of  connective  tissue  cross 
from  the  wall  of  the  bony  to  that  of  the  membranous  labyrinth  and  help  support 
the  latter.  That  part  of  the  membranous  labyrinth  lying  within  the  vestibule 
is  composed  of  two  separate  sacs — a  larger  posterior,  known  as  the  utricle  or 
utrimlus,  and  a  smaller,  more  anterior,  known  as  the  saccule  or  sacculus.  The 
plane  of  division  between  the  two  sacs  ends  opposite  the  fenestra  ovalis  (PI.  2, 
Fig.  4).    Though  the  sacs  are  quite  separate,  their  cavities  are  indirectly  continu- 


—  9 


Fig  '>78  -Diagram  of  right  membranous  labyrinth  seen  from  the  external  side  (after  Testut) :  1,  utri- 
cle -23  4  superior,  posterior,  and  horizontal  semicircular  canals ;  5,  saccule ;  6,  ductus  endolymphat- 
Icus.withV,  7',  its  twigs  of  origin ;  8,  saccus  endolymphaticus  ;  9,  caualis  cochlearis,  with  9',  its  vestibular 
cul-de-sac,  and  9",  its  blind  extremity ;  10,  canalis  reuniens. 

ous,  through  the  union  of  two  small  tubes  arising  from  either  sac,  which  tubes 
unite  to  form  the  ductus  endolijmphaficus,  a  tube  running  inward  through  a 
canal  in  the  petrosal  bone  and  ending  blindly  in  a  dilated  flattened  extremity, 
the  saccus  endolymphaticus,  this  being  supported  between  the  layers  of  the 
dura  mater  within  the  cavity  of  the  skull  (PI.  2,  Fig.  4).  Bundles  of  audi- 
tory-nerve fibres  penetrate  the  wall  of  each  sac.  The  utricle  gives  rise  to  the 
membranous  semicircular  canals,  which  communicate  with  it  at  five  points, 
it  being  remembered  that  the  anterior  and  posterior  canals  fuse  into  a  single 
tube  at*  the  ends  not  piwided  with  ampulla,  and  that  they  have  a  common 
entrance  into  the  utricle.  The  saccule  is  continuous  by  a  narrow  tube,  the 
canalis  rmniens,  with  that  division  of  the  membranous  labyrinth  contained 

52 


818 


^l.Y  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


withiu  tlie  cochlea  and  known  as  the  cdnalia  cochlearis.  The  auditory  nerve 
really  consists  of  two  distinct  divisions  having  separate  origins  and  different 
distributions.  One  of  these  branches  passes  finally  to  the  cochlea,  and  the 
other  to  the  vestibule  and  the  semicircular  canals.  The  nerve  approaches  the 
labyrinth  by  way  of  a  canal  known  as  the  meatus  andUorius  interntts,  and 
on  reaching  the  angle  i)etween  the  vestibule  and  the  base  of  the  cochlea  the 
cochlear  division  pa.sses  to  the  cochlea.  The  remainder  of  the  nerve  consists 
of  two  divisions,  the  supericn-  of  which  is  distributed  to  the  utricle  and  to  the 
ampullas  of  the  anterior  and  horizontal  semicircular  canals;  the  inferior  branch 
supplies  the  saccule  and  the  posterior  semicircular  canal.  The  inner  wall  of 
both  utricle  and  saccule  is  developed  at  a  particular  spot  into  a  low  mound, 
the  macula  acustica,  made  up  of  an  accumulation  of  the  connective-tissue  ele- 
ments of  the  membranous  wall  and  covered  by  a  peculiarly  modified  epithe- 
lium, the  auditory  epithelium  (Fig.  279).  All  the  auditory-nerve  filaments  that 
enter  the  saccule  and  utricle  respectively  pass  to  these  mounds  and  there  enter 
into  relation  with  the  auditory  epithelium. 

As  the  auditory-nerve  endings  are  confined  to  a  particular  ai-ea  in   the 
utricle  and  the  saccule,  so  the  nerve-fibres  supplying  the  semicircular  canals 

are  limited  to  a  certain  part  of  the 
ampulla  of  each  canal.  The  tissue  of 
the  wall  of  the  ampulla  is  developed 
into  a  ridge  projecting  into,  the  cavity 
in  a  direction  across  its  long  axis. 
This  ridge,  present  in  each  ampulla,  is 
called  the  crista  acustica  ;  it  is  capped 
by  a  thick  layer  of  columnar  epithelial 
cells,  the  auditory  epithelium,  which 
thins  away  at  the  border  of  the  crista 
into  the  sheet  of  flattened  cells  by 
which  the  rest  of  the  ampulla  is  lined. 
The  auditory  cells(Fig.  279)  are  said  to 
be  of  two  kinds — t)ne,  cylindrical  in 
shape  and  reaching  only  part  way  to 
the  basement  membrane,  the  hair-cells; 
the  other,  narrow  and  elongated,  the 
supporting  or  sustentacular  cells.  The  former  are  peculiar  in  the  fact  that 
from  their  free  ends  there  project  long,  stiff,  hair-like  processes.  The  fila- 
ments of  the  ampullary-nerve  branches  pass  through  the  cristas  and  encircle 
the  bodies  of  the  hair-cells.  The  cells  covering  the  maculee  acusticce  have 
essentially  the  same  structure  as  those  just  described,  though  in  the  maculae 
the  auditory  hairs  are  shorter  than  in  the  cristie.  Seated  on  the  free  surface 
of  the  macular  epithelium  is  a  fibrous  mass  which  is  said  to  be  a  normal 
structure,  and  not,  like  a  somewhat  similar  mass  found  covering  the  crista^  in 
post-mortem  sections,  a  coagulum  due  to  the  method  of  preparation.  Im- 
bedded in  the  membrane  over  the  maculae  of  both  saccule  aud  utricle  are 


Fig.  279.— Diagram  showing  the  epithelial  cells  of 
a  macula  or  a  crista  (after  Foster) :  1,  cylinder  or 
hair-cell ;  2,  the  same,  enveloped  in  a  nest  of  nerve- 
fibrils  ;  3,  4,  5,  forms  of  rod-  or  spindle-cells. 


THE  SENSE    OF  HEARING. 


819 


small  crvstals,  oioJUhs  or  ofocouia,  composed  chiefly  of  carlx>nate  of  lime.  Oto- 
conia are  also  found  less  constantly  in  the  ampullai  and  even  in  the  peri- 
lymph space  of  the  cochlea.  In  fishes  there  are  large  masses  of  calcareous 
matter,  otoliths,  attached  to  the  wall  (»f  the  auditory  sac. 

General  Anatomy  of  the  Cochlea. — ]5y  far  the  most  complex  structure  of 
the  ear  is  found  in  the  cochlea  (PI.  2,  Figs.  1, 3,  4 ;  Figs.  275-278).  The  bony 
cochlea  continues  from  the  anterior  wall  of  the  vestibule,  and  in  the  upright  posi- 
tion of  the  head  the  axis  of  the  modiolus  is  nearly  horizontal,  pointing,  from  base 


Fig.  280.-Diagram  of  a  transverse  section  of  a  whorl  of  the  cochlea  (after  Foster) :  Sc.V,  scala  vestib- 
uli-  Sc.T,  scala  tympani;  C.Chl,  canalis  cochlearis;  Lam.sp,  lamina  spiralis;  Gg.sp,  ganglion  spirale ; 
n.aud,  auditory  nerve;  m.R,  membrane  of  Reissner;  Str.v,  Stria  vascularis;  Lg.sp,  ligamentum  spirale; 
tl  Ivmphatic  epithelioid  lining  of  basilar  membrane  on  the  tympanic  side;  m.b,  basilar  membrane; 
Org.'c,  organ  of  Corti ;  L.t,  labium  tympanicum;  lb,  limbus ;  L.v,  labium  vestibulare;  m.t,  tectorial 
membrane. 

to  apex,  outward  and  slightly  down  and  forward,  the  base  of  the  cochlea  being 
formed  by  the  inner  surface  of  the  petrous  bone.  The  membranous  cochlea, 
canalis  or  ductus  cochlear^,  is  a  tube  of  nearly  triangular  cross-section  which 
winds  round  the  modiolus  from  base  to  apex  (Fig.  280).   The  base  or  outer  side 


820  AN  AMERICAN    TEXT- BOOK    OE   PHYSIOLOGY. 

of  this  triangle  is  attached  closely  to  tlie  bony  wall  of  the  cochlea;  the  upper 
bide,  supposing  the  modiolus  to  be  vertical  with  its  apex  above,  is  made  of  a  tliin 
sheet  of  cells  known  us  the  membrane  of  lieissner  ;  the  lower  side  is  made  up 
partly  of  the  bony  margin  of  the  lamina  spiralis  and  partly  of  a  membrane, 
radially  striated,  .•stretched  across  from  the  edge  of  the  spiral  lamina  to  the  side 
wall  of  the  cochlea;  this  is  called  the  basilar  membrane,  mcmbruna  basilaris. 
The  coiled  tube  forming  the  bony  cochlea  is  thus  divided  by  the  lamina  spiralis 
and  the  camdia  cocldcaris  into  three  tubes  which  wind  sj)irally  and  parallel 
round  the  modiolus.  The  canalis  cochlearis  contains  endolymph,  and  its  cav- 
ity ends  blindly  above  and  below,  but  is  continuous  by  way  of  the  narrow 
canalis  reuniens  with  that  of  the  saccule.  The  tubes  above  and  below  the 
canalis  cochlearis  are  perilymph-spaces ;  it  will  be  noticed  that  there  is  no 
such  space  on  the  outer  side  of  the  membranous  cochlea. 

The  upper  tube,  when  followed  down  to  the  base  of  the  cochlea,  is  found 
to  open  freely  into  the  vestibule  of  the  labyrinth  ;  it  is  therefore  known 
as  the  sca/a  vestibidi.  The  hjwer  tube  ends  blindly  at  the  base  of  the 
cochlea,  but,  where  this  part  bulges  into  the  tympanum  as  the  *'  promontory  " 
of  its  inner  wall,  it  is  perforated  by,  the  aperture  known  as  the  fenestra 
rotunda,  whose  ])roper  mend)rane  alone  prevents  the  i)erilymph  from  escaping 
into  the  middle  ear.  This  tube  is  therefore  known  as  the  scala  tymponi. 
From  its  central  position  the  membranous  cochlear  canal  is  frequently  known 
as  the  scala  media.  The  scala  vestibuli  and  the  scala  tympani  both  decrease  in 
size  as  they  wind  from  the  base  to  the  apex  or  cupola  of  the  cochlea ;  the 
membranous  cochlear  canal,  on  the  contrary,  increases  in  section  from  base  to 
apex  until  near  the  top;  hence  the  width  of  the  basilar  membrane  and  the 
length  of  its  radial  fibres  increase  from  below  upward.  The  scala  vestibuli 
and  the  scala  tympani  have  no  communication  except  through  a  small  ai)erture 
under  the  cupola  of  tiie  cochlea,  known  as  the  helirotrema  ;  this  is  bounded 
by  the  hook-like  termination,  the  hamnlns,  of  the  bony  lamina  spiralis,  which 
forms  the  greater  part  of  a  ring  completed  by  the  jiointed  blind  extremity  of 
the  eanalis  cochlearis  fastened  above  it  to  the  cupola. 

The  Transmission  of  Vibrations  through  the  Labjrrinth. — Vibrations 
of  the  tvmpanic  membrane  are  transmitted  as  pulses  of  very  small  amplitude  to 
the  membrane  covering  the  fenestra  ovalis.  The  relatively  considerable  body  of 
perilymph  bathing  the  inner  face  of  this  membrane  must  be  thus  set  in  motion, 
and  there  starts  a  fluid-wave  which  is  free  to  make  its  way  throughout  the 
perilvmph-spaces  of  the  vestibule  and  the  semicircular  canals.  It  may  pass 
from  the  vestibule  along  the  scala  vestibuli  to  its  top,  through  the  helicotrema, 
and  back  by  way  of  the  scala  tympani,  at  whose  bottom  it  finally  surges 
against  the  membrane  covering  the  fenestra  rotunda;  or  the  wave  may  be 
transmitted  directly  across  the  membranous  cochlea.  The  fluids  of  the  laby- 
rinth being  ])hysically  incompressible,  the  function  of  the  fenestra  rotunda  as 
a  sort  of  safety-valve  seems  evident.  Politzer  inserted  a  glass  tube  in  the 
round  window,  and  found  that  fluid  in  the  tube  rose  when  strong  air-i)ressure 
was  brought  to  bear  on  the  outer  side  of  the  tympanic  membrane.    The  cavity 


THE  SENSE   OF  HEARING.  821 

of  the  membranous  labyrinth  (PI.  2,  Fig.  4)  is  nowliere  in  communication  with 
the  perilymph-space  al)out  it,  and  we  must  therefore  assume  that  the  irritation 
of  the  auditory  cells  seated  in  its  wall  must  depend  on  vibrations  transmitted 
from  the  perilymph  directly  through  tlie  membranous  sacs  and  tubes. 

Like  the  perilymph-space,  the  cavity  of  the  membranous  labyrinth  is  in 
communication  throughout,  though  in  certain  situations  the  connection  of 
adjacent  parts  is  very  indirect.  Thus,  though  the  semi(;ircular  canals  open 
freely  at  both  ends  into  the  utricle,  the  utricle  and  saccule  are  only  brought 
into  union  by  the  two  narrow  tubes  that  unite  to  form  the  ductus  endolym- 
phaticus.  It  will  be  noted  that  by  means  of  this  duct  the  membranous  laby- 
rinth is  really  continued  into  the  cranial  cavity.  The  saccule  in  turn  is 
continuous  with  the  scala  media  of  the  cochlea  by  way  of  the  canalis  reuniens. 

The  Membranous  Cochlea  and  the  Organ  of  Corti  (Figs.  280-282).— 
The  cochlear  division  of  the  auditory  nerve,  together  with  the  nutrient  blood- 
vessels, penetrates  the  modiolus  at  its  base  and  runs  up  th'rough  the  spongy 
interior  of  the  bony  pillar.  As  the  nerve  ascends  through  the  modiolus  its 
fibres  are  gradually  all  diverted  to  run  in  a  radial  direction  between  the  bony 
plates  of  the  lamina  spiralis,  to  terminate  in  the  organ  of  Corti  of  the  canalis 
cochlearis.  A  collection  of  nerve-cells  is  interposed  in  the  course  of  the  audi- 
tory fibres  at  the  base  of  the  lamina  spiralis. 

A  complete  view  of  the  nerves  of  the  cochlea  would  show  a  central  pillar 
of  nerve-fibres  diminishing  in  thickness  from  below  upward,  and  winding 
round  this  pillar  a  spiral  sheet  of  radially-disposed  nerve-fibres  containing, 
near  their  point  of  departure  from  the  central  pillar,  a  spiral  line  of  ganglion- 
cells;  this  collection  of  cells  is  therefore  known  as  the  ganglion  spirale.  The 
thin,  free  edge  of  the  bony  lamina  spiralis  is,  in  the  recent  state,  thickened  by 
a  development  of  connective  tissue  forming  a  promontory  known  as  the  limbus. 
Tlie  free  edge  of  the  limbxis  is  in  turn  shaped  in  such  a  way  as  to  make  a  short, 
sharp  projection  in  the  plane  of  the  upper  surface  of  the  lamina  and  a  longer 
projection  in  the  plane  of  its  lower  surface,  leaving  the  free  margin  between 
them  hollowed  out.  The  upper  projection,  which  is  known  as  the  vestibular 
lip,  labium  vestibulare,  serves  for  the  attachment  of  the  tectorial  membrane, 
membrana  tecforia,  presently  to  be  described.  The  lower  projection  is  called 
the  tympanic  lip  {labium  tympanicum) ;  to  it  is  attached  the  inner  margin  of 
the  basilar  membrane,  on  whose  inner  half  is  seated  the  very  complex  struct- 
ure known  as  the  organ  of  Corti. 

The  basilar  membrane  is  a  thin  sheet  of  fibrillated  connective  tissue  stretched 
tightly  between  the  tympanic  lip  of  the  limbus  on  the  inside  and  the  spiral 
ligament  (see  p.  824)  on  the  outside.  The  more  median  part  of  the  membrane, 
which  supports  the  organ  of  Corti,  is  thin  and  rigid  and  is  fibrillated  in  a 
radial  direction.  The  outer  part,  which  is  first  thicker  and  then  thinner  again 
near  its  point  of  attachment,  is  distinctly  composed  of  radial  fibres  cemented 
together;  the  isolated  fibres  are  characterized  by  being  stiff  and  brittle. 

The  organ  of  Corti  (Figs.  280,  281)  has  as  its  supporting  basis  a  series  of 
peculiarly  modified  epithelial  cells,  known  as  the  rods  of  Coiii  (Fig.  282,  b,  b'), 


822 


AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 


which  are  disposed  iiloug  the  edge  of  the  spiral  lamina  iu  two  rows,  an  inner 
and  an  outer.  The  inner  rods  have  their  feet  on  the  basilar  membrane  near  its 
median  attachment;  thoy  lean  outward  and  upward,  and  at  their  uj)pcr  extrem- 
ity join  or  articulate  with  the  heads  of  the  outer  rods,  whose  feet  are  fastened  to 
the  basilar  membrane  more  exteraally.  The  two  rows  of  rods  are  thus  joined 
together  like  the  rafters  of  a  house,  and  enclose  beneath  them  a  canal  known 
as  the  tunnel  of  the  organ  of  Corti.  The  inner  rods  arc  more  numerous  than 
the  outer,  so  that  the  latter  are  fastened  rather  between  than  to  the  ends  of  the 
former.  Leaning  against  the  inner  or  median  side  of  the  inner  row  of  rods 
is  a  single  row  of  hair-cells  (Fig.  281),  much  like  those  described  as  seated  on 
the  maculae  and  cristas  of  the  labyrinth,  to  which  hair-cells  filaments  of  the 


m.t 


ig.sj) 


Fig.  281.— Diagram  of  the  organ  of  Corti  (from  Foster,  after  Retzius) :  i.r,  inner  rod  of  Corti ;  o.r,  outer 
rod  of  Corti;  i.hc,  inner  hair-cell ;  n.c,  the  group  of  nuclei  beneath  it;  o.hc,  outer  hair-cells,  or  cells  of 
Corti ;  CD,  the  twin  cells  of  Deiters  (four  rows) ;  n.aud,  the  auditory  nerve  perforating  the  tympanic  lip, 
U,  and  lost  to  view  among  the  nuclei  beneath  the  inner  hair-cells ;  i.spn,  the  inner  spiral  strand  of  nerve- 
fibrils  ;  t.»pn,  the  spiral  strand  of  the  tunnel ;  o.spn,  the  outer  spiral  strand  belonging  to  the  first  row  of 
outer  hair-cells  ;  the  three  succeeding  spiral  strands  belonging  to  the  three  other  rows  are  also  shown ; 
nerve-fibrils  arc  shown  stretching  radially  across  the  tunnel";  H.c,  Hensen's  cells ;  Cl.c,  Claudius'  cells ; 
t.l,  lymphatic  epithelioid  lining  on  the  side  toward  the  seala  tympani ;  l(/.sp,  ligamentum  spirale ;  c,  cells 
lining  the  spiral  groove,  overhung  by  the  vestibular  lip, /.r;  m.t,  tectorial  membrane;  a  fragment,  torn 
from  it,  remains  attached  to  the  organ  of  Corti  just  outside  the  outermost  row  of  hair-cells. 

auditory  nerve  are  distributed.  Closely  applied  to  the  single  row  of  hair- 
cells,  on  the  inner  side,  are  several  rows  of  columnar  cells  gradually  decreas- 
ing in  size  toward  the  median  line,  and  beneath  the  whole  is  a  group  of  nuclei. 
External  to  the  outer  row  of  rods,  and  separated  from  it  by  a  space,  are  four 
parallel  rows  of  hair-cells  known  as  the  cells  of  Corti ;  their  bodies  do  not 
reach  downward  as  far  as  the  basilar  membrane,  and  just  below  each  row  is  a 
bundle  of  nerve-fibres  which  have  traversed  the  tunnel  of  Corti  and  then  have 
changed  their  direction  from  a  radial  to  a  longitudinal  or  spiral  one.  These 
fibres,  and  others  having  a  more  direct  course,  one  by  one  end  in  clusters 
encircling  the  individual  hair-cells. 

Four  rows  of  peculiarly-modified  columnar  cells,  the  ceUs  of  Deiters,  are 
inserted  closely  between  the  cells  of  Corti,  the  outermost  row  being  external 
to  the  fourth  row  of  Corti.  These  cells  rest  below  on  the  basilar  membrane. 
Still  external  to  these  groups  of  cells  is  a  series  of  rows  of  tall  columnar  cells 
of  simple  character  supported  upon  the  basilar  membrane,  and  rapidly  decreas- 
ing in  height  externally  into  a  layer  of  cubt)idal  epithelium  covering  the  outer 
part  of  the  basilar  membrane.     The  rods  of  Corti  are  peculiarly  shaped  at  the 


THE  SENSE    OF  HEARING. 


823 


top,  the  upper  extremity  of  each  being  bent  at  an  angle  so  as  to  project  exter- 
nally and  parallel  with  the  basilar  membrane ;  these  projections  are  the  pha- 
lanyar  processes  of  the  rods,  the  phalanges  of  the  inner  row  overlapping  those 
of  the  outer  row.  These  phalangar  processes  of  the  rods  form  the  points  of 
attachment — in  fact,  the  beginning — of  the  reticulate  membrane  (viembrana 
reticulata),  a  peculiar  cuticular,  network-like  structure  formed  of  rings  and 
cross-bars,  having  the  appearance  of  certain  vegetable  tissues  seen  under  the 
microscope.     The  reticulate  membrane  stretches  across  the  outer  rows  of  hair- 


^o.r.h 


m.b 


Fig.  282.-Diagram  of  the  constituents  of  the  organ  of  Corti  (from  Foster,  after  Retzius) :  a,  inner  hair- 
cell;  A',  the  head,  seen  from  above;  b,  inner,  b',  outer,  rod  of  Corti;  ph,  in  each,  is  the  phalangar  pro- 
cess ;  c,  the  twin  outer  hair-cell ;  C.c,  the  cell  of  Corti ;  h,  its  auditory  hairs ;  n,  its  nucleus ;  x,  Hensen's 
body ;  D.c,  cell  of  Deiters ;  n',  its  nucleus ;  ph.p,  its  phalangar  process ;  fil,  the  cuticular  filament ;  m.b, 
basilar  membrane;  m.r,  reticulate  membrane;  c',  the  head  of  a  cell  of  Corti,  seen  from  above;  d,  the 
organ  of  Corti,  seen  from  above ;  i.hc,  the  heads  of  the  inner  hair-cells ;  i.r.h,  the  head  and  phalangar'pro- 
cess  of  the  inner  rod ;  o.r.k,  the  head  of  the  outer  rod,  with  ph.p,  its  phalangar  process,  covered  to  the  left 
hand  by  the  inner  rods,  but  uncovered  to  the  right;  o.h.c,  the  heads  of  the  cells  of  Corti,  supported  bj 
the  rings  of  the  reticulate  membrane ;  ph,  one  of  the  phalangae  of  the  reticulate  membrane. 

cells,  the  body  of  each  of  which  is  enclosed  and  is  held  at  its  top  within  a  ring 
of  the  network  (Fig.  282,  d). 

Each  of  the  cells  of  Deiters,  described  above,  is  continued  upward  in  a 
process  which  is  attached  to  a  cross-bar  or  a  ring  of  the  reticulate  membrane 
next  outside  its  companion-cell  of  Corti.  The  inner  or  median  line  of  the 
Deiters  cell  is  also  modified  into  a  cuticular  thread  fused  below  to  the  basilar 
membrane  and  above  to  a  ring  of  the  reticulate  membrane.  Thus  the  audi- 
tory hair-cells  of  Corti  may  be  regarded  as  suspended  from  the  reticulate  mem- 
brane, which  in  tarn  is  supported  by  the  cuticular  processes  of  the  cells  of 
Deiters,  which  rest  upon  the  basilar  membrane,  and  by  the  phalangar  pro- 


824  AN   AMERICAN    TEXT-BOOK    OF  PHYSIOLOaV. 

cesses  of  the  nxls  of  Corti.  The  pliysical  contact  of  the  cells  of  Corti  with 
those  of  Deitei-s  is  so  intimate — if,  indeed,  their  substance  is  not  continuous — 
that  impulses  generated  in  the  one  can  probably  easily  be  communicated  to 
the  other. 

The  upper  wall  of  the  canalis  cochlearis  is  made  of  a  sheet  of  homogenous, 
fibrillated  connective  tissue  covered  with  flat  cells,  and  stretches  from  the 
lirnbus  of  the  spiral  lamina  outward  and  upward  to  the  side  wall  of  the 
cochlea.  It  is  known  as  the  membrane  of  Re'iHsner.  The  periosteal  con- 
nective tissue  of  the  bony  wall  of  the  cochlea  is  generall}''  well  developed 
within  the  area  enclosed  between  the  membrane  of  Reissner  and  the  membrana 
basilaris;  it  is  particularly  thick  at  the  line  of  division  between  the  scala  media 
and  the  seala  tympani,  where  it  forms  a  projecting  ridge  at  the  outer  attach- 
ment of  the  basilar  membrane.  This  ridge  is  the  spiral  ligament ;  an  exten- 
sion from  it,  gradually  decreasing  in  thickness,  reaches  into  both  the  vestibular 
and  the  tympanic  scala. 

A  thick  layer  of  both  columnar  and  cuboidal  epithelium  lines  the  con- 
nective tissue  forming  the  outer  wall  of  the  canalis  cochlearis.  This  epithe- 
lium is  peculiar  in  that  the  blood-vessels  of  the  underlying  connective  tissue 
penetrate  between  the  epithelial  cells  themselves.  The  tectorial  membrane 
{membrana  tectoria)  is  a  sheet  of  radially-fibrillated  tissue,  thin  at  its  point  of 
attachment  to  the  vestibular  lip  of  the  lirnbus,  and  becoming  thicker  and  then 
thinner  again  as  it  stretches  out  over  the  organ  of  Corti,  reaching  as  far  as  the 
most  external  row  of  hair-cells.  It  is  said  to  lie  in  actual  contact  with  the 
rods  of  Corti  and  the  free  ends  of  the  hair-cells,  and  it  has  been  presumed  to 
serve  as  a  damper  for  the  vibrations  imparted  to  the  organ  of  Corti. 

Theory  of  Auditory  Sensation. — It  may  now  be  mentioned  that  the 
generally-accepted  theory  of  auditory  sensation,  as  concerned  with  irn])ulses 
generated  in  the  cochlea,  supposes  that  the  vibrations  of  the  perilym})h,  the 
endolymph,  or  of  both  are  imparted  to  the  basilar  membrane.  This  membrane, 
from  its  fibrillated  structure,  may  perhaps  rightly  be  regarded  as  a  sheet  of 
parallel  w^ires  like  those  of  a- piano-board.  As  the  wires  of  a  piano  have  dif- 
ferent rates  of  vibration  according  to  their  length,  and  respond  .'sympathetically 
to  correspondingly  different  notes  sounded  in  their  neighborhood,  so  it  has  been 
supposed  that  different  radial  fibres  of  the  basilar  membrane  are  set  into  sym- 
pathetic vibration  by  different  rates  of  vibration  in  the  fluids  bathing  them. 
These  vibrations  must  be  imparted  to  the  structures  in  the  organ  of  Corti,  and 
the  irritation  of  the  nerves  connected  with  the  cells  of  Corti  is  a  natural 
sequel.  It  may  be  repeated  that,  though  the  canal  of  the  bony  cochlea  as  a 
whole  diminishes  in  diameter  from  base  to  cupola,  the  canal  of  the  mem- 
branous cochlea,  the  .scala  media  with  its  hnver  wall  or  basilar  membrane, 
increases  in  diameter.  Thus  the  radial  fibres  of  the  basilar  membrane  are 
longest  near  the  apex  of  the  cochlea.  The  radial  width  of  the  basilar  mem- 
brane, measured  near  the  bottom,  middle,  and  top,  rcsjiectivcly,  is  given  as 
.21  millimeters,  .34  millimeters,  and  .30  millimeters.  The  number  of  fibres 
of  the  basilar  membrane  is  said  to  be  24,000;   the  number  of  inner  hair- 


THE  SENSE    OF  HEARING.  825 

i^ells,  3500,  and  of  outer  hair-cells  in  four  rows,  12,000;  outer  rods  of  Corti, 
3850 ;  and  inner  rods  of  Corti,  5600. 

C.  The  Relation  between  Physical  and  Physiological  Sound. 

Production  of  Sound-"waves. — Sound,  in  its  physiological  meaning,  is  a 
sensation  which  is  the  conscious  appreciation  of  internal  clianges  occurring  in 
certain  cells  of  the  cerebral  cortex.  Fibres  of  the  auditory  nerve  come  into 
close  relation  with  those  cells,  and  in  whatever  way  those  fibres  are  excited 
the  result  is  one  and  the  same,  a  sensation  of  sound. 

The  elaborate  apparatus  of  the  middle  and  internal  ear  is  so  constructed 
that  the  energy  of  mechanical  oscillations  in  the  external  air  is  transmitted  to 
the  terminations  of  the  auditory  nerves  in  a  manner  to  excite  them. 

Sound,  in  a  physical  sense,  consists  in  waves  of  alternate  condensation  and 
rarefaction  travelling  in  the  air  from  the  point  of  origin  of  the  sound,  much  as 
waves  radiate  over  the  surface  of  water  from  the  point  where  a  stone  is  dropped. 
Any  sudden  impulse,  such  as  a  ])uff  of  air,  or  the  vibration  of  a  solid  body, 
as  a  stretched  string  or  a  tuning-fork,  pushes  the  adjacent  molecules  of  air 
against  those  further  removed,  and  this  impulse  produces  an  area,  or  aerial 
shell,  of  increased  density  or  condensation.  The  air  being  perfectly  elastic, 
the  molecules,  relieved  from  pressure,  spring  back  even  beyond  the  position 
of  equilibrium,  and  leave  an  area  of  decreased  density  or  rarefaction.  Thus 
a  wave,  consisting  of  a  shell  of  condensation  succeeded  by  a  shell  of  corre- 
sponding rarefaction,  moves  through  the  air.  This  single  air-wave  is  the 
simplest  element  of  physical  sound.  When  a  number,  no  matter  how  great, 
of  sound-waves  simultaneously  excite  the  same  particle  of  air,  the  resultant 
motion  of  that  particle  is  the  algebraic  sum  of  all  the  motions  imparted  to  it 
by  the  single  sound-waves  considered  separately.  As  any  elastic  body,  when 
set  vibrating,  continues  its  oscillations  for  a  time,  so  is  it  probable  that  strictly 
isolated  air- waves  do  not  occur.  Any  elastic  body,  such  as  a  stretched  string, 
or  a  tuning-fork,  when  set  in  vibration,  sends  out  from  itself  a  series  of  air- 
Avaves  which  succeed  one  another  at  a  rate  identical  with  the  rate  of  vibration 
of  the  elastic  body.  Such  a  regular  succession  of  air-waves  striking  upon  the 
tympanic  membrane  sets  the  latter  into  correspondingly  regular  oscillations 
and   produces  in  the  auditory  apparatus  the  sensation  of  musical  tone. 

Loudness  and  Musical  Pitch. — The  more  vigorous  the  vibrations  of  the 
oscillating  body,  the  more  forcibly  are  the  air-molecules  which  are  struck  by  it 
driven  forward ;  and  thfe  greater  their  excursion  or  amplitude  of  movement, 
the  greater  is  the  force  with  which  the  tympanic  membrane  is  driven  inward 
when  the  moving  air-wave  strikes  it.  The  loudness  of  the  tone  manifestly 
depends  upon  the  extent  of  motion  of  the  tympanic  membrane,  as  does  this  on 
the  amplitude  of  air-motion.  Diiferent  elastic  bodies  have  different  natural 
rates  of  oscillation.  The  more  rapid  the  rate,  the  more  frequent  is  the  succes- 
sion of  air-waves  that  strike  upon  the  ear.  Musical  pitch  is  determined  by 
the  number  of  air-waves  which  pass  a  given  point  in  a  unit  of  time,  or,  in 
other  words,  by  the  rate  of  vibration  of  the  sound-producing  body.     When 


826  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

the  vibration-rate  increases  the  pitch  is  elevated,  and  vice  versd.  If  some  l)ody 
capable  of  producing  .sound  should  have  its  rate  of  vibration  changed  grad- 
ually from  5  or  10  vibrations  per  second  to  50,000  per  second,  no  sensation 
of  sound  would  be  aroused  until  the  vibrations  reached  the  rate  of  about  from 
16  to  24  per  second.  The  droning  note  of  the  16-foot  organ-pipe  and  the 
lowest  bass  of  the  piano  represent  a  vibration-rate  of  33  per  second.  In 
most  persons  sounds  cease  to  be  audible  when  the  air- waves  have  a  fre- 
quency of  16,000  per  second,  though  to  some  the  note  produced  by  40,000 
vibrations  is  perceptible.  It  seems  clear  that  some  animals  hear  tones  whose 
pitch  is  so  elevated  as  to  make  them  inaudible  to  human  ears.  When  a  mov- 
ing bell  or  whistle,  as  of  a  locomotive,  rapidly  approaches,  its  pitch  seems  to 
rise,  and  then  to  fall  as  it  recedes.  The  reason  for  this  variation  is  that  the 
motion  of  the  locomotive  adds  to  or  subtracts  from  the  number  of  sound- 
waves reaching  the  ear  in  a  given  time.  In  musical  execution  and  in  the 
ordinary  uses  of  life  the  limits  in  the  pitch  of  sounds  are  much  narrower. 
Thus,  as  just  stated,  the  lowest  bass  of  the  piano  (Ci)  represents  a  vibration- 
rate  of  33  in  a  second,  while  the  highest  treble  [c'"")  has  that  of  4224.  As 
to  the  absolute  number  of  vibrations  necessary  to  produce  the  sensation  of 
sound,  it  has  been  found  that  2  or  3  vibrations  excite  the  sensation  of  a  mere 
stroke ;  4  or  5  vibrations  are  necessary  to  give  a  tone ;  and  some  20  or  40  are 
required  to  develop  the  full  musical  qualities  of  a  tone.'  That  is  to  say,  when 
a  musical  tone  falls  upon  the  ear  its  characteristics  cannot  be  appreciated  until 
20  to  40  vibrations  have  been  completed. 

Thus,  from  a  physical  scale  representing  aerial  vibrations  of  indefinitely 
various  rapidity  the  mind  selects  and  appreciates  as  sound  a  very  small 
fraction. 

Tympanic  Membrane  as  an  Organ  of  Pressure- sense. — There  is  good 
reason  to  suj)pose  that  variations  in  air-pressure  succeeding  one  another  too 
slowly  or  too  irregularly  to  produce  sound-sen.sation  are  still  of  great  import- 
ance in  the  extensive  realm  of  sensations  which  but  obscurely  excite  our  con- 
sciousness. Slow  inward  movements  of  the  tympanic  membrane  may  still 
give  rise  to  a  perception  of  external  changes.  Thus,  a  blind  man  has  been 
able  to  say  correctly  that  he  has  passed  by  a  fence,  and  whether  it  be  of  solid 
board  or  of  open  picket.  If  any  one  with  clo-sed  eyes  holds  a  book  at  half-arm's 
length  in  front  of  the  ear,  a  different  sensation  will  be  experienced  according 
as  the  book  is  turned  flat  or  edgewise  to  the  face ;  the  feeling  is  one  of  "  shut- 
in-ne&s"  or  "  open-ne.ss,"  respectively.  The  air  is  in  cea.seless  agitation,  and 
its  waves,  striking  against  various  objects,  must  be  reflected  to  the  ear  with  an 
intensity  dependent  on  the  position  and  the  physical  character  of  the  reflecting 
media.  AVe  may  assert  that  the  tympanic  membrane  is  the  peripheral  organ 
of  a  2iressiire-seyise  by  which  we  become  more  or  less  accurately  aware  of  the 
nature  and  position  of  surrounding  objects,  irrespective  of  the  .sensations  of 
sight  and  hearing.     Whether  that  group  of  sensations  depends  on  the  excite- 

^  Mach :  Physikallschen  Notizen  Lotos,  Aug.,  1873;  V.  Kries  unci  Auerbach :  Du  Bois-Rey- 
mond's  Archiv  filr  Physiologic,  1877,  p.  297 ;  Helmlioltz :  Sensations  of  Tone,  translated  by  Ellis. 


THE  SENSE  OF  HEARING.  827 

ment  of  tactile  nerves  iu  the  tympanic  membrane  or  of"  tlie  auditory  filaments 
in  the  internal  ear  is  yet  uncertain.'  Such  sensations  probably  form  an  import- 
ant quota  of  that  complex  system  of  sensations  which  do  not  obtrude  themselves 
on  consciousness,  but  which,  nevertheless,  bring  information  from  the  outer 
world,  and  have  an  intimate  association  with  the  more  or  less  reflex  move- 
ments that  preserve  the  equilibrium  of  the  body. 

Over-tones  and  Quality  of  Sound. — We  have  thus  far  considered  only 
simple  tones  produced  by  simple  vibrations  of  elastic  bodies.  Thus,  a  stretched 
string  plucked  at  its  middle  vibrates  throughout  its  whole  length,  the  greatest 
amplitude  of  movement  being  at  the  middle  point,  which  moves  to  and  fro 
like  a  pendulum.  It  is  very  rare  that  a  body  set  vibrating  confines  itself  to 
a  single  pendular  movement.  Thus,  a  stretched  string  when  struck  not  only 
moves  as  a  single  cord,  but  the  string  may  break  up,  as  it  were,  into  two  halves, 
each  vibrating  independently,  but  with  twice  the  rate  of  movement  of  the 
whole  length  of  string.  Not  only  is  this  the  case,  but  the  string  in  its  vibra- 
tion also  breaks  up  into  chords  of  one-third,  one-fourth,  one-fifth,  etc.  of  its 
original  length,  giving  rise  to  vibrations  three,  four,  and  five  times  as  rapid  as 
those  produced  by  the  whole  string.  In  musical  phrase,  the  middle  c  of  the 
piano,  when  this  key  is  struck,  gives  not  only  a  note  c  representing  132  vibra- 
tions, but  also  its  octave  c'  of  264  vibrations,  the  fifth  above  this  of  396 
vibrations,  the  second  octave,  528,  the  third  above  this,  660,  and  so  on.  The 
vibration  of  a  string,  then,  sends  to  the  ear  a  complex  series  of  tones  each  of 
■which  represents  a  simple  pendular  motion  of  the  air.  The  lowest  tone,  that 
produced  by  the  slowest  rate  of  vibration  of  the  string  as  a  whole,  is  known 
as  the  fundamental  tone. 

The  pitch  of  the  fundamental  tone  determines  our  estimate  of  the  pitch 
of  the  whole  complex  note.  The  other  tones  produced  by  segmental  vibration 
of  the  string  are  known  as  partial  tones,  upper  partials,  or  overtones.  The 
fundamental  tone  is  usually  stronger  than  its  accompanying  overtones,  the 
successively  higher  upper  partials  diminishing  rapidly  in  intensity.  Some 
musical  instruments  produce  notes  with  a  longer  series  of  overtones  than  do 
others ;  the  human  voice  is  particularly  rich  in  overtones.  Instruments  differ 
also  in  the  greater  or  lesser  strength  and  in  the  relative  prominence  of  the 
individual  overtones  accompanymg  the  fundamental.  It  is  the  number  and  the 
relative  prominence  of  the  overtones  in  a  musical  note  that  determine  its  quality. 
Thus,  a  violin,  a  cornet,  and  a  piano,  though  sounding  a  note  of  the  same 
pitch,  would  never  be  mistaken  the  one  for  the  other ;  our  discrimination  of 
their  notes  depends  simply  upon  the  difference  in  the  relative  strength  and  the 
number  of  their  overtones,  the  fundamental  tone  being  the  same  throughout. 
The  brilliancy  and  richness  of  musical  notes  is  dependent  on  their  w^ealth  of 
upper  partials.  It  is  believed  that  a  sound-producing  body,  like  a  stretched 
string,  does  not  send  to  the  ear  a  separate  set  of  waves  representing  each  of  its 
segmental  vibrations,  but  that  all  the  waves  aroused  by  it  fuse  together  into 
a  single  series  of  waves  of  peculiar  form.  Such  a  composite  wave  may  be 
^  W.  James :  Psychology,  1890,  vol  ii.  p.  140. 


828 


AN  AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 


represented  graj)liic'ally  by  depicting  under  one  another  a  series  of  waves  having 
two,  three,  four,  etc.  times  the  rate  of  succession  of  the  curve  indicating  the 
fundamental  tone.  If  a  vertical  line  be  drawn  across  the  series  representing 
the  vibration-rates  of  the  various  tones,  and  an  algebraic  addition  be  made  of 
the  distance  of  each  point  of  intersection  above  or  below  the  line  of  rest,  the 
result  will  determine  the  position  of  the  composite  curve  on  the  same  vertical 
(Fig.  283).  It  is  evident  that  the  form  of  the  composite  wave  must  change 
with  every  change  in  the  number  and  relative  prominence  of  musical  overtones, 
and  the  movement  imparted  by  it  to  the  tympanic  membrane  and  the  wave 


B    e 


Fig.  283.— The  curve  b  represents  twice  the  vibration-rate  of  a.  When  the  two  curves  are  combined 
by  the  algebraic  addition  of  their  ordinates,  the  result  is  the  periodic  curve  c  (solid  line),  having  a  dif- 
ferent form  ;  the  dotted  line  of  c  is  a  reproduction  of  a.  If  b  is  displaced  to  the  right  until  e  falls  under 
d  in  A  (change  of  phase),  the  combination  of  a  and  b  will  give  the  curve  d,  the  dotted  line  in  d  repre- 
senting A  as  before. 

generated  in  the  perilymph  must  have  corresponding  differences.  Notes  of 
different  quality  are  produced  by  composite  air-waves  of  different  forms.  But 
waves  differing  in  form  may  still  produce  notes  of  the  same  quality ;  for  if, 
in  the  graphical  figure,  one  or  more  of  the  curves  representing  simple  tones 
be  slid  to  the  right  or  the  left,  the  form  of  the  composite  wave  will  thereby  be 
changed,  but  not  the  quality  of  the  sound  jiroduced  by  it.  In  other  words, 
change  of  phase  of  the  partial  tones  does  not  alter  the  quality  of  the  note.' 
The  quality  of  any  complex  note  may  be  reproduced  by  sounding  together 
a  series  of  tuning-forks  which  have,  respectively,  the  vibration-rate  of  the 
fundamental  tone  and  that  of  one  of  the  overtones  of  the  complex  note. 

Analysis  of  Composite  Tones  by  the  Ear. — According  to  the  theory 
outlined  on  page  824,  the  composite  wave,  beating  against  the  sensitive  organ 
of  the  cochlea,  is  again  analyzed  into  the  elements  composing  it,  one  j)art  of 
the  basilar  membrane  vibrating  synij)athetically  with  one  partial  tone,  another 
with  another.  The  isolated  irritation  of  each  nerve-element  arouses  in  the 
mind  the  idea  of  a  tone  of  a  certain  pitch  and  loudness;  but  when  a  number 

'  Ilelmholtz,  op.  cit.,  pp.  ."0-34. 


THE  SENSE  OF  HEARING.  829 

of  sucli  elements  are  simultaneously  stimulated,  the  mind  takes  note,  not  of  thft 
individual  sensations  thereby  aroused,  but  of  a  resultant  sensation  formed  by 
the  fusion  of  these. 

That  apparently  simple  tones  are  actually  made  up  of  a  ninnber  of  partials, 
having  rates  of  vibration  which  form  simple  multiples  of  the  fundamental 
tone,  may  easily  be  demonstrated  at  the  open  piano.  If  any  note,  as  c  in  the 
bass  clef,  be  struck  -while  the  key  of  its  octave  c  is  depressed,  and  then  the 
struck  string  be  damped,  it  will  be  found  that  the  octave  c  rings  out  with  its 
proper  note.  So  in  turn  the  g  above  that,  the  second  octave  and  the  e  above 
that,  may  be  made  to  sound  when  the  lower  c  is  struck,  because  each  of  these 
strings  is  so  tuned  that  its  fundamental  note  has  the  same  vibration-rate  as 
one  of  the  overtones  of  the  lower  c.  A  note  sung  near  the  piano  may  in 
the  same  way  be  analyzed  more  or  less  completely  into  its  component  tones. 
The  organ  of  hearing  certainly  has  some  such  power  of  musical  analysis,  for 
some  cultivated  ears  can  not  only  follow  any  special  instrument  in  a  play- 
ing orchestra,  but  can  even  distinguish  the  overtones  in  a  single  musical 
note. 

The  ear  has  little  or  no  power  of  distinguishing  difference  of  pitch  in  tones 
of  less  than  40  or  more  than  4000  vibrations  per  second ;  but  in  the  upper 
median  parts  of  the  musical  scale  the  sensitiveness  to  change  of  pitch  is  very 
acute.  Thus,  according  to  Preyer,^  in  the  double-accented  octave  a  difference 
of  pitch  of  one-half  vibration  in  a  second  can  be  detected ;  that  is,  in  the 
octave  included  between  500  and  1000  vibrations  per  second,  1000  degrees  of 
pitch  can  be  perceived. 

Every  elastic  body  is  capable  of  sympathetic  vibration;  that  is,  air- waves 
beating  upon  it  at  its  own  natural  rate  of  vibration  set  it  into  corresponding 
motion.  In  the  same  manner  a  heavy  pendulum  may  be  forced  into  violent, 
movement  by  exceedingly  light  taps  with  the  finger,  the  only  necessary  condi- 
tion being  that  the  impulses  imparted  by  the  finger  be  exactly  timed  to  the 
periodic  motion  of  the  pendulum  or  to  some  multiple  of  it.  A  body  cai)able 
of  sympathetic  vibration  with  some  particular  tone  is  set  into  vibration  by  that 
tone,  and  reinforces  or  magnifies  it,  whether  the  tone  exists  alone  or  as  the 
fundamental  of  a  complex  note,  or  is  contained  in  the  latter  simply  as  an 
upper  partial. 

The  analysis  of  musical  sounds  is  usually  carried  out  by  the  use  of  resona- 
tors, which  are  hollow  cylinders  or  spheres  of  glass  or  of  metal,  rather  widely 
open  at  one  pole,  and  narrow-pointed  at  the  opposite  end  for  insertion  into 
the  ear.  The  mass  of  enclosed  air  vibrates,  according  to  its  size  and  shape, 
at  some  particular  rate,  and  it  is  very  readily  set  into  sympathetic  vibration 
whenever  its  fundamental  tone  is  contained  in  any  sound  reaching  it.  By  this 
means  it  is  possible  strongly  to  magnify,  and  thus  select,  the  individual  over- 
tones contained  in  a  note.  The  vowel  sounds  of  human  speech  owe  their 
difference  of  quality  to  the  adjustment  in  size  and  shape  of  the  resonant  air- 
chambers  above  the  vocal  cords. 

'  Veber  die  Grenzen  der  Tonwahrnehmuny,  June,  1876. 


8.30  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

Inharmonic  Overtones. — It  will  be  remembered  that  all  the  overtones  eon- 
tainecl  in  a  miisii-al  note  are  produced  by  vibrations  which  are  simple  multiples 
of  the  rate  of  the  fundiimental  tone.  These  overtones  are  properly  called 
harmonic  upper  partials  ;  they  are,  according  to  Helmholtz,  particularly  charac- 
teristic of  stretched  strings  and  narrow  organ-pipes.  But  most  clastic  bodies 
have  proper  tones  which  are  not  exact  multiples  of  the  fundamental,  and 
which  may  be  termed  inharmonic  upper  partials.  The  high-pitched  jingle 
heard  when  a  tuning-fork  is  first  struck  represents  the  inharmonic  upper  par- 
tials of  the  fork.  Stretched  membranes  have  a  great  number  of  such  inhar- 
monic overtones.  Inharmonic  upper  partials,  as  might  be  expected,  rapidly 
die  out  in  a  note  of  which  they  form  a  part.  It  is  evident  that  inharmonic 
proper  tones,  when  nearly  of  the  same  pitch,  must  interfere  with  one  another 
and  repress  the  development  of  a  well-marked  fundamental  tone. 

Production  of  Beats. — When  two  tones  of  slightly  different  pitch  are 
sounded  together,  the  more  rapid  vibrations  overtake  the  slower,  so  that  at 
certain  periods  the  crests,  or  phases  of  condensation,  of  two  waves  fall  together, 
and  the  result  is  a  phase  of  increased  condensation  and  louder  sound.  The 
waves  immediately  cease  to  correspond,  and  diverge  more  and  more  until  the' 
crest  of  one  falls  upon  the  trough  of  another,  the  result  being  silence,  or  at 
least  great  diminution  in  the  intensity  of  the  sound.  Such  alternate  augmenta- 
tion and  diminution  of  the  waves  give  rise  to  pulses  in  the  sound,  known 
technically  as  beats.  This  is  one  of  the  most  familiar  and  important  phenom- 
ena of  musical  art.  If  two  tuning-forks  on  resonance-boxes  vibrate  in  unison, 
a  piece  of  wax  stuck  to  the  prong  of  one  fork  will  lower  its  tone  and  give  rise 
to  beats.  The  undulating  sound  caused  by  striking  a  bell  or  the  rim  of  a  thin 
glass  tumbler  is  due  to  beats.  When  two  notes  not  included  in  a  perfect  chord 
are  sounded  on  the  piano,  beats  are  heard  not  only  from  the  interference  of  the 
fundamental  tones,  but  of  the  upper  partials  as  well.  It  is  the  absence  of  beats 
in  notes  which  should  be  in  harmony,  as  those  of  the  major  chord,  that  deter- 
mines the  instrument  to  be  in  tune.  When  two  tones  produce  beats,  the 
number  of  beats  in  a  given  time  is  equal  to  the  diiference  between  the  number 
of  vibrations  involved  in  the  two  tones  in  the  same  time.  For  example,  a  tone 
produced  by  256  vibrations  in  a  second  sounded  with  one  of  228  vibrations 
would  give  28  beats  in  a  second.  It  is  evident  that  the  frequency  of  beats 
may  be  increased  either  by  increasing  the  interval  between  the  tones  or  by 
striking  tones  of  the  same  interval  in  a  higher  part  of  the  scale.  Beats  which  are 
not  too  frequent — from  four  to  six  in  a  second — have  important  musical  value, 
but  when  they  number  thirty  or  forty  in  a  second  they  become  exceedingly  dis- 
agreeable, irritating  the  ear  in  a  manner  analogous  to  the  etlcct  of  a  flickering 
light  on  the  eye.  When  sufficiently  near  together  the  beats  no  longer  produce 
an  intermittent  sensation.  The  number  of  beats  in  a  second  required  to  result 
in  this  fusion  increases  as  we  ascend  the  musical  scale,  varying  from  16  beats 
at  c  of  64  vibrations  per  second  to  1 36  beats  at  c'"  of  1024  vil)rations.'  The 
reason  for  this  variation  lies  in  the  progressive  shortening  of  the  waves  as  the 

»  Mayer:  Sound,  1891. 


THE  SENSE  OF  HEARING.  831 

sound  becomes  higher  in  pitch ;  for  it  is  obvions  that  as  we  ascend  the  scale, 
and  the  waves  of  sound  become  progressively  shorter,  spaces  would  be  left 
between  the  individual  waves  unless  their  number  w^ei'e  jH'oportionately 
increased. 

Harmony  and  Discord. — Tones  are  concordant,  or  harmonize,  when  they 
produce  no  beats  on  being  sounded  together ;  thoy  are  di.HCOi-dant  wlien  beats 
are  produced,  and  the  painful  sense  of  dissonance  increases  in  intensity  up  to 
about  33  beats  per  second.  Perfect  concord  is  obtained  by  blending  notes 
whose  vibrations  are  to  each  other  as  small  whole  numbers. 

Thus,  in  tiie  major  cord  c  E  G  c 

the  vibration-numbers  are       132  165  198  264 

their  ratios  are  4  5  6  8 

If  notes  the  ratios  of  whose  vibration-rates  can  be  represented  only  by  large 
w'hole  numbers  are  combined,  a  discord  is  formed,  for  the  reason  that  their 
upper  partials  interfere  with  one  another  and  cause  beats ;  there  is  no  especial 
virtue  in  the  small  integer.^ 

Thus,  in  the  discord  c  D  E 

the  vibration-numbers  are  132  148.5  165 

which  are  not  reducible  to  small  whole  numbers.^ 

Combinational  Tones. — When  two  tones  are  sounded  together,  there  is 
produced  a  new,  usually  weaker,  tone,  whose  vibration-number  is  the  numerical 
difference  between  the  vibration-rates  of  the  original  tones.  It  is  therefore 
known  as  a  differential  tone.  Such  tones  may  arise  from  upper  partials  as  well 
as  from  the  fundamentals;  they  do  not  appear  to  be  formed,  as  might  be  sup- 
posed, by  the  fusion  of  beats.  Other  "combinational"  tones  of  more  intricate 
relations,  as  well  as  beats,  arise  from  the  interaction  of  vibrations  when  many 
different  notes,  as  those  of  an  orchestra,  are  sounded  together.  To  calculate 
the  physical  result  of  the  combination  of  these  impulses,  which  it  is  the  duty 
of  the  tympanic  membrane  to  transmit,  is  a  problem  of  exceeding  complexity. 

ReswiiL — To  sum  up  the  subject,  musical  sounds  are  distinguished  in  sen- 
sation by  the  three  factors,  loudness,  pitch,  and  quality,  sometimes  called  color 
or  timbre.  These  sensations  depend  in  turn  on  definite  physical  characters  of 
air-waves :  their  amplitude,  or  the  extent  of  motion  of  the  air-molecules  ;  their 
frequency,  or  rate  of  succession  of  the  waves;  their  form,  which  is  deter- 
mined by  the  pitch  and  relative  predominance  of  the  upper  partials  combined 
with  the  fundamental  tone. 

Fatigue. — That  the  ear  is  subject  to  fatigue  toward  a  note  that  has  been 
sounded  is  easily  demonstrated  in  the  following  way :  Strike  a  single  note  of, 
say,  a  major  chord  on  the  piano,  and  immediately  afterward  sound  the  full 
chord;  the  quality  of  the  latter  will  be  altered  from  its  normal  character, 
owing  to  the  lessened  prominence  of  the  note  which  had  been  struck.*  We 
may  therefore  not  improperly  speak  of  a  successive  contrast  in  auditory  sensa- 

*Tyndall:  Sound.  *  Waller:  Human  Physiology,  1891. 

*  Foster  :   Text-book  of  Physiology,  5th  ed.,  1891. 


832  ^.V   AMERICAN   TEXT- BOOK   OF  PHYSIOLOGY. 

tions,  analogous  to  visual  successive  contrast,  by  which  our  perception  of  every 
sound  is  colored  by  the  sounds  which  have  preceded  it. 

Imperfections  of  the  Ear. — Notwithstanding  the  mechanical  provisions 
for  making  the  external  and  middle  ear  a  j)erfect  transmitting  apj)aratus^ 
sound-perception  is  more  or  less  modified  by  the  action  of  the  mechanism 
under  certain  conditions.  Thus,  Helmholtz  believed  that  various  combina- 
tional tones  owe  their  origin  chiefly  to  a  perio<lic  clicking  in  the  joint  between 
the  malleus  and  incus  bones.  The  resonance  of  the  ear  is  a  familiar  fact, 
and  througli  it  high-pitched  tones  between  e""  and  g""  are  reinforced  and 
heard  with  undue  loudness.  Certain  hissing  sounds,  the  chirp  of  a  cricket  or 
the  note  of  a  locust,  thus  gain  their  intensity.  This  resonance  probably  is  a 
feature  of  the  external  auditory  meatus,  since  it  is  at  once  destroyed  by  apply- 
ing a  small  resonator  to  the  ear  (Helmholtz). 

Perception  of  Time  Intervals. — The  ear  is  eminently  the  sense  apparatus 
for  determining  small  intervals  of  time.  Flashes  of  light  succeeding  each 
other  at  the  rate  of  twenty-four  in  a  second  are  fused  in  a  continuous  luminous 
impression  by  the  eye,  but  by  the  ear  at  least  one  hundred  and  thirty-two  audi- 
tory impulses  as  beats  may  be  heard  separately  in  a  second.  The  |X)wer  which 
the  ear  possesses  of  resolving  complex  air-waves  into  the  host  of  pendular 
vibrations  which  may  enter  into  their  formation  finds  no  analogy  in  the  eye 
(Helmholtz). 

Musical  Tones  and  Noises. — The  important  feature  of  the  physical 
processes  which  give  rise  to  musical  tones  is  their  penodicifi/.  Every  musical 
tone  is  produced  by  a  regular  succession  of  alternate  rarefactions  and  condensa- 
tions in  the  air.  The  remaining  class  of  sounds,  known  as  noises,  differs  from 
musical  sounds  in  the  respect  that  such  sounds  are  j)roduced  by  an  irregular 
succession  of  air-waves — one  in  which  tlie  interval  between  phases  of  conden- 
sation and  rarefaction  does  not  remain  constant  as  in  a  musical  note.  Noises 
are  for  the  most  part  made  up  of  short  musical  notes  so  associated  as  not  to 
"  harmonize  "  with  one  another.  As  expressed  by  Helmholtz,  the  sensation 
of  a  musical  tone  is  due  to  a  rapid  periodic  motion  of  a  sonorous  body  ;  the 
sensation  of  a  noise,  to  non-periodic  motions. 

Functions  of  Different  Parts  of  the  Ear. — Concerning  the  functions  of 
the  different  parts  of  the  internal  ear  in  their  relation  to  sound-perception,  it 
is  generally  believed,  as  previously  stated,  that  the  basilar  membrane  of  the 
cochlea,  with  the  nervous  elements  seated  on  it,  is  the  organ  concerned  in  the 
reception  and  transmission  of  musical  sounds.  There  are  a  sufficient  number 
of  fibres  in  the  basilar  membrane  to  allow  several  to  vibrate  with  every 
audible  tone. 

It  cannot,  however,  too  strongly  be  impressed  that  no  theory  of  physiolog- 
ical action  should  be  accepted  definitively  without  rigid  experimental  proof,  and 
such  evidence  concerning  the  definite  functions  of  the  cochlea  is  almost  wholly 
wantinor.  The  sensorv  hair-cells  on  the  maculfe  of  the  saccule  and  the  utricle 
have  been  thought  to  have  the  duty  of  vibrating  in  response  to  any  agitation 
imparted  to  the  perilymph,  without  regard  to  its  periodic  character ;    they 


THE  SENSE  OF  HEARING. 


833 


might  thus  be  termed  sense  organs  for  the  perception  of  noises.  Evidence 
will  be  adduced  later  (p.  848)  lor  the  belief  that  they  are  peripheral  organs 
for  the  preservation  of  static  equilibrium. 

The  hair-cells  on  the  cristae  of  the  ampullse  of  the  semicircular  canals  seem 
to  have  a  special  function  in  giving  rise  to  sensations  caused  by  changing  the 
position  of  the  head  ;  they  thus  are  organs  concerned  with  the  preservation  of 
the  equilibrium  of  the  body. 

Judgment  of  Direction  and  Distance. — The  distance  and  direction  from 
which  sounds  come  to  the  ear  are  not  perceived  directly,  but  our  estimate  of 
them  is  a  judgment  based  on  the  loudness  and  quality  of  the  sound  sensation, 
combined  with  a  power  of  reasoning  from  past  experience.  Thus,  in  seeking  to 
discover  the  direction  whence  a  sound  comes,  it  is  usual  for  an  observer  to  turn 


Fig.  284.— End-bulbs  from  human  conjunctiva  (from  Quain,  after  Lo'fagworth) :  A,  ramification  of  nerve- 
fibres  in  the  mucous  membrane,  and  their  termination  in  end-bulbs,  as  seen  with  a  lens;  b,  end-bulb, 
highly  magnified ;  a,  nucleated  capsule ;  b,  core,  the  outlines  of  its  component  cells  not  seen ;  c,  entering 
nerve-fibre  branching,  its  two  divisions  to  end  in  the  bulb  at  d. 


the  head  to  the  position  in  which  the  sound  is  heard  loudest,  and  thus  to  form 
an  opinion  a.s  to  the  direction  whence  it  comes.  Errors  of  judgment  as  to  the 
direction  are  frequent,  owing  to  the  sound  reflected  from  some  object  appearing 
louder  than  that  coming  in  a  direct  line  from  its  source.  It  is  said  that  when 
there  is  total  deafness  in.  one  ear  every  sound  seems  to  have  its  origin  on  the 
side  of  the  healthy  ear.  The  quality  as  well  as  the  loudness  of  a  sound  varies 
according  to  the  distance  of  its  source.  Thus,  the  lower  tones  die  away  earliest 
as  a  sound  recedes,  bringing  the  overtones  into  undue  prominence.  The  art  of 
the  ventriloqui.st  consists  largely  in  altering  the  quality  of  the  sounds  he  pro- 
duces to  imitate  the  quality  they  would  naturally  have  if  arising  under  the 
conditions  which  he  would  lead  his  hearers  to  i)elieve  to  be  their  origin.  A 
comparatively  feeble  sound  near  at  hand  may  have  the  same  quality  as  a  loud 

53 


834 


AN   AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 


one  lieard  at  a  distance;  thas,  a  frog  croaking  in  an  adjoining  room  was  once 
niistaiceu  by  the  writer  lor  a  large  dog  barking  outside  the  building, 

D.  Cutaneous  and  Muscular  Sensations. 

General  Importance  of  the  Cutaneous  and  Muscular  Sensations. — 
Cutaneous  sensations  arc  aroused  by  the  operation  of  some  form  of  energy  on 
the  skin,  and  they  include  the  sensations  of  touch,  of  temperature,  and  of  pain. 
By  vimcular  sensatio)i  is  meant  the  appreciation  which  we  have  of  the  intensity 
and  direction  of  muscular  etibrt.  Closely  allied  to  this  sensation  is  a  yeneral 
■sensibility  through  which  we  gain  a  c 

knowledge  of  the  relative  position 
of  the  parts  of  our  bodies,  irrespec- 
tive of  movements.  The  direction, 
size,  distance,  and  surface  features 
of  external  objects  are  usually  made 
known  to  us  through  the  sense  of 


4..       ^C9t 


Fig.  28.').  — Tactile  corpuscle 
within  a  papilla  of  the  skin  of 
the  hand  (from  Quain,  after  Ran- 
vier) :  n,  n,  two  nerve-fibres  pass- 
ing to  the  corpuscle :  a,  a,  ter- 
minal varicose  ramifications  of 
the  axis-cylinder  within  the  cor- 
puscle. 


Fig.  286.— other  tactile  corpuscles  (from  Quain ;  a,  b,  after  Meckel ; 
c,  after  Fischer) :  a,  longit\idinal  section  showinjc  the  interior  trav- 
ersed by  connective-tissue  septa  derived  from  the  capsule  ;  the  nerve- 
fibres  are  cut  across,  b,  transverse  section  at  the  point  of  entrance 
of  a  nerve-fibre,  showing  the  axis-cylinder  branching;  other  fibres 
cut  obliquely,  c:  1,  entering  nerve-fibre,  medullated  ;  2,  2,  the  same 
cut  variously  within  the  corpuscle;  3,3,  clear  spaces  around  the 
fibres  ;  4,  4,  nuclei  of  the  transverse  and  spirally-disposed  cells  of  the 
corpuscle. 


sight  or  of  hearing.  Yet  these  fundamental  facts  regarding  the  things 
about  us  do  not  become  a  part  of  knowledge  through  direct  visual  and  audi- 
tory perception.  Such  knowledge  is  ba.sed  on  complex  judgments  concern- 
ing the  meaning  of  auditory  and  visual  phenomena  according  as  they  have,  in 
past  experience,  been  interpreted  by  tactile  and  mu.scular  perceptions.  That  is, 
when  reduced  to  its  simplest  terms,  our  most  practical  and  important  knowledge 
of  the  world  is  the  outgrowth  of  tactile  and  mu.scular  perceptions ;  by  and 
with  them  all  other  sense-perceptions  of  objects  have  been  corrected  and  com- 
pared.    Thus,  so  simple  a  feat  as  the  estimate  of  the  size  of  a  distant  object  is 


CUTANEOUS   AND    MUSCULAR    SENSATIONS. 


835 


the  result  of  a  complex  juilj^ment  bii-sed  on  tactile  aud  muscular  experience. 
Through  tlie  sense  of  sight  we  perceive  the  ratio  of  the  visual  angle  subtended 
by  the  object  to  that  of  the  whole  tield  of  vision;  but  as  objects  of  different 
size  may  fill  the  siuue  visual  angle  when  at  difierent  distances  from  the  eye, 
our  estimate  of  their  size  depends  upon  the  distance  at  which  we  suppose 
them  to  be  situated.  The  distinctness  of  the  surface  features  of  the  body 
af!brd  the  mind  an  important  clue,  since  experience  shows  that  details  of 
surface  in  a  body  become  more  obscure  as  we  recede  from  that  body.  But 
more  important  data  C(Micerning  distance  come  from  the  sense  of  muscular 
innervation,  or  feeling  of  the  intensity  of  nniscular  contraction,  by  which  we 
estimate  the  degree  of  convergence  of  the  optic 
axes  when  the  object  is  focussed,  and  still  more  by 
the  jierception  of  the  amount  of  muscular  effort 
necessary  to  sweep  the  optic  axes  over  the  ground 
surface  intervening  between  the  observer  and  the 
object.  When  objects  approach  the  near-point  of 
vision  the  sense  of  innervation  of  the  pupillary 
muscles  affords  important  evidence  of  their  distance. 

That  fundamental  etlucation  concerning  the  outer 
world  which  engages  the  earliest  years  of  every  child 
consists  in  accunmlating  aud  systematizing  with 
other  sense-perceptions  tactile  and  muscular  im- 
]>ressions  of  objects.  A  sensation  is  no  sooner  felt 
than  some  muscular  movement  involving  a  definite 
muscular  feeling  is  made  by  which  the  character  of 
the  sensation  is  changed  and  experimentally  tested 
under  different  conditions.  The  physiological  pro- 
cess involved  in  building  up  sense-knowledge,  there- 
fore, embraces  in  alternation  sensation  excited  by 
external  objects,  motion  accompanied  by  muscular 
sensation,  and  change  in  the  original  sensation.  In 
other  words,  the  motor  and  sensory  impulses  form  a 
sort  of  balance,  and  both  are  necessary. 

Ending-  of  Sensory  Nerve-fibres  in  the  Skin. — 
The  afferent  nerves  supplied  to  the  skin  have  several 
modes  of  termination.  In  the  commonest  form  the 
plexus  of  medullated  nerve-fibres  found  in  the  dermis 
close  under  the  epidermis  gives  off  twigs  which,  losing  the  medullary  sheath, 
pierce  the  epidermis  and  here  form  a  network  among  the  cells  of  the  Mal- 
pighian  layer,  the  single  fibres  ending  freely  in  this  position  (Fig.  294).  Other 
sensory  nerves  do  not  penetrate  the  epidermis,  but  end  in  various  peculiar 
terminal  organs  in  the  dermis  or  in  the  subcutaneous  tissue  underneath.  These 
terminal  organs  are  known  respectively  as  end-bulbs,  touch-corpuscks,  and 
Pacinian  bodies  (Figs.  284-287).  Each  organ  consists  of  a  more  or  less  conical 
bodv  in  which  a  nerve-fibre  terminates.     The  end-bulbs  are  found  only  on  the 


Fig.  iST.-Magnified  view  of  a 
Pacinian  body  from  the  cat's 
mesentery  (from  Quain,  after 
Ranvier):  n,  stalk  with  ner\'e- 
fibre  enclosed  in  sheath  of  Henle, 
passing  to  the  corpuscle;  u',  its 
continuation  through  the  coil,  tn, 
as  a  j«ile  fibre ;  a,  termination  of 
the  nerve  in  the  distal  end  of  the 
core  (the  terminations  are  not 
always  arborescent^ ;  rf,  lines 
separating  the  tunics  of  the  cor- 
puscles; /,  channel  through  the 
tunics,  traversed  by  the  nerve- 
fibre  ;  c,  external  tunics  of  the 
corpuscle. 


83(3  AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

Senilis  of  tlie  conjunotiva  and  the  lips,  and  in  modified  form  on  the  sensitive 
surfaees  of  the  genital  organs  (Fig.  284).  The  toach-corpi(sc/e.s,  though  appar- 
ently absent  from  the  greater  part  of  the  body,  occur  in  great  nmnbers  in  the 
sUin  of  the  palmar  surface  of  the  hand  and  that  of  the  fingers,  especially  at 
their  tips;  at  the  edge  of  the  eyelids  and  the  lii)s;  on  the  soles  of  the  feet 
and  the  toes ;  and  on  the  surface  of  the  genital  organs.  The  touch-corpuscle 
often  occupies  a  papilla  of  the  dermis  directly  under  the  epidermis  (Fig.  285). 
The  Pacinian  bodie.s,  which  are  oval  corpuscles,  larger  than  the  foregoing, 
and  easily  visible  to  the  unaided  eye,  are  found  not  in  the  skin  proper,  but 
in  the  subcutaneous  connective  tissue  beneath  it.  They  are  found  in  abundance 
beneath  the  skin  of  the  })alm  of  the  hand  and  the  sole  of  the  foot;  they  are 
also  numerous  along  the  nerves  of  the  joints,  and  even  among  the  sympathetic 
nerves  supplying  the  abdominal  organs  (Fig.  287).  Sensory  nerves  also  end 
in  tendons  as  somewhat  arborescent  exi)ausions  of  axis-cylinder  matter  known 
as  the  organs  of  GoUji,  and  in  muscles  near  their  tendinous  attachments. 

1.  Sense  of  Touch. — The  Relations  between  Sensation  and  Stimulus. — 
Many  so-called  "  tactile  sensations,"  such  as  wetness,  hardness,  roughness,  etc., 
are  not  simple  sensations  at  all,  but  are  complex  judgments  built  up  out  of  the 
association  of  certain  tactile,  temperature,  and  nmscular  sensations,  and  con- 
veying to  us  a  knowledge  of  the  surface,  substance,  and  form  of  bodies. 

AVhen  analyzed,  the  sense  of  touch  is  nothing  more  than  a  sense  o^ pressure 
applied  to  the  skin.  To  test  the  pressure  sensihiliiy  of  the  skin  the  object 
whose  weight  is  to  be  estimated  must  not  be  lifted  in  the  ordinary  way,  for 
that  would  bring  into  j)lay  the  muscular  sensations.  If  the  skin  of  the  hand 
is  to  be  tested,  the  hand  must  be  placed  upon  some  firm  support,  such  as  a 
table,  and  the  weights  be  laid  upon  the  skin.  The  smallest  perceptible  weight 
that  can  thus  be  felt  varies  with  the  situation  to  which  it  is  api)lied.  Thus, 
the  greatest  sensitiveness  to  pressure  is  found  on  the  forehead,  the  temples, 
the  back  of  the  hand,  and  the  forearm,  where  a  weight  of  .002  gram  (^ 
grain)  can  be  perceived.  The  Aveight  nuist  be  increased  to  .005  to  .015  gram 
to  be  felt  by  the  fingers,  and  to  1.0  gram  when  laid  on  the  finger-nail.^ 

The  power  of  discriminating  differences  of  pressure  applied  to  the  skin  is 
tested  by  finding  the  smallest  increase  that  must  be  added  to  a  weight  in  order 
that  it  may  be  perceived  as  being  heavier.  This  increment  is  not,  as  might 
be  supposed,  the  same  for  weights  of  different  value,  but  it  bears  a  distinct 
proportion  to  them.  Thus,  a  weight  of  11  grains  may  just  be  perceptibly 
heavier  than  one  of  10  grains;  but  if  we  start  with  a  weight  of  100  grains, 
a  sinirle  iri'ain  added  to  it  will  arouse  no  difference  of  sensation,  an  increment 
of  10  grains  being  necessary  in  order  that  one  weight  may  a])j)car  heavier 
than  the  other.  This  fact  is  the  basis  for  Weber's  law  of  the  relation  between 
stimulus  and  sensation;  this  law  may  be  formulated  as  follows:  T7ie  amount 
of  stimulus  necessary  to  provoke  a  perceptible  increase  of  sensation  always  bears 
the  .same  ratio  to  the  amount  of  stimulus  already  applied.  This  law  is  found 
to  be  only  approximately  correct,  especially  when  very  small  and  very  large 
'  Aubert  and  Kammler:  MoleKchotCs  Untersnehungen,  1859,  vol.  v.  p.  145. 


TIIH   SKXSK    OF    rilESSURE.  837 

weights  lire  compaml.  I'Vcliiicr  attempted  to  express  more  exiidly  the  ivlation 
between  the  intensity  of  stinuilns  and  sensation  in  liis  "  psyelio-physical  law," 
tlnis:  The  Intemity  of  Komdion  varle.s  with  the  hf/arithm  of  the  dimiilns.  In 
other  words,  the  sensation  increases  in  arithmetieal  progression,  while  the 
stimulns  increases  in  geometrical  jirogression.  With  moderate  weights  a 
difference  of  ])ressnrc  is  perceptible  when  the  ratio  of  increase  is  smaller  tiian 
when  either  very  small  or  very  large  weights  are  nsed  ;  that  is,  sensitiveness 
to  jn-essnre-change  is  keenest  under  moderate  stimulation. 

It  is  said  that  the  forehead,  the  lips,  and  the  temples  appreciate  an  increase 
of  -jJ^^  to  ^V  of  t^'C  weight  estimated,  while  the  skin  of 'the  head,  the  fingers, 
and  the  fijrearm  requires  an  increase  of  ^\  to  j\  for  its  perception.  In  this 
as  in  other  kinds  of  sensation  it  is  the  difference,  or  variation  of  intensity,  of 
the  sensation  of  which  the  mind  takes  particular  cognizance.  One  touch- 
sensation  is  more  acutely  perceived  when  contrasted  with  another  than  wlien 
felt  alone.  Weber  ^  found  the  discrimination  of  pressure-differences  to  be 
finer  when  two  weights  were  laid  in  rapid  succession  on  the  same  skin-area 
than  when  the  weights  were  applied  either  sinniltaneously  or  successively  to 
different  parts.  If  a  finger  be  dipped  in  a  cup  of  mercury  or  of  water  having 
the  same  temi)erature  as  the  skin,  the  pressure  will  be  marked  only  at  the 
margin  between  the  air  and  the  fluid,  and  if  the  finger  be  moved  up  and 
down  it  will  seem  as  if  a  ring  were  being  slid  back  and  forth  njwn  it.  Tiie 
fingers  are  particularly  sensitive  to  intermittent  variations  of  pressure— a 
factlity  the  use  of  wliich  is  manifest  when  the  function  of  these  parts  is 
considered. 

Two  weights,  in  being  tested,  should  press  upon  equal  areas  of  skin ;  accord- 
incr  to  Weber,^  if  two  equal  weights  have  different  superficial  expanse,  that 
which  touches  the  larger  skin-surface,  and  thereby  excites  the  greater  number 
of  touch-nerves,  will  appear  to  be  the  heavier.  This  result,  however,  cannot 
always,  nor  indeed  usually,  be  verified.  The  simultaneous  excitement  of  other 
sensations  may  modify  that  of  pressure ;  thus,  when  two  coins  of  equal  weight, 
but  one  warm  and  the  other  cold,  are  laid  upon  the  hand  or  the  forehead,  the 
cold  one  appears  to  be  much  the  heavier. 

There  is  a  sensation  of  after-pressure  depending  for  its  strength  on  the 
amount  of  the  weight  and  the  length  of  time  this  weight  has  been  applied. 
In  fact,  this  after-sensation  may  produce  a  striking  effect  on  consciousness, 
a  familiar  example  of  which  is  the  persistence  of  the  sense  of  pressure  of 
the  hat-band  after  the  head-covering  is  removed.  Even  light  weights  leave 
an  after-sensation,  and,  in  order  to  be  perceived  as  separate,  must  be  applied  at 
intervals  of  not  less  than  -j|^  to  g|o  of  a  second.  It  is  said  that  when  the 
finger  is  applied  to  the  rim  of  a  rotating  wheel  provided  with  blunt  teeth,  the 
sep'arate  teeth  are  no  longer  felt,  and  the  margin  seems  smooth,  when  the  con- 
tacts succeed  each  other  at  the  rate  of  500  to  600  in  a  second.'     Vibrations  of 

1  "Tastsinn  nnd  Gemeinsefiihl,"  Wagner's  Handnwierbuch  der  Pkysiolngie,  1846. 
'Quoted  in  Hermann's  Handbuch  der  Physiologie,  Bd.  iii.  2,  S.  336. 
=*  Landois  and  Stirling:  Human  Physiology,  1886. 


838  ^l.y  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

a  string  cease  to  be  api)reciate(l  by  the  finger  when  tliey  have  a  rate  of"  between 
1500  and  1600  per  second. 

Tlie  Localization  of  Touch-sensation. — When  a  touch-sensation  is  felt,  the 
mind  inevitably  refers  the  irritation  to  some  particular  part  of  the  surface 
of  the  body,  and  the  sensation  seems  to  be  localized  in  this  area.  On  the 
accurate  localization  of  tactile  sensations  depends  not  only  the  safety  of  the 
individual,  but  also  the  performance  of  the  ordinary  acts  of  life. 

We  may  suppose  that  to  each  area  of  peripheral  distribution  of  tactile 
nerve-fibres  in  the  skin  there  corresponds  an  area  of  tactile  nerve-cells  in  the 
brain.  It  can  hardly  be  doubted  that  the  nerve-cells  are  divided  into  physio- 
logical groups  characterized  l)y  inherent  and  inborn  quality-ditierences  in  the 
sensations  aroused  by  their  respective  excitements.  The  reference  of  the  sen- 
sations aroused  by  the  excitement  of  definite  nerve-cells  to  definite  parts  of  the 
periphery  is  a  power  acquired  through  the  physiological  experiences  of  the 
earliest  months  of  life.  Through  the  sense  of  sight  the  seat  of  irritation  is 
recognized,  and  through  muscular  sensation  its  relation  to  surrounding  parts 
is  experimentally  explored,  so  that  cunmlative  harmonious  experiences  of  tactile, 
visual,  and  muscular  sensations  finally  bring  into  correspondence  the  various 
areas  with  definite  varieties  of  touch-sensation,  or,  to  use  an  expression  of 
Lotze's/  every  area  of  the  skin  acquires  a  "  local  sign  "  by  which  it  is  dis- 
tinguished in  consciousness. 

This  power  of  localization  differs  widely  for  different  parts  of  the  skin. 
The  fineness  of  the  localizing  sense  for  any  skin-area  is  easily  estimated  by 
determining  how  far  apart  the  tips  of  a  pair  of  compasses,  applied  to  the  skin, 
must  be  separated  in  order  to  be  felt  as  two.  For  this  experiment  the  compass- 
points  must  be  smooth,  and  they  should  not  be  applied  heavily.  The  general 
result  of  such  an  inquiry  is  that  the  compass-points  may  be  nearer  together, 
and  still  be  distinguished  as  two,  in  proportion  as  the  surfaces  to  which  they 
are  applied  have  greater  mobility.  Since  it  is  just  such  parts  of  the  body  as 
the  tips  of  the  tongue  and  the  fingers  that  are  chiefly  used  in  determining  the 
position  of  ol)jects,  the  advantage  of  such  an  arrangement  is  obvious.  The 
skin  can  thus  be  marked  out  in  area.s  (tactile  areas)^  within  each  of  which  the 
compass-points  are  felt  as  a  single  object,  but  if  they  are  separated  so  as  to  fall 
beyond  the  borders  of  these  areas,  they  are  at  once  perceived  to  be  two. 

The  following  figures"  represent  the  distances  at  which  the  compass-points 
can  just  be  distinguished  as  double  when  applied  to  various  parts  of  the  body : 

Tip  of  tongue 1-1  mni. 

Palm  of  last  phalanx  of  finger 22" 

Palm  of  second  phalanx  of  finger ,    .    .    .    .      4.4     " 

Tip  of  nose <'-6     " 

Back  of  second  phalanx  of  finger H.l     " 

Back  of  liand 29.8    " 

Forearm -^9.6 

Sternum 44 

Back 66        " 

'  Kunke.  in  Hermann's  Ifandbuch  der  Physiologie,  Bd.  iii.  2,  S.  404. 

2  Foster's  Physiology,  5th  ed.,  1891. 


THE  SENSE    OF  PRESSURE. 


839 


It  will  be  observed  that  accuracy  of  localization  and  sensitiveness  to  pre»5ure 
find  their  most  perfect  manifestations  in  widely  separate  regions  of  the  skin. 

Tactile  areas  are  found  to  have  a  general  oval  form  with  the  long  axis 
parallel  with  the  long  axis  of  the  member  investigated.    If  the  compass-points, 
separated,  say,  half  an  inch  apart,  be  pa.«^sed  over  the  skin  of  the  palm  from 
the  middle  of  the  hand  to  the  finger-tips,  the  sensation  will  be  that  ot  a  single 
line  gradually  separating   into  two  diverging   lines.     The  result,  of  course, 
depends  on  the  compass-points  passing  successively  through  areas  of   finer 
localization.     If  an  area  be  marked  out  on. a  part  of  the  skin  where  localiza- 
tion is  poor,  within  which  area  two  points  simultaneously  applied  appear  to  be 
one;  a  single  point  moved  within  it  is  still  perceived  to  change  its  place,  and 
two  points  successively  applied  may  be  perceived  to  occupy  different  positions 
The   mental   fusion  or  separation  of  the  two  compass-points  cannot  depend 
altogether  on  their  being  placed  over  the  terminal  twigs  of  the  same  or  of  two 
adjoining  nerve-fibres,  for,  were  this  the  case,  the  points  could  be  discriminated 
when  separated  by  a  verv  small  distance  across  the  line  drawn  between  the 
endinos  of  adjoining  nerve-fibres,  while  on  either  side  the  points  would  have 
to  be  much  more  widely  separated  in  the  area  of  distribution  of  a  single  filjre. 
The  important  factor  in  the  mental  separation  of  two  stimulated  points  is,  that 
between  such  points  there  shall  be  found  a  certain  number  of  sensory  elements 
which  are  unstimulated.^     Practice  in  such  experiments  greatly  increases  the 
power  to  localize  impressions.     This  improvement  is  evidently  due  not  to 
the  establishment  of  new  nerves,  but  to  a  more  perfect  discrimination  of  sen- 
sations in  the   nerve-centres.     When,  by  practice,  the  localizing  power  of 
the  skin  of  a  finder  of  one  hand  has  been  increased,  it  is  found  that  the 
same   improvement  has  been  acquired  by  the  corresponding,  but  untrained, 
fino-er  of  the  other  hand ;  in  other  words,  the  localizing  power  is  central, 

not  peripheral. 

Presmre-points.— It  has  been  found  that  if  a  light  object,  such  as  a  lead- 
pencil,  be  allowed  to  rest  by  a  narrow  extremity  successively  on  different  parts 
of  the  skin,  its  weight  will  appear  very  different  according  to  the  part  which 
is  touched.  If  the  spots  on  which  the  weight  appears  greatest  be  marked  with 
ink,  they  will  be  found  to  have  a  constant  position,  and  the  skin  may  therefore 
be  mapped  out  in  areas  of  pi-essure-points,  which  are  believed  to  indicate  the 
place  of  ending  of  pressure-nerve  filaments. 

The  Importance  of  the  End-organ.— The  sense  of  touch  or  pressure  is  a 
special  sense;  that  is,  any  irritation  conveyed  to  the  nerve-centres  in  which 
the  nerves  of  pressure  terminate  gives  rise  to  a  feeling  of  touch,  just  as  dis- 
turbance in  the  visual  or  the  auditorv  centre  is  recognized  in  consciousness  as 
a  sensation  of  sight  or  of  sound.  The  complex  anatomical  structures  known  as 
sense-organs  may  be  considered  as  instruments  each  of  which  is  differentiated 
in  a  manner  to  make  it  particularly  irritable  toward  some  special  form  of 
energy.  Thus, the  retina  is  most  sensitive  to  the  luminiferous  ether;  the  organ 
of  Corti,  to  waves  of  endolymph,  etc.     To  this  differentiation  of  structure  the 

1  Weber:  "Tastsinn  und  Gemeingefuhl,"  Wagne/s  Handworterbuch  der  Physiologic,  1846. 


840  AX  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

sensitiveness  of  the  body  to  the  forces  of  nature  is  chicHy  due.  'J'lic  j)erij)lieral 
ending  of  the  pressure  nerve,  whether  a  naked  axis-cylinder  or  a  touch-corpus- 
cle, is  no  doubt  niodificd  to  be  particidarly  irritable  toward  that  form  of  energy 
manifested  in  the  molecular  vibration  of  the  tissue  solids,  brought  about  by 
contact  with  foreign  objects. .  Hairs,  j)articularly  those  in  certain  localities  of 
some  animals,  as  the  whiskers  of  the  cat,  appear  to  have  the  function  of  trans- 
mitting mechanical  vibrations  to  the  nerve-endings  in  greater  intensity  than 
could  be  accomplished  through  the  skin  alone. 

No  true  sense  of  touch  is  aroused  by  direct  irritation  of  a  nerve-trunk  or 
exposed  tissue,  and  touch-sensations  do  not  arise  from  iri'itation  of  the  internal 
surfaces  of  the  body.  A  fluid  of  the  temperature  of  the  body  gives,  when 
swallowed,  no  sensation  in  the  stomach  ;  wlien  cooler  or  warmer  than  the 
body,  there  is  a  sensation  due,  probaljly,  to  a  transmission  of  temperature 
chanyce  to  the  skin  of  the  abdomen. 

Touch  Illusions. — Certain  peculiar  errors  in  judgment  may  arise  when 
tactile  sensations  are  associated  in  a  manner  unusual  in  experience.  Thus,  in 
an  experiment  said  to  have  b^en  devised  by  Aristotle,  if  the  forefinger  and 
the  middle  finger  be  crossed,  a  marble  rolled  between  their  tips  will  appear  to 
be  two  marbles;  if  the  crossed  finger-ends  be  applied  to  the  tip  of  the  nose, 
there  seems  to  be  two  noses.  The  illusion  is  due  to  the  fact  that  under 
ordinary  circumstances  simultaneous  tactile  sensations  from  the  radial  side  of 
the  forefinger  and  the  ulnar  side  of  the  middle  finger  are  always  caused  by 
two  different  objects.  It  is  a  not  uncommon  surgical  o})eration  to  replace  a 
loss  of  skin  on  the  nose  by  cutting  a  flap  in  the  skin  of  tiie  forehead,  without 
injury  to  the  nerves,  and  sliding  the  flap  round  ujjon  the  nose.  Touching 
the  piece  of  transplanted  skin  gives  the  patient  the  sensation  of  being  touched, 
not  upon  the  nose,  but  upon  the  forehead ;  after  a  time,  however,  a  new  fund 
of  experience  is  accumulated,  and  the  sensation  of  contact  with  the  transplanted 
flap  is  rightly  referred  to  the  nose.  Persons  who  have  suffered  amputation  of 
a  lower  limb  often  complain  of  cramps  and  other  sensations  in  the  lost  toes. 
The  illusion  no  doubt  comes  from  irritation,  in  the  nerve-stump,  of  fibres 
which  previously  bore  irritations  from  the  toes. 

2.  Temperature  Sense. — The  skin  is  also  an  organ  for  the  detection  of 
changes  of  temperature  in  the  outer  world.  Such  temj)erature  difllerenccs  ]>rob- 
ably  make  themselves  manifest  by  raising  or  lowering  the  temperature  of  the 
skin  itself,  and  thus  in  someway  irritating  the  terminal  parts  of  certain  sensory 
nerves,  the  tonperature  nerves.  The  sensitiveneas  of  the  skin  to  temj)erature 
variations  is  not  the  same  in  all  parts;  thus,  it  is  more  acute  in  the  skin  of  the 
face  than  in  that  of  the  hand  ;  in  the  legs  and  the  trunk  the  sensibility  is  least. 
We  refer  temperature  sensations,  somewhat  like  those  of  touch,  to  the  peri|)hcry 
of  the  body,  and  localize  them  on  the  surface.  The  skin  over  various  parts 
of  the  body  may  have  different  temperatures  without  exciting  corresponding 
local  differences  of  sensation.  Thus,  the  forehead  and  the  hand  usually  seem 
to  be  of  the  same  temperature,  but  if  the  palm  be  laid  upon  the  teniples, 
there  is  commonly  felt  a  decided  sensation  of  temperature  change  in  one  or 


THE  SENSE    OF   TEMPERATURE. 


841 


both  surfaces.  As  iu  other  sensations,  fatigue  and  contrast  play  an  ini}K)rtant 
j)art  in  the  sense  perceptions  of  temperature,  and  stimuli  of  rapidly-changing 
intensity  provoke  the  strongest  sensations;  thus,  when  two  fingers  are  both 
dipped  into  hot  or  cold  water,  the  Huid  seems  hotter  orcolder  to  that  finger 
which  is  alternately  raised  and  lowered. 

In  changing  to  a  place  of  different  temperature  the  skin  for  a  time  seems 
warmer  or  cooler,  but  soon  the  temperature  sensation  declines,  and  on  return- 
ing to  the  original  temperature  the  reverse  feeling  of  cold  or  of  warmth  is 
experienced.  For  every  part  of  the  skin,  then,  there  is  a  degree  of  tempera- 
ture, elevation  above  or  depression  below  which  arouses  respectively  the 
feeling  of  warmth  or  of  cold,  and  the  temperature  of  the  skin  determining 
the  pliysiological  null-point  may  vary  within  wide  limits. 

The  smallest  differences  of  temperature  that  can  be  perceived  fall,  for  most 
parts  of  the  skin,  within  1°  C.  The  skin  of  the  temples  gives  perception  of 
differences  of  0.4°-0.3°  C.  The  surface  of  the  arm  discriminates  0.2° ;  the 
hollow  of  the  hand,  0.5°-0.4° ;  the  middle  of  the  back,  1.2°.^ 

The  size  of  the  sensory  surface  affected  modifies  the  intensity  of  temperature 
sensation  :  if  the  Avhole  of  one  hand  and  a  single  finger  of  the  other  hand  be 
dipped  into  warm  or  cold  water,  the  temperature  will  seem  higher  or  lower  to 
the  member  having  the  greatest  surface  immersed. 

Cold  and  Warm  Points. — The  skin  is  not  uniformly  sensitive  to  tem- 
perature changes,  but  its  appreciation  of  them  seems  to  be  limited  to  certain 
points  distributed  more  or  less  thickly  over  the 
surface.  These  spots  appear  to  be  the  places  of 
termination  of  the  temperature  nerves  in  the  epi- 
dermis (Fig.  288).  There  is  little  doubt  that  there 
are  two  distinct  varieties  of  temperature  nerves, 
one  of  which  appreciates  elevation  of  temperature, 
or  heat,  and  the  other  diminution  of  temperature, 
or  cold.  Thus,  if  a  blunt-pointed  metal  rod  be 
warmed  and  be  touched  in  succession  to  various 
parts  of  the  skin,  at  certain  spots  it  will  be  felt  as 
very  warm,  while  at  others  it  will  not  seem  warm 
at  all.  If,  on  the  contrary,  the  rod  be  cooled,  a 
series  of  cold  points  may  in  the  same  way  be  made 
out.  The  point  of  an  ordinary  lead-pencil  may 
be  used  with  some  success  to  pick  out  the  cold 
spots.  The  "  cold  points "  are  more  numerous 
than  the  "  hot,"  and  those  of  each  variety  are 
more  or  less  distinctly  grouped  round  centres,  as 
would  be  expected  from  the  manner  of  nerve-distribution,  though  the  groups 
overlap  to  some  extent  (Fig.  288).  Certain  substances  appear  to  act,  prob- 
ably by  chemical  means,  as  specific  excitants  of  the  two  sets  of  nerves. 
Thus,  menthol  applied  to  the  skin  gives  a  sensation  of  cold,  while  an  atmo- 
'  Nothnagel:  Deutsche.  Archiv/iir  fcUnische  Medicin,  1866,  ii.  S.  284. 


Fii;.  -JSN— Cutaneous  "cold"  spots 
(vertical  shading)  and  "hot"  spots 
(horizontal  shading),  anterior  sur- 
face of  the  thigh  (from  Waller,  after 
Goldseheider). 


842  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

spliere  of  carbon  dioxide  surrouiidiug  uii  area  of  skin  gives  a  sensation  of 
Avarnitli.' 

The  specific  difference  of  the  two  sets  of  temperature  nerves  is  indicated  by 
the  fact  that  when  a  warm  and  a  cold  body  held  close  together  are  simulta- 
neously brought  near  the  sUiii,  the  sensation  is  either  one  of  both  warmth  and 
cold,  or  now  one  and  now  the  other  sensation  predominates.^  Any  stimulation, 
whether  mechanical  or  electrical,  applied  to  the  sensitive  points  thus  far  de- 
scribed in  the  skin,  for  the  appreciation  of  either  pressui'e,  heat,  or  cold,  pro- 
vokes, when  effective,  only  the  proper  sensation  of  that  point ;  any  irritation 
of  a  cold,  hot,  or  pressure  point  gives  rise,  respectively,  to  the  sensation  of 
cold,  heat,  or  pressure  alone. 

As  in  other  organs  of  special  sense,  the  peripheral  terminations  of  the 
temperature  nerves  seem  modified  to  be  especially  irritable  toward  their  appro- 
priate form  of  physical  stimulus.  Cold  or  heat  directly  applied  to  the  nerve- 
trunk  excites  no  temperature  sensation.  Thus,  if  the  elbow  be  dipped  into  a 
freezing  mixture,  as  the  lowered  temperature  penetrates  to  the  ulnar  nerve  the 
sensation  will  be  one,  not  of  cold,  but  of  dull  pain,  and  it  will  be  referred  to 
the  hand  and  the  fingers.  The  internal  nuicous  surfaces  of  the  body,  from 
the  oesophagus  to  the  rectum,  inclusive,  have  no  power  of  discriminating 
temperature  sensations  ;  a  clyster  of  water  cooled  to  from  7°  to  16°  C,  if  not 
held  too  long,  is  only  perceived  as  cold  when  the  water  escapes  through  the 
skin  of  the  anus. 

Tiie  doctrine  of  specific  nerve  energy,  enunciated  by  E.  H.  AVeber,  was 
intended  to  convey  the  idea  elaborated  above,  that  each  nerve  of  special  sense, 
however  irritated,  gives  rise  to  its  own  peculiar  quality  of  sensation.  But  it 
seems  clear  that  the  existence  and  quality  of  the  sensation  are,  respectively, 
properties  of  the  activity,  not  of  the  nerve-fibre,  but  of  the  peripheral  end- 
organ  and  the  nerve-centres. 

3.  Common  Sensation  and  Pain. — '^Fhe  sensations  thus  far  considered 
have  been  called  special  sensaiion.s,  because  each  affects  the  consciousness  in 
quite  a  different  way,  and  any  irritation  which  excites  the  sense  apparatus 
provokes  a  sensation  of  definite  quality  and  measurable  intensity. 

Pain  is  a  sensation  which,  according  to  common  but  erroneous  belief,  is  the 
result  of  sufficiently  intensifying  any  of  the  simple  sensations. 

Pains  have  received  various  names  to  distinguish  their  quality,  according  to 
the  mode  in  which  experience  shows  they  may  have  been  produced,  as  cutting, 
tearing,  burning,  grinding,  etc.  One  peculiar  mark  that  distinguishes  painful 
sensations  is  the  lack  of  complete  localization.  While  lesser  pains  are  referred 
with  fair  exactness  to  different  parts  of  the  body,  and  even  to  those  internal 
parts  devoid  of  tactile  sensibility,  greater  pains  radiate  and  seem  diffused  over 
neighboring  parts.     Pain  also  differs  from  special  sensation  in  the  long  latent 

'  Goldscheider :  Da  Bois-Reymon(V s  Archiv  fiir  Phydoloyie,  1886, 1887  ;  Blix  :  Zeilfchrlfl  fiir 
Biologic,  1884;  Donaldson  :  Mind,  vol.  39,  1885. 

*  Czermak:  Silzungsberichte  d.  Wiener  Akad.,  1855,  p.  500;  Klug:  Arb.  d.  physiol.  Anstall  zu 
Leipzig,  1876,  p.  168. 


THE  SENSE   OF  PAIN.  843 

period  preceding  its  development.  The  evidence  of  physiological  experiment 
is  against  the  belief  that  any  irritation  of  the  nerves  of  so-called  "special 
senses"  can  j)rodiU'e  j)ains,  bnt  it  teaches  that  this  sensation  is  the  resnlt  of  the 
excessive  or  unnatnral  stimulation  of  a  group  of  nerves  whose  function  is  to 
give  rise  to  what  is  indefinitely  called  "  common  sensation."  By  this  term  is 
designated  that  consciousness  which  we  more  or  less  definitely  have,  at  any 
moment,  of  the  condition  and  position  of  tiie  various  parts  of  our  bodies. 
When  tactile,  temperature,  and  visual  sensations  are  eliminated,  we  are  still 
able  to  designate  with  considerable  accuracy  the  position  of  our  limbs,  and  we 
become  aware  with  extraordinary  exactness  of  any  change  in  that  position, 
indicating  the  possession  of  a  podure  sense.  The  nerves  of  common  sensation 
must,  then,  be  continuously  active  in  carrying  to  the  sensorium  im])ulses 
which,  though  they  do  not  excite  distinct  consciousness,  probably  are  of  the 
utmost  importance  in  keeping  the  nerve-centres  informed  of  the  relative  posi- 
tions and  physiological  condition  of  the  various  parts  of  the  organism,  and  it 
is  not  improbable  that  they  are  the  afferent  channels  for  many  reflex  acts 
which  tend  to  preserve  the  equilibrium  of  the  body.  The  sudden  failure  of 
these  sensations  in  a  part  of  the  body  would  probably  be  felt  as  acutely  as  the 
silence  which  succeeds  a  loud  noise  to  which  the  ear  has  become  accustomed. 
Pain  is  thought  to  be  the  result  of  excessive  stimulation  of  the  nerves  of  com- 
mon sensation,  though  it  must  be  admitted  that  we  know  next  to  nothing 
of  the  anatomical  and  physiological  conditions  on  which  this  sensation  is 
dependent.  It  is  said  not  only  that  most  internal  organs  possess  no  def- 
inite tactile  or  thermal  sensibility,  but  that,  when  normal,  such  irritation  as 
is  caused  by  cutting,  burning,  and  pinching  seems  to  cause  no  pain ;  ^ 
let  them,  however,  become  inflamed,  and  their  sensitiveness  to  pain  is  suf- 
ficiently acute.  The  facts  of  labor-pains,  of  colic,  and  other  visceral  dis- 
turbances which  are  attended  by  no  inflammatory  condition  show,  however, 
that  the  factors  on  which  the  existence  of  pain  depends  are  not  as  yet  fully 
understood. 

The  physiological  facts  on  which  is  based  the  belief  in  "  common  sensa- 
tion "  are  indisputable,  but  the  evidence  for  a  special  nervous  apparatus  for 
such  sensibility  is  based  rather  on  exclusion  of  known  nerve-organs  than  on 
positive  demonstration.  In  the  category  of  common  sensations  have  been 
included  also  such  feelings  as  "  tickling,"  shivering,  hunger,  thirst,  and  sexual 
sensations.  The  feeling  of  fatigue  which  follows  either  muscular  or  mental 
exertion  may  be  })laced  in  the  same  group. 

A  general  feature  of  common  sensations  is  their  subjective  character;  they 
are  not  definitely  localized  within  the  body,  nor  are  they  projected  external  to 
it,  as  in  the  case  of  the  "  special  senses." 

Between  the  common  sensation  and  its  existing  cause  there  is  no  measurable 

proportion,  as  is  found,  for  instance,  in  the  study  of  the  pressure  sense.     It 

may  be  stated  that  pressure  and  temperature  sensations  were  within  a  recent 

period  grouped  among  common  sensations,  and  future  investigations  may  pos- 

»  Foster's  Physiology,  1891,  p.  1420. 


844  .l.V   AMERICAN    TEXT-HOOK    OF    I'JI  YsrOLOGY. 

sihlv  limit  eacli  of  tlie  looliii<j;8  now  cla-SisCtl  together  as  "coininoii  sensations" 
to  definite  anatomical  structures, 

AVlien  the  punctiform  distribution  of  various  sensations  iu  the  skin  is  inves- 
tisjated,  some  points  are  found  in  which  no  other  sensation  than  tiiat  of  jiain 
can  be  excited,  and  it  has  been  thought  that  such  spots  mark  the  jjlace  of 
ending  of  nerves  of  common  sensibility. 

Transferred  or  "  Sympathetic"  Pains;  Allochiria. — It  has  long  been  a 
matter  of  clinical  observation  that  disease  seated  in  certain  internal  organs  is 
often  accompanied  by  superficial  pain  and  tenderness  in  widely  removed  parts 
of  the  body;  for  example,  a  decayed  tooth  frequently  causes  intense  pain  in 
the  ear;  disease  of  heart  or  of  aorta  may  cause  pain  l)etween  the  shouKlers, 
etc.  The  subject  lias  received  most  accurate  investigation  from  Head,^  who 
has  shown  that  there  is  an  intimate  nervous  connection  between  tiie  internal 
organs  and  definite  areas  of  the  skin,  manifested  by  pain  and  tenderness 
appearing  in  sharply-localized  regions  on  the  surface  when  definite  organs 
become  disordered.  He  has  also  demonstrated  that  disorders  of  the  thoracic 
and  abdominal  viscera  not  only  ]m)duce  pain  and  tenderness  on  the  surface  of 
the  bodv,  l)ut  also  cause  pain  and  tenderness  over  certain  areas  of  the  scalp. 
Head  is  inclined  to  explain  the  topographical  association  of  skiu-tenderness 
with  visceral  disorders  by  the  assumption  that  the  nerve-supplies  of  the  parts 
so  related  find  their  origin  within  the  same  segment  of  the  spinal  cord.  The 
sensorv  result  of  visceral  irritation  may  be  summarized  in  the  following  way : 
"  When  a  painful  stimulus  is  applied  to  a  part  of  low  sensibility  iu  dose  cen- 
tral connection  with  a  part  of  much  greater  sensibility,  the  pain  produced  is 
felt  in  the  part  of  higher  sensibility  rather  than  in  the  part  of  lower  sensibility 
to  which  the  stimulus  was  actually  applied." 

That  this  transferred  localization  may  characterize  other  sensations  than 
those  of  pain  has  been  definitely  observed  by  Obersteiner,"  who  found  that  in 
patients  suffering  from  certain  central  nervous  lesions  tactile  irritation  of  a  cer- 
tain point  on  the  skin  was  referred  by  them  to  some  other  part  of  the  body, 
usually  the  corresponding  point  on  the  other  side.  He  designated  this  trans- 
ference of  sensation  by  the  term  al/ocJilria,  meaning  a  confusion  of  sides. 

4.  Muscular  Sensation. — Closely  allied  to  common  sensation,  if  not  a 
part  of  it,  is  muscular  sr)isation.  If  two  weights  are  to  be  compared,  we 
naturally  do  not  lay  them  on  the  skin  to  determine  their  pressure-difference, 
but  we  lift  and  weigh  them  in  the  hands,  and  experience  shows  that  a  nuich 
more  accurate  estimate  may  thus  be  made. 

We  undoubtedly  have  a  keen  perception  of  the  tension  of  a  muscle,  and 
therefore  of  the  amount  of  resistance  against  which  it  is  contracting.  This  per- 
ception mav  be  the  outcome  of  a  direct  consciousness  of  the  amount  of  motor 
energy  sent  out  from  the  motor  cells,  or  it  may  be  due  to  the  inflow  of  sensorv 
impulses  which  show  the  tension  to  which  the  muscles  have  been  subjected. 
The  latter  view  has  more  to  be  said  in  its  fixvor.  The  sensory  nerves  involved 
in  this  process  are  probably  distributed  rather  to  the  tendons  in  which  the  mus- 
1  Brain,  1893-94.  '  Ibid.,  1881. 


MUSCULAR    .SEiXSATION.  «4:) 

cles  terminate  than  to  the  muscular  suhstance  itself.  There  is  reason  to  believe 
that  the  joints  are  partieularly  rich  in  sueh  a  nerve-supply.  Golgi  ^  has  de- 
scribed two  distinct  modes  of  nerve-ending  in  tendon  and  at  the  line  of  divis- 
ion between  muscle  and  tendon  ;  and  Sherrington  -  has  shown  terminal  sensory 
fibres  to  be  enclosed  in  peculiar  isolated  groups  of  muscle-fibres,  the  "  muscle 
spindles,"  found  at  the  origin  of  tendons.  According  to  the  latter  author, 
from  one-third  to  one-half  of  all  the  spinal-nerve  fibres  found  in  muscle  are 
sensory  in  function. 

Wiien  we  consider  that  it  is  through  muscular  sensation  that  we  derive  our 
most  accurate  conceptions  of  the  form,  weight,  and  position  of  objects,  and  through 
which  we  explore  our  own  body-surface  and  distinguish  its  areas  of  localization  ; 
that  this  is  the  fundamental  sense  by  which  the  sensations  arising  in  most 
other  organs  are  tested  and  verified  ;  and  that  it  is  from  the  sense  of  muscular 
movement  that  we  can  form  ideas  of  time  and  space, — it  may  well  be  regarded 
as  the  mother  of  all  sense-perceptions.  Normal  muscles,  even  when  function- 
ally inactive,  are  still  in  a  state  of  tonic  contraction ;  it  is  not  improbable  that 
this  tone  is  a  reflex  action  whose  sensory  element  is  formed  by  the  impulses 
travelling  along  nerves  of  muscular  sensation.  Such  impulses  are  probai)ly 
indispensable  to  the  ])reservation  of  the  equilibrium  of  the  body. 

The  clinical  study  of  disease  in  the  central  nervous  system  affords  strong 
evidence  of  the  functional  independence  of  the  sense  organs  involved  in  the 
appreciation  of  touch,  heat,  cold,  and  pain.  In  certain  diseases  of  the  spinal 
cord,  areas  of  skin  may  be  mapped  out  in  which  sensations  of  pressure  are 
lost,  but  those  of  temperature  remain,  and  vice  versd.  In  other  diseases  the 
patient  can  appreciate  warmth  applied  to  the  skin,  but  not  cold. 

The  sensations  of  cold  and  pressure  seem  to  be  usually  lost  or  retained 
together,  while  those  of  warmth  and  pain  have  a  similar  connection.  It  is  a 
peculiar  fact  that  sometimes  in  the  early  stages  of  ether  and  chloroform  narco- 
sis the  sense  of  touch  remains  while  that  of  pain  is  abolished.  Funke*  refers 
to  two  cases  in  which,  while  the  tactile  sense  was  preserved,  muscular  sensation 
was  lost,  and  an  object  could  be  held  in  the  grasp  only  while  the  eyes  were 
turned  upon  it. 

Hunger  and  Thirst. — Hunger  and  thirst  are  peculiar  sensations  which 
depend  partly  on  local  and  partly  on  general  causes.  Diminution  in  the  bulk 
of  water  and  of  circulating  aliment  in  the  body  no  doubt  causes  excitement 
of  sensory  nerves  on  which  depend  the  feelings  of  thirst  and  hunger,  but  in 
ordinary  life  these  feelings  are  dependent  on  the  physical  condition  of  certain 
mucous  surfaces.  Any  circumstance  which  causes  drying  of  the  lining  mem- 
brane of  the  mouth  provokes  thirst,  and  some  condition  of  the  empty  stomach 
arouses  hunger.  Thirst  may  be  assuaged  by  introducing  water  directly  into 
the  stomach  through  a  gastric  fistula,  though  to  eifect  the  purpose  a  larger 
quantity  must  be  employed  in  this  way  than  by  the  mouth.     Hunger  in  a 

*  Hofmann  und  Schtvalbe's  Jahresbericht,  Abth.  I.  Bd.  vii.  S.  93. 

*  Journal  of  Physiology,  vol.  xvii.  p.  211. 

3  "  Der  Tastsinn,"  Hermann's  Handbuch  der  Physioloffie,  Bd.  iii.  S.  2. 


846  AN  AMERICAN   TEXT-BOOK   OF   PHYSIOLOGY. 

somewhat  similar  manner  may  be  appeased  by  rectal  alimentation.  It  seems 
probable,  however,  that  these  sensations  as  usually  felt  are  the  result  of  a 
sort  of  habit,  depending  on  the  ])hysiological  condition  of  the  secreting  and 
absorbing  mechanisms  of  the  alimentary  canal. 

Clinical  observation  has  shown  that  "bulimia,"  or  voracious  appetite,  is 
frequently  a  result  of  disease  in  certain  parts  of  the  central  nervous  system. 
We  are  therefore  justified  in  speaking  of  a  "  hunger-centre."  ' 

E.    The  Equilibrium  of  the  Body;    the  Function  of  the 
Semicircular  Canals. 

The  term  equilibrium,  as  a})plied  to  the  condition  of  the  body,  whether  at 
rest  or  in  motion,  indicates  a  state  in  which  all  the  skeletal  muscles  are  under 
control  of  nerve-centres,  so  that  they  combine,  when  required,  to  resist  the 
effect  of  gravitv  or  to  execute  some  co-ordinated  motion.  The  preservation 
of  equilibrium  is  manifestly  of  fundamental  importance  in  animal  life,  and  we 
find,  accordingly,  several  mechanisms  sharing  in  this  function.  That  the  motor 
co-ordinating  centres  may  act  projierly,  they  nuist  receive  sensory  imjires- 
sions  conveving  information  of  the  relative  position  of  the  body  at  any  given 
moment.  The  sum-total  of  these  sensations  may  be  characterized  as  the  sense 
of  equilibrium,  and  it  is  probably  not  going  too  for  to  assume  that  every  known 
sensation  contributes  to  this  fund  of  information.  Thus,  in  ordinary  life  the 
position  of  objects  is  commonly  determined  by  the  sense  of  sight :  when  one 
tries  to  walk  while  looking  through  a  prism,  objects  are  not  properly  localized 
bv  vision,  and  improper  co-ordination  results.  The  contact  of  the  soles  of  the 
feet  with  the  ground,  and  that  of  the  surface  of  the  body  with  various  objects, 
are  common  sources  of  information  as  to  our  relation  ^vitIl  the  environment. 
Standing  upright,  and  still  more  when  in  motion,  the  muscular  sense  is  active 
in  appreciating  the  tension,  active  or  passive,  of  the  muscles.  In  the  erect 
position,  with  eyes  closed,  a  writing  point  attached  to  the  head  will  show  that 
the  bod V  sways  in  a  peculiar  manner  indicating  successive  contraction  of  differ- 
ent groups  of  muscles;  and  a  person  with  failure  of  muscular  and  tactile  sen- 
sibility, as  in  locomotor  ataxy,  cannot  stand  with  eyes  closed,  and  his  move- 
ments, even  when  sight  is  employed,  are  exaggerated  and  unnatural.  Attention 
has  previously  been  called  to  the  fact  that  air- waves,  irrespective  of  those 
producing  sound-sensations,  exert  an  influence  upon  the  tympanic  membrane 
by  which  we  are  capable  of  appreciating  the  presence  and,  to  some  extent,  the 
phvsical  character  of  objects.  Whether  this  sensation  involves  the  nerves  of 
touch,  those  of  common  sensibility,  or  those  distributed  to  the  internal  ear,  is 
uncertain. 

In  the  absence  of  any  of  these  sensations  the  loss  may  be  made  up  by  more 
perfect  development  of  others.  Ordinarily,  the  sensory  information  from  all 
these  sources,  when  compared  in  consciousness,  harmonizes  and  gives  rise  to 
a  concrete  idea  of  position.  Frequently,  however,  one  of  the  sources  of  sense- 
impression  suddenly  fails  us  or  its  testimony  conflicts  with  that  of  other  sense 
'  Ewald :  Diseases  of  the  Stomach,  p.  397. 


THE  SENSE    OF   EQUILIBRIUM.  847 

organs ;  the  result  is  disturbance  of  equilibrium.  A  very  common  outcome 
of  this  conflict  of  sensations  is  dizziness  or  nausea.  The  distress  arising  from 
wearing  ill-fitting  glasses  and  the  sensations  experienced  when  one  looks  down 
from  a  high  eminence  are  examples  in  point.  Internal  disorders  exciting  nerves 
of  common  sensation  have  the  same  effect,  though  the  relation  borne  by  visceral 
sensations  to  equilibrium  is  very  ill  known.  A  false  idea  of  position  of  the 
body,  a  sense  of  falling  in  one  direction  or  another,  may  lead  to  sudden  effort 
of  recovery  by  which  the  person  is  precipitated  to  the  o})})osite  side.  Thus, 
when  looking  at  rapidly-moving  water  erroneous  ideas  of  equilibrium  are 
gained  through  the  visual  sense,  and  there  is  a  strong  tendency  for  the  body 
to  precipitate  itself  in  one  direction  or  another.  When,  in  going  up  a  stair- 
case, one  miscalculates  the  number  of  steps,  a  peculiar  sensation  of  want  of 
equilibrium  is  aroused  through  the  muscular  sense.  It  is  clear,  then,  that 
the  sense  of  equilibrium  is  served  by  various  sense  organs,  and  a  comj)lete 
discussion  of  this  function  would  entail  a  consideration  of  the  whole  field  of 
nerve-muscle  physiology.  There  is,  however,  good  reason  for  believing  that 
there  is  a  special  sense  organ  for  determining  the  position  and  direction  of 
movement  of  the  head  and,  by  inference,  of  the  whole  body.  The  terminal 
organ  of  this  sense  apparatus  of  equilibrium  is  found  in  the  system  of  semi- 
circular canals  of  the  internal  ear. 

Ex})eriments  on  the  lower  animals,  chiefly  performed  on  birds,  show  a  con- 
stant motor  disturbance  to  follow  division  of  any  or  all  of  the  semicircular 
canals.  These  disturbances  are  of  two  kinds.  When  the  animal  is  at  rest  it 
does  not  stand  in  a  natural  fashion,  but  sprawls  in  a  more  or  less  exaggerated 
degree.  It  holds  its  head  in  an  unnatural  position,  as  with  the  vertex  touch- 
ing the  back,  or  with  the  beak  turned  down  toward  the  legs  or  bent  over  to 
one  side.  Immediately  after  the  operation,  and  whenever  it  is  disturbed,  the 
animal  goes  through  peculiar  forced  movements,  together  with  rolling  or 
twitching  of  the  eyes,  of  various  kinds  and  degrees  of  violence,  depending  on 
the  position  and  number  of  canals  severed.  The  disturbance  varies  from 
simple  unsteadiness  in  gait,  with  swaying  motions  of  the  head,  to  complete 
lack  of  co-ordination  and  a  violence  of  movement  almost  comparable  to  that 
of  a  chicken  whose  head  has  been  cut  off.  Essentially  the  same  results  have 
been  determined  to  follow  injury  of  the  semicircular  canals  of  widely  different 
groups  of  animals. 

These  results  have  been  explained  by  the  assumption  that  the  hair-cells  on 
the  cristw  acustlca^  of  the  ampullae  of  the  semicircular  canals  are  irritated  by 
increase  or  decrease  of  pressure  of  the  endolymph  upon  them,  and  thus  give 
rise  to  sensory  impressions  from  which  ideas  of  change  of  position  are  derived. 
Section  of  the  canal,  by  draining  off  the  endolymph,  would  cause  abnormal 
pressure-irritation.  The  anatomical  relations  of  the  semicircular  canals  afford 
an  obvious  basis  for  this  view,  for  the  canals  of  each  ear  are  almost  exactly  at 
right  angles  to  one  another,  occupying  the  three  planes  of  space ;  considering 
the  two  ears,  the  horizontal  canals  are  nearly  in  the  same  plane,  and  the  ante- 
rior vertical  canal  of  one  side  is  nearly  parallel  with  the  posterior  vertical  canal 


848  A.X  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

of  the  other  side.  Any  possible  movement  of  the  head  would  thus  pioduce 
an  increase  of  eudolymph-pressure  upon  the  hair-cells  in  one  ampulla  and  a 
decrease  of  pressure  in  the  ampulla  of  the  parallel  ciuial,  and  every  change  of 
position  would  be  accompanied  by  the  irritation  of  definite  ampulhc  with  defi- 
nite degrees  of  excitement  (Fig.  289).  Experiments  on  man  allbrd  considerable 
,  support  to  this  theory  of  the  function  of  the 

I  semicircular  canals.     A  person  with  eyes  closed 

and  with  muscular  and  tactile  sensations  elimi- 
nated, supported  on  a  table  which  can  be  rotated 
in  all  directions,  can  determine  with  consider- 
able accuracy  not  only  thai;  he  is  moved,  but 
I  in  what  direction  and,  to  some  extent,  through 

'  how  great  an  angle.     Further,  mIicm  brought 

Fig.  289. —Diagrammatic  horizontal  °  .  „  . 

section  through  the  head  to  iihistrate     to  rcst  after  a  scries  of  rotations  the  person 
the  planes  occupied  hy  the  semicircu-     ^^^1^^.  observation  feels  a  scusatiou  of  motion 

lar  canals  (after  Waller):  s,  superior 

canal ;  p,  posterior  canal ;  H,  horizontal       in    the    Opposite    direction.      Eacll    of   thcSC    re- 
sults should   be  expected  to  follow   were  the 
theory  in  question  correct.     The   observations   of  James   have   shown  that 
with  deaf  mutes  in  whom  the  internal' ear  was  at  fault  rapid  rotation    in 
an  ordinary  "swing"  failed  to  produce  the  dizziness  which  is  the  common 
effect  in  ordinary  individuals.     On  the  other  hand,  diseases  which  may  be  sup- 
posed to  alter  the  intra-labyrinthine  pressure  are  characterized  by  the  symp- 
toms of  vertigo  and  inco-ordination  of  movement.     The  presumable  effect  of 
cutting  the  semicircular  canals  is  that  the  escape  of  endolymph  changes  the 
pressure  upon  the  sensory  hair-cells  and  gives  the  animal   the  sensation   of 
falling  in  one  direction  or  another,  so  that  he  is  impelled  to  make  compensa- 
tory QX  Jorocd  movements  to  counteract  this  imaginary  change  of  position.     In 
birds  and  in  fishes,  whose  life  is  passed  more  or  less  exclusively  in  a  medium 
in  which  tactile  and  muscular  sen.satiou  can  contribute  little  to  the  sense  of 
equilibrium,  the  semicircular  canals  are  especially  well  developed.^     In  fishes, 
though  section  of  the  canals  themselves  produces  no  disturbance,  division  of 
the  nerves  supplying  the  ampulla?  usually  gives  rise  to  marked  forced  move- 
ments, as  shown  in  somersaults,  spiral  swimming,  etc.  when  set  free  in  the 
water.     When,  however  the  nerves  are  cut  with  great  care,  with  sharp  scis- 
sors, .so  as  to  avoid  traction  on  or  crushing  of  the  nerves,  such  forced  move- 
ments do  not  follow.     The  movements  in  this  case,  then,  as  in  that  of  the 
pigeon,   are  the   outcome  of  direct  irritation  of  the  equilibrium  mechanism, 
and,  according  to  our  present  conception  of  the  function  of  the  .'semicircular 
canals  in  its  relation  to  equilibrium,  we  must  regard  it  as  a  terminal  organ 
which  is  exceedingly  .sensitive  to  such  mechanical  irritations  as  may  arise  from 
variations  of  eudolymph-pressure  upon   the  anipullary  hair-cells,  but  which 
may  be  destroyed  without  causing  inco-ordination  of  movement,  and   which 
may  therefore  more  or  less  com})letely  be  substituted  in  function   by  other 
sense  organs. 

'  Sewall :  Journal  of  Physiology,  1884,  iv.  p.  339. 


THE  SENSE    OF  SMELL. 


849 


According  to  Lee'  aiul  others,  the  equilibriurii  of  rest  and  motion,  or  static 
and  dynamic  equilibrium,  depends  upon  the  irritation  of  dit!erent  nerve-ter- 
minals. The  manner  of  action  of  the  latter  has  been  considered.  As  to  the 
nervous  mechanism  on  which  datic  equilibrium  depends,  Lee  is  of  the  opinion 
that  the  knowledge  of  the  position  of  the  head  while  at  rest  comes  from  the  rela- 
tion of  the  otoliths  in  the  vestibular  sacs  to  the  nerve-endings  on  the  viuculce 
acusticce.  These  otoliths  form  considerable  masses  in  the  ears  of  fishes,  and  the 
intensity  and  direction  of  their  pressure  upon  hair-cells  must  vary  with  the 
spatial  relations  of  the  head,  and  thus  be  comparable,  in  the  sense  of  i)Osi- 
tiou  which  they  Srouse,  to  the  tactile  sensations  derived  from  the  soles  of 
the  feet  in  man. 

F.  Smell. 

The  complex  paired  cavity  of  the  nose  is  divisible  into  a  lower  respiratory 
and  an  upper  olfactory  tract,  the  mucous  membrane  over  each  of  which  is 
distinctive.  The  covering  of  the  respiratory  tract  is  known  as  the  Sckneider- 
ian  or  pituitary  membrane;  its  surface  is  overlaid  with  cylindrical  ciliated 
epithelium,  the  ciliary  current  of  which  is  directed  posteriorly  toward  the 
pharynx. 

The  Schneiderian  membrane  lines  the  lower  two-thirds  of  the  septum,  the 
middle  and  inferior  turbinated  bodies,  and  the  bony  sinuses  which  communi- 
cate with  the  nasal  chamber.    The  mem- 
brane upon  the  turbinated  bodies  and 
the  lower  part  of  the  septum  is  composed 
largely  of  erectile  tissue. 

The  function  of  the  respiratory  tract 
is  threefold  :  it  restrains  the  passage 
of  solid  particles  into  the  lungs ;  it 
warms  the  air  inspired  to  approximately 


Fig.  290.— Section  of  olfactory  mucous  mem- 
brane (after  V.  Brunn) :  the  olfactory  cells  are  in 
•black. 


Fig.  291.-06118  of  the  olfactory  region  (after  V. 
Brunn) :  a,  olfactory  cells ;  6,  epithelial  cells :  n, 
central  process  prolonged  as  an  olfactory  nerve- 
fibril  :  I,  nucleus ;  c,  knob-like  clear  termination 
of  peripheral  process  ;  h,  bunch  of  olfactory  hairs. 


the  temperature  of  the  body ;  and  it  gives  up  moisture  sufficient  nearly  to 
saturate  the  air. 

^  Journal  of  Physiology,  xv.  p.  311 ;  xtii.  p.  192. 


54 


850 


^l.V   AMElUi'Ay    TEXT-BOOK    OF   PllYSlOLOOY 


The  oliiK'tory  inueous  nu'inbninc,  wliioli  alone  is  the  peripheral  or^aii  for 
smell,  is  sealed  in  the  iip})er  part  of"  the  na.sal  ehainber,  away  ironi  the  line 
of  the  direct  eurrent  of  inspired  air.  The  membrane  is  thick  and  is  covered 
by  an  epithelium  composed  ol'  two  kinds  of  cells,  columnar  and  rod  cells. 
The  latter  are  the  true  olfadovy  ct//*- (Figs.  290,  2U1),  with  which  the  fibres 
of  the  olfactory  nerve  are  known  to  be  connected.  These  olfactory  cells,  in 
fact,  are  comparable  to  nerve-cells  in  that  the  fibres  connected  with  them,  the 
fibres  composing  the  olfactory  nerve,  are  direct  outgrowths  from  the  cells 
(Fig.  292),  essentially  similar  in  every  way  to  the  uerve-fibre  processes  s])ringing 
from  nerve-cells  in  the  nerve-centres.  In  this  respect  the  olfactory  cells  differ 
from  the   sensory  cells   in   other   organs   of  special   sense.     The   membrane 


Fig.  292.— Diagram  of  the  connections  of  cells  and  fibres  in  the  olfactory  hnlh  (Schafer.  in  Quain'e  Anat- 
omy): oy.c,  cells  of  the  olfactory  mucous  membrane:  o[f.n,  deepest  layer  of  the  bulb,  comi>osed  of  the 
olfactory  nerve-tlbres  which  are  prolonged  from  the  olfactory  cells:  <?/,  olfactory  elomeruli,  containing 
arborization  of  the  olfactory  nerve-fibres  and  of  the  dendrons  of  the  mitral  cells:  vi.c,  mitral  cells; 
a,  tliin  axis-cylinder  process  passing  toward  the  nerve-fibre  layer,  n.tr,  of  the  bulb  tfi  become  continuoiis 
with  fibres  of  the  olfactory  tract :  these  axis-cylinder  processes  are  seen  to  give  off  collaterals,  some  of 
which  pass  again  into  the  deeper  layers  of  the  bulb;  «',  a  nerve-fibre  from  the  olfactory  tract  ramifying 
in  the  gray  matter  of  the  bulb. 

aj^pears  to  be  not  ciliated  except  near  its  juncture  with  the  Schneiderian 
membrane,  where  the  columnar  cells  acquire  cilia  and  gradually  pass  over 
into  the  cells  covering  the  respiratory  tract.  Substances  exciting  the  sense 
of  smell  exi.'it  as  gases  or  in  a  fine  state  of  division  in  the  air  inspired. 
They  reach  the  olfactory  mucous  membrane  by  diffusion,  assisted  by  the 
modified  inspiratory  movements  of  "sniffing"  and  "smelling,"  and  are 
most  acutely  jierceived  when  the  air  containing  them  is  warmed  to  the 
body-temperature.  The  amount  of  odoriferous  matter  that  may  thus  be 
recognized  is  extraordinarily  small ;  thus,  it  is  said  that  in  one  liter  of  air 
the  odor  of  0.000,005  gram  of  musk  and  of  0.000,000,005  gram  of  oil  of 
jiepperraint  can  be  perceived.*  The  odoriferous  particles  probably  excite  the 
J  Passy  :  Compte»-rendus  de  la  Sociite  de  Biologic,  1892,  p.  84. 


Till-:  si'Lxsi-:  or  taste.  851 

sense  of  stndl  l»y  coiniii*";  into  contact  witli  the  olfactory  cjtitlioliiirn  after  solu- 
tion iti  the  layer  of  moisture  covering  it.  This  epitlicliuin  is  easily  thrown 
out  of  function,  as  the  common  loss  of  smell  when  there  is  a  "cold  in  the 
head  "  testifies.  Wiien  the  nostiil  is  filled  with  water  in  which  an  odorous 
substance  is  dissolved,  no  sensation  of  smell  is  excited,  but  it  is  said  that  if 
normal  salt-solution,  whicli  injures  tlie  living  tissues  less  tlian  water,  be  used 
as  the  solvent,  the  odor  can  still  be  perceived.  In  many  lower  animals  the 
sense  of  smell  has  an  acuteness  and  an  importance  in  their  economy  unknown 
in  the  human  race.  It  is  probable  that  not  only  do  different  races  have  their 
distinctive  odors,  but  that  each  individual  exhales  an  odor  ]>eculiar  to  himself, 
distinguishable  by  the  olfactory  organs  of  certain  animals.  The  classification 
of  odors  is  not  very  definite,  and  the  relation  of  odors  to  one  anotiier  in  the 
way  of  contrast  and  harmony  is  ill  understood.  No  limited  number  of  pri- 
mary sensations,  as  in  vision,  have  been  discovered  out  of  which  otiier  sen- 
sations can  be  composed.  Certain  sensations,  as  those  due  to  the  inhalation 
of  ammonia  and  other  irritant  gases,  are  thought  to  be  due  to  excitement  of 
tile  nasal  filaments  of  the  fifth  nerve,  and  not  of  the  olfactory. 

Subjective  sensations  of  smell  are  sometimes  experienced,  the  result  of  some 
irritation  arising  in  the  olfactory  apparatus  itself. 

Finally,  in  man  sensations  of  smell  have  their  most  important  uses  in  con- 
nection with  taste;  many  so-called  "tastes"  owe  their  character  wholly  or 
partly  to  the  unconscious  excitement  of  the  sense  of  smell. 

G.  Taste. 

The  peripheral  surfaces  concerned  in  taste  include,  in  variable  degree,  the 
upper  surface  and  sides  of  the  tongue  and  the  anterior  surfaces  of  the  soft 
palate  and  of  the  anterior  pillars  of  the  fauces.  Other  parts  of  the  buccal 
and  pharyngeal  cavities  are,  in   most  persons,  devoid  of  taste.' 

The  chief  peripheral  sensor\^  organs  of  taste  are  groups  of  modified  epi- 
thelial cells,  known  as  tdste-hiuh  (Fig.  293),  seated  in  certain  papillae  of  the 
tasting  surfaces.  According  to  some  authors,  only  parts  provided  with  taste- 
buds  can  give  taste-sensations.^ 

The  structure  of  taste-buds  is  most  easily  studied  in  the  papilla  foliata  of 
the  rabbit,  a  patch  of  fine,  parallel  wrinkles  found  on  each  side  of  the 
back  part  of  the  tongue  of  the  animal.  The  taste-bud  is  a  somewhat  globular 
body  seated  in  the  folds  of  mucous  membrane  between  tlie  furrows  of  the 
pa])illa.  It  is  made  up  of  a  sheath  of  flattened,  fusiform  cells  enclosing  a 
number  of  rod-like  cells  each  of  which  terminates  in  a  hair-like  process.  These 
cells  surround  a  central  pore  which  opens  into  a  furrow  of  the  papilla. 
The  hair-bearing  cells  recall  the  appearance  of  the  olfactory  rod-cells,  and 
are  probably  the  true  sensory  cells  of  taste,  since  between  them  terminate  the 
filaments  of  the  gustatory  nerve.     In  the  human  tongue  taste-buds  are  con- 

'  V.  Vihtscligaii  :  "  Geruchsinn,"  Henminn's  Handhuch  der  Physiologie,  iii.  2,  1880. 
'Camerer:   Zeitschrift  filr  Biologie,  1870,  vi.  S.  440;  Wilczynsky :  Hofnann  und  Schwalbe's 
Jahresbericht  der  Physiol.,  1875. 


852 


.l.V   AMElilCAX    TEXT-BOOK    OF  PHYSIOLOGY. 


v^i  7/1  ft>->  >,sj^  '^^& 


fined  to  the  fuiifrifonn  papilljo,  scon  often  as  red  dots  scattered  over  the  upper 
surface;  to  the  circunivalhite  papilhe,  the  pores  of  the  buds  opening  into  the 
groove  around  the  papilhi ;  and  to  an  area  just  in  front  of  the  anterior  pillar 
of  the  fauces,  which  somewhat  resembles  the  papilla  foliata  of  the  rabbit. 

The  sensory  nerves  distributed  to  the  tongue  include  filaments  from  the 
glosso-pharyngeal,  the  lingual  branch  of  the  fifth,  and  the  chorda  tympani. 
The  relation  of  these  nerves  to  the  sense  of  taste  has  been  the  occasion  of 
much  dispute.  The  weight  of  evidence  probably  favors  the  belief  that  the 
glosso-pharyngeal  is  the  nerve  of  taste  for  the  ])osterior  third  of  the  tongue, 
while  the  lingual  and,  to  some  extent,  the  chorda  carry  taste-impressions  from 
the  anterior  two-thirds.  Clinical  cases  have  been  cited  to  show  that  all  the 
gustatory  fibres  arise  from  the  brain  as  part  of  the  glosso-pharyngeal  nerve, 
whatever  may  be  their  subsequent  course  to  the  tongue.     On  the  contrary, 

other  cases  have  shown  a  marked  loss 
of  taste-sensation  following  upon  lesions 
of  the  fifth  nerve  at  or  near  its  origin 
from  the  brain,  while  still  others  indi- 
cate that  some  of  the  taste-fibres  may 
arise  in  the  seventh  nerve.  The  point 
is  of  practical  importance  in  diagnosis, 
in  the  interpretation  of  loss  of  taste 
over  any  given  part  of  the  tongue,  but 
the  contradiction  in  the  clinical  cases 
reported  has  led  to  the  general  belief 
that  the  origin  and  course  of  the  gusta- 
tory fibres  are  subject  to  considerable 
individual  variations. 

Our  taste-percei)tions  are  ordinarily 
much  modified  by  simultaneous  olfac- 
tory sensations,  as  may  easily  be  dem- 
onstrated by  the  difficulty  experienced 
in  distinguishing  by  taste  an  apple,  an 
onion,  and  a  potato,  when  the  nostrils  are  closed.  Sight  has  also  an  import- 
ant influence,  at  least  in  quickening  the  expectancy  for  individual  flavors. 
Every  smoker  knows  the  blunting  of  his  perception  for  burning  tobacco 
while  in  the  dark  ;  various  dishes  having  distinctive  flavors  are  said  to  lose 
much  of  their  gustatory  characteristics  when  the  eyes  are  bandaged. 

The  intensity  of  gustatory  sensation  increases  with  the  area  to  which  the 
tasted  substance  is  applied.  The  movements  of  mastication  are  peculiarly 
adapted  to  bring  out  the  full  taste  value  of  substances  taken  into  the  mouth, 
and  the  act  of  swallowing,  by  which  the  morsel  is  rubbed  between  the  tongue 
and  the  palate,  has  been  proved  to  develop  tastes  not  appreciable  by  simple 
contact  with  the  sensory  surface.  A  considerable  area  in  the  mid-dorsum  of 
the  tongue  is  said  to  be  devoid  of  all  taste-sensibility.' 

■  Shore:  Journal  of  Physiology,  1892,  vol.  xiii.  p.  191. 


mM 


--;i//i? 


%%ii!v':ihl-3A.:iiVri^ 


Fig.  293.— Section  through  one  of  the  taste-buds 
of  the  papilla  foliata  of  the  rabbit  (from  Quain, 
after  Kanvier),  highly  magnificrl :  p,  gustatory 
pore;  »,  gustatory  cell;  r,  sustentacular  cell;  m, 
leucocyte  containing  granules ;  e,  superficial  epi- 
thelial cells ;  H,  nerve-fibres. 


THE   SENSE    OF    TASTE. 


85;i 


The  sensitiveuess  of  taste-sensation  is  greatest  when  the  exciting  substance 
is  at  the  temperature  of  the  body.  Weber  ^  found  tliat  when  the  tongue  was 
dipped  during  one-half  to  one  minute  in  water  either  at  the  freezing  tempera- 
ture or  warmed  to  50°  C,  the  sweet  taste  of  sugar  could  no  longer  be  appre- 
ciated by  it.  It  is  probable  that  sapid  substances  reach  the  sensory  endings 
of  the  nerves  of  taste  only  after  being  dissolved  in  the  natural  fluids  of  the 
mouth,  and  any  artificial  drying  of  the  buccal  surfaces  or  alteration  of  their 
secretion  must  affect  taste-perceptions. 

The  excitement  of  the  taste-nerves  appears  to  depend  not  so  much  on  the 
absolute  amount  of  the  substance  to  be  detected  as  on  the  concentration  of  the 


A  udiiory. 


Gustatory. 


Tactile. 


'^  y 


Fig.  294.— Diagram  showing  the  mode  of  termination  of  sensory  nerve-fibres  in  the  auditory,  gustatory, 
and  tactile  structures  of  vertebrata  (from  Quain,  after  Retzius).  Each  sense  organ  may  be  considered  as 
essentially  constructed  of  a  nerve-cell  with  two  processes,  one  finding  its  way  centrally  to  cluster  round 
other  nerve-cells  or  their  processes,  and  the  other  to  terminate  in  the  periphery.  Ir>the  organ  of  smell 
the  peripheral  process  is  very  short  and  is  directly  irritated  by  foreign  particles,  the  original  nerve-cell 
being  represented  by  the  olfactory  cell  (Fig.  291).  In  the  organs  of  touch  the  nerve-cell  is  found  in  the 
ganglion  of  the  posterior  spinal  nerve-root;  the  peripheral  process  is  very  long  and  is  acted  fm  indirectly 
through  the  modified  epithelium  round  which  it  clusters.  The  same  may  be  said  of  the  other  sense 
organs.    See  Quain's  Anatomy,  10th  ed.,  vol.  iii.  pt.  3,  p.  1.52. 


solution  containing  it.  Thus,  when  1  part  of  common  salt  to  213  of  water 
was  tasted  by  Valentin/  11  cubic  centimeters  of  the  fluid  was  suflicieut  to  give 
a  saltish  taste ;  when  diluted  so  that  the  ratio  of  salt  to  water  was  1  to  426, 
12  cubic  centimeters  taken  in  the  mouth  scarcely  gave  the  salt  taste.  Snl]>hate 
of  quinine  dissolved  in  the  proportion  1  to  33,000  gave  a  decided  bitter  taste, 
but  a  solution  1  to  1,000,000  was  with  difficulty  perceived  as  bitter. 

It  has  generally  been  conceded  that  all  gustatory  sensations  may  be  built 
up  out  of  four  primary  taste-sensations — namely,  bitter,  sweet,  sour,  and  salt. 
Some  authors  even  limit  the  list  to  tastes  of  bitter  and  sweet  (V.  Vintschgau). 

'  Archwfiir  Anatomie  und  Physiologic,  1847,  S.  342.  *  Lehrhuch  der  Phyaiologie,  1848. 


854  ^^V   AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

There  is  strnncr  reason  to  believe  that  corresponding  to  tlie  tour  prirnarv  taste- 
sensations  there  are  separate  centres  and  nerve-fibres,  each  of  which,  when 
excited,  gives  rise  only  to  its  appropriate  taste-sensation.  Substances  which 
arouse  the  sense  of  taste  are  not  appret.'iated  in  uniform  degree  over  the  surface 
of  the  tongue.  Thus,  to  V.  Vintschgau,  at  the  tip  of  the  tongue  acids  were 
perceived  acutely,  sweets  somewhat  less  plainly,  and  bitter  substances  hardly 
at  all.  It  is  generally  admitted  that  sweet  and  sour  tastes  are  recognized 
chiefly  at  the  front,  and  bitter,  together  with  alkaline  tastes,  by  the  posterior 
part  of  the  tongue.  Strong  evidence  in  favor  of  the  specific  difference  between 
various  taste-nerves  is  found  in  the  fact  that  the  same  substance  may  excite  a 
different  gustatory  sensation  according  as  it  is  aj)plied  to  the  front  or  the  back 
of  the  tongue.  Thus,  it  has  been  demonstrated  that  a  certain  compound  of 
saccharin  (para-brom-benzoic  sulphimide)  appears  to  most  persons  to  be  sweet 
when  ajiplied  to  the  tip  of  the  tongue,  but  bitter  in  the  region  of  the  circum- 
vallate  papilhe.' 

OehrwalP  has  examined  the  different  fungiform  papillae  scattered  over  the 
tongue  with  reference  to  their  sensitiveness  to  taste-stimuli.  One  hundred  and 
twenty-five  separate  papillae  were  tested  with  succinic  acid,  quinine,  and  sugar. 
Twenty-seven  of  the  papillae  gave  no  response  at  all,  indicating  that  they  were 
devoid  of  taste-fibres.  Of  the  remaining  ninety-eight,  twelve  reacted  to  suc- 
cinic acid  alone,  three  to  sugar  alone,  while  none  were  found  which  were  acted 
upon  by  quinine  alone.  The  fact  that  some  papillae  responded  with  only  one 
form  of  taste-sensation  is  again  evidence  in  favor  of  the  view  that  there  are 
separate  nerve-fibres  and  endings  for  each  fundamental  sensation ;  but  the 
figures  given  in  the  experiments  show  that  the  majority  of  the  papillae  are 
provided  with  more  than  one  variety  of  taste-fibre. 

An  extract  of  the  leaves  of  a  tropical  plant,  Gi/mnema  silvestre,  when 
applied  to  the  tongue,  renders  it  incapable  of  distinguishing  the  taste  of  sweet 
and  bitter  substances ;  it  probably  paralyzes  the  nerves  of  sweet  and  bitter 
sensations.  AVhen  a  solution  of  cocaine  in  sufficient  strength  is  painted  on 
the  tongue,  the  various  sensations  from  this  member  are  said  to  be  abolished 
in  the  following  order:  (1)  General  feeling  and  pain;  (2)  bitter  taste;  (3) 
sweet  taste;  (4)  salt  taste;  (5)  acid  taste;  (6)  tactile  perception  (Shore). 

That  there  are  laws  of  contrast  in  taste-sensation  has  long  been  empirically 
known.  Thus,  the  taste  of  cheese  enhances  the  flavor  of  wine,  but  sweets 
impair  it  (Joh.  Muller).  It  is  unfortunate,  from  a  hygienic  standpoint  at 
least,  that  in  this  most  important  department  of  the  physiology  of  sensation 
investigations  are  almost  wholly  wanting. 

Certain  tastes  may  disguise  others  without  physically  neutralizing  them; 
when,  for  example,  sugar  is  mixed  with  vinegar,  the  overcoming  of  the  acid 
taste  is  probably  effected  in  the  central  nerve-organ.^ 

1  Howell  and  Kastle :  Studies  from  the  Biological  Laboratory  of  Johns  Hopkins  University. 
1887,  iv.  13. 

*  SkandinavLsches  Archivfur  Physiologic,  1890,  vol.  ii.  p.  1. 

*  Br'ucke :   Vorlesungen  iiber  Physiologic,  1876. 


XII.  PHYSIOLOGY  OF  SPECIAL  MUSCULAR 
MECHANISMS. 


A.  The  Action  of  Locomotor  Mechanisms. 
The  Articulations. — The  form,  posture,  and  movements  of  vertebrates 
are  largely  determined  by  the  structure  of  the  skeleton  and  the  method  of 
union  of  the  bones  of  which  it  is  composed.  There  are  two  hundred  bones  in 
the  human  skeleton,  and  they  are  so  connected  together  as  to  be  immovable, 
or  to  allow  of  many  varieties  and  degrees  of  motion.  There  are  four  prin- 
cipal methods  of  articulation  : 

1.  Union  by  Bony  Substance  (Sutures). — This  form  of  union  occurs 
between  the  bones  of  the  skull.  These  bones,  which  at  birth  are  independent 
structures  connected  by  fibrous  tissue,  gradually  grow  together  and  make 
a  continuous  whole,  only  a  more  or  less  distinct  seam  remaining  as  witness 
of  the  original  condition. 

2.  Union  by  Pibro-Cartilages  (Symphyses). — The  bodies  of  the  verte- 
brse  and  the  pelvic  bones  are  closely  bound  together  by  disks  of  fibro-cartilage. 
This  material,  which  is  very  strong,  but  yielding  and  elastic,  permits  of  a 
slight  amount  of  movement  when  the  force  applied  is  considerable,  and  restores 
the  bones  to  their  original  position  on  the  removal  of  the  force.  The  inter- 
vertebral disks  act,  moreover,  as  elastic  cushions  or  buffers  to  deaden  the 
eflfect  of  sudden  jars. 

3.  Union  of  Fibrous  Bands  (Syndesmoses). — Some  of  the  bones,  as  of 
the  carpus  and  tarsus,  are  connected  by  interos.seous  ligaments  which,  at  the 
same  time  that  they  bind  the  bones  together,  admit  of  a  certain  amount  of 
play,  the  extent  of  the  movement  varying  with  the  character  of  the  surfaces 
and  the  length  of  the  ligaments. 

4.  Union  by  Joints. — The  adjacent  surfaces  of  most  of  the  bones  are  so 
formed  as  to  permit  of  close  contact  and  freedom  of  movement  in  special 
directions.  Tiie  parts  of  the  bones  entering  into  the  joint  are  clothed  with 
very  smooth  cartilage,  and  the  joint-surfaces  are  lubricated  by  synovial  fluid, 
a  viscid  liquid  secreted  by  a  delicate  membrane  which  lines  the  fibrous  capsule 
by  which  the  joint  is  sun-ounded.  The  joint-capsule  is  firmly  attached  to  the 
bones  at  the  margin  of  the  articular  cartilages,  and,  at  the  same  time  that  it 
completely  surrounds  and  isolates  the  joint-cavity,  helps  to  bind  the  bones 
together.  The  bones  are  further  united  by  strong  ligaments,  in  some  cases 
within  and  in  other  cases  Avithout  the  capsule.  These  ligaments  are  so  placed 
that  they  are  relaxed  in  certain  positions  of  the  joints  and  tightened  in  others ; 


855 


856  ^iV  AMERICAN    TEXT- BOOK    OF  PHYSIOLOGY. 

they  guitle  and  limit  tho  niovenient.s  of  the  joiuts.  Tlie  joint-surfaces  always 
toucli,  although  in  souie  joiuts  the  parts  in  contact  change  with  the  position 
of  the  joint.  If  coutiuuous  contact  of  the  joint-surfaces  is  to  be  maintained 
and  free  movement  is  to  take  place  in  special  dii-ections,  it  is  evident  that  the 
opposing  surfaces  must  not  only  be  so  constructed  that  they  shall  fit  each 
other  with  great  accuracy,  but  also  have  forms  especially  adapted  to  the  move- 
ments peculiar  to  each  of  the  joints. 

The  different  joints  exhibit  a  great  variety  of  movements  and  inav  be  clas- 
sified as  follows:  gliding  joints,  hinge  joiuts,  condyloid  joints,  saddle  joints, 
ball-and-socket  joints,  pivot  joints.  For  a  description  of  the  structure  and 
the  peculiarities  of  these  joints  the  student  is  referred  to  works  on  anatomy.' 
The  contact  of  the  surfaces  of  the  joint  is  secured  in  part  by  the  fibrous  capsule, 
in  part  by  the  joint  ligaments,  and  in  part  by  the  tension  of  the  muscles.  The 
elastic  muscles  are  attached  under  slight  tension,  and,  moreover,  during  wak- 
ing hours  are  kept  slightly  contracted  by  tonus  impulses  of  reflex  origin. 
Another  less  evident  but  no  less  important  condition  is  the  atmospheric  pres- 
sure. The  capsule  fits  the  joint  closely  and  all  the  space  within  not  occupied 
by  the  bones  is  filled  by  cartilages,  fibrous  bauds,  fatty  tissues  and  synovial 
fluid.  The  joint  is  air-tight,  and,  as  was  first  demonstrated  by  the  Weber 
brothers,  the  atmospheric  pressure  keeps  all  parts  in  close  apposition.  This 
force  is  sufficiently  great  in  the  case  of  the  hip-joint  to  support  the  whole 
weight  of  the  leg  even  after  all  the  surrounding  soft  parts  have  been  cut 
through.  The  proof  that  the  air-pressure  gives  this  support  is  found  in  the 
fact  that  the  head  of  the  femur  maintains  its  place  in  the  acetabulum  after 
all  the  soft  parts  which  surround  the  joint  have  been  divided,  but  falls  out 
of  its  socket  if  a  hole  be  bored  in  the  acetabulum  and  air  be  permitted  to 
enter  the  cavity  of  the  joint.  Though  the  air-pressure  keeps  the  boues  in 
constant  contact  it  offers  no  resistance  to  the  movements  peculiar  to  the  joints. 

The  movements  of  the  bones  is  effected  chiefly  by  muscular  contractions, 
but  the  direction  and  extent  of  the  movements  is  for  the  most  part  determined 
by  the  form  of  the  joint-surfaces  and  the  limitations  to  movement  which  result 
from  the  method  of  attachment  of  the  ligaments.  In  the  case  ot^  sliding  joints, 
in  which  the  articular  surfaces  are  nearly  flat,  a  sliding  movement  may  occur  in 
various  directions,  but  the  extent  of  the  movement  is  slight,  being  limited  by  the 
capsule  and  the  ligaments.  Hinge  joints  have  but  a  single  axis  of  rotation, 
because  the  convex  and  somewhat  cylindrical  surface  of  one  bone  fits  quite 
closely  the  concave  surface  of  the  other,  and  because  of  tense  lateral  ligaments 
which  permit  of  movements  only  in  a  single  plane.  The  joint  between  the 
humerus  and  the  ulnar  at  the  elbow  is  an  example.  The  knee-joint^  is  a  less 
simple  form  of  hinge  joint.     The  presence  of  the  semilunar  cartilages  and 

*  Qitain's  Anatomy,  vol.  ii.  pt.  1. 

'  W.  Braunne  and  Fischer  have  studied  with  mathematical  accuracy  the  construction  and 
movements  of  many  of  the  joints  of  the  human  body.  Their  articles  are  published  in  the 
Ahhandl ungen  der  math.-phys.  Classe  der  konigl.  Sikhsischer  GeaelUchaft  der  Wissenschaflen,  Bd. 
xvii.,  and  others. 


THE    ACTION    OF   LOCOMOTOR    MECHANISMS.  857 

the  shape  of  the  joiut-surluces  euu.se  flexion  to  be  produced  by  the  conibiued 
action  of  sliding,  rolling,  and  rotation  movements.  In  complete  extension 
the  lateral  ligaments  and  the  posterior  and  anterior  crucial  ligaments  are 
put  on  the  stretch,  and  there  is  a  locking  of  the  joint,  no  rotation  being 
possible;  in  complete  flexion,  on  the  other  hand,  the  posterior  crucial 
ligament  is  tight,  but  the  others  are  sufficiently  loose  to  allow  of  a  consider- 
able amount  of  pronation  and  supination.  In  the  mddk-joint  there  is  a 
double  axis  of  rotation — <\  fj.  the  articulation  of  the  trapezius  with  the  first 
metacarpal  bone  permits  of  rotation  about  an  axis  extending  from  before  back- 
ward, and  another,  at  nearly  right  angles  to  this,  extending  from  side  to  side. 

The  ball-and-socket  joint,  of  which  the  shoulder-  and  hip-joints  are  exam- 
ples, permits  of  the  greatest  variety  of  movements,  any  diameter  of  the  head 
of  the  bone  serving  as  an  axis  of  rotation. 

Method,  of  Action  of  Muscles  upon  the  Bones. — The  bones  can  be 
looked  upon  as  levers  actuated  by  the  forces  which  are  applied  at  the  points 
of  attachment  of  the  muscles.  All  three  forms  of  levers  are  represented  in 
the  body;  indeed,  they  may  be  illustrated  in  the  same  joint,  as  the  elbow. 

An  example  of  a  lever  of  the  first  class,  in  which  the  fulcrum  is  between 
the  power  and  the  resistance,  is  to  be  found  in  the  extension  of  the  forearm  in 
such  an  act  as  driving  a  nail :  the  inertia  of  the  hammer,  hand,  and  forearm 
offers  the  resistance,  the  triceps  muscle  acting  upon  the  olecranon  gives  the 
power,  and  the  trochlea,  upon  which  the  rotation  occurs,  is  the  fulcrum.  The 
l)alancing  of  the  head  upon  the  atlas  is  another  example:  the  front  part  of  the 
head  and  face  is  the  resistance,  the  occipito-atlantoid  joint  the  fulcrum,  and 
the  muscles  of  the  neck  the  power. 

In  the  case  of  a  lever  of  the  second  order,  the  resistance  is  between  the  ful- 
crum and  the  power ;  for  example,  when  the  weight  of  the  body  is  being 
raised  from  the  floor  by  the  hands :  the  fulcrum  is  where  the  hand  rests  on  the 
floor,  the  weight  is  applied  at  the  elbow-joint,  and  the  power  is  the  pull  of  the 
triceps  on  the  olecranon.  The  raising  of  the  body  on  the  toes  is  another  ex- 
ample :  the  fulcrum  is  at  the  place  where  the  toes  are  in  contact  with  the 
floor,  the  resistance  is  the  weight  of  the  body  transmitted  through  the  tibia  to 
the  astragalus,  and  the  power  is  applied  at  the  point  of  attachment  of  the 
tendo  Achillis  to  the  os  calcis. 

The  raising  of  a  weight  in  the  hand  by  flexion  of  the  forearm  through 
contraction  of  the  biceps  gives  an  example  of  a  lever  of  the  third  order,  in 
which  the  power  is  applied  between  the  fulcrum  and  the  weight.  This  form 
of  lever,  because  of  the  great  length  of  the  resistance  arm,  as  compared  with 
the  power  arm,  is  favorable  to  extensive  and  rapid  movements,  and  is  the 
most  usual  form  of  lever  in  the  body. 

The  power  is  applied  to  best  advantage  when  it  is  exerted  at  right  angles 
to  the  direction  of  a  lever,  as  in  the  case  of  the  muscles  of  mastication  and  of 
the  calf  of  the  leg.  If  the  traction  be  exerted  obliquely,  the  effect  is  the  less 
the  more  acute  the  angle  between  the  tendon  of  the  muscle  and  the  bone  ;  for 
example,  when  the  arm  is  extended  the  flexor  muscles  work  to  great  disad- 


858  .l.V  AMERICAX    TEXT-HOOK    OF   J'll  YSKjLOUY. 

vantage,  lor  a  large  part  ot"  the  force  i.s  expended  in  pulling  the  ulnar  and 
radius  against  the  liunierus,  antl  is  lost  for  movement,  but  as  the  elbow  is 
flexed  the  force  is  directed  more  and  more  nearly  at  right  angles  to  the  bones 
of  the  forearm,  and  there  is  a  gain  in  leverage,  which  is  of  course  again 
decreased  as  flexion  is  completed.  This  gain  in  leverage  which  accompanies 
the  shortening  of  the  muscles  is  the  more  important,  since  the  power  of  the 
muscle  is  greatest  when  the  muscle  has  its  normal  length,  and  continually 
lessens  as  the  muscle  shortens  in  contraction.  There  are  a  number  of  special 
arrangements  which  help  to  increase  the  leverage  of  the  muscles  by  lessening 
the  obliquity  of  attachment — viz.  the  enlarged  heads  of  the  bones,  and  in  some 
cases  special  processes  projecting  from  the  bones,  the  introduction  of  sesamoid 
bones  into  the  tendons,  and  the  presence  of  pulley-like  mechanisms. 

The  contraction  of  a  muscle  causes  the  points  to  which  it  is  attached  to 
approach  one  another,  and  the  direction  of  the  movement  is  often  determined 
by  the  direction  in  which  the  force  of  the  contracting  muscle  is  applied  to  the 
bones.  In  the  case  of  certain  joints,  however,  the  form  of  the  joint-surfaces 
and  the  method  of  attachment  of  the  ligaments  limits  the  direction  of  move- 
ment to  special  lines;  and  when  this  is  not  the  case  the  movement  is  usually 
the  resultant  of  the  action  of  many  muscles  rather  than  the  effect  of  the  con- 
traction of  any  one  muscle.  This  question  has  been  made  the  subject  of 
careful  study  by  Fiek.^ 

In  the  case  of  many  muscles,  both  of  the  bones  to  which  they  are  attached 
are  movable,  and  the  result  of  contraction  depends  largely  on  which  of  the 
extremities  of  the  muscles  becomes  fixed  by  the  contraction  of  other  muscles. 
Though  most  muscles  have  direct  influence  over  only  one  joint,  there  are  certain 
muscles  which  include  two  joints  between  their  points  of  attachment,  and  pro- 
duce correspondingly  complex  effects.  The  accurate  adjustment  and  smooth 
graduation  of  most  co-ordinated  muscular  movements  is  due  to  the  fact  that  not 
only  the  muscles  directly  engaged  in  the  act,  but  the  antagonists  of  these  mus- 
cles take  part  in  the  movement.  It  would  appear  from  the  observations  of 
certain  writers^  that  antagonistic  muscles  may  be  not  only  excited  to  contrac- 
tion, but  inhibited  to  relaxation,  and  that  the  tension  of  the  muscles  is  thereby 
accurately  adjusted  to  the  requirements  of  the  movement  to  be  performed. 
The  importance  of  the  elastic  tension  and  reflex  tonic  contractions  of  muscles 
to  ensure  quick  action,  to  protect  from  sudden  strains,  and  to  restore  the  parts 
to  the  normal  position  of  rest  has  been  referred  to  elsewhere. 

The  shape  of  the  muscle  has  an  important  relation  to  the  work  which  it 
has  to  perform.  A  muscle  consists  of  a  vast  number  of  fibres,  each  of  which 
can  be  regarded  as  a  chain  of  contractile  mechanisms.  The  longer  the  fibre, 
the  greater  the  number  of  these  mechanisms  in  series  and  the  greater  the  total 
shortening  effected  by  their  combined  action  ;  consequently,  a  muscle  with 
long  fibres,  such  as  the  sartorius,  is  adapted  to  the  production  of  extensive 
movements.     In   order  that  a  muscle  shall  be  capable  of  making  powerful 

'  JJermamx! »  Ilandbuch  der  Physiologie,  1871,  Bd.  i.  pt.  2.  p.  241. 
^  Sherrington:  Proceedings  of  the  Royal  Society,  Feb.,  1893,  vol.  liii. 


THE   ACTION   OF  LOCOMOTOR    MECHANISMS.  859 

movements  it  is  iiooessarv  that  inaiiy  lil)n>s  shall  be  placed  side  by  side,  as  in 
the  case  of  the  gluteus:  "  Many  liaiids,  li-;lit  work." 

Standing. — In  spite  of  the  ease  with  which  tin;  many  joints  of  the  body 
move,  the  erei't  position  is  maintained  with  comparatively  little  muscular 
exertion.  It  is  an  act  of  balancing  in  which  the  centre  of  gravity  of  the 
body  is  kej)t  directly  over  the  base  of  support.  In  the  natural  erect  position 
of  the  body  the  centre  of  gravity  of  the  head  is  slightly  in  front  of  the  oc- 
cipito-atlantoid  articulation,  so  that  there  is  a  tendency  for  the  head  to  rock 
forward,  as  is  seen  from  the  nodding  of  the  head  of  one  falling  asleep.  The 
centre  of  gravity  of  the  head  and  trunk  together  is  such  that  the  line  of 
gravity  falls  slightly  behind  a  line  drawn  between  the  centres  of  the  hip- 
joints,  which  would  incline  the  body  to  fall  backward.  The  line  of  gravity 
of  the  head,  trunk,  and  thighs  falls  slightly  behind  the  axis  of  the  knee- 
joints,  and  the  line  of  gravity  of  the  whole  body  slightly  in  front  of  a  line 
connecting  the  two  ankle-joints,  so  that  the  weight  of  the  body  would  tend  to 
flex  the  knee-  and  ankle-joints. 

We  cannot  here  consider  in  detail  the  mechanical  conditions  which  limit 
the  movements  possible  to  the  diflfereut  joints  in  the  erect  position  of  the  body. 
Although  these  conditions  help  to  support  the  body  in  the  upright  position, 
they  are  not  alone  sufficient  to  the  maintenance  of  this  posture,  as  is  shown  by 
the  fact  that  the  cadaver  cannot  be  balanced  upon  its  feet.  That  standing 
requires  the  action  of  the  muscles  is  further  proved  by  the  fatigue  which  is 
experienced  when  one  is  forced  to  stand  for  a  considerable  time.  The  body 
may  be  supported  in  the  standing  position  in  various  attitudes.  Thus,  the 
soldier  standing  at  "attention"  places  the  heels  together,  turns  the  toes  out, 
makes  the  legs  straight  and  parallel,  so  as  to  extend  the  knees  to  their  utmost, 
tilts  back  the  pelvis,  straightens  the  spine,  and  looks  directly  forward.  In 
this  position  many  of  the  muscles  are  relieved  from  action,  for  the  complete 
extension  of  the  knee,  by  bringing  the  line  of  gravity  slightly  in  front  of  the 
axis  of  rotation  and  tending  to  produce  further  extension,  puts  the  ligaments 
on  the  stretch  and  so  locks  the  joint.  Similarly,  in  the  case  of  the  hip-joint 
the  tilting  backward  of  the  pelvis  causes  the  line  of  gravity  to  fall  slightly 
behind  the  joint  and  puts  the  strong  ilio-femoral  ligament  on  the  stretch.  The 
ankle-joint  cannot  be  locked,  and  the  tendency  of  the  body  to  fall  forward  is 
resisted  by  the  strong  nuiscles  of  the  calf  of  the  leg.  The  erect  position  of 
the  spine  and  the  balancing  of  the  head  have  likewise  to  be  maintained  by 
the  action  of  muscles.  Although  this  position  gives  great  stability,  it  cannot 
be  long  maintained  with  comfort.  It  is  less  fatiguing  to  allow  the  joints  to 
be  a  little  more  flexed,  and  to  keep  the  balance  by  the  action  of  the  muscles, 
the  position  being  frequently  changed  so  as  to  bring  fresh  muscles  into  action. 
Perhaps  the  most  restful  standing  position  is  found  in  letting  the  weight  of 
the  body  be  supported  on  one  leg,  the  pelvis  being  tilted  so  as  to  bring  the 
weight  of  the  body  over  the  femur,  and  the  other  being  used  as  a  prop  to  pre- 
serve the  balance.  Absolute  stability  in  standing  is  impossible  for  any  length 
of  time  ;  the  body  is  continually  swaying,  and  a  pencil  resting  on  a  writing 


8(50  AN  AMERICAN   TKXT-HOOK   OF  PHYSIOLOGY. 

surface  })l:K'eil  upon  the  head  is  I'ouml  to  write  a  very  eouiplieuted  euive. 
There  is  a  normal  sway  for  every  individual,  and  this  may  become  markedly 
exaggerated  under  pathological  conditions.  The  maintenance  of  equilibrium 
requires  that  afferent  impulses  shall  continually  pass  to  the  co-ordinating  cen- 
tres which  control  the  muscles  involved  in  this  act,  and  if  any  of  these  normal 
impulses  fail  the  sway  of  the  body  is  increased  ;  for  example,  it  is  more  diffi- 
cult to  stand  steadily  when  the  eyes  are  closed  than  when  they  are  open  ;  the 
absence  of  tiie  normal  sensory  impulses  from  the  skin  of  the  feet,  the  muscles, 
joints,  etc.,  also  makes  standing  more  difficult  and  tends  to  increase  the  sway. 
The  effect  of  the  normal  sway  of  the  body  is  to  shift  the  pressure  and  strain 
from  point  to  point  and  to  relieve  the  different  muscles  from  continuous  action. 

Locomotion.' — The  movements  of  animals  were  first  studied  by  careful 
observation,  accompanied  by  more  or  less  accurate  direct  measurements,  and 
by  these  simple  methods  the  Weber  brothers  ^  arrived  at  quite  accurate  con- 
clusions as  to  the  nature  of  the  processes,  walking,  running,  jumping,  etc. 
These  results  were  greatly  extended  by  Marey,^  who  employed  elaborate 
recording  methods,  and  exact  pictures  of  all  stages  of  these  processes  were 
later  obtained  through  the  remarkable  revelations  of  instantaneous  photog- 
raphy.^ 

Walking. — During  the  act  of  walking,  at  the  same  time  that  the  body  is 
j)ropelled  forward  it  is  continually  supported  by  the  feet,  one  or  the  other  of 
which  is  always  touching  the  ground.  Preparatory  to  beginning  the  move- 
ment the  weight  of  the  body  is  thrown  upon  one  leg,  while  the  other  leg  is 
placed  somewhat  behind  it,  the  knee  and  ankle  being  slightly  flexed.  At  the 
start  the  body  is  given  a  slight  forward  inclination,  then  the  back  leg  is  ex- 
tended and  impels  the  body  forward.  As  the  centre  of  gravity  progresses  so 
as  to  be  no  longer  over  the  supporting  leg,  it  would  fall  were  it  not  that  the 
back  leg  is  at  the  same  instant  swung  forward  to  sustain  it.  As  the  body 
moves  forward  and  its  weight  is  received  by  the  leg  which  has  just  been 
advanced,  the  leg  which  has  been  its  support  is  freed  from  the  weight 
and  becomes  inclined  behind  it.  This  leg  and  foot  are  next  extended,  the 
body  thereby  receiving  another  forward  impulse,  and  then  the  hip-,  knee-, 
and  ankle-joints  flexing  slightly,  the  leg  swings  forward  past  the  supporting 
leg  and  again  becomes  the  support  of  the  body.  The  forward  movement  of 
the  body  is  due  in  part  to  a  slight  inclination  which  tends  to  cause  it  to  fall 
forward,  and  in  part  to  a  push  given  it  by  each  leg  in  turn  as  it  leaves  the 
ground. 

Tiie  amount  of  work  performed  by  the  legs  in  ordinary  walking  is  com- 
l)arutively  slight,  since  the  swing  of  the  leg  is,  like  that  of  a  pendulum,  largely 

^  Beannis:  Physiologic  humaine,  1888,  vol.  ii.  p.  2G9,  gives  many  references  to  the  litera- 
ture of  this  subject. 

*  W.  and  E.  Weber:  Mechnnih  der  menschlichen  Geheiverkzeufje,  1836. 
'  La  Melhode  graphique,  1885. 

*  Marey  :  Melhode  graphique  {supplement),  1885 ;  Muybridge :  The  Horse  in  Motion,  as  Shown 
by  Instantaneous  Photography,  1882. 


VOICE   AND   SPEECH.  861 

a  passive  act.  Speed  in  walking  is  attained  by  inclining  the  body  somewhat 
more  and  by  flexing  the  legs  somewhat  more,  so  that  the  hind  limb  in  extend- 
ing can  pnsii  the  body  forward  with  greater  force.  Tlu;  more  rapid  move- 
ment of  the  body  is  also  accompanied  by  a  more  rapid  forward  swing  of  the 
leg,  the  muscles  aiding  the  force  of  gravity.  The  transfer  of  the  weight  of 
the  body  from  one  leg  to  the  other  causes  it  to  oscillate  slightly  from  side  to 
side,  and  the  falling  motion,  interrupted  by  the  support  olfered  by  the  receiving 
limbs,  causes  a  slight  up-and-down  movement.  These  oscillations  are,  how- 
ever, very  slight ;  the  tendency  for  the  centre  of  gravity  to  move  from  side  to 
side  as  the  legs  alternately  {nish  the  body  forward  is  in  part  balanced  by  the 
swino-  of  the  opposite  arm  ;  and  the  vertical  oscillation  is  largely  obviated, 
because  the  supporting  leg  is  extending — i.  e.  lengthening— as  the  body  moves 
forward,  and  so  sustains  the  jwlvis  until  its  weight  is  taken  by  the  other  leg. 

In  running  the  body  is  inclined  more  than  in  walking,  and  the  legs  are 
more  flexed  in  order  that  the  extension  movement  of  the  back  leg,  which 
drives  the  body  forward,  may  be  more  effective.  In  running  the  body  is  pro- 
pelled by  a  series  of  spring-like  movements  and  there  are  times  when  both 
feet  are  oiF  the  ground,  the  back  leg  leaving  the  ground  before  the  other 
touches  it.  The  increase  in  speed  is  due  in  part  to  the  greater  forward  incli- 
nation of  the  body,  but  more  especially  to  the  vigorous  action  of  the  muscles. 

B.  Voice  and  Speech. 
1.  Structure  of  the  Larynx. 

Voice-production. — The  human  voice  is  produced  by  vibration  of  the 
true  vocal  cords,  normally  brought  about  by  an  expiratory  blast  of  air  passing 
between  them  while  they  are  approximated  and  held  in  a  state  of  tension  by 
muscular  action.  Mere  vibration  of  the  cords  could  produce  but  a  feeble 
sound ;  the  voice  owes  its  intensity  both  to  the  energy  of  the  expiratory  blast 
(Helmholtz)  ^  and  to  the  reinforcement  of  the  vibrations  by  the  resonating 
cavities  above  and  below  the  cords. 

A  true  conception  of  the  action  of  the  larynx  can  only  be  gained  by  a  pre- 
liminary study  of  the  organ  in  situ,  in  its  relations  with  the  trachea,  pharynx, 
tongue,  extrinsic  muscles,  and  hyoidean  apparatus.  Removed  froin  its  con- 
nections, the  larynx,  in  vertical  transverse  section,  is  seen  to  be  shaped  some- 
what like  an  hour-glass,  the  true  vocal  cords  forming  the  line  of  constriction 
half  way  between  the  top  of  the  epiglottis  and  the  lower  border  of  the  cri- 
coid cartilage  (Fig.  295).  In  median  vertical  section  the  axis  of  the  larynx 
above  the  vocal  cords  extends  decidedly  backward,  and  below  the  cords  the 
axis  is  nearly  perpendicular  to  the  plane  in  which  they  lie.  The  epiglottis  is  an 
ovoid  lamella  of  elastic  cartilage,  shaped  like  a  shoe-horn,  that  leans  backward 
over  the  laryngeal  orifice  so  that  the  observer  nuist  look  down  obliquely  in 
order  to*inspect  the  cavity  of  the  laiynx  (Fig.  299).  The  mucous  membrane 
is  thickened  into  a  slight  prominence,  known  as  the  "  cushion,"  at  the  base  of 
^  Quoted  by  Griitzner:  Hernumn's  Handb.  der  Phyxiohicjlr,  Bd.  11,  Th.  2,  S.  14,  1879. 


862 


AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 


\    -10 


the  oj)ii>;lottis.     The  e|)igh)tti.s,  \\\\\v\\  is  extremely  movable  in  a  median  ])lane, 
may  be  tilted  backward  so  as  to  close  completely  the  entrance  into  tlie  hirynx. 

Functions  of  the  Epiglottis. — One 
fnnetion  of  tlie  e])iglottis  seems  obviously 
to  serve  as  a  cover  lor  the  superior  entrance 
of  the  larynx,  over  which  it  is  said  to  shut 
in  the  act  of  swallowing.  But  it  is  found 
tiiat  deglutition  occurs  in  a  normal  manner 
when  the  epiglottis  is  wanting  or  is  too  small 
to  cover  the  aperture,  the  sphincter  nniscles 
surrounding  the  latter  being  cajiable  of  pro- 
tecting the  larynx  against  the  entrance  of 
foreign  substances.  It  is  held  by  some 
that  the  epiglottis  has  an  important  influ- 
ence in  modifying  the  voice  according  as  it 
more  or  less  completely  covers  the  exit  to 
the  column  of  vibrating  air.  It  is  also  held 
that  the  epiglottis  acts  as  a  sort  of  sounding- 
board,  taking  up  and  i-einforcing  the  vibra- 
tions of  the  air-column  impinging  against  it.' 
Sweeping  dowuAvard  and  backward  from 

Fig.  295.— Vertical  transverse  section  of     each    edge    of    the    epiglottis    is   a  sheet    of 
the  larvnx  (after  Testut):  1,  posterior  face  of  i  ,i  •    ;   .,•      rij 

epiglottis,  Ivith  1',  its  cushion;  2,  aryteuo-    MUCOUS  membrane,  the  ary-cpighftw  fold, 
epiglottic  fold;  3,  ventricular  band, or  false    which  forms  the  lateral  rim  of  the  Superior 

vocal  cord ;  4,  true  vocal  cord ;  5,  central  c   .\        ^  j       i  •   i  i      • 

fossaofMerkei;  6,  ventricle  of  larynx,  with    aperture  of  the  larvnx  and  Avhich  ends  lU, 
6',  its  ascending  pouch;  7,  anterior  portion    ^^^^  covers  posteriori V,  the  arytenoid  carti- 

of  cricoid ;  8,  section  of  cricoid ;  9,  thyroid,  mi  i     ^  •  ±\ 

cut  surface;  10,  thyrohyoid  membrane;  11,    lagcs.    The  rouuded  prominence  on  the  pos- 
thyrohyoid  muscle;  12,  aryteno-epigiottic    terior  corncr  of  this  fold  is  made  bv  the  car- 

muscle;    13,    thyro-arytenoid    muscle,   with  ^    _  " 

13',  its  inner  division,  contained  in  the  vocal   tilage  of  Santorini,  and  a  second,  less  marked, 
r«ti^r;:o4',^l%TX;"Mir.S»':   ^welUng  external  toit,l,ytl,e  ,a,iila,,e.f 

Wrisherg  (Fig.  302).  Looking  down  into 
the  larynx,  it  is  seen  that  its  lateral  walls  approach  each  other  by  the  develop- 
ment on  each  side  of  a  permanent  ridge  of  mucous  membrane,  known  as  the 
ventricular  hand  or  fahe  vocnl  cord  (Fig.  295). 

Ventricular  Bands  and  Ventricles  of  Morg-agni. —  The  ventricular  hands 
or  false  vocal  cords  arise  from  the  thyroid  cartilage  near  the  median  line,  a 
short  distance  above  the  origin  of  the  true  cords.  They  are  inserted  into  the 
arytenoid  cartilages  somewhat  below  the  apices  of  the  latter.  Their  free  bor- 
der is  more  or  less  ligamentous  in  structure.  They  are  brought  into  contact 
by  the  sphincter  muscles  of  the  larynx,  and  thus  protect  the  glottis.  It  has 
even  been  stated  that,  in  paralysis  of  the  true  cords,  they  may  be  set  in  vibra- 
tion and  be  the  seat  of  voice-formation.  So-called  "  oedema  of  tlie  glottis  "  is 
chiefly  due  to  accumulation  of  fluid  in  the  wide  lymph-spaces  found  in  the 
false  cords. 

'  Mills:  Journ.  of  Physiology,  1883,  vol.  iv.  p.  135. 


VOICE   AND   SPEECH.  863 

The  ventricular  bduds  are  luirallcl  with  and  just  above  tlic  true  vocal  cords, 
from  which  thov  arc  separated  by  a  narrow  slit.  They  do  not,  however,  reach 
so  near  the  middle  line  as  the  true  cords,  winch  can  be  seen  between  and  below 
the  bands.  The  ventricular  bands  project  more  or  less  into  the  cavity  of  the 
larynx  like  overhanging  lips,  so  that  each  band  forms  the  inner  wall  of  a 
space  closed  by  the  true  vocal  cords  below,  and  communicating  with  the  cavity 
of  the  larynx  through  the  narrow  slit  above  mentioned.  The  spaces  thus 
bounded  internally  by  the  false  cords  are  known  as 

Tlie  Ventndes  of  Morgagni  (Fig.  295). — No  complete  explanation  has  been 
offered  as  to  the  purposes  served  by  the  ventricles  of  Morgagni  and  the  false 
vocal  cords.  Numerous  mucous  and  serous  glands  seated  in  the  ventricular 
bands  pour  their  secretions  into  the  ventricles,  whence  the  fluid  may  be  trans- 
mitted bv  the  overhanging  lips  of  the  ventricular  bands  to  the  true  vocal 
cords;  hence,  an  important  function  of  the  former  structure,  probably,  is  to 
supply  to  the  vocal  cords  the  moisture  necessary  to  their  normal  action.  The 
secretion  contained  within  the  ventricle  is  protected  by  the  ventricular  band 
from  the  desiccating  influence  of  the  passing  air-currents.  The  existence  of 
the  ventricular  spaces  also  permits  free  upward  vibration  of  the  true  cords. 
The  ventricles  of  Morgagni  in  some  of  the  lower  animals,  as  the  higher  apes, 
communicate  with  extensive  cavities  which  serve  an  obvious  purpose  as  reso- 
nating chambers  for  the  voice,  and  perhaps  the  preservation  of  this  function  in 
the  ventricles  themselves  is  still  of  importance  in  the  human  being.  It  is  not 
improbable  that  the  ventricular  bands  find  their  most  important  function  as 
sphincters  of  the  larynx,  the  superior  opening  of  which  may  be  firmly  occluded 
by  their  approximation.  The  well-known  fact  that  during  strong  muscular 
effort  the  breath  is  held  from  escaping  is,  according  to  Brunton  and  Cash,' 
due  to  the  meeting  of  the  false  cords  in  the  middle  line.  The  overhanging 
shape  of  the  cords  allows  them  to  be  readily  separated  by  an  inspiratory  blast, 
but  causes  them  to  be  more  firmly  approximated  by  an  expiratory  effort.  This 
mechanism  recalls  the  mode  of  action  of  the  semilunar  valves  of  the  heart. 

The  true  vocal  cords  arise  from  the  angle  formed  by  the  sides  of  the  thyroid 
cartilage  where  they  meet  in  front,  a  little  below  its  middle  point,  and,  passing 
backward,  are  inserted  into  the  vocal  i)rocesses  of  the  arytenoid  cartilages. 
The  aperture  between  the  vocal  cords  and  between  the  vocal  processes  of  the 
arytenoids  is  known  as  the  glottis  or  rima  glottidis  (Figs.  301,  302).  Since,  as 
will  be  seen  later,  the  vocal  cords  may  be  brought  together  while  the  vocal  pro- 
cesses of  the  arytenoids  are  widely  separated  at  their  bases,  the  space  between 
the  cords  themselves  is  sometimes  called  the  rima  vocalis  and  that  between  the 
vocal  processes  the  rima  respiratoria. 

In  the  adult  male  the  vocal  cords  measure  about  15  millimeters  in  length 
and  the  vocal  processes  measure  8  millimeters  in  addition.  In  the  female  the 
cords  are  from  10  to  11  millimeters  in  length.  The  free  edges  of  the  cord  are 
thin  and  straight  and  are  directed  upward ;  their  median  surfaces  are  flattened. 
Each  cord  is  composed  of  a  dense  bundle  of  fibres  of  yellow  elastic  tissue, 

*  Brunton  and  Cash :  Journ.  Anat.  and  Phys.,  1883,  vol.  xvii. 


864 


AX  AMERICAN   TEXT- BO  OK   OF  PHYSIOLOdV 


which  fibres,  tliough  having  a  general  h)ngitutlinal  course,  are  interwoven,  and 
send  off  shoots  hiterally  into  the  subjacent  tissue.  The  compact  ligament, 
known  commonly  as  the  "  vocal  cord,"  forms  only  the  free  edge  of  a  reflexion 
from  the  side  wall  of  the  larynx.  Tiiis  reflexion  is  wedge-shaped  in  a  vertical, 
transverse  section  and  contains  much  elastic  tissue  and  the  internal  and  part 
of  the   external    thyro-arytenoid  muscle  (Fig.  295).     This  whole   structure 

properly  forms  the  vocal  cord,  and  by 
contraction  of  its  contained  muscle  its 
thickness  and  vibrating  qualities  may 
be  greatly   modi  tied. 

Like  the  trachea,  tiie  larynx,  with  the 
exception  of  the  vocal  cords,  is  lined 


Fig.  296.— Cartilages  of  the  larynx,  separated 
(Stoerk) :  1,  epiglottis ;  2,  petiolus ;  3,  median 
notch  of  thyroid ;  4,  superior  cornu  of  thyroid ; 
5,  attachment  of  stylo-pharyngeus  muscle ;  6, 
origin  of  thyro-epiglottic  ligament :  7,  origin  of 
the  thyro-arytenoid  muscle ;  8,  origin  of  true 
vocal  cord  :  9,  inferior  cornu  of  thyroid ;  10,  car- 
tilage of  Wrisberg ;  11,  cartilage  of  Santorini ;  12, 
12',  arytenoid  cartilages,  showing  attachments  of 
the  transverse  arytenoid  muscle ;  13,  13',  pro- 
cessus muscularis,  showing  attachments  of  the 
posterior  and  lateral  crico-arytenoid  muscles; 
14,  base  of  the  arytenoid  cartilage ;  15,  vocal  pro- 
cesses of  the  arytenoids  ;  16,  articular  surface  for 
the  base  of  the  arytenoid  cartilage  ;  17,  po.sterior 
view  of  cricoid  cartilage,  with  outline  of  attach- 
ment of  the  posterior  crico-arytenoid  muscle; 
18,  articular  surface  for  inferior  cornu  of  thyroid 
cartilage. 


Fig.  297.— Cartilages  and  ligaments  of  the 
larynx,  posterior  view  (after  Stoerk) :  1,  epiglot- 
tis :  2.  cushion  of  the  epiglottis :  3.  cartilage  of 
Wrisberg ;  4,  ary-epiglottic  ligament :  r>,  ^,  mucous 
membrane  ;  6,  cartilage  of  Santorini :  7,  arytenoid 
cartilage:  9,  its  processus  muscularis;  10,  crico- 
arytenoid ligament:  11.  cricoid  cartilage;  12,  in- 
ferior cornu  of  thyroid  cartilage:  13,  posterior 
superior  cerato-cricoid  ligament;  13'.  posterior 
inferior  cerato-cricoid  ligament ;  14,  cartilages 
of  the  trachea:  Ui,  membranous  jiortion  of 
trachea. 


by  columnar,  ciliated  epithelium,  the  direction  of  whose  movement  is  upward 
toward  the  pharynx.  The  vocal  cords  are  covered  by  thin,  flat,  stratified  epi- 
thelium. The  inner  surface  of  the  epiglottis,  the  walls  of  the  ventricles,  and 
the  ventricular  bands  contain  ranch  adenoid  tissue,  the  spaces  of  which  are  apt 
to  become  distended  with  fluid,  giving  ri,<e  to  a'dema  of  tho.se  parts.  The 
whole  mucous  membrane  of  the  larynx,  except  over  the  vocal  cords,  is  richly 
supplied  with  glands  both  mucous  and  .serous  in  character. 


VOICE  AND   SPEECH.  865 

Cartilages  of  the  Larynx. — The  niechanisin  of  the  larynx  is  supported 
by  a  skeleton  composed  of  several  pieces  of  cartilage.  The  lowermost  of  these 
cartilages  is  the  cricoid  cartilage,  so  called  from  its  resemblance  to  a  signet  ring 
(Fig.  296).  The  cricoid  cartilage  is  situated  above  the  topmost  ring  of  the 
trachea  to  which  it  is  attached  by  a  membrane.  The  vertical  measurement  of 
the  cricoid  cartilage  is  about  one  inch  on  its  posterior,  and  one-quarter  inch  on 
its  anterior  surface.  Superior  to,  and  partly  overlapping  the  cricoid,  is  the 
thyroid  cartilage,  which  forms  an  incomplete  ring,  being  deficient  postei'iorly 
(Fig.  296).  The  free  corners  of  the  thyroid  behind  are  prolonged  upward  or 
downward  into  projections  known  as  the  cornaa.  The  upper  pair  are  attached 
to  the  extremities  of  the  greater  cornua  of  the  hyoid  bone,  while  by  the  inner 
surface  of  the  ends  of  the  lower  cornua  the  thyroid  is  articulated  with  the 
cricoid  cartilage  and  rotates  upon  it  around  an  axis  drawn  through  the  points 
of  articulation.  The  lower  anterior  border  of  the  thyroid  cartilage  is  evenly 
concave,  but  its  upj)er  border  has  a  deep  narrow  notch  in  the  middle  line. 
The  upper  half  of  the  thyroid  in  front  projects  sharply  forward  in  an  elevation 
known  as  Adam's  apple  (pomum  Adami),  which  is  much  more  marked  in  adult 
males  than  in  females.  The  elliptical  space  between  the  cricoid  and  thyroid 
cartilages  in  front  is  covered  by  a  membrane.  Adam's  apple,  the  anterior  part 
of  the  cricoid  ring,  and  the  space  between  the  two,  can  easily  be  felt  in  the  liv- 
ingsubject ;  they  rise  perceptibly  toward  the  head  with  each  swallowing  movement. 

The  arytenoid  cartilages  are  two  in  number  and  are  similar  in  shape  (Figs. 
296,  297).  Each  cartilage,  which  has  somewhat  the  form  of  a  triangular 
pyramid,  is  seated  on,  and  articulates  with,  the  highest  point  on  the  posterior 
part  of  the  cricoid  cartilage  some  distance  from  the  middle  line.  Of  the  free 
faces  of  the  pyramid,  one  looks  backward,  one  toward  the  middle  line,  and  the 
third  outward  and  forward.  Each  face  is  more  or  less  concave.  The  apex  of 
each  arytenoid  cartilage  is  capped  by  a  small  body  called  the  cartilage  of  8an- 
torini  or,  from  its  bent  shape,  corniculum  laryngis  (Figs.  296,  297).  Outside 
and  in  front  of  the  latter  is  the  minute  cuneiform  cartilage  or  cartilage  of 
Wrisberg,  enclosed  in  the  ary-epiglottic  fold.  The  lateral  posterior  corner  of 
the  arytenoid  cartilage  forms  a  blunt  projection  which  serves  for  the  attach- 
ment of  muscles,  the  processus  muscidaris.  The  anterior,  lower,  and  median 
part  of  each  cartilage  is  of  especial  interest,  since  it  serves  for  the  posterior 
attachment  of  the  vocal  cord  ;  it  is  known  as  the  processus  vocalis. 

The  thyroid  and  cricoid  cartilages  and  the  body  of  the  arytenoids  are  of 
hyaline  cartilage,  and  tend  to  become  ossified  in  middle  life.  The  other  carti- 
lages and  the  vocal  processes  of  the  arytenoids  are  composed  of  the  elastic 
variety. 

The  Muscles  of  the  Larynx  may  be  divided  into  two  classes — the  extrinsic 
and  the  intrinsic  ;  the  former  find  their  origin  outside  the  larynx,  and  the  latter 
both  arise  and  are  inserted  within  it. 

Extrinsic  Muscles. — To  this  group  belong  the  sterno-hyoi.d,  the  sterno-thy- 
roid,  and  the  omo-hyoid  muscles,  which  depress  the  larynx  or  hyoid  bone ;  the 
thyro-hyoid  muscle,  which  depresses  the  hyoid  bone  or  elevates  the  thyroid 


866 


AiY  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 


cartilage.  To  the  elevators  of  the  laryux  belong  the  (jenio-hyoid ,  the  mylo- 
hyoid, the  digastric,  the  stylo-hyoid,  and  the  hyo-ylossiis.  The  muscles  of  the 
palate  and  the  constrictore  of  the  pharynx  enter  into  coordinated  action  with  the 
above.  When  food  is  passing  through  the  pharyx  in  the  act  of  swallowing, 
the  hyoid  bone  is  drawn  upward  and  forward,  raising  the  larynx  with  it ;  the 
tongue  is  thrown  backward  so  that  the  epiglottis  covers  the  entrance  into  the 
larynx,  and  the  constrictoi-s  of  the  larynx  contract,  completely  closing  the 
entrance  into  that  organ. 

The  intrinsic  muscles  of  the  larynx  are  the  crico-thyroids,  the  lateral  crico- 
arytenoids, the  posterior  crico-arytenoids,  the  arytenoid,  the  aryteno-epiglot- 
tideans,  and  the  thyro-arytenoids ;  all  being  in  pairs  except  the  arytenoid, 
which  crosses  the  middle  line.  The  crico-thyroid  muscle  arises  from  the  front 
and  side  of  the  cricoid  cartilage  and,  passing  upward  and  backward,  is  inserted 
into  the  lower  edge  of  the  thyroid  cartilage  (Fig.  298).  The  action  of  the  crico- 
thyroid muscle  is  to  diminish  the  distance  between  the  thyroid  and  cricoid  car- 
tilages in  front,  either  by  depressing  the  front  of  the  thyroid  or  by  elevating 
that  of  the  cricoid  cartilage,  or  both.  In  the  first  case  the  distance  between 
the  anterior  attachment  of  the  vocal  cords  and  the  vocal  processes  of  the 

arytenoid  cartilages  is  increased  by  movement  of 
the  thyroid,  and  in  the  second  case  the  same  effect 
is  produced  by  backward  rotation  of  the  edge  of 
the  cricoid  upon  which  the  arytenoid  cartilages  are 
seated  (Fig.  297).  The  muscle,  therefore,  is  a 
tensor  of  the  vocal  cords.  It  is,  probably,  the 
mechanism  we  ordinarily  use  in  raising  the  pitch 
of  the  voice  when  the  vocal  machinery  has  been 
"set"  by  the  other  muscles  (see  below).  If  the 
fingers  be  placed  on  the  cricoid  ring  and  on  the 
pomum  Adami  while  the  ascending  scale  is  sung 
in  the  middle  chest  register,  both  descent  of  the 
front  of  the  thyroid  and  ascent  of  the  cricoid  can 
be  made  out.  The  kdercd  crico-arytenoid  muscle 
arises  from  the  upper,  lateral  border  of  the  cricoid 
cartilage,  and  passes  upward  and  backward  to  be 
inserted  into  the  outer  edge  of  the  arytenoid  car- 
tilage, on  and  in  front  of  the  lateral  prominence 
(Fig.  299).  Its  main  action  is  to  wheel  the 
vocal  process  of  the  arytenoid  toward  the  middle 
line  and  thus  approximate  the  vocal  cords.  The  j^osterior  crico-arytenoid  is  a 
large  muscle,  which  rises  from  the  median  posterior  surface  of  the  cricoid  car- 
tilage and  passes  upward  and  outward  to  be  inserted  into  the  outer  surface  of  the 
ar}i;enoid  cartilage,  behind  and  above  the  insertion  of  the  lateral  crico-arytenoid 
(Fig.  300).  Its  action  is  to  turn  the  vocal  processes  outward  and  thus  abduct  the 
vocal  cords.  The  posterior  crico-arytenoid  occupies  an  important  position  in  the 
group  of  respiratory  muscles ;  during  vigorous  inspiration  it  is  brought  into  action 


Fig.  298.— Lateral  view  of  the 
cartilages  of  larynx  with  the  crico- 
thyroid muscle  {Qiiain'i'  Anatomy, 
after  Willis):  1,  crico-thyroid  mus- 
cle :  2,  crico-thyroid  membrane ;  3, 
cricoid  cartilage ;  4,  thyroid  carti- 
lage ;  5,  upper  rings  of  the  trachea. 


VOICE    AND    SPEECH. 


867 


and  widens  the  glottis.  Paralysis  of  tliis  muscle  is  a  most  serious  condition,  since 
it  is  followed  by  ai)})roximation  of,  and  inability  to  separate,  the  vocal  cords. 
The  arytenoid,  or  trmisva'se  or  posterior  arytenoid  muscle,  the  single  unpaired 


Fig.  300.— Larynx  with  its  muscles,  posterior 
view  (Stoerli) :  1,  epiglottis ;  2,  cushion ;  3,  ary- 
epiglottic  ligament ;  4,  cartilage  of  Wrisberg ; 
5,  cartilage  of  Santorini ;  G,  oblique  arytenoid 
muscles;  7,  transverse  arytenoid  muscle;  8, 
posterior  crieo-arytenoid  muscle ;  9,  inferior 
cornu  of  thyroid  cartilage;  10,  cricoid  car- 
tilage ;  11,  posterior  inferior  cerato-cricoid  lig- 
ament; 12,  cartilaginous  portion;  13,  mem- 
branous portion  of  trachea. 


Fig.  299.— Larynx  and  its  lateral  muscles  after 
removal  of  the  left  plate  of  the  thyroid  cartilage 
(Stoerk) :  1,  thyroid  cartilage  ;  2,  thyro-cpiglottic  mus- 
cle ;  3,  cartilage  of  Wrisberg ;  4,  ary-epiglottic  mus- 
cle; 5,  cartilage  of  Santorini;  6,  oblique  arytenoid 
muscles ;  7,  thyro-arytenoid  muscle ;  8,  transverse 
arytenoid  muscle ;  9,  processus  muscularis  of  aryte- 
noid cartilage ;  10, lateral  crico-arytenoid  muscle;  11, 
posterior  crico-arytenoid  muscle ;  12,  crico-thyroid 
membrane ;  13,  cricoid  cartilage  ;  14,  attachment  of 
crico-thyroid  muscle;  15,  articular  surface  for  the 
inferior  cornu  of  the  thyroid  cartilage;  16,  crico- 
tracheal  ligament;  17,  cartilages  of  trachea;  18, 
membranous  part  of  trachea. 

muscle  of  the  larynx,  is  a  considerable  baud  pa.ssing  across  the  middle  line  from 
the  posterior  surface  of  one  arytenoid  cartilage  to  that  of  the  other  (Fig.  300). 
Its  action  is  to  draw  the  arytenoid  cartilages  together  in  the  middle  line  and 
approximate  the  vocal  processes;  its  action  is  essential  in  closing  the  glottis.  In 
the  resting  larynx  the  arytenoid  cartilages  are  kept  apart  by  the  elastic  tension 
of  the  parts.  The  aryteno-epiglottidean,  sometimes  called  the  oblique  arytenoid, 
muscles  consist  of  two  bundles  of  fibres  seated  upon  the  surface  of  the  arytenoid 
muscle  (Fig.  300).  Each  muscle  arises  from  the  outer  posterior  angle  of  the 
arytenoid  cartilage,  and,  passing  upward  and  inward,  crosses  in  the  middle  line 
partly  to  be  inserted  into  the  outer  and  upper  part  of  the  opposite  cartilage, 
partly  to  penetrate  the  ary-epiglottic  fold  as  far  as  the  epiglottis,  and  the 
remainder  to  join  some  fibres  of  the  thyro-arytenoid  muscle.  The  action  of 
the  aryteno-epiglottidean  muscles  is  to  close  the  glottis.  The  thyro-arytenoid 
is  a  muscle  of  complex  mechanism,  usually  described  as  formed  of  two  parts, 
an  external  and  an  internal.    The  external  thyro-arytenoid  arises  from  the  lower 


sns 


,LV    AMKlilCAy    TEXT- HOOK    OF   PHYSIOLOGY. 


}>:irt  (it'  tilt'  uiiu'le  of  the  tliyroid  carlllajre;  its  fibres  jniss,  for  the  most  part, 
baekwanl  and  soinewliat  u])\vanl  and  outward  to  be  inserted  into  the  outer 
edge  of  the  arytenoid  cartilage  and  its  lateral  processus  miisculcn-ls  (Figs.  295, 
301).  Some  of  its  bundles  of  fibres,  however,  have  different  directions,  and 
a  portion  of  them  pai>s  upward  into  the  ventricular  bauds.  The  internal  thyro- 
(iri/tenoid,  wedge-shaped  in  trausverse  section,  lies  between  the  muscular  divis- 
ion just  described  and  the  vocal  ligament,  by  which  its  thin  median  edge  is 
covered.  The  internal  thyro-arytenoid  arises  from  the  anterior  angle  of  the 
thvroid  cartilage  and  is  inserted  into  the  processus  vocal  is  and  the  outer  face  of 
the  arytenoid  cartilage.  Certain  fibre-bundles  of  this,  as  of  the  external 
division  of  the  muscle,  pass  in  various  directions,  some  of  them  being  inserted 
into  the  free  border  of  the  vocal  cord.  The  action  of  the  muscle  is,  on  the 
whole,  to  draw  the  arytenoids  forward  and  thus  relax  the  vocal  cords;  but,  by 
its  contraction,  the  cords  may  also  be  approximated  and  their  thickness,  and 
probably  their  elasticity,  extensively  modified. 

Specific  Actions  of  the  Laryngeal  Muscles. — To  sum  uj)  the  various 
effects  of  the  muscular  action  on  the  larynx  :  A  sjiliincfer  action  of  the  laiyux 
is  brought  about  by  the  combined  contraction  of  all  the  muscles  with  the 
exception  of  the  crico-thyroids  and  the  posterior  crico-arytenoids ;  the  rocal 

cords  are  adducted  and  the  glottis  nar- 
ronrd  by  the  trausvei*se  and  oblique  ary- 
tenoids, the  external  thyrt)-arytenoids, 
.^m.thi/.ar.i.     mjj    ^\'^^,    lateral    crico-arytenoids ;    the 
.m.ihy.ar.e.  vocal  cords  are  abducted  and  the  glottis 
.Xm.thy.ar.  n-idcned  chiefly  or  wholly  by  the  poste- 
rior  crico-arytenoids ;    the    vocal   cords 
arc  made  toise    by  contraction  of  the 
crico-thyroids;  the  vocal  cords  arc  slack- 
ened  by  the   combined   action    of  the 
sphincter  group  and  especially  by  the 
external  thyro-arytenoids. 

It  will  easily  be  seen  that  in  the 
larynx,  as  in  the  skeleton  at  large,  the 
efficiency  of  any  single  nmscle  involves 
the  action  of  accessory  uniscles;  thus, 
contraction  of  the  crico-thyroid  could 
have  little  effect  in  tightening  the  vocal 
cords  were  not  the  arytent)id  cartilages 
fixed  by  contraction  of  the  posterior  crico-arytenoid  and  arytenoid  Jiniscles. 
Nerve-supply  of  the  Larynx. — The  larynx  receives  its  nerve-sui>])ly  from 
the  superior  and  the  inferior  or  recurrent  laryngeal  nerves.  The  extremely 
scnisitive  surface  of  the  mucous  membrane  of  the  organ  above  the  vocal  cords 
is  supplied  by  sensory  filaments  of  the  superior  laryngeal  nerve.  The  superior 
laryngeal  also  supplies  motor  fibres  to  the  crico-thyroid  muscle,  whose  action 
as  a  tightener  of  the  vocal  cords  is  peculiar.     All  the  other  muscles  of  the 


Fig.  301.— Diagram  to  illustrate  the  thyro-aryte- 
noid muscles;  the  figure  represents  a  transverse 
section  of  the  larynx  through  the  bases  of  the 
arytenoid  cartilages  (redrawn  from  Foster) :  Ary, 
arytenoid  cartilage:  p.m,  processus  nuiscularis; 
p.v,  processus  vocalis :  TTi,  thyroid  cartilage;  c.i;, 
vocal  cords ;  (E  is  placed  in  the  cesophagus ; 
m.thy.ar.i,  internal  thyro-arytenoid  muscle; 
vi.tky.ar.e,  external  thyro-arytenoid  muscle; 
m.thy.ar.ep,  part  of  the  thyro-ary-epiglottic  mus- 
cle, cut  more  or  less  transversely ;  m.ar.t,  trans- 
verse arvtenoid  muscle. 


VOICE  AND   SPEECH. 


869 


larynx  receive  tlioir  motor  impulsos  iVoiii  the  inferior  larvnt^otil  nerve.     Much 
of  the  nervous  mechanism  of  the  larynx  is  still  in  dispute. 

Laryngoscopic  Appearance  of  the  Larynx. — Much  may  be  learned  hy 
inspection  of  the  larvnx  dnrinji;  life  hy  means  <tf  tli<'  larynj^oscopic  mirror.  It 
is  not  difficult  for  an  observer  to  examine  his  own  larynx  by  placing  himself 
before  a  second  mirror  in  which  may  be  seen  the  image  reflected  from  the 
laryngoscope.  To  inspect  the  larynx  the  tongue  must  be  held  well  out  so 
as  to  pull  forward  the  epiglottis,  then  the  structures  below  appear  in  the 
laryngoscopic  mirror  in  reversed  position.  Beneath  the  middle  of  the  e])iglottis 
the  cushion  may  be  seen  as  a  slight  swelling,  and  continuing  downward  aud 
backward  from  the  edges  of  the  cartilage,  may  be  seen  the  ary-epiglottic  folds, 
each  marked  at  its  extremity  by  two  rounded  nodules,  the  cartilages  of  AVris- 
bergand  Santorini  (Fig.  302).  In  quiet  breathing  the  glottis  is  nearly  stationary 
and  opened  to  the  extent  of  from  3  to  5  millimeters.  The  vocal  cords  bounding 
it  look  white  and  glistening  in  contrast  with  the  red  color  of  the  general  mucous 
membrane.  The  cartilages  of  Santorini  are  several  millimeters  apart,  and  a 
sheet  of  mucous  membrane  reaches  from  one  to  the  other.     The  ventricular 


Fig.  302.— The  larj-ugoscopic  image  in  easy  breathing  (Stoerk):  1,  base  of  the  tongue;  2,  median 
glosso-epiglotticligament;  3,  vallecula;  4,  lateral  glosso-epiglottic  ligament;  5,  epiglottis;  6,  cushion  of 
epiglottis ;  7,  cornu  major  of  hyoid  bone ;  8,  ventricular  band,  or  false  vocal  cord ;  9,  true  vocal  cord ; 
opening  of  the  ventricle  of  Morgagni  seen  between  8  and  9:  10,  folds  of  mucous  membrane;  11,  sinus 
pyriformis;  12,  cartilage  of  Wrisberg;  13,  aryteno-epiglottic  fold;  14,  rima  glottidis;  15,  arytenoid  carti- 
lage ;  16,  cartilage  of  Santorini ;  17,  posterior  wall  of  pharynx. 

bands  are  seen  as  red  shelves  reaching  to  the  outer  margin  of  the  shining 
cords  and  separated  from  the  latter  by  a  dark  line  which  is  the  entrance  into 
the  ventricles  of  Morgagni. 

When  a  deep  inspiration  is  taken  the  glottis  is  widely  opened,  even  to  the 
extent  of  half  an  inch  ;  an  angle  is  formed  between  the  vocal  process  of  the 
arytenoid  and  the  vocal  cord,  the  space  between  the  cartilages  of  Santorini  is 
widened,  and  the  rings  of  the  trachea,  and  even  its  bifurcation  may  be  seen 
below.  With  the  succeeding  expiration  the  glottis  again  becomes  narrow. 
When  the  voice  is  sounded  the  picture  at  once  changes.  The  space  between 
the  cartilages  of  Santorini  is  obliterated,  the  vocal  processes  aud  cords  ar^ 


870  AN  AMERTCAN   TEXT-BOOK   OF  PHYSIOLOGY. 

brouj^C^it  togetlier,  aiul  the  ^vllole  rim  of  the  glottis  or  the  vocal  cords  alone, 
according  to  the  pitch  of  the  note,  may  be  seen  to  vibrate. 

2.  The  Voice. 

The  vocal  machinery  consists  of — (1)  the  motive  jiower  or  breath  ;  (2) 
the  larvnx,  which  forms  the  tone;  (3)  the  chest,  the  pharynx,  the  mouth,  and 
the  nose,  which  color  the  tone;  and  (4)  the  organs  of  articulation.^ 

The  production  of  voice  is  nndoubtedly  accomplished  by  the  vibration  of 
the  vocal  cords  which  have  previously  been  approximated  in  the  middle  line 
and  made  tense  through  action  of  the  nerve-muscular  ai)paratus  already  de- 
scribed. A  blast  of  air  from  below  pressing  against  the  cords  so  adjusted, 
causes  them  to  separate  and  fall  into  vibration.  We  have  to  distinguish  in 
voice  the  three  features  of  loudness,  jyitch,  and  quality. 

The  loudness  of  the  tone  depends  on  two  factors:  (1)  the  strength  of  the 
tone-producing  blast  as  determining  not  only  the  amplitude  of  vibration  of 
the  vocal  cords,  but  also  the  energy  with  which  the  air  is  expelled;  (2) 
the  resonance  of  the  two  chambers  between  which  the  vocal  cords  are  sus- 
pended, the  chest  below  and  the  cavities  of  the  head  above,  whose  walls  and 
contained  air,  by  their  sympathetic  vibration,  powerfully  reinforce  the  oscilla- 
tions imparted  to  them. 

The  pitch  of  the  voice  is  determined  by  the  thickness,  tension,  and  length 
of  the  vocal  cords,  conditions  which  regulate  the  pitch  of  the  note  obtained 
from  anv  vibrating  string.  The  thickness  and  the  elastic  quality  of  the  cords 
are  probably  largely  under  the  control  of  the  thyro-aryteuoid  muscle.  The 
principal  tensor  of  the  cords  is  the  crico-thyroid  muscle.  Other  muscles,  as 
described  above,  may  so  fix  the  arytenoid  cartilages  that  their  vocal  processes 
may  be  prevented  from  taking  part  in  the  vibration  of  the  cords  throughout 
the  whole  and  also,  possibly,  throughout  part  only  of  their  length.  This 
dampening  of  the  vocal  processes  of  the  arytenoids  may  be  accomplished  either 
by  pressure  applied  to  them  throughout  their  M'hole  length,  in  which  case  the 
posterior  part  of  the  glottis  is  closed,  or  they  may  be  pressed  together  at  the 
tips  alone,  leaving  the  respiratory  glottis  open  as  a  triangular  aperture. 

Quality. — Variation  in  the  quality  of  the  voice  depends  on  the  fact  that 
vibrations  of  the  vocal  cords  are  composite  in  character,  giving  rise  to  notes 
made  up  of  a  fundamental  tone  combined  with  upper  partial  tones  (see  p.  827). 
Bv  reason  of  the  varied  adjustments  that  may  be  imparted  to  it,  the  larynx  is 
capable  of  producing  many  more  qualities  of  tone  than  is  any  artificial  instru- 
ment.^ Change  in  the  size  and  shape  of  the  resonance-chamber  above  and 
below  the  vocal  cords  produces  a  corresponding  change  in  their  fundamental 
notes  and,  therefore,  in  the  partial  tones  of  the  voice  which  they  reinforce  by 
sympathetic  vibration  (see  p.  829).  According  to  Helmholtz,^  the  difference 
in  quality  between  the  various  vowel  sounds  of  the  human  voice  depends  on 

'  C.  H.  Davis:  The  Voice,  1879. 

»  Helmholtz:  Sensations  of  Tone,  trans,  by  Ellis,  1885,  p.  98. 

»  Op.  ciL,  p.  104. 


VOICE  AND   SPEECH.  871 

the  number  and   relative  promiiienee  of  the  various  overtones  determined  by- 
altering  the  shape  and  size  of  the  na.sal  and  buccal  resonance-chambers. 

By  a  simple  experiment  the  production  of  voice  by  the  vocal  cords  can 
easily  be  illustrated.  Take  a  glass  tube,  about  \  inch  in  diameter  and  of  con- 
venient length,  and  press  one  end  firmly  against  the  palmar  surfaces  of  the 
proximal  phalanges  of  two  fingers  at  their  line  of  division  when  they  are 
brought  together.  By  blowiug  smartly  into  the  other  end  of  the  tube,  a 
musical  note  will  be  produced  by  the  vibration  of  the  folds  of  the  skin  be- 
tween which  the  air  is  forced.  By  relaxing  the  pressure  with  which  the 
fingers  are  held  together,  the  length  of  the  vibrating  segment  of  skin  is  in- 
creased and  its  tension  diminished;  its  note  is  accordingly  lowered.  The 
reverse  conditions  are  produced  when  the  fingers  are  held  together  tightly  and 
the  tube  applied  firmly ;  the  pitch  of  the  note  is  then  raised.  In  these  ways 
the  pitch  of  the  note  may  be  varied  through  two  octaves,  which  is  the  range 
of  a  good  singing  voice.  Various  upper  partials  of  the  note  so  produced  may 
be  made  prominent  by  sympathetic  resonance,  if  the  vibrating  air-stream  is 
sent  across  the  opening  of  a  wide-mouthed  bottle,  of  about  a  pint  capacity. 
The  air  within  the  bottle  is  thrown  into  sympathetic  vibration  when  its  funda- 
mental tone  is  contained  in  the  note  emitted  through  the  fingers ;  when  the 
volume  of  the  air  is  diminished  by  slowly  pouring  water  into  the  bottle,  the 
fundamental  tone  of  the  resonator  is  changed,  and  it  responds  to  one  after 
another  of  the  partials  contained  in  the  musical  note. 

The  marvellous  adjustment  of  muscular  action  by  which,  at  will,  notes 
mav  be  struck  of  definite  pitch  and  quality,  is  evidence  of  an  elaborate 
nervous  machinery  for  the  larynx,  not  only  on  the  efferent  side  but,  possibly 
through  a  muscular  sense,  on  the  afferent  side  as  well.  The  various  phe- 
nomena of  aphasia,  and  the  anatomical  importance  of  the  cerebral  areas 
devoted  to  the  elaboration  of  speech,  point  in  the  same  direction.  The 
relations  between  the  centres  for  speech  and  hearing  are  most  intimate.  The 
ear  plays  a  constant  part,  as  a  critical  medium,  in  the  tuition  of  the  vocal 
organs  in  either  speech  or  song.  So-called  "dumbness"  is  the  result,  usually, 
not  of  defects  in  the  vocal  organs,  but  of  lack  of  hearing  and,  hence,  of 
inability  to  control  by  the  ear  the  pitch  or  quality  of  the  vocal  notes. 

The  voice  and  the  larynx  of  the  child  fall  naturally  in  a  group  with  those 
of  the  female  as  contrasted  with  the  adult  male.  At  the  age  of  puberty  a 
boy's  larynx  becomes  congested  and  undergoes  rapid  development.  The  voice 
changes  rapidly  from  the  juvenile  to  the  adult  quality.  During  this  change, 
the  voice  frequently  "breaks"  or  rapidly  returns  from  the  newly-acquired 
chest  register  to  the  head  or  falsetto  notes  of  childhood  (see  p.  873).  In  boys 
who  are  castrated  a  good  while  before  the  age  of  puberty  is  reached,  the  larynx 
does  not  undergo  its  characteristic  development,  and  the  voice  remains  of  a 
peculiar  quality,  much  valued  in  some  countries  in  the  rendition  of  vocal 
music.  The  practice  of  castration  for  aesthetic  purposes  has,  accordingly,  in 
certain  districts,  long  been  in  vogue.  In  the  female  the  changes  in  the  larynx 
and  in  the  voice  at  puberty  are  much  less  marked  than  in  the  male. 


872  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

Arrangements  for  Changing  the  Pitch  of  the  Voice. — As  has  i'niquently 
been  mentioned,  the  voeal  eords  are  stretehed,  and  tlie  piteh  of  their  note  is 
elevated,  by  contraction  of  the  crieo-thyroid  muscle.  But  the  change  that  is 
thus  produced  in  the  tension  of  the  vocal  cords  is  by  no  means  capable  of 
accounting  for  the  full  range  of  pitch  which  i'alls  within  the  com})ass  of  the 
voice.  AVhcn  the  arytenoid  and  the  crico-arytenoid  muscles  sufficiently  con- 
tract, the  vocal  ])rocesses  are  brought  tightly  together  and  their  vibration  is 
prevented.  Voice-production  must  then  be  limited  tc»  the  vocal  cords  them- 
selves, and  the  stretching  action  of  the  crico-thyroids  may  begin  anew  and 
reach  its  maximum  with  the  glottis  so  set  that  only  its  ligamentous  borders  can 
vibrate.  It  can  also  be  seen  that  the  vocal  cords  themselves  may  be  shortened 
functionally,  or  even  be  broken  uj)  into  segmeuts,  or  the  main  body  of  the  cord 
be  changed  in  thickness,  by  contraction  of  the  complex  thyro-arytenoid  muscles; 
each  such  condition  would  be  accompanied  by  a  change  in  the  rate  of  vibra- 
tion. We  are  j)robably  justified  in  assuming  that,  when  the  musical  scale  is 
sung,  the  lowest  notes  are  produced  by  vibration  of  the  glottic  borders  through- 
out their  full  length,  and  the  elevation  of  pitch  is  affected  by  the  gradually- 
increased  tension  of  the  vocal  ligaments  through  the  action  of  the  crico-thyroid 
muscle.  This  contraction  having  leached  its  maximum,  the  muscle  probably 
relaxes,  only  to  contract  again  after  the  vibrating  segments  of  the  glottis  are 
shortened  by  a  partial  or  complete  clamping  together  of  the  vocal  processes 
in  the  manner  described  above.  There  are  thus  two  or  three,  or  more, 
adjustments  which  may  be  imjiarted  to  the  vibrating  mechanism  of  the  lar- 
ynx, each  of  which  is  distinguished  by  giving  rise  to  a  note  of  different 
pitch  that  may  further  be  altered  by  action  of  the  crico-thyroid  muscle. 
It  might  be  anticipated  that  the  voice  whose  pitch  was  gradually  ele- 
vated in  the  manner  described  would  suffer  some  alteration  in  quality 
at  those  points  in  the  scale  where  there  is  a  change  in  the  set  of  the  lar- 
vnx    producing   a  shortening    of  the    vibrating    segment.     Such,    indeed,    is 

the  fact. 

Registers.— Ijong  before  the  invention  of  the  laryngoscope,  and  before  any- 
thing definite  was  known  of  the  method  of  voice-production,  it  was  recognized 
that  in  ascending  the  musical  scale  there  occur  certain  breaks,  as  it  were,  where 
the  voice  changes  in  quality  as  well  as  in  piteh.  It  is  an  object  in  musical 
education  to  render  these  breaks  as  little  prominent  as  possible.  The  kinds  of 
voice  included  between  these  breaks  were  distinguished  as  the  vocal  "registers." 
There  is  no  general  agreement  among  musicians  as  to  how  many  registers  are 
compassed  by  the  voice,  and  the  nomenclatures  used  to  distinguish  them  differ 
in  the  most  confusing  fashion.  According  to  some  authors,  the  range  of  the 
voice  is  included  within  two  registers  only;  more  commonly  three  distinct 
registers  are  described,  to  which,  in  certain  cases,  a  fourth  is  said  to  be  prob- 
ably added.  The  most  common  designation  of  the  lowest  register  is  the  "  chest 
voice,"  though  it  has  also  l)een  called  "  thick "  ^  as  distinguished  from  the 
"  thin  "  register ;  another  term  applied  to  it  is  the  "  long-reed  "  register  as  con- 
>  Browne  and  Behnke:   Voice,  Song,  and  Speech,  1890,  p.  135. 


VOICE   AND   SPEECH. 


873 


trasted  with  the  "  sliort-ret'd  "  register.'  Tlie  middle  register  of  all  voices  is 
by  some  authors  (Garcia,^  Mme»  Seiler')  denominated  the  "falsetto,"  while 
other  writers  use  this  t(!rni  to  distinguish  certiiin  higher  notes  of  the  male 
voice  of  a  peculiar  quality  not  in  ordinary  use.  The  third  and  highest  series 
of  vocal  sounds  is  usually  known  as  the  "  head  "  register. 

The  lowest  or  chest  register  is  that  used  in  ordinary  life.  It  is  so  called 
from  the  strong  vibrations  of  the  chest-wall  which  may  be  felt  while  the  voice 
is  sounded.  In  passing  to  the  higher  register  the  chest  vibration  is  found  to 
diminish  and  that  of  the  head  bones  to  increase;  in  the  one  case  the  cavity  of 
the  head  acts  strongly  as  a  resonance  chamber,  and  in  the  other  that  of  the 
thorax.  According  to  Madame  Seiler,  in  the  lowest  register  both  the  vocal 
ligaments  and  the  vocal  processes  of  the  arytenoids  vibrate.  In  the  middle 
register  the  vocal  processes  are  clamped  together  and  the  vibrati(ni  of  the  liga- 
ments seems  confined  chiefly  to  their  sharp  edges;  while  in  the  highest  register 
the  ligaments  themselves  appear  to  be  damped  throughout  the  greater  part  of 
their  length,  the  vibrations  being  confined  to  the  edges  of  an  oval  slit  at  their 
ABC 


Fig.  303.— The  voicing  (female)  larynx  (after  Browne  and  Behnke).  A,  Small  or  highest  register.  B, 
Upper  thin  or  middle  register.  C,  Lower  thin  or  middle  register:  T,T,  tongue;  F,F,  false  vocal  cords; 
S,S,  cartilages  of  Santoriui;   I^',  W,  cartilages  of  Wrisberg;  V,  V,  vocal  cords. 

anterior  ends  (Fig.  303).  Within  any  definite  register  the  quality  of  individual 
voices  is  determined  by  the  size  and  elasticity  of  the  parts  of  the  larynx,  and 
probably  also  by  peculiarities  of  the  resonating  chambers ;  voices  are  accord- 
ingly classified  as  base,  tenor,  alto,  and  soprano. 

A  Whistling  Register. — A  friend  and  former  pupil  of  the  author's  has  the  remark- 
able power  of  emitting  from  the  larynx  notes  which  are  indistinguishable  in  quality  from 
an  ordinary  whistle.  He  writes,  "The  whistle  cannot  be  made  to  'slide  '  into  vocal  tones 
of  any  sort,  nor  can  any  other  tones  be  produced  simultaneously  with  it.  Its  range  is 
about  one  and  a  half  octaves,  or  half  an  octave  less  than  my  singing  voice. 

"The  lips  have  nothing  to  do  with  the  sound  except  as  their  position  changes  the  reso- 
nance-quality of  the  tone  by  '  reinforcement '  or  otherwise,  for  I  can  whistle  almost  as  read- 
ily with  the  teeth  closed  and  the  lips  wide  parted  as  with  the  jaws  and  lijis  firmly  closed  as 
in  the  ordinary  position.  Any  other  movement  of  the  air-column  destroys  the  sound  at 
once."  Some  years  ago  the  author  made  a  laryngoscopic  examination  of  this  larynx  while 
it  was  in  the  act  of  whistling.  No  notes  were  written  at  the  time,  but  the  picture  remem- 
bered is  that  of  vocal  cords  closely  approximated,  except  for  an  oval  slit  between  their 
anterior  and  middle  portions,  as  in  singing  head  tones,  the  cords  vibrating  chiefly  along 
their  free  edges. 

Speech. — Language  consists,  in  general,  of  a  combination  of  short  musical 

sounds,  vowels  or  sonants,  which  are  produced  purely  by  vibration  of  the  vocal 

'  Mackenzie :  Hygiene  of  the  VocmI  Orgmifi,  1891,  p.  55. 

^  Garcia:  Lond.,  Edin.,  and  Dub.  Mag.,  vol.  x.  1855,  p.  218.     (Quoted  by  Seiler.) 

■*  Seiler  :  op.  cit. 


874  JliV  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

cords,  together  with  superadded  noises  or  modes  of  obstruction,  consonants, 
produced  by  action  of  the  mouth-parts.  The  vowel  sounds  usually  carry  the 
accent  of  syllables,  and  the  consonants,  for  the  most  part,  are  sounded  only 
with,  or  represent  peculiar  modes  of  obstructing  the  former.  No  classification 
of  vocal  signs  can  be  made  in  which  exceptions  do  not  form  important  addenda 
to  general  rules. 

Articulation  is  the  motlifieation  of  sound  in  speech,  usually  effected  by  action 
of  the  lips,  the  tongue,  the  palate,  or  the  jaws,  and  the  place  of  articulation 
depends,  in  any  definite  case,  on  the  mode  in  which  a  sound  is  formed.  Its  use 
as  an  expression  of  thought  is  the  chief  physiological  distinction  between  man 
and  the  lower  animals.  Distinctness  of  articulation,  so  essential  to  clearness 
of  language,  not  to  mention  its  aesthetic  value,  depends  on  the  accuracy  of  the 
muscular  adjustments  used  in  forming  sounds,  especially  consonantal  sounds. 

The  speaking  is  distinguished  from  the  singing  voice  partly  by  the  fact  that 
most  sounds  in  the  first  case  are  articulate  or  formed  in  the  mouth,  while  in 
the  latter  their  quality  is  only  there  modified.  In  singing  the  tone  is  sustained 
at  the  same  pitch  for  a  considerable  interval,  while  in  speaking  the  voice  is  con- 
tinually sliding  up  and  down  on  the  vowel  sounds.  In  speaking  the  conso- 
nantal noises  and  obstructions  are  more  prominent  because  of  their  more  abrupt 
formation.'-  ^ 

Voicel  sounds  owe  their  origin  to  vibration  of  the  vocal  cords,  and  their 
quality  to  the  selective  resonance  of  the  cavities  above  the  cords.  In  sounding 
the  series  of  vowels,  a,  e,  i,  o,  u  (pronounced  ah,  a,  e,  o,  oo),  it  is  found  that  the 


Fig.  304.— Section  of  the  parts  concerned  in  phonation,  and  the  changes  in  their  relations  in  sound- 
ing the  vowels  A(<^),I  («),  U (")  (after  Landois  and  Stirling) :  T,  tongue ;  p,  soft  palate ;  e,  epiglottis ;  g,  glot- 
tis ;  h,  hyoid  bone ;  1,  thyroid ;  2, 3,  cricoid ;  4,  arytenoid  cartilage. 

form  and  size  of  the  mouth-cavity,  the  position  of  the  tongue,  the  position  of 
the  soft  palate  separating  or  allowing  communication  between  the  nasal  and 
pharyngeal  cavities,  undergo  a  progressive  change  (Fig.  304).  Helmholtz  has 
shown  that  the  vowel  sounds  owe  their  differences  of  quality  to  the  varied 
resonance  of  the  mouth-cavity,  dependent  on  its  shape,  through  which  now  one, 
now  another,  of  the  overtones  in  the  note  produced  by  vibration  of  the  vocal 
cords  is  reinforced.^  This  result  is  dependent  on  the  fact  that  when  the  mouth 
is  set  in  position  for  the  formation  of  the  various  vowel  sounds  the  pitch  of  its 

*  Browne  and  Behnke :  op.  cit.,  p.  28. 

*  Monroe:  Manual  of  Physical  and  Vocal  Training,  1869,  p.  51. 
'  Helmholtz:  he.  cit. 


VOICE  AND   SPEECH.  875 

fundamental  note,  or  the  rate  of  vibration  to  which  it  sympathetically  responds, 
varies  accordingly.'  That  the  resonance  of  the  mouth  cavity  changes  with 
its  shape  is  ilkistratcd  in  the  various  pitch  of  the  notes  produced  by  flipping 
the  edge  of  an  incisor  touth,  the  cheek,  or  Adam's  apple  with  the  finger-nail, 
while  the  mouth  assumes  the  positions  for  production  of  the  different  vowels. 
Vowels  whose  normal  pitch  is  low,  as  o,  u,  cannot  be  sounded  easily  in  the 
higher  part  of  the  musical  scale ;  conversely,  high-pitched  vowels,  as  e  in  fed, 
lose  their  character  in  the  lower  part  of  the  scale.  Language  is,  therefore, 
much  less  distinct  in  song  than  in  speech.^^ 

Since  the  mouth  cavity  is  set  to  a  definite  pitch  for  each  vowel  sound,  it 
follows  that  when  the  same  vowel  is  voiced  in  different  parts  of  the  musical 
scale,  those  tones  which  are  strengthened  by  resonance  remain  the  same,  imt 
their  distance  from  the  fundamental  will  be  different.  That  is,  the  resonated 
partial  depends  not  only  on  its  relation  to  the  fundamental,  but  also  on  its 
vibration  nite.^  This  feature  of  vocal  resonance  distinguishes  the  human 
larvnx  from  most  musical  instruments.  That  the  ground  is  not  covered  by 
these  facts  was  shown  by  Auerbach,*  who  demonstrated  that  the  strength  of 
upper  partials  in  vowel  sounds  depends  also  on  the  strength  of  their  production 
by  the  vocal  cords  and,  therefore,  upon  their  relation  to  the  fundamental  tone. 
That  is  to  say,  the  quality  of  a  vowel  is  dependent  not  only  on  the  absolute 
vibration  numbers  of  its  upper  partials,  according  to  which  they  are  or  are  not 
reinforced  by  the  position  of  the  mouth,  but  also  on  the  relative  position  of  these 
upper  partials  as  compared  with  the  fundamental  tone. 

The  peculiar  esthetic  value  of  the  human  voice  is  dependent  on  the  fact 
that,  on  account  of  its  varied  powers  of  adjustment,  the  larynx  is  capable  of  pro- 
ducing manv  more  kinds  of  tone-qua]ity  than  any  artificial  instrument.  Helm- 
holtz^  found  no  less  than  sixteen  overtones  to  accompany  the  fundamental. 

The  posture  of  the  mouth-parts  differs  markedly  when  set  for  the  various 
principal  vowel  sounds ;  but  as  we  know  that  each  vowel  sound  has  several 
modifications  or  gradations  so  that  a  tone  may  pass  by  an  easy  glide  from  one 
to  another,  so  the  form  of  the  mouth  passes  by  insensible  steps  from  one  vowel 
position  to  another.  It  will  be  seen  later  that  several  articulate  sounds  play 
the  part  now  of  vowels,  now  of  consonants,  according  to  their  position  in  the 
syllable  or  mode  of  formation.  There  has  also  been  shown  reason  for  believ- 
ing that  the  form  of  the  chest  cavity  and  the  tension  of  its  walls  are  factors  in 
determining  the  pitch  of  its  fundamental  tone ;  so  that  through  the  varied 
sympathetic  resonance  of  the  thorax  the  reinforcement  of  laryngeal  tones  may 
here  be  altered  somewhat,  as  in  the  mouth  itself.®-  ^ 

Whispering  is  a  mode  of  speech  in  which  noise  largely  replaces  peudular 
musical  vibrations.  The  glottis  remains  more  or  less  widely  open  and  the 
vocal  cords  are  not  tense ;  the  vibrations  are  produced  both  in  the  larynx  and 
in  the  buccal-pharyngeal  chambers.     Vowel  sounds  may  be  produced  in  whis- 

1  Helmholtz :  op.  cit.,  p.  108.  '  Op.  cit.,  p.  114.  =>  Op.  cU.,  p.  118. 

*  Quoted  by  Griitzner:  op  cit,  p.  179.         *  Op.  cit,  p.  103.  *  Op.  cU.,  p.  93. 

♦  Sewall  and  Pollard  :  Journal  of  Physiology,  vol.  xi.,  1890,  p.  159. 


876  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

pering  as  well  as  in  true  voice  because,  from  the  multitude  of  irregular  vibra- 
tions, those  waves  are  reinforced  which  make  up  the  vowel  sounds  determined 
bv  the  set  of  the  mouth.  Gentle  whispering  requires  much  less  effort  than  does 
speaking,  and  inspiratory  whispering  is  less  easily  distinguished  from  expiratory 
than  is  the  strained  voice  of  ins])iration  from  the  natural  sound  of  expiration. 
Consonants,  as  already  indicated,  may  sometimes  play  the  part  of  vowels,  but 
})ure  consonants  do  not  appear  in  syllables  except  in  combinations  with  vowels, 
which  combinations  always  carry  the  syllable  accent. 

Consonants. — The  distinction  between  consonants  and  vowels  lies  in  the 
fact  that  the  tones  of  the  latter  are  produced  by  vibration  of  the  vocal  cords, 
the  parts  above  which  act  only  as  resonance-boxes  and  modify  the  sound,  and 
never  offer  marked  obstruction  to  the  exit  of  air ;  whereas  in  the  formation  of 
consonants  there  is  some  adjustment  in  the  mouth-passage  either  in  the  nature 
of  a  local  narrowing,  by  which  a  peculiar  noise  is  added  to  the  vocal  sound,  or 
in  the  nature  of  a  sudden  closing  or  opening  of  the  air-channel  by  which  a 
characteristic  noise  is  likewise  added  to  the  vocal  sound.  In  other  words,  the 
parts  above  the  larynx  mahc  the  sounds  of  consonants  but  only  modify  those 
of  vowels.'  No  sharp  line  of  separation  can  be  drawn  between  vowels  and 
consonants,  since  certain  characters,  according  to  their  associations,  now  fall 
into  one,  now  into  another  class.  In  the  classification  of  consonantal  sounds 
much  confusion  exists,  dependent  chiefly  on  the  fact  that  several  letter  charac- 
ters change  their  modes  of  formation  and  expression  with  their  place  in  the 
svllable.  The  same  facts,  also,  are  expressed  by  different  authors  l>y  different 
nomenclatures,  and  soiuids  occur  in  one  language  that  are  not  found  in  another. 
Adopting  the  general  classification  of  Griitzner,^  we  may  divide  consonants 
into  the  following  three  groups: 

1.  Semi-vowels  or  Uquids,\\\\\c\\  can  be  used  either  as  vowels  or  consonants; 
this  group  includes  the  sounds  m,  n,  ng,  I,  and  r.  In  expressing  the  function 
of  a  consonant,  the  letter  is  not  to  be  sounded  as  if  it  stood  alone,  but  its  cha- 
racter given  as  actually  expressed  in  a  syllable;  thus  the  sound  of  p  is  not  pee, 
but  is  the  abbreviated  labial  expression,  as  in  jjaeZ;  or  piece  when  all  the  letters 
are  eliminated  after  tiie  first.  Of  the  liquids  the  n,  m,  and  ng  (sometimes 
called  "resonants")  have  the  nature  of  vowels  when  final  (as  in  him,  hen, 
being),  and  are  then  produced  by  vibration  of  the  vocal  cords,  the  lij)s  having 
previously  been  closed  for  the  m,  and  the  tongue  applied  to  the  roof  of  the 
mouth  to  cut  off  the  exit  of  air  for  n  and  iig  ;  the  expelled  air  escapes  alto- 
gether through  the  nose,  which  acts  as  a  resonance-chamber.  Used  as  conso- 
nants, as  in  make  and  no,  m  and  n  are  seen  to  have  the  characters  of  the  second 
group, — Explosives.  L  is  pronounced  somewhat  like  n,  but  air  is  allowed  to 
escape  through  the  mouth  on  each  side  of  the  tongue ;  it  may  be  produced 
either  Avith  voice  or  without  voice  (in  whispers).  It  may  have  vowel  charac- 
ters as  in  play.  R  is  characterized  as  a  inbrative  and  may  have  several  seats 
of  articulation,  as  by  the  thrill  of  the  tip  of  the  tongue  against  the  hard 
palate,  or  that  of  tiie  hind  part  of  the  tongue  against  the  soft  palate,  or  even 
'  Grutzner:  op.  cit.,  p.  196.  ^  Op.  cit.,  p.  197. 


VOICE   AND   SPEECH. 


^11 


by  the  coarse  vibnitiou  of  the  vocal  cords  tlieniselves.  In  the  first  two  cases 
it  may  be  sounded  either  with  or  without  voice.  Its  vowel  nature  is  shown  in 
such  words  as  pray. 

2.  Explosives,  wliich  are  produced  either  when  an  obstruction  is  suddenly 
offered  to  or  removed  from  tlie  exit  of  air  from  the  mouth ;  at  the  same  time 
a  characteristic  noise  is  produced.  They  may  be  subdivided  according  to  the 
place  of  articulation  into  labuds  (p,  v) ;  Unguo-pcdutals  (f,  d) ;  gutturals  (k,  (j). 
The  similarity  in  the  method  of  formation  of  j)  and  6,  t  and  c?,  k  and  (j,  is 
striking.  They  are  frequently  characterized  as  being  formed  idtii  or  u-Hhout 
voice;  that  is,  6,  d,  and  g  require  voice  for  their  distinct  recognition,  and  when 
whispered  they  are  easily  mistaken  i'or  p,  t,  I:,  which  latter  do  not  require  voice 
(vibration  of  the  voeal  cords)  for  their  recognition.  A  consonant,  then,  is  said 
to  be  formed  icith  voice  when  it  can  be  rendered  distinctly  only  by  an  accom- 
panying vibration  of  the  vocal  cords,  without  voice  when  articulated  clearly 
without  laryngeal  aid.  The  former  are  sometimes  called  sonants,  the  latter 
surds.  This  classification  only  approximates  the  truth,  for  the  suddenness  and 
energy  with  which  the  obstruction  to  the  breath  is  removed  determines  our 
recognition  of  the  consonant  irrespective  of  voice.^ 

Table  of  Consonantal  Elements!^ 


Oral. 


Place  of  Articulation. 


Lips 

Lips  and  teeth 

Tongue  and  teeth  .  .  . 
Tongue  and  hard  palate 

(forward) 

Tongue  and  hard  palate 

(back)     

Tongue,  hard  palate,  and 

soft  palate 

Tongue  and  soft  palate  . 
Various  places 


Momentarj'. 


Continuous. 


Surds  I      Sonants  Surds  '     Sonants 

(without  voice),  (with  voice),  (without  voice),  (with  voice). 


Nasal. 
Continuous. 


Sonants 
(with  voice). 


t 
ch 


f 
th(in) 

s 

sh 


th(y) 
z,  r 
zh,  r 

V,  1 


3.  Friction  sounds  or  frictionals,  often  called  asjnrates,  are  all  noises  pro- 
duced by  the  expired  blast  pa.ssing  through  a  constriction  in  its  passage,  at 
which  point  a  vibration  is  set  up.  No  obstruction  being  offered  to  the  sound, 
they  are  known  as  continuous  as  di.stinguished  from  the  momentari/  sounds  of 
group  2.  They  may  be  divided  into  labio-dental  frictionals,  f  (v^^'ithont  voice) ; 
V,  w  (with  voice) ;  the  Ungual  frictionals  s,  th  (as  in  them);  sh,  ch  soft  (with- 
out voice) ;  z,  j  (with  voice).  The  sound  of  h  may  be  regarded  as  due  to  the 
viljration  of  the  separated  vocal  cords.  It  is  peculiar,  however,  in  appearing 
to  be  formed  in  any  part  of  the  vocal  chamber ;  when  it  is  formed  the  mouth 
parts  take  on  no  peculiar  position,  but  assume  that  of  the  vowel  following  the 
h,  as  hark,  hear,  etc. 

'  Grtitzner,  op.  cit.,  pp.  211,  213. 

'  Webster  s  International  Dictionary.  1891,  p.  Ixvi. 


XIII.  REPRODUCTION. 


The  principles  and  problems  of  Physiology  that  have  been  already  pre- 
sented in  this  voluino,  compri.sing  nutrition  and  the  functions  of  the  mu.scular 
and  tiie  nervous  sy.stems,  have  reference  to  the  individual  man  or  woman. 
Through  the  normal  activity  of  those  functions  and  tlieir  appropriate  co- 
ordination the  individual  lives  his  daily  life  or  performs  his  daily  tasks  as  an 
indo}iendent  organism.  But  man  is  something  more  than  an  independent 
orgaiiism ;  he  is  an  integral  part  of  a  race,  and  as  such  he  has  the  instincts  of 
racial  continuance.  The  continuance  of  the  race  is  assured  only  by  the  pro- 
duction of  new  individuals,  and  the  strength  of  the  human  reproductive 
instinct  is  indicated  in  some  measure  by  the  large  proportion  of  energy  that  is 
expended  by  woman  in  the  bearing  of  children  and  by  both  sexes  in  the  nur- 
ture and  education  of  the  young.  The  function  of  reproduction  is  not  limited 
to  the  daily  life  and  well-being  of  independent  organisms.  It  has  a  deeper 
significance  than  that.  Its  essence  lies  in  the  fact  that  it  has  reference  to  the 
species  or  race.  Many  of  its  problems  are,  therefore,  broad  ones ;  they  in- 
clude not  only  the  immediate  details  of  individual  reproduction,  but  larger 
ones  relative  to  the  nature  and  significance  of  reproduction  and  of  sex,  and  to 
heredity.  In  the  following  discussion  some  of  these  broader  aj)plications  of 
the  facts  presented  will  be  indicated. 

A.  Reproduction  in  General. 

In  all  forms  of  organic  reproduction  the  essential  act  is  the  separation  from 
the  body  of  an  individual,  called  the  parent,  of  a  portion  of  its  own  material 
living  substance,  which  under  suitable  conditions  is  able  to  grow  into  an  inde- 
pendent adult  organism. 

Among  living  beings  two  methods  of  reproduction  are  recognized,  the 
asexual  and  the  sexual  methods.  Both  are  widespread  among  animals  and 
plants,  but  the  asexual  method  is  the  more  primitive  of  the  two  and  is  rela- 
tivelv  more  frequent  in  low  organisms.  The  sexual  method,  the  only  one 
present  in  the  production  of  new  individuals  among  the  higher  animals,  has 
evidently  been  acquired  gradually,  and  has  probably  been  developed  from  the 
asexual  method. 

Asexual  Reproduction. — Asexual  reproduction,  or  agamogcnesis,  is  the 
chief  method  of  reproduction  among  unicellular  plants  and  animals,  and 
throughout  the  plants  and  in  the  lower  multicellular  animals  it  is  important. 
Among  various  species  it  takes  various  forms,  known  as  fission  or  division, 
gemmation  or  budding,  endogenous  cell-formation  or  spore-formation  or  multi- 

878 


REPRODUCTION.  879 

pie  fission  ;  but  all  the  varieties  are  luodiHcations  of  the  simplest  form,  fission 
or  division.  In  fission,  found  only  in  unicellular  orjj^anisms  and  typified  in 
Amoeba,  the  protoplasm  of  the  single  cell,  together  with  the  nucleus,  becomes 
divided  into  two  approximately  equal  portions  which  separate  from  one 
another.  In  the  process  no  material  is  lost,  and  two  independent  nucleated 
organisms  result,  each  approximately  half  the  size'  of  the  original.  The 
parent  has  become  bodily  transformed  into  the  two  offspring,  which  have  only 
to  increase  in  size  by  the  usual  processes  of  assimilation  in  order  themselves 
to  become  parents.  In  higher  organisms,  even  where  sexual  processes  alone 
prevail  in  the  production  of  new  individuals,  the  asexual  method  has  per- 
sisted in  the  multiplication  of  the  individual  cells  that  constitute  the  body; 
embryonic  growth  is  an  asexual  reproductive  process,  a  continued  fission,  dif- 
fering from  the  amreboid  type  in  the  facts  that  the  resulting  cells  do  not  sepa- 
rate from  one  another  to  form  independent  organisms,  but  remain  closely 
associated,  undergo  morphological  differentiation  and  physiological  specializa- 
tion, and  together  constitute  the  individual.  Likewise  in  the  adult  the  pro- 
duction of  blood-corpuscles  and  of  epidermis,  the  regrowth  of  lost  tissues,  and 
the  healing  of  wounds  are  examples  of  asexual  cell-reproduction.  From  the 
standpoint  of  multicellular  growth  Spencer  and  Haeckel  have  happily  termed 
the  process  of  asexual  reproduction  in  unicellular  organisms  "  discontinuous 
growth." 

Sexual  Reproduction. — Sexual  reproduction,  or  gamogenesis,  occurs  in 
unicellular  organisms,  where  it  is  known  as  conjugation,  and  is  the  prevailing 
form  of  reproduction  in  most  of  the  multicellular  forms.  In  most  of  the 
invertebrate  and  vertebrate  animals  it  is  the  sole  form  of  reproduction  of 
individuals.  In  its  simple  form'  of  conjugation,  typified  in  the  minute  monad, 
Heteromita,  it  consists  of  a  complete  fusion  of  the  bodies  of  two  similar  indi- 
viduals, protoplasm  and  nuclei,  followed  by  a  division  of  the  mass  into 
numerous  spore-like  particles,  each  of  which  grows  into  an  adult  Heteromita. 
In  the  higher  infusorian,  Paramoecium,  the  fusion  of  the  two  similar  individ- 
uals is  a  partial  and  temporary  one,  during  which  a  partial  exchange  of 
nuclear  material  takes  place ;  this  is  followed  by  separation,  after  which  each 
individual  proceeds  to  live  its  ordinary  life  and  occasionally  to  multiply  by 
simple  fission. 

In  the  highly  specialized  sexual  reproduction  of  higher  animals,  including 
man,  the  individuals  of  the  species  are  of  two  kinds  or  sexes,  the  male  and 
the  female,  with  profound  morphological  and  physiological  differences,  between 
them  ;  in  each  the  protoplasm  of  the  body  consists  of  two  kinds  of  cells,  somatic 
cells  and  germ-cells,  the  former  subserving  the  nutritive,  muscular,  and  nervous 
functions  of  daily  life,  the  latter  subserving  reproduction.  The  germ-cells  of 
the  male,  called  spermatozoa,  are  relatively  small  and  active,  those  of  the 
female,  called  ova,  are  relatively  large  and  passive ;  the  reproductive  process 
consists  of  a  fusion  of  a  male  and  a  female  germ-cell,  the  essential  part  being 
a  fusion  of  their  nuclei ;  and  this  is  followed  by  continued  asexual  cell-division 
and  growth  into  a  new  individual.     Among  both  plants  and  animals  it  is  not 


880  AN  AMERICAN   TEXT-BOOK    OF   PIIYSIOLOOY. 

difficult  to  find  a  series  of  forms  showing  pro<;ressively  greater  and  greater 
deviations  from  the  typical  asexual  toward  the  typical  sexual  method  of 
reproduction,  and  the  existence  of  such  a  series  is  indicative  of  the  derivation 
of  tiie  latter  from  tlie  former  tvjie. 

Origin  of  Sex,  and  Theory  of  Reproduction. — It  is  obvious  that  the 
production  of  new  individuals  is  necessary  to  tiie  continued  existence  of  any 
species.  It  w^ould  be  interesting  to  know  the  origin  and  significance  of  the  two 
existing  methods  of  reproduction.  Apropos  of  the  asexual  })rocess,  Leuckart,. 
and  especially  Herbert  Spencer,  have  pointed  out  that  during  the  growth  of 
a  cell  the  mass  increases  as  the  cube,  but  the  surface  oidy  as  the  square,  of 
the  diameter — i.  e.  the  quantity  of  protoplasm  increases  much  more  rapidly 
than  the  absorptive  surface.  It  follows  from  this  tliat  during  the  growth  of  a 
unicellular  organism  a  size  will  ultimately  be  reached  beyond  which  the  cell 
will  not  be  able  to  absorb  sufficient  food  for  the  maintenance  of  the  proto- 
plasm. In  order  that  growth  may  continue  beyond  this  point,  a  division  of 
the  cell,  which  ensures  a  relative  increase  of  surface  over  mass,  is  absolutely 
necessary.  Fission  is,  therefore,  a  necessary  corollary  of  growth,  and,  although 
we  are  ignorant  of  the  details  of  its  mechanism,  it  is  conceivable  that  the  method 
of  asexual  reproduction  arose  through  causes  connected  with  growth. 

The  explanation  of  sexual  reproduction  is  much  more  difficult,  for  here,  in 
addition  to  the  budding  off  of  the  germ-cells  from  the  parental  bodies,  which 
has  probably  the  same  fundamental  cause  as  fission  in  unicellular  forms,  we 
must  account  for  the  differentiation  into  sexes,  the  existence  of  special  sexual 
cells,  and  the  fusion  of  the  male  and  the  female  germinal  substance ;  in  short, 
we  must  account  for  the  conception  of  sexuality  itself  and  all  that  it  implies. 

Regarding  the  origin  of  sexuality  itself,  as  fo  the  question  whether  sexuality 
is  an  original  and  fundamental  attribute  of  protoplasm  or  has  been  acquired, 
we  may  say  at  once  that  at  present  we  know  really  nothing.  Yet,  whatever 
view  is  held  as  to  the  origin  of  sexuality,  it  seems  entirely  probable  that  the 
method  of  reproduction  known  as  sexual  is  a  derivative  of  the  method  known 
as  asexual — the  latter  is  primitive,  the  former  has  arisen  from  it.  From  the 
wide  distribution  and  prominence  of  the  former  among  vital  phenomena  we 
must  believe,  with  biologists  generally,  that  sexual  differentiation  and  sexual 
processes  have  arisen  from  natural  causes,  and  for  the  reason  that  sexual  repro- 
duction is  of  advantage  to  living  beings  and  to  species.  In  what  way  it  is  of 
advantage,  however,  is  disputed.  Three  views,  all  of  which  have  evidence  in 
their  favor  and  which  are  not  mutually  exclusive,  are  at  present  engaging  the 
attention  of  scientific  men.  The  first  to  be  mentioned  is  the  theory  advocated 
by  Hen.sen,  Edouard  van  Beneden,  and  Butschli,  according  to  whom  the  fusion 
of  the  cells  in  sexual  reproduction  exists  for  the  purpose  of  rejuvenating  the 
living  substance.  The  power  possessed  by  cells  of  dividing  asexually  is 
limited;  in  time  the  protoplasm  grows  old  and  degenerates;  its  vital  powers  are 
weakened,  and  without  help  the  extinction  of  the  race  must  follow.  But  the 
mingling  of  another  strain  with  such  senescent  protoplasm  gives  it  renewed 
youth  and  vigor,  restores  the  power  of  fission,  and  grants  a  new  lease  of  life  to 


REPROD  UCTION.  881 

the  species.  From  his  observations  upon  the  Infusoria,  Maupas'  has  brought 
forward  valuable  evidence  which  has  been  quoted  in  favor  of  this  view.  Sty- 
loni/rhid  norniallv  })ro(hK'es  by  fission  130  to  180  (generations  or  individuals, 
Onijcluxlroiaus  140  to  230,  and  Leacophrys  patuta  300  to  450,  after  which  con- 
jugation is  necessary  to  continued  division.  If  conjugation  be  prevented,  the 
individuals  become  small,  their  ]>liysiological  ])owers  become  weakened,  their 
nuclei  atrophy,  and  the  chromatin  disappears;  all  of  which  changes  are  evidence 
of  the  oncoming  of  senile  degeneration,  and  this  ultimately  results  in  death. 
Analogous  to  this  is  doubtless  the  fact,  pointed  out  by  Hertwig,^  that  in  sexual 
animals  an  unfertilized  ovum  within  the  oviduct  soon  becomes  over-mature 
and  enfeebled,  and  subsequent  fertilization,  even  though  possible,  is  abnormal. 
Even  if  the  idea  of  "  rejuvenescence"  be  regarded  as  fanciful  and  as  a  com- 
parison rather  than  an  explanation,  it  seems  to  be  a  principle  of  nature  that 
occasional  fusion  of  one  line  of  descent  with  another  is  necessary  to  continued 
reproduction  and  continued  life. 

A  second  theory,  defended  by  Hatschek  and  Hertwig,  argues  that  sexual 
reproduction  prevents  variation,  and  thus  preserves  the  uniformity  of  the  race. 
The  mingling  of  two  different  individuals  possessing  different  qualities  must 
give  rise  to  an  individual  intermediate  between  the  parents,  but  differing  from 
them.  Such  differences  between  parents  and  offspring  are  numerous,  but  in  a 
single  generation  are  minute,  and  they  are  easily  obliterated  by  a  subsequent 
union,  which  latter  in  turn  gives  rise  to  other  minute  differences.  Hence  sexual 
reproduction,  although  constantly  producing  variations,  as  constantly  eradicates 
them,  and,  by  striving  always  toward  the  mean  between  two  extremes,  tends 
toward  homogeneity  of  the  species.  The  essential  truth  of  such  a  view  seems 
obvious. 

A  third  theory,  advocated  by  Weismann  and  Brooks,  is  quite  the  0})posite 
of  the  last,  and  maintains  that  the  meaning  of  sexual  reproduction  lies  in  the 
production  of  variations.  "  The  process  furnishes  an  inexhaustible  supply  of 
fresh  combinations  of  individual  variations."  These  minute  variations,  seized 
upon  by  natural  selection,  are  augmented  and  made  serviceable,  and  a  variety, 
better  able  to  cope  with  the  conditions  of  existence,  results.  The  transformation, 
not  the  homogeneity,  of  the  species  is  thereby  assured.  The  two  latter  views  are 
not  necessarily  mutually  exclusive.  Both  claim  that  fertilization  brings  into 
evidence  variations.  It  is  quite  conceivable  that  subsequent  fertilizations  may 
obliterate  some  and  augment  others,  the  result  of  union  being  the  algebraic  sum 
of  the  characteristics  contributed  by  the  two  sexes. 

Primary  and  Secondary  Characters. — In  the  human  species,  as  in  all 
the  higher  sexual  animals,  the  characters  of  sex,  anatomical,  physiological,  and 
psychological,  are  divisible  into  two  classes,  called  primary  and  secondary. 
Primary  sexual  characters  are  those  that  pertain  to  the  sexual  organs  them- 
selves and  to  their  functions.     They  are  naturally  the  most  pronounced  of  all 

^  E.  Maupas  :  Archives  de  Zoologie  experimentale  ei  generate,  2e  serie,  vii.,  1889. 
*  O.  und  R.  Hertwig :  Experimentelle  Studien  am  thierischen  Ei  vor,  wdhrend  und  nach  der 
Befruohtung,  i.,  1890. 
56 


882  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

sexual  attributes.  Secondary  sexual  characters  comprise  those  attributes  that 
are  not  directly  connected  with  the  sexual  organs,  but  that,  nevertheless,  con- 
stitute marked  differences  between  the  sexes ;  such  are  the  greater  size  and 
strength  of  man's  body  as  compared  with  woman's,  the  superior  grace  and 
delicacy  of  woman's  movements,  the  deeper,  rougher  voice  of  man,  and  the 
higher,  softer  voice  of  woman.  In  reality,  all  secondary  sexual  characters  are 
accessorv  to  the  primary  ones,  and  the  greater  portion  of  the  present  article 
will  be  devoted  to  a  discussion  of  the  latter.  The  primary  seximl  characters 
of  the  male  centre  in  the  production  of  spermatozoa  and  the  process  of  impreg- 
nation, those  of  the  female  in  the  production  of  ova  and  the  care  of  the  devel- 
oping embryo. 

Sexual  Organs. — Sexual  organs  are  classified  into  essential  and  accessory 
organs.  The  essential  organs  are  the  two  testes  of  the  male  and  the  two 
ovaries  of  the  female.  The  accessory  organs  of  the  male  comprise  the  vasa 
deferentia,  the  seminal  vesicles,  the  urethra,  the  penis,  the  prostate  gland,  Com- 
peres glands,  and  the  scrotum  and  its  attached  parts.  The  accessory  organs  of 
the  female  comprise  the  oviducts  or  Fallopian  tubes,  the  iderus,  the  vagina,  the 
various  external  parts  included  in  the  imlva,  and  the  mammary  glands.  During 
the  greater  part  of  life  the  sexual  organs  perform  but  a  portion  of  their  duties  ; 
only  at  intervals,  and  in  some  individuals  never,  do  they  complete  the  cycle 
of  their  functions  by  engaging  in  the  reproductive  process  itself.  In  the  fol- 
lowing account  we  shall  discuss  first  the  habitual  physiology  of  the  organs  of 
the  male  and  of  the  female,  and  later  their  special  activities  in  the  repro- 
ductive process. 

B,  The  Male  Reproductive  Organs. 

The  male  reproductive  organs,  already  mentioned,  have  as  their  specific 
functions  the  production  of  the  essential  male  germ-cells,  the  spermatozoa,  the 
production  of  a  fluid  medium  in  which  the  spermatozoa  can  live  and  imdergo 
transportation,  the  temporary  storing  of  this  seminal  fluid,  and  its  ultimate 
transference  to  the  outside  world  or  to  the  reproductive  passages  of  the  female. 

The  Spermatozoon. — Spermatozoa  were  first  discovered  by  Hamm,  a 
student  at  Leyden,  in  1677.  Hamm's  teacher,  Leeuwenhoek,  first  studied 
them  carefully.  They  were  long  believed  to  be  parasites,  even  until  near  the 
middle  of  the  present  century,  when  their  origin  and  fertilizing  function  were 
established.  Spermatozoa  are  cells  modified  for  locomotion  and  entrance  into 
the  ovum.  Human  spermatozoa  are  slender,  delicate  cells,  averaging  0.055 
millimeter  (^i^  of  an  inch)  in  thickness,  and  consisting  of  a  head,  a  middle- 
piece,  and  a  tail  (Fig.  305).  The  head  (A)  is  flattened,  egg-shaped,  with  a  thin 
anterior  edge  and  often  slightly  depressed  sides.  It  terminates  anteriorly  in  a 
slender  projecting  and  sharply  pointed  thread  or  spear.  Its  chief  component 
appears  to  be  chromatic  substance,  and  it  is  to  be  regarded  probably  as  a 
nucleus  covered  by  an  excessively  thin  layer  of  cytoplasm,     von  Bardeleben  ' 

^  K.  V.  Bardeleben:  Verhandlungen  der  Anatomischen  Gesellschaft ;  Anatomischer  Anzeiger, 
vii.,  1892. 


REPRODUCTION.  883 

claims  the  number  of  chromosomes  in  the  chromatic  substance  after  matura- 
tion to  be  eight. 

The  middle-piece  (m)  is  a  short,  cytoplasmic  rod,  probably  containing  a  cen- 
trosome.     The  tail  {()  is  a  delicate  filiform,  apparently  cytoplasmic  structure, 
and  analogous  to  a  single  cilium  of  a  ciliated  cell.     The  tail  is  tipped  by  an 
excessively  fine,  short  filament,  the  end-piece  (e).     The  most 
abundant  of  the  solid  chemical  constituents  of  the  spermato- 
zoon is  nuclein,  probably  in  the  form  of  nucleic  acid,  which 
is  found  in  the  head.     Other  constituents  are  proteids,  prota- 
mine, lecitiiin,  cholesterin,  and  fat. 

The  structure  and  power  of  movement  of  the  spermatozoon 
plainly  show  it  to  be  adapted  to  activity.  It  is  not  burdened 
by  the  presence  of  food-substance  within  its  protoplasm.  It 
is  the  active  element  in  fertilization  ;  it  seeks  the  ovum,  and 
it  is  modified  from  the  form  of  the  typical  cell  for  the  special 
purpose  of  fertilization.  The  nucleus  is  the  fertilizing  agent- 
The  head  is  plainly  fitted  for  facilitating  entrance  into  the 
ovum.  The  tail  is  a  locomotor  organ  capable  of  spontaneous 
movements,  and,  after  expulsion  of  the  semen,  it  propels  the 
cell,  head  forward,  through  the  fluid  in  ^vhich  it  lies.  The 
movement  is  a  complex  one,  and  is  effected  by  the  lashing 
of  the  tail  from  side  to  side,  accompanied  by  a  rotary  move- 
ment about  the  longitudinal  axis.  The  rate  of  movement  has  fig.  sos.-Human 
been  variouslv  estimated  at  from  1.2  to  3.6  millimeters  in  the  spermatozoa    (after 

'  .  Retzius) :  A,  sperm- 

minute.     loward  heat,  cold,  and  chemical  agents  spermatozoa  atozoon seen e?; /ace,- 
behave  like  ciliated  cells.  "'.  ^''^'^'-  ™;  °^^'^'^^^- 

piece ;  t,  tail ;  e,  end- 

Ripe  spermatozoa  appear  to  be  capable  of  living  for  months  piece:  b,  c,  seen 
within  the  male  genital  passages,  where  they  are  probably  ^''*^°^  ^^^  s^^®- 
quiescent.  Outside  of  the  body  they  have  been  kept  alive  and  in  motion  for 
forty-eight  hours.  It  is  not  certain  how  long  they  may  remain  alive  within 
the  genital  passages  of  the  human  female.  They  have  been  found  in  the  os 
uteri  and  capable  of  movement  more  than  eight  days  after  their  discharge.  It 
seems  not  improbable  that  within  the  female  organs  their  environment  is  favor- 
able to  a  somewhat  prolonged  existence.  In  this  connection  it  is  of  interest  to 
know  that  spermatozoa  capable  of  fertilizing  have  been  known  to  live  within 
the  receptaculum  seminis  of  a  queen  bee  for  three  years. 

Spermatozoa  are  produced  in  large  numbers.  Upon  the  basis  of  observa- 
tions in  several  individuals,  Lode  ^  computes  the  average  production  per  week 
as  226,257,000,  and  in  the  period  of  thirty  years  from  twenty-five  to  fifty-five 
years  of  age  the  total  production  as  339,385,500,000.  This  excessive  produc- 
tion is  an  adaptation  by  nature  that  serves  as  a  compensation  for  the  small 
size  of  the  cells  and  the  small  chance  of  every  cell  finding  an  ovum.  With- 
out large  numbers  fertilization  would  not  be  ensured  and  the  continuance  of 
the  species  would  be  endangered. 

•A.  Lode  :  Ffluger^s  Archivf'dr  die  c/esammte  Physiologie,  1.,  1891. 


884  AN   AMERICAN    TEXT-BOOK    OF   PIIYSIOLOO  Y. 

Maturation  of  the  Spermatozoon. — Considerable  thcijretieal  interest 
attaches  to  tlie  question  as  to  tiie  real  niorphologieal  value  of  tiie  spermatozoon. 
It  is  undoubtedly  a  cell,  and  has  arisen  by  division  from  one  of  the  testicular 
cells,  called  the  primary  spermatocyte  or  sometimes  the  mother-cell  of  the 
spermatozoon.  But  is  it  the  morphological  equivalent  of  one  of  the  mother- 
cells?  In  most  animals,  and  probably  also  in  man,  each  primary  spermatocyte 
gives  rise  to  four  spermatids,  which  grow  directly  into  four  spermatozoa.  The 
process  of  derivation  of  the  spermatozoa  may  be  called,  by  analogy  with  the 
process  in  the  ripening  of  the  ovum,  maturation.  The  details  and  essence  of 
the  process  have  been  much  discussed.  Van  Beneden  foun<l  in  an  interesting 
worm,  AHi'drxH,  that  the  number  of  chromosomes  in  the  nucleus  of  a  single 
spermatozoon  is  only  half  that  in  the  original  testicular  cell ;  that  is,  the  pro- 
cess of  maturation  of  the  spermatozoon  consists  in  a  reduction  of  the  chromo- 
somes by  one  half.  This  discovery  has  since  been  extended  to  many  otiicr 
forms,  including  mammals  and  man,'  and  it  has  been  shown  further  that  the 
mature  spermatozoon  contains  only  one-half  the  number  of  chromosomes  cha- 
racteristic of  the  tissue-cells  of  the  species  in  question.  In  the  light  of  the 
subsequent  process  of  fertilization  these  facts  are  interesting.  Hertwig  and 
Weismann,  who  reo;ard  the  chromatic  substance  of  the  nucleus  as  the  bearer 
of  the  hereditary  qualities,  interpret  this  halving  of  the  chromatin  as  a  pro- 
vision for  the  reduction  of  the  hereditary  mass,  which  later  will  be  restored  to 
its  full  amount  by  unifju  with  the  egg.  As  we  shall  see,  the  maturation  of 
the  ovum  follows  a  somewhat  similar  course,  and,  since  the  process  has  been 
more  fully  studied  there,  we  shall  reserve  further  discussion  until  that  subject 
is  reached  (p.  889). 

Semen. — Semen  consists  of  spermatozoa,  together  with  fluid  and  dissolved 
solids,  coming  partly  from  the  testes  themselves,  but  chiefly  secreted  by  the 
accessory  sexual  glands — namely,  the  glands  within  the  va.srt  deferoitia,  the 
seminal  vesicles,  the  prostate  gland,  and  Cowper's  glands.  It  is  a  whitish, 
viscid,  alkaline  fluid,  with  a  slight  characteristic  odor.  The  amount  passed  out 
at  any  one  time  has  been  estimated  at  between  0.5  and  6  cubic  centimeters-  Its 
chemical  composition  has  not  been  examined  exhaustively.  Besides  water,  it 
contains  approximately  18  per  cent,  of  solid  substances,  which  comprise  nuclein, 
protamine,  })roteids,  xanthin,  lecithin,  eholesterin,  and  other  extractives,  iiit,  and 
sodium  and  potassium  chlorides,  sulphates,  and  phosphates.  Under  proper  treat- 
ment colorless  crystals,  called  Charcot's  crystals,  may  be  obtained  from  semen. 
They  appear  to  be  a  phosphate  of  a  nitrogenous  base,  which  has  been  called  ftpenn- 
ine.  Interest  in  the  semen  centres  in  its  histological  rather  than  its  chemical 
features.  The  fluid  portion  serves  as  a  vehicle  for  the  transportation  of  and  pos- 
sibly also  for  the  nutrition  of  the  ripe  spermatozoa.  Colorless  j)articles,  called 
seminal  granules,  exist  in  semen.  They  are  possibly  parts  of  nuclei  of  disin- 
tegrated cells.  Comparatively  little  is  known  of  the  composition  or  the  specific 
function  of  the  individual  secretions  contributed  by  the  various  organs.  The 
disintegration  of  the  nutritive  cells  of  the  testis  probably  furnishes  some  of  the 

*  V.  Bardeleben  :  loc  cit. 


lirj'iionrcTiox. 


885 


nutritive  substance  of  the  fluid.  I'rostatic  secu-etion  is  viscid  and  opalescent,  and 
contains  1.")  jut  cent,  of  solids,  comprising  niaitdy  |)rotcids  and  sails.  It  con- 
tributes the  substance  of  Charcot's  crystals  to  tiic  scnicn,  and  their  partial  decom- 
position is  said  to  be  responsible  for  the  characteristic  odor  of  the  seminal  fluid. 
The  secretion  from  the  seminal  vesicles  is  fairly  abundant,  is  albuminous,  and 
in  some  animals  at  least  seems  to  contain  fl])rino<>:en.  This  enables  the  fluid  to 
clot  after  its  reception  in  the  female  passages,  and  thus  to  i)revent  loss  of  sper- 
matozoa. Cowper's  glands  secrete  a  mucous  fluid.  By  careful  experiments 
upon  white  rats  Steinach '  has  shown  that  removal  of  the  seminal  vesicles  and 
the  prostate  gland,  while  not  diminishing  the  sexual  passion  and  the  ability  to 
j)erform  the  sexual  act,  including  the  actual  discharge  of  spermatozoa,  j)revents 
entirely  the  fertilization  of  the  ova;  removal  of  the  seminal  vesicles  alone 
markedly  weakens  the  fertilizing  power 
of  the  semen.  The  secretions  of  these 
accessory  glands  are  essential  to  the  mo- 
bility of  the  spermatozoa,  and  they  may 
have  other  important  functions. 

The  Testis.— The  testes  (Fig.  306,  t) 
are  compound  tubular  glands  with  a 
unique  structure.  Formed  early  in  em- 
bryonic life  as  solid  structures,  with  the 
seminiferous  tubules  {ts)  represented  by 
solid  cords  of  cells,  they  remain  in  the 
embryonic  condition  until  the  time  of 
puberty.  Some  of  the  cells,  the  mother- 
ed Is  of  the  spermatozoa,  then  begin 
actively  to  divide,  and  the  result  of  di- 
vision with  differentiation  is  the  mature 
spermatozoa.  These  latter  accumulate 
at  the  centre  of  the  tubules,  the  walls 
being  formed  largely  of  the  dividing 
cells  or  immature  spermatozoa.  Other 
cells  do  not  produce  spermatozoa,  but 
seem  to  disintegrate  and  give  rise  to  the 
nutritive  fluid  and  nuclear  particles  that 
are  found  mixed  with  the  sperm-cells. 
From  the  time  of  puberty  on,  usually 
throusrhout   life,  this  cellular  activitv 

proceeds,  the  rate  and  regularity  proba-  entia ;  e,  canal  of  the  epididymis ;  v.a,  vas  aberrans ; 

,,  .  J,         -ii    ^    T    •  1*      1  1  v.d,  v.d,  vas  deferens ;  v.s,  seminal  vesicle ;  d.e,  ejac- 

blyvaryinggreatlyWlthindlVldualsand  ulatoryduct;   pr,  prostate  gland;  6,  urinary  blad- 

depending  largely  on  the  frequency  of  «^er  ;  C.g,  Cowper's  gland  ;  u,  urethra;  pn,  penis. 

discharge  of  the  semen.     Spermatozoa 

may  be  wanting    in  old    men,  but  they  have  been  found    in  individuals  at 
eighty  or  ninety  years  of  age.    The  spermatozoa  accumulate  within  the  seminal 
'  K.  Steinach  :  PflUrjer's  ArchivfOr  die  gesammte  Fhysiologie,  Ivi.,  1894. 


t 

Fig.  306.— Diagram  of  the  male  reproductive 
organs:  t,  testis;  t.s,  seminiferous  tubules;  t.r, 
tubuli  recti ;  r.v,  rete  vasculosum ;  v.e,  vasa  eflTer- 


886  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

tubules,  and  by  the  constant  formation  of  others  behind  them  are  gradually 
pushed  outward  along  the  ducts. 

The  Duds  of  the  Testis. — The  ducts  of  the  testis  (Fig.  306)  comj>rise  a 
succession  of  tubes  of  different  morphological  and  physiological  values. 
They  are  approximately  twenty-five  feet  in  length,  and  are  named,  in 
order,  tubuli  recti,  rete  vascidosum,  vasa  effercntia,  canal  of  the  epididymis, 
vas  deferens,  and  ejacidatory  duct.  The  tubuli  recti  (t.r)  and  rete  vasculosum 
(r.v),  being  mere  channels  for  the  passage  of  spermatozoa,  present  no  special 
physiological  features.  The  vasa  efferentia  {v.e)  and  the  canal  of  the  epididymis 
{c)  contain  smooth  muscular  tissue  in  their  walls,  and,  moreover,  are  lined 
by  ciliated  epithelium,  the  cilia  causing  a  movement  outward  ;  both  of 
these  features  doubtless  aid  in  the  outward  passage  of  the  spermatozoa. 
The  excretory  duct  of  the  testis,  or  vas  deferens  (v.d),  wath  its  offshoot,  the 
seminal  vesicle,  is  more  important  physiologically.  It  is  nearly  two  feet  in 
length,  with  a  diameter  throughout  the  greater  part  of  its  course  of  one-tenth 
of  an  inch.  Near  its  termination,  however,  it  is  larger  and  sacculated,  and 
resembles  the  seminal  vesicle ;  it  is  known  here  as  the  ampulla  of  Henle.  Its 
epithelium  is  not  ciliated,  but  its  walls  contain  a  very  thick,  plain  muscular 
layer  consisting  of  outer  longitudinal  and  inner  circular  fibres.  In  the  walls 
of  the  ampulla  of  Henle  exist  small  tubular  glands.  The  vas  deferens  is  an 
important  storehouse  for  the  spermatozoa.  The  glands  near  its  termination 
supply  a  part  of  the  fluid  of  the  semen.  The  muscles  in  its  walls,  by  contract- 
ing, aid  in  the  seminal  discharges.  The  seminal  vesicle  (v.s)  is  a  branched  diver- 
ticulum from  the  vas  deferens.  In  structure  it  is  not  radically  unlike  the 
ampulla  of  Henle,  its  walls  containing  muscular  layers  and  glands.  Its  chief, 
if  not  its  only,  function  is  to  contribute  fluid  to  the  semen.  Of  all  the  organs, 
the  seminal  vesicles  contribute  probably  the  greatest  share  of  fluid.  Micro- 
scopic examination  does  not  confirm  the  old  belief  that  the  vesicles  are  store- 
houses for  semen,  and  this  idea  is  now  largely  laid  aside.  The  ejacidatory 
duct  (d.e)  on  each  side  is  a  short,  thin-walled  muscular  tube,  passing  partly 
through  the  substance  of  the  prostate  gland  and  serving  to  convey  the  semen 
to  the  urethra. 

The  Urethra. — The  urethra  (Fig.  306,  w),  the  common  excretory  duct 
for  the  urine  and  the  semen,  is  commonly  described  as  consisting  of  three  parts, 
named,  respectively,  the  prostatic,  the  membranous,  and  the  spongy  portions. 
The  first  is  characterized  by  the  presence  of  the  prostate  gland,  the  second  by 
the  absence  of  special  features,  and  the  third  by  the  presence  of  Cowper's  glands 
and  the  penis.  Throughout  its  length  the  wall  of  the  urethra  contains  plain 
muscular  tissue  arranged  longitudinally  within  and  circularly  without ;  and, 
except  at  the  external  opening,  the  small  racemose  mucous  [/lands  of  LUtrL 
Its  wall  is  hence  contractile  and  its  lumen  is  kept  moist.  Beyond  these  its 
special  physiological  features  are  given  it  by  the  organs  above  mentioned. 

The  Prostate  Gland. — The  prostate  gland  (Fig.  306,  pr)  is  a  compound 
tubular  gland  whose  alveoli  are  mingled  with  a  large  quantity  of  plain  mus- 
cular tissue.     It  completely  surrounds  the  urethra  at  the  base  of  the  bladder, 


REPRODUCTION.  887 

and  opens  into  it  b}'  numerous  small  ducts  situated  about  the  openings  of  the 
vasa  deferentia.  Its  function  is  to  contribute  prostatic  fluid  to  the  semen.  The 
composition  of  this  fluid  has  been  already  mentioned  (p.  885) ;  its  specific  use 
is  not  known. 

Cowper's  Glands. —  Chwper's  glands  (Fig.  306,  C.g),  two  in  number,  are 
tubulo-raccmose  glands,  the  ducts  of  which  open  into  the  spongy  portion  of 
the  urethra  by  two  orifices  situated  some  two  inches  below  the  openings  of  the 
vasa  deferentia.  Their  viscid  secretion  is  thought  to  be  one  of  the  components 
of  the  seminal  fluid,  but  its  specific  function  is  unknown.  It  has  been  sug- 
gested that  Cowper's  fluid  cleanses  the  urethra  of  urine  and  of  semen,  instead 
of  contributing  actually  to  the  seminal  fluid. 

The  Penis. — The  penis  (Fig.  306,  pii)  has  as  its  constant  function  merely 
the  conveying  of  the  urine  to  the  outside  world,  and  for  this  purpose  it  has  no 
special  features  beyond  those  belonging  to  the  urethra,  which  rinis  throughout 
its  whole  length.  Specifically,  however,  it  is  the  intromittent  organ,  and 
serves  to  convey  the  semen  into  the  genital  passages  of  the  female.  This 
function  is  based  upon  its  power  of  erection,  and  this  power  is  dependent 
upon  the  presence  of  the  erectile  tissue  which  constitutes  the  bulk  of  the 
organ.  The  erectile  tissue  is  arranged  in  the  form  of  three  long  cylindrical 
masses  imperfectly  separated  from,  but  parallel  to,  one  another  and  extending 
lengthwise.  Of  these,  the  two  corpora  cavernosa  lie  at  the  sides,  and  meet  each 
other  in  the  middle  line  along  the  upper  side  of  the  penis ;  the  corpus  spongi- 
osum lies  in  the  middle  line  below,  and  is  pierced  throughout  its  length  by  the 
urethra.  At  its  proximal  end  each  corpus  is  enlarged  into  a  bulbous  part, 
and  is  covered  by  a  layer  of  muscular  fibres  constituting  a  distinct  muscle — the 
bulbs  of  the  corpora  cavernosa  by  the  ischio-cavernosi  {erectores  penis),  that  of 
the  corpus  spongiosum  (called  bulbus  urethra;)  by  the  bulbo-cavernosus  {accel- 
erator urince).  At  its  distal  end  each  corpus  cavernosum  terminates  bluntly, 
while  the  corpus  spongiosum  projects  farther  and  enlarges  to  form  the  extrem- 
ity of  the  organ,  the  glans  penis.  Each  corpus  is  spongy  in  consistence,  being 
formed  of  a  trabecular  framework  of  white  and  elastic  connective  tissue  and 
plain  muscular  fibres,  with  cavernous  venous  spaces,  and  is  covered  by  a  tough 
fibrous  tunic.  When  the  spaces  are  distended  with  blood  the  whole  organ 
becomes  hard,  rigid,  and  erect  in  position.  The  mechanism  of  erection  will 
be  studied  more  in  detail  later  (p.  901).  The  penis,  especially  toward  its  ter- 
mination, is  beset  with  end-bulbs.  Pacinian  bodies,  and  other  nerve-termina- 
tions, that  make  it  particularly  sensitive  to  external  stimulation. 

C    The  Female  Reproductive  Organs. 

The  female  reproductive  organs,  already  mentioned,  have  as  their  specific 
functions  the  production  of  the  essential  female  germ-cells,  the  ova,  their  trans- 
ference to  the  uterus,  and,  if  unfertilized,  to  the  outside  world ;  if  fertilized, 
the  protection  and  nutrition  of  the  developing  embryo,  its  ultimate  transfer- 
ence to  the  outside  world,  and  the  nutrition  of  the  child  during  early  in- 
fancy. 


888 


AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 


Fig.  307.— Human  ovum  (modified  from  Na- 
Kel):  n,  nucleus  (germinal  vesicle)  containing 
the  amceboid  nucleolus  (germinal  spot);  d,  deu- 
toplasniie  zone;  p,  protoplasmic  zone;  z,  zona 
radiata ;  «,  perivitelline  space. 


The  Ovum. — The  ljunmn  ovum  wjls  discovered  in  1827  by  Von  JJaer,  and 
it  was  he  who  first  conipletely  traced  tlie  connection  between  ova  in  the  gene- 
rative passages  and  ova  in  the  Graafian 
. "  ^~^^  follicles  of  the  ovary.     The  conception 

of  ova  as  the  essential  female  element 
had,  however,  long  been  held,  and  Har- 
vey's dictum  of  the  seventeenth  century, 
that  everything  living  is  derived  from 
an  egg  {omne  vivum  ex  ovo),  is  well 
known.  The  human  ovum,  as  it  comes 
from  the  ovary,  is  a  spherical,  proto- 
plasmic cell  (Fig.  307),  averaging  with 
the  zona  radiata,  approximately  0.2  milli- 
meter (y^  inch)  in  diameter.  As  in 
other  cells,  the  cell-body  may  be  distin- 
guished fron\  the  nucleus,  the  proto- 
plasm of  the  former  being  called  cyto- 
plasni.  In  its  finer  structure  the  cyto- 
plasm consists  of  an  excessively  delicate 
network  of  protoplasmic  substance.  As  in  other  mammalian  eggs,  it  proba- 
bly contains,  adjoining  the  nucleus,  a  minute,  specially  differentiated  portion, 
consisting  of  a  single  or  double  centrosome  surrounded  by  an  attraction  sphere 
(Fig.  308,  A).  For  some  distance  inward  from  the  border  the  cytoplasm  is 
pure  and  transparent,  and  this  portion  is  oflen  called  the  protoplasmic  zone 
(Fig.  307,  ])).  Throughout  the  centre  of  the  cell,  however,  it  is  obscured  by 
the  presence  of  an  abundance  of  yolk-substance,  or  deutoplasm,  from  which 
the  corresponding  part  of  the  ovum  is  sometimes  called  the  deutoplasmic 
zone  (d).  Deutoplasm  is  non-living  substance ;  it  consists  of  granules  of 
yolk  imbedded  in  the  meshes  of  the  cytoplasmic  network,  and,  like  its  ana- 
logue, the  yolk  of  the  hen's  egg,  it  serves  as  food  for  the  future  cells  of  the 
embryo. 

A  comparison  of  the  respective  amounts  of  food  in  the  human  and  the 
fowl's  egg,  with  the  manner  of  embryonic  development,  is  suggestive.  The 
chick  develops  outside  the  body  of  the  hen,  and,  therefore,  requires  a  large 
supply  of  nutriment,  which  it  finds  in  the  yolk  and  the  white  of  the  eg^.  The 
child  develops  within  the  mother's  body  and  receives  its  nourishment  from  the 
maternal  blood;  hence  the  supply  of  food  within  the  egg  is  only  enough  to 
ensure  the  beginning  of  growth,  special  blood-vessels  being  formed  to  facilitate 
its  continuance. 

The  miclcuK  ()i),  commonly  called  by  its  early  name,  the  gcrmincd  i^caicle,  is 
spherical,  and  usually  occupies  a  slightly  eccentric  position.  Its  protoplasm 
consists  of  a  network  composed  of  two  kinds  of  material :  the  more  delicate, 
slightly  staining  threads  are  the  achromatic  substance,  the  coarser,  deeply 
staining  portion,  the  chromatic  substance  or  chromatin.  The  former  is  con- 
tinuous with,  and   probably  of  exactly  the  same  nature  as,  the  cytoplasm. 


REPRODUCTION.  889 

The  diroinatiii  is  peculiar  to  tlic  iiiieleiis,  and  at  certain  stages  in  the  nuclear 
history  is  resolved  into  distinct  grannies  or  filaments,  the  chromosomes  (Fig. 
308,  A),  the  nun\l)er  of  which  in  the  human  ovum  is  iniknown.  There 
is  much  reason  for  believing  that  the  chromatin  is  the  hearer  of  whatever  is 
inherited  from  the  mother.  The  nucleus  is  limited  by  a  nuclear  membrane, 
and  contains  a  strongly  marked  nucleolus,  which  has  likewise  retained  its 
original  name  of  germinal  spot.  Tiiere  is  probably  no  j)roj)er  cell-wall,  or 
vitelline  membrane,  such  as  is  said  to  exist  in  many  mammalian  and  other  eggs. 
The  ovum  is,  liowever,  surrounded  by  a  thick,  tough,  transparent  membrane  of 
ovarian  origin,  about  0.02  millimeter  {^i^-j^  inch)  in  thickness,  and  called  the 
zona  radiata  or  zona  pcUucida  (Fig.  307,  z).  It  is  pierced  by  a  multitude  of  fine 
lines  radiating  from  the  surface  of  the  zona  to  the  ovum  ;  these  are  thought 
to  represent  pores,  to  contain  fine  protoplasmic  processes  of  the  surrounding 
ovarian  cells,  and  thus  to  serve  as  channels  for  the  passage  of  nutriment  to 
the  egg.  Between  the  zona  radiata  and  the  ovum  a  narrow  space,  the  peri- 
vitelline  space  (s),  exists.  Attached  to  the  outside  of  the  zo7ia  radiata  are 
usually  patches  of  cells  derived  from  the  discus  prolige^'us  of  the  Graafian  fol- 
licle of  the  ovary,  which  may  form  a  complete  covering  and  constitute  the  corona 
radiata.     They  disappear  soon  after  the  egg  is  discharged  from  the  ovary. 

Regarding  the  chemistry  of  the  mammalian  ovum  little  is  known  definitely, 
and  of  the  human  ovum  nothing  whatever  except  by  inference  from  the  eggs 
of  lower  animals.  The  protoplasmic  basis  undoubtedly  resembles  other  undif- 
ferentiated protoplasm  in  its  general  composition,  with  an  abundance  of  proteid 
among  its  solid  constituents.  Deutoplasm  is  a  rich  mixture  of  food-substance 
in  concentrated  form,  and  contains  among  its  solids  probably  vitellin,  nuclein, 
albumin,  lecithin,  fats,  carbohydrates,  and  inorganic  salts. 

The  form  and  the  structure  of  the  egg  suggest  the  part  that  it  plays  in 
reproduction.  It  is  not  locomotor;  in  fertilization  it  is  the  passive  element; 
it  remains  in  its  place  and  is  sought  by  the  spermatozoon.  Its  nucleus  is  the 
equivalent  of  that  of  the  spermatozoon.  Its  form  renders  easy  the  entrance  of 
the  male  element.  Its  bulk  consists  largely  of  food  in  a  very  concentrated 
form,  and,  as  development  proceeds,  it  supplies  this  food  to  the  growing  cells. 

In  lower  forms  of  animal  life,  where  eggs  are  fertilized  outside  the  body 
of  the  parent  in  the  water  into  which  they  are  set  free,  they  are  usually  pro- 
duced in  enormous  numbers.  Some  fail  of  fertilization,  while  others  are 
destroyed  by  enemies,  and  the  large  number  is  a  compensatory  adaptation  by 
nature  for  their  poor  chance  of  survival.  In  mammals  and  man,  however, 
ova  have  a  much  better  opportunity  of  being  fertilized  and  of  developing  into 
adults,  and  their  number  is  correspondingly  reduced.  Their  relative  fewness, 
as  compared  with  the  spermatozoa,  is  in  harmony  with  their  larger  size  and 
the  fact  that,  wdiile  awaiting  fertilization,  they  are  carefully  protected  within 
the  body  of  the  mother. 

Maturation  of  the  Ovum. — Attention  has  been  called  to  the  maturation 
of  the  spermatozoon.  The  ovum  undergoes  an  analogous  process  of  ripening, 
which  has  been  studied  very  carefully,  and  from  its  theoretical  interest  has 


890 


AN  AMERICAN   TEXT-BOOK  OF  PHYSIOLOGY. 


Fig.  308.— Stages  in  the  matviration  of  the  ovum  ;  diagraminatic  (mainly  from  Wilson) :  A,  the  orig- 
inal ovarian  ovum ;  n,  its  nucleus,  containing  four  chromosomes ;  c,  its  double  centrosome,  surrounded 
by  the  attraction  sphere;  in  6  much  of  the  chromatin  has  begun  to  degenerate;  the  rest  has  become 
arranged  into  two  quadruple  groups  of  chromosomes,  or  tetrads;  the  formation  of  the  spindle  and  the 
asters  has  begun;  in  Cthe  first  polar  amphiaster,  bearing  the  chromosomes,  is  completed  ;  in  D  the  am- 
phiaster  has  become  rotated  and  has  travelled  toward  the  surface  of  the  ovum ;  g.  v,  the  degenerated 
remains  of  the  nucleus;  in  E  the  division  of  the  tetrads  into  double  groups  of  chromosomes,  or  dyads, 
has  begun,  and  the  first  polar  body,  p.  6',  is  indicated  ;  in  Fthe  first  polar  body,  containing  two  dyads,  has 
been  extruded ;  the  formation  of  the  second  polar  amphiaster  has  begun ;  in  G  the  first  polar  body  is  pre- 
paring to  divide ;  the  second  polar  amphiaster  is  fully  formed ;  in  //  the  division  of  the  dyads  into  single 
chromosomes  in  both  the  first  polar  body  and  the  egg  has  begun,  and  the  second  polar  body,  p.  b^.  is  in- 
dicated ;  in  /  the  formation  of  the  polar  bodies  is  completed  ;  9 ,  the  egg-nucleus,  containing  two  small 
chromosomes,  one-half  the  original  number.  In  fertilization  the  spermatozoon  will  bring  in  two  addi< 
tional  chromosomes,  thus  restoring  the  total  number  of  four. 


REPRODUCTION.  891 

given  rise  to  a  large  amount  of  discussion.  Maturation  occurs  approximately 
as  the  ovum  is  leaving  the  ovary,  the  exact  time-relations  being  not  yet  deter- 
mined. It  consists  of  a  karyokinetic  division  of  the  nucleus,  essentially  like 
karyokinesis  (mitosis)  in  ordinary  cell-division,  and  an  expulsion  of  one  por- 
tion from  the  cell.  This  occurs  twice  in  succession.  The  cast-off  bits  of  pro- 
toplasm are  known  as  -polar  bodies.  The  details  of  the  process  of  maturation 
are  as  follows  (Fig.  308)  :  The  nucleus  of  the  original  ovarian  ovum  contains 
the  same  number  of  chromosomes  as  the  ordinary  tissue-cells  (A).  At  the  begin- 
ning of  maturation  much  of  the  chromatic  substance  begins  to  degenerate,  and 
later  it  disappears  wholly  (B,  C,  D).  The  remainder  is  rearranged  into  groups 
of  chromosomes,  usually  four  in  each  group,  which  is  called  a  "quadruple- 
group  "  or  "  tetrad  "  {B).  The  number  of  tetrads  is  always  one-half  the  num- 
ber of  original  chromosomes,  while  the  total  number  of  chromosomes  in  the 
nucleus  at  this  stage  is  double  the  original  number.  The  nucleus  moves  from 
its  position  in  the  interior  of  the  egg  toward  the  surface,  and  the  nuclear  mem- 
brane begins  to  disappear.  At  the  same  time  the  two  minute  cytoplasmic 
structures,  the  centrosomes,  which  lie  close  beside  the  nucleus,  separate  and 
take  up  positions  at  a  considerable  distance  apart  from  each  other,  in  some 
cases  even  upon  opposite  sides  of  the  nucleus.  The  substance  lying  between 
them — either  the  cytoplasmic  network  or  the  achromatic  substance  of  the 
nucleus — loses  its  reticular  appearance,  becomes  filamentous,  and  arranges  itself 
in  the  form  of  a  spindle  with  the  threads  extending  from  pole  to  pole  (C,  D). 
The  groups  of  chromosomes  become  attached  to  the  spindle  threads  midway 
between  the  poles.  At  each  pole  lies  a  centrosome,  and  about  it  the  cytoplasm 
becomes  arranged  in  the  form  of  a  star,  the  aster.  The  spindle  with  the  two 
asters  is  known  as  the  polar  amphiaster,  and  the  complicated  structure  seems 
to  be  formed,  as  in  ordinary  cell-division,  for  the  sole  purpose  of  dividing 
the  nucleus  into  two  portions.  This  is  now  performed  (E) ;  each  quadruple- 
group  of  chromosomes  splits  into  two,  and  these,  known  as  "  double-groups," 
or  "  dyads,"  are  drawn  apart  from  each  other  and  toward  the  spindle  poles, 
probably  by  contraction  of  the  fibres  of  the  spindle.  The  nucleus  is  thus  di- 
vided into  halves.  While  the  division  has  been  proceeding,  the  spindle  has 
wandered  halfway  outside  the  egg,  and,  when  it  is  completed,  one  of  the  result- 
ing nuclear  halves,  comprising  one-half  of  the  full  number  of  dyads,  together 
with  the  centrosome  and  the  aster,  finds  itself  entirely  extruded  from  the  egg 
and  lying  within  the  perivitelline  space.  It  is  known  as  the  first  polar  body 
{F,p.  b^).  The  diminished  nucleus  within  the  ovum  proceeds  at  once  to  under- 
go a  second  karyokinetio  division  similar  to  the  first  (G,  H,  I) ;  each  of  the 
remaining  dyads  divides  into  two  single  chromosomes,  which  are  pulled  apart 
from  each  other ;  and  a  second  polar  body  (p.  b^),  containing  one-half  the 
number  of  single  chromosomes  characteristic  of  the  tissue-cells,  is  extruded. 
Apparently  the  two  polar  bodies  are  of  no  further  use.  In  many  animals  the 
first  divides  into  two,  but  sooner  or  later  both  degenerate  and  disappear.  The 
remnant  of  the  nucleus  left  within  the  egg,  much  reduced  in  size,  wanders 
back  to   the  interior.      Its   chromosomes,  reduced  to   one-half  the  number 


892  AN  AMERICAN    TEXT-BOOK    OF   PIIYSIOLOd  Y. 

helonging  to  the  ovarian  ovum,  are  resolved  again  into  seatterecl  clironiatio 
.substance.  Jt  develops  a  membrane  and  becomes  again  a  resting  nucleus.  It 
is  known  henceforth  as  the  egg-nucleus,  or  female  pronucleus,  and  it  awaits  the 
coming  of  the  male.     Its  centrosome  gradually  degenerates  and  disa})pears. 

Thus  the  curious  process  of  maturation  of  the  ovum  is  different  in  detail 
from  that  of  maturation  of  the  S])ermatozoon.  In  the  latter  the  primary 
spermatocyte  divides  into  four  functional  spermatozoa;  in  the  former  the  pri- 
mary ovocyte  divides  into  two  functionless  polar  bodies  (or,  by  subdivision  of 
the  first,  three,  which  have  been  called  abortive  eggs)  and  one  functional  ovum. 
It  is  entirely  probable,  however,  that  the  essence  of  the  process  is  exactly  the 
same  in  the  two  cases,  and  lies  in  the  reduction  of  the  chromatic  substance  of 
the  nucleus.  Van  Beneden  found  in  Ascaris  that  in  the  maturation  of  the 
ovum,  as  in  that  of  the  spermatozoon  already  referred  to,  the  number  of  chro- 
mosomes is  halved  and  that  the  number  in  the  two  germ-cells  is  the  same. 
This  has  since  been  proved  abundantly  in  other  forms,  as  well  as  the  further 
associated  fact  that  the  mature  germ-cells  contain  each  one-half  the  number 
of  chromosomes  that  are  characteristic  of  the  somatic  cells ;  it  is  wholly  })rob- 
able  that  these  facts  are  universal  in  sexual  reproduction.  Each  mature  germ- 
cell,  therefore,  while  in  reality  a  cell,  is,  when  compared  with  the  somatic  cells, 
incomplete.  The  subsequent  union  of  the  two  in  fertilization  restores  the 
chromosomes  to  their  normal  inimber.  Inasmuch  as  the  chromatin  is  probably 
the  all-important  constituent  of  the  germ-cells,  the  bearer  of  the  paternal  and 
the  maternal  inherited  characteristics,  the  phenomena  of  maturation  are  of 
great  interest.  Most  biologists  follow  Hertwig  and  Weismann  in  regarding 
maturation  as  an  adaptation  for  the  ]>revention  of  the  constant  increase  in 
quantity  of  the  hereditary  substance  that  would  otherwise  take  place  with 
every  union  of  ovum  and  spermatozoon.  Without  a  reducing  process  the 
quantitv  of  chromatin  in  cells  would  become  in  a  very  few  generations  incon- 
veniently great.  Maturation  is  a  j)reparation  of  each  germ-cell  for  union  with 
its  mate. 

The  Ovary ;  Ovulation. — The  ovaries  (Fig.  309,  o)  are  often  spoken  of  as 
glands,  but  they  are  not  glands  according  to  the  ordinary  histological  and 
physiological  use  of  the  term.  They  are  solid  organs  with  a  structm-e  peculiar 
to  themselves,  and  their  function  is  the  production  of  ova.  Their  stroma  con- 
sists of  fine  connective  tissue  with  numerous  connective-tissue  cells.  The  ova 
are  developed  in  the  interior  within  cavities  called,  from  their  discoverer, 
Graafian  follicks{G.f),  from  primitive  ova  that  are  modified  cells  of  the  germinal 
epithelium  of  the  embryo.  It  has  been  calculated  that  the  two  human  ovaries 
at  the  age  of  eighteen  years  contain  an  average  of  72,000  primitive  ova,  but 
that  not  more  than  four  hundred  of  these  arrive  at  maturity.  Each  Graafian 
fi)llicle  is  lined  by  an  ei)ithelial  layer  several  cells  thick,  the  membrava 
granulosa,  and  is  filled  with  clear  viscid  fluid,  the  liquor  follmiU,  which  con- 
tains albuminoid  matter.  Imbedded  in  the  epithelium  upon  one  side  is 
usually  a  single  ovum,  completely  surrounded  by  the  cells  and  forming  a 
prominent  hillock  which  projects  well  into  the  cavity  of  the  follicle.     The 


BEPROD  UCTION. 


893 


epitlu'Iiuni  iiuinodiatcly  surroimdintr  the  ovum  is  the  discus  prol'icjerus.  Within 
the  discus  the  ovum  grows  and  becomes  surrounded  by  tl»e  zona  pellucida.  In 
the  process  of  growth  the  (Jraafian  loUide  approaches  the  surface  of  the  ovary, 


Fig.  309.— Diagram  of  the  female  reproductive  organs  (modified  from  Henle  and  Symington) :  o,  ovary  ; 
O.f,  Graafian  follicle  containing  an  ovum ;  c.l,  corpus  luteum ;  p,  parovarium ;  /,  fimbriated  end  of  F.  t, 
Fallopian  tube ;  u,  body,  and  c,  cervix  of  uterus ;  o  e,  os  uteri  externum ;  vg,  vagina ;  h,  hymen ;  u,  open- 
ing of  urethra ;  v,  vulval  cleft ;  n,  labia  minora,  or  nymphiE ;  l.m,  labia  majora. 

and  finally  comes  to  form  a  minute  rounded  vesicular  projection  covered  only 
by  the  ovarian  epithelium.  When  fully  ready  for  discharge,  the  wall  of  the 
follicle  becomes  ruptured,  probably  by  the  increasing  pressure  of  the  contained 
liquid,  and  the  ovum  with  its  zona  pellucida  and  a  portion  or  all  of  the  discus 
proUyerus,  now  called  the  corona  radiata,  is  cast  out  upon  the  surface  of  the 
ovary  to  be  taken  up  by  the  Fallopian  tube.  The  empty  follicle  undergoes 
changes  and  becomes  the  corpus  luteum  (cl).  Usually  the  corpus  luteum  de- 
generates within  a  few  days  and  ultimately  disappears.  If,  however,  pregnancy 
follows  ovulation,  it  grows  very  large,  perhaps  because  of  the  congested  state 
of  the  reproductive  organs,  and  remains  for  months  before  the  retrograde 
metamorphosis  sets  in.  Not  all  Graafian  follicles  reach  maturity  and  burst, 
for  many,  after  developing  to  a  considerable  size,  undergo  degenerative 
changes,  characterized  by  liquefaction  and  disappearance  of  their  contents. 

The  discharge  of  the  ovum  is  known  technicallv  as  ovulation.  In  most 
animals  ovulation  is  a  periodic  phenomenon  accompanying  certain  seasons,  and 
is  marked  by  general  sexual  activity.  In  woman  and  many  domesticated  ani- 
mals the  relation  to  the  seasons  no  longer  exists,  but  too  little  is  known  of  the 
causes  and  time-relations  of  the  phenomenon  and  its  general  bearings  upon 
other  physiological  processes,  notably  upon  menstruation  in  woman.     A  lar;;e 


894  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

but  not  wholly  decisive  literature  upon  the  subject  in  the  human  being  has 
been  written.  It  is  a  common  belief",  originating  in  the  seventeenth  century, 
that  ovulation  in  woman  is  a  periodic  phenomenon  occurring  regularly  every 
month  and  contemporaneous  with  the  occurrence  of  the  menstrual  flow,  and 
numerous  post-mortem  observations  of  the  presence  in  the  ovary  of  freshly- 
discharged  Graafian  follicles  at  the  menstrual  ])eriod  afford  evidence  of  the 
frequent  coincidence  of  the  two  phenomena.  But  ovulation  at  the  time  of 
menstruation,  though  probably  usual,  is  not  exclusive  of  ovulation  at  other 
times,  for  intermenstrual  observations  of  fresh  ovarian  sears  are  not  rare,  and 
prove  without  doubt  that  discharge  of  an  ovum  may  occur  at  any  time  between 
two  successive  periods  (see  under  Menstruation,  p.  895).  Graafian  follicles 
develop  even  during  infancy  ;  most  of  them,  and  perha])s  all,  retrograde  with- 
out discharging  their  ova,  but  the  occasional  instances  of  pregnancy  at  the  ages 
of  seven,  eight,  or  nine,  prove  that  ovulation  may  occur  during  childhood. 
Ovulation  usually  begins  at  puberty,  its  commencement  thus  coinciding  with  that 
of  menstruation,  and  continues  until  the  climacteric.  After  the  climacteric  it 
may  occur  in  exceptional  cases,  although  here,  as  before  puberty,  retrogressive 
degeneration  of  the  Graafian  follicles  is  the  rule.  It  is  commonly  believed  that 
ovulation  is  at  a  standstill  during  both  pregnancy  and  lactation.  The  un- 
doubted possibility  of  a  pregnancy  originating  during  lactation  would,  how- 
ever, seem  to  prove  the  possibility  of  ovulation  during  the  latter  period.  It  is 
not  decided  whether  removal  of  the  uterus  does  away  wholly  with  ovulation. 

The  Fallopian  Tube. — Each  of  the  Fallopian  tubes  (Fig.  309,  F.  t),  or 
oviducts,  opens  into  the  peritoneal  cavity  about  one  inch  from  the  correspond- 
ing ovary.  Around  the  opening  is  an  expanded  fringe  of  irregular  processes, 
ihejimhrice  (/),  one  of  which  is  attached  to  the  ovary.  The  length  of  the  tube  is 
between  three  and  four  inches,  and  the  opening  into  the  uterus  is  extremely 
small.  The  chief  structures  in  the  walls  of  the  oviducts  that  are  of  physio- 
logical interest  are  the  double  layer  of  plain  muscle,  an  outer  longitudinal 
and  an  inner  circular  coat,  longitudinal  fibres  from  which  pass  also  into  the 
fimbriae ;  and  the  cilia  with  which  the  tube  is  lined  throughout,  and  which  are 
present  also  upon  the  inner  side  of  the  fimbriae.  The  direction  of  the  ciliary 
movement  is  from  the  ovary  toward  the  uterus.  The  primary  function  of  the 
Fallopian  tubes  is  to  convey  ova  from  the  ovary  to  the  uterus ;  they  also  con- 
vey spermatozoa  in  the  reverse  direction  ;  and  within  them  the  union  of  ovum 
and  spermatozoon  usually  takes  place. 

The  mechanism  of  the  receipt  of  the  ovum  by  the  tube  is  not  fully  under- 
stood. After  ovulation  the  ovum  is  slightly  adherent  to  the  surface  of  the 
ovary  by  the  agency  of  the  viscid  liquor  folliculi.  It  is  possible,  but  it  has 
not  been  proved,  that  in  the  human  being,  as  has  been  seen  in  some  animals, 
the  expanded,  fimbriated  end  of  the  Fallopian  tube  clasps  the  ovary  when 
the  egg  is  discharged.  The  passage  of  the  ovum  into  the  tube  is  probably 
brought  about  by  the  cilia  lining  the  fimbriae.  Once  within  the  tube,  the 
ciliarv  action,  assisted  perhaps  by  contraction  of  the  muscular  fibres  in  the 
walls,  carries  the  ovum  slowly  along  toward  and  finally  into  the  uterus.     In 


REPRODUCTION.  895 

some  luaiuraals  the  passage  occupies  three  to  five  clays;  tlie  time  in  woman  is 
not  known. 

The  Uterus. — The  uterus  (Fig.  309,  w),  or  womb,  receives  tlie  ovum  from 
the  Fallopian  tube  and  passes  it  on,  if  unimpregnated,  to  the  vagina ;  on  the 
other  hand,  it  receives  from  the  vagina  spermatozoa  and  transmits  them  to  the 
Fallopian  tubes ;  it  is  the  seat  of  the  function  of  menstruation  ;  when  impreg- 
nation has  taken  place,  it  retains  and  nourishes  the  growing  embryo,  and  ulti- 
mately expels  the  child  from  the  body.  Its  structure  accords  with  these  func- 
tions. Its  thick  walls  consist  largely  of  plain  muscular  tissue  arranged 
roughly  in  the  form  of  three  indistinctly  marked  layers.  Of  these,  the  exter- 
nal and  the  middle  coats  are  thin ;  the  fibres  of  the  former  are  arranged  in 
general  longitudinally,  those  of  the  latter  more  circularly  and  obliquely. 
The  third,  most  internal  layer,  which  is  regarded  by  some  as  a  greatly  hyper- 
trophied  muscularis  mucosae,  forms  the  greater  part  of  the  uterine  wall.  Its 
fibres  are  arranged  chiefly  circularly  ;  toward  the  upper  part  they  become  trans- 
verse to  the  Fallopian  tubes,  and  at  the  cervix  longitudinal  fibres  lie  within 
the  circular  ones.  The  individuality  of  the  muscular  layers  and  uniformity 
in  the  course  of  the  fibres  is  largely  interfered  with  by  the  numerous  blood- 
vessels of  the  uterine  walls.  The  uterus  is  lined  by  an  epithelium  composed 
of  columnar  ciliated  cells,  except  in  the  lower  half  of  the  cervix,  where  a  stratified 
non-ciliated  epithelium  exists.  The  direction  of  the  ciliary  movement  in  woman 
is  not  definitely  known  ;  in  other  mammals  the  cilia  appear  to  sweep  toward  the 
OS  uteri.  The  mucous  membrane  is  thick,  and  contains  very  numerous  branch- 
ing tubular  glands  that  are  lined  by  ciliated  epithelium  and  have  a  tortu- 
ous course,  terminating  in  the  edge  of  the  muscular  layer.  They  secrete  a 
viscid  mucous  fluid.  Between  the  glands  are  branched  connective-tissue 
cells  that  are  not  unlike  the  connective-tissue  cells  of  embryonic  structures, 
and  wandering  cells.  Lymph-spaces  and  blood-capillaries  exist.  The 
development  of  the  tissue  goes  on  slowly  up  to  the  time  of  puberty,  and, 
as  we  shall  see,  after  puberty  the  mucous  membrane  is  subject  to  constant 
change. 

Menstruation. — Except  during  pregnancy  the  most  striking  activities  of 
the  uterus  are  associated  with  that  peculiar  female  function  which,  from  its 
monthly  periodicity,  is  called  menstruation.  The  most  obvious  external  fact 
of  this  phenomenon  is  the  discharge  every  month  of  a  bloody,  mucous  fluid 
through  the  vagina  ;  the  most  obvious  internal  facts  are  the  bleeding  and  the 
degeneration  and  disappearance  of  a  portion  of  the  mucous  membrane  of  the 
body  of  the  uterus.  This  curious  process,  though  having  analogies  in  lower 
animals,  occurs  most  markedly  in  the  human  female,  and  from  before  the  time 
of  Aristotle  to  the  present,  among  both  primitive  and  civilized  races,  its  signifi- 
cance has  been  the  cause  of  much  speculation.  The  detailed  phenomena  of 
menstruation  are  not  as  well  known  as  they  should  be.  Experimentation  is 
practically  out  of  the  question,  and  the  opportunities  of  careful  post-mortem 
study  of  normal  healthy  uteri  at  different  stages  are  rare.  The  main  facts  are 
as  follows : 


896  .l.V    AMKRlCAy    TEXT-BOOK    OF   PHYSIOLOGY. 

Some  (lays  hefoi-i'  tlio  flow  occurs  the  raucous  membrane  of  the  body  of  the 
uterus  begins  to  tliicken,  partly  by  an  active  growth  of  its  connective  tissue 
elements  and  partly  by  an  excessive  filling  of  its  capillaries  and  veins  with 
blood.  The  cause  of  this  swelling  is  not  known.  It  continues  until  the 
membrane  has  doubled  or  trebled  in  thickness,  and,  according  to  some  authori- 
ties, the  uterine  cavity  becomes  a  mere  slit  between  the  walls.  Then  occurs  an 
infiltration  of  blood-corpuscles  and  plasma,  probably  largely  by  diapedesis, 
although  possibly  assisted  by  rupture,  through  the  walls  of  the  swollen  capil- 
laries into  the  connective-tissue  spaces  beneath  the  epithelial  lining  of  the 
uterine  wall.  The  epithelium  is  thus  pressed  up  from  beneath,  and  begins 
rapidlv  to  undergo  disintegration  (perhaps  fatty  degeneration)  and  to  disa])pear. 
The  immediate  cause  of  the  degeneration  is  not  definitely  known.  The  con- 
nective-tissue elements  and  the  upper  portion  of  the  glands  are  involved  in 
the  degenerative  change.  The  capillaries,  thus  laid  bare,  burst,  and  the  dark 
blood  oozes  forth  and,  mixed  with  disintegrated  remains  of  the  uterine  tissues, 
with  the  mucous  secretion  of  the  uterus  and  the  vagina,  and  with  the  escaped 
Ivniph,  passes  away,  drop  by  drop,  from  the  body.  There  is  great  difference  of 
opinion  as  to  the  extent  of  the  destruction  of  uterine  tissue.  On  the  one  extreme 
side  are  those  who  claim  that  the  loss  of  tissue  is  normally  wholly  trivial  and 
secondary,  the  hypersemia  and  the  bloody  glandular  discharge  being  the 
important  events.  Other  authorities,  equally  extreme,  have  observed  a  disap- 
pearance of  the  whole  mucous  membrane  except  the  deepest  layers  containing 
the  bases  of  the  glands  ;  this  is  probably  pathological.  From  all  the  evidence  an 
opinion  intermediate  between  these  two  views  seems  most  reasonable — namely, 
that  usually  and  physiologically  only  the  superficial  portion  of  the  mucous 
membrane  disintegrates.  Differences  in  the  amount  undoubtedly  occur. 
Occasionally  it  happens  that  the  membrane^  instead  of  disintegrating,  comes 
away  in  pieces  of  considerable  size.  The  term  decidua  memtrualis  is  ai)plied 
to  the  lost  coat.  The  flow  continues  upon  an  average  four  days  or  more. 
From  observations  upon  2080  American  women  Emmet '  finals  the  average 
duration  of  the  flow  at  puberty  to  be  4.82  days,  the  average  in  later  life  4.66 
days.  The  amount  of  blood  discharged  can  be  determined  only  with  great  diflR- 
culty.  It  probably  varies  greatly,  but  is  commonly  estimated  at  from  100 
to  200  cubic  centimeters  (4-5  ounces).  The  blood  is  slimy,  with  abundant 
mucus ;  usually  it  does  not  coagulate.  Epithelium  cells,  red  corpuscles,  leuco- 
cytes, and  detritus  from  the  disintegrated  tissues,  occur  in  it,  and  it  has  a  cha- 
racteristic odor.  As  the  flow  ceases,  a  new  growth,  of  connective-tissue  cells, 
capillaries,  glands,  and  from  the  glands  superficial  epithelium,  begins,  and  the 
raucous  membrane  is  restoretl  to  its  original  amount.  Whether  a  resting  period 
fijllows  before  the  succeeding  tumefaction  occurs,  is  not  definitely  known,  but 
it  seems  probable.  The  durations  of  the  various  steps  in  the  uterine  changes 
are  not  well  known,  and  probably  vary  in  individual  cases.  Minot^  suggests 
the  following  approximate  times  : 

'  T.  A.  Emmet:   The  Principkn  and  Practice  of  Oyncecology,  2d  ed.,  1880. 
*C.  S.  Minot:  Human  Embryology,  1892. 


REPB  OD  UCTION.  897 

Tumefaction  of  the  mucosa,  with  accompanying  structural  changes 5  days. 

Menstruation  proper ....    4 

Restoralion  of  the  resting  mucosa     ...        7 

Resting  period 12 

Total 28  days. 

The  menstrual  ehanges  in  tlie  uterus  are  accompanied  by  characteristic 
phenomena  in  other  parts  of  tlie  body.  The  FaUopian  tubes  are  congested, 
and,  according  to  some  authorities,  their  mucous  membrane  degenerates  and 
bleeds  like  that  of  the  uterus.  The  ovaries  are  likewise  congested.  As  has 
been  stated,  it  is  commonly  believed,  but  not  definitely  proved,  that  ovulation 
accompanies  each  period.  Frequent  accompaniments  are  turgescence  of  the 
breasts,  swelling  of  the  thyroid  and  the  parotid  glands  and  the  tonsils,  con- 
gestion of  the  skin,  dull  complexion,  tendency  toward  the  development  of  pig- 
ment, and  dark  rings  about  the  eyes.  The  skin  and  the  breath  may  have  a 
characteristic  odor.  In  singers  the  voice  is  often  impaired,  which  is  one 
instance  of  a  general  nervous  and  muscular  enervation.  Mental  depre.>?sion 
often  exists.  In  most  cases  sexual  instincts  do  not  appear  to  be  heightened. 
Pain  is  a  frequent  accompaniment,  and  nervous  and  congestive  pathological 
phenomena  may,  at  times,  become  very  pronounced.  Recent  work  has  shown 
that  the  various  phenomena  accompanying  menstruation  are  evidences  of  a 
profound  physiological  change,  with  a  monthly  periodicity,  that  the  female 
human  organism  undergoes,  and  of  which  the  uterine  changes  are  only  a  part. 
Thus,  during  the  intermenstrual  period  there  is  a  gradual  increase  of  nervous, 
tension  and  general  mobility,  of  vascular  tension  manifested  by  turgescence  of 
the  blood-vessels,  a  gradual  increase  of  nutritive  activity  manifested  by 
increased  production  and  excretion  of  urea  and  increased  temperature,  and 
a  gradual  increase  of  the  heart's  action  in  strength  and  rate,^  These  various 
activities  of  the  organism  usually  attain  a  maximum  a  few  days  before  the 
menstrual  flow  begins  and  then  undergo  a  rapid  fall,  which  reaches  a  minimum 
toward  the  close  of  the  flow ;  a  second  lesser  maximum  may  occur  a  few  days 
after  the  flow  ceases.  All  organic  activities  that  have  been  carefully  investi- 
gated show  evidences  of  such  a  monthly  rhythm.  It  is  not  known  that  the 
male  pos.sesses  such  a  period. 

The  first  menstruation  is  usually  regarded  as  the  index  of  the  oncoming  of 
puberty  or  sexual  matiu'ity,  and  in  temperate  climates  occurs  usually  at  the  age 
of  fourteen  to  seventeen.  Its  onset  is  earlier  in  warm  than  in  cold  climates,  in 
city  than  in  country  girls,  and  varies  in  time  with  food,  growth,  and  environ- 
ment. Exceptionally  menstruation  may  begin  in  infancy  or  later  than  puberty, 
and  it  has  even  been  known  to  be  wholly  wanting  in  otherwise  normal  women. 
Normally,  it  ceases  during  pregnancy,  and  probably  usually  during  lactation, 
although  there  are  frequent  exceptions  to  the  latter  rule.  Complete  removal 
of  the  ovaries  appears  to  put  an  entire  end  to  menstruation.    Its  final  cessation, 

^  Cf.  Mary  Putnam   .Jacobi  :  "  The   Question   of  Rest   for  Women   during  Menstruation," 
B&ylston  Prize  Essay,  1876  ;   C.  Reinl :   Sammlung  kliuische  Vorlrdge,  2^o.  243,  1884 ;  O.  Ott : 
Nouvdles  archives  d'obstetrique  et  de  gynecologie,  v.,  1890. 
67 


898  AN  AMERICAN    TEXT-BOOK   OF  PHYSIOLOGY. 

-which  is  a  gnuliial  process  extending  over  several  months,  usually  marks  the 
climacteric  (menopause)  or  end  of  the  sexual  life,  and  occurs  usually  at  the 
aije  of  fortv-four  to  foi'ty-scvcn.  Excei)tionally  the  flow  may  cease  early  in 
life  or  extend  to  extreme  old  age. 

Comparative  Physiology  of  Ilenstruation. — The  comparative  physiology  of 
menstrnation,  although  it  has  been  studied  only  incompletely  in  a  few  domesti- 
cated animals  and  some  monkeys,^  sheds  some  valuable  light  upon  the  phe- 
nomenon in  woman.  In  animals  lower  than  man,  in  a  wild  state,  the  desire 
and  power  of  reproduction  are  usually  limited  to  seasonal  periods.  At  such 
times  conception  is  possible,  and  probably  usually  takes  place.  Snch  periods 
are  known  as  "rut,"  "heat,"  and  "oestrus."  During  the  rest  of  the  year 
sexual  activities  arc  in  abeyance.  Domestication,  with  its  artificial  condi- 
tions of  regular  food-supply,  warmth,  and  care,  has  increased  productiveness 
(Darwin)  and  rendered  the  reproductive  periods  more  frequent.  If  imj)regna- 
tion  be  prevented,  as  is  often  the  case  in  domesticated  animals,  the  periods  of 
"heat"  appear  with  great  frequency  and  regularity  (monkey,  mare,  buffalo, 
zebra,  hippopotamus,  four  weeks ;  cow,  three  weeks ;  sow,  fifteen  to  eighteen 
days  ;  sheep,  two  weeks  ;  bitch,  nine  to  ten  days.)  They  are  characterized  by 
general  nervous  excitement,  desire  and  power  of  conception,  congestion  and 
swelling  of  the  external  genital  organs,  and  a  uterine  discharge.  The  latter  is 
scanty,  mucous,  and  bloody,  the  amount  of  blood  increasing  in  ascending  the 
evolntionary  scale.  The  histological  processes  occurring  in  the  uterns  have 
been  studied  carefully  by  Retterer  in  the  dog  and  by  Heape  in  the  monkey. 
In  the  latter  the  processes  seem  to  be  nearly  identical  with  those  of  man.  In 
the  dog,  growth  and  congestion  of  the  mucosa  occur,  and  are  followed  by  rup- 
tnre  of  the  capillaries,  extravasation  of  blood,  and  degeneration  of  the  tissues, 
but  it  is  doubtful  whether  the  epithelium  is  actually  shed.  It  is  generally 
believed  that  "  heat "  in  the  lower  mammals  is  accompanied  by  ovulation.  It 
is  not  necessarily  so  in  monkeys.  The  phenomena  of  "  heat "  are  thus  closely 
similar  to  those  of  human  menstruation,  the  similarity  being  most  marked  in 
the  monkeys.  In  addition  to  these  more  hidden  phenomena  there  is  present 
sexual  desire,  which  in  the  human  female  is  largely  absent  at  such  periods. 

Theory  of  Menstruation. — The  significance  of  menstruation  is  in  great  dis- 
pute. All  modern  theories  agree  in  regarding  it  as  associated  in  some  way 
with  the  function  of  childbearing.  The  flow  was  early  believed  to  be  a  means 
employed  by  the  body  to  get  rid  of  a  plethora  of  nutriment.  This  was  fol- 
lowed by  the  well-known  hypothesis,  put  forward  especially  by  Pfliiger  (18G5), 
and  even  now  widely  accepted.  According  to  this  hypothesis,^  the  menstrual 
bleeding  and  the  uterine  denudation  occur  for  the  purpose  of  providing  a  fresh 
uterine  surface  to  which  the  egg,  if  impregnated,  can  readily  attach  itself,  just 
as  in  o-rafting,  the  gardener  provides  a  wounded  surface  upon  which  the  young 

^  Of.  A.  Wiltshire:  Brilii^h  Medical  Journal,  March,  18S3;  E.  Rettercr :  Comptes  rendm  des 
seances  et  memoires  dc  la  Societe  de  biologie,  1892;  W.  Heape  :  Philosophical  Transactions  of  the 
Eoyal  Society  (B).  vol.  185,  pt.  i.,  1894. 

^  E.  F.  W.  Pfliiger :   Untersuchungen  axis  dem  physiologischen  Laboratorium  zu  Bonn,  1865. 


REPR  OD  UCTION.  899 

scion  is  set,  or,  in  miiting  two  menibrane-coveral  tissues,  the  surgeon  first  wounds 
or  freshens  their  surfaces.  The  mechanism  of  this  uterine  process  is  as  fol- 
lows :  The  constant  growth  of  tiie  ovarian  cells  and  the  consequent  swelling  of 
the  ovary  subject  the  ovarian  nerve-fibres,  and  through  them  the  spinal  cord, 
to  a  constant  slight  stimulation.  Through  the  summation  of  the  stimuli  within 
the  cord  a  reflex  dilatation  of  the  vessels  in  the  genital  organs  is  produced. 
The  excessive  blood-supply  leads  in  turn  to  the  tumefaction  of  the  uterus,  and 
frequently  to  the  ripening  of  a  Graafian  follicle.  The  bleeding  follows,  and 
at  the  same  time  or  slightly  later  the  rupture  of  the  follicle  occurs,  provided 
the  latter  be  sufficiently  advanced  in  growth.  The  menstrual  flow  and  ovulation 
are,  therefore,  two  phenomena  conditioned  usually  by  the  same  cause,  namely, 
the  menstrual  congestion,  yet  either  may  occur  without  the  other.  Pfluger's 
hypothesis  accounts  clearly  for  the  absence  of  menstruation  after  removal  of 
the  ovaries.  Numerous  other  theories  have  been  proposed,  no  one  of  which 
can  be  said  to  be  widely  and  generally  accepted.  The  present  tendency  in 
belief  is  as  follows  :  Ovulation  and  menstruation  are  in  great  part  independent 
phenomena  ;  they  may  or  they  may  not  coexist  •  the  uterine  growth  is  a  prep- 
aration for  the  future  embryo  ;  the  tissue  of  the  decidua  mmstrualis  is  the  fore- 
runner of  the  decidua  graviditatis  (p.  909) ;  if  an  ovum,  whenever  it  is  discharged, 
be  fertilized,  it  attaches  itself  to  the  thickened  uterine  wall,  the  tissues  become 
the  decidua  graviditatis,  pregnancy  follows,  and  the  decidua  is  not  discharged 
until  the  time  of  parturition  ;  if,  however,  fertilization  does  not  take  place, 
there  is  no  attachment,  the  tissues  degenerate  and  become  the  decidua  men- 
strualis,  and  the  flow  occurs.  The  suggestion  of  Jacobi  ^  is  not  an  extreme 
one  :  "  The  menstrual  crisis  is  the  physiological  homologue  of  parturition." 
Its  monthly  periodicity  is  not  explained.  Regarding  its  mechanism  the  above 
hypothesis  of  Pfliiger,  although  not  yet  proven  experimentally,  seems  not 
unreasonable. 

The  mysterv  of  menstruation  largely  ceases  when  we  recognize  what  is  un- 
doubtedly a  fact,  that  the  phenomenon  is  a  highly  developed  inheritance  from 
our  mammalian  ancestors,  and  that,  although  in  the  human  race  under  the 
influence  of  civilization  and  social  life  it  has  largely  lost  its  technical  sexual 
significance,  it  is,  nevertheless,  primarily  a  reproductive  phenomenon  derived 
directly  from  the  lower  females.  Nature  has  endowed  the  latter,  in  a  manner 
yet  unknown,  with  reproductive  periods  that  are  pronounced  in  the  wild  state 
and  are  coincident  with  certain  of  the  seasons.  A  primitive  seasonal  period 
may  perhaps  still  be  shown  in  woman  by  the  greater  proportion  of  births  that 
take  place  during  the  winter  months  than  at  other  times  of  the  year :  this  sig- 
nifies greater  sexual  activity  during  the  months  of  spring,  as  is  the  case  in 
most  animals.^ 

*  Mary  Putnam  Jacobi :  American  Jotimal  of  Obstetrics,  xviii.,  1885. 

'^  "  The  largest  number  [of  human  births]  almost  always  falls  in  the  month  of  February, 

....  corresponding  to  conceptions  in  May  and  .June Observations  tend  to  show  the  largest 

number  of  conceptions  in  Sweden  falling  in  June ;  in  Holland  and  France,  in  May-June ;  in 
.  Spain,  Austria,  and  Italy,  in  May ;  in  Greece,  in  April.     That  is,  the  farther  south  the  earlier 
the  spring  and  the  earlier  the  conceptions."— Mayo-Smith  :  Statistics  and  Sociology,  1895. 


900  ^^V  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

Domestication  has,  however,  interfered  with  the  original  plan  of  nature. 
It  has  rendered  the  lower  forms  more  prolific  and  has  made  more  frequent 
their  reproductive  periods.  Civilization  has  done  exactly  the  same  for  woman. 
It  has  rendered  her  more  prolific  and  has  made  more  frequent  her  reproduc- 
tive periods.  It  is  wholly  probable  that  the  menstrual  periods  of  woman  are 
the  homologues  of  the  frequent  reproductive  periods  of  the  lower  forms.  It 
has  been  seen  that  the  latter  are  characterized  by  the  same  kind  of  phenomena 
that  exist  in  the  former ;  the  characteristic  human  menstrual  phenomena  are 
least  developed  in  the  lower  mammals,  much  more  so  in  the  monkey,  and  are 
most  pronounced  in  the  human  female.  For  what  purpose  this  evolution  of 
function  has  taken  place  we  do  not  know.  Below  the  human  species  concep- 
tion is  confined  to  these  times  of  "  heat ; "  in  woman  it  is  possible  at  other 
than  her  menstrual  periods.  In  this  respect  woman  is  more  highly  endowed 
than  her  mammalian  ancestors. 

The  Vagina. — The  vagina  (Fig.  309,  vg)  is  the  broad  passage  from  the 
uterus  to  the  external  organs.  Its  walls  consist  of  smooth  muscle  fibres, 
arranged  both  circularly  and  longitudinally.  It  is  lined  by  stratified  scaly 
epithelium  and  is  surrounded  by  erectile  tissue.  Its  walls  contain  few  glands. 
Its  specific  functions  are  connected  solely  with  the  reproductive  process ;  in 
copulation  it  receives  the  penis  and  the  semen.  Its  cavity  is  the  pathway  out- 
ward for  the  products  of  menstruation  and,  in  parturition,  for  the  child. 

The  Vulva  and  its  Parts. — The  vulva  (Fig.  309)  comprises  the  genital 
organs  that  are  visible  externally — viz.  the  moy\s  Veneris,  the  labia  majora  (l.m), 
the  labia  minora  or  nymphce  (71),  the  clitoris,  w'hicli  is  the  diminutive  homologue 
of  the  penis  of  the  male,  and  the  hymen  (/*),  or  perforated  curtain  that  guards  the 
entrance  to  the  vagina  and  is  usually  ruptured  at  the  time  of  the  first  coition. 
The  vulva  receives  the  openings  of  the  vagina,  the  urethra  (m),  and  the  ducts  of 
Bartholini's  glands.  Its  parts  are  capable  of  turgidity  through  its  rich  vas- 
cular supply,  and  perform  minor  ill-defined,  adaptive,  and  stimulating  func- 
tions in  copulation.  Their  surface  is  covered  by  mucous  membrane  which  is 
moistened  and  lubricated  by  a  secretion  from  numerous  mucous  follicles,  seba- 
ceous glands,  and  the  glands  of  Bartholini.  Tiie  latter  are  comparable  to 
Cowper's  glands  of  the  male  and  secrete  a  viscid  fluid. 

The  Mammary  Glands. — The  mammary  glands,  being  active  only  during 
the  period  of  lactation,  may  best  be  studied  in  connection  with  that  function 
(see  p.  201). 

Internal  Secretion. — A  priori,  the  reproductive  organs  can  scarcely  be 
regarded  as  organs  that  are  quiescent  during  the  greater  part  of  life  and  pas- 
sively await  the  reproductive  act.  The  view  that  they  are  more  than  this  is 
sn})ported  by  some,  although  slight,  experimental  evidence.  Notwithstanding 
the  fact  that  removal  of  the  testis  or  the  ovary  in  adult  life  is  often  unaccom- 
panied by  great  somatic  changes,  the  profound  effects  of  early  castration  upon 
development,  in  both  the  male  and  female,  show  that  upon  the  presence  of  the 
sexual  organs  depends  the  appearance  of  many  of  the  secondary  sexual  cha- 
racters— characters  which  apparently  are  independent  of  those  organs,  and  yet 


REPR  OD  UCTION.  901 

of  themselves  distinguish  the  individual  as  specifically  masculine  or  feminine. 
Tiie  mode  of  dynamic  reaction  of  the  sexual  organs  upon  the  other  organs  can 
at  present  be  little  more  tiiau  hinted  at.  It  is  entirely  probable  that  such 
reaction  is  either  nervous  or  chemical,  or  perhaps  it  is  both  combined.  Regard- 
ing the  former  little  is  known.  Regarding  the  latter,  recent  assertions  of  the 
general  invigorating  effects  of  injections  of  testicular  extracts  in  the  adult, 
although  in  most  cases  not  founded  upon  careful  experimentation,  are,  never- 
theless, suggestive,  and  point  to  a  possible  normal  and  constant  contribution 
of  specific  material  by  the  reproductive  glands  to  the  blood  or  lymph,  and 
thus  to  the  whole  body.  Such  a  process  is  spoken  of  as  internal  secreiion,  and 
in  the  case  of  the  thymus  and  thyroid  glands  its  occurrence  seems  undoubted 
(p.  205).  As  to  the  reproductive  organs,  investigation  of  the  subject  is  yet  in 
its  mere  infancy,  and  it  is  too  early  to  say  with  any  degree  of  authority  what 
the  truth  of  the  matter  is.  Very  recently  Zoth  ^  has  shown  that  daily  injec- 
tions of  testicular  extract  during  one  week  increased  by  50  per  cent,  the  work- 
ing power  of  a  man's  neuro-muscular  system.  The  increase  manifested  itself 
both  by  lessened  susceptibility  to  fatigue  and,  in  a  still  higher  degree  dur- 
ing the  periods  of  rest  from  labor,  by  increased  power  of  recovery.  What 
part  of  the  whole  neuro-muscular  system  is  affected  by  the  specific  substance 
is  not  decided. 

D.  The   Reproductive  Process. 

Attention  has  heretofore  been  given  to  the  general  functions  of  the  repro- 
ductive organs.  We  come  now  to  the  special  phenomena  connected  with  the 
reproductive  process  itself,  and  have  to  trace  the  history  of  the  spermatozoon, 
the  ovum,  and  the  embryo.  It  should  be  borne  clearly  in  mind  that  the 
essential  part  of  the  reproductive  process  is  the  fusion  of  the  nuclei  of  the  two 
germ-cells.  Investigation  is  making  it  more  and  more  probable  that  the 
spermatozoon  and  the  ovum,  although  so  different  in  appearance  and  general 
behavior,  are  fundamentally  and  in  origin  both  morphologically  and  physi- 
ologically equivalent  cells.  In  the  proc&sses  of  their  growth  and  maturation 
they  are  secondarily  modified,  the  one  into  an  active  locomotive  body,  the  other 
into  a  passive  nutritive  body.  The  modifications  in  both  are  confined,  how- 
ever, to  the  cell-protoplasm  (cytoplasm  and  centrosome)  ;  the  essential  parts, 
the  nuclei,  remain  unmodified  and  both  morphologically  and  physiologically 
equivalent  down  to  the  time  of  their  fusion  in  the  process  of  fertilization. 
The  many  and  complex  details  of  the  reproductive  process  exist  for  the  sole 
purpose  of  bringing  together  these  two  minute  masses  of  chromatin.^ 

Copulation. — Copulation  is  the  act  of  sexual  union,  and  has  for  its  object 
the  transference  of  the  semen  from  the  genital  passages  of  the  male  to  those  of 
the  female.  It  is  preceded  by  erection  of  the  penis  and  turgidity  of  the  organs 
of  the  vulva.     These  latter  occurrences  are  in  the  main  vascular  phenomena, 

'  O.  Zoth  :  Pfiiiger's  Archivfiir  die  gesammte.  Physiologie,  Ixii.,  1896. 

'  Compare  Th.  Boveri :  "  Befruchtung,"  Merkel  und  Bonnet's  Ergebnisse  der  Anatomie  und 
Entwickelungsgeschichie,  i.,  1892. 


902  .l.V  AMEJRICA^'    TEXT-BOOK   OF  PHYSIOLOGY. 

and  are  brought  about  by  a  distention  of  the  cavernous  spaces  of  the  erectile 
tissues  with  blood.  The  vascular  phenomena  are,  however,  accompanied  by 
conijilex  nervous  and  muscular  activities.  As  regards  the  penis,  the  arteries 
supplying  the  organ  relax  and  allow  blood  to  flow  in  quantity  to  the  corpora 
cavernosa  and  the  corpus  spongiosum.  Simultaneous  relaxation  of  the  smooth 
muscle  fibres  scattered  throughout  the  trabecular  framework  of  the  corpora 
increases  the  capacity  of  the  blood-spaces.  Furthermore,  the  iscMo-cavernosus 
(erector  penis)  and  bulbo-cavernosus  muscles  contract  and  compress  the 
proximal  or  bulbous  ends  of  the  corpora  and  the  outgoing  veins.  The  result 
of  this  combined  muscular  relaxation  and  contraction  is  a  free  entrance  of 
blood  into  and  a  difficult  exit  from  the  vascular  spaces ;  this  leads  to  a  swelling 
and  distention  which  aid  further  in  compressing  the  venous  outlets  and,  being 
limited  by  the  tough,  fibrous  tunics  of  the  corpora,  result  in  making  the  organ 
stiff,  hard,  erect  in  position,  and  well  adapted  to  its  specific  function.  During 
the  process  of  erection  the  cresta  of  the  urethra  or  caput  gallinaginis,  which  is 
an  elevation  extending  from  the  cavity  of  the  bladder  into  the  prostatic  por- 
tion of  the  urethra  and  containing  erectile  tissue,  becomes  turgid  and,  by  the 
aid  of  the  contraction  of  the  sphincter  urethras,  effectually  closes  the  passage 
into  the  bladder.  Erection  is  a  complex  reflex  act,  the  centre  of  which  lies 
in  the  lumbar  spinal  cord  and  may  be  aroused  to  activity  by  nervous  impulses 
coming  from  different  directions.  Impulses  may  originate  in  the  walls  of  the 
ducts  of  the  testis  from  the  pressure  of  the  contained  semen  or  in  the  penis 
from  external  stimulation  of  the  nerve-endings  in  the  skin,  in  both  cases 
passing  along  the  sensory  nerves  of  the  organs  to  the  spinal  centre ;  or  they 
mav  originate  in  the  brain  and  pass  downward  through  the  cord,  the  impulses 
in  this  case  corresponding  to  sexual  emotions.  The  centrifugal  paths  for  the 
arteries  are  along  the  nervi  erigentes,  which  are  true  vaso-dilator  nerves,  and 
in  the  mammals,  where  experiment  has  proved  their  existence,  pass  from  the 
spinal  cord  along  the  posterior  lumbar  (monkey)  or  anterior  sacral  (monkey, 
dog,  cat)  nerves  to  their  arterial  distribution.  The  ischio-  and  bulbo-caverno- 
sus muscles  are  under  the  control  of  their  motor  nerve  supply,  consisting  of 
branches  of  the  perineal  nerve. 

In  the  female,  anatomists  recognize  the  homologues  of  the  male  erectile 
parts  as  follows  :  the  clitoris  with  its  corpora  cavernosa  and  glans  as  the  homo- 
logue  of  the  penis,  the  two  bulbi  vestibuli  as  that  of  the  bulb  of  the  corpus 
spongiosum,  the  pars  intermedia  perhaps  as  that  of  the  corpus  spongiosum 
itself,  and  the  erector  clitoridis  muscle  as  the  homologue  of  the  erector  penis 
{ischio-cavemosus).  The  mechanism  of  erection  is  similar  to  that  in  the  male, 
and  the  result  is  a  considerable  degree  of  firmness  in  the  external  genital 
organs. 

The  sexual  excitement  attendant  upon  copulation  is  usually  much  greater 
in  man  than  in  woman,  and  culminates  in  the  sexual  orgasm,  when  the  emis- 
sion of  semen  from  the  penis  into  the  vagina  occurs.  It  will  be  remembered 
that  the  prepared  semen  is  stored  in  the  ducts  of  the  testes.  The  discharge 
of  the  fluid  is  a  muscular  act  which  begins  probably  in  the  vasa  effereniia 


REPRODUCTION.  903 

and  the  canal  of  the  epklldynm,  and  sweeps  along  the  powerful  muscular 
walls  of  the  V((s<i  dcj'croUia  in  the  form  of  a  scries  of  peristaltic  waves.  The 
seminal  vesicles  also  contract,  and  the  mixed  fluid  and  spermatozoa  are  poured 
through  the  ejaculatory  ducts  into  the  prostatic  portion  of  the  urethra.  Tlie 
umscles  of  the  prostate  expel  the  prostatic  fluid  and  help  to  pass  the  semen 
onward.  The  glands  of  Cowper  possil)ly  add  their  contribution.  But  the 
final  urethral  discharge  is  effected  especially  by  powerfid  rhythmic  contractions 
of  the  already  partially  contracted  striped  muscles,  viz.  the  ischio-  and  bulbo- 
cavei'nosi,  the  conslridov  urethrcv,  and  probably  the  anal  muscles,  the  result  of 
the  complex  series  of  actions  being  to  expel  the  semen  with  some  force  into 
the  upper  part  of  the  vagina  close  to  the  os  uteri.  Ejaculation  is  a  reflex  act. 
The  centre  lies  in  the  lumbar  spinal  cord  ;  the  centripetal  nerves  are  the  sen- 
sory nerves  of  the  penis,  stimulation  of  the  glans  being  especially  effective; 
the  centrifugal  nerves  are  the  nerves  to  the  various  muscles.  In  the  female 
during  ejaculation  the  glands  of  Bartholini  pour  out  a  mucous  fluid  upon  the 
vulva.  There  is  possibly  a  downward  movement  of  the  uterus,  brought  about 
by  contraction  of  its  round  ligaments  and  accompanied  perhaps  by  a  contrac- 
tion of  the  uterine  walls  themselves.  But  all  muscular  and  erectile  activity, 
as  well  as  sexual  passion,  is  less  pronounced  in  woman  than  in  man. 

Locomotion  of  the  Spermatozoa. — The  union  of  the  spermatozoon  and  the 
ovum  probably  takes  place  usually  in  the  Fallopian  tube  not  far  from  its  ovarian 
end,  and  to  this  place  the  spermatozoa  at  once  proceed.  Their  mode  of  entrance 
into  the  uterus  is  not  wholly  clear;  it  is  quite  generally  believed,  but  without 
conclusive  experimental  proof,  that  relaxation  of  the  uterus  immediately  after 
copulation  exerts  a  suction  upon  the  fluid  which  aids  in  its  passage  through 
the  OS  and  the  cervix.  It  is  possible  that  active  contraction  of  the  vaginal 
walls  assists.  However  these  may  be,  the  main  agency  in  the  locomotion  of 
the  spermatozoa  through  the  body  of  the  uterus  and  the  Fallopian  tubes,  and 
probably  also  from  the  vagina  into  the  uterus,  is  the  spontaneous  movement  of 
the  spermatozoa  themselves.  By  the  lashing  of  their  tails  they  wriggle  their 
way  over  the  moist  surface,  being  stimulated  to  lively  activity  probably  by  the 
opposing  ciliary  movements  in  the  epithelium  lining  the  passages.  Kraft*  has 
shown  in  the  rabbit  that,  when  spermatozoa  in  feeble  motion  are  placed  upon 
the  inner  surface  of  the  oviduct,  not  only  are  they  thrown  into  active  contrac- 
tions, but  they  move  against  the  ciliary  movement,  i.  e.  up  the  oviduct.  The 
capacity  of  the  male  cells  thus  to  respond  by  locomotion  in  the  opposite  direc- 
tion to  the  stimulating  influence  of  the  ciliary  cells  over  which  they  have  to 
pass,  is  an  interesting  adaptation.  Probably  this  is  the  directive  agency  that 
enables  the  spermatozoa  to  follow  the  right  path  to  the  ovum,  while  the  ovum, 
being  in  itself  ]>assive,  is  by  the  same  ciliary  movement  brought  toward  the 
active  male  cell.  The  time  occupied  in  the  passage  of  the  spermatozoa  is  un- 
known in  the  human  female,  but  is  probably  short ;  in  the  rabbit  spermatozoa 
have  been  known  to  reach  the  ovary  within  two  and  three-quarter  hours  after 
copulation.     As  has  been  seen,  spermatozoa  are  probably  capable  of  living 

'  H.  Kraft :  Pfliiger's  Archiv  fur  die  gesammte  Physiologic,  xlvii.,  1890. 


904  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

within  the  genital  passages  for  several  days,  when,  if  ovulation  has  not  taken 
place,  they  perish.  If,  however,  an  ovum  appears,  they  at  once  approach  and 
surround  it  in  great  numbers,  being  apparently  attracted  to  it  in  some  myste- 
rious manner.  Tiie  work  of  Pfeffer,'  who  found  that  in  the  fertilization  of 
ferns  malic  acid  within  the  female  organs  attracts  the  spermatozoids  to  their 
vicinity,  suggests  strongly  that  also  among  animals  the  attraction  may  be  a 
ciiemical  one,  the  ovum  containing  or  producing  something  for  which  the  sper- 
matozoon has  an  affinity.  If  so,  the  meeting  of  the  two  germ-cells  is  an  illus- 
tration of  a  widespread  principle  of  nature  known  as  chemotropism,  or  chemo- 
iaxis.     Experimental  evidence  upon  the  subject  in  animals  is  wanting. 

Fertilization. — It  will  be  remembered  that  the  ovum  and  the  spermatozoon 
undergo  in  their  growth  the  process  of  maturation,  and  that  this  process  con- 
sists essentially  of  a  loss  of  one-half  of  the  chromosomes  of  their  nuclei.  The 
germ-cells  thus  matured  meet,  as  we  have  seen,  in  the  distal  half  of  the  Fal- 
lopian tube  and  fuse  into  one  cell,  the  process  of  fusion  being  caWed  fertilization 
or*  impregnation.  The  details  of  fertilization  have  not  been  observed  in  the 
case  of  the  human  being,  and  the  following  account  is  generalized  from  our 
knowledge  of  the  process  in  other  mammals  and  lower  animals.  In  its  broad 
outlines  fertilization  is  probably  the  same  in  all  animals,  the  differences  being 
confined  to  details. 

The  ovum  at  the  time  of  fertilization  is  surrounded  by  the  zona  radi- 
ata  alone,  the  corona  radiata  having  been  lost.  The  spermatozoa  swarm 
about  the  2071a,  lashing  their  tails  and  attempting  to  worm  their  way  through 
it.  Several  may  succeed  in  reaching  the  perivitelline  space,  but  for  some 
unknown  reason  in  most  cases  one  only  penetrates  the  substance  of  the  ovum ; 
the  others  ultimately  perish.  In  mammalian  ova  there  is  no  micropyle,  and 
apparently  the  successful  spermatozoon  may  enter  at  any  point,  the  protoplasm 
of  the  egg  rising  up  as  a  slight  protuberance  to  meet  it  (Fig.  310,  c).  In  some 
animals  the  tail  is  left  outside  to  perish  ;  in  others  it  enters,  but  then  disap- 
pears ;  in  no  case  does  it  appear  to  be  of  further  use.  The  head  and  probably 
the  middle-piece  are  of  vital  importance.  The  head,  now  known  as  the  sperm- 
nucleus  or  male  pronucleus,  proceeds  by  an  unknown  method  of  locomotion 
toward  the  centre  of  the  egg,  and  becomes  enlarged  by  the  imbibition  of  fluid 
(Fig.  310,  B,  s).  The  matured  nucleus  of  the  ovum,  ov  egg-nucleus  {e),  remains 
in  the  resting  stage  from  the  time  of  maturation  until  the  entrance  of  the  sperm. 
Then,  without  changing  its  character,  it  moves  slowly  toward  the  future  meet- 
ing-place of  the  two  nuclei,  which  is  near  the  centre  of  the  egg.  The  sperm- 
nucleus  finally  reaches  the  egg-nucleus  (Fig.  311,  c),  its  chromatin  enters  into 
the  latter,  and  the  two  fuse  together  to  form  a  new  and  complete  nucleus, 
called  the  first  segmentation  nucleus  (Fig.  311,  d).  This  body  has  the  con- 
ventional nuclear  structure — namely,  an  achromatic  network  with  the  chro- 
matic reticulum  mingled  with  it — and  the  whole  is  covered  by  a  nuclear  mem- 
brane. The  chromatic  substance,  it  will  be  perceived,  is  now  restored  to  the 
original  amount  present  in  either  germ-cell  before  its  maturation,  one-half  of 
'  W.  Pfeffer  :    Untersuchungen  aus  dem  Botanischen  Institvl  zu  Tiibingen,  i.,  1884. 


BE  PROD  UCTION. 


905 


it  having  come,  how- 
ever, from  the  male  cell 
and  oiio-half  from  the 
female  cell.  On  the 
com mon ly  accepted 
theory  that  this  is  the 
hereditary  substance, 
the  first  segmentation 
nucleus  contains  within 
itself  potentially  all  the 
inherited  qualities  of 
the  future  individual. 

While  the  head  of 
the  spermatozoon  is 
making  its  way  through 
the  substance  of  the  egg 
there  appears  beside  it 
a    minute    cytoplasmic 


r^j^^-  <^ 


Fig.  310— Stages  in  the  fertilization  of  the  egg  (after  Wilson).  The 
drawings  were  made  from  sections  of  the  eggs  of  the  sea-urchin,  Toxo- 
pneu)<teH  variegatus,  Ag. 

A.  The  surface  of  the  egg  has  become  elevated  to  form  c,  the  entrance- 
cone  for  the  spermatozoon;  the  head  (h)  and  the  middle-piece  (m)  of  the 
latter  have  entered  the  egg. 

B.  Five  minutes  after  entrance  of  the  spermatozoon.  The  head  (s), 
now  the  male  pronucleus,  has  rotated  180  degrees,  and  has  travelled 
deeper  into  the  ovum.  The  cytoplasm  of  the  latter  has  become  arranged 
in  a  radiate  manner  about  the  middle-piece  of  the  spermatozoon,  now  the 
centrosome,  to  form  the  sperm-aster;  e,  the  egg-nucleus,  now  the  fe- 
male pronucleus,  is  approaching  the  sperm-nucleus ;  its  chromatin  forms 
an  irregular  reticulum ;  c,  the  entrance  cone. 


Fig.  311.— Stages  in  the  fertilization  of  the  egg  (continued  from  Fig.  310). 

c.  Ten  minutes  after  entrance  of  the  spermatozoon.  The  male  and  the  female  pronuclei  have  met 
near  the  centre  of  the  egg  and  the  fusion  has  begun ;  the  former  has  become  enlarged  and  its  chromatin 
has  become  loosely  reticulated.  The  sperm-aster  has  become  enormously  enlarged.  The  single  centro- 
some has  been  divided  into  two,  which  lie  upon  either  side  of  the  sperm-nucleus. 

D.  The  pause  thirty  minutes  after  entrance  of  the  spermatozoon.  The  two  pronuclei  have  fused  com- 
pletely to  form  the  first  segmentation-nucleus,  all  trace  of  a  distinction  between  paternal  and  maternal 
chromatin  being  lost.  The  sperm-aster  has  become  divided  into  two  asters,  which  have  moved  to  oppo- 
site poles  of  the  nucleus;  the  astral  rays  have  become  shortened.  The  egg  is  now  ready  to  .undergo 
segmentation. 


906 


AN  AMERICAN   TEXT-BOOK    OF    PHYSIOLOGY. 


1    1 1 


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Fio.  312.— Stages  in  the  segmentation  of  the  egg  (after  Wilson). 
The  drawings  were  made  from  sections  of  eggs  of  the  sea-urchin, 
Toxopneusles  variepatus,  Ag. 

A.  Beginning  of  the  formation  of  the  amphiaster.  Tlic  nuclear 
membrane  has  disappeared  at  the  two  poles  of  the  spindle-shaped 
nucleus.  Within  the  nucleus  a  distinction  between  the  chromatic 
and  the  achromatic  substance  is  being  made,  the  former  existing  as 
irregular  rod-shaped  bodies  lying  at  the  centre,  the  latter  as  delicate 
filaments  extending  irregularly  from  pole  to  pole.  The  asters  arc  well 
marked. 

B.  The  nuclear  membrane  has  wholly  disappeared.  The  chro- 
mosomes are  clearly  defined  and  aggregated  in  the  centre  of  the 
spindle  to  form  the  equatorial  plate.  The  achromatic  filaments  of 
the  spindle  are  well  marked.  The  connection  of  the  astral  rays  with 
the  cytoplasmic  reticulum  of  the  egg  is  shown. 

c.  Each  chromosome  has  become  split  into  two,  and  the  latter, 
ch,  are  being  pulled  toward  the  poles. 


»  Th.  Boveri :  loc.  cit.        *  E.  B.  Wilson  and  A.  P.  Mathews 


body,  the  centrosomc,  and 
around  the  latter  tlie  fila- 
ments of  the  cytoplasm  of 
the  egg  arrange  themselves 
in  the  form  of  a  star,  the 
whole  body  being  known 
as  t\i(i  sperm-aster  (Y'\g.  310, 
b).  We  have  previously 
recognized  such  a  structure 
in  the  ovum  at^the  time  of 
maturation,  and  have  found 
it  functional  in  the  forma- 
tion of  the  polar  bodies ; 
after  maturation  it  disap- 
pears. The  sperm-aster 
accompanies  the  sperm-nu- 
cleus, becomes  gradually 
enlarged,  and  finally  comes 
to  lie,  a  large  and  promi- 
nent body,  beside  the  seg- 
mentation nucleus.  Its 
origin,  or,  more  exactly, 
the  origin  of  its  centro- 
some,  has  been  greatly 
disputed,  and,  at  the  pres- 
ent time,  is  understood  in 
few  species  of  animals. 
Boveri  ^  and  Wilson  ^  find 
in  the  sea-urchins  that  the 
centrosome  is  the  middle- 
piece  of  the  spermatozoon 
and  is  exclusively  of  male 
origin.  Several  other  in- 
vestiirators  have  observed 
in  other  animals  its  origin 
from  one  germ-cell  only, 
usually  the  male,  and  it  is 
a  question  whether  its  male 
origin  may  not  be  the  com- 
mon one.  The  significance 
of  this  discovery  and  the 
function  of  the  aster  will 
be  explained  in  the  follow- 
ing section. 
:  Journal  of  Morphology,  x.,  1 895. 


REPR  OD  UCTION.  907 

There  results  tii»in  lortilization,  it  is  juTceivocl,  a  single  cell  complete  in  all 
its  essential  parts.  This  is  the  startint^-point  of  the  now  individual.  A  pause 
or  rostino;  p(>riod  usually  follows  fertilization,  and  then  growth  begins. 

Segmentation. — The  process  of  growth  is  a  complex  process  of  repeated 
cell-division,  increase  in  bulk,  morphological  differentiation,  and  physiological 
division  of  labor. 

Cell-division  is  largely,  if  not  wholly,  indirect  or  karyokinetic.  The  term 
segmentation,  or  cleavage,  of  the  ovum  is  conveniently  applied  to  the  first  few 


/ 


,^^^^jllI/o.    ^^^IjiM^ 


m 


\ 


\  j     '       / 


E 
Fig.  313.— Stages  in  the  segmentation  of  the  egg  (continued  from  Fig.  312). 

D.  The  divergence  of  the  chromosomes  has  ceased  and  the  latter  have  become  converted  into  vesicu- 
lar masses  beside  the  eentrosomes.  The  spindle  is  becoming  resolved  into  ordinary  cytoplasm.  The 
division  of  the  cytoplasm  is  beginning  with  a  constriction  at  the  surface  of  the  egg. 

E.  The  vesicular  chromatic  masses  have  become  converted  into  two  typical  resting  nuclei,  each  with 
a  chromatic  network.  The  single  aster,  formerly  connected  with  each  nuclear  mass,  has  become  divided 
into  two,  which  have  taken  positions  at  opposite  poles  of  the  nuclei.  The  division  of  the  cytoplasm  is 
complete,  and  the  two  resulting  cells,  or  blastomeres,  are  resting,  preparatory  to  a  second  division  in  a 
plane  at  right  angles  to  that  of  the  first. 

divisions,  although  the  details  of  segmentation  are  not  different  fundamen- 
tally from  those  manifested  later  in  the  division  of  more  specialized  cells. 
Each    division    may   be   resolved    into  three  definite    acts,   which,   however, 


908  AN  AMERICAN    TEXT-BOOK   OE  PHYSIOLOGY. 

overlap  each  other  in  time.  The  first  act  is  characterized  by  the  appear- 
ance of  two  centrosoraes,  each  with  its  astral  rays,  in  place  of  the  one 
already  existing  (Fig.  311,  c).  The  two  take  >ij)  positions  on  opposite  sides  of 
the  nucleus  (Fig.  311,  d)  and  await  the  time  when  tiiey  can  exert  their  specific 
function.  We  have  spoken  of  the  difference  of  opinion  regarding  the  origin 
of  the  original  ccntrosome  of  fertilization.  The  origin  of  tiie  two  centrosonies 
present  in  segmentation  has  likewise  been  disputed.  The  question  is  of  consid- 
erable theoretical  interest  in  connection  with  the  problem  of  the  physical  basis 
of  inheritance.  Certain  observers  have  claimed  that  the  centrosomes  have  a 
double  origin,  one  being  derived  from  the  male  and  one  from  the  female  germ- 
cell.  Upon  this  theory  sexuality  is  shown  by  the  cytoplasmic  centrosomes  as 
well  as  by  the  nuclear  chromosomes,  and  the  inference  is  possible  that  cytoplasm, 
as  well  as  nucleus,  transmits  hereditary  qualities.  The  observations  of  Boveri, 
Wilson,  and  others  refute  this  claim  by  show^ing  that  the  two  centrosomes  arise 
by  a  splitting  of  the  original  centrosome,  which  is  derived  from  the  middle- 
piece  of  the  spermatozoon.  They  are,  therefore,  not  male  and  female,  and 
cannot  be  regarded  as  bearers  of  inherited  characteristics.  These  observa- 
tions not  only  allow,  but  tend  to  strengthen,  the  prevailing  view  of  the 
exclusive  hereditary  role  of  the  nucleus.  (See  below  under  Heredity, 
p.  931). 

The  second  act  of  segmentation  is  more  complicated  than  the  first,  and  con- 
sists of  a  halving  of  the  nucleus.  The  nuclear  membrane  gradually  disap- 
pears. The  achromatic  network  resolves  itself  into  long  cytoplasmic  filaments 
arranged  in  the  form  of  a  spindle,  and  meeting  at  the  two  centrosomes  (Fig. 
312,  a).  The  spindle,  centrosomes,  and  asters  form  the  body  known  as  the  am- 
phiasfer.  The  chromatic  substance  becomes  changed  into  the  definite  rod-like 
chromosomes  which  are  collected  in  the  equatorial  zone  of  the  spindle  and  con- 
stitute the  equatorial  plate  (Fig.  312,  b).  From  the  observations  of  Van 
Beneden,  Riickert,^  ^oj^?^  s»^^  others,  it  seems  probable  that  the  male  and 
the  female  chromosomes  do  not  fuse  together,  but  remain  distinct  from  each 
other,  perhaps  throughout  all  the  tissue-cells.  Each  chromosome  proceeds 
to  split  lengthwise,  and  the  two  halves  are  drawn  toward  the  two  centro- 
somes, being  mechanically  pulled,  it  is  commonly  believed,  by  contraction 
of  the  spindle-filaments,  assisted  by  the  astral  rays  (Fig.  312,  c).  The  two 
halves  of  the  amphiaster,  each  with  its  centrosome,  are,  in  fact,  commonly 
believed  to  be  composed  of  contractile  cytoplasm  and  to  be  organs  possessing 
the  definite  function  of  separating  the  two  halves  of  the  nucleus  in  karyokinesis. 
The  evidence  for  this  view  is  not  wholly  satisfactory.  In  the  process  of  divis- 
ion each  nuclear  half  obtains  half  of  the  original  male  and  half  of  the  original 
female  chromatin,  and  hence  contains  inherited  potentialities  of  both  parents. 
After  division  each  half  gradually  assumes  the  structure  of  a  typical  resting 
nucleus  with  its  accompanying  aster. 

The  third  act  of  segmentation  consists  of  a  simple  division  of  the  cytoplasm 

'  J.  Riickert:  Archiv  fur  mihroskopische  Anatomie,  xlv.,  1895. 
'  K.  Zoja:  Anatomischer  Ameiger,  xi.,  1896. 


REPRODUCTION.  909 

into  two  equal  parts,  the  separation  taking  place  along  the  plane  of  nuclear 
division  (Fig.  313,  d,  e).  Each  part  contains  one  of  the  new  nuclei,  and  the 
result  of  the  first  division  is  the  existence  of  two  cells,  two  blastomeres,  in 
place  of  the  one  fertilized  ovum.  The  beginning  of  differentiation  is  shown 
sometimes  even  as  early  as  this,  for,  according  to  Van  Beneden,  in  some  mam- 
mals at  least,  one  blastomere  is  often  somewhat  larger  and  less  granular  than 
the  other. 

Each  blastomere  proceeds  now  to  divide  by  a  similar  karyokinetic  process 
into  two,  the  result  being  four  in  all,  and  by  subsequent  divisions,  eight,  six- 
teen, and  more,  the  divisions  not  proceeding,  however,  with  mathematical  regu- 
larity. By  such  repeated  karyokinetic  processes  the  original  fertilized  ovum 
becomes  a  mass  of  small  and  approximately  similar  cells,  the  morula,  from 
which  by  continued  increase  of  cells,  morphological  differentiation,  and  physi- 
ological division  of  labor,  the  embryo  with  all  its  functions  is  destined  to  be 

built  up. 

Polyspermy. — It  happens  occasionally  that  two  or  more  spermatozoa  enter 
the  ovum  ;  such  a  phenomenon  is  known  as  dispenny  ov  polyspermy,  according 
to  the  number  of  entering  sperms.  Each  sperm  with  its  nucleus  and  centro- 
some  becomes  a  male  pronucleus  and  proceeds  to  conjugate  with  the  female 
pronucleus.  In  the  case  of  dispermy  the  one  female  and  the  two  male  pro- 
nuclei fuse  together ;  each  centrosome  divides  as  usual  into  two,  making  four 
in  all,  which  take  up  a  quadrilateral  position  about  the  first  segmentation 
nucleus ;  the  chromatic  figure  consists  of  two  crossed  spindles ;  and  the  egg 
segments  at  once  into  four  instead  of  two  blastomeres.  When  three  sperma- 
tozoa enter,  six  centrosomes  appear  and  six- blastomeres  result  from  the  first 
division,  and  analogous  phenomena  result  from  more  complex  cases  of  poly- 
spermy. Apparently  normal  larval  forms  are  produced  from  such  double- 
or  multi-fertilized  eggs,  but  as  a  rule  their  development  ceases  very  early  and 
death  occurs. 

During  cleavage  the  ovum  proceeds,  after  the  manner  of  the  non-fertilized 
ovum,  slowly  along  ihe  Fallopian  tube  and  enters  the  uterus.  Unlike  the  non- 
fertilized  ovum,  however,  the  morula  is  not  cast  out  of  the  body,  but  remains 
and  undergoes  further  development.  The  morphological  development  of  the 
embryo  in  utero  does  not  fall  within  the  scope  of  the  present  article.  Some 
attention  may,  however,  be  given  to  the  immediate  environment  of  the  develop- 
ing child  and  its  relations  to  the  maternal  organism. 

Decidua  Graviditatis. — While  the  segmentation  of  the  ovum  is  proceed- 
ing within  the  Fallopian  tube,  the  uterus  prepares  for  the  future  guest  by  begin- 
ning to  undergo  a  profound  change,  probably  being  stimulated  to  activity  re- 
fiexly  by  centripetal  impulses  originating  in  the  walls  of  the  tube  through  con- 
tact with  the  ovum.  This  change  comprises  an  enlargement  of  the  whole  uterus 
and  a  great  and  rapid  growth  in  thickness  of  its  mucosa  and  its  muscular 
coat.  At  first  the  alterations  are  not  unlike  the  phenomena  of  growth  pre- 
ceding the  menstrual  flow,  but,  as  they  proceed,  they  become  much  more  pro- 


910 


AN   AMERICAN    TEXT-lUKtK    OF   J'lIYSIOLOGY 


IouikI  tlmn  tliosc.  Tlio  supply  of  blood  to  the  walls  i.s  greatly  incroa.sed,  the 
vessels  forming  large  irregular  sinuses  within  the  mucosa.  The  supply  of  lymph 
is  increase<l.  The  glands  become  tortuous  and  dilated  into  flattened  cavernous 
spaces,  and  their  walls  atrophy,  the  epithelium  breaking  down  except  in  their 
deepest  parts.  The  mucosa  is  thus  converted  into  a  spongy  tissue,  the  frame- 
work of  which  contains  numerous  large  irregular  cells,  derived  probably  from 
the  original  connective  tissue  and  called  decidual  cells.     The  musculature  is 


Ikcidua  serotinn. 
Chorum  frondonum. 


—  Muscle. 
— Uterine  glands. 
Chorion  Iseve. 


Mucous  plug  nithin  cenical  canal. 


Fig.  314.— Diagram  of  the  human  uterus  at  the  seventh  or  eiphth  week  of  pregnancy  (modified  from 
Allen  Thompson).  The  fetal  villi  are  shown  growing  into  the  sinuses  of  the  decidua  serotina  and  the 
decidua  reflexa ;  in  the  latter  they  are  becoming  atrophied.  They  are  marked  by  the  black  fetal  vessels, 
which  can  be  traced  backward  along  the  umbilical  cord  to  the  embryo.  The  placenta  comprises  the 
decidua  serotina  and  the  chorion  frondosum. 

greatly  thickened  by  an  increa.se,  partly  in  number  and  partly  in  size,  of  its 
constituent  fibres,  and  the  nerve-supply  is  increased.  These  general  structural 
changes  proceed  through  the  early  part  of  gestation  and  are  accompanied  by 
special  changes  to  be  discussed  later.  It  is  not  definitely  known  how  far  the 
alterations  have  gone  before  the  advent  of  the  segmented  ovum  in  the  uterus. 


BEPR  OD  UCTION.  911 

With  the  latter  instead  of  tlie  uiiiinpregnated  ovum  j)reseiit  in  the  Fallopian 
tube,  the  hv|K  rtrophied  uterine  mucosa  does  not  break  away  as  in  menstrua- 
tion, but  remains,  and  henceforth  is  called  the  daddua  graviditath,  special 
names  being  given  to  special  parts.  Entering  the  uterus,  tlie  ovum  attaches 
itself  in  an  unknown  manner  to  the  wall  of  the  womb.  The  part  of  the  mucous 
membrane  that  forms  its  bed  is  henceforth  known  as  the  decidua  serothia  ;  as 
the  seat  of  the  future  placenta,  it  is  physiologically  the  most  interesting  and 
important  portion  of  the  uterine  mucosa.  The  surrounding  cells  and  tissues 
are  stimulated  to  active  proliferation  and  grow  around  and  over  the  ovum, 
com])letoly  covering  it  with  a  layer,  the  decidua  refiexa.  The  remainder  of 
the  uterine  liniu"-  membrane  constitutes  the  decidua  vera.  Between  the  reflexa 
and  the  vera  is  the  uterine  cavity.  At  first  thickened,  the  reflexa  later  thins 
away  as  the  embryo  growls,  and  approaches  close  to  the  vera ;  finally  it  touches 
the  latter,  and  the  original  cavity  of  the  body  of  the  uterus  becomes  oblit- 
erated. By  the  sixth  month  the  reflexa  disappears,  either  coalescing  with  the 
vera  or  undergoing  total  degeneration  (Minot).  During  the  latter  half  of 
gestation  the  vera  itself  thins  markedly.  This  atrophy  of  the  comparatively 
unimportant  reflexa  and  vera,  in  contrast  to  the  placental  hypertrophy  of  the 
serotina,  is  interesting.  The  arrangement  of  the  parts  is  well  shown  in  the 
accompanying  illustration  (Fig.  314). 

The  Fetal  Membranes. — The  segmented  ovum  absorbs  nutriment  at  first 
directly  from  its  surrounding  maternal  tissues,  and  later  through  the  mediation 
of  the  placenta.  Its  growth  and  cell-division  are  active,  and  it  increases  in 
size  and  complexity.  It  early  takes  the  form  of  a  generalized  vertebrate  em- 
bryo, and  by  the  fortieth  day  begins  to  assume  distinctly  human  characteristics. 
It  becomes  surrounded  early  by  the  fetal  membranes,  which  are  two  in  num- 
ber, the  amnion  and  the  chonon  or,  as  it  is  usually  called  in  other  vertebrates, 
false  amnion.  The  amnion  is  a  thin,  transparent,  non-vascular  membrane  imme- 
diately siuTounding  the  embryo  (Fig.  314).  In  origin  a  derivative  of  the  embry- 
onic somatojileure,  later  it  becomes  completely  separated  from  the  body  of  the 
embryo.  The  space  enclosed  by  the  amnion,  the  amniotic  cavity,  within  which 
the  embryo  lies,  is  traversed  by  the  umbilical  cord  and  contains  a  serous  fluid, 
the  liquor-  amnii.  This  fluid,  highly  variable  in  quantity,  averages  at  full 
term  nearly  a  liter  (If  pints).  It  has  in  general  the  composition  of  a  serous 
fluid.  It  contains  between  1  and  2  per  cent,  of  solids,  consisting  of  proteids 
(0.06-0.7  per  cent.),  mucin,  a  minute  and  variable  quantity  of  urea,  and  inor- 
ganic salts.  It  is  derived  perhaps  in  part  by  exudation  from  the  fetus,  but 
doubtless  chiefly  by  transudation  from  the  maternal  fluids,  as  is  indicated  by 
the  ready  appearance  within  the  amniotic  cavity  of  solutions  injected  into  the 
maternal  veins.  It  bathes  the  entire  surface  of  the  embryonic  body,  and  is, 
moreover,  apparently  swallowed  at  times  into  the  stomach,  as  the  presence  of 
fetal  hairs  and  epidermal  scales  within  the  alimentary  canal  attests.  Its  chief 
fimctions  appear  to  be  those  of  protecting  the  fetus  from  sudden  shocks  and 
from  pressure,  maintaining  a  constant  temperature,  and  supplying  the  fetal 
body  with  water.     The  proteid  possibly  confers  upon  it  a  slight  nutritive 


912  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

value,  and  the  minute  quantity  of  urea  is  perhaps  indicative  of  an  unimport- 
ant excretory  function.  As  growth  proceeds,  the  amnion  expands  and  becomes 
loosely  attached  to  the  outer  fetal  membrane,  the  chorion. 

The  chorion  (Fig.  314),  or  false  amnion,  is  formed  simultaneously  with  the 
true  amnion,  and  like  it  from  somatopleure.  It  is  a  thickened  vascular  mem- 
brane, completely  surrounding  the  amnion  witii  the  contained  embryo.  Be- 
tween it  and  the  amnion  there  is  at  first  a  considerable  space,  traversed  by  the 
umbilical  cord  and  filled  with  the  chorionic  fluid  (which  is  probably  of  the 
same  general  nature  as  the  amniotic  fluid).  But  later  this  space  is  obliterated 
by  the  enlargement  of  the  amnion.  Externally  the  chorion  presents,  at  first, 
a  shaggy  appearance  due  to  the  existence  of  very  numerous  columnar  pro- 
cesses, called  villi,  extending  outward  in  all  directions  and  joining  by  their 
tips  the  decidua  serotina  and  the  decidua  reflexa.  Later  the  villi  are  aborted 
except  in  the  region  of  the  serotina,  where  they  become  more  prominent  and 
constitute  an  important  part  of  the  placenta.  The  blood-vessels  of  the  chorion 
are  fetal  vessels  coming  from  the  embryonic  structure,  the  allantois.  They 
comprise  the  branches  and  uniting  capillaries  of  the  two  allantoic  or  umbilical 
arteries,  and  the  one  (at  first  two)  allantoic  or  umbilical  vein.  They  are 
especially  well  developed  within  the  villi.  As  growth  proceeds,  the  chorion 
comes  into  close  contact  with  the  decidua  reflexa,  and,  as  the  latter  disappears^ 
with  the  decidua  vera  ;  this  portion  of  it  is  called  chorion  Iceve.  In  the  region 
of  the  decidua  serotina  it  enters  into  the  formation  of  the  placenta,  and  is 
here  called  chorion  frondosum. 

The  Placenta. — The  placenta  (Fig.  314),  or  organ  of  attachment  of  mother 
and  fetus,  is  a  disk-shaped  body,  approximately  20  centimeters  (7-8  inches)  in 
diameter,  attached  to  the  inner  surface  of  the  uterine  wall,  usually  either  upon 
the  dorsal  or  the  ventral  side,  more  frequently  upon  the  former,  and  connected 
by  the  umbilical  cord  with  the  navel  of  the  fetus.  It  consists  of  a  maternal 
part,  the  modified  decidua  serotina,  and  a  fetal  part,  the  modified  chorion,  inti- 
mately united  together.  The  modifications  of  the  serotina  consist  of  a  degen- 
eration of  the  superficial  layers  of  the  mucosa,  especially  of  the  epithelium 
and  the  glands,  and  the  development  of  very  large  irregular  sinuses  at  the 
surface,  into  which  the  uterine  arteries  and  veins  appear  freely  to  open.  It 
should  be  said  that  it  is  a  disputed  question  among  histologists  whether  the 
sinuses  are  maternal  or  fetal  in  origin,  or  really  spaces  between  maternal  and 
fetal  tissues.  It  is  also  disputed  whether  they  actually  contain  blood  or  only 
fluid  from  the  surrounding  tissues  ;  the  former  has  by  far  the  weight  of  evi- 
dence in  its  favor  and  is  the  prevailing  view.  The  modifications  of  the  chorion 
consist  of  a  great  increase  in  lengtli  and  complexity  of  branching  of  the  villi, 
a  great  development  of  their  contained  blood-vessels,  and  a  firm  attachment 
of  their  tips  to  the  uneven  surface  of  the  serotina,  so  that  their  branches  come 
to  float  freely  within  the  uterine  sinuses  and  to  be  bathed  in  uterine  blood 
(Fig.  315).  The  analogy  between  the  mammalian  placental  villi  and  the  gills 
of  a  fish,  also  highly  vascular  and  floating  in  liquid,  is  striking.  We  shall 
see  later  that  the  analogy  is  not  only  morphological,  but  also  physiological. 


REPROD  UCTION. 


913 


Amnion. 


Chorion. 


ina.simich  as  the  villi  have  impctrtant  respiratory  functions.  The  bulk  of  the 
placenta  is  this  intravillous  portion,  of  spongy  consistence,  comprising  the 
maternal  sinuses  permeated  by  the 
fetal  villi ;  this  is  in  contact  upon 
the  fetal  side  with  the  thin  un- 
modified chorion  covered  within 
by  the  amnion,  and  upon  the 
maternal  side  with  the  thin  rela- 
tively unmodified  serotina  covered 
without  by  the  uterine  muscle. 
The  pui-e  maternal  blood  brought 
by  the  uterine  arteries  moves 
slowly  through  the  sinuses  and 
retires  by  the  uterine  veins ;  the 
fetal  blood  is  propelled  by  the  fe- 
tal heart  along  the  umbilical  cord 
within  the  allantoic  arteries  and 
through  the  villous  capillaries,  and 
returns  by  the  allantoic  vein.  The 
two  kinds  of  blood  never  mix,  but 
are  always  separated  by  the  thin 
capillary  walls  and  their  thin  vil- 
lous investment  of  connective  tissue 
and  epithelium.  Thus  the  anatom- 
ical conditions  for  ready  diffusion 
are  present,  and  this  is  the  chief 
means  of  transfer  of  nutriment  and 
oxygen  from  mother  to  child,  and 
of  wastes  from  child  to  mother. 
The  physiological  role  of  the  pla- 
centa is,  therefore,  an  all-important 
and  complicated  one.  The  placenta  is,  technically,  the  nutritive  organ  of 
the  embryo. 

Nutrition  of  the  Embryo. — We  have  seen  that  a  fundamental  and  most 
striking  difference  between  the  minute  human  ovum  and  the  large  e^^  of  the 
fowl  lies  in  the  relative  quantity  of  food  contained  in  the  two.  The  fowl  has 
retained  the  primitive  habit  of  discharging  the  ovum  from  the  maternal  body, 
and  discharges  w'ithin  its  shell  at  the  same  time  sufficient  food  for  the  needs  of 
the  developing  chick.  Evolution  has  endowed  the  human  mother,  in  common 
with  other  mammals,  with  the  peculiar  custom  of  retaining  the  offspring  within 
her  body  until  its  embryonic  life  is  completed,  and  of  doling  out  its  nuti'iment 
molecularly  throughout  the  period  of  gestation.  The  store  of  nutritive  deuto- 
plasm  with  which  the  egg  leaves  the  ovary  is,  therefore,  only  sufBcient  for  the 
early  segmentative  activities.  Within  the  Fallopian  tube  absorption  from  the 
surrounding  walls  doubtless  goes  on.     Arrived  in  the  uterus  and  imbedded  in 

58 


Fig.  315. — Diagram  of  the  placeuta  (Schafer) :  s,  pla- 
cental sinuses,  into  which  project  the  fetal  villi,  con- 
taining the  red  fetal  vessels  ;  d.  s,  decidua  serotina ;  s.p, 
spongy  layer,  and  m,  muscular  layer,  of  the  uterus ;  a, 
uterine  artery,  and  v,  uterine  vein,  opening  into  the 
placental  sinuses. 


914  AN   AMERICAN    TEXT-BOOK    OE  PllYSlOLOGY. 

its  (locidiuil  wall,  the  .segmented  ovum  eontimies  to  take  nutriment  from  its 
immediate  environing  cells.  It  has  been  suggested,  but  without  much  basis 
of  fact,  that  the  uterine  glands,  which  at  this  time  are  greatly  dilated,  may 
furnish  a  nutritive  secretion  for  the  use  of  the  embryo;  but,  a 'priori,  it  would 
seem  more  reasonable  that,  just  as  the  ovum  within  the  Graafian  follicle 
obtains  its  food  from  its  surrounding  stroma,  so  within  the  highly  vascular 
decidua  it  absorbs  directly  from  the  decidual  tissue.  But  that  this  source 
soon  proves  insufficient  for  the  rapid  growth  is  indicated  by  the  early  develop- 
ment of  the  chorion  with  its  villi  and  the  embryonic  vascular  system.  In 
Rei(!hert's  ovum,  the  earliest  known  human  embryo,  and  believed  to  be 
between  twelve  and  thirteen  days  old,  the  villi  are  already  well  marked 
over  an  equatorial  zone.  From  this  time  on\vard  throughout  gestation  the 
chorion  takes  an  important  part  in  the  embryonic  nutrition,  becoming,  as  we 
have  seen,  an  integral  part  of  the  placenta.  The  placenta  is  'pav  exceUenee 
the  medium  of  nutritive  communication  between  mother  and  child. 

Let  us  consider  briefly  the  needs  of  the  embryo.  The  fetal  energies  must 
be  directed  almost  wholly  to  the  all-important  functions  of  growth  and  prepa- 
ration for  the  future  independent  existence.  The  organism  requires,  therefore, 
an  abundance  of  food  containing  all  the  chief  kinds  of  food-stuifs.  With  the 
alimentary  canal  in  its  embryonic  and  functionless  state,  this  food,  when  it 
reaches  the  embryo,  must  necessarily  be  already  digested  and  ready  for  absorp- 
tion by  the  cells.  A  supply  of  oxygen,  not  necessarily  great  in  quantity,  is 
also  needed.  The  fetal  lungs  are  not  ready  for  respiration,  and  the  oxygen 
must  come  to  the  blood  by  another  channel  than  them.  Carbonic  acid  must 
be  got  rid  of,  and  through  other  than  pulmonary  paths.  Urea  and  its  fore- 
runners and  other  wastes,  probably  not  in  great  quantity,  must  be  excreted. 
The  fetal  kidneys  and  the  skin  are  probably  never  very  active,  as  is  made  rea- 
sonably certain  by  the  late  external  opening  of  the  male  urethra,  the  late 
development  of  the  cutaneous  glands,  and  the  composition  of  the  amniotic 
fluid,  into  which  they  would  naturally  pour  their  secretions.  Thus  the  paths 
of  income  and  outgo  that  are  normal  to  the  individual  after  birth  are  only 
partially  open  during  fetal  life;  nevertheless,  the  processes  of  income  and 
outgo  must  be  performed.  The  placenta,  with  its  close  relationship  but  non- 
communication of  maternal  and  fetal  blood-vessels,  has,  therefore,  been  evolved 
phylogenetically,  and  appears  early  in  the  course  of  ontogeny.  To  it  is 
brought  (m  the  part  of  the  embryo  and  discharged  into  the  villous  cajiillaries 
a  mixed  blood,  comprising  venous  blood  from  the  various  capillary  systems 
of  the  body,  and  containing,  therefore,  the  carbonic  acid  and  other  wastes 
of  venous  blood,  and  a  certain  i)roportion  of  ])urified  blood  that  has  passed 
directly  by  way  of  the  ductus  rcnosus,  inferior  vena  cava,  right  auricle, /ora- 
men  ovale,  and  the  left  side  of  the  heart  to  the  aorta  and  the  umbilical  arte- 
ries. To  it  is  brought  on  the  part  of  the  mother  and  discharged  into  the 
sinuses  pure  arterial  blood,  laden  with  food  and  with  oxygen.  Through  the 
membrane  intervening  between  maternal  and  fetal  vessels  there  passes  from 
the  fetus  carbonic  acid  and  other  wastes,  and  from  the  mother  food  and  oxy- 


R  EPROD  UCTION.  *J  1 5 

gen.  Back  to  the  fetal  liver  and  heart  goes  the  nutritive  and  arterialized 
blood,  and  back  to  the  maternal  excretory  organs  the  vessels  convey  the  fetal 
wastes.  The  placenta  is  thus  a  peculiar  organ  intermediate  between  the  living 
cells  of  the  embryo  on  the  one  hand  and  the  digestive  organs,  lungs,  kidneys, 
and  skin,  of  the  mother  on  the  other.  Little  is  known  of  the  actual  details 
of  the  placental  process.  The  structure  of  the  intervening  cells  indicates  that 
the  interchange  may  be  after  a  manner  analogous  to  that  taking  place  in  the 
lungs,  rather  than  to  that  of  a  typical  secreting  gland—?',  e.  that  known  physi- 
cal processes,  such  as  diffusion  and  filtration,  play  a  prominent  role.  It  has 
been  shown  by  several  investigators  that  the  fetus  may  be  poisoned  by  car- 
bonic oxide  and  strychnine,  and  may  receive  other  harmless  diffusible  sub- 
stances that  are  introduced  in  solution  into  the  maternal  circulation.  The 
mother  raav  be  affected  similarly  from  the  fetal  circulation.  But,  as  in  the 
case  of  the  lungs,  so  the  placental  membrane  can  scarcely  be  regarded  as 
acting  in  the  same  passive  way  as  a  lifeless  membrane  would  act  (compare 
Respiration).  As  accessory  to  the  main  nutritive  source  it  has  been  sug- 
gested that  a  diapedesis  of  maternal  leucocytes  into  the  fetus  may  take  place. 
The  uterine  glands  are  thought  by  some  to  afford  a  nutritive  secretion  to  the 
sinuses,  and  to  the  amniotic  fluid  has  been  ascribed  a  nutritive  function. 
Theoretically,  these  various  means  are  not  impossible,  but  true  placental  diffu- 
sion must  be  regarded  as  the  chief  principle  at  work.  The  result  is  that  the 
mother  relieves  the  child  of  all  the  labor  of  nutrition  except  that  connected 
directly  with  the  latter's  own  cellular  and  protoplasmic  metabolism.  The 
fetal  energies  are,  therefore,  free  to  be  expended  in  the  process  of  growth, 
while  gestation  profoundly  affects  the  maternal  organism. 

Physiological  Effects  of  Pregnancy  upon  the  Mother. — As  might  have 
been  expected,  there  is  probably  not  one  organic  system  wdthin  the  mother's 
body  that  is  not  more  or  less  altered  by  pregnancy,  often  morphologically,  but 
especially  in  regard  to  function.  And  such  normal  alterations  pass  so  gradu- 
ally and  so  frequently  into  genuine  pathological  conditions  that  it  is  sometimes 
difficult  to  draw  the  line  between  the  two.  The  most  marked  changes  are 
connected  with  the  body  of  the  uterus,  and  have  already  been  described.  The 
walls  of  the  cervix  ttteri  become  hypertrophied,  though  to  a  less  degree  than 
the  body,  and  their  glands  secrete  a  quantity  of  mucus  that  forms  a  plug  com- 
pletely closing  the  passage-way  of  the  cervix  (Fig.  314).  The  rest  of  the 
reproductive  organs  from  the  uterus  outward  become  involved  in  the  increased 
venous  hypersemia.  The  walls  of  the  vagina  become  infiltrated  with  serous 
fluid.  The  parts  of  the  vulva  partake  in  the  general  tumefaction.  From  the 
second  month  of  gestation  onward  the  mammary  glands  undergo  gradual  devel- 
opment as  a  preparation  for  the  post-partum  lactation.  The  increase  in  size  of 
the  laden  uterus  brings  gradually  increasing  pressure  to  bear  upon  the  abdom- 
inal viscera,  and  thus  mechanically  causes  functional  derangements  of  the 
dio-estive  and  the  urinary  organs.  The  stretching  of  the  abdominal  skin 
results  in  localized  ruptures  of  the  connective  tissue  of  the  cutis,  the  charac- 
teristic scars  forming  the  strice  gravidarum,  which  persist  after  pregnancy. 


916  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

Otlier  organic  changes  arc,  however,  more  profound  than  these  mechanical  ones. 
In  accordance  with  the  increased  nutritive  labor  thrown  upon  tiie  mc^ther,  the 
total  quantity  of  blood  in  her  body  is  increased,  if  we  can  reason  from  deter- 
minations made  upon  the  lower  animals.'  The  condition  of  the  blood  is  dis- 
puted. The  old  view  was  that  the  blood  of  pregnancy  is  more  watery  and 
contains  less  haemoglobin  than  at  other  times.  This  is  perhaps  true  for  the 
earlier  months,  but  Schroedcr"  and  others  have  shown  that  the  ])ro]X)rtion  of 
hajmoglobin  and  the  number  of  red  corpuscles  rise  above  the  normal  during 
the  later  stages.  The  work  of  the  maternal  heart  is  increased  during  gestation. 
It  is  maintained  by  some  that  the  heart  beats  more  rapidly — according  to 
Kehrer,^  over  eighty  in  the  minute.  It  has  also  been  thought,  mainly  from 
the  results  of  percussion  and  from  sphygmographic  tracings,  that  the  left  ven- 
tricle is  hypertrophied  during  pregnancy.  Post-mortem  examination,  although 
scanty,  cannot  be  said  to  confirm  this  inference.  Pregnancy  necessarily  throws 
increased  labor  upon  both  the  liver  and  the  kidneys,  and  these  organs  are  prone 
to  functional  disorders.  Gastric  disturbances  are  marked  by  frequent  vomit- 
ing. A  tendency  to  increased  pigmentation  in  the  skin  is  present.  The  ner- 
vous system  is  affected,  manifesting  its  alterations  both  by  nutritional  disturb- 
ances and  by  mental  irritability,  depression  of  spirits,  disordered  senses,  easily 
passing  into  temporary  pathological  states,  and  occasionally  by  feelings  of 
heightened  well-being.  The  body-weight  usually  increases  independently  of 
the  added  weight  of  the  embryo. 

Duration  of  Gestation. — For  centuries  the  duration  of  gestation  in 
woman  has  been  commonly  regarded  as  280  days.  The  beginning  of  preg- 
nancy, the  union  of  the  ovum  and  the  spermatozoon,  however,  presents  no 
obvious  signs  by  which  it  may  be  recognized,  and  hence  the  actual  length  of 
pregnancy  in  the  human  female  is  no  moi'e  known  than  in  other  mammals. 
The  obstetrician  is  obliged,  therefore,  to  use  artificial  schemes  in  computing  its 
probable  length.  Several  tables  have  been  publisiied  of  the  time  elapsing 
between  a  single  coition  resulting  in  pregnancy  and  the  terminal  parturition. 
Veit,*  in  collecting  503  such  cases  reported  by  several  obstetricians,  finds  the 
duration  to  be  from  265  to  280  days  in  396  cases,  and  longer  in  the  remaining 
107  cases,  the  variation  thus  being  marked.  It  is  obvious  that  the  date  of  the 
effective  coition  can  rarely  be  known.  One  of  the  first  and  most  evident  signs 
of  pregnancy  is  the  non-appearance  of  the  menses,  and,  probably  largely  from 
the  long-prevailing  idea  of  the  close  relation  existing  between  ovulation  and 
menstruation,  it  has  been  customary  to  regard  gestation  as  dating  from  the  last 
menstruation.  FoIlo\ving  Naegelc,  obstetricians  estimate  the  date  of  parturi- 
tion as  280  days  from  the  first  day  of  the  last  menstruation ;  and  this  simple 
but  artificial  rule  is  doubtless  approximately  correct. 

In  accordance  with  modern  biological  theories,  it  must  be  supposed  that  for 

'  O.  Spiegelberg  und  R.  Gscheidelen:  Arehivfiir  Oiinakologie,  iv.,  1872. 
^  R.  Schroeder  :  Arehivfiir  Gyndkoloyie,  xxxix.,  1890-91. 
^  F.  A.  Kehrer:    Ueber  die  Verdnderungen  der  Pulscurve  im  Puerperinm,  1886. 
*  J.  Veil :  Midler's  Handbuch  der  GeburtshiUfe,  1,  1888. 


RE  PR  OD  UCTION.  917 

eac'li  species  tliero  has  been  developed  a  gestative  period  of  a  length  most 
favorable  to  the  continuance  of  the  species;  this  has  been  a  matter  of  natural 
selection.  But  this  ])rinciple  does  not  account  for  the  termination  of  the  period 
in  any  individual  case.  The  proximate  cause  of  the  oncoming  of  birth  must 
be  sought  in  more  specific  anatomical  or  physiological  phenomena.  This  cause 
has  been  sought  long,  and  not  wholly  successfully.  Among  the  agents  sug- 
gested may  be  mentioned  the  pressure  which  the  uterine  tissues,  the  cervical 
ganglion,  and  the  adjacent  nerves,  receive  between  the  fetal  head  and  the  pelvic 
wall,  the  stretching  of  the  uterine  wall,  the  fatty  degeneration  of  the  deciduae, 
the  thrombosis  of  the  placental  vessels,  the  venosity  of  the  fetal  blood  due  to 
the  growing  functional  importance  of  the  fetal  right  ventricle  acting  as  a 
stimulus  to  the  placental  area,  and  a  gradual  increase  in  irritability  of  the 
uterus  as  the  nerve-supply  of  the  organ  increases.  Some  of  these,  such  as  the 
fatty  degeneration  of  the  deciduae  and  the  placental  thrombosis,  are  not  con- 
stant phenomena,  and  the  others  are  not  definitely  proved  to  be  efficient  causes. 
It  is  probable  that,  with  the  uterus  undoubtedly  irritable,  in  different  cases 
different  stimuli  act  to  inaugurate  the  process  of  birth,  and  a  priori  the  above 
causes  seem  not  improbable  ones. 

Parturition  in  General. — Parturition,  birth,  or  labor,  is  the  process  of 
expulsion  of  the  developed  embryo,  the  membranes,  and  the  placenta  from  the 
body  of  the  mother.  It  is  executed  by  contraction  of  the  muscles  of  the  so- 
called  wpper  segment  of  the  uterus  and  those  of  the  abdominal  walls.  The 
lower  segment  of  the  uterus,  comprising  approximately  that  portion  of  the 
body  lying  below  the  attachment  of  the  peritoneum,  the  cervix,  the  vagina, 
and  the  vulva,  are  largely,  if  not  wholly,  passive  in  parturition.  The  obstet- 
ricians have  found  it  convenient  to  divide  labor  into  three  stages,  although 
physiologically  these  are  not  sharply  differentiated  from  each  other.  The  first 
stage  is  characterized  by  the  dilatation  of  the  os  uteri,  the  second  by  the  expul- 
sion of  the  fetus,  the  third  by  the  expulsion  of  the  after-birth.  The  customary 
position  of  the  fetus  within  the  uterus  at  the  end  of  pregnancy  is  that  in  which 
the  head  is  downward  or  nearest  the  os,  the  back  toward  the  ventral  and  left 
side  of  the  mother,  and  the  arras  and  legs  folded  upon  the  trunk. 

First  Stage  of  Labor. — For  several  weeks  toward  the  close  of  pregnancy 
there  are  occasional  periods  when  rhythmic  muscular  contractions  pass  over  the 
uterine  walls.  These  are  mostly  painless,  and  apparently  are  not  in  themselves 
of  special  functional  importance.  The  first  stage  of  labor  is  ushered  in  by 
various  phenomena,  prominent  among  which  are  an  increase  in  the  intensity 
of  the  contractions,  their  painfulness,  and  their  frequency  and  continuance. 
In  women  they  are  confined  practically  to  the  upper  segment  of  the  uterus  and 
its  attached  ligaments,  ceasing  at  a  circular  ridge  that  projects  inward  and  is 
called  the  "contraction  ring."  For  some  reason,  at  present  disputed,  the 
lower  segment  of  the  uterus,  and  the  cervix,  are  passive.  The  contractions 
are  probably  peristaltic  in  character,  as  in  lower  animals.  Schatz^  has  graphi- 
cally recorded  the  uterine  movements  by  means  of  a  bladder  filled  with  water 
*  F.  Schatz :  Archil  fur  Gyndkologie,  xxvii.,  1885-86. 


918  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

and  iiitrcxliiced  into  tlie  uterus.  During  the  earlier  part  ot"  parturition  the 
contractions  grachially  increase  in  intensity  up  to  a  maximum  which  they 
then  maintain.  Their  rhythm  is  somewhat  irregular ;  the  duration  of  each 
contraction  averages  about  one  minute,  and  a  })ause,  which  ensues  between  suc- 
cessive contractions,  extends  from  one  and  one-half  to  several  minutes.  The 
relaxation  of  the  muscle-fibres  during  the  period  of  rest  is  incomplete,  the 
result  being  that  the  fibres  enter  gradually  into  a  tonically  contracted  state. 
Each  contraction  is  accompanied  by  a  pain,  localized  in  the  early  part  of  labor 
in  the  uterus  alone,  but  later  extending  outward,  upward  into  the  abdomen, 
and  downward  into  the  thighs.  The  pains  of  labor  vary  greatly  in  intensity 
in  individuals,  but  are  usually  more  intense  during  the  first  gestation  than 
during  later  ones.  They  are  due  chiefly  to  direct  mechanical  stimulation  of 
the  sensory  uterine  and  other  nerves  by  compression,  tension,  and  even  lacera- 
tion. 

As  a  result  of  the  tonic  contraction  of  the  uterine  walls,  gradually  increas- 
ing with  each  new  peristaltic  wave,  the  uterus  becomes  gradually  narrower  in 
diameter  and  longer,  and  the  walls  press  more  and  more  firmly  upon  the  bag 
of  amniotic  fluid  containing  the  embryo.  Schatz  finds  that  the  uterine  pres- 
sure under  the  uterine  contractions  rarely  reaches  and  never  exceeds  100  milli- 
meters of  mercury.  Tlie  direction  of  least  resistance  to  this  pressure  lies 
along  the  cervical  canal,  the  walls  of  which  do  not  take  part  in  the  uterine  labor. 
With  each  succeeding  contraction  this  canal  is  forced  wider  open  and  the  uterine 
contents  are  pressed  tightly  downward  and  into  the  cervix.  The  head  of  the 
embryo  is  preceded  by  a  bulging  portion  of  the  membrane,  filled  with  fluid 
and  forming  a  distinct  bladder-like  advance  guard.  This  bag  a})pears  at  the 
OS  uieri,  its  contents  increase  under  the  increasing  pressure,  and  in  the  majority 
of  cases,  when  the  os  is  fully  expanded,  it  bursts  and  allows  the  amniotic  fluid 
to  escape  to  the  exterior.  In  some  cases  the  rupture  is  delayed  until  the  sec- 
ond stage  of  labor,  and  rarely  the  child  is  born  with  the  membranes  intact. 

Second  Stage  of  Labor. — The  uterine  contractions  frequently  cease  for  a 
period  following  the  rupture  of  the  membrane.  They  then  begin  anew  with 
increased  force,  and  are  accompanied  by  a  new  feature,  namely,  analogous 
vigorous  rhythmic  contractions  of  the  muscles  of  the  abdominal  walls.  These, 
following  deep  inspiration  and  accompanied  by  forced  attempts  at  expiration 
with  a  closed  glottis,  diminish  the  longitudinal  and  the  lateral  diameters  of  the 
abdominal  cavity,  compress  the  abdominal  organs,  and  help  to  augment  greatly 
the  uterine  pressure.  At  the  beginning  of  the  second  stage  the  force  of  the 
contractions  is  expended  mainly  upon  the  head  of  the  embryo,  which  lies  like 
a  plug  in  the  cervical  canal.  This  is  squeezed  gradually  through  the  os  into 
the  vagina,  followed  by  the  more  easily  passing  trunk  and  limbs.  The  con- 
tractions are  frequent,  vigorous,  and  painful,  the  pains  reaching  a  maximum 
as  the  sensitive  vulva  is  put  upon  the  stretch  arKl  traversed.  The  vertex  is 
usually  presented  first  to  the  exterior,  the  head  and  body  following  as  the  suc- 
cessive contractions  of  the  maternal  muscles  develoj)  sufficiout  power  to  over- 
come the  resistance  offered  to  their  passage  by  the  surrounding  walls.     In 


RE  PR  OD  UCTION. 


919 


the  human  female  the  vaginal  muscles  do  not  appear  to  engage  in  the  expel- 
ling act,  the  uterine  and  the  abdominal  muscles  alone  sufficing  and  finally 
forcing  the  child  wholly  outside  the  mother's  body.  In  this  gradual  manner, 
painfid  and  dangerous  alike  to  mother  and  child,  the  maternal  organism  forces 
the  offspring  to  forsake  its  sheltering  and  nutritive  walls  and  begin  its  inde- 
pendent existence. 

Third  Stage  of  Labor.— During  the  later  expulsive  contractions  of  the 
second  stage  the  placenta,  being  greatly  folded  by  the  diminution  in  the  uterine 
surface  of  attachment,  is  loosened  from  the  uterine  wall  by  a  rupture  takmg 
place  through  the  loose  tissue  in  the  region  of  the  blood-sinuses.  The  child, 
when  born,  is  joined  to  the  loosened  placenta  by  the  umbilical  cord,  until  the 
latter  is  tied  and  cut  by  the  obstetrician.  The  muscular  contractions,  now 
almost  painless,  continue  through  the  third  stage,  and  the  placenta  is  torn 
from  its  attachment,  everted,  and  carried  gradually  outward.  The  lining 
membrane  of  the  uterus  from  the  placenta  outward  and  for  a  considerable 
depth  is  gradually  torn  free  from  the  deeper  parts  through  the  spongy  layer, 
and  with  the  attached  chorion  and  amnion  follows  the  placenta.  As  a  rule, 
this  after-birth  appears  at  the  vulva  within  fifteen  minutes  after  the  expulsion 
of  the  child ;  it  consists  of  the  placenta,  the  amnion,  the  chorion,  the  decldua 
reflexa,  and  a  considerable  portion  of  the  decidua  vera. 

Previous  to  the  third  stage  slight  bleeding  from  laceration  of  the  passages 
occurs.  But  with  the  loosening  of  the  placenta  and  the  accompanying  rupture 
of  the  placental  vessels  the  maternal  blood  flows  freely  and  continues  to  flow 
from  the  uterine  wall,  chiefly  from  the  placental  area,  until  the  after-birth  is 
discharged.  The  average  loss  of  blood  amounts  to  about  400  grams.  At  the 
close  of  the  third  stage  of  labor  the  uterine  contractions  have  so  far  proceeded 
that  the  organ  is  compressed  into  a  hard  compact  mass,  the  ruptured  vessels 
are  contorted  and  compressed,  and  the  bleeding  is  thereby  largely  stopped. 
For  several  hours,  however,  slight  hemorrhage  continues  as  an  accompaniment 
to  the  pod-partum  contractions,  but  finally  this  ceases  with  the  formation  of  a 
blood-clot  over  the  wounded  surface. 

The  third  stage  of  labor  may  continue  through  one  or  two  hours.  It  is 
customary,  however,  for  the  obstetrician  speedily  to  put  an  end  to  it  by  assist- 
ing the  removal  of  the  after-birth. 

Nature  of  Labor. — Our  knowledge  of  the  nature  of  the  muscular  phe- 
nomena of  labor  is  incomplete.  The  uterine  contractions  are  in  part  automatic 
and  in  part  reflex,  but  to  what  extent  the  former,  and  to  what  the  latter,  is  not 
known.  Nerves  reach  the  uterus  partly  through  the  abdominal  sympathetic 
chain  and  partly  directly  from  the  spinal  cord  through  the  sacral  plexus. 
Rein^  found  that  in  the  rabbit  after  section  of  all  uterine  nerves  normal 
conception,  pregnancy,  and  birth  may  occur.  In  some  animals  uterine  move- 
ments may  continue  after  removal  of  the  organ  from  the  body.  Such  and 
other  observations  indicate  the  existence  of  an  automatic  contractile  power 
resident  in  the  organ  itself.  Since  nerve-cells  are  not  found  in  its  walls,  it 
'  G.  Rein  :  Pfliiger's  ArcMv  fur  die  gesammte  Physiologic,  xxiii.,  1880. 


920  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

seems  probable  that  the  automatism  resides  in  the  muscle  tissue.  The  uterus 
is,  moreover,  very  sensitive  to  direct  stimulation,  even  after  excision.  In  ani- 
mals higher  than  rabbits  a  connection  with  the  lumbar  spinal  cord  seems 
essential  to  normal  labor.  Goltz  ^  obtained  in  dogs  conception,  pregnancy,  and 
delivery  after  section  of"  the  spinal  cord  at  the  height  of  the  first  lumbar 
vertebra.  In  jwraplegic  women,  with  conduction  in  the  cord  broken  in  the 
dorsal  region,  delivery  is  possible.  A  centre  for  uterine  contraction  must 
hence  be  supposed  to  exist  in  the  lumbar  cord.  Centripetal  and  centrifugal 
fibres  exist  in  both  sympathetic  and  spinal  nerves,  and  reflex  uterine  contrac- 
tions are  readily  obtained  by  stimulation  of  the  central  ends  of  the  divided 
nerve-trunks.  According  to  von  Basch  and  Hofmann,^  in  the  dog  the  sym- 
pathetic trunks  supply  the  circular  muscular  coat  of  the  uterine  walls  and  con- 
tain vaso-constrictor  fibres,  while  the  spinal  trunks  supply  the  longitudinal 
coat  and  contain  vaso-dilator  fibres.  Stimulation  of  the  uterus  itself,  the 
vagina,  the  vulva,  the  sciatic  and  the  crural  nerves,  and  various  sensory 
regions,  notably  the  ni])ples,  causes  reflex  contractions  of  the  uterus.  The 
same  result  occurs  upon  stimulation  of  various  portions  of  the  brain,  such  as 
the  medulla  oblongata,  the  cerebellum,  the  pons,  the  corpora  quadrigemina, 
the  optic  thalamus,  the  corpus  striatum,  and  even  the  corpus  callosum.  In 
Moman  psychic  influences  may  call  forth  or  inhibit  uterine  contractions.  How 
largely  the  well-known  stimulating  effects  of  the  blood  in  asphyxia  and  of 
drugs,  like  ergot,  are  due  to  central,  and  how  largely  to  direct  uterine,  influence 
is  undecided.  The  regular  co-ordinated  course  of  labor  and  many  experi- 
mental facts  make  it  probable  that,  normally,  reflex  influences  constitute  a  large 
part  of  tlie  process,  the  centripetal  impulses  arising  within  the  uterus  itself. 
In  fact,  it  is  customary  to  speak  of  labor  as  a  complex  reflex  action.  The 
undoubted  automatism  of  the  uterine  muscle-fibres  must,  however,  be  taken 
into  account,  and  the  act  should  be  regarded  as  composed  of  both  automatic 
and  reflex  elements.  AVe  have  here  to  deal  with  that  variety  of  contractility 
peculiar  to  smooth  muscle,  in  which  central  and  peripheral  influences  work 
together  to  bring  about  the  result.  It  is  perhaps  not  going  too  far  to  regard  all 
such  actions,  like  that  of  the  heart,  as  primarily  automatic  and  called  out  by 
direct  stimulation,  but  as  modified  and  controlled  by  reflex  influences.  The 
parturitive  contractions  of  the  striated  muscles  of  the  abdominal  walls  are 
probably  more  generally  reflex  iu  nature,  modified,  however,  by  voluntary 
efforts. 

Multiple  Conceptions. — According  to  the  records  given  by  different  stat- 
isticians, the  frequency  of  twin  births  varies  considerably  in  different  coun- 
tries. In  13,000,000  births  in  Prussia,  G.  Yeit^  found  the  number  of  twins 
to  be  1.12  per  cent.,  or  1  in  89  births.  In  the  cities  of  New  York  and 
Philadelphia  recent  reports  give  the  ratio  of  twins  to  single  births  as  1  :  120, 
or  0.83  per  cent. 

'  Fr.  Goltz  :  Pfluger's  Archiv  fiir  die  ijesammte  Physiolorfie,  ix.,  1874. 

*  S.  von  Bascli  und  E.  Hofmann  :  Medizinische  Jahrbitcber,  Wien,  1877. 

'  G.  Veit :  Mmatsschrift  fiir  Geburtskunde  und  Franenkrankheiten,  vi..  1855. 


RKPR  OD  LCTION.  92 1 

Observations  of  discharged  Graafian  folli(!les  in  cases  of  raultii)le  concep- 
tions show  that  twins  may  arise  eitlier  from  separate  eggs  or  from  a  single  egg. 
The  presence  at  birth  of  a  double  chorion  is  commonly  regarded  as  diagnostic 
of  the  former  origin,  that  of  a  single  chorion  of  the  latter.  In  the  former 
ease  the  two  ova  may  come  from  a  single  Graafian  follicle,  or  from  two  folli- 
cles situated  within  one  ovary,  or  from  both  ovaries,  direct  observation  of  the 
ovaries  themselves  being  required  to  determine  the  origin  in  any  particular 
case.  The  two  ova  are  discharged  and  fertilized  probably  at  approximately 
the  same  time.  There  are  two  distinct  amnions.  The  two  placentas  may  be 
either  fused  into  one  or  wholly  separated  from  each  other,  and  accordingly  the 
deeidua  reflexa  may  be  single  or  double.  The  two  offspring  may  be  of  sep- 
arate sexes,  and  do  not  necessarily  closely  resemble  each  other.  In  cases 
where  the  two  embryos  come  from  a  single  ovum  their  origin  is  little  under- 
stood. It  is  conceivable  that  it  may  arise  from  the  presence  of  two  nuclei 
within  the  one  ovum.  It  is  more  probable,  however,  that  it  is  due  to  a 
mechanical  separation  of  the  blastomeres  after  the  first  cleavage  or  later  in 
segmentation.^  Driesch,^  Wilson,^  Zoja,*  and  others  have  shown  that  in  various 
invertebrates  and  the  low  vertebrate  Amphioxus,  single  blastomeres,  isolated 
from  the  rest  by  shaking  or  other  unusual  treatment,  are  capable  of  develop- 
ing into  small  but  otherwise  normal  and  complete  embryos.  No  reason  is 
obvious  why  such  an  occurrence  cannot  take  place  in  human  development,  if 
in  any  accidental  manner  within  the  Fallopian  tube  the  blastomeres  become 
separated.  Driesch  observed  in  the  sea-urchins  and  Wilson  in  Amphioxus 
incomplete  separation  of  blastomeres  to  produce  two  incomplete  organisms 
more  or  less  united  together.  It  is  not  improbable  that  even  in  man  cases 
like  the  Siamese  Twins,  and  greater  monstrosities^  may  be  similarly  accounted 
for.  In  cases  of  double  pregnancy  from  a  single  ovum  the  two  amnions  are 
usually  separate,  in  rare  cases  a  breaking  away  of  their  partition  wall  throwing 
them  into  one ;  the  two  placentas  usually  fuse  more  or  less  into  one,  the  blood- 
vessels of  the  two  halves  always  anastomosing ;  and  a  single  deeidua  rejiexa 
covers  both.  The  two  offspring  are  uniformly  of  the  same  sex  and  their  per- 
sonal resemblance  is  always  close. 

In  Veit's  statistics  of  13,000,000  births  in  Prussia,  triplets  occur  with  a 
frequency  of  0.012  per  cent.,  or  1  in  7910,  and  quadruplets  1  in  371,126  births. 
There  are  well-authenticated  cases  of  quintuplets.  In  all  of  these  cases  a 
single  ovum  rarely,  if  ever,  contributes  more  than  two  embryos,  and  these 
are  characterized,  as  in  the  case  of  twins,  by  being  of  similar  sex,  by  pos- 
sessing a  single  chorion,  and  by  close  personal  resemblance. 

The  Determination  of  Sex. — In  most,  if  not  all,  civilized  races  more  boys 
are  born  than  girls.     This  is  shown  in  the  following  table  :  ^ 

'  Cf.  Fr.  Ahlfeld  :  Archiv  fur  Gyndkologie,  ix.,  1876. 

2  H.  Driesch:  Zeitschrift  fiir  ivisHenschaftliche  Zoologie,  liii.,  1892*,  Iv.,  1893;  Mittheilungen 
cms  der  Zoologischen  Statimi  zu  Neapel,  xi.,  1893. 

^  E.  B.  Wilson  :  Journal  of  Morphology,  viii.,  1893. 

*  R.  Zoja  :  Archiv  fur  Entwickelungsmechanik  der  Organismen,  ii.,  1895. 

*  Bulletin  de  I'institut  international  de  slatislique,  vii. 


922  AN   AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

Boys  born  to  1000   Girls  born  (1887-91). 


Italy 1058 

Ireland      1056 

German  Empire 1052 

France 1046 


England 1036 

Connecticut 107'J 

Rhode  Island 1049 

Massachusetts       1046 


Tlie  proportional  birtli-rate  ot"  tlie  two  sexes  is  usually  fairly  constant  from 
year  to  year.  This  means  that  constant  rej^iilating  factors  are  at  work. 
What  determines  sex  in  any  one  individual  is  ill  understood.  The  sexual 
oigans  in  the  human  embryo  are  well  differentiated  at  the  eighth  week  of 
intra-uterine  life,  hence  the  sex  of  the  child  must  be  settled  previously  to  this 
time.  It  is  at  present  quite  impossible  to  say  whether  it  is  settled  in  the 
germ-cells  previous  to  their  union,  in  the  act  of  fertilization,  or  during  the 
early  uterine  life.  Many  facts,  both  observational  and  experimental,  and 
more  hypotheses,  bearing  upon  the  determination  of  sex,  have  been  i)rought 
forward.  The  Hofackcr-Sadlcr  law  (Hofacker,  1828;  Sadler,  1830)  is  well 
known,  as  follows :  If  the  father  be  older  than  the  mother,  more  boys  than 
girls  will  be  born  ;  if  the  parents  be  of  equal  age,  slightly  more  girls  than 
boys ;  if  the  mother  be  older  than  the  father,  the  probability  of  girls  is  still 
greater.  Since  its  promulgation  this  so-called  law  has  received  evidence  both 
confirmatory  and  contradictory  of  its  truth.  Thury  in  1863  claimed  that  the 
earlier  after  its  liberation  the  egg  is  fertilized,  the  greater  is  the  tendency  to 
the  production  of  a  female ;  the  later  the  fertilization,  the  greater  the  prob- 
ability of  a  male.  Breeders  have  made  use  of  this  principle  apparently  with 
success — offspring  conceived  at  the  beginning  of  "heat"  seem  to  be  more 
usually  females.  Likewise,  it  is  frequently  believed  that  in  human  beings 
conceptions  immediately  after  menstruation  produce  a  larger  proportion  of 
females  than  later  conceptions.  Diising  ^  accepts  Thury's  view  and  extends  it 
to  the  male  element — the  younger  the  spermatozoon  the  greater  the  tendency 
toward  tlie  production  of  males.  Hence  among  animals  the  scarcity  of  one 
sex  leads  to  the  more  frequent  exercise  of  its  rejM-oductive  function,  the  em- 
ployment of  younger  germ-cells,  and  therefore  the  relative  increase  of  that 
sex.  Further,  the  nearer  a  parent  is  to  the  height  of  his  reproductive  capacity 
the  less  will  be  the  probability  of  transmitting  his  own  sex  to  the  oflfspring. 
By  feeding  tadpoles  with  highly  nutritious  flesh  Yung^  increased  the  percent- 
age of  females  from  56  to  92.  Mrs.  Treat  ^  showed  that  the  butterflies  of 
well-fed  caterpillars  become  females,  those  of  starved  caterpillars  males.  Sta- 
tistics among  mammals  and  human  beings  indicate  that  the  ])roportion  of  male 
to  female  offspring  varies  inversely  with  the  nutrition  of  the  parents,  especially 
of  the  mother.  Thus,  more  boys  are  born  in  the  country  than  in  the  city, 
and  in  poor  than  in  prosperous  families;  the  relative  number  of  boys  is  said  to 
vary  even  with  the  prices  of  food.  It  is  contended,  moreover,  and  with  some 
statistical  support,  that  in  the  human  race  an  epidemic  or  a  war,  either  of  whicli 
affects  adversely  the  well-being  of  the  peo})le,  is  followed  by  a  relative  increase 

^  K.  Diising:  Jenaische  Zeitschrift fiir  Natunoissenschaft,  xvi.,  1883,  and  xvii.,  1884. 
'■'  E.  Yung :   Comptes  rendun  de  PAcademie  des  scienceK,  Paris,  xcii.,  1881. 
'  Mrs.  Mary  Treat:   The  American  Nataralu<l,  vii.,  1873. 


RE  PR  on  UCTION.  928 

of  male  births.  It  is  claimed  that  ethnic  intermixture  causes  a  decrease  in  the 
relative  number  ot"  males  born.  This  is  strongly  supported  by  a  recent  sta- 
tistical study  by  Ripley  '  of  the  two  races  inhabiting  Belgium,  the  Walloons, 
of  the  same  origin  as  the  Kelts  in  France,  and  the  Flemish,  of  German  stock. 
Where  these  races  are  purest,  the  number  of  boys  born  to  1000  girls  is  1064; 
along  the  region  where  the  two  races  come  into  contact,  however,  the  number 
may  fall  as  low  as  1043.  Maupas  "^  found  that  sex  in  the  rotifer,  Hydaiina 
senfa,  could  be  controlled  by  altering  the  temperature  of  the  medium  surround- 
ing the  egg-laying  females.  In  various  experiments  at  a  temperature  of  2G°- 
28°  C,  81-100  per  cent,  of  the  eggs  gave  rise  to  males,  the  rest  to  females ;  at 
14°-15°  C.  only  5— 24.  per  cent,  were  males,  the  much  larger  majority  females. 
The  above  considerations  are  highly  interesting  and  suggestive,  but  they 
have  not  yet  been  brought  under  general  laws  sufficiently  to  make  their  bear- 
ing upon  the  main  problem  wholly  clear.  It  is  probable  that  numerous 
factors  are  of  influence  in  the  determination  of  sex.  The  general  deduction 
from  all  the  facts  seems  justified  that  unfavorable  nutritive  conditions  sur- 
rounding the  parents  tend  to  the  production  of  males,  favorable  conditions 
to  the  production  of  females.  The  experimental  results  indicate,  moreover, 
that  the  conditions  surrounding  the  parents  or  the  developing  embryo  are 
largely  responsible  for  the  resulting  sex.  Watase^  regards  the  embryo  as 
neutral  as  regards  sex  from  the  time  of  fertilization  up  to  a  certain  stage  of 
its  development ;  external  conditions  act  as  a  stimulus  to  the  sexless  proto- 
plasm, and  the  resulting  response  is  a  development  in  the  direction  of  either 
raaleness  or  femaleness  according  to  the  nature  of  the  stimulus.  How  largely 
and  in  what  manner  this  may  be  true  of  the  human  species  is  wholly  unknown. 
Diising  urges  that  the  various  factors  determining  sex  have  arisen  through 
natural  selection  ;  they  are  conducive  to  the  continuance  of  the  species,  and 
they  act  in  such  a  way  that  sex  is  in  a  certain  sense  self- regulating — the 
scarcity  of  one  sex  tends  to  the  greater  production  of  individuals  of  that  sex  ; 
this  is  instanced  by  the  fact  mentioned  above  that  after  the  destruction  of 
males  by  war  relatively  more  males  are  born  than  previously. 

E.  Epochs  in  the  Physiological  Life  of  the  Individual. 

Fertilization  begins,  somatic  death  ends,  the  physiological  life  of  the  indi- 
vidual. Between  these  two  events  the  life-processes  go  on  gradually,  and, 
with  the  exception  of  birth,  are  marked  by  few  abrupt  changes.  It  is  some- 
times convenient  to  divide  the  individual  life  into  a  number  of  successive 
stages,  as  follows :  the  embryonic  period,  the  fetal  period,  infancy,  childhood, 
youth,  or  adolescence,  maturity,  and  old  age,  or  senescence.  Such  a  division, 
however,  is  not  physiologically  exact,  the  stages  are  not  sharply  limited,  and 
the  terms  are  employed  in  very  different  senses  by  different  writers.  Between 
fertilization  and    birth  the  functions  originate  and  are  developed  gradually. 

'  W.  Z.  Ripley  :  Quarterly  Publications  of  the  American  Statistical  Association,  v.,  March,  1896. 
^  E.  Maiipas  :  Comptes  rendus  de  I' Academic  des  sdences,  Paris,  cxiii.,  1891. 
•'  S.  Watase  :  Journal  of  Morphology,  vi.,  1892. 


924  AIV  AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 

At  birth  tlir  eiiviroiinient  of  the  individual  is  abruptly  oliaugcd,  or<2:anic' 
connection  with  the  mother  suddenly  ceases,  and  profound  pliysiological 
changes  occur.  At  this  time,  or  shortly  after  it,  the  individual  is  capable 
of  performing  all  the  functions  of  adult  life  with  the  exception  of  reproduc- 
tion, the  functions  needing,  however,  to  be  exercised  and  improved  before 
they  are  at  their  best.  From  birth  to  maturity,  therefore,  the  physiological 
history  is  mainly  a  history  of  progressive  modifications  of  function — modi- 
fications, indeed,  of  great  importance,  but  secondary  to  the  primary  fact  of 
function  itself.  The  same  may  be  said  of  the  period  of  old  age,  with  the  dif- 
ference that  here  the  modifications  of  function  are  retrogressive.  In  the  present 
book,  devoted  mainly  to  the  physiology  of  the  adult  at  the  time  of  maturity, 
little  can  be  said  of  the  origin  and  development  of  function  in  the  embryo : 
the  modifications  of  function  at  different  periods  of  life  have  been  discussed  in 
connection  with  the  various  functions  themselves;  certain  topics  of  special  physio- 
logical significance  have,  however,  been  left  for  brief  treatment  in  this  chapter. 

Growth  of  the  Cells,  the  Tissues,  and  the  Organs. — All  growth, 
whether  of  the  cells,  the  tissues,  or  the  organs,  is  the  result  of  no  more  than 
three  processes,  viz.  multiplication  of  cells,  enlargement  of  cells,  and  deposition 
of  intercellular  substance,  the  first  two  processes  being  the  most  potent  of  all. 
Increase  in  the  number  of  cells  is  largely,  although  not  wholly,  an  embryonic 
phenomenon ;  increase  in  the  size  of  cells  and  deposition  of  intercellular  sui)- 
stance  are  especially  important  from  the  later  embryonic  period  through  the 
time  of  birth  and  up  to  the  cessation  of  the  body-growth.  The  periods  of 
growth  of  the  several  tissues  differ ;  in  view  of  this  it  is  quite  impossible  to 
designate  any  period  except  that  of  death  at  which  the  growth  of  the  tissues 
wholly  terminates.     Detailed  statistics  of  the  growth  of  organs  are  wanting. 

Gro\v1;h  of  the  Body  before  Birth. — The  most  obvious  result  of  growth 
of  the  cells,  the  tissues,  and  the  organs,  is  growth  or  increase  in  size  of  the 
body.  Growth  of  the  body  continues  actively  from  the  beginning  of  the  seg- 
mentation of  the  ovum  up  to  about  the  age  of  twenty-five  years,  and  results  in 
an  increase  in  all  dimensions  and  in  weight.  In  determining  the  extent  of 
growth,  the  two  most  convenient  and  most  commonly  used  measurements  are 
those  of  length,  or  height,  and  weight.  For  the  embryo  the  following  table 
has  been  compiled  by  Hecker :  * 

Table  showing  the  Average  Length  and  Weigld  of  the  Human  Embryo  at 

Different  Ages. 

Month.                          Length  of  embryo  in  centimeters.  Weight  of  embryo  in  grams. 

Third 4  to    9  11 

Fourth 10  to  17  57 

Fifth        18  to  27  284 

Sixth       28  to  34  634 

Seventh 35  to  38  1218 

Eighth 39  to  41  1569 

Ninth       42  to  44  1971 

Tenth       45  to  47  2334 

'  C.  Hecker  :   Monaisachrift  fur  Oeburtskunde  vnd  Frauenkrankheiten,  xxvii.,  1866. 


REPROD  UCTION. 


925 


Tilt'  length  and  the  weight  at  birtli  vary  very  greatly.  The  average  measure- 
ments, as  given  for  over  450  infants  in  Great  Britain,  are,  for  height,  males 
19.5  inches,  females  19.3  inches;  for  weight,  males  7.1  pounds,  females,  6.9 
pounds.  The  weight  at  birth  is  said  to  be  greater  the  nearer  the  mother's 
age  is  to  thirty-five  years,  the  greater  the  weight  of  the  mother,  the  greater 
the  number  of  ])revious  pregnancies,  and  tlic  earlier  the  appearance  of  the  first 
menstruation.  Race  and  climate  are  also  of  influence.  Minot^  believes  that  all 
of  these  influences  work  principally  through  prolonging  or  abbreviating  the 
period  of  gestation,  and  that  the  variations  at  birth  depend  partly  upon  the 
duration  of  gestation  and  partly  upon  individual  differences  of  the  rate  of 
growth  in  the  uterus. 

Gro"wi;h  of  the  Body  after  Birth. — In  studying  the  growth  of  the  body 
after  birth  two  methods  have  been  employed,  named  the  "generalizing"  and 

0         A(je.  5  10  15  20        Years.         25 


140 


l:iO 


100 


Fig.  316.— Diagram  showing  increase  of  stature  and  weight  of  both  sexes,  as  determined  by  the  Anthropo- 
metric Committee  of  the  British  Association.' 

the  "  individualizing  "  methods.  The  former  consists  in  deducing  the  course 
of  growth  by  averages  or  other  central  values  from  statistics  taken  from  a 
large  number  of  individuals  at  different  ages.  It  is  the  method  more  com- 
monly employed ;  it  shows  the  cour.se  of  growth  of  the  typical  child,  but  is 
inexact  in  enabling  future  growth  to  be  predicted  in  individual  cases.  The 
individualizing  method  consists  in  measuring  the  actual  growth  of  the  same 
individual  through  successive  years ;  it  shows  well  the  relation  of  the  indi- 

'  C.  S.  Minot :  Human  Embryology,  1892. 
^  Roberts :  Manual  of  Anthropometry,  1878. 


926  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

vicinal  to  the  type  throughout  the  period  of"  growth.  The  course  of  growth 
ot"  British  boys  and  girls  from  birth  up  to  the  age  of  twenty-four  is  graphically 
shown  in  the  accompanying  diagram  (Fig.  316).  Growth  is  here  seen  to  be 
rapid  during  the  first  five  years  of  life,  then  slower  up  to  the  tenth  or 
the  twelfth  year.  From  thence  up  to  the  fifteenth  or  the  seventeenth  year 
— that  is,  preceding  and  including  puberty — marked  acceleration  occurs, 
which  in  turn  is  followed  by  slow  increase  up  to  the  twentieth  or  the 
twenty-fifth  year.  For  from  five  to  ten  years  thereafter  slight  increase  in 
height  occurs,  while  from  the  accumulation  of  fat  the  weight  usually  rises 
markedly  up  to  the  fiftieth  or  the  sixtieth  year.  One  of  the  most  interesting 
results  revealed  by  statistics  is  the  relative  growth  of  the  two  sexes.  From 
birth  up  to  about  the  age  of  ten  or  twelve,  boys  show  a  slight  and  increasing 
prej^onderance  over  girls,  but  the  two  curves  are  nearly  parallel.  The  jirepu- 
bertal  acceleration  of  growth  in  girls,  however,  precedes  that  of  boys,  and  is 
even  accompanied  by  some  check  in  the  male  growth,  with  the  result  that 
between  the  ages  of  twelve  and  fifteen  girls  are  actually  heavier  and  taller 
than  boys.  This  fact,  first  pointed  out  in  1872  by  Bowditch  ^  from  observa- 
tions on  several  thousand  Boston  school  children,  has  been  abundantly  con- 
firmed by  Pagliani  in  Italy,  Key  in  Sweden,  Schmidt  in  Germany,  Porter  in 
St.  Louis,  and  others.  At  about  fifteen  years  boys  again  take  the  lead  and 
maintain  it  throughout  life.  Boys  grow  most  rapidly  at  sixteen,  girls  at  thir- 
teen or  fourteen,  years  of  age ;  the  former  attain  their  adult  stature  approxi- 
mately at  twenty-three  to  twenty-five,  the  latter  at  twenty  to  twenty-one  years. 
The  details  of  growth  and  the  actual  measurements  vary  considerably  with 
race ;  thus  the  supremacy  of  the  American  girl  over  her  brother  appears  to  be 
less  marked  and  to  cover  a  shorter  period  than  that  of  the  English,  German, 
Swedish,  or  Italian  girl.  Children  of  well-to-do  families  are  superior  to 
others  in  both  weight  and  stature.  Disease  may  alter  the  form  of  the  curve 
of  growth.  But  the  final  result  seems  to  depend  less  upon  external  condi- 
tions than  upon  race  and  sex.  As  an  interesting  accessor}'  fact  it  was  found 
by  Porter-  that  well-developed  children  take  a  higher  rank  in  school  than-  less- 
developed  children  of  the  same  age.  If  the  percentage  annual  increase  of 
the  total  weight  be  computetl,  it  is  found  to  diminish  throughout  life,  very 
rapidly  during  the  first  two  or  three  years,  later  more  slowly  and  with  minor 
variations  of  increase  and  decrease  ;  that  is,  as  growth  proceeds  and  the  powers 
of  the  individual  mature,  the  power  to  grow  becomes  rapidly  less.  This  is  a 
peculiar  and  most  interesting  fact  and  has  not  been  explained.  It  would  seem 
to  signify  that  the  sum  of  the  vital  powers  declines  from  birth  onward.  Many 
facts  indicate  that  the  common  conception,  dating  from  the  time  of  Aristotle, 
of  human  life  as  consisting  of  the  three  periods  of  rise,  maturity,  and  decline, 
must  give  way  to  a  more  rational  idea  of  a  steady  decline  from  birth. 

'  H.  P.  Bowditch :  Eighth  Annual  Report  of  the  State  Board  of  Health  of  Massachusetts,  1877. 

*  W.  T.  Porter :  "  The  Physical  Basis  of  Precocity  and  Dullness,"  Transactions  of  the  Acad- 
emy of  Science  of  St.  Louis,  vi.,  No.  7,  1S93.  See  also  "The  Growth  of  St.  Louis  Children," 
Transactions  of  the  Academy  of  Science  of  St.  Louis,  vi.,  Xo.  12,  1894. 


REPR  OD  UCTION.  927 

Puberty. — By  puberty  is  meant  tlie  period  of  sexual  maturity,  at  which 
the  individual  becouies  able  to  reproduce.  In  the  male  the  exact  time  of  its 
onset,  characterized  primarily  by  the  appearance  of  fully  ripe  spermatozoa,  is 
not  well  known,  but  is  believed  to  be  about  one  year  later  than  in  the  female. 
In  temperate  climates,  therefore,  it  usually  appears  in  boys  not  before  the  age 
of  fifteen  ;  it  is  earlier  in  warmer  regions.  It  is  preceded  and  accompanied  by 
acceleration  in  bodily  growth,  already  spoken  of.  Other  bodily  changes,  such 
as  general  maturation  of  the  functions  of  the  reproductive  organs,  alterations  in 
the  bodily  proportions,  increase  of  strength,  and  growth  of  the  beard,  all  of  which 
are  elements  of  the  transformation  from  boyhood  to  manhood,  either  occur  at 
that  time  or  follow  soon  after.  One  of  the  most  obvious  external  chang-es  is 
that  of  the  voice.  Its  tone  may  fall  permanently  an  octave,  and  for  the  time  being 
become  rough,  broken,  and  uncontrollable.  This  is  due  to  a  sudden  general 
enlargement  of  the  laryngeal  cartilages  and  a  lengthening  of  the  vocal  cords. 

In  the  girl  the  oncoming  of  puberty  is  marked  more  exactly  than  in  the 
boy  by  the  appearance  of  menstruation,  in  the  majority  of  girls  in  temperate 
climates  at  the  age  of  fourteen  to  seventeen.  But  other  characteristic  anatom- 
ical and  physiological  changes  in  the  body  occur.  The  uterus,  the  external 
reproductive  organs,  and  the  breasts  become  larger,  while  the  ])elvis  wndens. 
The  prepubertal  acceleration  of  growth  has  been  mentioned.  Nervous  disor- 
ders are  especially  prone  to  make  their  appearance  at  this  time.  The  subcuta- 
neous layer  of  adipose  tissue  develops  and  confers  upon  the  outlines  the  grace- 
ful curves  characteristic  of  the  woman's  body.  The  mental  faculties  mature, 
and  the  girl  becomes  a  woman  earlier  and  more  rapidly  than  the  boy  a  man. 

Climacteric. — From  the  sixtieth  year  the  power  of  producing  spermato- 
zoa, and,  therefore,  the  reproductive  power  of  man,  begins  to  wane.  It  con- 
tinues, however,  in  a  diminishing  degree,  even  to  extreme  old  age,  and  there 
is  no  recognized  period  of  ending  of  the  male  sexual  life. 

In  woman,  on  the  other  hand,  the  sexual  period  continues  for  only  thirty 
to  thirty-five  years,  and  the  climacteric,  menopause,  or  change  of  life,  marks  a 
definite  ending  of  the  power  of  reproduction.  In  temperate  climates  it  occurs 
usually  between  the  ages  of  forty-four  and  forty-seven  ;  in  w^armer  regions  it 
comes  early,  in  colder  late.  It  is  earlier  in  the  laboring  classes,  and  later 
where  menstruation  has  first  appeared  early.  Its  most  characteristic  feature  is 
the  cessation  of  menstruation,  which  is  a  gradual  process  extending  over  a 
period  of  two  or  three  years  and  characterized  by  irregularity  in  the  oncoming 
and  the  quantity  of  the  flow  and  by  gradual  diminution.  But  the  cessation 
of  the  menses  is  but  one  phenomenon  in  a  long  series  of  changes  that  pro- 
foundly affect  the  w^hole  organism  and  endanger  life.  The  reproductive  organs 
and  the  breasts  diminish  in  size,  and  ovulation  ceases.  The  changes  in  the 
pelvic  organs  are  in  general  the  reverse  of  those  occurring  at  puberty.  The 
organic  functions  generally  are  rendered  irregular ;  dyspepsia,  palpitation, 
sweating,  and  vasomotor  changes  are  frequent ;  vertigo,  neuralgia,  rheuma- 
tism, and  gout  are  not  rare;  a  tendency  to  obesity  occurs,  though  sometimes 
the  reverse ;  irritability,  fear,  hysteria,  and  melancholia  may  be  present ;  the 


Nucleoli  observ- 

Pigment 

Pigment 

able  in  nuclei. 

much. 

little. 

in  53  per  cent. 

in    5 

67  per  cent. 

33  per  cent. 

928  AN   AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

disposition  may  be  temporarily  altered, — all  of  which  changes  indicate  that 
the  female  organism  at  this  time  suffers  a  profound  nervous  shock.  The  loss 
of  the  weighty  fimction  of  reproduction  and  the  adaptation  to  the  new  order 
of  events  is  not  accoinplisheil  (piietly. 

Senescence. — The  progressive  diminution  in  the  power  of  growth  from 
birth  onward  throughout  life  has  been  mentioned,  and  may  be  interpreted  as 
indicating  that  the  process  of  senescence  begins  with  the  beginning  of  life.' 
Jn  the  broadest  sense  this  is  true,  and  is  confirmed  by  a  study  of  various 
organic  functions.  In  the  more  restricted  sense  senescence  or  old  age  com- 
prises the  period  from  about  fifty  years  (in  woman  from  the  climacteric) 
onward,  during  which  there  is  a  noticeable  progressive  waning  of  the  vital 
powers.  The  leading  somatic  changes  accompanying  old  age  are  atrophic  and 
degenerative,  but  detailed  statistics  of  this  period  arc  almost  wholly  wanting. 
A  marked  cellular  difference  between  the  young  and  the  old,  which  is  shown 
by  nearly  if  not  (piitc  all  tissues,  is  the  relatively  large  nucleus  and  small 
quantity  of  cytoplasm  in  the  young,  the  proportions  being  reversed  in  the  old. 
This  has  recently  been  pointed  out  as  follows  by  Hodge  ^  in  the  nerve-cells  of 
the  first  cervical  spinal  ganglion  : 

Volume  of 
nucleus. 

Fetus  (iit  birtli) 100  per  cent. 

Old  man  (at  ninety-two  years)     64.2     " 

Thus  with  the  progress  of  age  the  nuclei  become  small  and  irregular  in  out- 
line, and  the  cytoplasm  pigmented,  while  the  nucleoli  are  often  wanting.  The 
nuclear  differences  are  even  more  marked  in  the  cerebral  ganglia  of  bees,  where, 
moreover,  aged  individuals  possess  a  smaller  number  of  nervc-cclls  than  the 
young.  They  are  in  harmony  with  the  growing  belief  in  the  function  of  the 
nucleus  as  the  formative  centre  of  the  cell.  It  has  been  shown  that  a  decrease 
in  the  weight  of  the  whole  brain  occurs  in  both  men  and  women,  beginning  in 
the  former  at  about  fifty-five  years,  in  the  latter  at  about  forty-five  years.  In 
eminent  men  the  decrease  begins  later.  The  thickness  of  the  cortex  and  the 
number  of  tangential  fibres  in  it  diminish  especially  after  fifty  years,  and  this 
probably  signifies  a  loss  of  cells.  There  is  a  decrease  in  general  brain-power, 
in  power  of  origination,  in  the  power  to  map  out  new  paths  of  conduction  and 
association  in  the  central  nervous  system  and  thus  to  form  habits.  Reaction- 
time  is  lengthened.  The  delicacy  of  the  sense-organs  is  noticeably  less,  and  in 
the  eye  the  hardening  of  the  crystalline  lens  and  the  weakening  of  the  ciliary 
muscle  diminish  the  power  of  accommodation.  The  muscles  atrophy  and  mus- 
cular .strength  is  reduced.  The  pineal  gland,  ligaments,  tendons,  cartilage,  and 
the  walls  of  the  arteries,  show  a  tendency  toward  calcification,  and  the  bones 
become  more  brittle.  Subcutaneous  adipose  tissue  disappears,  but  a  fatty  de- 
generation of  cells  is  not  uncommon,  notably  in  all  varieties  of  muscle-cells, 
in  nerve-cells,  and  probably  in  gland-cells.     The  pigment  of  the  hairs  disap- 

*  Cy.  C.  S.  Minot:  Journal  of  Physiology,  xii.,  1891. 

"•C-  F.  Hodge:  AruUomischer  Anzeiger,  ix.,  1894;  Journal  of  Physiology,  xvii.,  1894. 


REPRODUCTION.  929 

pears.  The  size  of  the  muscles,  the  liver,  tlie  spleen,  the  Ij'^mphatic  and  prob- 
ably the  (lijjjestive  glands,  decreases.  The  heart  and  the  kidneys  seem  to  retain 
their  adult  size.  The  vital  capacity  of  the  lungs,  the  amounts  of  carbonic  acid 
and  of  urine  excreted,  diminish.  The  rate  of  respiration  and  of  the  heart-beat 
rises  slightly.  Ovulation  is  wanting,  and  the  power  of  producing  spermatozoa 
is  lessened.  The  stature  undergoes  a  slight  and  steady  decrease.  Boas '  has 
shown  that  in  the  North  American  Indian  this  continues  from  about  thirty 
years  of  age  onward.  All  of  these  changes,  the  details  of  which  should  be  care- 
fully studied  and  reduced  to  anatomical  and  physiological  exactness,  demonstrate 
that  senescence  is  characterized  by  a  steady  diminution  of  vitality. 

Death. — Sooner  or  later  vitality  must  cease  and  the  change  that  is  called 
death  must  come.  The  term  "  death  "  is  used  in  two  senses,  according  as  it  is 
applied  to  the  whole  organism  or  to  the  individual  tissues  of  which  the  organ- 
ism is  composed.  The  former  is  distinguished  as  somatic  death,  or  death 
simply,  the  latter  as  the  death  of  the  tissues. 

Somatic  death  occurs  when  one  or  more  of  the  organic  functions  is  so  dis- 
turbed that  the  harmonious  exercise  of  all  the  functions  becomes  impossible. 
Thus,  if  the  brain  receives  a  severe  concussion,  the  co-ordination  of  the  organs 
may  be  interrupted  ;  if  the  respiration  ceases,  the  necessary  oxygen  is  withheld  ; 
if  the  heart  fails,  the  distribution  of  oxygen  and  food  and  the  collection  of 
wastes  come  to  an  end ;  if  the  kidneys  are  diseased,  the  poisonous  urea  is 
retained  within  the  tissues.  A  continuation  of  any  one  of  these  profound 
abnormal  conditions,  which  may  be  brought  about  by  accident  or  disease,  or  a 
simultaneous  occurrence  of  several  slight  disturbances  of  function,  such  as  is 
not  infrequent  in  aged  persons,  may  prevent  the  restoration  of  that  concordance 
among  the  organs  Avithout  which  the  individual  cannot  live.  The  most  con- 
venient and  most  certain  sign  by  which  somatic  death  may  be  recognized  is  the 
absence  of  the  beat  of  the  heart,  and  in  nearly  all  cases  this  is  the  criterion 
employed.  But  it  should  be  borne  in  mind  that  the  failure  of  the  heart  to 
beat  is  but  one  of  the  causes,  and  frequently  a  very  secondary  one,  the  primary 
cause  being  then  associated  with  other  functions,  It  is  at  present  in  most  cases 
quite  impossible  to  trace  the  course  of  events  by  which  the  derangement  of  one 
function  leads  to  the  ultimate  cessation  of  individual  life. 

Death  of  the  tissues  or  of  the  living  substance  is  neither  necessarily  nor 
usually  simultaneous  with  somatic  death.  Constantly  throughout  life  the  mole- 
cules of  living  matter  are  being  disintegrated,  and  whole  cells  die  and  are  cast 
away ;  life  and  death  are  concomitants.  With  the  cessation  of  the  individual 
life  the  nervous  system  dies  almost  immediately.  "With  the  muscular  tissue  it 
is  very  diiferent.  The  stopping  of  the  beat  of  the  heart  is  a  gradual  process, 
and,  as  Harvey  long  ago  pointed  out,  the  last  portion  to  beat,  the  ultimum 
moi'iens,  is  the  right  auricle.  For  many  minutes  after  death  the  heart,  if 
exposed,  will  be  found  to  be  excitable  and  to  respond  by  single  contractions  to 
single  stimuli.  Irritability  is  said  to  continue  in  the  smooth  muscle  of  the 
stomach  and  the  intestines  for  forty-five  minutes,  and  considerably  later  than 

'  F.  Boas :  Verhandlungen  der  Berliner  Anthropologischen  Gesellschaft,  1895. 
59 


930  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

this  the  striated  muscles  of  the  limbs  can  be  made  to  twitch  by  proper  stimuli. 
Gland-cells  probably  die  within  a  few  minutes.  As  to  the  chemical  changes 
undergone  by  the  protoplasm  in  the  process  of  dying,  little  can  be  said.  The 
composition  of  dead  protoplasm  is  comparatively  well  known,  that  of  living 
protoplasm  is  at  present  a  blank  ;  and,  although  investigation  has  gone  suf- 
ficiontly  far  to  offer  a  basis  for  several  suggestive  hypotheses,  the  latter  are  too 
abstru.se  for  lucid  discussion  in  the  present  space.  Neither  in  somatic  death 
nor  in  the  death  of  the  tissues  does  the  body  lose  weight.  Within  fifteen  or 
twenty  hours  it  cools  to  the  temperature  of  the  surrounding  medium.  Rigor 
mortis,  due  to  the  coagulation  of  the  muscle-plasma  within  the  muscle-cells, 
begins  within  a  time  varying  with  the  cause  of  death  from  a  half  hour  to 
twenty  or  thirty  hours,  and  continues  upon  an  average  twenty-four  to  thirty- 
six  hours.     Then  the  tissues  soften,  and  soon  putrefactive  changes  begin. 

Theory  of  Death. — It  has  been  intimated  that  all  the  tissues  are  destined 
to  die.  An  exception  must  be  made  in  the  case  of  those  germ-cells,  both  male 
and  female,  that  arc  employed  in  the  production  of  new  individuals.  They 
pass  from  one  individual,  the  parent,  to  another,  the  offspring,  and  thus  cannot 
be  said  to  undergo  death.  This  .is  the  basis  of  Weismann's  theory  of  the 
orioin  and  sis>;nificance  of  death  in  the  organic  world.*  Accordino-  to  Weis- 
mann,  primitive  protoplasm  was  not  endowed  with  the  property  of  death. 
As  found  in  the  simplest  individuals,  like  the  Amoeba,  even  at  the  present 
day,  Avith  a  continuance  of  the  proper  nutritive  conditions  protoplasm  does  not 
grow  old  and  die;  the  single  individual  divides  into  two  and  life  continues 
unceasing,  unless  accident  or  other  untoward  event  interferes.  With  the 
progress  of  evolution,  however,  the  cells  of  the  individual  body  have  become 
differentiated  into  germ-cells  and  somatic  cells,  the  former  subserving  the 
reproduction  of  the  species,  the  latter  all  the  other  bodily  functions.  Germ- 
cells  are  passed  on  from  parent  to  offspring ;  they  never  die,  they  are  immor- 
tal. Somatic  cells,  on  the  other  hand,  grow  old,  and  at  last  perish.  Death 
was,  therefore,  in  the  beginning,  not  a  necessary  adjunct  to  life ;  it  is  not  inhe- 
rent in  primitive  protoplasm,  but  has  been  acquired  along  with  the  differen- 
tiation of  protoplasm  into  germ-plasm  and  somatoplasm,  and  the  introduction 
of  a  sexual  method  of  reproduction.  It  has  been  acquired  because  it  is  to  the 
advantage  of  the  species  to  possess  it ;  in  the  simplest  cases  it  should  occur  at 
the  close  of  the  reproductive  period,  and  in  fact  it  frequently  does  occur  then. 
A  superabundance  of  aged  individuals,  after  they  have  ceased  to  be  reproduc- 
tive, would  be  detrimental  to  the  race ;  it  is  to  the  advantage  of  the  species  that 
they  be  put  out  of  the  way.  Death  of  the  individual  in  order  that  the  species 
may  survive  has,  therefore,  become  an  established  principle  of  nature.  The 
higher  animals  are  better  able  to  protect  themselves  from  destruction  than  the 
lower,  and,  moreover,  they  are  needed  to  rear  the  young ;  hence  the  duration 
of  life  is  frequently  prolonged  beyond  the  reproductive  period. 

Weismann's  theory  has  been  the  cause  of  much  discussion,  and  the  pros 
and  cons  have  been  set  forth  by  eminent  biological  authorities.  In  its  appli- 
^  A.  Weismann :  Essays  upon  Heredity,  i.,  1889. 


REPRODUCTION.  931 

cation  to  the  human  race  it  would  seem  that  the  factors  of  social  evolution 
have  brought  it  about  that  the  aged  are  protected  in  the  struggle  for  existence 
for  k)ni>-  after  their  reproductive  usefulness  has  ceased,  and  thus  the  working 
of  a  pitiless  biological  law  has  become  modified. 

F.  Heredity. 

Biologists  are  accustomed  to  recognize  two  factors  as  responsible  for  the 
character  and  actions  of  the  living  organism.     These  are  heredity  and  the 
environment.     Heredity  includes  whatever  is  transmitted,  either  as  actual  or 
as  potential  characteristics,  by  parents  to  offspring.     The  environment  com- 
prises both  material  and  immaterial  components,  such  as  food,  water,  air,  or 
other  substances  that  surround  the  organism,  and  the  forces  of  nature,  such  as 
light,  heat,  electricity,  and  gravity,  that  act  as  conditions  of  existence  or  as 
sthnuli  to  action.     The  same  principles  apply  to  the  character  and  actions  of 
every  cell  of  a  many-celled  organism,  but  here  we  must  include  in  the  envi- 
ronniental  factor  the  mysterious  influences  that  are  exerted  upon  the  cell  by 
the  other  cells  of  the  body.     Of  these  two  factors  heredity  acts  from  within, 
the  environment  from  without  the  living 'substance.     Among  unicellular  or- 
ganisms the  individual  begins  its  career  when  the  bit  of  protoplasm  that  con- 
stitutes its  body  is  separated  from  the  parent  bit  of  protoplasm.     Among 
hio-her  forms,  including  man,  the  terra  individual  may  be  applied  to  the  fer- 
tilized ovum ;  the  union  of  the  ovum  and  the  spermatozoon  inaugurates  the 
new  being.     From  the  inception  to  the  death  of  the  individual,  life  consists 
partly  of  manifestations  of  the  powers  conferred  by  the  germ-cells  and  partly 
of  reactions  to  environmental  influences.     In  considering  the  details  of  vital 
action  we  are  apt  to  overlook  these  fundamental  facts  and  to  evolve  narrow 
and  erroneous  views  as  to  the  causes  of  vital  phenomena.     Biologists  are 
seeking  with  increasing  vigor  to  determine  the  relative  importance  of  the  parts 
played  by  these  two  principles  in  development  and  in  daily  life.     It  is  need- 
less to  say  that  the  problem  is  a  difficult  one  and  is  still  far  from  solution. 
In  previous  chapters  of  this  book  attention  has  been  directed  more  especially 
to  the  external  than  to  the  hereditary  factor.     A  work  upon  physiology  would 
be  incomplete,  however,  if  it  did  not  include  an  examination  of  the  latter, 
especially  since  at  the  present  time  heredity  is  one  of  the  leading  subjects  of 
biological  research  and  discussion.     It  is  proposed,  therefore,  in  this  section 
to  present  a  brief  outline  of  the  focts,  the  principles,  and  the  attempted  ex- 
planations of  the  modes  of  working  of  heredity.     It  should  be  premised  that, 
because  of  the  present  incomplete  state  of  our  knowledge  of  the  facts,  the 
highly  speculative  and  involved  character  of  most  of  the  theories,  and  the  con- 
stant, active  shifting  of  ideas  and  points  of  view,  such  an  outline  must  neces- 
sarily be  incomplete  and  in  many  respects  unsatisfactory. 

Facts  of  Inheritance.— It  is  not  proposed  in  this  paragraph  to  enter  into 
a  discussion  of  the  question  as  to  whether  a  particular  vital  phenomenon  is  a 
fact  of  inheritance  or  a  reaction  to  external  influences.  For  our  present  pur- 
poses it  is  sufficient  to  record  the  common  facts  of  resemblance  to  ancestors, 


932  J^V   AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

and  tu  u.s.sume  that  such  re.semblaiRv,  when  present,  has  been  inherited. 
Resemblances  are  strongest  between  child  and  parents,  and  appear  in  a  dimin- 
ishing ratio  backward  aloiii;  the  ancestral  line.  Galton  '  has  comijiited  that, 
of  the  total  heritage  t)t'  the  child,  each  of  the  two  parents  contributes  one- 
fourth,  each  of  the  four  grandparents  one-sixteenth,  and  the  remaining  one- 
fourth  is  handed  down  by  more  remote  ancestors.  The  correctness  of  this 
estimate  has  been  disputed  by  Weismann.  The  fact  must  not  be  overhjoked 
that,  in  addition  to  and  back  ol'  all  the  particular  individual  features  that  are 
inherited,  a  host  of  racial  characteristics  are  transmitted — the  progeny  of  a 
given  species  belongs  to  that  species;  the  human  being  is  the  father  of  the 
human  child,  the  child  of  Caucasian  parents  is  a  Caucasian,  of  negro  parents 
a  negro. 

Congenital  resemblances  may  be  anatomical,  physiological,  or  psychological, 
and  in  each  of  these  classes  they  may  be  normal  or  pathological.  Anatomical 
resemblances  are  the  most  commonly  recognized  of  all :  facial  features,  stature, 
color  of  eyes  and  of  hair,  sujiernumerary  digits,  excessive  hairiness  of  body, 
cleft  palate,  monstrosities,  and  various  defects  of  the  eye,  such  as  tho.se  that 
give  rise  to  hypermetropia,  myopia,  cataract,  color-blindness,  and  strabismus, 
are  all  known  examples.  Physiological  peculiarities  that  may  be  transmitted 
include  the  tendency  to  characteristic  gestures,  locomotion  and  other  muscular 
movements,  longevity  or  short  life,  tendency  to  thinness  or  obesity,  handwriting, 
voice,  hsematophilia  or  tendency  to  profuse  hemorrhage  from  slight  wounds, 
gout,  epilepsv,  and  asthma.  Psychological  inheritances  comprise  habits  of 
mind,  talent,  artistic  and  moral  qualities,  tastes,  traits  of  character,  tempera- 
ment, ambition,  insanity  and  other  mental  diseases,  and  tendencies  to  crime 
and  to  suicide. 

Latent  Characters  ;  Reversion. — Characters  that  never  apjiear  in  the  parent 
mav  yet  be  transmitted  through  him  from  grandparent  to  child  ;  such  charac- 
ters are  called  latent.  Among  the  most  striking  latent  characters  are  those  con- 
nected with  sex.  Darwin  ^  says  :  "  In  every  female  all  the  secondary  male 
characters,  and  in  every  male  all  the  secondary  female  charactei-s,  apparently 
exist  in  a  latent  state,  ready  to  be  evolved  under  certain  conditions."  Thus,  a 
girl  may  inherit  female  secondary  sexual  peculiarities  of  her  paternal  grand- 
mother that  are  latent  in  her  father,  or  a  boy  may  inherit  from  his  maternal 
grandfather  characteristics  that  never  show  in  his  mother.  An  excellent 
example  of  such  transmission,  taken  from  the  herbivora,  is  the  common  one 
of  a  bull  conveying  to  his  female  descendants  the  good  milking  qualities  of 
his  female  ancestors.  In  the  human  species  hydrocele,  necessarily  a  disease  of 
the  male,  has  been  known  to  be  inherited  from  the  maternal  grandfather,  and 
hence  must  have  been  latent  in  the  mother's  organism.  That  in  such  cases  the 
character  is  really  potential,  though  latent  in  the  intermediate  ancestor,  is 
rendered  probable  by  such  well-known  facts  as  the  appearance  of  female  cha- 

'  Francis  Galton  :  Xatund  Inheritnnce,  1889,  p.  134. 

-  Charles  Darwin:  The  Variation  of  Animals  and  Plants  under  Domeaticntinn,  vol.  ii..  2<\  ed., 
1892. 


BEPR  OD  UCriON.  9-^^ 

rac'teristics  in  castrated  niaks,  tiiul  of  inalo  clmractoristics  in  females  with  dis- 
eased ovaries  or  after  the  end  of  the  normal  sexual  life. 

Latency   may  be  offered   as  the   explanation   of  the   numerous    eases    of 
atavism,  or  reversion,  by  whieh  is  meant  the  appearance  in  an   individual  of 
peculiarities  that  were  formerly   known  only  in  the  grandparents  or    more 
remote  ancestors,  but  not  in  the  parents  of  the  individual.     This  subject  is  one 
of  the  most  important  in  the  whole  field  of  heredity.     Almost  any  character 
may  reappear  even  after  many  generations.     In  the  human  species  stronger 
likeness   to   grandparents   than    to   parents   is   a   frequent   occurrence.     The 
majority  of  the  frequent  anomalies  of  the  dissecting-room  arc  regarded  as 
reversions  toward  the  simian  ancestors  of  the  human  race.     The  crossing  of 
two  strains  develops  a  strong  tendency  to  reversion,  and  because  of  this  the  prin- 
ciple of  atavism  must  constantly  be  taken  into  account  by  breeders  of  animals 
and   o-rowers  of  plants.     As   an  example  of  reversion  after  crossing  may  be 
mentioned  the  well-known  one,  studied  by  Darwin,  of  the  frequent  appear- 
ance of  marked  stripes  upon  the  legs  of  the  .mule,  the  mule  being  a  hybrid 
from  the  horse  and  the  ass,  both  of  which  are  comparatively  unstriped  but 
are  undoubtedly   descended  from  a  striped   zebra-like   ancestor.     Here   the 
capacitv  of  developing  stripes  is  regarded  as  latent  in  both  the  horse  and  the 
ass,  but  as  made  evident  in  the  mule  by  the  mysterious  influence  of  crossing. 
Darwin  thinks  likewise  that  the  customary  degraded  state  of  half-castes  may 
be  due  to  reversion  to  a  primitive  savage  condition  which,  usually  latent  in 
both  civilized  and  savage  races,  is  rendered  manifest  in  the  offspring  that 
results  from  the  union  of  the  two.     Reversionary  characters  are  often  more 
prominent  during  youth  than  during  later  life — a  fact  that  has  been  quoted  in 
favor  of  their  explanation  on  the  theory  of  latency. 

Regeneration. — The  facts  of  regeneration  of  lost  parts  must  also  be  taken 
into  account  in  a  theory  of  heredity.  Such  regeneration  may  be  either  physi- 
ological or  pathological.  Physiological  or  normal  regeneration  has  reference 
to  the  reproduction  of  parts  that  takes  place  during  the  normal  life  of  the 
individual,  such  as  the  constant  growth  of  the  deeper  layers  of  the  epidermis 
to  replace  the  outer  layers  that  are  as  constantly  being  shed.  Pathological 
regeneration  refers  to  the  replacement  of  parts  lost  by  accident,  and  presents 
the  more  interesting  and  striking  examples.  The  power  of  pathological 
regeneration  in  man  and  the  higher  mammals  is  limited.  A  denuded  surface 
raav  be  re-covered  with  epitliclium  ;  the  central  end  of  a  cut  nerve  may  grow 
anew  to  its  termination ;  the  parts  of  a  broken  bone  may  reunite ;  muscle  may 
reappear ;  connective-tissue,  blood-corpuscles,  and  blood-vessels  may  develop 
readilv ;  and  in  the  healing  of  every  wound  a  regeneration  of  parts  takes 
place.  But  in  descending  the  scale  of  animal  life  the  regenerative  power 
becomes  progressively  stronger,  and  in  many  plants  and  low  animals  it  is 
marvellous.  Thus,  the  newt  may  replace  a  lost  leg,  the  crab  a  lost  claw,  the 
snail  an  eyestalk  and  eye.  If  an  earth-worm  be  cut  in  two,  one  half  may 
regenerate  a  new  half,  complete  in  all  respects.  A  hydra  may  be  chopped 
into  fragments  and  each  fragment  may  re-grow  into  a  complete  hydra.     From 


934  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

a  small  piece  of  the  leaf  of  a  begonia,  planted  in  moist  earth,  a  new  plant 
with  all  its  parts  may  arise.  It  is  evident  that  the  existing  parts  of  an  organ- 
ism, if  not  too  specialized,  possess  the  power  of  restoring  parts  that  are  lost ; 
nnder  ordinary  circnmstances  this  power  is  latent.  The  growth  of  tumors  is 
perhaps  allied  in  nature  to  regeneration.  A  study  of  regeneration  shows  that 
in  many  cases  the  process  of  building  anew  follows  the  same  course  as  the 
original  embryonic  growth.     It  is  properly  a  phenomenon  of  heredity. 

The  Inheritance  of  Acquired  Characters. — No  topic  in  heredity  has  been 
more  debated  during  the  past  fifteen  years  than  that  of  the  possibility  of  the 
transmission  to  the  offspring  of  characteristics  that  are  acquired  by  the  parents 
previous  to  the  discharge  of  the  germ-cells,  or,  in  the  case  of  the  mammalian 
female,  previous  to  parturition.  Obviously,  no  one  denies  this  possibility  in 
the  unicellular  organisms,  where  reproduction  by  fission  prevails,  for  there  the 
protoplasm  of  the  body  of  one  parent  becomes  the  substance  of  two  offspring ; 
in  the  transformation  nothing  is  lost,  and  hence  whatever  peculiarities  the  ances- 
tral protoplasm  has  acquired  are  transferred  bodily  to  the  descendants.  But 
in  multicellular  forms,  where  sexual  reproduction  exists,  the  case  is  very  dif- 
ferent, for  here  whatever  is  transmitted  is  transmitted  through  germinal  cells, 
or  germ-plami,  as  the  hereditary  substance  contained  in  the  germ-cells  is  now 
commonly  called.  The  problem  then  resolves  itself  into  that  of  the  relation 
of  the  germ-plasm  to  the  protoplasm  of  the  rest  of  the  body,  the  so-called 
somatoplasm;  and  the  question  to  be  answered  is  this:  Are  variations  in  the 
parental  somatoplasm  capable  of  inducing  such  changes  in  the  germ-plasm  that 
somatic  peculiarities  appear  in  the  offspring  similar  to  those  possessed  by  the 
parent?  Weismann  classifies  all  somatic  variations  according  to  their  origin 
into  three  groups — viz.  injuries,  functional  variations,  and  variations,  mainly 
climatic,  that  depend  upon  the  environment.  The  problem  of  their  inherit- 
ance is  a  far-reaching  one,  and  upon  its  correct  solution  depend  principles  that 
are  of  much  wider  application  than  simply  to  matters  of  heredity ;  for  if 
acquired  characters  can  be  inherited,  there  is  revealed  to  us  a  most  potent  fac- 
tor in  the  transformation  of  species,  and  the  whole  question  of  the  possibility 
of  use  and  disuse  as  factors  of  evolution  is  presented.  The  larger  evolutionary 
problem  need  not  here  be  considered. 

Regarding  the  problem  of  the  inheritance  of  acquired  characteristics  we  may 
say  at  once  that  it  is  not  yet  solved.  To  the  lay  mind  this  may  seem  strange, 
for  at  first  thought  it  appears  self-evident  that  parents  may  transmit  to  their 
children  peculiarities  that  they  themselves  have  acquired.  Affirmative  evidence 
seems  all  about  us,  as  witness  the  undoubted  cases  of  inheritance  of  artistic 
tastes,  of  talent,  of  traits  valual)le  in  professional  life,  which  seem  to  originate 
in  the  industry  of  the  parent.  But  scientific  analysis  by  Weismann  and  others 
of  popular  impressions,  popular  anecdotes,  and  hearsay  evidence,  and  accurate 
original  observation  have  revealed  little  that  cannot  as  well  be  explained  on 
other  hypotheses.  Anatomical  and  functional  peculiarities  of  the  body  that  are 
apparently  new  often  reappear  in  successive  generations,  but  to  assume  that 
they  are  acquired  by  the  somatoplasm  and  have  become  congenital,  rather  than 


REPRODUCTION.  935 

that  they  are  geriuiiuil  Iroin  the;  fast,  is  unwarranted.  Direct  experiments  by 
various  investigators  are  ahnost  as  inconclusive.  Weismann  '  has  removed  the 
tails  of  white  mice  for  five  successive  generations,  and  yet  of  901  young  every 
individual  was  born  with  a  tail  normal  in  length  and  in  other  respects.  Bos^ 
has  experimented  similarly  upon  rats  for  ten  generations  without  observing  any 
diminution  of  the  tails.  The  practice  of  circumcision  for  centuries  has  resulted 
in  no  reduction  of  the  prepuce.  The  binding  of  the  feet  of  Chinese  girls  has 
not  resulted  in  any  congenital  malformation  of  the  Chinese  foot.  Brown- 
S6quard,^  and  later  Obersteiner/  have  artificially  produced  epilepsy  in  guinea- 
pigs  by  various  operations  upon  the  central  nervous  system  and  the  peripheral 
nerves,  and  the  offspring  of  such  parents  have  been  epileptic.  At  first  this 
would  seem  to  amount  to  proof  of  the  actual  hereditary  transmission  of  mutila- 
tions, yet  in  these  cases  the  mutilation  itself  was  not  transmitted  ;  the  offspring 
were  weak  and  sickly  and  exhibited  a  variety  of  abnormal  nervous  and  nutri- 
tional symptoms,  among  which  was  a  tendency  toward  epileptiform  convulsions, 
the  cause  of  which  is  still  to  be  explained.  Evidence  from  palaeontology 
regarding  the  apparent  gradual  accumulation  of  the  effects  of  use  and  disuse 
throughout  a  long-continued  animal  series  seems  to  require  the  assumption  of 
such  a  principle  as  the  inheritance  of  acquired  characters,  but  even  here  the 
principle  of  natural  selection  may  perhaps  be  equally  explanatory. 

The  Inheritance  of  Diseases. — The  question  of  the  inheritance  of  diseases 
has  also  been  much  discussed.  The  same  general  principles  apply  here  as  in 
the  inheritance  of  normal  characteristics.  The  fact  has  been  mentioned  above 
that  pathological  characters,  whether  anatomical,  physiological,  or  psycholog- 
ical, are  capable  of  transmission.  If,  however,  a  pathological  character  has 
been  acquired  by  the  parent  and  is  not  inherent  in  his  own  germ-cells,  it 
is  extremely  doubtful  whether  it  can  be  passed  on  to  the  child.  A  diseased 
parent,  on  the  other  hand,  may  produce  offspring  that  are  constitutionally 
weak  or  that  are  even  predisposed  toward  the  parental  disease,  and  such  off"- 
spring  may  develop  the  parent's  ailment.  In  such  cases  constitutional  weakness 
or  predisposition,  and  not  actual  disease,  is  inherited ;  the  disease  itself  later 
attacks  the  weak  or  predisposed  body.  Proneness  to  mildness  or  severity  of, 
and  immunity  toward,  certain  diseases  seem  to  be  transmissible.  These  sub- 
jects, however,  are  so  little  understood,  and  the  real  meaning  of  such  terms  as 
predisposition,  inherited  constitutional  weakness,  and  inherited  immunity,  is  so 
little  known,  that  it  is  idle  to  discuss  them  here. 

Considerable  experimental  work  has  been  performed  recently  upon  the 
transmissibility  of  infectious  diseases.  Undoubtedly  infectious  diseases  cling 
to  a  particular  family  for  generations.  The  transmitted  factor  is  probably  fre- 
quently, if  not  usually,  simple  predisposition.  But  in  an  increasing  number 
of  cases  there  appears  to  be  transmission  of  a  specific  micro-organism.     Such 

*  A.  Weismann :  Essays  upon  Heredity,  vol.  i.,  1889,  p.  432. 
^  .J.  E.  Bos :  Biologisches  Ceniralblatt,  xi.,  1891,  p.  734. 

'  E.  Brown-S^quard  :  Researches  on  Epilepsy,  etc.,  Boston,  1857  ;  also  various  later  papers. 

*  H.  Obersteiner :  Medizinische  Jahrbikher,  Wien,  1875,  p.  179. 


936  .l.V   AMERICAN    TEXT- HOOK    OF   PllYSIOLOGY. 

transmission  is  called  germbud  when  the  niiero-organisui  is  conveyed  in  the 
ovum  or  the  semen,  and  placental  or  intra-uterine  when  the  micro-organism 
reaches  the  fetns  after  nterinc  development  has  begnn,  and  chieHy  throngh  the 
circulation.  Of  germinal  infections  syphilis  seems  undoubtedly  caj)able  of 
transmission  within  either  the  ovum  or  the  semen.  The  possibility  of  germinal 
transmission  of  tuberculosis  has  been  maintained,  but  is  not  fully  proven.  Of 
intni-nterine  infections  there  have  been  observed  in  human  beings  apj)arently 
undoubted  cases  of  typhoid  fever,  relapsing  fever,  scarlatina,  small-pox, 
measles,  croupous  pneumonia,  anthrax,  and  possibly  tuberculosis,  syphilis,  and 
Asiatic  cholera.  It  is  obvious  that  neither  germinal  nor  placental  iidieritance, 
both  taking  place  through  the  medium  of  a  specific  mi(;rt)-organism,  and  not 
through  the  modification  of  germ-plasm,  is  comparable  to  inheritance  in  the 
customary  sense. 

Theories  of  Inheritance. — From  early  historical  times  theories  of  inher- 
itance have  iiot  been  wanting.  Physical  and  metaphysical,  materialistic  and 
spiritualistic  theories  have  had  their  day.  Previous  to  the  discovery  of  the 
spermatozoon  (Hamm,  Leeuwenhoek,  1677)  all  theories  were  necessarily 
fantastic,  and  for  nearly  two  hundred  years  later  they  were  crude.  The 
theories  that  are  now  rife  may  be  said  to  date  from  1864,  when  Herbert 
Spencer  published  his  Principles  of  Biology.  Since  that  date  they  have 
become  numerous.  Even  the  modern  theories  are  highly  speculative  ;  none 
can  be  regarded  as  being  accepted  to  the  exclusion  of  all  others  by  a  large 
majority  of  scientific  workers,  and  the  excuse  for  introducing  them  into  a 
text-book  of  physiology  is  the  hope  that  a  brief  discussion  of  them  may  jjrove 
suggestive,  stimuhiting,  and  productive  of  investigation. 

Germ-plasm. —  Germinal  substance,  germ-plasm  (Weismann),  or,  as  it  is 
sometimes  called,  idioplasm  (Nageli),  must  lie  at  the  basis  of  all  scientific 
theories  of  heredity.  The  father  and  the  mother  contribute  to  the  child  the 
spermatozoon  and  the  ovum  respectively,  and  within  these  two  bits  of  proto- 
plasm there  must  be  contained  potentially  the  qualities  of  the  two  parents. 
There  is  much  evidence  in  favor  of  the  prevailing  view  that  the  nucleus  alone 
of  each  germ-cell  is  essentially  hereditary,  or,  more  exactly,  that  the  chromatic 
substance  of  the  nucleus  is  the  sole  actual  germinal  substance.  We  have  seen 
that  the  tail  of  the  spermatozoon  is  a  locomotive  organ,  and  that  the  body  of 
the  ovum  is  nutritive  matter.  We  have  seen  also  that  the  essence  of  the 
whole  process  of  fertilization  is  a  fusion  of  the  male  and  the  female  nuclei,  or, 
more  exactlv,  a  mingling  of  male  and  female  chromosomes.  Hence  most 
physiologists  agree  with  Stra,sburger  and  Hertwig  that  the  chromatic  substance 
of  the  nuclei  of  the  germ-cells  transmits  the  hereditary  qualities. 

As  to  the  origin  of  the  germ-plasm,  two  hypotheses  have  been  suggested. 
Spencer,  Darwin,  Galton,  and  Brooks  have  argued  in  favor  of  a  production 
of  germ-plasm  within  each  individual  by  a  collocation  within  the  reproductive 
organs  of  minute  elementary  vital  particles — "  physiological  units  "  (Spencer), 
"gemmules"  (Darwin) — that  come  from  all  parts  of  the  body;  hence  each 
part  of  the  body  has  its  representative  within  every  germ-cell.    This  hypothesis 


REPRODUCTION.  937 

affords  a  rciuly  ox})laiuiti()n  of  miiiRToiis  facts,  but  its  highly  speculative  cha- 
racter, the  entire  absence  of  direct  observational  or  experimental  ])roof  of  its 
tnitli,  and  the  demand  that  its  conception  makes  upon  human  credulity,  mili- 
tate against  its  general  acceptance.  Weisnaann,  the  j)romulgator  of  the  second 
hypothesis,  denies  altogether  tlie  formation  of  the  germ-plasm  from  the  body- 
tissues  of  the  individual,  and  maintains  its  sole  origin  from  the  germ-plasm  of 
the  parent  of  the  individual.  Through  the  ])arent  it  comes  from  the  grand- 
parent, thence  from  the  great-grandparent,  and  so  may  be  traced  backward 
through  families  and  tribes  and  races  to  its  origin  in  simple  unicellular 
oro-anisms.  According  to  Weismann,  therefore,  germ-plasm  is  very  ancient 
and  is  directly  continuous  from  one  individual  to  another;  the  parts  of  an 
individual  body  are  derivatives  of  it,  but  they  do  not  return  to  it  tlieir  rei)re- 
sentatives  in  the  form  of  minute  particles.  The  general  truth  of  Weismann's 
conception  can  hardly  be  denied. 

As  to  the  morphological  nature  of  germ-plasm,  two  views  likewise  are  held. 
One  school,  led  by  His  and  Weismann,  holds  that  germ-plasm  ])ossesses  a 
complicated  architecture;  that  the  fertilized  ovum  contains  within  its  structure 
the  rudiments  or  primary  constituents  of  the  various  cells,  tissues,  and  organs 
of  which  the  body  is  destined  to  be  composed ;  and  that  growth  is  a  develop- 
ment of  these  already  existing  germs  and  largely  independent  of  surrounding 
influences.  In  accordance  with  this  idea,  segmentation  of  the  ovum  is  specifi- 
<3allv  a  qualitative  process,  one  blastomere  representing  one  portion  of  the 
future  adult,  another  blastomere  another  portion,  and  so  on.  This  theory 
recalls  in  a  refined  form  the  crude  theory  of  Preformation  that  was  advocated 
during  the  seventeenth  and  eighteenth  centuries  by  Haller,  Botmet,  and  many 
others,  according  to  which  the  germ-cell  was  believed  to  contain  a  minute  but 
perfectly  formed  model  of  the  adult,  which  needed  only  to  be  enlarged  and 
unfolded  in  growth.  The  other  modern  school,  in  which  Oscar  Hertwig  is 
prominent,  maintains  that  the  fertilized  e^g  is  isotropous — that  is,  that  one 
part  is  essentially  like  another  part — that  the  architecture  of  the  egg  is  rela- 
tively simple,  and  that  growth  is  largely  a  reaction  of  the  living  substance  to 
external  influences.  The  idea  of  isotropy  is  based  largely  upon  the  experi- 
mental results  of  Pfluger,  Chabry,  Driesch,  Wilson,  Boveri,  and  the  brotliers 
Hertwig,  who  by  various  methods  and  in  various  animals  have  found  that 
single  blastomeres  of  a  segmenting  ovum,  when  separated  from  the  others,  will 
develop  into  normal  but  dwarfed  larvse  ;  that  is,  a  portion  of  the  original  germ- 
plasm  is  capable  of  giving  rise  to  all  parts  of  the  animal.  These  results  are 
interpreted  to  signify  that  segmentation,  instead  of  being  qualitative,  is  quanti- 
tative, each  blastomere  being  like  all  the  others.  The  second  theory,  like  the 
first,  resembles  in  some  degree  a  theory  of  the  past  two  centuries,  advocated 
by  Wolff  and  Harvey,  and  known  as  the  theory  of  Epigenesis.  According  to 
this  there  was  no  preformation  in  the  germ-cells,  but  rather  a  lack  of  organi- 
zation which  during  growth,  under  guidance  of  a  mysterious  power  supposed 
to  be  resident  in  the  living  substance,  gave  place  to  differentiation  and  the 
appearance  of  definite  parts. 


938  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

Modern  microscopes  have  revealed  no  miniature  of  the  adult  in  the  egg, 
nor  has  modern  physiology  found  necessary  an  assumption  of  extra-physical 
forces  within  living  matter.  With  the  increase  of  knowledge  the  old  and 
crude  preformation  of  Haller  and  Bonnet  and  the  speculative  epigenesis  of 
"Wolff  and  Harvey  have  given  ])lace  to  the  new  preformation  and  epigenesis 
of  the  present  time,  and  all  modern  theories  of  heredity  may  be  classed  in 
the  one  or  the  other  category  or  as  intermediate  between  them.  The  mod- 
ern advocates  of  preformation  explain  hereditary  resemblance  by  the  supposed 
similarity  of  all  germ-plasm  in  any  one  line  of  descent.  The  modern  advocates 
of  epigenesis,  while  allowing  the  necessity  of  a  material  basis  of  germ-plasm, 
ascribe  hereditary  resemblance  to  similarity  of  environment  during  develop- 
ment. 

Variation. — It  is  a  commonplace  in  observation  that,  however  close  hereditary 
resemblance  may  be,  it  is  never  absolute ;  the  child  is  never  the  exact  image 
of  the  parent  either  physically  or  mentally.  Variations  from  the  parental  type 
may  be  either  acquired  by  the  offspring  subsequent  to  fertilization  or  to  birth, 
and  hence  are  to  be  traced  to  the  action  of  the  environment ;  or  they  may  be 
congenital,  that  is,  inherent  in  the  germ-plasm.  Although  it  is  not  always 
easy  in  the  case  of  any  one  variation  to  determine  to  which  class  it  belongs, 
yet  the  fact  remains  that  the  two  classes  exist ;  and  a  complete  theory  of 
heredity  must  recognize  and  explain  congenital  variation  as  fully  as  congenital 
resemblance.  It  is  unnecessary  to  say  that  the  origin  of  congenital  variation 
is  one  of  the  much  discussed  and  still  unsettled  questions.  At  least  two  causes 
of  congenital  variations  are  commonly  recognized,  although  opinions  differ  as 
to  the  relative  importance  of  the  role  played  by  each.  These  causes  are  differ- 
ences in  the  nutrition  of  the  germ-plasm,  and  sexual  reproduction.  As  to  the 
former,  it  is  evident  that  the  germ-plasm  in  no  tAvo  individuals,  even  father 
and  son,  has  exactly  identical  nutritional  opportunities.  Since  the  life  of  one 
individual  is  not  the  exact  counterpart  of  the  life  of  another,  the  germ-plasm 
of  one  individual  has  a  different  nutrition  from  that  of  another.  It  would 
hence  be  strange,  even  although  we  regard  the  germ-plasm  as  relatively  stable, 
if  with  succeeding  generations  there  did  not  appear  variations  that  are  sufficient 
to  give  rise  to  unlikeness  in  relatives.  Differences  in  the  nutrition  of  the  germ- 
plasm  in  different  individuals  are,  therefore,  a  true  cause  of  variations.  As 
regards  sexual  reproduction,  it  must  be  remembered  that  a  new  individual  is 
the  product  of  two  individuals,  that  the  two  individuals  have  descended  along 
different  genealogical  lines,  and  hence  that  the  two  conjugating  masses  of  germ- 
plasm  are  different  in  nature.  It  is  only  to  be  expected,  therefore,  that  the 
resulting  individual  shall  be  different  from  the  two  contributing  parents.  Thus 
sexual  reproduction  is  a  true  cause  of  variations. 

Having  outlined  the  main  facts  and  principles  of  heredity,  let  us  now  review 
a  few  of  the  specific  theories  that  have  been  of  value  in  clearing  the  clouded 
atmosphere. 

Darwin's  Theory  of  Pangenesis. — Darwin's  "  Provisional  Hypothesis  of 
Pangenesis"  was  published  in  1868  as  chapter  xxvii.  of  his  work  on  The  Vari- 


REPRODUCTION.  939 

ations  of  Animals  and  Plants  under  Domestication.  It  was  the  first  of  the 
modern  theories  to  attempt  to  cover  the  whole  ground  of  heredity ;  it  was 
accompanied  by  a  most  exhaustive  presentation  and  analysis  of  facts,  and  it 
stimulated  abundant  discussion  and  investij^ation.  In  Darwin's  own  words 
the  hypothesis  was  formulated  as  follows  :  "  It  is  universally  admitted  that  the 
cells  or  units  of  the  body  increase  by  cell-division  or  proliferation,  retaining 
the  same  nature,  and  that  they  ultimately  become  converted  into  the  various 
tissues  and  substances  of  the  body.  But  besides  this  means  of  increase  I  assume 
that  the  units  [cells]  throw  off  minute  granules  which  are  dispersed  throughout 
the  whole  system  ;  that  these,  when  supplied  with  proper  nutriment,  multiply 
by  self-division,  and  are  ultimately  developed  into  units  like  those  from  which 
they  were  originally  derived.  These  granules  may  be  called  gemmules.  They 
are  collected  from  all  parts  of  the  system  to  constitute  the  sexual  elements,  and 
their  developnient  in  the  next  generation  forms  a  new  being ;  but  they  are 
likewise  capable  of  transmission  in  a  dormant  state  to  future  generations,  and 
may  then  be  developed.  Their  development  depends  on  their  union  with  other 
partially  developed  or  nascent  cells  which  precede  them  in  the  regular  course 

of  growth Gemmules  are  supposed  to  be  thrown  off  by  every  unit, 

not  only  during  the  adult  state,  but  during  each  stage  of  development  of 
every  organism ;  but  not  necessarily  during  the  continued  existence  of  the 
same  unit.  Lastly,  I  assume  that  the  gemmules  in  their  dormant  state  have  a 
mutual  affinity  for  each  other,  leading  to  their  aggregation  into  buds  or  into 
the  sexual  elements.  Hence,  it  is  not  the  reproductive  organs  or  buds  which 
generate  new  organisms,  but  the  units  of  which  each  individual  is  composed. 
These  assumptions  constitute  the  provisional  hypothesis  which  I  have  called 
Pangenesis." 

Since  the  cells  of  the  body  are  represented  by  gemmules  within  the  germ- 
cells,  Darwin's  theory  is  a  theory  of  Preformation.  It  explains  the  facts  of 
the  regeneration  of  lost  parts  by  the  assumption  that  the  gemmules  of  the  part 
in  question  are  disseminated  throughout  the  body  and  have  only  to  unite  with 
the  nascent  cells  at  the  point  of  new  growth.  Pangenesis  explains  reversion, 
since  gemmules  may  lie  dormant  in  one  generation  and  develop  in  the  next. 
It  explains  congenital  variation,  since  the  mixture  of  maternal  and  paternal 
gemmules  is  plainly  different  from  the  two  kinds  taken  separately.  It  explains 
how  acquired  variations  may  become  congenital,  since  an  altered  part  throws 
off  altered  gemmules,  and  by  the  collocation  of  these  in  the  germ-cells  the 
alteration  may  be  transmitted.  It  thus  allows  the  transmission  of  acquired 
characters. 

Darwin's  assumptions  of  gemmules  and  their  behavior  are  pure  assump- 
tions, for  which  subsequent  investigation  has  not  provided  a  basis  of  facts. 
As  we  have  seen,  also,  the  inheritance  of  acquired  characters  is  greatly  in 
doubt,  and,  if  they  are  heritable  at  all,  they  can  be  so  only  comparatively 
feebly.  Besides  these  objections  it  was  early  found  that,  w'ith  the  increase 
of  knowledge  of  the  facts  of  heredity,  it  was  necessary  to  modify  very  mate- 
rially the  theory  of  Pangenesis.     This  has  been  ably  done  successively  by 


940  AN  AMERICAN    TEXT- BOOK   OF  PHYSIOLOGY. 

G:ilt(»n,'   Brooks,^  and  de    Vrios.^     But   neither   the   ()ri<;iiial    theory   nor   its 
nioditiciitions  have  been  generally  aceej)ted. 

Weismann's  Theory. — Since  1880,  Professor  Weismann*of  Freiburg  has 
published  numerous  essays  upon  heredity  and  allied  subjects,  in  which,  besides 
reviewing  the  views  of  others,  he  has  developed  in  detail  a  new  and  elaborate 
theory  of  his  own,  that  is  the  most  ambitious  attempt  yet  made  to  solve  the 
problem  of  inheritance.  In  the  course  of  their  development  Wcismann's 
ideas  have  undergone  some  modification.  Their  leading  features  are  as 
follows : 

The  essential  hereditary  substance,  or  germ-plasm,  is  the  chromatin  of  the 
luicleus  of  the  germ-cells.  One  of  the  fundamental  tenets  of  Wcismann's 
system  is  expressed  by  his  own  phrase,  "the  continuity  of  germ-plasm."  By 
this  is  meant  that  the  germ-plasm  of  one  individual,  instead  of  arising  de  novo 
in  the  individual  by  the  collocation  of  multitudinous  "gcmmules"  derived 
from  the  body-cells,  originates  directly  from  the  germ-plasm  of  the  parent, 
thence  from  that  of  the  grandparent,  and  so  oji  backward  through  all  genera- 
tions to  the  origin  of  all  germ-])lasms  that  took  place  simultaneously  with  the 
origin  of  sex — germ-plasm  is  continuous  from  individual  to  individual  along 
any  one  line  of  descent.  Weismann  draws  u  sharp  line  between  germ-plasm 
and  Hoiiiatoplasm,  or  body-plasm,  which  latter  comprises  all  protoplasm  that 
the  body  contains  except  the  germ-plasm.  Germ-plasm  once  originated  con- 
tinues from  generation  to  generation  ;  somatoplasm  develops  anew  in  each  gen- 
eration from  germ-plasm  by  growth  and  differentiation,  resulting  in  a  loss  of  its 
specific  germinal  character.  Germ-plasm  is  stable  in  composition  ;  somatoplasm 
is  variable.  Germ-plasm,  being  passed  on  from  parent  to  offspring,  is  immortal ; 
somatoplasm  dies  when  the  individual  dies.  Weismann  believes  that  "the 
germ-plasm  ]iossesses  a  fixed  architecture,  which  has  been  transmitted  histori- 
callv  "  and  which  represents  the  parts  of  the  future  organism.  It  consists  of 
material  particles  or  hereditary  units  called  determinants,  each  of  which  has  a 
definite  localized  position  within  the  germ-plasm.  The  determinants  are  sug- 
gestive of  Darwin's  gemmules,  yet  they  arc  not  the  same,  for,  while  gcmmules 
were  supposed  to  represent  individual  cells,  determinants  are  representatives 
of  cells  or  groups  of  cells  that  are  variable  from  the  germ  onward.  Deter- 
minants consist  of  definite  combinations  of  simpler  units,  or  biophors,  which 
are  the  smallest  particles  that  can  exhibit  vital  phenomena.  Below  biophors 
there  come  in  order  of  simplicity  of  material  structure  the  molecules  and 
the  atoms  of  the  physicist.  Above  biophors  and  determinants  Weismann 
finds  it  necessary  to  assume  the  existence  of  higher  units,  named  in  order  ?V/.s' 
and  idants,  the  former  being  groups  of  determinants,  and  actually  visible  as 
granules  of  chromatin,  the  latter  being  the  chromosomes  of  the  nucleus.    Each 

'  Francis  (xalton:  "A  Theory  of  Heredity,"  Journal  of  the  Anthropological  Inxtttiite,  1875. 

2  W.  K.  Brooks:   Tlie  X«w'«  of  Heredity,  1883. 

'  H.  de  Vries:  Die  Intro celluldre  Pangenesis,  1889. 

*  August  Weismann:  Essays  upon  Heredity  and  Kindred  Biological  Problems,  authorized 
translation,  vol.  i.,  1889;  vol.  ii.,  1892;  The  Germ-plasm,  authorized  translation,  1893;  Tlie 
Effect  of  External  Influences  upon  Development,  the  Konianes  Lecture,  1894. 


REPRODUCTION.  941 

one  of  these  various  units  is  possessed  of  the  fundamental  vital  properties  of 
growth  and   uuiltiplieation  by  division.     Such  a  complex  system  is  Preforma- 
tion in  an  extreme  form.     In  fertilization  idants  of  the  sperm  join  with  idauts 
of  the  ovum,  and  the  resulting  segmentation  nucleus  consists  of  a  mixture  of 
paternal  and  maternal  determinants.      Within  this  mixture  there  exist  in  a 
potential   state  the   primary  constituents  of  a   considerable  number  of  forms 
wiiich   the  future   individual   may  assume.     In  ontogeny,  or  development  of 
the  individual,  these  primary  constituents  take  two  paths:  some  of  the  ids 
remain  inactive  and  enter  the  germ-cells  of  the  embryo  for  the  production  of 
future  generations ;  otiier  ids  disintegrate  into  determinants,  the  determinants 
enter  the  embryonic  cells  that  result  from  segmentation,  and  there  themselves 
disintegrate  and  set  free  into  the  cytoplasm  their  constituent  biophors ;  thus 
they  determine  the  future  character  of  the  cells  of  the  organism.     Tiie  division 
of  primary  constituents  into  those  that  shall  remain  latent  and  those  tliat  siiall 
become  active  is  effected  largely  by  the  stimulation  of  external  influences ; 
hence,   given  several   potential  formations  in  the  germ,   external   influences 
decide  which  one  shall  become  the  actual   structure  in  the  adult  organism. 
Once  set  free  and  having  become  somatoplasm,  neither  the  biophors  nor  the 
determinants  are  able  to  return  to  the  germ-cells.     In  the  adult,  germ-plasm  is 
never  capable  of  reflecting  in  any  way  the  characteristics  of  the  somatoplasm 
which  surrounds  it  on  all  sides.     With  its  ancient  ancestry  it  leads  a  charmed 
existence,   largely   independent    of   environmental   changes.     It   follows  that 
characters  acquired  by  the  adult  are  incapable  of  acquisition  by  the  germ- 
plasm,  and  hence  may  not  be  transmitted.     The  non-inhet^itance  of  acquived 
characters  is  thus  another  of  the  fundamental  tenets  of  Weismann's  theory, 
and  one  about  which  he  is  most  positive. 

If  these  two  principles  of  continuity  of  stable  germ-plasm  and  non-inheri- 
tance of  acquired  characters  be  true,  why  are  not  all  individuals  in  any  one 
line  of  descent  exactly  like  each  other?  Ho\v  is  congenital  variation  possible? 
In  the  first  place,  Weismann  allows  that  germ-plasm,  while  eminently  stable, 
is  not  absolutely  so ;  it  is  subject  to  slight  continual  changes  of  composition 
resulting  from  inequalities  in  nutrition  ;  and  "  these  very  minute  fluctuations, 
which  are  imperceptible  to  us,  are  the  primary  cause  of  the  greater  deviations 
in  the  determinants  which  we  finally  observe  in  the  form  of  individual  varia- 
tions." The  accumulation  of  minute  deviations  may  be  aided  greatly  by  sex- 
ual reproduction,  or,  to  use  Weismann's  more  exact  term,  which  is  equally 
applicable  to  the  combination  of  sexual  elements  in  sexual  organisms  and  to 
the  process  of  conjugation  in  the  asexual  forms,  amphimixis.  Given  the  in- 
finitesimal beginning  of  a  variation,  the  mingling  of  two  lines  of  descent,  with 
different  past  surroundings,  may  be  a  most  powerful  factor  in  strengthening 
the  deviation  and  bringing  it  into  recognition  as  a  new  character.  Moreover, 
natural  selection  becomes  here  also  potent  as  soon  as  the  variation  has  assumed 
sufficient  proportions  to  be  seized  upon  by  this  important  factor  of  evolution. 
In  cases  of  reversion  Weismann  supposes  the  determinants  to  remain  inactive 
in  the  germ-plasm  for  one  or  more  generations  and  later  to  develop.     The 


942  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

tlieorv  accounts  fur  tlic  regeneration  of  lost  parts  by  the  assunij)tion  that  the 
colls  in  the  vicinity  of  the  wound,  by  the  proliferation  of  which  the  new  })art 
grows,  contain,  besides  tlie  active  determinants  that  have  given  them  their 
specific  character,  other  determinants  that  are  latent  until  the  o])portunity  for 
regeneration  arrives.  Some  cells  do  not  possess  such  latent  determinants,  and 
hence  some  parts  of  a  body  are  incapable  of  reproducing  lost  parts. 

Such  are  the  main  features  of  Weismann's  theory — a  germ-plasm  of  highly 
complex  architecture  and  independent  of  somatoplasm  ;  continuity  of  germ- 
j)lasm  and  non-inheritance  of  acquired  somatic  characters  tending  to  preserve 
the  uniformity  of  the  species ;  slight  nutritional  variation  of  germ-plasm  and 
sexual  reproduction  tending  to  destroy  that  uniformity ;  the  result  is  inherited 
resemblance  and  congenital  variation.  The  theory  is  now  being  most  actively 
discussed. 

Theory  of  Epigcnesis. — Among  epigenesists  no  one  theory  may  be  said  to 
be  pre-eminent.  The  main  features  of  the  epigenetic  conception,  already 
referred  to,  may  be  summarized  as  follows :  The  fertilized  ovum  is  isotropous, 
i.  e.  all  parts  are  essentially  alike;  germ-plasm  probably  consists  of  minute 
particles,  but  these  particles  do  not  represent  definite  cells  or  groups  of  cells 
of  the  adult;  segmentation  is  a  quantitative  process;  the  early  blastomeres 
are  essentially  alike,  and  any  one  of  them,  if  isolated  from  the  rest,  may 
give  rise  to  a  whole  organism,  although  under  ordinary  circumstances  they 
react  upon  each  other  in  bringing  about  the  resultant  individual ;  there  is 
no  predetermination,  either  in  the  germ-cells  or  in  the  segmenting  ovum, 
of  the  ultimate  form  or  function  of  the  various  constituent  parts ;  morpho- 
logical differentiation  and  physiological  specialization  are  phenomena  of 
comparatively  late  embryonic  life,  and  the  prospective  character  of  any  one 
cell,  wiiether  it  is  to  be  a  muscle-cell,  gland-cell,  nerve-cell,  or  germ-cell,  is 
determined  by  the  influence  of  the  surrounding  cells  and  the  surrounding 
physical  and  chemical  conditions — "  the  prospective  character  of  each  cell  is  a 
function  of  its  location."  Extreme  epigenetic  views  are  not  so  numerous  as 
those  of  preformation.' 

The  more  moderate  thinkers  of  the  present  time  recognize  truth  in  both 
preformation  and  epigcnesis,  and  are  endeavoring  l)y  cx})ori  mental  methods  to 
determine  how  much  share  in  the  production  of  the  characteristics  of  the  off- 
spring is  to  be  ascribed  to  the  original  qualities  of  the  germ-plasm  and  how 
much  to  the  physical,  chemical,  and  physiological  phenomena  of  the  immediate 
environment  of  the  developing  embryo.  Such  experimental  work  is  per- 
formed at  present  upon  the  simpler  and  lower  animals,  mostly  marine  inverte- 
brates, and  has  reference  to  the  effect  of  changes  in  the  composition  of  the  water 
surrounding  the  embryo,  the  effects  of  various  salts,  of  changes  in  temperature, 
of  pressure,  of  electricity,  etc.,  etc.  Such  work  is  now  in  its  infancy,  but  it  is 
doubtless  destined  to  yield  results  of  the  highest  value  in  an  understanding  of 
the  true  nature  of  horodity. 

*  The  best  statement  of  a  moderate  epigenetic  theory  is  to  be  found  in  Zcil-  unci  Streiifragen 
der  Biologic :  I.  Pr&Jorvmtion  oder  Epigcnesis  f    O.  Hertwig,  1894. 


XIV.  THE  CHEMISTRY  OF  THE  ANIMAL  BODY. 


Introduction. — T^iving  matter  contain.s  hydrogen,  oxygen,  sulphur,  clilo- 
rine,  Huorine,  nitrogen,  phosphorus,  carbon,  siHcon,  potassium,  sodium,  calcium, 
magnesium,  and  iron.  Abstraction  of  one  of  these  elements  means  death  to 
the  organization.  The  compounds  occurring  in  living  matter  may  for  the 
most  part  be  isolated  in  the  laboratory,  but  they  do  not  then  exhibit  the  prop- 
erties of  animate  matter.  In  the  living  cell  the  smallest  particles  of  matter 
are  arranged  in  such  a  manner  that  the  phenomena  of  life  are  possible.  Such 
an  arrangement  of  materials  is  called  protoplmm,  and  anything  which  disturbs 
this  arrangement  results  in  sickness  or  in  death.  Somatic  death  may  result 
from  physical  shock  to  the  cell ;  or  it  may  be  due  to  the  inability  of  the  cell  or 
the  organism  to  remove  from  itself  poisonous  products  which  are  retained  in 
the  body  so  affecting  the  smallest  particles  that  functional  activity  is  impossible. 
Pure  chemistry  adds  much  to  our  knowledge  of  phy.siology,  but  it  mu.st  alw^ays 
be  remembered  that  the  conditions  present  in  the  beaker  glass  are  not  the  con- 
ditions present  in  the  living  cell,  physical  and  chemical  results  being  dependent 
on  surrounding  conditions  ;  hence  the  necessity  and  value  of  animal  experimen- 
tation. From  chemical  changes,  the  physical  activities,  i.  e.  the  motions  cha- 
racteristic of  life,  result.  Hence  the  chemistry  of  protoplasm  is  the  corner-stone 
of  biology.  The  plan  of  this  section  is  designed  to  consider  the  substances 
concerned  in  life  in  the  order  usually  followed  by  chemical  text-books. 

The  Non-metallic  Elements. 
Hydrogen,  H  =  1. 

This  gas  is  found  as  a  constant  product  of  the  putrefaction  of  animal 
matter,  and  is  therefore  present  in  the  intestinal  tract.  It  is  found  in  the 
expired  air  of  the  rabbit  and  other  herbivorous  animals,  and  in  traces  in  the  ex- 
pired air  of  carnivorous  animals,  having  first  been  absorbed  by  the  blood  from 
the  intestinal  tract.  By  far  the  greater  amount  of  hydrogen  in  the  animal 
and  vegetable  worlds,  as  well  as  in  the  world  at  large,  occurs  combined  in  the 
form  of  water,  and  it  will  be  shown  that  the  proteids,  carbohydrates,  and  fats, 
characteristic  of  the  organism,  all  contain  hydrogen  originally  derived  from 
water.  In  the  atmosphere  is  found  ammonia  in  traces,  which  holds  hydrogen 
in  combination,  and  this  is  a  second  source  of  hydrogen,  especially  for  the  con- 
struction of  the  proteid  molecule. 

Preparation. — (1)  Through  the  electrolysis  of  water,  by  which  one  volume 

943 


it44  .l.V   AMERICAX    TEXT- BOOK    OP   PHYSIOLOGY. 

of  oxvnren  is  evolved  on  the  })ositive  pole  and  two  volumes  of"  liydrogeu  on  the- 
Degative. 

(2)  Throiigli  the  aetion  of  zinc  on  sulphuric  acid/ 

Zn  +  H^SO,  -  ZnSO,  +  Hj. 

(3)  Throuixh  putrefaction  (hy  which  is  understood  the  change  effected  in- 
organic matter  through  certain  lower  organisms,  bacterid)  hydrogen  is  liberated 
in  tlie  intestinal  canal  from  proteid  matter,  and  especially  from  the  fermenta- 
tion of  carbohydrates : 

CeH.  A  =  QHA  +  2CO,  +  2H,. 

Sugar.         Butyric  acid. 

In  putrefaction  in  the  presence  of  oxygen  the  hydrogen  formed  immediately 
unites  with  oxygen,  producing  \vater ;  hence,  notwithstanding  the  enormous 
amount  of  putreiaction  in  the  world,  there  is  no  accumulation  of  hydrogei> 
in  the  atmosphere. 

Both  bacteria  and  an  enzyme  can  liberate  hydrogen  by  acting  on  calcium  formate, 
Ca  (CHO.,)^  -:-  H.,0  =  CaCOs  +  CO,  -  2H„ 
and  this  same  reaction  may  be  brought  about  by  the  action  of  metallic  iridium,  rhodium,, 
or  ruthenium  on  formic  acid.  An  enzyme  is  a  substance  probably  of  proteid  nature  capa- 
ble of  producing  change  in  other  substances  without  itself  undergoing  apparent  change 
(example,  pepsin).  Bunge  *  calls  attention  to  the  fact  that  the  above  reaction  may  be  brought 
about  by  living  cells  (bacteria),  by  an  organic  substance  (enz>Tne).  and  by  an  inorganic 
metal.  Tiiis  similarity  of  action  between  organized  and  unorganized  material,  between 
living  and  dead  substances,  is  shown  more  and  more  conspicuously  as  science  advances. 

Properties. — Hydrogen  burns  in  the  air,  forming  water,  and  if  two  volumes 
of  hydrogen  and  one  of  oxygen  be  ignited,  they  unite  with  a  loud  explosion. 
Hydrogen  will  not  support  respiration,  but,  mixed  with  oxygen,  may  be 
respired,  probably  being  dissolved  in  the  fluids  of  the  body  as  an  inert  gas^ 
without  effect  u|)on  the  organism.  Hydrogen  may  jmss  through  the  intes- 
tinal tissues  into  the  blood-vessels,  according  to  the  laws  of  diffusion,  in  ex- 
change for  some  other  gas,  and  may  then  be  given  off  in  the  lungs.  Xascent 
hydrogen — that  is  to  say,  hydrogen  at  the  moment  of  generation — is  a  powerful 
reducing  agent,  uniting  readily  with  oxygen  (see  p.  952). 

Oxygen,  O  =  16. 
Oxygen  is  found  free  in  the  atmosphere  to  the  amount  of  al)out  21  per 
cent,  bv  volume,  and  is  found  dissolved  in  water  and  chemically  combined  in 
arterial  blood.  It  is  swallowed  with  the  food  and  may  be  present  in  the  stom- 
ach, but  it  entirely  disappears  in  the  intestinal  canal,  being  absorbed  by  respir- 
atory exchange  through  the  mucous  membrane.  It  occurs  chemically  com- 
bined with  metals  so  that  it  forms  one-half  the  weight  of  the  earth's  crust ; 
it  likewise  occurs  combined  in  water  and  in  mo.st  of  the  materials  forming 
animal  and  vegetable  organisms.     It  is  found  in  the  blood   in   loo.se  chemical 

1  It  is  not  within  the  scope  of  this  work  to  give  more  than  typical  metho(is  of  hihoratory 
preparation.     For  greater  detail  the  reader  is  referred  to  works  on  genenil  chemistry. 
»  Physiologische  Chemie,  2d  ed.,  1889,  p.  167. 


THE    CHEMISTRY    OF    THE   ANIMAL    liODY.  945 

coiubiuatiun  as  oxylitcinoglobin.  It  is  present  dissolved  in  the  saliva,  so  great 
is  the  amount  of  o.\y«2;en  furnished  by  the  blood  to  the  salivary  gland ;  it 
is,  however,   not   found    in   the  urine  or   in  the  bile, 

l\rp<tr<ttlt)ii. — (I)  Thruujih  the  elcctrnlysis  of  wuter  (sec  Hydrogen). 

(2)  IJy  lieutiiig  auuigiiiicse  dioxide  with  sulijhuric  iicid, 

2MnO,  +  H,SO,  =  2M11SO4  +  211,0  +  0,. 

(3)  By  licatiiig  potassium  chlorate, 

2KC10,  =  2KCl+30,. 

(4)  By  the  aetion  of  a  vacuum,  or  an  atmosphere  containing  no  oxygen,  on 
a  solution  of  oxyhsemoglobin, 

Hb-O^^Hb  +  O^. 

This  latter  is  the  method  occurring  in  the  higher  animals.  Any  oxygen  present 
in  a  cell  in  the  body  combines  with  the  decomposition  products  formed  there, 
consequently  entailing  in  such  a  cell  an  oxygen  vcwtium,  which  now  acts  upon 
the  oxyhaemoglobin  of  the  blood-corpuscles  in  an  adjacent  capillary,  dissociating 
it  into  oxvgen  and  haemoglobin. 

(5)  By  the  action  of  sunlight  on  the  leaf  of  the  plant,  transforming  the 
carbonic  oxide  and  water  of  the  air  into  sugar,  and  setting  oxygen  free, 

6CO2  +  6H2O  =  CgHiA  +  6O2. 

Properties. — All  the  elements  except  fluorine  unite  with  oxygen,  and  the 
products  are  known  as  oxides,  the  process  being  called  oxidation.  It  is  usually 
accompanied  by  the  evolution  of  energy  in  the  form  of  heat,  and  often  the 
energy  liberated  is  sufficiently  great  to  cause  the  production  of  light.  The 
light  of  a  candle  comes  from  vibrating  particles  of  carbon  in  the  flame,  which 
particles  collect  as  lampblack  on  a  cold  plate.  In  pure  oxygen  combustion  is 
more  violent  than  in  the  air;  thus,  iron  burns  brilliantly  in  pure  oxygen,  while 
in  damp  air  it  is  only  very  slowly  converted  into  oxide  (rust).  This  latter 
process  is  called  slow  combustion,  and  animal  metabolism  is  in  the  nature  of  a 
slow  combustion.  In  the  burning  candle  has  been  noted  the  liberation  of  heat, 
and  motion  of  the  smallest  particles  :  in  the  cell  there  is  likewise  oxidation,  with 
dependent  liberation  of  heat  and  motion  of  the  smallest  particles  in  virtue  of 
which  the  cell  is  active.  Phenomena  of  life  are  phenomena  of  motion,  and 
the  energy  supplying  this  motion  comes  from  chemical  decomposition.  The 
amount  of  oxidation  in  the  animal  is  not  increased  in  an  atmosphere  of  pure 
oxygen,  nor,  wathin  wide  limits,  is  it  affected  by  variations  in  atmospheric 
pressure,  for  oxygen  is  not  the  cause  of  decomposition.  In  putrefaction  it  is 
known  that  bacteria  cause  decomposition,  and  the  products  subsequently  unite 
with  oxygen.  But  the  cause  of  the  decomposition  in  the  cell  remains  unsolved, 
it  being  only  known  that  the  decomposition-products  after  being  formed  unite 
with  oxygen.  So  the  quantity  of  oxygen  absorbed  by  the  body  depends  on  the 
decomposition  going  on,  not  the  decomposition  on  the  absorption  of  oxygen. 
This  distinction  is  fundamental  (see  further  under  Ozone  and  Peroxide  of 
Hydrogen). 

60 


946  AX  AMJ:UJrAX    TEXT-BOOK    OF  PHYSIOLOGY. 

By  reduction  in  its  sim])lost  sense  is  meant  the  removal  of  oxv<;en  wholly 
or  in  })art  from  the  molecule.  Example :  reduced  h;emo<^lobin  from  oxy- 
hremoglobin,  iron  from  oxide  of  iron  (FegOs)-  Reduction  may  likewise  be 
accomplished  hy  simj)le  addition  of  hydrogen  to  the  molecule,  or  by  the  sub- 
stitution of  hydrogen  for  oxygen.  These  two  processes  may  be  represented 
respectively  by  the  reactions  : 

CiyilO    +H2    =CH3CH/)H. 

Ktliyl  iil.U'hyde.  Ktlivl  alc^)liol. 

CH.Ci )( )H  +  2II2  =  C'HgCH/)!!  +  HgO. 

Acetic  acid.  Ethyl  alcohol. 

Ozone,  O.j. — Ozone  is  a  second  form  of  oxygen  possessing  more  active  oxi- 
dizing properties  than  common  oxygen.  It  is  found  in  neighborhoods  where 
large  quantities  of  w^ater  evaporate,  and  after  a  thunder-storm. 

Preparation. — (1)  An  induction  current  in  an  oxygen  atmospliere  breaks  up  some  of 
the  molecules  jjresent  into  atoms  of  nascent  or  "active"  oxygen  — 0 — ,  the  powerful 
affinities  of   whose  free  bonds  enter  into  combination  with  oxj'gen,   0  =  0  to  form 

O 
ozone,    /^\^ 

(2)  Through  the  slow  oxidation  of  phosphorus, 

P.,  I   3IL0  -r  20,  =  2H3PO3  +  (-0-). 

(-0-)  +  0,  =  03. 

(3)  On  the  positive  pole  in  the  electrolysis  of  water. 

In  each  of  the  above  eases  ozone  is  formed  by  the  action  of  nascent  oxygen  on  oxj'gcn. 

Properties. — Ozone  is  a  colorless  gas,  hardly  soluble  in  water,  and  having 
the  peculiar  smell  noted  in  the  air  after  thunder-storms.  Ozone  has  powerful 
oxidizing  properties  due  to  its  third  unstable  atom  of  oxygen,  oxidizing  silver, 
which  oxygen  of  itself  does  not.  But  ozone  is  not  as  oxidizing  as  nascent  or 
"active"  oxygen,  which  may  convert  carbon  monoxide  into  dioxide,  and 
nitrogen  into  nitrous  acid.  Ozone  cannot  occur  in  the  cell,  as  any  nascent 
oxygen  formed  would  naturally  unite  not  with  oxygen,  but  with  the  more 
readily  oxidizable  materials  of  the  cell  itself.  Ozone  acts  on  an  alcoholic  solu- 
tion of  guaiacum,  turning  it  blue ;  blood-corpuscles  give  the  same  reaction 
with  guaiacum,  hence  it  was  thought  that  haemoglobin  converted  oxygen  into 
ozone.  However,  this  test  is  not  a  test  for  ozone,  but  for  "  active "  atomic 
oxygen,  which  is  produced  from  the  ozone  and  in  the  decomposing  yood-cor- 
puscle  (see  theory  of  Traube  below,  and  that  of  Ho}>pe-Seyler  under  Peroxide 
of  Hydrogen).     Ozone  converts  oxyhsemoglobin  into  metha^moglobin. 

Theory  of  Traube  ctf^  to  the  Cause  of  O.vidation  in  the  Bodi/. — Indigo-blue 
dissolved  in  a  sugar-solution  gives  np  oxygen  in  the  atomic  state  for  the  oxida- 
tion of  sugar,  and  the  solution  becomes  white.  If  shaken  in  the  air  the  blue 
coloration  reappears,  owing  to  the  absorption  of  oxygen  by  the  indigo.  Hence 
indigo  has  the  power  of  splitting  oxygen  into  atoms,  and  acts  as  an  "oxygen- 
carrier"  between  the  air  and  the  sugar.  Traube  is  of  the  opinion  that  an 
"  oxygen-carrier  "  exists  in  the  blood-corpuscles.  Sugar  is  destroyed  by  stand- 
ing in  fresh  defibrinated  blood  ;  scrum  alone  does  not  effect  this,  nor  does  a 
solution  of  oxyhsemoglobin,  but  it  may  take  place  in  the  extract  obtained  by 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  947 

the  action  of  a  0.6  per  cent,  sodiiiiii-cliloi-ide  solution  on  blood-corpuscles.' 
The  action  here  has  been  described  as  that  of  ca/a/y.s/.s,  that  is,  an  action  in 
Avhich  some  substance  effects  decomposition  in  another  substance  without  per- 
manent change  in  itself.  In  this  case  the  substance  in  the  blood-corpuscle, 
whatever  it  may  be,  is  defined  as  an  "oxygen-carrier,"  tjdving  molectilcs  of 
oxygen  from  oxyhaemoglobin  and  giving  atomic  oxygen  for  the  oxidation  of 
the  sugar. 

01(1  turpentine  is  highly  oxidizing.  Tills  action  was  once  believed  to  be  due  to  absorbed 
ozone.  If  old  turpentine  be  mixed  with  water  and  filtered,  the  aqueous  extract  has  the 
same  properties,  due  to  the  fact  that  an  oxidized  product  which  is  soluble  in  water,  gives 
off',  under  favorable  conditions,  atomic  oxj'gen.* 

Di'tirtnut. — Moist  strips  of  filter-paper  soaked  in  starch-paste  containing  potassium 
iodide  turn  blue  when  exposed  to  the  action  of  ozone,  due  to  the  liberation  of  free  iodine, 
which  colors  the  starch  : 

2KT  +  H.,0  +  03  =  2K0II  +  0,  +  21. 
This  liberation  of  iodine  is  likewise  accomplished  by  chlorine,  bromine,  some  nitrous  oxides, 
and  peroxide  of  hydrogen." 

Water,  HoO. — Water  is  found  on  the  earth  in  large  quantities,  and  its 
vapor  is  a  constant  constituent  of  the  atmosj)here.  It  is  a  product  of  the 
combustion  of  animal  matter,  and  occurs  in  expired  air  almost  to  the  point  of 
saturation.  It  is  furthermore  given  off  by  the  kidneys  and  by  the  skin.  It 
is  a  necessary  constituent  of  a  living  cell,  and  forms  67.6  per  cent,  of  the 
weight  of  the  human  body  (Moleschott).  Removal  of  5  to  6  per  cent,  of 
water  from  the  body,  as  for  example  in  cholera,  causes  the  blood  to  become 
very  viscid  and  to  flow  slowly,  no  urine  is  excreted,  the  nerves  become  excess- 
ively irritable,  and  violent  convulsions  result.'^ 

Pveparatim. — (1)  By  passing  an  electric  spark  through  a  mixture  of  one  volume  of 
oxj'gen  and  two  volumes  of  hydrogen. 

(2)  By  the  combustion  of  a  food — as,  for  example, 

C^HiA  +  120  =  6CO,  +  6H2O. 

Sugar. 
(3)  Distilled  loater  is  made  in  quantity  by  boiling  ordinary  water  and  condensing  the 
vapors  formed  in  another  vessel. 

Properties. — Water  is  an  odorless,  tasteless  fluid  of  neutral  reaction,  colorless 
in  small  quantities,  but  bluish  when  seen  in  large  masses.  It  is  a  bad  conductor 
of  heat  and  electricity.  It  conducts  electricity  better  when  it  contains  salts. 
It  is  nearly  non-compressible  and  non-expansible;  thus  in  plant-life,  through 
evaporation  on  the  surface  of  the  leaf,  sap  is  continuously  attracted  from  the 
roots  of  the  tree.  The  solvent  properties  of  Avater  give  to  the  blood  many  of 
its  uses,  soluble  foods  being  carried  to  the  tissues  and  soluble  products  of 
decomposition  to   the   proper  organs  for  elimination. 

When  water  is  absorbed  by  any  substance  the  process  is  called  hydration, 
as  an  example  of  which   may  be  cited  the  change  of  calcium  oxide  into 

1  Read  W.  Spitzer :  PJluger's  Arckiv,  1895,  Bd.  60,  p.  307. 

'^  N.  Kowalewsky:  Centralblatt  filr  die  medicinische  Wissenschaft,  1889,  p.  113, 

'  C.  Voit:  Hermann's  Handbuch,  1881,  Bd.  vi.,  1,  p.  349. 


948  ^l.Y  AMERICAN    TEXT-BOOK    OF    rilVSIOLOGY. 

liydroxide  when  thrown  into  water.  When  a  substance  breaks  down  into 
simpler  bodies  throiigli  absorption  of  water  the  process  is  called  In/droli/fii.s  or 
hifdrolytlc  cleavaf/e.  Thus  caiu'-siigar  may  take  up  water  and  be  roolvcd  into 
a  mixture  of  dextrose  and  levnlose,  which  are  called  c/cardf/c-prodKcts.  80, 
likewise,  starch  and  proteid  are  resolved  into  series  of  simpler  b(;dies  through 
hydrolytic  cleavage — changes  which  take  place  in  intestinal  digestion.  All 
forms  of  fermentation  and  puticfaction  are  (jharacterizcd  i)y  hydrolysis  (exam- 
ples, p.  94-1),  and  hence  complete  drying  prevents  such  j)roccsse.s.  Alcoholic, 
butyric,  and  lactic  fermentatiou  are  apparent  though  not  real  exceptions  to  the 
above.  Alcoholic  fermentation,  for  example,  is  usually  represented  by  tin? 
reaction,  (.'6^1,206  =  202115011  +  200,,  but  the  CO2  is  in  fact  united  Mith 
water,  and  hence  the  true  reaction  should  read, 

CgHiaOg  +  2H2O  =  2C2H5OH  +  2112003. 

Sugar.  Alcohol. 

Driiikincj-watcr  contains  salts  and  air  dissolved,  giving  it  an  agreeable  taste. 
One  does  not  willingly  take  distilled  water  on  account  of  its  tastelessness. 
Drinking  large  quantities  of  water  produces  a  slight  increa.se  in  the  decom- 
position of  proteid  in  the  body. 

Dry  animal  membranes  and  cells  aksorb  water  in  quantities  varj'ing  with  the  concentra- 
tion and  the  quality  of  salts  in  the  solution  in  wliicli  they  are  suspended  (Liebig).  This  is 
called  imbibition.  Membranes  will  absorb  a  solution  of  potassium  salts  in  greater  quantity 
than  of  sodium  salts,  and  so  the  potassium  salts  are  found  predominating  in  the  cells,  the 
sodium  salts  in  the  fluids  of  the  body.  A  blood-corpuscle  treated  with  distilled  water 
swells  because  it  can  hold  more  distilled  water  than  it  can  salt-containing  ])lasma.  A  cor- 
puscle i)laceil  in  a  ().f>5  percent,  solution  of  sodium  chloride  (the  ])hysiological  salt-solution) 
remains  unchanged,  for  this  corresponds  in  concentration  to  the  plasma  of  the  blood.  If 
the  cor])Uscle  be  placed  in  a  strong  solution  of  a  salt  it  shrivels,  because  it  cannot  hold  as 
much  of  that  solution  as  it  can  one  having  the  strength  of  the  salts  of  the  i^lasma.  Oysters 
are  often  planted  at  the  mouths  of  fresh-water  rivers,  since  they  imbibe  more  of  the  weaker 
solution  and  appear  fatter.  If  salt  be  ])laccd  on  meat  and  left  to  itself  a  brine  is  formed 
around  the  meat,  not  on  account  of  the  hygroscopic  projicrties  of  the  salt,  but  because 
salt  penetrates  the  tissues,  which  can  then  hold  less  water  than  they  could  before,  and 
so  water  is  forced  out  from  the  meat. 

Different  bodies  require  different  quantities  of  heat  to  warm  them  to  the  same  extent. 
The  amount  of  heat  required  to  raise  the  temperature  of  water  is  greater  than  that  for  any 
other  substance.  A  caloric  or  heat-unit  is  the  amount  of  heat  required  to  raise  1  cubic 
centimeter  of  water  from  0°  to  1°  C.  The  specific  heat  of  the  human  body— that  is,  the 
amount  of  heat  required  to  raise  I  gram  1°  C— is  about  0.8  that  of  water.  On  the  trans- 
formation of  a  substance  from  the  solid  to  the  liquid  state,  a  certain  amount  of  heat  is 
absorbed,  known  as  latent  heat.  To  melt  1  gram  of  ice  producing  J  gram  of  water  at  0°. 
7'.»  calories  are  required,  or  sufficient  to  raise  1  gram  of  water  from  0°  to  79°.  Upon  the 
basis  of  these  facts  a  determination  may  Ije  made  by  means  of  the  icc-cnloriineter  of  tlie 
number  of  heat-units  produced  in  the  combustion.  For  exami)le,  1  gram  of  sugar  (dex- 
trose) burned  in  an  ice-chamber,  melts  49. S6  grams  of  ice.  Since  each  gram  required 
79  calories  to  melt  it,  3939  calories  must  have  been  produced  altogether.  If  1  gram  of 
sugar  be  burned  in  the  body,  the  heat  produced  is  identically  the  same,  and  may  be  meas- 
ured with  great  accuracy.' 

In  the  transformation  of  water  at  100°  to  steam  at  100°  there  is  a  further  absorption  of 

'  M.  Kubner:  Zeilschrift  fur  Bioloyk,  1893,  Bd.  30,  p.  73. 


THE    CHEMISTRY   OF    THE    AXIMAL    BODY.  049 

heat,  tlio  huont  lioat  of  stoaiii.  For  I  jrraiii  ol' water  this  alisorptiuii  amounts  to  536.5 
cjilories.  Tliis  projierty  of  water  is  of  jrreat  vahie  to  life,  lor  through  tlie  heat  al)Sorbed  in 
the  evaporation  of  sweat  the  tenijierature  of  the  body  is  in  part  ref,'ulated. 

Peroxide  of  Hydrogen,  ll20^,  is  found  in  very  small  quantities  in  the  air, 
in  rain,  f^now,  and  sleet,  and  where  there  is  oxidation  of  organic  matter. 
rrcjutnifioii. — (!)  By  the  action  ol'  sulphurie  acid  on  peroxide  of  barium, 
BaO,  i   II, SO,       BaSO«+II,(),. 

(2)  Peroxide  of  hyfh'ogen  is  a  product  of  the  oxidation  of  phosplionis,  and  L^'iierally 
exists  wherever  ozone  is  produced. 

(3)  Peroxide  of  hydrogen  exists  wlierevcr  nascent  hydrogen  acts  on  oxygen. 
It  is  therefore  found  mixed  with  hydrogen  evolved  at  the  negative  pole  in  the 
electrolysis  of  water.  This  action  happens  in  putrefaction,  where  the  na.scent 
hydrogen  unites  with  any  oxygen  pi-esent,  and  the  residting  H.JO^  strongly 
oxidizes  the  organic  matter  through  the  free  — O —  atom  liberated.' 

Properties. — Peroxide  of  hy(h"ogen  is  a  colorless,  odorless,  bitter-tasting 
fluid,  which  decomposes  slowly  at  20°  F.,  and  with  great  violence  at  higher 
temperatures.  It  oxidizes  where  ordinary  oxygen  is  ineffective  ;  it  is  a  powerful 
bleaching  agent,  and  is  used  to  produce  blonde  hair.  It  destroys  bacteria.  Bk)od- 
corpnscles  brought  into  a  solution  of  H^02  bring  about  its  ra})id  decomposition 
into  water  and  atomic  oxygeji,  whereby  oxygen  is  evolved  and  oxyhaeinoglobin 
is  converted  into  methfemoglobin.  If  oxyhsemoglobiu  be  brought  into  a 
putrefying  fluid,  the  nascent  hydrogen  withdraws  oxygen  from  combination 
to  form  HgOo,  and  then  the  atomic  oxygen  reacts  on  haemoglobin  to  form 
methaemoglobin.^  The  formula  for  the  peroxide  is  probably  H — O — O — H. 
In  certain  cases  peroxide  of  hydrogen  has  a  reducing  action. 

Tlieori/  of  Hoppe-Seykr^  to  account  for  the  Oxidation  in  the  Body. — This 
maintains  that,  as  in  putrefaction,  hydrogen  is  produced  in  the  decomposition 
of  the  cell,  and  acting  on  the  oxygen  present  converts  it  into  peroxide  with 
its  unstable  atom,  which  then  splits  off  as  active  oxygen  and  effects  the  oxida- 
tion of  the  substances  in  the  cell.  This  theory  is  easier  to  reconcile  with  the 
fact  that  oxidation  is  dependent  on  the  amount  of  decomposition  (see  p.  945) 
than  is  the  theory  of  Traube. 

Detection. — Solutions  of  H2O2  do  not  liberate  iodine  from  ])otassium  iodide  imme- 
diately, but  only  on  the  addition  of  blood-corpuscles  or  of  ferrous  sujpliate,  which  cause 
liberation  of  — 0 — ,  and  then  any  starch  present  may  be  colored  blue  (see  p.  947). 
Guaiacum  is  not  affected  by  H.^O,  unless  blood-corpuscles  or  ferrous  sulphate  be  added 
which  make  the  oxygen  active. 

Sulphur,  S  =  32. 

Sulphur  is  built  in  the  proteid  molecide  of  the  plant  from  the  sulphates 
taken  from  the  grotnid.  It  is  found  in  albuminoids,  especially  in  keratin.  As 
taurin  it  occurs  in  muscle  and  in  bile,  as  iron  and  alkaline  sulphide  in  the 

^  Hoppe-Seyler  :  Zeilscfirift  fiir  physioloyiscfie  Chemie,  1878,  Bd.  2,  p.  22. 
^  Hoppe-Seyler,  Op.  cit.,  p.  26. 

■*  Pfl'dger's  Arctiiv,  Bd.  12,  p.  16,  1876.  See  also  Bericfite  der  deutsctien  chanisctien  Geselhctiafty 
Bd.  22,  p.  2215. 


950  AiY  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

feces,  as  sulphuretted  liydrogcn  iu  the  intestiual  gas,  as  sulphate  and  other 
unknown  compounds  in  the  urine. 

Detection. — If  a  sulphur  compound  be  fused  with  sodium  carbonate  on  charcoal,  the 
sulphur  will  be  reduced  to  sodium  sulphide.  The  melted  mass  if  placed  with  a  drop  of 
water  on  a  silver  coin  leaves  a  black  spot  of  silver  sulphide. 

Sulphuretted  Hydrogen,  H.,^. — This  gas  is  found  iu  the  intestines,  and 

pathologically  in  the  urine. 

Preparation. — (1)  Action  of   hydrochloric  or   sulphuric   acid  on  ferrous 

sulphide, 

^  FeS  +  H2SO,  =  FeSO,  +  H.S. 

This  same  reaction  takes  place  by  treating  feces  (which  contain  FeSj  M'ith  acid. 

(2)  From  the  putrefaction  of  proteids,  and  by  boiling  proteid  with  mineral 
acid. 

Proijerties. — Sulphuretted  hydrogen  unites  readily  with  the  alkalies  and 
with  iron  salts,  forming  sulphide ;  hence  little  HgS  is  found  in  the  intestinal 
tract.  It  is  a  strong  poison  when  respired.  It  has  been  shown  in  frogs  to 
enter  into  combination  with  oxyhsemoglobin  to  form  sulph-hsemoglobin, 
and  likewise  rapidly  kills  the  nerves.*  Sulphuretted  hydrogen  diluted 
with  hydrogen  and  introduced  into  the  rectum  of  a  dog  produces  symptoms 
of  poisoning  in  one  to  two  minutes  (Planer).  It  has  an  offensive  odor  similar 
to  Ibul  eggs. 

Detection. — If  a  piece  of  filter-paper  soaked  in  acetate  of  lead  be  brought  in  contact 
with  Ha8,  it  turns  black,  owing  to  the  formation  of  sulphide  of  lead  (PbS).  Soluble  sul- 
phides in  alkaline  solution  give  with  sodium  nitro-prussiate,  Na2Fe(CN)5NO  +  2H2O,  an 
intense  violet  color,  given  also  bj^  acetone  and  aceto-acetic  acid. 

Sulphurous  Acid,  H2SO3. — This  acid  has  been  found  in  the  urine  of  cats  and  dogs, 
and  has  been  detected  bj'  Striimpell  in  human  urine  in  a  case  of  typhoid  fever. 

Sulphuric  Acid,  H2SO4. — This  acid  is  found  in  the  urine  in  combination 
with  alkali  (preformed  sulphate),  and  with  indol,  skatol,  cresol,  and  phenol 
(ethereal  sulphates).     It  is  found  in  the  saliva  of  various  gastropods. 

Preparation. — (1)  By  oxidation  of  sulphur  with  nitric  acid, 

S  +  2HNO3  =  H2SO,  +  2NO. 

(2)  By  oxidation  of  sulphur-containing  proteid. 

Properties. — Sulphuric  acid  is  a  very  powerful  acid.  It  is  produced  in  the 
body  by  the  burning  of  the  proteids  (which  contain  0.5  to  1.5  per  cent.  S), 
80  per  cent,  or  more  being  oxidized  to  acid,  while  tlie  remainder  appears  iathe 
urine  in  the  unoxiuized  condition  tqi'uied  neutral  sulphur.  When  proteid,  fat, 
and  starch  free  from  ash  is  fed  to  dogs,  they  live  only  half  as  long  as  they 
would  were  they  starving,^  for,  according  to  Bunge,^  the  sulphuric  acid  formed 
abstracts  necessary  salts  from  the  tissue.  (For  further  discussion  of  this  see 
pp.  956  and  969). 

Detection. — If  100  cubic  centimeters  of  urine  be  treated  with  5  cubic  centimeters  of 

'  Ilarnack  :  Archir  fiir  erpei-imentelle  Palholof/ie  nnd  Pbarmukologie,  1894,  Bd.  34,  p.  156. 
2  J.  Foster:  Ze.itschrift fiir  Biologic,  1873,  Bd.  9,  p.  297. 
»  Physiologische  Chemie,  2d  ed.,  1889,  p.  104. 


THE    CHEMISTRY   OF   THE   ANIMAL    BODY.  951 

hydrochloric  acid  and  barium  cliloride  be  added,  the  preformed  sulphuric  acid  iw  precip- 
itated as  barium  sulpliato  (BaS(^4),  which  may  be  washed,  dried,  and  weij^died.  If  100 
cubic  centimeters  of  urine  be  mixed  with  an  equal  volume  of  a  solution  containin.i^  barium 
chloride  and  hydrate,  filtered,  and  one-half  the  filtrate  (  =50  cubic  centimeters  of  urine, 
now  free  o^ preformed  sulphate)  be  stronjrly  acidified  with  hydrochloric  acid  and  boiled,  the 
ethereal  sulphates  will  be  broken  up,  and  the  resulting  precipitate  of  barium  sulphate  will 
correspond  to  the  ethereal  sulphuric  acid.  To  determine  the  neittrol  sulj)hur,  evaporate 
the  urine  to  dryness,  fuse  the  residue  with  potassium  nitrate  (KNO3),  which  oxidizes  all 
the  sulphur  to  sulphate,  take  uj)  with  water  and  hydrochloric  acid,  add  barium  chloride, 
and  the  precipitate  (BaS04)  represents  the  total  sulphur  present.  Deduct  the  amount 
belonging  to  sulphuric  acid,  previously  determined,  and  the  remainder  represents  the 
neutral  sulphur. 

Metabolism  of  Sulphur. — The  total  amount  of  sulphur  in  the  urine 
runs  proportionally  parallel  with  the  amount  of  nitrogen  ;  that  is  to  say,  the 
amomit  is  proportional  to  the  amount  of  proteid  destroyed.  The  amount  of 
ethereal  sulphate  is  dependent  upon  the  putrefactive  production  of  indol, 
skatol,  phenol,  and  cresol  in  the  intestinal  caiial,  which  on  absorption  form  a 
synthetical  combination  with  the  traces  of  sulphate  in  the  blood.  Concerning 
neutral  sulphur  it  is  known  that  taurin  is  one  source  of  it.  If  taurin  be  fed 
directly,  the  amount  of  neutral  sulphur  in  the  urine  increases  (Salkowski),  and 
in  a  dog  with  a  biliary  fistula  the  neutral  sulphur  decreases  but  does  not  en- 
tirely disappear.*  In  a  well-fed  dog  with  a  biliary  fistula  Voit^  foimd  the 
quantity  of  sulphur  in  the  bile  to  be  about  10  to  13  per  cent,  of  that  in  the 
urine.  This  biliary  sulphur  (taurin)  is  normally  reabsorbed,  as  the  quantity 
of  sulphur  in  the  feces  (FeS,  NaaS)  is  small  and  derived  principally  from  pro- 
teid putrefaction.  The  amount  of  neutral  sulphur  in  the  urine  is  greatest 
under  a  meat  diet,  least  when  fat  or  gelatin  is  fed ;  the  sulphur  of  gelatin 
burns  apparently  to  sulphuric  acid.^  The  neutral  sulphur  of  the  urine  includes 
potassium  sulphocyanide  (originally  derived  from  the  saliva),  likewise  a  sub- 
stance which  on  treatment  with  calcium  hydrate  yields  ethyl  sulphide, 
(03115)28,*  and  there  are  present  other  unknown  compounds.  When  an 
animal  eats  proteid  and  neither  gains  nor  lo.ses  the  same  in  his  body,  the 
amount  of  sulphur  ingested  is  equal  to  the  sum  of  that  found  in  the  urine 
and  feces.  If  sulphur  be  eaten  it  partially  appears  as  sulphate  in  the  urine. 
Sulphates  eaten  pass  out  through  the  urine.  They  play  no  part  in  the  life  of 
tlie  cell. 

Chlorine,  CI  =  35.5. 

Free  chlorine  is  not  found  in  the  organization,  and  when  breathed  it  vigor- 
ously attacks  the  respiratory  mucous  membranes.  Chlorine  is  found  combined 
in  the  body  as  sodium,  potassium,  and  calcium  chloride,  as  hydrochloric  acid, 
and  it  is  said  to  belong  to  the  constitution  of  pepsin.* 

^  Kunkel :  Archiv  fur  die  gesammte  Physiologie,  1877,  Bd.  14,  p.  353. 
^  Zeitschrift  fiir  Biologie,  1894,  Bd.  30,  p.  554.  ^  Voit,  Op.  cit.,  p.  537. 

*  J.  J.  Abel :  Zeitschrift  fiir  physiologische  Chemie,  1 894,  Bd.  20,  p.  253. 

5  E.  O.  Sehoumow-Simanowski :  Archiv  fiir  exper.  Pathologie  und  Fharmakologie,  1894,  Bd. 
33,  p.  336. 


952  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

Hydrochloric  Acid,  HCl,  is  IouikI  to  a  small  extent  in  the  gastric  juice. 

Preparation. — (1)  If  sunlight  acts  on  a  mixture  of  equal  volumes  of  chlorine  and 
hydroirei),  they  unite  with  a  loud  ex])losion. 

(2)  By  the  action  of  strong  sulphuric  acid  on  common  salt, 

2NaCl  +  HjSO,  =  Na,SO,  +  2HC1. 

(3)  By  the  action  of  primary  acid  phosphate  of  sodinm  on  common  salt, 

XaH^PO,  +  NaCl  =  Na^HPO,  +  HCl. 

This,  according  to  Maly,  represents  the  process  in  the  cells  of  the  gastric  glands. 
Properties. — Hydrochloric  acid  readily  unites  with  most  metals,  forming 
chlorides.  It  causes  a  gelatinization  of  the  proteids  and  seems  to  unite  with 
them  ciiemically.  Such  gelatinization  is  a  necessary  forerunner  of  peptic  di- 
gestion. The  cleavage  products  of  peptic  digestion  (peptones,  ])roteoses,  etc.) 
combine  with  more  hydrochloric  acid  than  the  original  more  complex  proteid.' 
Hydrochloric  acid  of  the  strength  of  the  gastric  juice  (0.2  per  cent.)  inverts 
cane-sugar  at  the  temperature  of  the  body,  and  inhibits  the  action  of  bacteria. 
Hydrocidoric  acid  is  indis[)utably  derived  from  decomposition  of  chlorides  in 
the  secreting  cells  of  the  stomach.  It  has  been  shown  that  the  excretion  of 
common  salt  in  the  urine  is  decreased  during  those  hours  that  the  stomach  is 
active,  while  the  alkalinity  of  the  urine  increases.  If,  in  a  dog  with  a  gastric 
fistula,  the  mucous  membrane  of  the  stomach  be  stimulated  and  the  gastric 
juice  be  removed  as  soon  as  formed,  the  urine  becomes  strongly  alkaline  with 
sodium  carbonate  (the  excess  of  Na  liberated  taking  this  form)  while  the  chlo- 
rides may  entirely  disappear  from  the  urine.^  Respiration  in  an  atmos])here 
containing  0.5  per  cent.  HCl  gas  becomes  very  uncomfortable  after  twelve 
minutes.^ 

Detection. — Hydrochloric  acid  and  the  chlorides  give  with  silver  nitrate  a  white  itrecipi- 
tate  of  silver  chloride,  insoluble  in  nitric  acid,  very  soluble  in  ammonia.  If  the  bases 
(K,  Na,  Ca,  Mg,  Fe)  of  gastric  juice  and  then  the  acid  radicals  (01  and  P.-Oj)  be  deter- 
mined, after  uniting  by  calculation  phosphoric  atdiydride  with  the  proper  bases,  then  chlo- 
rine with  the  rest  of  the  bases,  there  still  remains  an  excess  of  chlorine  which  could  only 
have  belonged  to  hydrochloric  acid  present.  To  detect  free  hydrochloric  acid,  put  three  or 
four  drops  of  a  saturated  alcoholic  solution  of  tropaeolin  (10  in  a  small  white  iiorcelain 
cover,  add  to  this  an  equal  quantity  of  gastric  juice,  evaporate  slowly,  and  tlie  presence 
of  hydrochloric  acid  is  shown  by  a  beautiful  violet  color,  not  given  by  any  organic  acid.* 
Giinzburg's  reagent  con.sisting  (5f  pliloroglucin  and  vanillin  in  alcoholic  solution,  warmed 
(as  above)  with  gastric  juice  containing  free  hydrochloric  acid,  gives  a  carmine-red 
mirror  on  the  porcelain,  not  given  by  an  organic  acid.* 

Chlorine  in  the  body  is  ingested  as  chloride,  and  leaves  the  body  as 
such,  principally  in  the  urine,  likewise  through  the  sweat  and  tears,  and  in 
traces  in  the  feces. 

^  Chittenden:   Carturighi  Lecture-^  on  Digestive  Proteolm-'^,  1895,  p.  52. 

"  E.  O.  Schoiimow-Simanowski :  Arehiv  fiir  erper.  Pathotoyie  und  Pharmakologif,  1894,  Bd. 
33,  p.  336. 

■*  Lehmann:  Archie  far  Hygiene,  Bd.  5,  p.  1. 

*  Boas:  Deutsche  medicinische  Wochenschrift,  1887,  No.  39- 

*  Giinzburg  :  Centralblatt  fiir  klinische  Medicin,  1887,  No.  40. 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  953 

Bromine,  \^Y  =  80. 

Salts  of  bromine  are  found  in  marine  plants  and  animals,  but  their  physiological  im- 
portance has  not  been  established.  Bromine  is  a  fluid  of  intensely  disagreeable  odor, 
whose  vapors  strongly  attack  the  skin,  turning  it  brown,  and  likewise  the  mucous  mem- 
lirancs  of  tlie  respiratory  passages. 

Hydrobromic  Acid,  11  Br,  may  be  jirepared  by  the  action  of  water  on  phosphorus 

tri  bromide, 

PBr^  +  311,0  =  3HBr  -r  ll.l^Oa- 

It  is  a  colorless  gas  of  penetrating  odor.  If  sodium  bromide  be  given  to  a  dog  in  the 
place  of  sodium  chloride,  fifty  per  cent,  and  more  of  the  hydrochloric  acid  may  be  sup- 
I>lanted  by  hydrobromic  acid  in  the  gastric  juice.' 

Iodine,  I  =  127. 

Like  bromine,  the  salts  of  iodine  are  found  in  many  marine  plants  and  animals,  espe- 
cially in  the  alga'.  It  is  found  in  the  thjToid  gland.  Iodine  is  prepared  in  metallic-looking 
plates,  almost  insoluble  in  water,  but  soluble  in  alcohol  (tincture  of  iodine).  Iodine  is  still 
more  strongly  corrosive  in  its  action  on  animal  tissue  than  is  chlorine  or  bromine,  and  is  an 
antiseptic  and  disinfectant.     A  slight  trace  of  free  iodine  turns  starch  blue. 

Hydriodic  Acid,  HI,  is  prepared  like  hydrobromic  acid,  by  the  action  of  water  on 
tri-iodide  of  phosphorus.  An  aqueous  solution  of  hydriodic  acid  introduced  into  the 
stomach  is  absorbed,  and  shortly  afterward  iodine,  as  alkaline  iodide,  may  be  detected 
in  the  urine.  On  administration  of  sodium  iodide  to  a  dog  with  his  food,  only  very 
little  hydriodic  acid  appears  in  the  gastric  juice.  ^ 

Circulation  in  the  Body. — Iodine  or  iodides  given  are  rapidly  eliminated  in  the 
urine,  in  smaller  amounts  in  saliva,  gastric  juice,  sweat,  milk.  etc.  It  is  noticed  that  for 
weeks  after  the  administration  of  the  last  dose  of  potassium  iodide,  traces  of  iodine  are 
found  in  the  saliva,  and  none  in  the  urine.  The  explanation  lies  in  the  presumption  that 
iodine  has  been  united  with  proteid  to  a  certain  extent,  and  appears  in  such  secretions  as 
sahva,  which  contains  materials  derived  from  proteid  through  glandular  manufacture.' 
A  similar  explanation  avails  in  the  case  of  Drechsel's*  discovery  that,  in  patients  who 
have  been  treated  with  iodides,  iodine  may  be  detected  in  the  hair  (the  keratin  of  hair 
being  derived  from  other  proteid  bodies.)  Baumann*  has  recently  announced  the  dis- 
covery of  an  organic  compound  of  iodine  occurring  in  the  thyroid  gland  and  containing  as 
much  as  9. 3  per  cent,  of  iodine.  This  tliyro-iodin  is  the  effective  principle,  or  at  least  one 
of  the  effective  principles,  of  the  thyroid  gland. "^  Whether  free  iodine  or  hydriodic  acid 
is  liberated  in  the  tissues  from  ingested  iodides  is  a  disputed  point. 

Fluorine,  F  =  19. 

Fluorine  i.s  found  in  the  bones  and  teeth,  in  muscle,  brain,  blood,  and  in 

all  iuve.stigated  tissues  of  the  body,  though  in  .small  quantities.     In  one  liter 

of  milk  0.0003  gram  of  fluorine  have  been  detected.^     Fluorine  is  found   in 

])lants,  and  in  soil  without  fluorine  plants  do  not  flourish.     It  seems  to  be  a 

necessary  constituent  of  protoplasm.     Free  fluorine  is  a  gas  which  cannot  be 

preserved,  as  it  unites  with  any  vessel  in  Avhich  it  is  prepared. 

^  Xencki  and  Schoiimow-Siinanowski :  Archiv  fiir  exper.  Pathologic  und  Fharmakologie,  1895, 
B(l.  34,  p.  320.  ^  Nencki  and  Schouniow-Simanowski,  loc.  cit. 

*  Schmiedeberg :   Grundri.is  der  Arzneiiniltellehre,  2d  ed.,  1888,  p.  197. 

♦  Centmlblatt  fur  Physiologie,  1896,  Bd.  9,  p.  704. 

^  Zeit.<chriJI  fiir  phi/niologische  Cheinie,  1895,  Bd.  21,  p.  319. 

«  See  Dreclisel :   Cenlralblatt  fiir  Physiologie,  1896,  Bd.  9,  p.  705. 

'  G.  Tammann :  Zeitschrift  fiir  physiologische  Chemie,  1888,  Bd.  12,  p.  322. 


954  AX  AMERICAN    TEXT-BOOK    OF  PHYSTOLOGY. 

Hydrofluoric  Acid,  IIF,  is  prepared  by  heating  a  fluoride'  with  coiieeiitrated  sul- 
phuric acid,  in  a  platinum  or  lead  dish, 

CaF,  +  H,S04  =  CaSO*  +  2HR 

Prnpertu's.—\\yi\vo^\iov\c  acid  is  a  colorless  pas,  so  powerfully  corrosive  that  breathing 

its  fumes  results  fatally.     Its  aqueous  solutions  are  stable,  but  can  be  kept  only  in  vessels 

of  platinum,  gold,  lead,  or  india-rubber.     It  etches  glass,  uniting  to  form  volatile  silicon 

fluoride, 

Si02  +  4HF  =  SiF,  +  2H.A 

Detection. — If  silicon  be  absent  from  the  substance  to  be  tested,  the  above  reaction  maybe 
used,  and  if  the  glass  be  etched,  after  treating  the  substance  with  sulphuric  acid,  fluorine 
is  present.  In  the  organism  silicon  is  found,  and  the  method  of  detection  is  different. 
The  principle  of  the  method  depends  on  the  flict  that  SiF^  in  contact  with  water  forms 
silicic  acid  (HiSiOJ,  and  hydrofluor-silicic  acid  (HjSiFg).  If  the  ash  of  the  organ  be 
mixed  with  powdered  silica  (Si02),  transferred  to  a  flask,  mixed  with  concentrated  sul- 
phuric acid,  then  heated,  and  if  a  current  of  dry  air  remove  the  SiF4  from  the  flask 
through  a  tube  into  water,  the  slightest  trace  of  fluorine  is  proven  by  the  appearance 
of  a  whitish  cloud  of  silicic  acid  at  that  part  of  the  tube  where  SiF^  first  comes  in  con- 
tact with  moisture.     This  may  be  noted  when  0.0001  gram  of  fluorine  is  present.^ 

Circulation  in  the  Body. — Tappeiner  and  Brand!  ^  have  shown,  on 
feeding  sodium  fluoride  (XaF)  to  a  dog  in  doses  varying  between  0.1  and 
1  gram  daily,  that  the  fluorine  fed  was  not  all  recoverable  in  the  urine  and 
feces,  but  was  partially  stored  in  the  body.  On  subsequently  killing  the  dog, 
fluorine  was  found  in  all  the  organs  investigated,  and  was  especially  found  in 
the  dry  skeletal  ash  to  the  extent  of  5.19  per  cent,  reckoned  as  sodium  fluoride. 
From  the  microscopic  appearance  of  the  crystals  seen  deposited  in  the  bone,  the 
presence  of  calcium  fluoride  was  concluded.  In  this  form  it  normally  occurs 
in  bones  and  teeth. 

NiTEOGEN,   X  =  ]  4. 

Free  nitrogen  constitutes  79  per  cent,  of  the  volume  of  atmospheric  air.  It 
is  found  dissolved  in  the  fluids  and  tissues  of  the  body  to  about  the  same  extent 
as  distilled  water  would  dissolve  it.  It  is  swallowed  with  the  food,  may  par- 
tially diffuse  through  the  mucous  membrane  of  the  intestinal  tract,  but  forms 
a  considerable  constituent  of  any  final  intestinal  gas.  It  is  found  in  the  atmos- 
phere combined  as  ammonium  nitrate  and  nitrite,  which  are  nsefid  in  furnish- 
ing the  roots  of  the  plant  with  material  from  which  to  build  up  proteid. 
Bacteria  upon  the  roots  of  certain  vegetables  combine  and  assimilate  the  free 
nitrogen  of  the  air  (Hellriegel  and  Willforth).     Cultures  of  alga  do  the  same.^ 

Preparation.— {\)  By  abstraction  of  oxygen  from  air  through  burning  phosphorus  in 
a  bell  jar  over  water,  pentoxide  of  phosphorus  being  formed,  which  dissolves  in  the  water 
and  almost  pure  nitrogen  remains. 

(2)  By  heating  nitrite  of  ammonium, 

NH.NO.,  =  2N  -f  211,0. 
Properties. — Nitrogen  is  especially  distinguished  by  the  absence  of  chemical 
affinity  for  other  elements.     It  does  not  support  combustion,  and  in  it  both  a 

*  Tammann,  he.  cit.  *  Zeitschrifl  fiir  Biologic,  1892,  Bd.  28,  p.  518. 

^  P.  Kossowitch :  Bolanische  Zeitung,  1894,  Jahrg.  50,  p.  97. 


THE    CHEMISTRY   OF    THE   ANIMAL   BODY.  955 

flame  and  animal  life  are  extinguisiied,  owing  to  lack  of  oxygen.  It  acts  as 
a  diluent  of  atmospheric  oxygen,  thereby  retarding  combustion,  but  on  higher 
animal  life  it  is  certainly  without  direct  influence. 

Ammonia,  NII3,  is  ibund  in  the  atmosphere  as  nitrate  and  nitrite  to  the 
extent  of  one  part  in  one  million.  It  is  found  in  the  urine  in  small  quantities, 
is  a  constant  product  of  the  putrefaction  of  animal  matter,  and  is  a  product  of 
trypsin  proteolysis. 

Preparation,— {})  Through  the  action  of  nascent  hydrogen  on  nascent 
nitrogen.     This  may  be  -brought  about  by  dissolving  zinc  in  nitric  acid, 

3Zn  +  6HNO3  =  3Zn(X03)2  +  6H. 

lOH  +  2HNO3  =  6H2O  +  2N. 

N  +  3H  =  NH3. 

Ammonia  is  produced  in  a  similar  way  in  the  dry  distillation  of  nitro- 
genous organic  substances  in  absence  of  oxygen,  being  therefore  a  by-product 
in  the  manufacture  of  coal-gas.  In  putrefaction  nascent  hydrogen  acts  on 
nascent  nitrogen,  producing  ammonia,  which  in  the  presence  of  oxygen  becomes 
oxidized  to  nitrate  and  nitrite,  or  in  the  presence  of  carbonic  oxide  is  con- 
verted into  ammonium  carbonate.  Ammonium  nitrite  is  likewise  formed  on 
burning  a  nitrogenous  body  in  the  air,  in  the  evaporation  of  water,  and  on  the 
discharge  of  electricity  in  moist  air, 

2N  +  2H2O  =  XH.XO^. 

At  the  same  time  a  small  amount  of  nitrate  is  formed  in  the  above  three 

processes, 

2N  +  2H2O  +  O  -  NH,N03. 

Hence  these  substances  find  their  way  into  every  water  and  soil,  and  furnish 
nitrogen  to  the  plant.  The  value  of  decaying  organic  matter  as  a  fertilizer  is 
likewise  obvious. 

Properties. — Ammonia  is  a  colorless  gas  of  pungent  odor.  It  readily  dis- 
solves in  water  and  in  acids,  entering  into  chemical  combination,  the  radical 
NH4  appearing  to  act  like  a  metal  with  properties  like  the  alkalies,  and  its 
salts  will  be  described  with  them.  Very  small  amounts  of  ammonia  instantly 
kill  a  nerve,  but  upon  muscular  substance  it  acts  first  as  a  stimulant,  provok- 
ing contractions. 

Detection. — On  Marming  an  ammonium  salt  with  sodium  hydrate,  ammonia 
is  set  free,  recognizable  by  its  smell,  by  the  fact  that  it  turns  turmeric  paper 
brown,  and  that  even  in  smallest  traces  it  gives  a  yellow  coloration,  or,  in 
greater  amounts,  a  reddish  precipitate  in  Xessler's  reagent  (mercuric  iodide  dis- 
solved in  potassium  iodide  and  potassium  hydrate). 

Ammonia  in  the  Body.— If  it  be  agreed  with  Hoppe-Seyler  that  normal 
decomposition  in  the  tissues  is  analogous  to  putrefiiction,  then  nascent  hydrogen 
acting  on  nascent  nitrogen  in  the  cell  produces  ammonia,  which  in  the  presence 
of  carbonic  acid  becomes  ammonium  carbonate,  and  in  turn  may  be  converted 
into  urea  by  the  liver.     If  acids  (HCl)  be  fed  to  carnivora  (dogs)  the  amount 


956  ^.V  AMERICA X    TEXT-BOOK    OF   PHYSIOLOGY. 

of  ammonia  present  in  the  nrine  is  increased,  which  indicates  that  an  amount 
of  ammonia  usually  converted  into  urea  has  been  taken  for  the  neutralization 
of  tiie  acid.^  In  a  similar  manner  acids  formed  from  decomposing  proteid 
may  be  neutralized  (see  ])p.  950  and  993). 

[        The  ammoniacal  fn-mentdtion  of  the  urine  consists  in  the  decomposition  ol'  urea  into 
I    ammonium  carbonate  by  the  micrococcus  ?/?•<««%  the  urine  becoming  alkaline. 

Compounds  of  Nitrogen  with  Oxygen. — There  are  various  oxides  of  nitrogen,  the 
hiiiluT  (iiu's  being  pdWeit'iilly  cdrrusivt-.  uiul  some  of  these  unite  with  water  to  form  acids, 
of  which  nitric  acid  (HNO3)  is  the  strongest.  Only  nitrous  and  nitric  oxides  are  of  phj'si- 
ological  interest. 

Nitrous  Oxide,  N^O,  likewise  called  ''laughing-gas,"  is  prepared  by  heating  ammo- 
nium nitrate, 

NH,N03  =  N20-r2H.A 

It  supports  ordinary  combustion  almost  as  well  as  pure  oxygen,  but  it  will  not  sustain  life. 
Mixed  with  oxygen  it  may  be  respired,  producing  a  state  of  unconsciousness  preceded  by 
hysterical  laughter. 

Nitric  Oxide,  NO,  is  prepared  by  dissolving  copper  in  nitric  acid, 

.3Cu  +  8HNO3  =  3Cu(N03)2  +  4H.,0  -T  2N0. 

• 

Contact  with  oxygen  converts  it  into  peroxide  of  nitrogen  (NO.,),  which  is  an  imtating 
irrespirable  gas  of  reddish  color.  Nitric  oxide  in  blood  first  unites  with  the  oxj'gen  of 
oxyha^moglobin,  forming  the  peroxide  (NO,)-  and  then  the  nitric  oxide  combines  with 
hfemoglobin,  forming  a  highly  stable  compound,  nitric-oxide  haemoglobin  (Hb-NO). 

XiTROGEX  IX  THE  BoDY. — Nitrogen  is  taken  into  the  body  combined  in 
the  great  group  of  proteid  substances,  which  are  normally  completely  absorber! 
bv  the  intestinal  tract.  It  pas.ses  from  the  body  in  the  form  of  simple  decom- 
position-products, in  larger  part  through  the  urine,  but  likewise  through  the 
juices  which  pour  into  the  intestinal  canal.  The  uuabsorbed  residues  of  these 
latter  juices,  mixed  with  intestinal  epithelia  constitute  in  greater  part  the/«?ces.^ 
An  almost  insignificant  amount  of  nitrogen  is  further  lost  to  the  body  through 
the  hair,  nails,  and  epidermis,  but,  generally  speaking,  the  .sum  of  the  nitrogen 
in  the  urine  and  feces  corresponds  to  the  proteid  decomposition  for  the  .same 
time  (1  gram  X  =  6.25  grams  proteid).  When  the  nitrogen  of  the  proteid  eaten 
is  equal  in  quantity  to  the  sum  of  that  in  the  urine  and  feces,  the  body  is  said 
to  be  in  niirogenons  equUibr'nim.  When  the  ingested  nitrogen  has  been  larger 
than  that  given  off,  proteid  has  been  added  to  the  substance  of  the  body ;  when 
smaller,  proteid  has  been  lost.  Tliese  propositions  were  established  by  Carl 
Voit. 

A  small  amount  of  urea  and  other  nitrogenous  substances  may  be  excreted  in  profuse 
sweating.  Proteid  nitrogen  never  leaves  the  body  in  the  form  of  free  nitrogen  or  of 
auiinonia.  That  ammonia  is  not  given  off  by  the  lungs  may  be  demonstrated  by  perform- 
ing tracheotomy  on  a  rabbit,  and  passing  the  expired  air  first  through  pure  potassium 
hydrate  (to  absorb  CO2)  and  then  through  Nessler's  reagent.  The  experiment  maybe 
continued  for  hours  with  negative  result.' 

'  Fr.  Walther:  Archiv  fiir  exper.  Pathologk  und  Pharmakologie,  1877,  Bd.  7,  p.  164. 
■^  Menichanti  and  Prausnitz :  ZeilAchrift  ftir  Biologic,  1894,  Bd.  30,  p.  353. 
'  Bachl :  Zeitgchrifl  fur  Biologic,  1869,  Bd.  5.  p.  61. 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  957 

Piiosi'iioiius,  P  =-32. 

Phosphorus  is  found  combined  as  phosphate  in  the  soil ;  it  is  necessary  to 
the  developiucnt  of  phints.  As  phospliate  it  is  present  in  hirge  quantity  in 
the  hones,  and  is  found  also  in  all  the  cells,  tissues,  and  fluids  of  the  body, 
probably  in  loose  eheniieal  combination  with  the  proteid  molecule.  It  is  pres- 
ent in  nuclein,  protagon,  and  lecithin. 

Preparation. — Phosphorus  was  first  prepared  by  igniting  evaporated  urine, 
SNaH.PO^  +  5C  =  3H,0  +  5C0  +  2P  +  NusPO,. 

In  a  similar  way  it  may  be  obtained  y)y  chemical  treatment  of  bones.  The  vapors  of 
phosphorus  may  be  condensed  by  passing  them  under  water,  where  at  a  temperature  of 
44.4°  it  melts  and  may  be  cast  into  sticks. 

Properties. — Phosphorus  is  a  yellow,  crystalline  substance,  soluble  in  oils  and  carbon 
disulphide.  It  is  insoluble  in  water,  in  which  it  is  kept,  since  in  moist  air  it  gives  off"  a 
feeble  glowing  light,  accompanied  by  white  fumes  of  phosphorous  acid  (II3PO3)  and  small 
amotuits  of  ammonium  nitrate,  peroxide  of  hydrogen,  and  ozone,  to  which  latter  the 
peculiar  odor  is  ascribed.  Phosphorus  ignites  spontaneously  at  a  temperature  of  60°,  and 
tliis  may  be  produced  by  mere  handling,  the  resulting  burns  being  severe  and  dangerous. 
This  form  of  phosphorus  is  poisonous,  but  if  it  be  heated  to  250°  in  a  neutral  gas  (nitrogen) 
it  is  changed  into  red  phosphorus,  which  has  different  properties  and  is  not  poisonous. 

Phosphorus-pokoning. — On  injecting  })hosphorus  dissolved  in  oil  into  the 
jugular  vein,  embolisms  are  produced  by  the  oil  in  the  capillaries  of  tlie  lungs, 
the  expired  air  contains  fumes  of  phosphorous  acid,  and  the  lungs  glow  when 
cut  out  (Magendie).  If  the  phosphorus  oil  be  injected  in  the  form  of  a  fine 
emulsion,  embolism  is  avoided,'  and  the  fine  particles  of  phosphorus  are  generally 
distributed  throughout  the  circulation.  On  autopsy  of  a  rabbit  after  such  injec- 
tion in  the  femoral  vein,  all  the  organs  and  blood-vessels  glow  on  exposure  to 
the  air.^  If  two  portions  of  arterial  blood  be  taken,  and  one  of  them  be  mixed 
with  phosphorus  oil,  and  they  be  let  stand,  both  portions  become  venous  in  the 
same  time.^  Hence  phosphorus  in  blood,  as  in  water,  is  not  readily  oxidized. 
Persons  breathing  vajior  of  phosphorus  acquire  phosphorus- jioisoning.  AMiat 
the  direct  action  of  j)hosphorus  is,  is  unknosvn,  but  the  results  are  most  inter- 
esting. To  understand  the  results  it  mu.st  be  made  clear  that  proteid  in  decom- 
posing in  the  body  splits  up  into  a  nitrogeneom  portion  which  finds  its  exit 
through  the  urine  and  feces,  and  a  non-nitrogenous  portion  which  is  resolved 
into  carbonic  oxide  and  water,  just  as  are  the  sugars  and  the  fats.  This  car- 
bonic acid  is  given  off,  for  the  most  part,  through  the  lungs.  Now  if  a  .starv- 
ing dog,  which  lives  on  his  own  flesh  and  fat,  be  poisoned  with  phosphoru.s, 
the  proteid  decomposition  as  indicated  by  the  nitrogen  in  the  urine  is  largely 
increased,  while  the  amount  of  carbonic  acid  given  off  and  oxygen  ab.sorbed 
are  largely  decreased ;  on  post-mortem  examination  the  organs  are  found  to 
contain  excessive  quantities  of  fat.  We  have  here  presumptive  evidence  that  a 
part  of  the  proteid  molecule  usually  completely  oxidized  has  not  been  burned, 

1  L.  Hermann:  Pfliiger's  Archiv,  1870,  Bd.  3,  p.  1. 

*  H.  Meyer  :  Archiv  fiir  exper.  Pathologie  und  Pharmnfcoiogie,  1881,  Bd.  14,  p.  327. 

'  Meyer,  Op.  cit.,  p.  329. 


958  .l.V   AMERICAN    TEXT-BOOK    OE  ElIYSJOLOGY. 

hut  has  hoen  converted  into  fat.'  Similar  resnUs  are  cliaraoteristic  of  areenic 
and  antimony  poi.soning,  and  of  yellow  atrophy  of  the  liver. 

Dctt'ctinn. — If  any  organ  containing  phosphorus  he  boiled  with  water  in  a  flask  with  a 
long  ui>right  tube,  a  ring  of  luminous  phosphorus  will  condense  at  a  certain  point  of 
the  tuV)e. 

Compounds  of  Phosphorus  -with  Oxygen. — Of  these  corapound.s  three 
oxides  and  several  acids  exist,  but  only  meta-  and  orthophosphoric  acid  need 
attention  here. 

Phosphorus  Peroxide,  V.f)^,  is  a  white  ])o\vder,  which  rapidly  absorbs 
moisture;  it  is  produced  by  burning  phosphorus  in  dry  air. 

Metaphosphoric  Acid,  HPO3,  is  said  to  occur  combined  in  nucleiu. 

rreparation, — (1)  By  dissolving  P2O5  in  cold  water, 

P205  +  H20  =  2HP03. 

(2)  By  fusing  phosphoric  acid, 

H3PO,  =  HP03  +  H20. 

It  is  converted  slowly  in  the  cold,  rapidly  on  heating,  into  phosphoric  acid. 
Crystalline  it  forms  ordinary  glacial  phosphoric  acid.  Metaphosphoric  acid 
precipitates  proteid  from  solution,  yielding  a  body  having  the  properties  of 
nuclein,'^  but  this  has  been  denied.^ 

Orthophosphoric  Acid,  H3PO4. — Salts  of  this  acid  constitute  all  the  in- 
organic compounds  of  phosphorus  in  the  body,  and  are  called  phosphates. 

Preparation. — (1)  By  heating  solutions  of  metaphosphoric  acid, 

HP03  +  H20  =  H3PO,. 

(2)  By  treating  bone-ash  with  sulphuric  acid, 

Ca3(PO,)2  +  SH^SO,  ==  SCaSO,  +  2H3PO,. 

Properties. — On  evaporation  of  the  liquors  obtained  above,  the  acid  separates  in  color- 
less hygroscopic  crystals. 

Phosi)horic  acid  forms  different  salts  according  as  one,  two,  or  three  atoms  of  hydrogen 
are  supplanted  by  a  metal.     Thus  there  exist  primary  sodium  or  calcium  phosphates, 

Nall.PO,  and  Ca<j|-'pQ';  the  secondary  phosphates,  Na,HPO,  and  CaHPO^ ;  and  the 

tertiary  phosphates,  Na^POi  and  CaglPOi)^.  On  account  of  their  reaction  to  litmus 
these  salts  have  been  falsely  called  acid,  neutral,  and  basic,  but  the  secondary  salts  are, 
chemically  speaking,  acid  salts. 

The  bones  contain  a  large  quantity  of  tertiary  phosphate  of  calcium  ;  the 
fluids  and  cells  of  the  body  contain  likewise  the  jirimarv  and  secondary  pho.s- 
phates,  while  to  primary  sodium  phosphate  carnivorous  urine  mainly  owes  its 
acid  reaction. 

In  speaking  of  the  ash  of  proto])lasm,  Xencki  *  advocates  the  idea  of  .separate 
combinations  of  the  base  and  acid  radicles  with  the  proteid  molecule,  as,  for 

'  J.  Bauer:  Zeitschrift  fiir  Biologie,  1871,  Bd.  7,  p.  63. 

■^  L.  Lieberraann :  Berichte  der  deutschen  cheml.tchen  Gesellschaft,  Bd.  22,  p.  598. 

'  Salkowski :  PflugeT>s  Archir,  1094,  Bd.  59,  p.  245. 

*  Archiv  fiir  exper.  Pathologie  und  Pharmakologie,  1894,  Bd.  34,  p.  334. 


THE    CHEMISTRY   OF    THE  ANIMAL    BODY.  959 

example,  the  separate  uiiiuii  of"  potassium  witli  piott-id  and  of  j)hosplioric  acid 
with  proteid,  iu  tlie  functionally  active  cell.  However  combined,  phosphoric 
acid  is  necessary  for  the  organism. 

Ddection. — A  solution  of  phoy])hate  treated  with  a  magnesium  salt  dissolved  in  am- 
monia containing  ainmitiiium  chloride,  gives  a  fine  cr.vstalline  precipitate  of  magnesium- 
ammonium  j)hosphatc,  which  on  ignition  loses  ammonia  and  is  converted  into  magnesium 
pyrophosphate. 

Phosphorus  in  the  Body. — The  principal  source  of  supply  is  derived 
from  the  phosphates  of  the  alkalies  and  alkaline  earths  in  the  foods;  it  may  be 
absorbed  in  organic  combinations  in  nucleiu,  casein,  and  caseoses ;  and  it  may 
further  be  absorbed  as  glycerin  phosphoric  acid,  which  is  an  intestinal  decompo- 
sition product  of  lecithin  ^  and  probably  also  of  protagon.  Phosphorus  leaves 
the  body  almost  entirely  in  the  form  of  inorganic  ])liosphate,  the  only  exception 
being  glycerin  phosphoric  acid,  which  has  been  detected  in  traces  in  the  urine. 
In  man  and  carnivora  the  soluble  primary  and  secondary  phosphates  of  the 
alkalies  are  found  in  the  urine,  together  with  much  smaller  amounts  of  the 
less  soluble  primary  and  secondary  phosphates  of  the  alkaline  earths.  There 
is  likewise,  even  during  hunger,  a  continuous  excretion  of  tertiary  phosphate 
of  calcium,  magnesium,  and  iron  in  the  intestinal  tract.  In  herbivora  the  ex- 
cretion is  normally  into  the  intestinal  tract,  and  no  phosphates  occur  in  the 
urine.  This  is  because  herbivora  eat  large  quantities  of  calcium  salts  which 
bind  the  phosphate  in  the  blood,  and  they  likewise  eat  organic  salts  of  the 
alkalies,  which  become  converted  into  carbonate  and  appear  in  the  urine  as 
acid  carbonates;  such  a  urine  has  no  solvent  action  on  calcium  phosphate.^ 
In  a  similar  manner  a  great  reduction  of  phosphate  in  the  urine  of  man  may 
be  effected  by  feeding  alkaline  citrate  and  calcium  carbonate,  the  first  to  furnish 
the  more  alkaline  reaction  to  blood  and  urine,  the  second  to  bind  the  phosphate 
in  the  blood.  The  more  alkaline  reaction  itself  is  insufficient  to  prevent  the 
appearance  of  phosphates  in  the  urine.^  On  the  other  hand,  starving  herbiv- 
ora, or  herbivora  fed  with  animal  food,  give  urines  acid  from  primary  phos- 
phate.* 

Excreted  phosphates  may  be  originally  derived  froiu  the  phosphates  of  the 
bones,  or  from  phosphates  arising  from  the  oxidation  of  nuclein,  protagon,  and 
lecithin,  but  by  far  the  greater  quantit}'  is  derived  from  the  food,  or  from  pro- 
teid metabolism.  In  a  starving  dog,  which  feeds  on  its  own  proteid,  it  was 
found  that  a  ratio  existed  between  nitrogen  and  phosphoric  acid  in  the  urine  as 
6.4:1,  w^hicli  approximates  that  in  muscle,  i.e.  7.6:1.  On  feeding  meat  till 
nitrogenous  equilibrium  was  established,  the  ratio  became  8.1 :1.^  On  addi- 
tion of  proteid  to  the  body,  a  proportionate  amount  of  phosphoric  acid  is  re- 
tained for  the  new  protoplasm,  Mobile  on  destruction  of  proteid  the  phosphoric 
acid  corresponding  to  it  is  eliminated.    The  larger  excretion  of  phosphoric  acid 

^  Bokay :  Zeitschrift  fiir  physialogisehe  Ckemie,  1877-78,  Bd.  1,  p.  157. 

*  J.  Bertram  :  Zeitschrift  fiir  Biologic,  1878,  Bd.  14,  p.  354.  ^  Op.  eit.,  p.  354. 

*  Weiske:  Ibid.,  1872,  Bd.  8,  p.  246. 

5  E.  Bbchoff:  Ibid.,  1867,  Bd.  3,  p.  309. 


960  yl.Y  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

during  hunger  shown  in  the  ratio  above,  has  been  ascribed  to  the  decomposi- 
tion of  tiie  bones.^  Thus  Munk  found  on  Cetti,  wiio  lived  many  days  without 
footl,  a  ratio  as  low  as  4.5:1.  In  starvation  the  brain  and  nerves  do  not 
decrease  in  weight,  so  the  })rotagon  can  hardly  yield  any  great  amount  of  phos- 
phoric acid  (Voit).  Casein  and  other  nucleo-albumins,  when  fed,  are  oxidized 
and  furnish  phosphoric  acid  for  the  urine. 

Carbon,  C  =  12. 

This  element  is  found  combined  in  every  organism,  and  in  many  decom- 
position-products of  organized  matter.  Elementary  carbon  occurs  as  lanij)- 
black,  diamond,  and  graphite,  the  two  latter  having  tiieir  origin  from  the  action 
of  high  heat  on  coal.  Carbon  occurs  combined  in  coal,  petroleum,  and  natural 
gas,  which  are  all  products  of  the  decomposition  of  wood  out  of  contact  with  the 
air.  Further  it  is  found  in  vast  masses,  principally  consisting  of  calcium  car- 
bonate, having  their  origin  from  sea-shells.  Tiie  maintenance  of  life  depends,  as 
will  be  shown,  on  the  small  percentage  of  carbon  dioxide  which  is  contained  in  the 
atmosphere.  Lavoisier  believed  that  compounds  of  carbon  were  all  products 
of  life,  formed  under  the  influence  of  a  "  vital  force,"  which  was  a  property 
of  the  cell.  It  is  now  known  that  almost  every  constituent  of  the  cell  may  be 
prej)arcd  from  its  elements  in  the  laboratory  without  the  aid  of  any  ''  vital 
force"  whatever.  Notwithstanding  its  loss  of  strict  scientific  significance,  the 
old  term  "organic"  for  a  carbon  compound  is  still  in  vogue,  and  conveniently 
describes  a  large  number  of  bodies  which  are  treated  under  the  head  of  "  or- 
ganic chemistry,"  while  the  term  "inorganic"  is  applied  to  the  rest  of  the 
chemical  world. 

Elementary  Carbon. — This  burns  only  at  a  high  heat.  It  is  unaffected 
by  the  intestinal  tract.  This  is  shown  by  the  fact  that  diamonds  have  been 
stolen  by  swallowing  them,  and  that  finely  divided  jiarticles  of  lampblack  pass 
unchanged  and  unabsorbed  to  the  feces,  coloring  them  black  (proof  that  the 
intestinal  canal  does  not  absorb  solid  particles).  If  lampblack  be  eaten  with  a 
meal  its  appearance  in  the  feces  may  be  used  as  a  demarcation  line  between  the 
feces  belonging  to  the  period  before  the  meal,  and  the  ]x>riod  subsequent  to  it. 
Carbon  unites  directly  with  hydrogen,  oxygen,  and  sulphur  only. 

Carbon  Monoxide,  CO. — Tiiis  gas  is  a  product  of  tlie  incomplete  combus- 
tion of  carbon,  is  present  in  illuminating  gas,  and  burns  on  ignition  to  carbon 
dioxide.     It  is  usually  prepared  by  heating  oxalic  acid  with  sulphuric  acid, 

COOH 

I  ^H.,0-f  CO.,+CO, 

COOH 

the  carbon  dioxide  being  removed  by  passing  through  calcium  iiydroxide. 

Properties. — A  colorless,  odorless  gas.     Inspired,  it  unites  with  the  blood 
to   form  a  carbon-monoxide    haemoglobin  (Ilb-CO).     This    is    a  very  stable 
bright-red  compound  which  may  even  be  boiled  without  decomposing.     Ani- 
^  See  Voit :  Hermann's  Handbuch,  1881,  vi.  1,  p.  79. 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY. 


9G1 


luals  poisoned  with  VO  die  from  want  of  oxygen,  since  the  latter  cannot  dis- 
place the  carbon  nionoxiile  from  combination  with  haemoglobin. 

Carbon  Dioxide,  CO.,.— This  is  the  highest  oxidation  compound  of  carbon, 
the  product  of  its  complete  combustion.  It  is  present  in  the  air  to  the  extent 
of  0.04  per  cent.  It  is  formed  in  all  living  cells,  and  in  higher  animals  is 
collected  by  the  blood  and  brought  to  the  lungs  and  skin  for  excretion  ;  it  is 
also  a  product  of  putrefaction  ;  it  gives  an  acid  reaction  to  herbivorous  urine. 
It  is  found  dissolved  in  all  natural  waters,  and  is  present  combined  in  sea 
shells.  It  is  found  in  the  blood  principally  combined  with  sodium  in  the 
serum,  and  is  likewise  combined  with  calcium  and  magnesium  in  the  bones. 

Preparation.— {})  By  burning  carbon  or  a  carbon-containing  substance, 

C^H,  A  +  120  =  6CO2  +  mf>. 

Sugar. 

(2)  By  heating  a  carbonate, 

CaC03=CaO  +  C02. 

(3)  By  the  action  of  an  acid  on  a  carbonate, 

Na^COa  +  2HC1  =  2NaCl  +  CO^  +  Hp. 

In  the  blood,  haemoglobin  and,  to  a  less  extent,  serum-albumin  and  primaiy 
sodium  phosphate  act  like  acids.  If  the  gases  be  extracted  from  fresh  defib- 
rinated  blood  in  a  vacuum,  all  the  CO2  is  removed.  If  sodium  carbonate  be 
added  to  blood,  the  carbonic  acid  belonging  to  this  is  likewise  given  up  in  a 
vacuum,  while  a  simple  aqueous  solution  of  sodium  carbonate  is  not  affected. 
If  serum  be  extracted  in  vacuo,  only  a  little  more  than  half  the  carbonic  acid 
contained  in  it  is  dis.sociated  from  combination,  indicating  that  in  the  previous 
experiment  hsemoglobin  had  acted  like  an  acid.  If  a  solution  of  bicarbonate 
of  sodium  (NaHCOj)  be  exhausted  under  the  air-pump,  just  one-half  of  the 
CO2  is  given  off,  sodium  carbonate  (NajCOj)  remaining.  In  the  serum  more 
than  one-half  of  the  CO2  is  obtained  in  vacuo,  because  the  serum-albumin, 
like  the  hsemoglobin,  though  less  effectively,  acts  like  an  acid  in  fixing  the 
alkali  and  liberating  fhe  gas.  There  is  likewise  present  the  action  of  pri- 
mary phosphate  on  the  acid  carbonate, 

NaH^PO,  -f  NaHCOs  =  Na^HPO,  +  H^O  -f  CO^. 

Through  these  agencies  the  tension  of  carbonic  acid  is  kept  high  in  the  blood, 
and  its  escape  through  the  walls  of  the  alveolar  capillary  is  not  unlike  the 
escape  of  gas  on  uncorking  a  bottle  of  carbonated  water. 

After  drinking  a  carbonated  water,  carbonic  oxide  may  be  detected  dissolved 
in  the  urine. 

Properties. — A  colorless,  odorless  gas.  It  is  poisonous,  its  accumulation  at 
first  stimulating  and  afterwards  paralyzing  the  nervous  centres.  It  affects  the 
irritability — not,  however,  the  conducting  power — of  the  nerves.  A  solution 
of  carbonic  oxide  in  water  forms  carbonic  acid,  HoCOj,  and  from  this  are  derived 
two  series  of  salts,  primary  or  acid  salts,  MHCO3,  and  secondary  or  neutral 
salts,  M2CO3. 


962  AN  AMERICAN    TEXT-BOOK   OF   PHYSIOLOGY. 

Detection. — If  exj)irecl  air,  or  air  I'roiii  a  bag  enclosing  any  part  of  the  skin^ 
be  passed  through  a  solution  of  calcium  or  barium  hydrate,  a  precipitate  of 
white  insoluble  carbonate  will  be  thrown  down. 

ISIetabolism  of  Carbon. — It  will  be  remembered  that  there  is  a  union  of 
chlorine  and  hydrogen  on  exposure  to  sunlight.  In  a  similar  manner  the  chloro- 
plivll-containing  leaf  of  the  plant,  through  the  medium  of  the  energy  of  the  sun's 
rays,  brings  the  molecules  of  water  and  carbonic  oxide  derived  from  the  air  in 
such  a  j)osition  with  regard  to  each  other  that  they  unite  to  form  sugar  with  the 
elimination  of  oxygen  (reaction  on  p.  945).  This  process  is  called  synthesis — 
the  construction  of  a  more  complicated  body  from  simpler  ones.  The  active  or 
"  kinetic  "  energy  from  the  sun  required  to  build  up  the  compound  is  stored, 
becoming  "  potential "  energy  in  that  compound,  and  is  liberated  again  in 
exactly  the  same  quantity  on  the  resolution  of  the  substance  into  its  original 
constituents.  So  the  amount  of  energy  liberated  in  the  decomposition  of  a 
food  in  the  body  is  exactly  equal  to  the  energy  needed  to  build  it  up  from 
its  excreted  constituents,^  and  this  liberated  energy  appears  in  the  body  as 
heat,  work,  and  electric  currents. 

The  plant  has  the  power  of  converting  sugar  into  starch  and  cellulose,  and 
likewise  into  fat.  Further  the  sugar  undoubtedly  unites  with  certain  nitrogen- 
containing  bodies,  and  the  synthesis  of  proteids  results.  Plants  containing  this 
mixture  of  food-stuffs  become  the  sustaining  basis  of  animal  life.  The  animal 
devours  these  substances  and  either  adds  them  to  his  body,  or  burns  them  to 
prevent  destruction  of  his  own  substance  :  such  are  the  objects  of  food.  In 
contradistinction  to  synthesis  in  plants,  animal  life  is  said  to  be  characterized  by 
analysis,  i.  e.,  the  resolution  of  a  complicated  substance  into  simpler  ones.  This 
classification  is  not  entirely  accurate, many  exceptions  occurring  on  both  sides; 
for  example,  animals  may  convert  sugar  into  fat,  which  is  synthesis.  The 
animal  expires  its  carbon  partly  as  carbonic  acid,  and  partly  in  the  form  of 
more  complex  organic  compounds  such  as  urea  and  uric  acid.  Since  these 
latter  after  leaving  the  body  eventually  become  oxidized,  and  the  carbon 
becomes  completely  changed  to  carbon  dioxide,  it  follows  that  all  animal  carbon 
is  finally  restored  to  the  air  in  the  form  of  carbon  dioxide.  Thus  is  established 
the  revolution  of  the  carbon  atom,  made  possible  by  the  energy  of  the  sun, 
between  air,  plants,  animals,  and  back  to  air  again.  Burning  coal,  lime-kilns, 
volcanoes,  give  carbonic  acid  to  the  air.  Rain  water  receives  carbonic  acid 
from  the  atmosphere,  from  putrefying  organic  matter  in  the  soil  and  from  the 
roots  of  trees,  and  ultimately  much  of  this  combines  with  mineral  matter,  or 
contributes  to  form  shells  in  marine  life. 

Silicon,  Si  =  28. 

Silicon  is  found  in  the  ash  of  plants,  and  in  traces  in  the  cells  and  tissues  of 
animals,  being  a  constant  constituent  of  hen's  eggs.    It  appears  in  traces  in  the 
human  urine,  and  in  considerable  quantity  in  herbivorous  urine.    It  is  especially- 
present  in  hair  and  feathers.    It  does  not  seem  to  be  of  great  importance  to  the 
'  See  Rubner,  Zeitschrift  fiir  Biologic,  1893,  Bd.  30,  p.  73. 


THE    CHEMISTRY   OF    THE   ANIMAL    BODY,  963 

life  of  the  plant,  i'ov  if  corn-stalks,  whose  ash  usually  contains  20  per  cent,  of 
silica  (SiOa),  be  grown  in  a  soil  free  from  it,  the  plant  flourishes  though  only 
0.7  per  cent,  of  silica  is  found  in  the  ash,  this  having  been  derived  from  the 
vessel  holding  the  soil. 

Silicon  Dioxide,  or  Silica,  SiOa- — This  is  the  oxide  of  the  element,  and  is  found  in 
quartz  and  sand,  but  nut  in  the  organism. 

Silicic  Acids. — The  ortho-silicic  acid  (IliSiOJ  is  formed  by  the  action  of  an  acid  on  a 

metallic  silicate, 

Ca^SiO*  +  2H2CO3  =  2CaC03  +  H.SiO,. 

This  reaction  takes  place  in  the  soil,  and  the  silicic  acid  so  obtained  is  soluble  in  water  and 
is  a  colloid — that  is  to  say,  is  of  gelatinous  consistence,  will  not  crystallize,  and  does  not 
osmose  through  vegetable  and  animal  membranes.  However,  it  is  in  this  form  or  in  the 
form  of  vsoluble  alkaline  silicate  that  it  is  probably  received  by  the  root  of  the  plant.' 

Metasilicic  acid  has  the  formula  IlaSiO;,,  while  the polysilicic  acids  (H2Si05,H6Si.207,  etc. ) 
are  numerous,  and  constitute  the  acid  radicals  of  most  mineral  silicates.  If  silicic  acid  be 
evaporated  and  dried,  it  leaves  a  gritty  residue  of  silica. 

The  Metallic  Elements. 
The  metals  in  the  body  are  the  alkalies  potassium  and  sodium,  the  alkaline 
earths  calcium  and  magnesium,  and  the  heavy  metal  iron. 

Potassium,  K  =  39. 

Potassium  salts  are  found  predominating  in  all  animal  cells  (see  p.  943), 
and  in  the  milk  which  is  manufactured  from  the  disintegration  of  such  cells. 
They  are  found  in  the  blood -corpuscle  to  the  almost  complete  exclusion  of 
sodium  salts.  Only  to  a  small  extent  do  they  occur  in  the  fluids  of  the  body 
and  in  the  blood  plasma  (K2O  =  0.02  per  cent,  in  plasma).  They  are  excreted 
in  the  urine.  Potassium  salts  are  retained  on  the  surface  of  the  ground  for  the 
use  of  vegetation,  and  occur  in  the  plant  not  only  as  inorganic  but  also  as 
organic  salts  (tartrate,  citrate,  etc.). 

Potassium  Chloride,  KCl. — Potassium  chloride  is  a  constant  constituent 
of  all  animal  cells  and  tissues,  and  may  be  absorbed  with  the  food  or  be  pro- 
duced in  the  body  after  eating  potassium  carbonate  or  phosphate,  since  these  salts 
may  react  with  the  sodium  chloride.  If  fed,  it  is  ordinarily  balanced  by  its  ex- 
cretion, but  if  0.1  gram  be  introduced  into  the  jugular  vein  of  a  medium-sized 
dog,  immediately  paralysis  of  the  heart  ensues.  It  is  a  powerful  poison  for  nerves 
and  nervous  centres.  It  melts  when  heated  to  a  low  red  heat,  and  volatilizes 
at  a  higher  heat. 

Potassium  Phosphates. — The  primary  (KH2PO4)  and  secondary  (KgHPO^) 
phosphate  of  potassium  are  the  principal  salts  of  the  cells  of  the  body,  and  are 
likewise  present  in  the  urine,  and  to  a  very  small  extent  in  the  blood-plasma. 
They  are  undoubtedly  intimately  connected  with  the  functional  activity  of  proto- 
plasm. Presence  of  carbonic  acid  causes  the  conversion  of  the  secondary  phos- 
phate into  the  primary  salt,  and  this  occurs  in  the  blood-corpuscle  as  well  as  in  the 

plasma : 

^  K^HPO,  +  CO,  +  HP  =  KH^PO,  +  KHCO3. 

'  Bunge:  Physiologische  Chemie,  3d  ed.,  1894,  p.  25. 


964  ^l.V  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

Priinarv  acid  jihospliate  of  potassium  contributes  to  the  acid  reaction  of  the 
urine,  tliougli  in  presence  of  sodium  chloride  there  is  a  tendency  to  the  forma- 
tion of  primary  sodium  phosphate  and  potassium  chloride.  It  is  the  cause  of 
the  acid  reaction  in  muscle  in  rigor  mortis  (see  j).  989). 

Potassium  Carbonates, — The  priniary  and  secondary  carbonates  exist 
in  the  body  only  in  trifling  quantities.  They  may  be  j)roduced  as  above  de- 
scribed by  the  action  of  carbonic  acid  on  the  phosphates,  tluy  may  be  ingested 
with  the  food,  or  they  may  result  in  the  body  froin  tlie  combustion  of  an  organic 
salt  of  potassium,  according  to  the  same  reaction  as  would  take  place  by  burn- 
ing it  in  the  laboratory, 

KX\H  A  +  'iO  =  K2CO3  +  3CO2  +  2H2O, 

K  tartrate. 

Feeding  potassium  carbonate  or  an  organic  salt  of  potassium  makes  the  urine 
alkaline  owing  to  the  excretion  of  potassium  carbonate. 

Potassium  salts  are  poisonous  if  introduced  into  the  blood  in  too  large  quantities.  In 
concentrated  solutions  in  the  stomach  they  ijroduoe  ffostn'tis,  even  with  quickly  fatal 
results. ' 

Zuntz  believes  that  potassium  is  combined  with  haemoglobin  in  the  blood-corpuscle,  and 
may_  be  dissociated  from  it  by  the  action  of  carbonic  oxide.* 

Potassium  in  the  Body, — The  various  salts  of  j)otassium  are  received 
with  the  food  in  the  manner  described  ;  the  pho.sphate  may  be  retained  for 
new  tissue,  but  the  other  salts  are  removed  in  the  urine.  They  are  all  quite 
completely  absorbed  in  the  intestinal  tract.  In  starvation,  or  in  fever,  where 
there  is  high  tissue-metabolism,  the  body  suffers  greater  lo.ss  of  the  potassium 
phosphate-containing  tissue  than  it  does  of  the  sodium-rich  blood,  and  j)otas- 
sium  exceeds  sodium  in  the  urine  (reverse  of  the  usual  proportion),  lounge  ^ 
has  noted  an  important  influence  of  potassium  salts.  If  a  potassium  .<alt  be  in 
solution  together  with  sodium  chloride,  the  two  partially  react  on  each  other, 
with  formation  of  potassium  chloride.  If  now  potassium  carbonate,  for  example, 
be  eaten,  the  same  reaction  occurs  in  the  body, 

K2CO3  H-  2NaCl  =  2KC1  +  Na^COj. 

The  kidney  has  the  power  of  removing  soluble  substances  which  do  not  belong 
to  the  blood  or  are  pre.'^ent  in  it  to  excels,  and  con.^equently  the  two  salts 
formed  as  above  are  excreted.  Hence  potassium  carbonate  has  caused  a  direct 
loss  of  sodium  and  chlorine.  For  this  reason,  if  potatoes  and  vegetables  very 
rich  in  potassium  salts  are  eaten,  sodiimi  chloride  must  be  added  to  the  food  to 
compensate  for  the  loss.  Nations  living  on  rice  do  not  need  salt,  for  here  the 
potassium  content  is  low.  Tribes  living  solely  on  moat  or  fish  do  not  use 
salt,  but  care  is  taken  that  the  animals  slaughtered  for  food  shall  not  lose  the 
blood,  rich  in  sodium  salts,  and  strips  of  meat  dipped  in  blood  are,  by  some 
races,  considered  a  delicacy.* 

*  Biinge:  Pkyniologische  Chemie,  3d  ed.,  1894,  p.  136. 

*  A.  Loewy  und  N.  Zuntz:  Pflilger's  Archiv,  1894,  Bd.  58,  p.  522. 

'  ^p.  cit.,  p.  108.  *  Bunge,  Op.cit.,  p.  116. 


THE    CHEMISTRY   OE    THE   ANIMAL    BODY.  9(j5 

Sodium,  Na  =  23. 

Sodium  salts  belong  particularly  to  the  fluids  of"  the  boily  (see  p.  948), 
blood-plasnia  containing  0.4  per  cent,  calculated  to  NagO. 

Sodiura  chloride,  NaCl,  is  found  in  all  the  fluids  of  the  body.  It  is  found 
in  blootl  and  lynij)h  to  an  extent  of  about  O.Go  j)er  cent.,  in  the  saliva,  gastric 
juice,  milk,  sweat,  urine,  etc.  Sodium  chloride,  like  potassium  chloride,  melts 
at  a  low  red  heat,  hence  the  fluids  of  the  body  yield  a  fluid  asii,  with  the  single 
exception  of  milk,  which  contains  a  high  percentage  of  infusible  calcium  phos- 
phate. Sodium  chloride  is  very  readily  soluble.  In  the  blood  it  acts  as  a 
solvent  on  serum-globulin  and  other  proteids,  and  its  inert  presence  in  proper 
concentration  affords  a  medium  in  which  the  functional  activity  of  cells  and 
ti&sues  is  maintained.  (For  "physiological  salt-solution"  see  p.  948.)  From 
sodium  chloride  the  hydrochloric  acid  of  the  gastric  juice  is  prepared  (see  p. 
952) ;  it  is  also  a  necessary  addition  to  every  food  where  potassium  salts  are 
in  great  preponderance  (see  p.  964),  but  it  is  taken  by  most  races  in  amounts 
far  above  these  physiological  necessities. 

If  a  mixture  of  necessary  food-stuffs — proteid,  fats,  starch,  salts,  and  water — in  proper 
proportion,  but  without  flavor,  be  set  before  a  dog,  he  will  starve  rather  than  touch  it.  A 
raan  will  attempt  its  digestion,  but  the  permanent  support  of  life  is  impossible.  A  food 
to  support  life  must  be  a  well-tasting  mixture  of  food-stufFs,  for,  through  the  action  of  the 
flavor  on  the  mucous  membrane  of  the  mouth  and  stomach  there  is  established  reflexly  a 
nervous  influence  causing  a  proper  flow  of  the  various  digestive  juices.  Hence  salt, 
pepper,  mustard,  beer,  wine,  and  other  condiments  are  taken  with  the  food.  What  the 
change  is,  when  a  substance  acts  on  the  taste-buds  of  the  tongue,  for  example,  start- 
ing a  motion  such  as  is  afterwards  interpreted  in  the  brain  as  flavor,  is  unknown. 
Chemical  constitution  gives  no  hint  how  a  body  will  taste  or  smell. 

In  carnivora  every  trace  of  sodiura  chloride  is  absorbed  by  the  villi  from 
the  intestinal  tract.  This  is  a  proof  that  absorption  does  not  depend  on  simple 
physical  osmosis,  in  which  case  the  intestinal  contents  would  tend  to  have  the 
same  percentage  composition  as  the  blood,  but  upon  the  selective  capacity  of  the 
exposed  protoplasm  of  the  villi.  Sodium  chloride  is  the  principal  solid  con- 
stituent of  sweat  and  of  tears.  Usually,  however,  it  is  lost  to  the  body 
through  the  urine,  of  whose  ash  it  forms  the  chief  constituent.  The  quantity 
of  salt  in  the  urine  is  decreased  during  gastric  digestion  (see  p.  952).  Sodium 
chloride  does  not  pa.ss  to  the  urine  as  soon  as  it  rises  above  a  certain  quantity 
in  the  blood,  but  the  tissues  retain  or  give  it  up  according  to  circum,stances. 
Experiments  ^  have  been  made  on  a  man  who  ate  normally  27  grams  of  salt 
daily;  on  reducing  this  to  1.4  grams  the  following  daily  excretions  occurred 
in  the  urine:  9.9,  6.5,  3.8,  4.1,  3.2,  2.9,  2.9,  2.5.  Then,  on  returning  to  27 
grams  daily:  3.4,  7.9,  11.2,  15.8,  17.4.  Experiments  of  abstention  have  never 
been  carried  so  far  as  to  produce  vital  disturbances,  but  the  physiological  min- 
imum is  probably  very  low.  A  dog  weighing  35  kilograms  may  live  on  0.6 
gram  of  salt  daily.'^     Sodium  chloride,  fed,  produces  of  itself  alone  an  increase 

'  Klein  und  Verron  :  Sitzungsberichte  der  Wiener  Academie,  Mathematisch-physikalische  Classe,  ■ 
1867,  iv.  (2),  p.  622. 

*  Voit:  Hermann's  Handbuch,  1881,  vi.  1,  p.  367. 


i'OG  Ay   AMEIilCAX    TEXT-BOOK    OF  PHYiSIOLOUY. 

of  water  and  of  urea  in  the  urine.*  The  increase  of  urea  means  increase  in 
proteid  metabolism,  and  is  prothiced  by  all  sidts;  it  is  to  be  explained  by  the 
increased  motion  of  water  from  the  cell,  the  same  eifect  being  seen  on  drinking 
large  (juantitics  of  water  (see  p.  948). 

Sodium  sulphate,  'S'a.^O^  called  "  Glauber's  s:ilt,"  is  found  together  with 
potassium  sulphate  in  the  urine  in  the  condition  of  preformed  sulphuric  acid 
(see  p.  951).  If  fed,  it  reappeare  in  the  urine.  It  acts  on  the  epithelial  cells 
of  the  intestines,  preventing  the  absorption  of  water,  consequently  causing  diar- 
rhoea.    Other  laxatives  act  in  the  same  way. 

Sodium  Phosphates. — The  primary  (XaHgPO^)  and  the  secondary 
(NaoHPOJ  salts  are  found  to  a  small  extent  in  the  blood-])lasnia  and  other 
fluids,  and  in  the  urine.  As  with  the  jiotassium  ph()S|»liates,  carbonic  oxide 
acts  when  in  certain  excess  to  convert  the  secondary  phosphate  into  NalloPO^ 
and  XaHC03.  These  two,  however,  may  react  on  one  another  to  drive  ulf  car- 
bonic acid  (see  p.  961).  Carnivorous  urine  owes  its  acid  reaction  principally 
to  primary  sodium  phosphate.  If  a  mixture  of  XaHjPO^  and  Xa2HPO^  be 
permitted  to  diffuse  through  membranes,  the  XaHoPO^  passes  through  in 
greater  quantity,  and  this  process  may  take  place  in  the  kidney."  Secondary 
sodium  phosphate  dissolves  uric  acid  on  warming,  forming  sodium  acid  urate 
and  primary  phosphate,  which  solution  reacts  acid  (Voit).  Urine  standing  in 
the  cold  precipitates  uric  acid  with  the  formation  of  secondary  phosphates, 
while  the  reverse  reaction  with  return  of  original  acidity  takes  place  on  warm- 
ing the  urine. 

Sodium  Carbonates. — Of  these  there  are  two,  the  primary,  XaHCOg,  and 
the  neutral,  Xa.X'Oj.  The  organization  owes  its  alkaline  reaction,  and  also  its 
])ower  of  combining  with  carbonic  acid,  almost  entirely  to  sodium  carbonate. 
Saliva,  pancreatic  and  intestinal  juice  are  strongly  alkaline  with  sixliuin  carbonate, 
as  are  also  blood,  lymph,  and  other  fluids.  If  the  organization  be  acidified,  by 
feeding  acid  to  a  rabbit,  for  example,  death  occurs  even  before  complete  loss 
of  the  blood's  alkalinity,  while  venous  injections  of  sodium  carbonate  at  the 
proper  time  restore  the  animal.  Carbonic  oxide  cannot  be  remtn-ed  from  the 
tissues  in  the  acidified  blood.  Sodium  carbonate  treated  with  carbonic  acid 
becomes  acid  sodium  carbonate,  and  this  change  is  effected  in  the  internal  res- 
piration, where  the  cells  give  COo  to  the  blood.  Treated  with  acids,  both  car- 
l)onates  liberate  carbonic  oxide — a  reaction  which  takes  place  in  the  blood 
(see  p.  961).  Bunge  suggests  that  the  acid  chyme  of  the  stomach,  into  whose 
finest  particles  the  alkaline  intestinal  juice  diffuses,  is  especially  penetrable  by 
the  latter's  enzymes,  because  liberated  carbonic  oxide  has  separated  the  j)articles 
of  chyme  from  each  other.  The  same  principle  would  hold  true  of  a  morsel 
well  mixed  with  saliva,  which,  as  is  well  known,  is  more  easily  penetrable  by 
gastric  juice  than  one  not  so  mixed.  Sodium  carbonate  mav  be  obtained  for 
the  body  either  directly  from  the  food  by  absorption,  or  indirectly  through 

1  Voit :  Op.  ciL,  p.  160. 

^  Soubiranski:  Archiv  fiir  exper.  Pathologic  und  Pharmakologie,  1895,  Bd.  35,  p.  178. 


THE    CHEMISTRY   OF   THE  ANIMAL   BODY.  967 

combustion  of  siKliuiu  organic  salts.  Ingested  in  sufficiently  large  quantities, 
it  makes  the  urine  alkaline. 

Sodium  salts  are  undoubtedly  united  witii  serum-albumin  in  the  pla.sma, 
forming  a  combination  which  may  be  dissociated  by  carbonic  oxide. 

Detection. — Sodium  gives  a  yellow  coloration  to  a  colorless  flame,  and  a  distinctive 
bright  line  in  the  j-ellow  ot"  the  spectroscope. 

SoDU'M  IN  THE  BuDY. — This  suhject  has  been  discussed  under  the  diflerent  salts,  and 
likewise  under  potassium  and  hydrochloric  acid ;  repetition  here  is  therefore  needless. 

Ammonium,  XH^. 

Ammonia,  NH.v  has  already  been  described  (p.  955). 

Sodium- Ammonium  Phosphate,  NaNH^HPOi,  is  an  insoluble  salt  formed  in  the 
urine  durinu  ammoniacal  fermentation. 

Ammonium  Carbonate,  (XHJgCOg,  is  formed  by  the  union  of  carbonic 
oxide  and  ammonia  in  the  presence  of  water,  and  is  therefore  a  usual  product 
of  putrefaction.  If  introduced  into  the  blood,  it  is  converted  into  urea  by  the 
liver.  In  uremia  urea  passes  from  the  blood  into  the  stomach  and  is  there 
converted  into  ammonium  carbonate,  which  produces  vomiting  through  irrita- 
tion of  the  mucous  membrane.  (See  further  discussion  under  Carbamic  Acid 
and  Urea.) 

Calcium,  Ca  =  40. 

Calcium  is  by  far  the  most  abundant  metallic  element  in  the  body,  and,  as 
has  been  found  in  the  dog,  99.5  per  cent,  belongs  to  the  composition  of  the 
bones.^  Outside  the  bones  it  occurs  most  abundantly  in  blood-plasma.  It  is 
found  in  all  the  cells  and  fluids  of  the  body,  probably  loosely  combined  with 
proteid.     Calcium  is  always  accompanied  by  magnesium. 

Calcium  Chloride,  CaCl,,  is  found  in  small  quantities  in  the  bones. 

Calcium  Fluoride,  CaFj,  a  salt  insoluble  in  water,  is  found  in  bone,  den- 
tine, and  enamel  (see  p.  954). 

Calcium  Sulphate,  CaSO^,  is  found  in  small  quantities  in  bones  and  rarely 
as  part  of  the  sediment  in  strongly  acid  urine. 

Calcium  Phosphates. — Of  these  there  are  three — primary,  CaH^(POJ2, 
secondary,  CaHPO^,  and  tertiaiy,  Ca3(P04)2-  The  tertiary  phosphate  is  insol- 
uble in  water,  the  secondary  only  very  slightly  soluble,  but  the  primary  salt  is 
soluble.  The  tertiary  and  secondary  phosphates  are  insoluble  in  alkali,  but 
soluble  in  mineral  acids  and  in  acetic  acid.  The  tertiar\^  phosphate  forms  the 
largest  mineral  constituent  of  the  bones  (83.89  per  cent.,  Zalesky)  and  of  den- 
tine and  enamel.  Tertiary  phosphate  of  calcium  likewise  occurs  in  the  blood; 
how  it  is  held  in  solution  it  is  difficult  to  say,  though  it  is  probably  loosely 
combined  with  proteid.  In  a  similar  way  it  is  combined  with  the  protoplasm 
of  the  cell.  It  is  largely  found  in  the  ash  of  milk,  having  been  in  previous 
chemical  combination  with  casein.  Tertiary  phosphate  of  calcium  is  continu- 
ously excreted  into  the  intestinal  tract.  It  is  present  in  the  acid  gastric  juice, 
but  only  in  traces  in  the  alkaline  saliva,  pancreatic  juice,  and  in  the  nearly 
1  Heiss  :  Zeitschrift  fiir  Biologie,  1876,  Bd.  12,  p.  165. 


968  AN  AMERICAN  TEXT-BOOK   OF  PHYSIOLOGY. 

neutral  bile.  Tertiary  phosphates  never  occur  in  the  urine,  except  as  a  sedi- 
ment after  the  urine  has  attained  an  alkaline  reaction,  being  formed  from  the 
acid  phosphates.  In  carnivorous  urine  the  calcium  jiresent  occurs  as  primary 
and  secondary  phosphate,  the  sokition  of  the  latter  being  aided  by  the  primary 
alkali  phosphate  and  sodium  cldoride.  Occasionally  a  coat  is  noticed  on  the 
surface  of  the  urine,  an  appearance  once  thought  to  be.  a  sign  of  pregnancy. 
Tins  coat  is  now  known  to  consist  chiefly  of  secondary  phosphate  of  calcium, 
which  may  crystallize  out  on  the  urine  becoming  alkaline.  Calcium  dues  not 
occur  as  phosphate  in  an  alkaline  urine  (see  p.  959). 

Calcium  Carbonates. — Of  these  there  are  two,  the  primary  or  acid, 
CaH2(C03)2,  and  the  secondary  or  neutral  carbonate,  CaCOa.  Neutral  calcium 
carbonate  is  the  substance  of  which  sea  shells,  coral,  egg-shell,  and  otoliths 
consist.  It  is  found  in  the  ash  of  bones  to  the  extent  of  13.032  per  cent. 
(Zalesky).  Ajuitite  is  a  mineral  having  the  formula  CaioF2(P04)6,  and  Hoppe- 
Seyler,  using  Zalesky's  figures,  believes  that  bone  has  a  composition  repre- 
sented by  Cai,C03(PO,)6,  or  3Ca3(P0,)2,CaC03,  in  which  CO3  has  the  position 
of  F2  in  apatite.  In  the  wasting  of  the  mineral  matter  of  bones  in  osteoma- 
lacia this  formula  of  composition  remains  constant, •  one  molecule  of  calcium 
carbonate  always  being  removed  for  every  three  molecules  of  the  phosphate. 
Neutral  calcium  carbonate  is  insoluble  in  water  or  alkali,  but  dissolves  in 
water  containing  carbonic  oxide  to  form  the  soluble  acid  carbonate,  CaH2(C03)2, 
This  is  found  in  blood  and  lymph,  and  in  minute  quantities  in  all  the  tissues. 
It  is  found  in  herbivorous  urine,  which  contains  carbonic  acid  in  excess,  but  it 
is  soon  deposited  as  neutral  carbonate  as  the  carbonic  oxide  diffuses  into  the 
air.  It  occurs  in  all  alkaline  and  neutral  urines,  though  to  a  less  extent  than 
calcium  phosphate  in  acid  urines.  It  is  found  in  pancreatic  juice  and  in  the 
saliva,  from  which  latter  is  derived  the  calcic  carbonate  which,  mixed  with 
bacteria  and  other  organic  matter,  is  deposited  as  tartar  on  the  teeth. 

The  ferment  rennet  does  not  act  in  the  absence  of  calcium  salts.  The 
coagulation  of  the  blood  requires  the  presence  of  calcium  salts,'-^  and  fibrin 
always  contains  calcium.  If  ten  parts  of  blood  be  drawn  into  one  part  of  a 
1  per  cent,  solution  of  potassium  oxalate,  thus  precipitating  the  calcium,  no 
coagulation  takes  place,  but  on  the  addition  of  calcium  chloride  a  typical  fibrin 
forms.  A  solution  of  sodium  oxalate  passed  through  a  beating  excised  heart 
causes  it  to  cease  beating'  and  nerves  and  muscles  lose  their  irritability  when 
calcium  salts  are  abstracted  from  them  with  sodium  oxalate.*  These  facts 
illustrate  the  intimate  relation  between  calcium  salts  and  the  functional  activity 
of  protoplasm. 

Detection. — Ammonium  oxalate  in  neutral  or  alkaline  solutions  of  calcium 
salts  gives  a  precipitate  of  calcium  oxalate — a  white  powder,  insoluble  in  acetic 
or  oxalic  acid. 

1  M.  Levey:  Zeitschrift  fiir  phijsiolofjische  Chemie,  1894,  Bd.  19,  p.  239. 
"  Arthus  et  Paget:  Archives  de  Physiologie,  vlo.  ii.  p.  739. 
'  Howell  and  Cooke  :  Journal  of  Phy.volofjy,  1893,  vol.  14,  p.  219,  note. 
*  Howell  :  Journal  0/  Physiology,  1894,  vol.  16,  p.  476. 


THE    CHEMISTRY    OF    THE   ANEMAL    BODY.  969 

Calcium  in  tiik  Body. — Calcium  salts  arc  especially  needed  in  childliood  for  the 
growth  of  the  bones.  It  lias  been  estimated  that  the  human  suckling  retjuires  0.32  gram 
CaO  dail}',  and  in  the  milk  for  that  time  is  contained  0.55  gram  to  2.37  grams,  so  that 
there  may  easily  be  lack  of  CaO  when  absorption  is  unfavorable.  In  children  with  rickets 
the  bones  contain  too  little  calcium,  and  are  abnormally  weak  and  flexible.  This  same  con- 
diti(m  may  be  reproduced  in  young  growing  dogs  by  feeding  them  entirely  on  meat  and  I'at, 
which  contain  too  little  calcium  lor  j)roper  skeletal  devel()|)ment. '  Such  dogs  iivovf  rapidly 
in  size,  especially  around  the  thorax,  while  the  pelvis  remains  ludicrously  small,  the  extrem- 
ities become  bent  and  finally  incapable  of  supporting  the  weight  of  the  body.  A  puppy 
of  the  same  litter  fed  on  the  same  food  but  with  the  addition  of  bones  grows  normally.  In 
certain  cases  even  when  children  are  fed  with  sufficient  calcium  they  still  have  the  rickets. 
This  might  be  due  to  a  lack  of  ability  to  absorb  the  salts,  but  this  Riidel  ^  has  disproved. 
To  a  child  having  rickets  he  administered  a  calcium  salt,  and  confirmed  its  absorption 
by  the  increase  in  the  calcium  contents  of  the  urine,  the  result  being  the  same  as  with 
a  normal  child.  (Example:  Normal  da}%  0.0196  gram  CaO  in  urine;  after  I'eeding 
1.4  grams  CaO  dissolved  in  acetic  acid  the  amount  in  the  urine  rises  to  0.0396  gram  for 
the  twenty-four  hours. )  Riidel  therefore  concludes  that  the  cause  of  rickets  may  be  in  a 
local  change  of  the  bones  themselves,  whereby  calcium  salts  are  not  deposited  in  the  normal 
manner. 

In  osteomalacia  there  occurs  a  solution  of  the  salts  of  the  bones  in  adult  life,  called 
softening  of  the  bones.  In  osteoporosis,  which  is  a  simple  atrophy  of  the  bones,  similar 
effects  are  produced.  Voit '  fed  a  pigeon  for  a  year  on  washed  wheat  and  distilled  water, 
at  the  end  of  which  time  the  pigeon  apparently  did  not  diff'er  from  the  normal  bird.  A 
few  months  later  a  wing  was  broken,  and  the  autopsy  discovered  osteoporosis  in  high 
degree,  the  skull  being  especially  attacked.  Weiske  *  has  shown  that  rabbits  ultimately 
die  when  fed  on  oats  which  are  poor  in  calcium  ;  the  oats  yield  an  acid  ash  and  produce  an 
acid  urine.  On  autopsy  osteoporosis  is  found.  This  does  not  take  place  when  calcium 
carbonate  is  added  to  the  food.  Whether  the  loss  of  salts  to  the  bone  is  due  to  a  normal 
metabolism,  or  to  solution  due  to  the  production  of  acids  in  the  metabolism  of  proteid, 
is  an  unanswered  problem  (see  pp.  950,  955)  the  discussion  of  which  lack  of  space  forbids.* 
In  such  experiments  as  the  above,  the  percentage  of  ash  is  always  diminished,  while  the 
percentage  of  organic  matter  always  rises,  whereas  the  actual  percentage  composition  of  the 
ash  itself  remains  the  same.  This  is  a  strong  argument  in  favor  of  the  view  that  bone  is 
a  mineral  of  definite  chemical  composition.  The  mineral  matter  of  bone  is  believed  by 
some  to  be  loosely  combined  with  the  organic  material,  principally  ossein,  but  of  this  there 
is  no  proof. 

The  exact  amount  of  calcium  salt  necessary  to  keep  up  the  supply  in  the  adult  body  is 
unknown,  but  it  must  be  exceedingly  small.  A  dog  of  3.8  kilograms  eating  with  his  food 
0.043  gram  CaO  maintains  his  calcium  equilibrium  (Heiss). 

Regarding  the  absorption  of  calcium  salts,  it  has  long  been  questioned 
whether  inorganic  salts  can  be  absorbed,  since,  it  was  argued,  insoluble 
phosphate  would  immediately  be  precipitated  in  the  blood.  It  has,  however, 
been  conclusively  shown  that  such  .salts  when  eaten  produce  an  increase  in  the 
calcium  of  the  urine®  and  it  is  known  that  blood  has  a  special  capability  for 
carrying  calcium  phosphate.     Calcium  carbonate  and  chloride  are  capable  of 

'  E.  Voit:  Zeitschrift  fur  Biologie,  1880,  Bd.  16,  p.  70. 
'  Archiv  fiir  exper.  Pathologie  und  Pltarm-akologie,  1893,  Bd.  33,  p.  90. 
'  Hermann's  Handbuch,  1881,  vi.  1,  p.  379. 
*  Zeitschrift  fiir  Biologie,  1894,  Bd.  3],p.  421. 

5  See  Weiske,  loc.  cit. ;  Bunge,  Physlologische  C'hemie,  3d  ed.,  1894,  p.  104;  V.  Noorden,  Path- 
ologie der  Stoffwechsels,  1893,  pp.  48  and  413.  ^  Riidel,  Op.  at.,  p.  79. 


970  ^l.V  AMERICAN    TEXT-BOOK    OF  rilY^IOLOGY. 

absorption,  while  al)sorj)tioii  of  the  phuspliate  may  be  consitlerod  as  still  in 
doubt.  If  calcium  chloride  be  given,  a  little  of  the  calcium  appears  in  the 
urine,  and  all  of  the  chlorine,  this  being  due  to  the  conversion  in  the  intes- 
tine of  calcium  chloride  into  calcium  carbonate  and  sodium  chloride,  which 
latter  is  completely  absorbed.  Organic  salts  of  calcium  such  as  the  acetate  are 
absorbable,  as  are  probably  proteid  combinations  with  calcium  such  as  casein. 
Milk  and  egg-yolk  are  the  foods  richest  in  calcium  salts,  cow's  milk  containing 
more  calcium  to  the  liter  than  does  lime-water.' 

The  excretion  of  calcium  takes  place  in  major  part  as  triple  phosphate  from 
the  wall  of  the  intestine,  in  minor  part  through  the  urine  (for  the  latter  see  pp. 
959  and  968).  It  is  excreted  during  starvation,  and  is  the  principal  constituent 
of  starvation  feces  (Yoit).  The  secretions  of  the  intestines,  according  to  Fr. 
MUller,"  hardly  contain  enough  calcium  to  account  for  that  found  in  the  feces,, 
so  that  it  is  probably  excreted  by  the  epithelial  cells  of  the  villus.  In  starva- 
tion the  source  of  excreted  calcium  is  principally  from  the  breaking  down  of  tis- 
sue, but  partially  from  the  metabolism  of  the  bones.  The  excretion  is 
never  large.  On  subcutaneous  injection  of  small  amounts  of  calcium  acetate 
in  dogs,^  the  calcium  excretion  may  be  raised  for  several  days.  On  venous 
injection  of  0.8  gram  CaO  as  acetate,  after  one  hour  but  0.3  gram  could  be 
found  above  the  normal  in  the  blood,  and  analysis  of  the  liver,  kidney,  spleen, 
and  intestinal  wall  failed  to  reveal  more  than  the  usual  minimal  amounts  of 
calcium.  As  it  is  never  rapidly  excreted  it  must  have  been  temporarily  depos- 
ited in  some  unknown  part  of  the  body.  Rey  *  believes  the  large  intestine  to 
be  the  principal  organ  of  calcium-excretion,  while  F.  Voit  ^  attributes  this 
function  to  thfe  small  intestine. 

Strontium,  Sr  ==  87.5. 

Cremer®  has  shown,  on  adding  strontium  phosphate  to  almost  calcium-free  food  of  young 
growing  dogs,  that  the  strontium  line  could  be  detected  in  the  subsequent  spectral  anab'sis 
of  their  bones.  Weiske,'  on  feeding  j'oung  rabbits  with  food  nearly  free  from  calcium, 
and  with  addition  of  strontium  carbonate,  found  the  ash  in  some  of  the  bones  to  contain, 
in  the  place  of  CaO,  as  high  as  4.09  per  cent,  of  SrO.  In  both  of  the  above  experiments 
the  skeleton  remained  very  undeveloped  in  comparison  with  the  normal,  so  that  strontium 
cannot  be  considered  a  physiological  substitute  for  calcium. 

Magnesium,  Mg  =  24.3. 

This  is  the  second  in  importance  of  the  alkaline  earths.  It  is  present 
wherever  calcium  is  found,  but  in  comparison  with  calcium  it  has  been  little 
investigated.  It  occurs  principally  as  pho.sphate,  but  is  found  as  carbonate 
in  herbivorous  urine.     Of  the  total  quantity  of  magnesium  in  the  dog,  Heiss 

^  Bnnge:  Physiologiache  Chemie,  3d  ed.,  1894,  p.  101. 
'  Zeitschrift  fUr  Biologie,  1894,  Bd.  20,  p.  356. 

'  Rey:  Archiv  fur  exper.  Pathologic  und  Phorrhokologie,  1895,  Bd.  35,  p.  298. 
*  Rey,  loc.  cit.  *  Zeitschrift  fiir  Biologie,  1893,  Bd.  29,  p.  325. 

®  Sitzungsberichie  der  Gesellschaft  fiir  Morphologic  und  Physiologic  in  MUnchen,  1891,  Bd.  7, 
p.  124. 

^  Zeitschrift  fiir  Biologie,  1894,  Bd.  31,  p.  437. 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  971 

found  that  71  per  cent,  belonged  to  the  boue.s.  It  is  found  decidedly  pre- 
dominating over  calcium  in  muscle,  but  is  less  in  quantity  than  calcium  in 
the  blood. 

Magnesium  Phosphates. — Magnesium  tertiary  phos[)hate,  Mg2(P04)3,  is 
found  in  the  ash  of  bones  to  the  extent  of  about  1  per  cent.,  is  present  in  blood 
and  especially  in  muscle,  probably  in  combination  with  proteid,  and  contrib- 
utes to  the  functional  activity  of  protoplasm.  It  is  continuously  excreted 
by  the  walls  of  the  intestinal  canal.  The  primary  and  secondary  phosphates 
of  magnesium  are  found  in  carnivorous  urine,  solution  of  the  latter  being 
aided  by  the  presence  of  primary  alkali  phosphate  and  sodium  chloride. 
Tertiary  phosphate  of  magnesium  is  insoluble  in  water,  the  secondary  very 
slightly  so,  the  primary  quite  soluble ;  but  all  are  soluble  in  acids.  In  the  am- 
moniacal  fermentation  of  the  urine,  ammonium  magnesium  phosphate,  MgXIT^- 
PO4,  is  precipitated  as  a  fine  crystalline  powder  insoluble  in  alkalies.  When- 
ever this  fermentation  takes  placed,  whether  in  the  bladder  or,  by  similar 
reaction,  in  the  intestines  (herbivora  especially),  stones  are  formed. 

Magnesium  Carbonates. — The  neutral  carbonate,  MgCOg,  is  insoluble  in 
water,  but  soluble  in  water  containing  carbonic  oxide,  forming  secondary  or  acid 
carbonate,  MgH2(C03)2.     This  latter  occurs  in  herbivorous  urine. 

Detection. — A  mixture  of  sodium  phosphate  and  ammonia  containing  an 
ammonium  salt  (NH^Cl)  precipitates  from  magnesium  solutions  magnesium 
ammonium  phosphate. 

Magnesium  in  the  Body. — Considerations  regarding  the  absorption  of 
calcium  apply  likewise  to  magnesium.  It  is  absorbed  by  the  intestine  as  inor- 
ganic and  probably  as  organic  combinations.  If  growing  rabbits  be  fed  on 
a  diet  poor  in  calcium  salts,  but  containing  magnesium  carbonate,  the  bones 
may  be  brought  to  contain  double  the  normal  quantity  of  magnesium,  but  the 
skeletal  development  remains  far  behind  that  of  a  normal  rabbit,  and  there- 
fore magnesium  can  in  no  sense  be  considered  a  substitute  for  calcium.^  The 
magnesium  salts,  whether  phosphate  or  carbonate,  being  more  soluble  than  the 
calcium  salts,  occur  in  the  urine  in  greater  abundance.  Indeed,  in  carniv- 
orous urine  the  major  part  of  excreted  magnesium  is  found  in  the  urine,  the 
balance  being  given  oif  through  the  intestinal  wall  to  the  feces.  In  starvation 
the  source  of  the  excreted  magnesium  is  from  the  bones,  and  especially  from 
destruction  of  its  combination  in  proteid  metabolism. 

Iron,  Fe  =  56. 

This  is  the  one  heavy  metal  which  is  an  absolute  necessity  for  the  organ- 
ism. About  three  grams  occurs  in  the  average  man.  It  has  been  demon- 
strated of  certain  bacteria  that  they  will  not  develop  in  the  absence  of  iron, 
and  this  is  believed  to  be  true  of  all  protoplasm.  Iron  is  found  through- 
out the  body,  and  is  especially  an  ingredient  of  haemoglobin  (0.4  per  cent.), 
which  carries  oxygen  to  the  tissues.  It  is  found  deposited  in  the  liver  and 
the  spleen  as  ferratin,  hepatin,  and  other  less  investigated  organic  compounds. 
1  Weiske  :  Zeitschrift  fur  Biologie,  1894,  Bd.  31,  p.  437. 


972  AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

It  is  found  in  muscle  washed  free  from  blood.  Iron  appears  in  urine  and  in 
milk  as  organic  compounds,  and  in  the  bile,  gastric  juice,  and  intestines  as 
phosphate,  in  the  feces  as  sulphide.  Iron  occurs  in  two  forms,  the  ferro-  and 
ferri-  compounds,  in  which  it  has  respectively  two  and  three  bonds. 

Ferrosulphide,  FeS. — This  is  found  in  the  feces  and  is  the  ])rotluct  of 
the  action  of  sulphuretted  hydrogen  or  alkaline  sulphide  on  both  inorganic 
iron  and  likewise,  more  slowly,  on  organic  iron-containing  com])ounds  (fer- 
ratin,  haematogen,  etc.).  Ammonium  sulphide  acts  in  a  similar  manner,  and, 
in  all  cases,  ferric  salts  are  reduced  to  ferrous : 

2FeCl3  +  3(NH,)2S  =  2FeS  +  6XH,C1  +  S. 

Ferric  chloride. 

Ferric  Phosphate,  FePO^. — This  is  found  in  the  gastric  juice,  bile,  and 
probably  in  the  intestinal  juice  ;^  it  is  not,  as  many  have  believed,  given  off 
by  the  epithelia  of  the  intestines.  It  is  soluble  in  mineral  acids,  but  insoluble 
in  water,  alkalies,  or  acetic  acid. 

Detection. — Ammonium  sulphide  gives  a  black  precipitate  of  ferrous  sulphide  in  all 
iron  solutions.  Ferrocj-anide  of  potassium  gives  a  deep  blue  coloration  (Berlin-blue)  to 
solutions  of  ferric  salt.  Ferricj'anide  of  potassium  gives  TurnbuU's  blue,  very  similar 
to  Berlin-blue,  with  solutions  of  ferrous  salts. 

Irox  in  the  Body. — The  amount  of  iron  in  the  urine  is  very  small, 
amounting  daily  in  a  large  starving  dog  to  0.0013-0.0049  gram.'  Feeding 
iron  compounds  does  not  increase  the  amount  of  iron  in  the  urine.  Forster' 
fed  a  dog  of  26  kilograms  for  thirty-eight  days  with  washed  meat  containing 
0.93  grams  of  iron,  and  in  the  feces  were  found  3.59  grams  belonging  to  the 
same  period.  Here  there  was  a  loss  of  2.66  grams  *  of  iron  from  the  body, 
and  the  necessity  of  iron  as  a  food  was  established. 

Concerning  the  method  and  the  amount  of  iron-absorption,  considerable  difficulty  has 
been  encountered  owing  to  the  fact  that  both  absorj^tive  and  secretive  organs  lie  in  the 
intestinal  canal.  On  feeding  a  dog  for  thirteen  days  with  meat  containing  0.  ISO  gram  Fe, 
there  were  found  in  urine  and  feces  for  the  same  time  0.1765  gram  Fe ;  then  to  the  same 
food  for  a  similar  length  of  time  were  added  0.441  gram  Fe  (as  sulphate),  making  in  all 
0.636  gram  Fe,  and  of  this  0.6084  gram  were  recovered  in  the  excreta.^  This  experiment 
proves  only  that  such  absorption  as  may  take  jjlace  is  pretty  nearly  balanced  by  the  excre- 
tion. After  eating  blood  the  feces  are  found  to  contain  much  lutimatin,  and  it  is  believed 
that  iron  cannot  be  absorbed  in  that  way.  Bunge®  has  sought  for  one  oi'  the  antecedents 
of  haemoglobin  in  egg-yolk,  and  has  described  it  as  an  iron-containing  nucleo-albumin, 
which  he  names  hfematogen.  That  and  similar  nueleo-albumins  existing  in  plants  he  con- 
ceives to  be  the  source  of  absorbable  iron,  while  inoriranic  salts  of  iron  aid  only  indirectly 
by  forming  iron  sulphide,  thus  i>reve!iting  the  same  formation  from  organic  iron  (see  above). 
IMarfori^  has  jncparcd  a  substance  from  i)roteid  and  iron  salts,  called  fcrratin,  which  con- 
tains 4  to  s  ]HT  cent,  of  iron  :  it  is  a  coiiiiiound  unaffected  by  gastric  juice  or  by  boiling ;  it 

'  Macallum :  Journal  of  Phyxioloyy,  1894,  vol.  15,  p.  268. 

^  Forster:  Zeilschrift  fur  Biologie,  187.3,  Bd.  9,  p.  297.  ''  Loc.  cit. 

*  This  figure  is  probably  too  high,  but  the  principle  itself  is  fundamental.  See  Voit, 
Hermann'ii  Handbook,  1881,  vi.  1,  p.  385. 

^Hantburger:  Zeiischrift  filr  phynioloffij^rhe  Chemie,  187S,  l?d.  2.  p.  191. 

*  Zelt.frlirit't  filr  physiologiiicJie  Ckeiiiie.  1884,  Bd.  9,  p.  49. 

'  Archil-  fiir  ejrper.  Pathologic  und  Pharmakologie,  1891,  Bd.  29,  p.  212. 


THE    CHEMISTRY   OF    THE   ANIMAL    BODY.  97'J 

is  soluble  in  thealkaliiio  iiiti'stini',  wlicic  it  is  l)iit  slowly  affected  by  alkaline  sulphide.  Now 
this  same  forratin  is  louiid  in  tlu;  body  itscU",  esijccially  in  \.\ni  liver/  althoui-di  not  the  only 
iron-containing  substance  of  the  liver. '^  If  ferratin  be  fed,  the  (juantity  of  it  incirease.s  in 
the  liver.  If  a  dog  be  fed  on  milk,  which  is  alway.s  poor  in  iron,  and  he  be  bled  from 
time  to  time,  the  ferratin  disappears  from  the  liver,  being  used  for  the  formation  of  new 
red  blood-corpuscles.^  Such  a  liver  does  not  change  color  when  placed  in  dilute  ammo- 
nium sulphide,  while  one  containing  ferratin  or  other  iron  compounds  gradually  turns  black 
from  iron  sulphide.  As  it  is  not  decomposed  by  boiling,  i'crratin  is  found  in  the  usual 
cooked  moat.  Concerning  the  influence  of  inorganic  salts,  Schmiedcberg  agrees  with  Bunge 
that  the  formation  of  iron  sulphide  protects  the  ierratin  Irom  attack. 

The  insolubility  of  iron  salts  in  alkaline  solutions  has  raised  the  question  of  their 
absorption  by  the  blood.  If  inorganic  iron  salts  be  injected  into  a  vein,  the  iron  reappears 
chiefly  in  the  intestines,  with  only  3  to  4  per  cent,  in  the  urine  (Jakobj) :  in  too  great 
quantities  they  have  jiowerful  to.xic  properties.  Gottlieb*  administered  0.1  gram  of  iron 
as  sodium  iron  tartrate  subcutaneously  to  a  dog  during  a  period  of  nine  days ;  twenty-eight 
days  after  the  first  injection  0.0969  gram  Fe  had  been  removed  in  the  excreta  over  and 
above  the  normal  excretion  calculated  for  the  same  time.  It  was  shown  that  this  iron  was 
especially  stored  in  the  liver.  It  may  be  argued  that  such  iron,  being  foreign  to  the  organ- 
ization, was  deposited  in  the  liver  and  gradually  excreted  through  the  bile,  as  other  heavy 
metals,  mercury,  copper,  lead,  would  be.  Kunkel*  fed  mice  and  to  the  food  of  half  their 
number  added  a  solution  of  oxychloride  of  iron  (FeCl:„4Fe(OII)3,  liquor  ferri  oxychlorati) : 
in  the  livers  of  those  fed  with  iron,  iron  was  present  to  a  greater  extent  than  in  the  others ; 
but  here,  again,  the  surplus  can  be  attributed  to  the  sulphide-forming  protective  power  of 
the  added  salts,  which  Kunkel  admits,  though  maintaining  the  contrary  ground.  The  only 
proof  of  the  absorption  of  inorganic  salts  emanates  from  Macallum,®  who  showed,  after 
feeding  chloride,  phosphate,  and  sulphate  to  guinea-pigs,  that  the  epithelial  cells  and  the 
subepithelial  leucocytes  of  the  intestines  gave  a  strong  microchemical  reaction  for  iron 
with  ammonium  sulphide.  With  small  doses  this  was  observed  only  near  the  pylorus,  for 
iron  is  soon  precipitated  by  the  alkali  of  the  intestines,  but  where  the  iron  salt  was  in  suf- 
ficient quantity  to  neutralize  the  intestinal  alkali  it  could  be  absorbed  the  whole  length  of 
the  small  intestines.  Whether  inorganic  iron  unites  with  proteid  before  absorption  or  not 
is  unknown. 

Regarding  the  transformation  of  iron  compounds  after  absorption  into  haemoglobin, 
little  is  known  except  that  the  necessary  synthesis  takes  place  in  the  spleen,  in  the  bone- 
marrow,  and  probably  in  the  liver.  On  the  destruction  of  red  blood-corpuscles,  proteid 
bodies  holding  iron  in  combination  are  deposited  in  the  cells  of  the  liver  and  spleen,  this 
being  noticeable  in  pernicious  anaemia.  On  the  production  of  icterus  with  arseniuretted 
hydrogen,  similar  iron  compounds  are  noted  in  the  liver,  being  cleavage  products  of  h;«mo- 
globin  in  its  transformation  to  biliary  coloring  matter.  The  amount  of  iron  normally 
excreted  from  the  body  is  far  less  than  the  corresponding  biliary  coloring  matter  (see 
Haemochromogen),  showing  that  the  rest  of  the  iron  is  retained  for  further  use  in  con- 
structing new  haemoglobin. 

Iron  is  excreted  as  phosphate  in  the  gastric  juice,  in  bile  (in  considerable  quantity),  and, 
according  to  Macallum,^  in  the  intestinal  juice.  In  the  urine  it  is  present  as  an  unknown 
organic  compound. 

A  newborn  child  or  animal  has,  proportionately  to  its  weight,  far  more  iron  than  at  any 

^  Maifori,  loc.  cit.,  and  Schmiedeberg,  Arckiv  fur  exper.  Pathologie  und  Pharmakologie,  1894, 
Bd.  33,  p.  101. 

^  Vay:  ZeitMchrift  fur  phyniologische  Chemie,  1895,  Bd.  20,  p.  398. 
^  Schmiedeberg,  Op.  cit,  p.  110. 

*  Zeitschrift  fiir  phyi^iologische  Chemie,  1891,  Bd.  15,  p.  371. 

*  Pflugers  Archiv,  1891,  Bd.  50,  p.  11.  "  Journal  of  Physiology,  1894,  vol.  16,  p.  268. 
'  Op.  cit.,  p.  278. 


974 


AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 


other  time  of  its  lil'c.  This  iron  is  lost  only  very  slowly,  lu'iu-e  the  very  small  (jtiantity  of 
iron  in  the  milk  answers  all  necessities.  The  other  salts  of  the  milk  arc  in  the  same  pro- 
portion to  one  another  as  are  the  salts  in  the  newborn  animal. 

Tables  representing  generally  accejjtetl  analyses  of  the  mineral  constituents  of  the  more 
important  fluids  and  cells  of  the  body  are  subjoined.  Only  very  i)ronounced  differences 
are  to  be  taken  into  consideration  in  drawing  conclusions,  for  analyses  of  animals  of  dif- 
i'orent  species,  or  of  the  same  species,  or  even  of  the  same  animal  at  different  times,  show 
wide  variations.     The  tables  rejjresent  parts  in  1000  of  fresh  substance : 

I. 


KsS04. 

KCl. 

NaCl. 

NajCOa. 

CaCOa. 

CajPO^. 

MgCOj. 

Mg3(P04)j. 

FePO«. 

Saliva  1  (dog)  .... 
Pancreas  *•'  (dog)    .   . 
Gastric  juiced  (dog). 
Fresh  bile<  (dog)  .  . 

0.209 

6.022 

0.940 

0.93 

1.125 

1.546 
2.53 

2.507 
0.185 

0.940 
3.30(NaaO) 

0.056 

0.150 

0'.624(CaOj) 
0.030 

0.113 
0.07 
1.729 
0.039 

O.Ol(MgO) 
0.007(MgO) 

0.01 
0.226 

0.082 
0.021 

11. 


Blood-scrum  s  (dog)  .  . 
Blood-corpuscles  0  (pig) 
Blood-serum  fi  (pig)    .   . 

Muscle "  (ox)     

Milk  8  (cow) 


KjO. 

NajO. 

CaO. 

MgO. 

FeaOg, 

0.202 

4.341 

0.176 

0.041 

0.01 

5.543 

0 

0 

0.158 

0.273 

4.272 

0.136 

0.038 

4.654 

0.770 

0.086 

0.412 

0.057 

1.67 

1.05 

1.51 

0.20 

0.003 

CI. 


3.%1 
1.504 
3.611 
0.672 
1.86 


PA- 


0.489 
2.067 
0.188 
4.644 
1.60 


THE  CHEMISTRY  OP  THE  COMPOUNDS  OF  CARBON. 

Derivatives  of  Methane. 

The  complicated  structure  aud  the  great  variety  of  the  compounds  of  car- 
bon are  due  to  the  fact  that  carbon-atoms  have  a  greater  power  for  union 
with  one  another  than  liave  tlie  atoms  of  otlier  elements. 

Saturated  Hydrocarbons  or  Paraffins  (formula,  CuHgn  +  ^ ). — 

Methane,  CH^,  gas.  Pentane,  C5H12,  liquid  at  38°. 

Ethane,  CHe,     "  Hexane,  CoHu:  "     '1°- 

Propane,  C3H,,    "  Heptane,  CH.e,  "     98°. 

Butane,  C4Hio,    "  etc. 

These  are  the  constituents  of  petroleum  and  natural  cas,  and  are  formed  by  the  action 
of  low  heat  on  coal  under  pressure  in  the  absence  of  oxygen,  and  are  probably  derived 
from  fossil  animal  fat,  since  it  has  been  shown  that  the  paraffins  may  be  obtained  in  large 

'  Herter:  Hoppe-Seyler's  Phijsiologmhe  Chemie,  p.  192. 

*  Kroner :  Quoted  liy  Halliburton,  Chenmtry,  Phyxiological  and  Pathological,  p.  656. 
'  liidder  and  Scliniidt:  Quoted  by  Halliburton,  Op.  ciL,  p.  638. 

*  Hoppe-Seyler  :  Physiolof/ische  Chemie,  p.  302. 

*  Bunge:  Ibid.,  3d  ed.,  p.  2G5. 

*  Op.  cit.,  p.  222  (Bunge  finds  NajO  exceeds  K^O  in  the  blood-corpuscles  of  cattle). 
'  Bunge:  Zeitschrifl  Jilr  phisiologb^che  Chemie,  1885,  Bd.  9,  p.  00. 

*  Bunge  :  Physiologische  Chemie,  3d  ed.,  p.  100. 


THE    CHEMISTRY   OF    THE  ANIMAL   BODY.  975 

quantity  by  heating  fish  oil  at  u  pressure  of  fen  atmospheres.'  The  i)araffins  may  all  be 
formed  synthetically  from  methane  by  the  action  of  sodium  on  halogen  compounds  of  the 
group : 

2CII3I  +  2Na  -  C,He  +  2NaI. 

0,115!  +  Cir,l  +  2Na  =  CJIs  +  2NaI. 

'i'lii.s  may  be  continued  to  ronii  a  theoretically  endless  number  of  compounds.  Paraffins  are 
notably  resistant  to  chemical  reagents,  not  being  affected  })y  either  concentrated  nitri(;  or 
sii]i)huric  acids.  Vaseline  contains  a  mixture  of  paraffins  melting  between  30°  and  40°. 
By  massage  vix^ivVmc  may  be  absorbed  by  the  skin,  through  tbe  epithelial  cells  of  the  seba- 
ceous glands.  In  rabbits  and  dogs,  directly  after  such  treatment,  it  may  be  detected  de- 
posited especially  in  muscle,  but  it  is  for  the  greater  part  destroyed  in  the  body.* 

MoNATOMic  Alcohol  Radicals. 

These  are  radicals  which  may  be  considered  as  paraffins  less  one  atom  of  hydrogen,  and 
therefore  having  one  free  bond.  They  ibrm  the  basis  of  homologous  series  of  alcohols 
and  acids. 

Monatomic  Alcohols  (general  formula,  C„H2„  +  lOH). — 

Methyl  alcohol,  CII3OH.  Amyl  alcohol,  CaHnOH. 

Ethyl  alcohol,  C^HjOH.  Hexyl  alcohol,  CV,Hi,OH. 

Propyl  alcohol,  CH^OH.  Heptyl  alcohol,  C^H.^OH. 
Butyl  alcohol,  C4H9OH.  etc. 

General  Reactions  for  Primary  Alcohols. — (1)  Alcohols  treated  with  sulphuric  acid 
give  ethers  (see  Ethyl  ether) : 

2CH3OH  -f  H.,S04  =  ch;>^  +  ^^^  +  ^*^^*- 

Methyl  ether. 

(2)  Alcohols  oxidized  give  first  aldehyde  and  then  acid : 

CH3OH  +  0  =  HC  ^g  +  H,0. 

Methyl  aldehyde. 

CH,0-fO  =  HC<gjj 

Formic  acid. 

(3)  Primary  alcohols  may  be  prepared''  by  reduction  of  the  aldehyde  with  nascent 
hydrogen, 

CH3CHO  +  H,  =  CHgCH-^OH 

Ethyl  aldehyde.  Ethyl  alcohol. 

and  similarly  by  reduction  of  the  acid. 

Secondaiy  Alcohols. — From  propyl  alcohol  upward  there  are  alcohols  isomeric  with  the 
primary  alcohols,  but  in  which  the  grouping  R  —  CHOH  —  R  is  characteristic.  These  are 
secondary  alcohols,  and  may  be  produced  by  the  action  of  nascent  hydrogen  on  ketones : 

CH3  -  CO  -  CH3  +  H,  =  CH3  -  CHOH  -  CH3. 

Acetone.  Isopropyl  alcohol. 

Tertiary  Alcohols. — These  have  the  general  formula  R3  — COH. 

^  Engler :  Berichte  der  deutschen  chemischen  Gesellsehaft,  1S88,  Bd.  21,  p.  1816. 

'  Soubiranski :  Archivfur  exper.  Pathologie  und  Pharmakologie,  1893,  Bd.  31,  p.  329. 

'  Again  attention  is  called  to  the  fact  that  the  list  of  these  reactions  is  in  no  wise  complete, 
but  only  intended  to  be  suggestive  of  what  should  be  mastered  from  a  text-book  on  general 
chemistry. 


976  AX   AMERICAN   TEXT-BOOK    OF   PHYSIOLOGY. 

Monobasic  Acids — The  Fatty  Acids  (fbnniila,  CllonOg). — 

Formic  acid,  II  COOII.  Capric  acid,  CsH.sCOOH. 

Acetic  acid.  CH.rOOII.  Laurie  acid,  C„H.^COOH. 

Propionic  acid,  CJIjCOOH.  Myristie  acid,  C,3H,;C00H. 

Butyric  acid,  C3H,C00H.  Palmitic  acid,  C.sHs.COOH. 

Valerianic  acid,  C^HsCOOH.  Stearic  acid,  CnHo/JOOH. 

Caproic  acid,  CsHuCOOH.  Arjichidic  acid,  CsII^^COOH. 

(Enanthylic  acid,  CJI^COOH.  Cerotic  acid,  C^sHmCOOH. 

Caprylic  acid,  CjH.sCOOH.  Melissic  acid,  C29H59COOH. 

These  are  organic  compounds  of  acid  reaction  in  which  one  atom  of  h}'dro«ren  is  replace- 
able by  a  metal  or  an  organic  radical.  Combined  with  glycerin  the  higher  members  of  the 
series  (from  C4  up)  form  the  neutral  fats  of  the  organization.  By  distillation  of  a  fatty 
acid  with  alkaline  hydrate,  a  hydrocarbon  is  obtained  containing  one  carbon  atom  less  than 

the  acid  used. 

CH3C00Na  +  NaOH  =  CH,  +  Na^CO,. 

Preparation. — [a)  Through  oxidation  of  alcohols  or  of  aldehydes, 

CHjOH  +  0,  =  CH3COOH  +  H3O. 

(h)  Through  the  action  of  carbon  dioxide  on  the  sodium  compound  of  alcohol  radicals, 

CHjNa  +  CO2  =  CH3C00Na. 

Compounds  of  Methyl. 
Methane,  or  Marsh-gas,  CH^. — This  ga.s  is  produced  by  intestinal  putre- 
faction, and  is  the  only  hydrocarbon  found  in  the  body.  It  is  formed  in  largest 
quantities  from  the  fermentation  of  cellulose,  which  takes  place,  according  to 
Hoppe-Seyler,  thus : 

C,H,oO,H-H,0  =  CeH,A- 
CeHi206  =  3CH,H-3C02. 

Tappeiner  ^  finds  that  less  CH^  than  CO^  is  prcKluced  in  cellulose  fermenta- 
tion in  the  intestine,  and  that  the  lower  fatty  acids  (acetic  to  valerianic)  are 
also  formed.  This  putrefaction  is  especially  great  in  the  ccscum  of  herbivora. 
Methane  is  also  a  product  of  putrefiictiou  of  proteid  (but  not  of  casein,  since 
it  is  not  present  when  milk  is  fed).  Through  the  putrefaction  of  cholin,  a 
decomposition  product  of  lecithin,  methane  is  likewise  evolved  in  small 
quantity.^  Further,  methane  may  be  produced  from  the  putrefaction  of  metal- 
lic acetates  : 

CaC\HA  +  2H2O  =  CaCOj  H-  CO^  +  H^O  +  2CH,. 

PropeHies. — A  colorles.s,  odorless  gas  which  burns  with  a  didl  flame.  It  is 
absorbed  by  the  blood,  and  in  the  herbivora  is  given  off  by  the  lungs  often  in 
laro-er  quantity  than  from  the  rectum.^  In  man  only  little  is  produced.  Methane 
is  not  oxidized  in  the  body,  and  is  harmless  when  respired,  even  when  10  or  20 
per  cent,  in  volume  is  present.* 

•  Zeitschrifl  fur  Bioloffie,  1884,  Bd.  20,  p.  84. 

'  Hasebroek  :  Zeitschnft  fur  physiologi.tche  Chemie,  1888,  Bd.  12,  p.  148. 
'  B.  Tacke:  Quoted  by  Bimge,  Phynologuoche  Chemie,  3d  ed.,  1894,  p.  284. 

*  Paul  Bert:  Comptes  rendus  de  la  Societe  de  Biologic,  1885,  p.  523.  Abstract  in  Maly'a 
Jahre-fbericht  Uber  Thierchemie,  1886,  Bd.  16,  p.  364. 


THE    CHEMISTRY   OF    THE  ANIMAL   BODY.  977 

Trichlormethane,  or  Chloroform,  CHCI3. — This  temporarily  paralyzes  nerves  and 
nerve  centres.  It  is  principally  removed  as  vapur  through  the  lun.Lrs,  but  is  ))artially 
burned,  thereby  increasing  the  inorganic  chlorides  in  the  urine.'  After  giving  chloroform 
it  may  itself  occur  in  the  urine,  and  likewise  a  substance  which  reduces  Fehling's  solu- 
tion, glycuronie  acid  (which  see). 

Methyl  Aldehyde,  or  Formic  Aldehyde,  ll.CllO. — Tlii.s  may  be  pro- 
duced synthetically  by  pa.ssing  vapor  of  inetiiyl  alcohol  mixed  with  air  over 
an  ignited  platinum  spiral, 

CH3OH  +  O  =  H.CHO  +  H2O. 

On  cooling  the  vapor,  the  aldehyde  is  found  dis.solvecl  in  the  alcohol.  On 
evaporation  of  the  alcohol,  the  aldehyde,  through  condensation  of  three  of 
its  molecules,  forms  a  crystalline  body  having  the  composition  (HCHO)^  and 
•  called  paraformic  aldehyde.  This  latter  treated  with  calcium  or  magnesium 
hydrate  again  suffers  condensation  with  the  production  o^  formose,  CgHijOg,  a 
sweet-tasting  sugar  (Butlerow,  Loew)  identical  with  i-fructose  (Fischer). 
Baeyer  ^  first  suggested  that  the  sugar  synthesis  in  the  plant  was  analogous 
to  the  above  process.  He  conceived  the  reduction  of  carbon  dioxide  to 
carbon  monoxide,  which  united  with  chlorophyll,  and  afterward  through 
hydrogen  addition  became  formic  aldehyde ;  then  in  upward  stages  became 
metaformic  aldehyde,  sugar,  starch,  and  cellulose.  Reinke^  has  shown  the 
presence  of  formic  aldehyde  in  chlorophyll  leaves,  and  believes  its  produc- 
tion due  to  the  reduction  of  carbonic  acid  through  the  power  of  the  sun 
on  the  leaf,  thus : 

H2CO3  =  HCHO  +  O2. 

Bach  *  states  that  carbonic  acid  and  water  in  the  presence  of  uranium  acetate 
yield  formic  aldehyde  and  nascent  oxygen  when  placed  in  the  sun.  According 
to  Stocklasa,^  400  grams  of  fresh  leaves  (128  grams  dry)  of  the  sugar  beet 
form  synthetically  and  send  to  the  beet  root  31  grams  of  cane-sugar  in 
thirty  days. 

General  Behavior  of  Aldehydes. — They  act  as  reducing  agents,  being  readily  oxidized 
to  the  corresponding  acid.  With  nascent  hydrogen  they  are  reduced  to  alcohols.  A  dis- 
tinctive reaction  of  aldehydes  and  ketones  is  their  union  with  phenyl  hydrazin,  CgHj — 
NH — NH.,,  giving  hydrazones : 

CH3CHO  -f  CeHsNHNH^  =  CH3.CH:N.NH.C6H5  +  H.,0. 

I^eparation. — By  distillation  of  the  salt  of  an  acid  with  a  salt  of  formic  acid  : 

CHaCOONa  +  HCOONa  =  Na^COa  +  CH3CHO. 

Aceto-aldehyde. 

Methyl  Mercaptan,  CH3SH. — This  is  a  product  of  bacterial  action  on 
proteid,^   and    is    found    with    HgS   in    the    intestine.      It    is,    furthermore, 

'  A.  Zeller :  Zeitschrift  fur  physioloffische  Chemie,  1883,  Bd.  8,  p.  74. 
^  Berichte  der  deutschen  chemischen  Gesellschaft,  1870,  Bd.  3,  p.  67. 
3  Ibid.,  1881,  Bd.  14,  p.  2144. 

*  Ibid.,  1894,  Bd.  26,  pp.  502  and  689. 

'  Stocklasa:  Zeitschrift  fiir  physiologische  Chemie,  1895,  Bd.  21,  p.  83. 

•  M.  Nencki :  Archivfiir  exper.  Pathologic  und  Pharmnkologie,  1891,  Bd.  28,  p.  206. 

62 


978  AN  AMERICAN   TEXT- BOOK    OF   PHYSIOLOGY. 

given  off*  on  fusing  proteid  with  potash.'  Mctiiyl  niercapttin  boils  at  5°, 
and  has  a  strong  odor.  It  is  found  in  the  urine,  especially  after  eating 
asparagus,  giving  to  it  a  peculiar  sniell.^  According  to  Ilubner^  the  smell  of 
cooked  cabbage,  ctmliflower,  and  the  like,  is  due  to  methyl  niercaptan. 

Methyl  Telluride,  (CUsl^Te. — A  f?as  of  penetrating  odor  found  in  all  excreta  of  an 
animal  after  feeding  salts  of  telluric,  H2Te04,  or  tellurious,  HjTeOa,  acid.  The  salt  is  re- 
duced to  metallic  tellurium  in  the  body,  which  unites  with  a  methyl  group  in  some  way 
liberated  in  the  cells/  3Ictallic  tellurium  may  be  microscopically  seen  deposited  in  various 
cells,  and  the  odor  of  (CII^l.Te  may  be  detected  for  months  after  the  last  dose  has  been 
given  to  a  dog.^ 

Methyl  Selenide,  (CH:j).^Se. — This  is  very  similar  to  the  last-named  substance,  but 
more  poisonous. 

Formic  Acid,  HCOOH. — Found  in  ants,  and  obtained  by  distilling  them 
with  water.  Present  likewise  in  stinging-nettles  and  in  the  sting  of  honey-- 
bees,  wasps,  and  hornets.  Its  salts  are  found  in  minute  quantities  in  normal 
urine,  and  are  present  especially  in  both  blood  and  urine  in  such  diseases  as 
include  an  abnormal  proteid  decomposition — such  as  leucocythsemia,  fever, 
diabetes.^  Formic  acid  may  be  obtained  from  the  oxidation  of  methyl  alcohol, 
of  sugar,  and  of  starch,  but  not  from  the  latter  two  in  the  body.  -  Likewise 
by  heating  oxalic  acid, 

COOH 

60011  =  »c«««  +  ^°=- 

It  is  found  in  the  urine  after  feeding  methyl  alcohol  and  other  methyl  deriv- 
atives, such  as  oxymethyl-sulfouic  acid,  or  formic  aldehyde.  Ethyl  alcohol,  on 
the  contrary,  does  not  yield  it.^  It  is  the  lowest  member  of  the  fatty-acid  series, 
the  most  volatile,  and  the  least  readily  oxidized  in  the  body.  If  formates  be 
fed  they  apjiear  readily  in  tlie  urine.  It  has  a  penetrating  odor,  acts  as  a 
reducing  agent  ( HCOOH  +  O  =  COg  +  II2O),  and  therefore  precipitates 
Fehling's  solution.  Outside  of  the  body  it  readily  undergoes  oxidation  to 
water  and  carbonic  acid.  It  produces  inflammation  of  the  skin.  A  7  per 
cent,  solution  given  to  a  rabbit  per  os  has  a  most  powerful  corrosive  action  and 
results  fatally,  formic  acid  being  found  in  the  urine. 

Ethyl  Compounds. 
Ethyl  Hydroxide,  or  Ethyl  Alcohol,  CgH.pH. — This  has  been  detected 
in  minute  quantity  in  the  normal  muscle  of  rabbits,  horses,  and  cattle.^  It  is 
formed  by  the  fermentation  of  dextrose,  the  process  taking  place  in  the  yeast- 
cell  itself,  alcohol  and  carbonic  acid  being  the  chief  excretory  products ;  like- 
wise, to  a  very  small  extent,  the  higher  alcohols,  propyl,  isobutyl,  amyl,  the 

1  M.  Riibner  :  Archiv  fur  Hygiene,  1893.  *  Nencki,  loc.  cit.  '  Loc  cU. 

*  Hofmeister :  Archiv  fiir  erper.  Patholnpie  nvd  Pharmakologie,  1894,  Bd.  33,  p.  198. 

*  Beyer  :  Archiv  fiir  Physiologie,  Jahrgang  1895,  p.  225. 

'  See  R.  Jaksch  :  Zeiti^chrift  fiir  'physiologiache  Chemie,  1886,  Bd.  10,  p.  537. 
'  Pohl :  Archiv  fiir  exper.  Physiologic  und  Pharmakologie,  1893,  Bd.  31,  p.  298. 
8  Rajewsky:  Ffliiger's  Archiv,  1875,  Bd.  11,  p.  122. 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  979 

estei*s  of  the  fatty  acids  (fusel  oils),  jrjycerin,  and  succinic  acid  are  ])r()duced. 
Such  fermentation  may  to  a  small  extent  take  place  in  the  intestine,'  and  like- 
wise iu  the  bladder  (occurrence  in  diabetic  urine).  Pure  alcohol  is  a  colorless, 
almost  odorless  li(|uid,  havinsji;  a  burning  taste.  It  is  a  valuable  solvent  of 
resins,  fats,  volatile  oils,  bromine,  iodine,  and  many  medicaments. 

Tincturex  arc  alcoliolic  solutions  of  various  druirs  and  salts. 

Liqwurs  arc  nianufaclurcd  I'roin  alcohol  i)roi)crly  diluted,  and  treated  with  sugar  and 
characteristic  ethereal  oils  and  aroniatics. 

JJistilled  liquors  are  ohtained  bj'  the  distillation  of  the  fermentative  products  of  various 
substances,  whiskey  from  corn  and  rye,  rum  from  molasses,  brandy  from  wine.  The  cha- 
racterizing taste  dejiends  on  the  different  ethereal  and  fusel  oils. 

Wines  are  jiroduced  from  the  natural  fermentation  of  grape-juice.  Sherry,  madeira, 
and  port  are  fortified  by  the  further  adchtion  of  alcohol  and  sugar. 

Beer  is  made  by  converting  the  starch  of  barley  into  maltose  and  dextrin  throutrh 
diastase.  To  an  aqueous  solution  of  the  above  hops  are  added,  and  the  whole  is  boiled. 
After  the  settling  of  precipitated  proteid,  etc.,  the  clear  supernatant  fluid  is  drawn  off  and 
treated  with  yeast,  with  ultimate  conversion  into  beer.    The  taste  is  furnished  by  the  hops. 

Alcohol  in  the  Body. — Alcohol  in  the  stomach  at  first  prevents  the 
gelatinization  necessary  in  proteid  for  peptic  digestion,  but  this  difficulty  is  of 
no  great  moment  because  the  absorption  of  alcohol  is  rapid  and  complete. 
It  makes  the  mucous  membrane  hyperaeraic,  promotes  the  absorption  of 
accompanying  substances  (sugar,  peptone,  potassium  iodide),  and  stimulates 
the  flow  of  the  gastric  jiiice.^  In  this  matter  it  acts  as  do  other  condiments 
(salt,  pepper,  mustard,  peppermint),^  but  if  there  be  too  great  an  irritation 
on  the  mucous  membrane  there  is  less  activity  (dyspepsia).  The  rapid 
absorption  gives  to  alcohol  its  quick  recuperative  efiect  after  collapse,  and 
its  value  in  administering  drugs,  especially  antidotes.  Alcoholic  beverages 
combining  alcohol  and  flavor  promote  gastric  digestion  and  absorption,  but 
often  stimulate  the  appetite  in  excess  of  normal  requirement.  Alcohol  is 
burned  in  the  body,  but  may  also  be  found  in  the  breath,  perspiration,  urine, 
and  milk.  Alcohol  has  no  effect  on  proteid  decomposition,  but  acts  to  spare 
fat  from  combustion.*  The  addition  of  50  to  80  grams  of  alcohol  to  the 
food  has  no  apparent  effect  on  the  nitrogenous  equilibrium.^  Alcohol  in  the 
body  acts  as  a  paralyzant  on  certain  portions  of  the  brain,  destroying  the  more 
delicate  degrees  of  attention,  judgment,  and  reflective  thought,  diminishing  the 
.sense  of  weariness  (use  after  great  exertion — furnished  to  armies  in  the  last 
hours  of  battle)  and  raising  the  self-esteem ;  it  paralyzes  the  vaso-constrictor 
nerves,  producing  turgescence  of  the  skin  with  accompanying  feeling  of  warmth 
and  thereby  indirectly  aiding  the  heart."  The  higher  alcohols,  propyl,  butyl, 
amyl  (see  p.  983)  are  more  })oisonous  as  the  series  ascends,^  and  are  less  vol- 

'  Macfadyen,  Nencki,  and  Sieber :  Archiv  fiir  exper.  Pathologie  imd  Pharmakologie,  1891, 
Bd.  28,  p.  347. 

-  Brand! :  Zeitsrhriff  fiir  Biologie,  1892,  Bd.  29,  p.  277.  '  Brandl,  Op.  cit.,  p.  292. 

*  See  V.  Noorden  :  Pathologie  des  Stojfwechsels,  1893,  p.  227. 

'"  Strom :  Abstract  in  CeniralblaU  fiir  Physiologic,  1894,  Bd.  8,  p.  582. 

^  Schmiedeberg :   Grundriss  der  Arzneimiflellekre,  2d  ed.,  1888. 

'  Gibbs  and  Reichert :  Archiv  fiir  Physiologie,  1893,  Suppl.  Bd.  p.  201. 


980  ^iV^  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

atile,  less  easily  burned,  and  therefore  more  tenaciously  retained  by  the  body, 
with  more  pernicious  results. 

Ethyl  Ether,  CjHj.O.CjHj. — This  is  formed  hy  Ihe  action  of  sulphuric  acid  on 
alcohol,  thus : 

C2H5OH  +  H,SO,  =  CHjHSO^  +  H,0. 

C,H,HSO,  +  CH^OH  =(C,H5),0  +  H,SO,. 

Ether  is  a  solvent  for  fats,  resins,  and  ethereal  oils.  Respired  with  air  its  action  is  like  that 
of  chloroform,  producing  temjiorary  paralysis  of  the  nerves  and  nervous  centres.  Since  it 
boils  at  35.5°  its  tension  in  the  blood  is  always  high,  and  it  is  probably  not  burned  in  the 
body  to  any  great  extent,  but  when  present  is  eliminated  through  the  breath. 

Ethera  in  general  are  neutral  and  very  stable  bodies,  and  may  be  considered  oxides  of 
organic  radicles.  They  may  all  be  prepared  by  boiling  the  corresponding  alcohol  with  sul- 
phuric acid.  Mixed  ethers,  in  which  the  radicles  are  different,  are  prepared  by  boiling  two 
different  alcohols  with  sulphuric  acid : 

CH3HSO,  +  C^HjOH  =  CHaOC,!!,  -f  H.SO^. 

Methyl-ethyl  ether. 

Chloral  Hydrate,  CCL.CHO  +  H.O  or  CClsCHCOH).,.— This  is  the  hydrated  form  of 
trichlor-ethyl  aldehyde,  CCI3CHO,  and  is  used  as  an  anaasthetic.  It  is  an  interesting  fact 
that  when  fed  it  partially  reappears  in  the  urine  as  urochlordlic  acid,  which  consists  of 
trichlor-ethyl  alcohol,  CCljCH./JH,  combined  with  glycuronic  acid  (which  see).  This  is  a 
notable  illustration  of  reduction  in  the  body,  the  change  from  an  aldehyde  to  an  alcohol. 

Acetic  Acid,  CH3COOH. — Acetic  acid,  the  second  of  the  fatty-acid  series, 
is  found  in  the  intestinal  tract  and  in  the  feces,  being  a  product  of  putrefaction 
(see  p.  988).  It  is  more  easily  burned  than  formic  acid,  and  when  aksorbed  is 
resolved  *  into  COg  and  water.  It  is  found  in  traces  in  the  urine,  the  total 
amount  of  fatty  acids  normally  present  being  0.008  gram  })er  day.^  Like 
formic  acid,  and  accompanied  further  by  the  higher  acids  of  the  series,  it  is 
present  in  the  blood,  sweat,  and  urine  whenever  there  is  an  abnormal  proteid 
decomposition  (leucocythaemia,  diabetes). 

Acetic  acid  is  the  product  of  the  oxidation  of  alcohol.  This  may  be 
brought  about  through  the  presence  of  sj)ongy  platinum,  or  through  the  action 
of  bacteria  {Mycoderma  aceti)  on  dilute  alcohol  (})reparation  of  vinegar,  sour- 
ing of  wine  :  for  reaction  see  p.  976).  Acetic  acid,  as  well  as  other  higher  fatty 
acids,  is  one  of  the  products  derived  from  proteid  through  its  putrefaction,  its  dry 
distillation,  its  fusion  with  potash,  and  its  digestion  with  baryta  water  in  sealed 
tubes.  Formic,  acetic,  and  propionic  acids  are  products  of  dry  distillation  of 
sugar  (formation  of  caramel).  These  facts  are  of  importance  in  their  rela- 
tion to  the  question  of  the  production  of  fat  in  the  body.  Acetic  and  the 
higher  fatty  acids  are,  further,  products  of  the  dry  distillation  of  wood  and 
of  the  fermentation  of  cellulose  (see  p.  976).  Putrefaction  of  acetates  may 
take  place  in  the  intestines,  the  reaction  being  as  follows: 

2CH3COONa  +  2H2O  =  ISa.CO,  +  2CH,  +  H^O  -f  CO.. 

These  products  are  similar  to  those  in  the  marsh-gas  fermentation  of  cellulose. 
Vinegar,  whose  acidity  is  due  to  acetic  acid,  is  used  as  a  condiment. 

Acetyl-acetic  Acid,  or  Aceto-acetic  Acid,  CH3.CO.CH2.CX^OH. — This 
'  V.  .Taksch  :  Zeitschrij't  fur  physiologische  Chemie,  1886,  Bd.  10,  p.  536. 


THE   CHEMISTRY   OF   THE  ANIMAL    BODY.  981 

may  be  eoiisitlerod  as  acetic  acid  in  which  one  H  atom  is  replaced  by  acetyl, 
CH3CO — ;  or  as  /9-keto-butyric  acid.  Treated  with  hydrogen  it  is  reduced 
to /?-oxybutyric  acid  (CH3.CHOH.Cir2.COOIl),  which  in  turn  nmy  be  oxi- 
(\\7An\  to  the  original  substance.  Aceto-aceticacid  readily  breaks  up  into  acetone 
and  carbonic  acid : 

CHgCOCH.COOH  =  CH3COCH3  +  CO„. 

Aoeto-acctic;  acid,  acetone,  and  /i-oxybutyric  acid  are  found  in  the  urine  sometimes  singly, 
sometimes  together,  but  only  as  the  result  of  a  metabolism  of  the  body's  oriianized  protcid 
(lencocythii3mia,  diabetes,  fever,  inanition),  not  of  that  of  the  proteid  ingested.  Indeed, 
these  substances  under  the  above  circumstances  seem  to  appear  in  the  urine  in  direct  pro- 
l)ortion  to  the  nitrogen  present — in  other  words,  to  the  protcid  decomposition.'  From  their 
chemical  relations  already  mentioned  they  may  be  regarded  as  of  common  origin,  coming 
from  the  proteid  molecule  under  peculiar  conditions  of  metabolism,  and  in  contirmation  of 
this,  Araki  '^  has  shown  that  on  feeding  /?-oxybutyric  acid  it  is  oxidized  and  aceto-acetic 
acid  and  acetone  may  be  detected  in  tlie  urine.  The  production  of  the  two  acids  seems  to 
further  a  gradual  neutralization  of  the  blood,  ultimately  causing  coma.^  In  the  i)resence 
of  these  substances  ammonia  runs  high  in  the  urine,  and  in  amounts  proportional  to  their 
excretion*  (compare  p.  993). 

Aceto-acetic  acid  gives  to  urine  in  the  absence  of  phosphates  a  red  coloration 
with  ferric  chloride  (j)rinciple  of  the  reaction  of  Gerhardt). 

Amido-acetic  Acid,  or  GlycocoU,  CHg.NHg.COOH. — This  is  a  substance 
obtained  by  boiling  gelatin  with  acids  or  alkalies.  It  is  found  in  human  bile 
and  in  that  of  other  animals  combined  with  eholic  acid  and  called  glycocholic 
acid.  Chittenden^  has  found  glycocoU  in  the  muscles  of  Peden  irradians. 
It  is  found  in  the  urine  combined  with  benzoic  acid  as  hippuric  acid  after 
feeding  benzoic  acid  or  compoinids  which  the  body  converts  into  benzoic  acid. 
In  a  similar  manner  phenaceturic  acid  is  found  in  the  urine  from  the  grouping 
together  of  glycocoU  and  j^henyl  acetic  acid.  GlycocoU  and  urea  are  to  be 
obtained  by  the  decomposition  of  uric  acid  through  hydriodic  acid.  GlycocoU 
forms  colorless  crystals,  soluble  in  water  and  having  a  sweet  taste. 

GlycocoU  in  the  Body. — If  glycocoU  be  fed  it  is  absorbed  and  appears  as 
urea  in  the  urine.  The  fact  that  dogs,  whose  bile  never  contains  glycocholic 
acid,  nevertheless  excrete  hippuric  acid  after  being  fed  with  benzoic  acid,  indi- 
cates that  glycocoU  may  be  considered  a  normal  nitrogenous  decomposition 
product  of  proteid.  Its  easy  cleavage  from  gelatin,  a  product  manufactured 
from  proteid  in  the  body,  confirms  this. 

Amido'  Acids  in  General. — These  acids,  such  as  glycocoU.  aspartic  acid,  glutamic  acid, 
leucin,  and  tyrosin  are  found  as  putrefactive  products  of  albumin  and  gelatin.  In  these 
acids  the  amido-  group  is  very  stable,  and  cannot  be  removed  by  boiling  with  KOH.  They 
are  all  converted  in  the  body  into  the  amide  of  carbonic  acid  (urea).  Amido-  acids  may  in 
general  be  synthetically  formed  by  heating  mono-halogen  compounds  of  the  fatty  acids  with 
ammonia : 

CH5CICOOH  +  NH3  =  CH.NH^COOH  +  HCl. 

*  Wright :  Grocers'  Research  Scholarship  Lecture,  London,  1891  ;  V.  Noorden :  Pathologic  des 
Stoffwechsels,  1893,  p.  178. 

'  Zeitechrijt  fiir  physiologische  Chemie,  1893,  Bd.  18,  p.  6. 

•*  Miinzer  and  Strasser  :  Archiv  fiir  exper.  Pathologic  und  Pharmakologie,  1893,  Bd.  32,  p.  372. 

*  Loc.  cit.  5  Annalen  der  Chemie  und  Pharmakologie,  1875,  Bd.  178,  p.  266. 


982  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

Methyl  Amido-acetic  Acid,  or  Sarcosin,  CII5.NII.CII2.COOII. — This  is  not  found 
in  the  liotly,  but  is  derived  from  ereatin,  theobroniin,  and  cafiein  by  heating  with  barium 
hj'droxidc. 

Propyl  Compounds. 

Normal  or  Primary  Propyl  Alcohol,  CII3CH2CH2OH. — This  is  one  of 
the  higlier  aleohols  foi'ined  in  the  ienueutation  of  sugar,  and  on  oxidation 
yiekls  projnd  ahh-hyde  and  propionie  acid. 

Propionic  Acid,  CII3CH2COOH. — Combined  with  glycerin  this  iorras  the 
simplest  fat ;  salts  of  this  acid  feel  fatty  to  the  touch.  Propionic  acid  is  a 
product  of  the  dry  distillation  of  sugar,  of  the  butyric-acid  fermentation  of 
milk-sugar,  and  of  the  putrefaction  of  proteid.  It  is  said  to  be  present  in  the 
sweat,  in  the  bile,  and  sometimes  in  the  contents  of  the  stomach.  Like  others 
of  the  lower  fatty  acids,  it  may  partially  escape  oxidation  and  appear  in  traces  in 
the  urine  (see  p.  980). 

/3-Acetyl  Propionic  Acid,  or  Levulic  Acid,  CIIsCOCH.CHjCOOH.— This  is  the  next 
higher  honiologue  to  aceto-acetic  acid.  It  lias  been  obtained  only  by  boiling  sugars,  espe- 
cially levulose,  with  acid  and  alkalies,  and  since  Kossel  and  Neumann '  found  that  it  is 
yielded  by  some  nucleins  they  conclude  that  this  indicates  the  presence  of  the  carbo- 
hydrate radical  in  these  nucleins. 

Dimethyl  Ketone,  or  Acetone,  CH3COCH3. — This  is  found  normally  in 
the  blood  and  urine,  and  in  especially  large  quantities  in  patients  suft'ering 
from  an  abnormal  decomposition  of  organized  proteid  (see  p.  981).  During 
the  first  day  of  starvation  by  Cetti,  the  starvation  artist,  the  amount  of  acetone 
in  the  urine  rose  to  forty-eight  times  that  of  the  day  previous.^  It  may  like- 
wise appear  in  the  breath,  giving  a  characteristic  odor.  Acetone  is  a  product 
of  the  dry  distillation  of  tartaric  and  citric  acids,  of  woofl,  and  of  sugar.  Its 
occurrence  in  the  urine,  in  diabetes,  however,  is  not  proportional  in  any  way 
to  sugar-metabolism  or  non-metabolism  (.see  p.  981).  Oxidized,  acetone  yields 
acetic  and  formic  acids,  whereas,  treated  with  hydrogen,  it  is  resolved  into  sec- 
ondarv  propyl  alcohol.  When  acetone  is  in  the  urine  it  is  al^^o  found  in  the  in- 
testinal canal  and  in  the  feces,  ]>robably  by  passage  through  the  intestinal  wall. 

Butyl  Compounds. 

Normal  Butyric  Acid,  CHgCHgCHjCOOH. — Butyric  acid  was  first  found 
in  butter,  combined  with  glycerin.  When  free  it  gives  the  rancid  odor  to 
butter,  and  likewise  contributes  to  the  odor  of  sweat.  It  has  been  detected  in 
the  spleen,  in  the  blood,  and  in  the  urine,  but  usually  only  in  traces.  As  a  pro- 
duct of  putrefaction  of  proteid,  and  especially  of  carbohydrates,  it  is  found  in 
the  intestines  and  in  the  stomach  when  the  acidity  is  insufficient  to  be  bacteri- 
cidal. It  contributes  to  the  unpleasant  taste  after  indigestion,  through  the 
return  of  a  small  portion  of  the  chyme  to  the  mouth.  In  cheese  it  is  a 
product  of  the  putrefaction  of  casein. 

If  starch,  sugar,  or  dextrin  be  treated  with  water,  calcium  carbonate,  and 

^  Verhandlung  der  Berliner  physiologischen  Gesellscliaft,  Archivfur  Physiologic,  1894,  p.  536. 
*  Fr.  Miiller :  Berliner  klinische  Wochemchrift,  1887,  p.  428. 


THE    CHEMISTin'    OF    TlIK    ANIMAL    BODY.  983 

foul  cheese,  tlie  earl )oliy(l rates  are  slowly   eoiivertetl   into  a  mass  of  calcium 
lactate.     On  further  stiinding  the  lactic  acid  is  resolved  into  butyric  acid  : 
2CH3CI1()II(  'OOI I      Cy  I/'(K)TI  +  4H  +  CO.. 

Ijictic  nt'id. 

Calcium  salts  are  foiuid  to  putrefy  more  readily  than  others,  and  the  carbon- 
ate is  added  above  to  neutralize  any  acids  formed  in  the  putrefactive  process 
which  mii^ht  inhibit  the  action  of  the  spores.  This  same  fermentation  takes 
place  in  the  intestinal  tract. 

Iso-butyl  Alcohol,  (CHa)^ :  CH.CH,OH.— This  is  found  in  fusel  oil. 
Iso-butyric  Acid,  (CHj)^:  CH.COOIL— This  is  a  product  of  protcid  putrefaction 
and  is  I'ound  in  the  feces. 

Pentyl  Compounds. 

Iso-pentyl  Alcohol,  or  Amyl  Alcohol,  (CH3)2CHCH,CH20H.— This  is  the  principal 
constituent  of  fusel  oil,  prodiu-in.ir  the  after-effects  of  distilled-liquor  intoxication.  The 
poisonous  dose  in  the  dog  per  kiloirrum  for  the  different  alcohols  has  been  found  to  be — for 
ethyl  alcohol  5-6  grams,  for  propyl  alcohol  3  grams,  for  butyl  alcohol  1.7  grams,  for  amyl 
alcohol  1.5  grams'  (see  p.  979). 

Iso-pentoic  or  Iso-valerianic  Acid,  (CH3)2CHCH2COOH. — This  is  found 
in  cheese,  in  the  sweat  of  the  foot,  likewise  in  the  urine  in  sfnall-pox,  in  typhus, 
and  in  acute  atrophy  of  the  liver.  It  is  a  product  of  proteid  putrefaction,  and 
has  a  most  unplea.sant  odor. 

Alcohols  containing  More  than  Five  Carbon  Atoms. 

Of  tliese,  cetyl  alcohol  C16H35OH,  is  found  combined  with  palmitic  acid  in  spermaceti ; 
cerotyl  alcohol,  C27H55(OH),  is  found  as  an  ester  in  Chinese  wax;  and  melicyl  alcohol^ 
CaoHfiiOH,  is  combined  with  palmitic  acid  in  beeswax. 

Acids  containing  More  than  Five  Carbon  Atoms. 

Caproic  Acid,  CsHjjCOOH. — This  is  formed  from  the  putrefaction  of 
proteid,  being  found  in  cheese  and  in  feces;  it  may  likewise  be  detected  in  the 
sweat.     United  wnth  glycerin  it  occurs  in  butter-fat. 

Iso-butyl  Amido-acetic  Acid,  or  Leucin,  (CHa), :  CH.CHo.CHNH^. 
COOH. — This  substance  is  a  constant  product  of  proteid  })utrefaction,  is  there- 
fore found  in  cheese,  and  may  likewi.se  be  obtained  by  boiling  proteid  or  gelatin 
with  sulphuric  acid  or  with  alkali.  When  fed  it  is  converted  into  urea.  When 
fed  to  birds  the  tissues  decompose  it  with  elimination  of  ammonia,  which  latter 
may  be  converted  into  uric  acid  by  the  liver.^  It  is  said  to  occur  in  pancreatic 
juice.  According  to  Kiihne  it  is  produced  in  trypsin  proteolysis  to  the  extent 
of  9.1  per  cent,  of  the  proteid  used.  Since  this  weakly  alkaline  medium  in 
pancreatic  digestion  is  especially  favorable  to  bacterial  activity,  Kiihne  added 
antiseptic  salicylate  of  sodium  and  still  found  leucin  (and  tyrosin).  The  sam6 
results  are  obtained  with  thymol.  It  is  generally  accepted  that  leucin  (and 
tyro.sin)  are  normal  products  of  tryptic  digestion.     In  certain  diseases  of  the  liver 

'  Dnjardin-Beauraetz  et  Audig^ :  Comptes  rendus,  vol  81,  p.  19. 

*  Minkowski :  Archiv  fur  exper.  Pathologic  und  Pharmakologie,  1886,  Bd.  21,  p.  85. 


984  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

leucin  (and  tyrosin)  appear  in  tho  urint',  which  may  he  interjireted  to  mean  that 
thi-se  siihstance.s,  normally  produeed  Ironi  proteid  metalK)li.sni  in  the  tissues,  are 
not  normally  burned  but  accumulate  within  the  body,  and  are  excreted  (.see 
below). 

Another  view,  advanced  by  Von  Noorden  *  and  ba.sed  on  the  unconfirmed  experiments  of 
Harris  and  Tooth.*  claim.s  that  leucin  and  tyro.sin  are  not  luund  in  tryptic  dige.stion  if  bac- 
teria be  excluded.  Leucin  and  tyrosin  are  found  in  yellow  atrni)hy  of  the  liver  both  in  the 
urine  and  in  the  liver  it.self.  under  conditions  indicating  tlieir  production  by  bacteria  and 
their  non-combustion  after  production.  In  phosphorus-poisoning  and  acute  annc^mia  leucin 
and  t\Tosin  occur  in  the  urine,  but  apparently  without  good  ground  for  considering  them 
of  V)acterial  origin,  ^'on  Noorden  argues  that,  as  in  yellow  atrophy  of  the  liver,  the  tissue- 
cells  have  become  incapable  of  decomposing  leucin  and  tyrosin,  and  tliese  substances 
absorbed  as  products  t)f  intestinal  putrefaction  cannot  be  burned  but  are  eliminated  by  the 
urine.    That  leucin  is  a  product  of  proteid  metabolism  in  the  tissues  has  never  been  shown. 

Leucin  crystallizes  in  characteristic  ball-shaped  crystals.  It  was  formerly  supposed  to 
be  amido-caproic  acid,  but  Schulze'  has  shown  its  true  composition.  Inactive  leucin  con- 
sists of  a  mixture  of  d-  and  Meucin,  and  may  be  obtained  by  treating  conglutin  with 
BalOHij.  The  two  leucins  maybe  separated  by  fermentation  of  (Z-leucin  with  PenidUium 
gJancnm.     Cleavage  of  proteid  by  acids  and  by  putrefaction  seems  to  yield  c?-leucin.* 

Caprylic,  CjHjpOo.  and  Capric, '  CioHjoOj,  Acids. — The.«e  are  found  as 
glveerin  esters  in  milk-fat.     They  are  likewise  present  in  sweat  and  in  cheese. 

Palmitic,  C,6H3202,  and  Stearic,  CigHg^O,,  Acids. — As  glycerin  esters 
these  two  acids  are  found  in  the  ordinary  fat  of  adipose  tissue,  and  in  the  fat 
of  milk.  The  acids  may  occur  in  the  feces,  and  are  found  combined  with 
calcium  in  adipocere  (p.  1002).  "Wool-fat  consists  in  the  cholesterin  esters  of 
thase  acids. 

The  bile  contains  palmitic,  .stearic,  and  oleic  acids,^  and  to  these  have  been 
attributed  its  very  slight  acid  reaction.® 

Compounds  of  the  Alcohol  Radicals  with  Nitrogen. 

Amines. — ^These  are  bodies  in  which  either  one.  two.  or  three  of  the  hydrogen  atoms 
in  ammonia  are  replaced  by  an  alcohol  radical,  and  are  termed  respectively  primar>',  second- 
ary, and  tertiary  amines.  Methyl,  ethyl,  and  propyl  amine  bases  are  the  jiroducts  of  pro- 
teid putrefaction.     Tliey  resemble  ammonia  in  their  basic  properties. 

Methylamine,  NHjlCH,,).— This  is  found  in  herring-brine.  It  has  the  fishy  smell 
noted  in  decaying  fish.  It  is  a  product  of  the  distillation  of  wood  and  of  animal  matter. 
Feeding  methylamine  hydrochloride  is  said  to  cause  the  apj)earance  of  methylated  urea  in 
a  rabbit's  urine '  (analogous  to  the  formation  of  urea  from  ammonia  salts! : 
21101.  NH,(CH3)  +  C0,=  0C(NHCH3),  +  2HCI  +  H,0. 
According  to  Schiffcr.*  the  body,  probably  through  intestinal  putrefiiction.  has  the  power 
of  partially  converting  creatin  into  oxalic  acid,  ammonia,  carbonic  acid,  and  methylamine, 
which  last  is  finally  excreted  as  methylated  urea  in  the  urine. 

»  Paihnlogie  des  Stoffu-echseh,  1893,  p.  296.  '  Journal  of  P/it/.sio/o.T?/,  1SS8,  vol.  9,  p.  220. 

»  Berichte  der  deutschen  chemkchen  Ge,«elkchaft.  1891,  Bd.  24,  i>.  669;  also,  Gmelin  :  Zeilschri/I  fur 
physfiologi^che  Chemie,  1893,  Bd.  18,  p.  38. 

*  rrmelin :  Zeitschrifi  fur  phyaiologische  Chemie,  1893,  Bd.  18,  p.  28. 

*  Lassar-Cohn  :  Ibid.,  1894,  Bd.  19,  p.  571. 

«  .Idles:  Pfiiiger's  Archiv,  1894,  Bd.  57,  p.  13. 

'  Schiffer:  ZeiUchnft  fiir  physiologische  Chemie,  1880,  Bd.  4,  p.  245.  "  Loc.  cit 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  985 

Ethylamine,  C.^lIjNIIj,  when  fed  as  eurbonule  appears  in  part  as  ethylated  urea  in  the 
urine.' 

Trimethylamine,  NiCH,),. — Like  ethyhiuiine.  this  is  found  in  herrinp-brine  and 
ainonir  the  pnKhicis  dT  proteid  putrefaetion  ami  distiUation.  In  the  putrefaction  of  meat 
the  first  ptomaine  ajipearini:  is  elioHn,  wliich  certainly  is  derive<l  from  lecithin;  the  cholin 
(sue  p.  986)  gradually  disappears,  and  in  its  jilace  trimethylamine  may  Ijc  detected.' 

Compounds  with  Cyanogen. 

The  radicle  NC —  forms  a  scries  of  bodies  not  unlike  the  halogen  com- 
pounds. Owing  to  the  mobility  of  the  cyanogen  group,  Pfliiger'  has  sought 
to  attribute  the  proj)ertie.-;  of  living  proteid  to  its  presence  in  the  niolecide, 
whereas  in  the  dead  proteid  of  the  blood-})lasma,  for  example,  he  imagines  that 
the  nitrogen  is  contained  in  an  amido-  group.  When  the  cyanogen  radical 
occurs  in  a  comjiound  in  the  form  of  N=:C —  the  body  is  called  a  nitril,  when 

in  the  form  of  C    :N —  an  iso-nitril. 

Cyanogen  Gas,  NC  — CX. — A  very  poisonous  gas. 

Hydrocyanic  Acid,  IICN. — This  is  likewise  a  strong  poison.  Amygdalin  is  a  glucoside 
oc-eurring  in  cherry-pits,  in  bitter  almonds,  etc..  together  with  a  ferment  called  emulsin, 
which  latter  has  the  powerof  transforming  amygdalin  into  dextrose,  benzaldehyde,  and  hN'dro- 
cyanic  acid.  Hydrocyanic  acid,  therefore,  gives  its  taste  to  oil  of  bitter  almonds,  and  it 
may  likewise  be  detected  in  diem*  brandy. 

Potassium  Cyanide,  KCN. — Tliis  and  all  other  soluble  cyanides  are  fatal  poi.sons. 

Acetonitril,  or  Methyl  Cyanide,  CII3CX. — This  and  its  higher  homologous  nitrils 
are  violent  poisons.  After  feeding  acetonitril  in  small  doses,  formic  acid  (see  p.  978)  and 
thiocyanic  acid  (see  below)  appear  in  the  urine,  the  thiocyanic  acid  being  a  sjiithetic  prod- 
uct of  the  inge.sted  cyanogen  radical,  and  the  HS —  group  of  decomposing  proteid.*  After 
feeding  higher  homologues  of  acetonitril  or  hydrocyanic  acid,  thiocyanide  likewise  appears 
in  the  urine.  Since  the  amount  of  thiocyanide  in  the  urine  is  normally  very  small,  there 
i.s  no  reason  for  believing  that  cyanogen  radicals  similar  to  those  described  above  are  ever, 
to  any  great  extent,  cleavage-products  of  proteid.'  Through  intravenous  injections  of 
sodium  sulphide,  and  especially  of  sodium  thiosulphate,  poisonous  cyanogen  compounds 
may  be  administered  much  beyond  the  dose  ordinarily  fatal:® 

XaCX  -  SO,  <  ^^  4-  0  =  NCSNa  +  Na^SO^. 

Cyanamide,  NC.NHj. — This  is  a  laboratory  decomposition-product  of  creatin,  but  does 
nut  occur  in  the  body.  It  is  poisonous  when  administered.  When  boiled  with  dilute 
sulphuric  or  nitric  acids  it  is  converted  into  urea : 

NCNH2  +  H2O  =  H^XX'ONHj. 
It  is  to  be  remembered  that  creatin  in  the  body  is  not  converted  into  urea. 

Ammonitim  Cyanate,  OCN(NH^). — Boiling  ammonium  cyanate  converts  it  into 
urea.  This  was  shown  by  Wohler  in  1828,  and  was  the  first  authoritative  laboratory 
production  of  a  body  characteristic  of  living  organisms : 

OCN(NHJ=OC(NH,),. 
This  reaction  illu.strates  Pfliiger's  idea  of  the  transformation  of  the  c.vanogen  radical  in 
living  proteid  into  the  amido-  compound  in  the  dead  substance.     According  to  Hoppe- 

'  Schmiedeberg :  ArchivfUr  erper.  Pnlhologie  und  Pharmakologie,  1877,  Bd.  8,  p.  5. 
'  Brieger  :  Abstract  in  Jnhn'sbericht  iiber  Thierchemie,  1885,  p.  101. 
'  PAuger's  Archiv,  1875,  Bd.  10,  p.  251. 

*  Lang :   Archiv  fiir  exper.  Pathologie  und  Pharmaiologie,  1894,  Bd.  34,  p.  247. 
-'  Op.  cit.,    p.  256. 

*  Lang  :  Archiv  fiir  exper.  Pathologie  vnd  Pharmakologie,  1895,  Bd.  36,  p.  75. 


l»cSO  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

Sevier  the  urea-formation  in  the  body  is  as  indicated  in  the  above  reaction,  but  that  no 
cyanic  acid  or  aninioiiiuin  cyaiuite  is  to  be  detected  on  account  of  their  extreme  instabihty. 
Potassium  Thiocyanide,  NCSK. — This  substance  is  usually  found  in  human  saliva 
and  ill  the  urine.  Since  it  contains  nitrogen  and  sulphur  its  oriirinal  source  must  be  I'rom 
proteid.  The  amount  in  the  urine  is  probably  wholly  and  ((uaiititatively  derived  i'roni  that 
in  the  saliva.'  If  thiocyanides  be  fed,  they  appear  quickly  in  the  urine  without  change. 
Thiocyanides  are  less  poisonous  than  the  simple  cyanides  (see  discussion  under  Acetonitril 
above).     Thiocyanides  give  a  red  color  with  ferric  chloride  in  acid  solution. 

Diatomic  Alcohol  Radicals. 
Thus  far  only  derivatives  of  monatoniic  radicals  have  been  disciis.sed ;  next 
in  order  follow  diatomic  alcohol  radicals,  represented  by  the  formula  CnHgn,  and 
including;  the  bodies  ethylene,  HgC  =  CH2,  j^^'opyleiie,  CH3 — HC  =  CHo,  etc. 
This  set  of  hydrocarbons  is  called  the  defines.  The  first  series  of  compounds 
which  are  of  physiological  interest  are  the  amines  of  the  olefines. 

Amines  of  the  Olefines. 

These  include  the  group  of  ptomaines — basic  substances  which  are  formed 
from  proteid  through  bacterial  putrefaction.  Those  which  arc  jwi.^^onous  are 
called  toxines.  These  bodies  are  diamines  of  the  olefines,  and  have  been 
investigated  especially  by  Brieger.^ 

Tetramethylene-diamin,  or  Putrescin,  H2N.CH.,.CH,.CH,.CH,,.NHo.— This  com- 
pound is  found  in  putrefying  proteid,  and  has  been  detected  in  the  urine  and  feces  in 
cystitis. 

Pentamethylene-diamin,  or  Cadaverin,  HjN.CiHjo.NHj.— This  is  found  with 
putrescine  wherever  produced.  They  are  both  found  in  cultivations  of  Koch's  cholera  bacil- 
lus and  in  cholera  feces.  In  cystitis  they  are  a  result  of  special  infection  of  the  intestinal 
tract,  are  principally  excreted  in  the  feces,  but  are  partially  absorbed,  and  prevent,  perhaps 
through  chemical  union,  the  burning  of  cystein  normally  produced.^  Diamines  are  not 
normally  present  in  the  urine. 

Neuridin  and  Saprin. — These  are  isomers  of  cadaverin  and  are  produced  by  the  same 
putrefactive  processes. 

Cholin.— This  is  trimethyl  oxyethyl  ammonium  hydroxide, 

and  has  its  source  in  lecithin  decomposition,  and  putrefaction  (see  p.  1001). 

Musearin,  or  Oxycholin.— This  is  a  violent  heart-poison,  and  may  be  obtained  by 
treating  cholin  with  nitric  acid. 

Neurin.— This  is  trimethyl-vinyl  ammonium   hydroxide,  (€113)3  ^  N  <  ^jj  _  qjj 

and  is  derived  from  lecithin.  Theoretically  it  may  be  considered  as  derived  from  cholin, 
with  the  elimination  of  a  molecule  of  water,  but  it  has  never  been  shown  that  bacteria 
make  this  conversion.     It  is  a  powerful  poison. 

Dertyattves  of  Diatomic  Ai>coiioi^. 
Taurin,  or  Amido-ethyl  Sulphonic  Acid,  H2N.CH2.CH2.SO3H. — This 
has  been  detected  in  muscle,*  in  the  spleen,  and  in  the  suprarenal  capsules. 

'  Gscheldlen  :  Pfluger's  Archiv,  1877,  Bd.  14.  p.  411. 
^  Abstract,  Jahreahericht  iiber  Thierchemie,  1885,  p.  101. 

3  Baumann  und  Udranszky :  ZeUschrift  fur  physiologische  Chemie,  1889,  Bd.  13,  p.  562,  and 
1891,  Bd.  15,  p.  77. 

*  Reed,  Kiinkenberg,  and  Wagner:  Zeitschri/tfur  Biologie,  1885,  Bd.  21,  p.  30. 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  987 

It  is  likewise  a  usual  constituent  of"  tlio  liuniau  bile  in  combination  with 
eholic  acid,  the  salt  present  being  known  as  sodium  taurocholate.  Taurin 
is  of  proteid  orii;in  as  is  shown  by  its  nitrogen  and  sulphur  content.  Little 
is  known  regarding  its  fate  in  the  body,  except  as  it  indicated  through  the 
behavior  of  its  sulphur  atom  (see  p.  951). 

The  BUim-ji  Salts. — Taui'in  and  glycocoll  are  found  in  the  bile  of  cattle  in 
combination  with  eholic  acid  {t\^ll^JJ^).  In  human  bile,  according  to  Lassar- 
Cohn,^  there  is  more  fellic  acid  (CgjH^OJ  present  than  eholic,  and  there  is 
likewise  present  some  choleic  acid,  (C24H^(,02).  These  acids  are  of  similar  chemi- 
cal structure,  though  what  the  structure  is,  is  unknown.  Still  other  acids 
occur  in  the  bile  of  pigs,  geese,  etc.  Taurin  and  glycocoll  form  compounds 
with  these  acids,  the  sodium  salts  of  which  usually  make  up  the  major  part  of 
the  solids  of  the  bile.  It  has  been  shown  that  glycocoll  and  taurin  are  found 
in  various  parts  of  the  body.  Cholic,  fellic,  etc.  acids  are  only  found  as  products 
of  hepatic  activity.  In  a  dog  with  a  biliary  fistula  the  solids  of  the  bile  increase 
on  feeding  much  meat,  but  the  hourly  record  of  the  solids  compared  with 
the  nitrogen  in  the  urine  shows  that  the  great  production  of  biliary  salts  con- 
tinues after  the  nitrogen  in  the  urine  has  begun  to  decrease."  The  experiments 
of  Feder^  have  shown  that  the  greater  part  of  the  nitrogen  in  proteid  eaten  by 
a  dog  leaves  the  body  within  the  first  fourteen  hours,  whereas  the  excretion  of 
the  non-nitrogenous  moiety  is  more  evenly  distributed  over  twenty-four  hours. 
It  may  be  fairly  concluded  that  cholic  and  fellic  acids  are  produced  from  the 
non-nitrogenous  portion,  or  from  sugar  or  fat/  Furthermore  Tappeiner '  has 
8hown  that  cholic  acid  on  oxidation  yields  fatty  acids.  A  synthesis  may  there- 
fore be  effected  in  the  liver  between  the  non-nitrogenous  cholic  acid  formed  in 
the  liver  from  fat  or  materials  convertible  into  fat,  and  glycocoll  and  taurin 
formed  from  proteids,  whether  the  latter  be  produced  in  the  liver  or  brought  to 
it  from  the  tissues  by  the  blood.  That  the  liver  is  the  place  for  the  synthesis 
is  shown  by  the  fact  that  the  biliary  salts  do  not  colkct  in  the  body  after  extir- 
pation of  the  liver. 

In  the  intestine  either  the  acid  of  the  gastric  juice  or  bacteria  may  split  up 
the  biliary  salt  through  hydrolysis  : 

Glycocholic  acid.  Glycocoll.  Cholic  acid. 

Taurin  and  glycocoll  may  be  absorbed,  while  cholic  acid  is  precipitated  if  in 
an  acid  medium,  but  may  be  dissolved  and  absorbed  in  an  alkaline  intestine. 
Hence  cholic  acid,  fellic  acid,  etc.,  may  often  be  found  in  the  feces.  Meco- 
nium, that  is,  the  fecal  matter  of  the  fetus,  contains  quantities  of  the  biliary 
.salts,  but  unaltered,  since  putrefaction  is  absent  in  the  fetus.  Kiihne  has  de- 
scribed dyslysin  as  a  putrefactive  product  of  cholic  acid,  but  its  existence  is 
denied  by  Hoppe-Seyler  and  Yoit.       In  icterus  (jaundice),  a   condition    in 

^  Zeitschrift  fiir  physiologiscbe  Chemie,  1894,  Bd.  19,  p.  570. 

»  Voit :  Zeitschriftfur  Blologie,  1894,  Bd.  30,  p.  545.  '  Ihid.,  1881,  Bd.  17,  p.  531. 

*  Voit,  Op.  cit,  p.  556.  *  Zeitschriftfur  Biologie,  1876,  Bd.  12,  p.  60. 


988  AN  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

which  the  biliary  sah^?  return  to  the  blood  from  the  liver,  they  are  burned  in 
the  body,  sometimes  so  completely  that  none  appear  in  the  urine.  They  have 
the  power  of  dissolving  liaMuoglobin  from  the  blood-corpuscles,  and  in  con- 
sequence the  urine  may  be  highly  colored,  perhaps  from  bilirubin.' 

Pettenkofer,  experimenting  once  on  the  conversion  of  sugar  into  fat,  warmed  together 
cane-sugar,  bile,  and  concentrated  sulj)huric  acid.  He  obtained  no  fat,  but  a  strong  violet 
coloration.  This  is  "  Pettenkofer' s  test''  for  biliary  acids  (cholic  acid,  fellic  acid,  etc.). 
This  coloration  is  likewise  given  by  i)roteid,  oleic  acid,  and  other  bodies.  The  test  of  Neu- 
konim,  however,  is  said  to  be  absolutely  characteristic.  Here  a  drop  of  a  substance  con- 
taining biliary  acids  is  placed  on  a  small  white  porcelain  cover,  with  a  drop  of  dilute 
cane-sugar  solution,  and  one  of  dilute  sulphuric  acid ;  the  mixture  is  then  very  carefully 
evaporated  over  a  flame  and  leaves  a  brilliant  violet  stain. 

OxY-  Fatty  Acids,  Lactic-acid  Group. 

These  are  diatomic  monobasic  acids  of  the  glycols.  A  glycol  is  a  diatomic 
alcohol.     The  oxy-  fatty  acids  have  the  general  formula  CnHjnOg,  and  include  : 

Carbonic  acid,  CHgOg.  Oxy-butyric  acid,  C4H^03. 

GlycoUic  acid,  CgH^Oj.  Oxy- valerianic  acid,  C5H,o03. 

Lactic  acid,  C3Hg03.  etc. 

Carbonic  Acid,  or  Oxy-formic  Acid,  HO.CO.OH. — This  is,  in  reality, 
a  dibasic  acid  on  account  of  the  symmetric  structure  of  the  two  — OH  radicals. 
It  has  already  been  considered  (see  p.  1003). 

Lactic  Acids,  or  Oxy-propionic  Acids. — Of  these  there  are  two  isomeres, 
which  vary  in  the  position  of  their  — OH  group,  the  a-  and  /9-  lactic  acids. 
Physiology  is  concerned  only  with  the  first. 

a-Lactic  Acid,  or  Ethidene  Lactic  Acid,  CH3.CHOH.COOH. — Tiiis 
is  called  fennentation  lactic  acid,  being  a  product  of  the  fermentation  of  carbo- 
hydrates (see  p.  982) : 

CeH,A  =  2C3HA. 
On  lactic  fermentation  of  milk-sugar  depends  the  souring  of  milk.  This  fer- 
mentation does  not  take  place  in  tiie  presence  of  sufficiently  acid  gastric  juice, 
but  it  is  very  active  in  the  more  nearly  neutral  (or  alkaline)  intestine.  After 
a  meal  which  includes  carbohydrates  the  intestinal  contents  may  remain  quite 
distinctly  acid  down  to  the  ileo-csecal  valve,  due  to  acetic  and  lactic  acid  pro- 
duction, to  such  an  extent  even  that  proteid  putrefaction  is  inhibited,  as  indicated 
bv  the  total  absence  of  Icucin  and  tyrosin.^  It  has  been  noticed  that  the  fecal 
excrements  after  a  carbohydrate  diet  react  acid,  after  proteid  diet  alkaline. 
The  acid  reaction  is  due  chiefly  if  not  wholly  to  acetic  acid,  since  lactic  acid, 
being  the  stronger  acid,  is  first  neutralized  by  the  intestinal  alkali.  Lactic 
acid,  when  absorbed,  is  completely  burned  in  the  body.  Lactic-acid  fermenta- 
tion between  the  teeth  dissolves  the  enamel,  and  gives  bacteria  access  to  the 
interior.     The  fermentation  lactic  acid  is  inactive  to  polarized  light,  and,  since 

^  HoppeSeyler :  Physiolofjische  Chemie,  1877,  p.  476. 

*  Macfadyen,  Nencki,  und  Sieber  :  Archiv  fiir  exper.  Pathologic  und  Phavmakologie,  1891, 
Bd.  28,  p.  347 


THE    CHEMISTRY   OF    THE   ANIMAL    BODY.  989 

it  has  in  its  lorimiiu  an  asynuuctrii'  carbon  atom,'  it  is  necessary  to  assume  that 
it  consists  of  an  equal  mixture  of  right  and  left  ethidene  lactic  acid.  On 
standing  with  Pcnicllliuni  f/hmcum  tlie  left  lactic  a(ud  is  destroyed  more  freely 
than  is  the  right,  and  the  solution  rotates  polarized  light  to  the  right.^ 

The  right  ethidene  lactic  acid,  CiiUed  also  sareo-  or  para-lactic  acid,  is  that 
which  is  found  in  muscle,  blood,  in  various  blood-glands,  in  the  pericardial 
fluid,  and  in  the  aqueous  humor.  Likewise  it  is  found  in  the  urine  after 
streiuious  physical  effort,  after  CO-poisoniug,  in  yellow  atrophy  of  the  liver, 
in  phosphorus-poisoning,  in  trichinosis,  and  in  birds  (geese  and  ducks)  after 
the  liver  has  been  extirpated.  It  is  sometimes  present  in  diabetic  urine.  Para- 
lactic  acid  is  a  normal  constituent  of  the  blood  and  increases  in  amount  after 
work  or  tetanus.  It  accunudates  in  the  dying  muscle  {rigor  mortis),  causing 
the  formation  of  KH2PO4,  whicii  gives  the  acid  reaction  and  causes  coagula- 
tion.^ Some  believe  that  free  lactic  acid  itself  is  present  and  aids  in  the  coag- 
ulation. Regarding  its  origin  it  has  been  shown  that  it  increases  in  amount  in 
the  dying  muscle  without  simultaneous  decrease  in  the  amount  of  glycogen.* 
On  extirpation  of  the  liver  in  geese,^  ammonia  and  lactic  acid  replace  the  cus- 
tomary uric  acid  in  the  excreta,  and  previous  ingestion  of  carbohydrates  or  of 
urea  will  not  increase  the  amount  of  lactic  acid.  The  lactic  acid  excreted  is 
proportional  in  amount  to  the  proteid  destroyed  and  to  the  ammonia  present. 
It  may  fairly  be  concluded  that  it  owes  its  origin  to  proteid. 

Hoppe-Seyler  ®  says  that  lactic  acid  appears  in  the  urine  only  when  there  is  insufficient 
oxidation  in  the  body,  and  attributes  its  derivation  to  the  decomposition  of  glycogen.  In 
CO-poisoning  Araki '  finds  as  much  as  2  per  cent,  of  lactic  acid  (reckoned  as  zinc  lactate)  in 
a  rabbit's  urine.  Minkowski,**  on  the  other  hand,  denies  the  insufficient-oxidation  theory, 
and  maintains  that  the  destruction  of  lactic  acid  depends  on  a  specific  property  of  the 

'  An  asymmetric  carbon  atom  is  one  in  wliich  the  four  atoms,  or  groups  of  atoms,  united  to 

CH3 

■      .  I 

it  are  all  different.     In  lactic  acid  we  find  the  following  grouping,  H — C — OH.     The  central 

COOH. 
carbon  represents  the  asymmetric  atom.     Such  an  arrangement  is  always  optically  active.    One 
is  able  to  conceive  the  arrangement  of  the  atoms  in  space,  according  to  the  above  grouping,  or 
CH3 

as  follows:  HO— C— H.     This  latter  represents  a  different  configuration.     The  two  arrange- 

I 
COOH 

ments  are  optically  antagonistic.     A  mixture  of  the  two  is  optically  inactive.     The  reader  is 

referred  to  a  text-book  on  general  chemistry  for  the  suggestive  illustrations  of  the  tetrahedral 

space  pictures. 

'•^  BericMe  der  deutschen  ehemischen  Geselhchaft,  Bd.  16,  p.  2720. 

^  Astaschewski :  Zeitschrift  fiir  physioloffische  Chemk,  1880,  Bd.  4,  p.  403;  Irisawa,  Ibid., 
1893,  Bd.  17,  p.  351. 

*  Boehm  :  Pfluger's  Archiv,  1880,  Bd.  23,  p.  44. 

'  Minkowski :  Archiv  fur  exper.  Pathologie  und  Phamiakologie,  1886,  Bd.  21,  p.  41. 

*  Festschrift  zu  R.  Virchmv's  70.  Geburtstarj. 

^  Zeitschrift  fiir  phyaiologische  Cheniie,  1894,  Bd.  19,  p.  42ti. 

^Loc.  cit.,  and  Archiv  fiir  exper.  Pathologie  und  Pharmakoloyie,  1893,  Bd.  31,  p.  214. 


{){)()  .I.Y  AMERICAN    TEXT-BOOK    OE   PTTYSIOLOGY. 

liver,  the  normal  action  bein^  cither  ilcstruction  in  the  liver  itscll"  or  in  other  organs 
through  the  medium  of  a  substance  (enzyme  ?)  produced  in  the  liver. 

One  may  inter|)ret  Araki's  experiment  as  showing  that  consideral)le  (juantities  of  lactic 
acid  are  constantly  produced  in  metabolism,  but  are  normally  swept  away  and  burned;  the 
C'()-pt»isoning  would  prevent  the  normal  combustion.  'I'hc  accumulation  in  mu.scle  after 
stoppage  of  blood-current  [rigor  mortis)  woidd  then  be  oidy  a  continuation  of  the  normal 
process  of  decomposition. 

Cystein,  a-Araido-a-thiopropionic  Acid. — This  substance  has  the  formula 
Nil, 

OH3 — C — COOH.     It  is  a  product  of  proteid  metabolism  and  is  normally 

SH 

destroyed  in  the  body.  On  the  introduction  of  a  halogen  derivative  of  benzol 
into  the  body,  compounds  are  formed  with  cystein,  called  mercapturic  acids, 
which  appear  in  the  urine : 

NH,  NH, 

I  I 

CH3-C— COOH  +  CgH^Br  +  O  -  CH3— C— COOH  +  H^O. 

I  I 

SH  SCgH.Br. 

Bromophenyl-mercapturic  acid. 

This  proves  that  cystein  (like  glycocoll,  for  example)  is  at  lea.st  an  intermediary  and 
possibly  a  primary  product  of  proteid  metabolism  (.see  p.  951).  If  cy.'^tein  be  fed, 
the  greater  part  (two- thirds)  of  the  sulphur  appears  in  the  urine  as  sulphuric  acid, 
the  rest  as  neutral  sulphur.  Thiolactic  acid  has  been  found  ^  as  a  decomposition 
product  of  horn.  Baiunann  ^  demonstrates  the  reduction  of  cy.stein  to  thiolactic 
acid,  i^hows  that  the  latter  yields  an  odor  of  ethyl  sulj)hide  on  evaporation, 
and  asks  if  thiolactic  acid  be  not  the  mother  substance  of  Abel's  compound 
(see  p.  951) : 

NH, 
CH3— C— COOH  +  H2  =  CH3CH(SH)COOH  +  NH3. 

I  Thiolactic  acid. 

SH 

Cystein  itself  is  never  directly  detected  in  the  urine  or  in  the  body. 

Cystin,  Dithio-diamido-ethidene  Lactic  Acid. — Cystein  is  converted  by 
atmospheric  oxygen  into  cystin  : 

NH, 


2CH,— C— COOH  +  20  = 


CH3— CSNH2— COOH 
CH3— CSNH2— COOH* 


oil  ("y.stiii. 

Cystin  is  very  insoluble  in  water.    In  particular  cases  it  appears  in  considerable 

'  Ruter:  Zeitschrift  filr  physiohgische  Chemie,  1895,  Bd.  20,  p.  564. 
^  Baumann :  Ibid.,  1895,  Bd.  20,  p.  583. 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  991 

quantities  as  a  urinary  sediment,  still  more  rarely  as  a  stone  in  the  bladder 
(see  p.  986).      It  is  hevo-rotatoi-y. 

It  is  reported'  that  bodies  having;  the  conipositioii  C — S — H  (thio-  acids,  mercaptaris) 
may  form  sulphuric  acid,  while  most  of  those  having  the  composition  ~C — S — C— 
(ethyl  sulphide)  are  not  oxidized  in  the  body. 

/3-Oxybutyric  Acid,  CHsCIiOIlCIIaCOOlI.— A  Itevo-rotatory  aeid  (see 
p.  981). 

Amido-  Derivatives  of  Carbonic  Acid. 
^'"^OH  ^'"^OH  '^'^^NH; 

Carbonic  acid.  Carbamic  acid.  Carbamide. 

Carbamic  Acid. — This  is  not  known  free,  but  its  calcium  salts  have  been 
found,  especially  in  herbivorous  urine,  and  its  presence  in  the  blood  as  ammo- 
nium carbamate  is  maintained.^  The  latter  has  been  obtained  by  DrechseP  by 
oxidizing  glycocoll  and  leucin  in  ammoniacal  solution,  and  he  has  converted  it 
into  urea  by  electrolysis.  From  these  facts  he  concludes  that  ammonium  car- 
bamate is  the  antecedent  of  urea. 

Ammonium  carbamate  is  formed  by  the  direct  union  of  ammonia  with  car- 
bonic oxide  in  their  nascent  states,  and  is  therefore  found  in  commercial  ammo- 
nium carbonate  and  as  the  product  of  the  oxidation  of  the  amido-  compounds 
above  mentioned  : 

2NH3  +  C0.3=OC<g^|j^- 

Water  converts  it  into  ammonium  carbonate  : 

Carbamide,  or  Urea,  OC(NH2)2. — This  is  the  principal  end-product  of  the 
nitrogenous  portion  of  proteid  in  all  mammals,  being  found  in  considerable 
concentration  in  the  urine.  It  may  be  detected  in  the  blood  in  traces,  in 
lymph,  and  in  the  liver,  but  Liebig  could  find  no  trace  of  it  in  muscle.  In 
ursemia  it  may  collect  in  all  tissues  of  the  body,  and  may  then  be  excreted 
in  slight  amount  by  the  gastric  and  intestinal  juices.  It  is  given  off  in  profuse 
sweating,  though  only  in  small  proportion  to  that  lost  in  the  urine. 

Preparotion. — (1)  Like  other  amides,  by  heating  ammonium  carbonate ; 
further,  by  the  electrolysis  of,  or  by  heating,  ammonium  carbamate : 

oc<8nS:  =  of^<IS:  +  2HP. 

OC<™k,  =  OC<^W=  +  H,0. 

>  W.  J.  Smith  :  PJluger's  Archiv,  1894,  Bd,  55,  p.  542,  and  1894,  Bd.  57,  p.  418. 
'  Drechsel:  Ludwig's  Arbeitm,  1875,  p.  172;  Drechsel  und  Abel,  Archiv  fiir  Physiologie,  1891, 
p.  242. 

*  Loc  cit. 


992  AN  AMERICAN    TEXT-BOOK    OF   PHYSIOLOGY. 

(2)  Through  the  union  of  ammonia  with  carhonyl  chloride : 

OCCI2  +  2NH3  -  OC(NH,)2  +  2IIC1. 

(3)  By  evaporating  an  aqueous  soKition  of  ammonium  cyanate: 

0:C:N.NH,  =  OqNHj,. 

This  was  Wohler's  notable  preparation  in  1828  of  an  "organic"  compound, 
a  product  of  life,  without  the  aid  of  a  "  vital  force." 

(4)  As  a  decomposition  ])rodiict  of  guanin,  xanthin,  crcatin,  uric  acid,  etc. 

(5)  From  proteid,  through  hydrolytic  cleavage'  (see  p.  994).  This  origin 
has  not  as  yet  been  confiriuod. 

Properiiea. — Urea  is  a  weak  base,  of  great  stability  when  within  the  alka- 
line fluids  and  tissues  of  the  body.  It  is  soluble  in  water  in  all  proportions, 
very  soluble  in  hot,  less  so  in  cold  alcohol,  whence  it  crystallizes  in  needle-like 
forms.  It  melts  at  132°  and  recrvstallizes  on  cooling.  Heated  higher  it  is 
converted  into  biuret,  a  substance  which  giv&s  a  violet  color  with  dilute  cupric 
sulphate  in  a  sodium-hydrate  solution  (called  the  biuret  reaction)  : 

NH, 

Heating  urea  with  water  over  100°  in  sealed  tubes,  boiling  it  with  alkalies 
or  acids,  bacterial  action  (see  p.  956),  all  convert  it  through  hydrolysis  into 
carbonic  oxide  and  ammonia.  Such  decomposition  may  take  place  in  the 
stomach  in  uraemia.^     Nitrous  oxide  breaks  up  urea,  thus: 

OC(NH2)2  +  2HNO,  =  CO2  -^  3H2O  +  4N, 

and  hypobromite  of  soda  acts  in  like  manner  in  the  presence  of  alkali : 

OaNH^)^  +  SNaBrO  =  CO^  +  2H,0  +  2N  +  3NaBr. 

The  alkali  present  absorbs  the  CO^i  and  the  volumes  of  N  afford  a  measure  tor  the 
amount  of  urea  present  (method  of  Hiifner,  apparatus  by  Doremus). 

Urea  combines  with  nitric  acid  to  form  urea  nitrate,  ()C(NH2)2.HN03, 
which  is  insoluble  in  nitric  acid.  Urea  oxalate,  which  is  formed  in  similar 
manner  by  the  combination  of  urea  with  oxalic  acid,  is  insoluble  in  water. 
Many  combinations  with  metallic  salts  have  been  prepared,  of  which  one  with 
mercuric  nitrate,  of  uncertain  formula,  is  the  ba«?is  of  Liebig's  method  of  titra- 
tion for  urea. 

Urea  in  the  Body. — This  subject  has  l)een  discussed  under  Nutrition. 
It  can  only  be  briefly  considered  here.  When  urea  is  fed  it  is  i-aj>idly  excreted 
in  the  urine.  The  excreted  nitrogen  of  proteid  appears  in  mammalia  in  greater 
part  as  urea.  Amido-  products  of  proteid  decomposition,  glycocoll,  leucin, 
aspartic  acid,  uric  acid,  when  ^ad  are  converted  by  the  body  into  urea.  So  like- 
wise are  ammonium  carbonate,  lactate,  and  tartrate.     Ammonium  chloride,  on 

'  Drechsel :   Archiv  fiir  Physiologle,  1891,  p.  2fil. 
'  Voit:  Zeitachrift  fur  Bidogk,  1.%S,  VA.  4,  p.  150. 


THE    CHEMISTliY    OF    Till':  ANIMAL    BODY. 


993 


acooimt  of  tho  ^{vimv^  ac-id  radical,  passes  tlin.tiuh  can.ivora  unclian^^od,  but   in 
herbivora,  the  blood  of  which  is  more  stron};ly  alkaline,  a  certain  part  of  tiie 
ammonia  is  converted  first  into  carbonate  and  then  into  urea.     This  conversion 
of  ammonium  carbonate  into  urea  is  of  striking  interest.     Artificial  irrij,^ation 
of  a  liver  with  blood  containing  annnouium  carbonate  increases  the  urea  in 
the  blood,  while  similar  treatment  of  muscle  or  kidney  shows  no  such  results.' 
In  other  experiments  it  has  been  shown  that  annnouium  salts  appear  in  the 
urine  after  feeding  acids  to  carnivora,  and  that  in  disease  in  which  acids  are 
produced  (lactic,  aceto-acetic,  oxybutyric  acids)  ammonia  accompanying  them 
is  found  in  the  urine,  in  all  ca.ses  representing  that  ordinarily  converted  into 
urea.     In  disease  of  the  liver  (cirrhosis,  phosphorus-poisoning)  ammonia  is 
found  in  the  urine  above  the  normal.     Admitting  the  fact  that  ammonium 
ciirbonate  (and  carbamate  likewise)  may  be  converted  into  urea  by  the  liver, 
there  is  no  ground  for  believing  that  this  is  the  normal  process  for  the  produc- 
tion of  the  whole  amount  of  urea,  nor  is  there  at  present  any  measure  of  the 
amount  of  ammonium-salts  produced  in  the  body.     The  liver  may  be  very 
completely  destroyed  by  disease,  and  large  quantities  of  urea  still  be  excreted.^ 
In  getse  extirpation  of  the  liver  has  no  effect  on  the  urea  excreted,  therefore  in 
geese  it  is  formed  elsewhere.'     For  aught  that  is  known,  therefore,  urea  may 
be  formed  in  other  organs  than  the  liver,  and  it  is  not  at  all  improbable  that 
it  is  formed  in  all  organs  where  proteid  decomposition  is  progressing.     The 
greater  part  of  urea  from  proteid  is  eliminated  in  the  dog  fourteen  hours  after 
his  meal  (see  p.  987). 

Guanidin,  HN:  C<  ^Jg'.  This  is  the  imide  of  urea,  and  has  been  obtained  by  the 
oxidation  of  guanin.  It  iinites  with  alcohol  and  acid  radicals— forming,  for  example, 
methyl  guanidin,  HNC  <  NHCH3'  ^"*^  guanidin  acetic  acid,  HN  <  NHCH^COOH. 

NH 

Creatin,  or  Methyl  Guanidin  Acetic  Acid,  HNC  <  ts^^/qjj  \qy{  COOH. 

Creatin  is  a  product  of  proteid  decomposition  and  found  in  muscle  to  the  ex- 
tent of  0.3  per  cent.,  in  traces  in  the  blood,  and  in  varying  amounts  in  the 
urine.  It  is  the  principal  constituent  of  meat-extracts  (liiebig's).  Creatin 
may  be  formed  synthetically  by  the  union  of  cyanamide  w^ith  sarcosin,  and  it 
may  be  broken  up  into  these  constituents  by  boiling  with  barium  hydrate,  but 
the  cyanamide  is  immediately  converted  into  urea  through  the  addition  of 
water : 

H,N.CN  +  HN(CH3)CH,COOH  =  HN  :C  <  ^T(ck)3CH,C00H. 

Cyanamide.  Sarcosin.  Creatin. 

Creatin,  however,  is  not  converted  into  urea  in  the  body  if  fed,  but  is  ex- 
creted in  the  urine  as  creatinin.*     The  amount  of  creatinin  found  in  the  urine 

>  Von  Scliroeder :  Archivfur  exper.  Pathohgie  und  Pharmakologie,  1882,  Bd.  15,  p.  364. 
'  Marfort :  Ibid.,  1894,  Bd.  33,  p.  71. 
»  Minkowski:  Ibid.,  1886,  Bd.  21,  p.  62. 
♦  Volt :  Zeitschrift  fur  Bioloffie,  1868,  Bd.  4,  p.  114. 
63 


994  AJV   AMKlilCAy    TEXT-BOOK    OF   PHYSIOLOGY. 

corresponds  normally  to  the  amount  of  creatin  contained  in  tlic  meat  food  ;  in 
starvation  urine  it  is  proportional  in  amount  to  the  proteid  (muscle)  destroyed, 
being  present  even  on  the  thirtieth  day  (experiment  on  Succi^);  and  it  is 
]>resent  only  in  traces,  or  not  at  all,  in  the  urine  of  milk-fed  children  (ci-eat in- 
free  food).  In  convalescence  creatin  is  said  to  be  retained,  possibly  for  the 
building  of  new  muscle.^  There  is  no  reason  for  believing  that  much  creatin 
is  ever  formed  in  the  body. 

Creatin  gives  its  flavor  to  meat.  If  .trently  heated  it  gives  the  odor  of  roasting  beef. 
Creatinin  in  the  urine  reduces  alkaline  solutions  of  copper  salts  (care  must  be  taken,  there- 
fore, in  making  the  sugar  test  after  using  meat  extracts).  The  action  of  creatin  is  simply  that 
of  a  ]ileasant-tasting.  pleasant-smelling  substance,  which  prepares  the  stomach  for  food 
but  has  no  nourishing  value /)<"/•  ac.     It  is  considered  by  some  to  be  a  nerve-stimulant. 

Creatinin,  or  Glycolyl  Methyl  Guanidin. — Heating  creatin  Avith  acids 
changes    it    into    creatinin    with    loss   of    water,    and     having    the    formula 

NH  — CO 
HX:C!^  I       .     Warming   at  60°  with  phosphoric  acid   causes  this 

\N(CH3)CH, 
conversion.  In  like  manner  when  the  kidney  prepares  an  acid  urine,  creatin 
becomes  creatinin  :  if  tlu;  acid  reaction  be  effaced  through  feeding  alkaline 
salts  the  creatin  is  excreted  unchanged.'  Creatinin  with  chloride  of  zinc 
forms  a  characteristic  very  insoluble  white  powder  of  creatinin  zinc  chloride, 
(C,H7N30)2.ZnCl2. 

Lysatin,  C,;H,3X202,  and  Lysatinin,  C|.H,,N302. — These  substances  are 
obtained,  like  lysiu  (see  below),  from  the  hydrolytic  cleavage  of  proteid,  as  for 
example  from  casein  or  conglutin  heated  with  hydrochloric  acid  and  zinc 
chloride;  they  are  probably  likewise  produced  in  trypsin  digestion.* 

According  to  Drech.sel^  they  are  homologues  of  creatin  and  creatinin,  and 
therefore  should  yield  urea  on  heating  with  barium  hydroxide.  This  is 
Drechsel's  method  of  direct  production  of  urea  from  proteid  by  hydrolytic 
cleavage. 

Diamido-  Fatty  Acids. — Of  these  four  have  been  described : 

Diamido-acetic  Acid,  CH(NH..,)2C00II. — This  was  found  byDrechsel®  among  other 
compounds  after  lieating  casein  in  sealed  tubes  with  concentrated  hydrochloric  acid  at  140°- 
J)lnmido-i[)r(qvonic  acid  has  not  l)een  found  in  the  body. 

Diamido-valeric  Acid,  or  Ornithin,  C4H7(NH2)2COOII.— This  has  been  detected  by 
Jatfe  in  the  urine  and  excrements  of  fowls. 

a-e-Diamido-caproic  Acid,  or  Lysin,  CH2NH2CH2CH2CH2CHNH2- 
COOH. — This  is  a  hydrolytic  cleavage  product  of  casein  after  boiling  with 
hydrochloric  acid,  or  baryta  water,'^  and  may  be  similarly  obtained  from  gela- 

'  Luciani :  Dan  Hnngei'v,  Leipzig,  ]S00,  p.  144. 
^  Von  Noorden  :  Patltolor/ie  des  Stoffuechseh,  1 893,  p.  1 69. 
3  Voit :  Zeitschrift  fur  Binlogie,  1868,  Bd.  4,  p.  150. 

*  See  Drechsel,  and  his  pupils  Fisher,  Siegfried,  and  Hedin  :  Archivfiir  rin/siologie,  1891,  p. 
248  et  seq. 

^  Op.  cit.,   p.  261.  *  Abstract  in  Maly's  Jahrcsbericht  liber  Thierchemie,  1892,  p.  9. 

'  Drechsel :  Archivfiir  Physiolof/ie,  1891,  p.  248. 


THE    CHEMISTRY   OF   THE   ANIMAL    BODY.  995 

tin,  from  vegetable  proteid  (conglutin),  and  from  tlie  pancreatic  digestion  of 
fibrin.' 

Alloxuric  Bodies  and  Bases. 

The  alloxuric  bodies  comprise  those  containing  in  combination  two  radicals, 
one  of  aUoxan,  OC  <  ^{^  ~  ^  >  CO,  the  other  of  urea.  The  skeletal  struc- 
ture of  all  alloxuric  bodies  may  be  written  thus : 

N— C 

C  C     — N. 

N— C     — N-^ 

Alloxan.  Urea. 

These  bodies  fall  into  three  groups,  that  of  hypoxanthin,  of  xanthin,  and  of 
uric  acid.  Bodies  belonging  to  the  first  two  groups  are  called  alloxuric  bases, 
or  more  commonly  xanthin  bases,  or  nudein  bases,  because  they  are  derived 
from  nuclein.  The  strong  family  analogy  of  the  three  groups  is  shown  by 
the  following  reactions — results  of  heating  with  hydrochloric  acid  in  sealed 
tubes  at  180°  to  200°:'^ 

CsH.N.O  +  7H2O  =  3XH3  +  C2H5NO2  +  CO2  +  2CH  A- 

Hypoxanthin.  Glycocoll.  Formic  acid. 

C^H.XP^  +  6HP  -  3NH3  +  C^H.NO^  +  2CO,  +  CH  A- 

Xanthin. 

CsH.N  A  +  5H,0  =  3NH3  +  C2H5NO2  +  3CO2. 

Uric  acid. 

Reference  to  the  formulae  below  will  show  that  the  molecules  of  COg  given 
oft*  correspond  to  the  number  of  CO  radicals  in  the  alloxuric  body,  while  the 
molecules  of  formic  acid  correspond  to  the  number  of  CH  groups. 

(a)  Hypoxanthin  Bases. 

XH  — C  — H 

/  II 

Hypoxanthin,  or  Sarcin,  HC  C — NHv 

^  I  >  CO.— This  is  found  in 

N  —   C=N   / 

small  amounts  in  the  tissues  and  fluids  of  the  body  and  in  the  urine.  The 
action  of  water  or  dilute  acids  on  nuclein  yields  hypoxanthin.^ 

NH— C— H 

/  II 

Adenin,  or  Imidosarcin,  HC  C — NHv 

vv  I  >CNH.— This  is  found 

N  — C=N    / 

»  For  literature  on  these  diamido-  fatty  acids  see  Klebs  :  Zeitschrift  fur  lyhysiologische  Cheniie, 
1895,  Bd.  19,  p.  301. 

2  Kriiger:  Ibifl.,  1894,  Bd.  18,  p.  463.  ^  Kossel :  Tbid.,  1881,  Bd.  5,  p.  268. 


996  AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

in  the  tissues  and  fluids  of  the  body  and  in  the  urine.  It  is,  like  hypoxan- 
thin,  a  decomposition  product  of  nuclei.'  It  is  convertetl  into  hypoxanthin 
through  the  action  of  nitrous  acid. 

{b)  Xantiiin  Bases. 

NH— C— H 

/  II 

Xanthin,  OC  C— NH. 

\  I  J>CO. — This   substance,  like  the  two  last 

NH— C-N    / 

named,  is  found  in  the  tissues  and  the  fluids  of  the  body,  and  is  a  decomposi- 
tion product  of  niiclein.  Occasionally  it  occurs  in  the  form  of  a  urinary  cal- 
culus, as  a  stone  of  exce])tional  hardness. 

Monomethyl  Xanthin,  or  Heteroxanthin,  C'gHgN/X- — This  has  likewise 
been  detected  in  the  urine  (see  Cafl'ein). 

Theobromin,  Dimethyl  Xanthin,  or  Paraxanthin. — 

XCH3— C— H 

/  II 

0  =  C  C— XCH3. 

XH  —  C  =  N       ^ 

This  is  the  principal  alkaloid  in  cacao  (chocolate).     When  fed  it  is  in  part 
excreted  as  monomethyl  xanthin  in  the  urine  (see  Caff'ein).     Its  silver  com- 
pound treated  with  methyl-iodide  yields  caffein. 
NCH3-C-H 

Theophyllin,  0=r^  ('-NIK  ^.        .      ,. 

\  I  /CO. — This  is  found  in  tea  and  uiav  be 

>X'H,— C  =  N    / 

converted  into  caffein  through  the  addition  of  a  third  methyl  group.^ 

XX^H,— C— H 

Caffein,  Thein,  Trimethyl  Xanthin,  0  =  C  C — NCHjv 

\  I  y  CO. 

This  is  the  alkaloid  of  coflee,  tea,  guarana,  and  the  cola  nut,  imparting  the 
nerve-stimulating  proj)erties  to  each.  A  cup  of  coflee  contains  0.1  gram  of 
cafleiu.  If  caffein  be  fed  it  a})pcars  in  part  as  methyl  xanthin  in  the  urine.* 
That  the  compounds  theobromin  and  caffein  may  be  demethylated  in  the  tissue 
is  an  interesting  commentary  on  the  methylation  of  tellurium,  selenium,  and 
pyridin  by  the  tissues. 

Guanin,  Imido -xanthin,  C.H^XpXH. — This  is  found,  like  hypoxanthin, 
adenin,  and  xanthin,  in  tissues  rich  in  nuclei,  and  in  the  blood.*    It  is  a  decom- 

*  Kossel  :  Zeitschrift  Jiir  physiobgische  Chemie,  1886,  Bd.  7,  p.  250. 

*  Jbid.,  1889,  Bd.  13,  p.  298. 

'  Boudzynski  iind  Gottlieb  :  Archlvfur  eiper.  Palholofjif  und.  Pharmakoloyie,  1895,  Bd.  36,  p.  45. 

*  Kossel :  Zeitschri/l  fiir  physiologische  Chemie,  1884,  Bd.  8,  p.  404. 


THE    CHEMISTRY    OF    THE   AMMAL    BODY.  997 

position  product  o^  miclcin.  Combined  with  calciuni  it  gives  tiie  brilliant 
iridescence  to  fish-scales.'  It  is  found  in  the  fresher  layers  of  deposited  guano, 
according  to  Voit  being  very  probably  derived  from  the  fish  eaten  by  the 
\vater-fowl. 

(c)  Uric  Acids. 

NH— C  =  O 

/  I 

Uric  Acid.  O  =  C  C— NH 

\  II  >CO. — This  acid  is  found  in  the  nor- 

NH— C— NH 

mal  urine  in  small  amounts,  and  may  be  detected  in  the  blood  and  tissues, 
esi)ecially  in  gout.  It  is  the  principal  excrement  of  birds  and  snakes,  that  of 
the  latter  being  almost  pure  ammonium  urate. 

Preparation. — (1)  By  heating  glycocoU  with  urea  at  200°  : 

C2H5XO2  +  3CO(NH2)2  =  QH.X.Oj  +  3NH3  +  2H2O. 

(2)  By  heating  the  amide  of  trichlorlactic  acid  with  urea : 

CCI3CHOH.CO.NH2  -f  2CO(NH2)2  -  CsH.NA  +  3HC1  +  NH3  +  H^O. 

Properties. — Uric  acid  may  be  deposited  in  white  hard  crystals,  which  are 
tasteless,  odorless,  and  almost  insoluble  in  water,  alcohol,  or  ether.  (For  its 
solution  in  the  urine  see  p.  966.)  Presence  of  urea  adds  to  its  solubility.^  Its 
most  soluble  salts  are  those  of  lithium  and  piperaziu.  Uric  acid  is  dibasic — 
that  is,  two  of  its  hydrogen  atoms  may  be  replaced  by  monad  elements. 

(1)  Nitric  acid  in  the  cold  converts  uric  acid  into  urea  and  alloxan  : 

C5H,NA+  0  +  H,0  =  OC<5jgZco>^^  +  OC(NH,),. 

Alloxan. 

(2)  Whereas,  if  the  hot  acid  acts,  it  produces  parabanic  acid  : 

/NH  — CO.  /NH  — CO 

0C<  >CO  +  0-OC<  J    +C0,. 

\NH-CO/  \NH  — CO 

Parabanic  acid. 

(3)  Throujrh  water  addition  parabanic  acid  becomes  oxaluric  acid: 

/NH  — C  =  0  /NH,    ■ 

0C<  I         +H.,0  =  OC< 

\NH  — C  =  0  \NH.CO.COOH 

Oxaluric  acid. 

(4)  And  still  another  molecule  of  water  added  produces  oxalic  acid  and  urea :  * 

/NH,  COOH 

0C<  +H.,0=  I  +OC(NH.J,. 

\NH.C0.C00H  COOH 

Oxalic  acid. 

The  above  reactions  lead  up  to  the  constitutional  formula  of  uric  acid,  and  show  its 
decomposition  into  urea  and  oxalic  acid  through  oxidation  and  hydrolysis.  It  is  known 
that  uric  acid  when  fed  increases  the  amount  of  urea  in  the  urine,  and  it  is  possible  that 
the  oxalic  acid  in  the  urine  may  have  the  same  source. 

*  Voit :  Zeitsehrift  fur  tvissemchaflliche  Zoologie,  Bd.  15,  p.  515. 

^  G.  Riidel:  Archiv  fiir  exper.  Pathologie  und  Pharmakologie,  1893,  Bd.  30,  p.  469. 

^  See  Bunge :  Physiologische  Chemie,  1894,  p.  312. 


998  ^l.V   AM  Kill  C A. \    TEXT- BOOK    OF   PHYSIOLOGY. 

Uric  iiciil  oxidized  witli  iit'rmaiiiraiiatc  of  i)ota.s]i  is  converted  into  aUdtitoin,  CiHgN^O,, 
a  substance  which  is  found  in  the  allantoic  fluid,  and  in  the  urine  of  jire^'nant  women  and 
of  newborn  children. 

If  uric  acid  be  carefully  evaporated  with  nitric  acid  on  a  small  white  porcelain  cover, 
a  reddish  residue  remains,  which  moistened  with  ammonia  gives  a  brilliant  purple  color 
due  to  the  formation  of  mnrexid,  CgHjlNHilNsOg;  subsequent  addition  of  alkali  gives 
a  red  coloration.     This  is  known  as  the  mnrexid  test  and  is  very  delicate. 

Carnin,  or  Dimethyl  Uric  Acid. — The  formula  is  unknown.     Carnin  i.s 
found  in  tissue,  aud  has  been  detected  in  extracts  of  meat  and  in  the  urine. 
A  synthetic  dimetiiyl  uric  acid  of  the  following  formula, 

NCH3— c  =  o 

/        1 

OC  C— NHv 

\  II         >co, 

NCH3— C— NH'^ 

when  fused  with  oxalic  acid  is  converted  into  theophyllin.^  This  is  the  only 
transformation  between  the  uric-acid  group  and  the  xanthin  buses  known  in  the 
laboratory. 

The  Alloxuric  Acids  and  Bases  in  the  Body — To  the  definitely 
determined  facts  belong  (1)  that  these  substances  when  fed  are  generally  con- 
verted into  urea ;  (2)  that  some  nucleins  under  proper  chemical  treatment 
break  up  as  follows : 

Nuclein. 
I 

Proteid.  Nucleic  acid. 


Phosphoric  acid.  Adenin. 

Guanin. 


Xanthin. 
Hypoxanthin. 

(3)  that  these  last  named  substances  have  been  obtained  from  no  j)roteid  other 
than  nuclein  (see  Nuclein).  The  idea  that  the  alloxuric  bodies  in  mammals  were 
metabolic  products  of  nuclein,  the  uric  acid  being  derived  from  oxidation  of  the 
bases,  was  especially  emphasized  by  Horbaczewski.-  His  statement  that  uric 
acid  and  the  bases  are  increased  in  the  urine  after  feeding  nuclein  has  been  con- 
firmed.^ The  increase  of  alloxuric  bodies  in  the  urine  in  leucocytha?niia  has  long 
been  known,  and  is  now  explained  by  the  increa.-ed  nuclein-metabolism  following 
the  destruction  of  the  white  blood-corpuscles.  An  interesting  investigation  of  a 
case  of  leucocvthsemia  *  has  shown  that  ingested  theobromin  is  burned  as  in  the 
normal  person  ;  the  explanation  is  offered  that  the  alloxuric  bodies  produced 

'  Fischer  and  Acht:  Berichte  der  Berliner  Acad^mk,  1895,  p.  259. 

^  Sitzungsberichte  der  Wiener  Akademie  der  Wvisenschaften,  1891,  Bd.  C.  Abtli.  iii.  p.  13. 

'  Weintraud  :  Verhandlung  der  Berliner  physiologische  Gesellschaft,  Arrhiv  filr  Physioloyie, 
1895,  p.  .382. 

*  Boudzynski  and  Gottlieb:  Archiv  fUr  exper.  Pathologic  und  Pharmakologie,  1895,  Bd.  36, 
p.  127. 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  999 

iu  the  body  in  some  way  have  lesser  opjwrt unities  for  oxidation  than  those 
introduced  into  it.  Experiments  on  this  kuuc  case  have  shown  tliat,  though 
the  pro[)ortion  of  daily  uric-acid  nitrogen  to  total  nitrogen  in  the  urine  may 
vary  considerably  (1  :  63  to  1  :  88),  the  proi)ortiou  of  the  nitrogen  of  uric  acid 
plus  the  bases  to  total  nitrogen  is  quite  constant  (1  :  48.3  to  1  :  40.8) ;  from 
this  may  be  interred  that  there  is  greater  or  less  production  of  uric  acid  through 
oxidation  of  the  bases  on  different  days.  This  may  be  interpreted  as  affording 
the  missing  link  in  explanation  of  the  conversion  of  the  ba.>es  into  uric  acid. 
If  xanthin  itself  be  fed,  it  is  not  converted  into  uric  acid.  According  to 
Horbaczewski/  uric  acid  is  produced  from  nuclein  by  digesting  putrid  extract 
of  the  spleen  with  blood. 

Ximthin  fed  to  birds  is  converted  into  uric  acid.  In  birds  the  formation  of  uric  acid 
depends  on  a  synthetic  union  of  ammonia  and  lactic  acid  in  the  liver,  since  on  extirpation 
of  the  liver  tlie  last  two  substances  appear  in  the  urine  in  amounts  proportional  to  the 
normaljj'  formed  uric  acid  (see  p.  989). 

The  literature  on  the  subject  of  gout  is  enormous.  It  is  sufficient  to  re- 
mark here  that  it  is  not  even  known  whether  gout  is  due  to  an  increased  for- 
mation or  an  increased  retention  of  uric  acid.  The  amount  of  uric  acid  in  the 
blood  is  certainly  increased.  The  normal  amount  of  uric  acid  in  the  daily 
urine  is  put  at  0.7  gram,  that  of  the  alloxuric  bases  at  0.1325.^  The  amount 
of  the  bases  may  be  quadruplet!  in  leucoeythsemia.''  Whether  all  the  alloxuric 
bodies  produced  in  the  organism  are  eliminated,  or  whether  they  are  partially 
burned,  is  a  matter  of  controversy. 

Diatomic  Dibasic  Acids,  CJ^on-iO^. 

COOH 
Oxalic  Acid,  |  . — This  is  found  as  calcium  oxalate  in  the  urine,  and 

COOH 
is  present  in  most  plants.     Its  possible  origin  from   uric  acid  has  been  men- 
tioned.    It  is  a  product  of  boiling  proteid  with  barium  hydrate.     It  may  be 
obtained  .synthetically  by  heating  sodium  formate  : 

COONa 
2HCOONa=  |  +2H. 

COONa 

Oxalic  acid  and  its  alkaline  .^^alts  are  very  soluble  in  water.  Its  calcium  salts 
are  insoluble  in  water  and  dilute  acetic  acid,  but  are  soluble  in  the  acid  phos- 
phates of  the  urine. 

If  oxalic  acid  be  given  subcutaneously  it  appears  unchanged  in  the  urine.^ 
Given  per  os  it  undoubtedly  unites  with  the  calcium  salts  of  the  gastric  and 
other  juices,  and  is  therefore  but  partially  absorbed.  After  feeding  a  man 
with  meat  alone,  or  with  meat,  fat,  and  sugar,  Bunge*  could  find  no  oxalates 

'  Loc.  cit.         2  Kruger  and  Wulff :  ZeUschrift  fur  physidogische  Chemie,  1895,  Bd.  20,  p.  184. 
^  Boudzynski  and  Gottlieb,  Op.  cit.,  p.  132. 

*  Gaglia:  Archiv  fur  exper.  Pathologie  und  Pharmakologie,  1887,  Bd.  22,  p.  246. 

*  Physiologische  Chemie,  1894,  p.  340. 


1000         AN  AMERICAN   TEXT-BOOK   OF  PHYSIOLOGY. 

in  tlic  iirino.  ]Ie  therefore  concludes  that  the  oxalic  acid  in  the  urine  is 
derived  from  the  oxalates  of  the  food  and  not  from  metabolism  in  the  body. 
Stones  in  the  bladtler  are  sometimes  composed  of  calcium  oxalate,  as  are  also 
urinary  sediments  when  formed  in  consequence  of  aramoniacal  fermentation. 

Succinic  Acid,  HOOC.CgH^.COOH. — This  has  been  detected  in  the 
spleen,  thymus,  thyroid,  in  echinococcus  fluid,  and  often  in  hydrocele  fluid.  It 
is  a  product  of  alcoholic  fermentation,  and  of  proteid  putrefaction.  It  is  often 
found  in  plants. 

Amido-succinic  Acid,  or  Aspartic  Acid,  nOOC.CJl3NIl2.C'OOH. 
This  is  a  product  of  boiling  proteid  with  acid  or  alkalies,  and  it  is  also  formed 
under  the  influence  of  tryj)siu  in  proteid  digestion. 

Monamide  of  Amido-succinic  Acid,   or  Asparagin,   H,^NOC.C2H3NH2.COOH. 

— This  is  found  widely  distributed  in  plants,  especially  in  the  germinating  seed.  If  a  plant 
be  placed  in  the  dark  its  proteid  nitrogen  decreases,  whereas  the  non-i)roteid  nitrogen 
increases,'  the  cause  of  tliis  being  attributed  to  proteid  metabolism  with  tlie  produCTion  of 
amido-  acids,  i.  c.  aspartic  and  glutamic  acids,  leucin,  and  tyrosin.  In  the  sunlight,  it 
is  believed,  these  bodies  are  later  reconverted  into  proteid.  One  view  regarding  the  for- 
mation of  asparagin  is  based  theoretically  on  the  production  of  succinic  acid  from  carbo- 
hydrates (as  in  alcoholic  fermentation)  and  the  subsequent  formation  of  oxymccinic  acid 
(or  malic  acid,  IIOOC.C,H:tOII.rOOII),  which  the  inorganic  nitrogenous  salts  change 
to  asparagin.^  At  any  rate  asparagin  in  the  plant  has  the  ])0wer  of  being  constructed  into 
proteid.  Since  proteid  in  the  animal  body  may  yield  45  per  cent,  of  dextrose  in  its 
decomposition,  as  will  be  shown,  it  seems  fair  to  surmise  that  the  synthesis  of  proteid  in 
the  plant  may  in  part  depend  upon  the  union  of  asparagin  or  similar  amido-  compounds 
with  the  carbohydrates  present.  Asparagin  if  fed  is  converted  into  urea.  It  forms  no 
proteid  synthesis  in  the  animal,  and  has  only  a  very  small  effect  as  a  food-stuff.' 

Glutamic  acid,  H00C.CIINH2.CH,.CH,.C00n.— This  is  found  as  a  cleavage- 
product  of  tryi)tio  digestion  in  the  intestinal  canal.  GJntamin,  its  amido-  compound,  is,  like 
asparagin,  widely  distributed  in  the  vegetable  kingdom  and  in  considerable  amounts.  It 
probably  jilays  the  same  role  as  asi)aragin  in  the  plant.  Glutamin  is  more  soluble  than 
asparagin  and  is  therefore  less  easily  detected. 

Compounds  of  Triatomic  Alcohol  Radicals. 
Glycerin,  or  Propenyl  Alcohol,  CTI2OH.CHOH.CH2OIT.     The  glycerin 
esters   of  the  fatty  acids  form  the  basis  of  all  animal    and   vegetable  fats. 
Glycerin  is  furthermore  formed  in  small  quantities  in  alcoholic  fermentation. 

Preparation.— {I)  Through  the  action  of  an  alkali  on  a  fat,  glycerin  and  a 
soap  are  formed,  a  process  called  saponification: 

2C3H,(C,8H3,02)3  +  6NaOH  =  2C3H,(OH)3  +  6NaC,8H3,02. 

stearin.  Sodium  stcarate. 

(2)  Fats  may  be  decomposed  into  glycerin  and  fatty  acid  by  superheated 
steam,  and  likewi.se  by  the  fat-splitting  ferment  in  the  pancreatic  juice.  Thu.s, 
if  a  thoroughly  washed  butter-ball,  consisting  of  pure  neutral  fat,  be  colored 
with  blue  litmus,  and  a  drop  of  pancreatic  juice  be  placed  upon  it,  the  mass 

'  Schulze  and  Kisser :  Lamlmrthschatfliche  Versuchs-Slation,  1889,  Bd.  36,  p.  1. 

2  MUller:  Ibid.,  1886,  Bd.  33,  p.  326. 

'  See  Voit :  Zeitschrift  fur  Biologic,  1892,  Bd.  29,  p.  125. 


THE    CHKMISTny    OF    TTTE    AMMAL    BODY.  1001 

will  gradually  grow  rrd  in  virtue  of  tlic  fatty  acid  liberated  from  its  glycerin 
couibiiiation.     This  reaction  takes  place  to  some  extent  in  the  intestine. 

If  lattv  acid  be  led,  the  chyle  in  the  thoracic  duct  is  ibund  to  contain  much 
neutral  fat.'  This  synthesis  indicates  the  presence  of  glycerin  in  the  body — 
perhaps,  in  this  case,  in  the  villus  of  the  intestine:  the  source  of  this  glycerin, 
whether  from  proteid  or  carbohydrates,  is  problematical.  If  glycerin  be  fed, 
only  little  is  absorbed  (since  diarrhoea  ensues),  and  of  that  little  some  apjjcars 
in  the  urine.  In  its  pure  form,  therefore,  it  seems  to  be  oxidized  with  dif- 
ficulty in  the  body. 

Glycerin  Aldehyde,  IIOCH.,.CIIOH.CHO,  and  Dioxyacetone,  IIOCII,.CO.Cn, 
OIL— These  sul. stances  arc  formed  by  tlie  careful  oxidation  of  t,dycerin  with  nitric  acid, 
and  together  are  termed  glycerose.  They  have  a  sweet  taste  and  are  the  lowest  known 
members  of  the  glycose  (sugar)  series — i.  c.  substances  which  are  characterized  by  the 
presence  of  either  aldehyde-alcohol,  — CHOH— CHO,  or  ketone-alcohol,  — CO— (;il,0ll, 
radicals.  The  constituents  of  glycerose,  from  the  number  of  their  carbon  atoms,  are 
called  trioscs.  On  boiling  glycerose  with  barium  hydrate  the  two  constituents  readily 
unite  to  form  i-fructose  (levulose). 

Glycerin  Phosphoric  Acid,  (HO)AH5.H2P04.— This  is  the  only  ethe- 
real phosphoric  acid  in  the  urine.  It  is  found  in  mere  traces,  its  source  being 
the  lecithin  decomposed  in  the  body.^ 

^(C„H2„_i02)2' 

Lecithin.    CsH,^^  p^^^^^^^^^^^.^^,^^^^Qjj  _-^^^,.^j^.^     .^     ^^^^^^^ 

in  every  cell,  animal  or  vegetable,  and  especially  in  the  brain  and  nerves. 
It  is  found  in  egg-yolk,  in  muscles,  in  blood-corpuscles,  in  lymph,  pus-cells, 
in  bile,  and  in  milk.  On  boiling  lecithin  with  acids  or  alkalies,  or  through 
putrefaction  in  the  intestinal  canal,  it  breaks  up  into  its  constituents,  fatty 
acids,  glycerin  phosphoric  acid,  and  cholin  (see  p.  986),  substances  which  the 
intestine  may  absorb.  The  fatty  acids  may  be  stearic,  palmitic,  or  oleic,  two 
molecules  of  different  fatty  acids  sometimes  uniting  in  one  molecule  of 
lecithin  :  hence  there  are  varieties  of  lecithins.  Through  further  putrefaction 
cholin  breaks  up  into  carbonic  oxide,  methane,  and  ammonia.^  Lecithin 
treated  with  distilled  water  swells,  furnishing  the  reason  for  the  "  myelin 
forms"  of  nervous  tissue.  Lecithin  is  readily  soluble  in  alcohol  and  ether. 
It  feels  waxy  to  the  touch.  Protagon,  which  has  been  obtained  especially 
from  the  brain,  is  a  crystalline  body  containing  lecithin  and  cerebrin — which 
is  a  glucoside  (a  body  separable  into  proteid  and  a  sugar).  The  chemical 
identity  of  protagon  is  shown  in  that  ether  and  alcohol  will  not  extract  lecithin 
from  it.*  Protagon  readily  breaks  up  into  its  constituents.  While  protagon 
seems  to  be  regarded  as  the  principal  form  in  which  lecithin  occurs  in  the 
brain,  simple  lecithin  is  believed  to  be  present  in  the  nerves  and  other  organs. 
This  subject  has  not  been  i)roperly  worked  out.     Regarding  the  synthesis  of 

»  Munk:  Virchovfs  Archiv,  1880.  Bd.  80,  p.  17. 

*  Sotnitschewsky :  ZeiU^chrift  fiir  physiohr/ische  Chemie,  1880,  Bd.  4,  p.  214. 
3  Hasebroek  :  Ibid.,  1888,  Bd.  12.  p.  148. 

*  Gamgee  and  Blankenhorn:  Journal  of  Physiology,  1881,  vol.  ii.  p.  113. 


I(K)2         AX  AMERICAN    TEXT-BOOK    OF  PIIVSIOLOOY. 

lecithin  in  the  hody,  or  the  physiologieal  importance  of  the  substance,  abso- 
lutely nothin«^  is  known. 

Fat  in  tiik  Body. — Animal  and  vegetabh;  fats  consist  principally  of 
a  mixture  of  the  triglycerides  of  })ahnitic,  stearic,  and  oleic  acids.  In  the 
intestines  the  fat-splitting  ferments  convert  a  small  portion  of  fat  into  glycerin 
and  tatty  acid  ;  the  fatty  acid  unites  with  alkali  to  form  a  soap,  in  the  presence 
of  which  the  fat  breaks  up  into  fine  globules  called  an  emulsion;  if  now  the 
fine  globules  and  the  intestinal  wall  be  wet  with  bile,  fat  is  absorbed,  and  may 
be  burned  in  the  cells  or  deposited  in  the  adipose  tissue. 

Fat  may  likewise  be  derived  from  ingested  carbohydrates.  The  chemical 
derivation  of  fatty  acid  from  carbohydrates  has  already  been  mcntionetl  in 
the  case  of  formic,  acetic,  propionic  (see  p.  980),  and  butyric  acids.  The  fatty 
acids  of  fusel  oils  are  likewise  formed  from  carbohydrates  in  fermentation. 
The  laboratory  synthesis  of  sugar  from  glycerin  has  been  already  related. 
These  reactions,  however,  furnish  only  the  smallest  indication  of  the  large 
transformation  of  carbohydrates  into  fiit  possible  in  the  body. 

If  geese  be  fed  with  rice  in  large  quantitj',  and  the  excreta  and  air  respired  be  ana- 
lyzed, it  may  be  shown  that  carbon  is  retained  in  large  amount  by  the  body,  in  amount 
too  great  to  be  entirely  due  to  the  formation  of  glycogen,  and  must  therefore  have  been 
deposited  in  the  form  of  fat.'  8uch  fattening  of  geese  produces  the  delicate  2)d(4  de  foie 
gras.     The  principle  has  been  established  in  the  case  of  the  dog  as  well.^ 

The  formation  of  fat  from  proteid  (fatty  degeneration)  has  been  established 
with  all  certainty  in  pathological  cases  (see  p.  957).  Recollection  of  the  fact 
that  proteid  may  yield  45  per  cent,  of  sugar  aids  in  the  comprehension  of  this 
problem. 

.  Other  usually  cited  proofs  of  the  formation  of  fat  from  proteid  include  the  conversion 
of  casein  into  fat  incident  to  the  ripening  of  cheese ;  and  the  transformation  of  muscle  in 
a  damp  locality  into  a  cheese-like  mass  called  adipocere,  which  is  probably  effected  by 
bacteria.*  Adipocere  contains  double  the  original  quantity  of  fatty  acid,  occurring  as  cal- 
cium, and  sometimes  as  annnonium  salts. 

Experiments  of  C.  Voit  show  that  on  feeding  large  quantities  of  proteid.  not  all  the 
carbonic  acid  is  expired  that  belongs  to  the  proteid  destroyed  as  indicated  by  the  nitrogen 
in  the  urine  and  feces.  The  conclusion  follows  that  a  non-nitrogenous  substance  has  been 
stored  in  the  bod}'.  Too  much  carbon  is  retained  to  be  present  only  in  the  form  of  glyco- 
gen; fat  from  proteid  must  therefore  have  been  stored.*  The  formation  of  fat  normally 
from  proteid  has  been  violently  combated  by  Pfliiger,  it  would  seem  without  proper  founda- 
tion.    For  behavior  of  fat  in  the  cell  see  p.  999. 

Oleic  Acid,  CisHg^O,. — This  acid  belongs  to  the  series  of  fatty  acids  hav- 
ing the  formula  CDH2n_202.  Its  glyceride  solidifies  only  as  low  as  +4°  C.  It  is 
the  principal  compound  of  liquid  oils.  Pure  stearin  is  solid  at  the  body's 
temperature,  but  mixed  with  olei'n  the  melting-point  of  the  mixture  is  reduced 
below  the  temperature  of  the  body  aiM  its  absorption  is  thereby  rendered  possi- 
ble.    The  fat  in  the  body  is  all  in  a  fluid  condition,  due  to  the  presence  of  olein. 

'  Voit:  Abstract  in  Jahresbericht  iiber  Thierchemie,  1885,  Bd.  15,  p.  51. 
'  Kiibner  :  Zeitschrift  filr  Biologie,  1886,  Bd.  22,  p.  272. 

*  Read  Lehmann:   Abstract  in  Jahresbericht  iiber  Thierchemie,  1889,  Bd.  19,  p.  516. 

*  Erwin  Voit :  Miinchener  rrudieinische  Wochenschrift,  No.  26,  1892  ;  abstract  in  Jahresbericht 
iiber  Thierchemie,  1892,  p.  34. 


THE    CIIEMISTRV   OF    THE  ANIMAL    BODY.  1003 

Carbohydrates. 

The  important  sugar  of  (he  1)100(1  and  the  tissues  is  dextrose.  It  is 
derived  from  the  hydration  of  starchy  loods,  and  from  protcid  metabolism. 
From  dextrose  the  laetie  glands  manufaeture  another  carbohydrate,  milk- 
sugar.  Cane-sugar  forms  an  article  highly  prized  as  a  food.  The  study  of 
the  various  sugars  or  carbohydrates  is  of  especial  interest  because  their  chemi- 
cal nature  is  now  well  known. 

Carbohydrates  were  formerly  defined  as  bodies  which,  like  the  sugars  and 
substances  of  allied  constitution,  contain  carbon,  hydrogen,  and  oxygen,  the 
carbon  atoms  being  present  to  the  number  of  six  or  multiples  thereof,  the 
hydrogen  and  oxygen  being  present  in  a  proportion  to  form  water.  Glycoses 
include  the  monosaccharides  like  dextrose,  CgHjgOg ;  disaccharides  include, 
for  example,  cane-sugar,  CigHjoOn,  which  breaks  up  into  dextrose  and  levu- 
lose,  while  jwlysacchdvides  comprise  such  bodies  as  starch  and  dextrins,  which 
have  the  formula  (CgHjoOs)^. 

In  recent  years  the  term  glycose  has  been  extended  to  cover  bodies  having 
three  to  nine  carbon  atoms  and  possessing  either  the  constitution  of  an 
aldehyde-alcohol,  — CII(OH)CHO,  called  aldoses,  or  of  a  ketone-alcohol, 
— COCH^OH,  called  ketoses.  These  bodies  also  have  hydrogen  and  oxygen 
present  in  a  proportion  to  form  water,  and  the  number  of  carbon  atoms  always 
equals  in  number  those  of  oxygen.  According  to  their  number  of  carbon 
atoms  they  are  termed  trioses,  tetroses,  pentoses,  hexoses,  heptoses,  octoses,  and 
nonoses. 

It  has  been  shown  (foot-note,  p.  989)  how  from  the  asjiiiinetric  carbon  atom  in  lactic 
acid  two  configurations  are  derived.  If  a  body  (such  as  trioxybutyric  acid)  contains  two 
asymmetric  carbon  atoms,  four  configurations  are  possible, 

CH.OH  CH^OH       CH,OH  CH.OH 

HCOH  OHCH  OHCH  HCOH 

HCOH  OHCH  HCOH  OHCH 

COOH  COOH       COOH  COOH 

Similarly  among  the  glycose-aldoses,  a  triose  has  two  modifications ;  a  tetrose,  four ;  a  pen- 
tose, eight :  a  hexose,  sixteen,  etc.  Thus  in  the  following  formula  by  the  variations  of  H 
and  OH  on  the  four  asymmetric  carbon  atoms,  sixteen  possible  hexoses  may  be  obtained. 

CH^OH 
-C— 

— C— 

— c- 
-c-     . 

CHO 

The  carbohydrates  have  well-defined  optical  properties,  rotating  polarized  light  to  the 
right  or  left,  and  are  therefore  designated  as  d-  (dextro-)  and  I-  (laevo-)  respectively.  An 
inactive  («'-)  form  consists  in  an  equal  mixture  of  the  two  others.  Where  the  OH  group 
is  attached  on  the  right  it  may  be  indicated  by  the  sign  -f ,  on  the  left  by  — ,  or  the  4-  OH 
may  be  written  below,  the  —  OH  above. 

H     H  OH  H 
or  CH.OH  C      C     C    C    CHO 
OH  OH  H  OH 


CHO 

CHO 

HCOH 

C-f 

OHCH 

c-     , 

HCOH 

c-f     ' 

HCOH 

c  + 

CH.OH 

CH,OH 

d-Glucose. 

1004         ^iV'  AMERICAN   TEXT-BOOK    OF  PHYSIOLOGY. 

The  Glycoses. 

The  triose  called  glycerose  has  already  been  described. 

A  tetrose  called  erythrose,  which  is  the  aldose  of  erythrite,  C4He(OH)^,  a 
tetratoniic  alcohol,  is  known. 

Of  the  possible  pentoses,  arabinose,  xylose,  and  rhamnose  (raethyl-arabinose) 
occur  in  the  vegetable  kingdoms  in  considerable  quantity.  They  may  be 
absorbed  by  the  intestinal  canal. ^ 

Hexoses,  or  Glucoses. — Through  the  oxidation  of  hexatomic  alcohols 
there  may  be  obtained,  first,  glucoses,  tiien  monocarbonic  acids,  and  lastly 
saccharic  acid,  or  its  isomer  mucic  acid : 

C6H6(OH)3CH20H.        QH6(OH),CHO.        C5H6(OH)5COOH. 

Mannite.  Mannose  Mannonic  acid, 

(and  levulose). 

C,H,(OH),(COOH),. 

Saccharic  acid. 

Mannose  and  levulose  are  respectively  the  aldose  and  ketose  of  mannite, 
galactose  is  the  aldose  of  dulcite,  whereas  glucose  is  probably  the  aldose  of 
sorbite — dulcite  and  sorbite  being,  like  mannite,  hexatomic  alcohols. 

Properties. — (1)  The  hexoses  are  converted  into  their  respective  alcohols  on 
reduction  with  sodium  amalgam. 

(2)  The  hexoses  act  as  reducing  agents,  converting  alkaline  solutions  of 
cuprous  oxide  salts  (obtained  through  presence  of  tartrate)  into  red  cnprous 
oxide,  which  precipitates  out  (Trommer's  test).  Levulic  acid  is  among  the 
products  formed  (see  p.  982).  Of  the  higher  saccharides  only  maltose  and 
milk-sugar  give  this  reaction. 

(3)  Strongly  characteristic  are  the  insoluble  crystalline  compounds  formed 
by  all  glycoses  with  phenylhydrazin,  called  osazones  (see  p.  977)  : 

QH,  A  +  2H2N.NH(CeH,)  =  C6HioO,(:N.NH.C,H,)2  +  m.O  +  H,. 

Levulose.  Phenylhydrazin.  Glycosazone. 

Levulose,  dextrose,  and  mannose  give  the  same  glycosazone.      The   glycos- 
azones  are  decomposed  into  osones  by  fuming  hydrochloric  acid  : 

CeH,A(:^^NH.CfiH,)2  +  2H2O   =   QH,A  +  2H2N.NH.C6H5. 

Glycosone. 
Osones   are    converted    into    sugar    by   nascent    hydrogen.       The    osone    de- 
rived from  levulose,  dextrose,  and  mannose  yields  levulose  by  this  treatment, 
and  the  transformation  of  dextrose  and  mannose  into   levulose  is  therefore 
demonstrated. 

(4)  Only  trioses,  hexoses,  and  nonoses  are  capable  of  alcoholic  fermenta- 
tion. 

Synthesis  of  the   Glucoses. — Formose  may  be  purified  by  means  of  phenyl- 
hydrazin as  above,  so  that  pure  /-fructose  is  obtained  ;  this  treated  with  sodium 
amalgam  yields  i-mannite,  which  on  oxidation  is  converted  into  /-mannonic 
acid  ;  this  last  is  separated  by  a  strychnin  salt  into  its  two  components ;  the 
^  "NVeiske  :  Zeitschrift  fur  physioloyische  Chemie,  1895,  Bd.  20,  p.  489. 


THE    CHEMISTRY   OF    THE   ANIMAL    BODY.  1005 

d-mannonic  acid  is  divideil  and  one  ptirt  treated  witli  hydrogen,  with  resulting 

d-raauno.se,  which,  as  has   been  showu  above,   is  convertible  into  tZ-fructose 

or  ordinary  fruit-sugar ;  the  second  part  of  the  d-mannonic  acid  treated  with 

chinolin    is   transformed    throngh    change   in   configuration    into   its   isomer, 

tZ-gluconic  acid,  which  on  reduction  yields  rZ-glucose,  or  ordinary  dextrose. 

This  shows  the  preparation  of  the  common  sugars  from  their  elements.     The 

transformation  of  levulose  into  dextrose  is  especially  to  be  noted,  since  it  takes 

place  in  the  body. 

^  H    H     OHH 

(7-Glucose,  Dextrose,  Grape-sugar,  CHgOH  C      C      C      C     CHO. — 

OH  OHH    OH 

This  is  the  sugar  of  the  body.  It  is  found  in  the  blood  and  other  fluids  and  in 
the  tissues  to  the  extent  of  0.1  per  cent,  and  more,  even  during  starvation.  The 
principal  source  of  the  dextrose  of  the  blood  is  that  derived  from  the  digestion 
of  starch,  and  also  of  cane-sugar,  in  the  intestinal  tract.  Dextrose  is  likewise  pro- 
duced from  proteid,  for  a  diabetic  patient  fed  solely  on  proteid  may  still  excrete 
sugar  in  the  urine.  Minkowski^  finds  that  in  starving  dogs  after  extirpation 
of  the  pancreas  the  proportion  of  sugar  to  nitrogen  is  2.8  : 1.  The  same  ratio 
has  been  shown  to  exist  in  phlorizin  diabetes  in  rabbits^  when  the  drug  is 
administered  in  a  certain  way. 

In  calculating  this  production  of  glucose  from  proteid,  it  is  discovered  to  i)e 
a  process  of  oxidation,  in  which  45  grams  of  dextrose  are  formed  from  eveiy 
100  grams  of  proteid  decomposed.^  The  sugar  so  formed  contains  44  per  cent, 
of  the  physiologically  available  energy  of  the  proteid  consumed.  The  pancreas 
may  perhaps  manufacture  a  ferment  which,  supplied  to  the  tissues,  becomes  the 
first  cause  of  the  decomposition  of  dextrose,  and  in  whose  absence  diabetes 
ensues.  Excess  of  dextrose  in  the  body  is  stored  up,  especially  in  the  liver- 
cells,  as  glycogen,  which  is  the  anhydride  of  dextrose ;  the  glycogen  may  be 
afterwards  reconverted  into  dextrose.  The  presence  of  sugar  in  the  body  in 
starvation,  even  when  little  urea  may  be  detected  there,  shows  the  readier  excre- 
tion of  the  nitrogenous  radical  of  proteid.  Traces  of  dextrose  are  found  in 
normal  urine. 

Dextrose  is  a  sweet-tasting  crystalline  substance ;  its  solutions  rotate  polar- 
ized light  to  the  right. 

^  H    H    OH 

(i-Fnictose,  Levulose,  Fruit-sugar,  CHjOH  C     C      C     COCHgOH.— 

OH  OHH 
This  occurs  in  many  fruits  and  in  honey.  It  is  sweeter  than  dextrose,  and 
rotates  polarized  light  to  the  left.  It  is  a  product  of  the  decomposition  of 
cane-sugar  in  the  intestinal  canal.  If  levulose  be  fed,  any  excess  in  the  blood 
may  be  converted  into  glycogen,  and  through  the  glycogen  into  dextrose.  It 
is  possible  thus  to  convert  50  per  cent,  of  the  levulose  fed  into  dextiose.* 

'  Archiv  fur  Physiologie  und  Pharmakologie,  1893,  Bd.  31,  p.  85. 

*  Lusk:  Paper  read  before  the  American  Society  of  Physiology,  Philadelphia,  1895. 
'  Weintraud  and  Laues:  Zeilschrift  fiir  physiolcgische  Chemie,  1894,  Bd.  19,  p.  632. 

♦  Minkowski :  Archiv  fur  Pathologie  und  Pharmakologie,  1893,  Bd.  31,  p.  157. 


1006         AN  AMERICAN   TEXT- BOOK    OF  PHYSIOLOGY. 

Wliou  levulose  is  fed  to  a  diabetic  i)atieiit,  it  may  be  burned,  though  j)o\ver  to 
burn  dextrose  has  been  lost.^ 

H    OHOHH 
(/-Galactose,  CHjOH  C      C      C      C      CHO.— This  is  found  combined 

OHH  H  OH 
■with  proteid  in  the  brain,  forming  the  ghicoside  cerebriu.  It  is  produced 
together  with  dextrose  in  tiie  hydrolytic  decomposition  of  milk-sugar.  It  does 
not  undergo  alcoholic  fermentation,  at  least  not  with  Saccharomyces  apicidatus. 
WJien  fed  it  is  not  converted  directly  into  glycogen,  but  through  its  burning 
it  spares  the  decomposition  of  some  of  the  dextrose  produced  from  proteid, 
"which  latter  may  of  course  be  converted  into  glycogen.^ 

The  Disacch abides,  CigHojOu. 

These  are  di-multiple  sugars  in  ether-like  combination.  To  cane-sugar  and 
milk-sugar,  Fisher  has  ascribed  the  following  formuh«  :  * 

Cane-sugar.  Milk-sugar. 

€H-^^__^  CHPH  CH3OH     CHO 

^/ CHOH   ^\C  CHOH     CHOH 

^\CHOH    /CHOH  CH        CHOH 

CH     0\CHOH  ^/CHOH     CHOH 

CHOH    ^CH  ^\CHOH     CHOH 
CH2OH     CH2OH  CH   — O— CH2 

Dextrose  group.        Levulose  group.  Galactose  group.  Dextrose  group. 

Cane-sugar,  or  Saccharose. — Cane-sugar,  obtained  from  the  sugar-cane 
and  the  beet-root,  is  largely  used  to  flavor  the  food,  and  likewise  assumes 
importance  as  a  food-stuff.  On  boiling  with  dilute  acids,  cane-sugar  is  con- 
verted through  hydrolysis  into  a  mixture  of  levulose  and  dextrose.  The  same 
result  is  obtained  by  warming  with  0.2  per  cent,  hydrochloric  acid  at  the 
temperature  of  the  body.  This  inversion,  therefore,  takes  place  in  the  stomach. 
In  the  inte.'^tinal  canal  the  inversion  is  accomplished  through  the  action  of  a 
ferment  present  in  the  intestinal  juice.  Subcutaneous  injection  of  cane-sugar 
shows  that  it  is  not  directly  converted  into  glycogen,  but  that  in  burning  it 
spares  some  dextrose  coming  from  proteid  decomposition,  and  this  latter  is 
converted  into  glycogen  and  may  be  found  in  the  liver  and  muscles.  But  fed 
per  OS,  cane-sugar  is  the  cause  of  a  large  glycogen  storage,  in  virtue  of  its 
srreater  or  le.^^s  conversion  into  dextrose  and  levulose  in  the  intestines. 

Milk-sugar,  or  Lactose. — This  is  found  in  the  milk  and  in  the  amniotic 
fluid.  It  is  probably  manufactured  from  dextrose  in  the  mammary  glands, 
for  the  blood  does  not  contain  it.  It  is  sometimes  present  in  the  urine  during 
the  last  days  of  pregnancy,  and  almost  always  during  the  first  days  of  lactation. 
It  readily  undergoes  lactic  fermentation,  producing  lactic  acid,  which  then 
causes  clotting  of  the  milk.  This  fermentation  may  take  place  in  the  intestinal 
tract.    Boiling  with  dilute  acids  splits  up  milk-sugar  into  galactose  and  dextrose. 

1  Loc  cU.  »  C.  Voit :  Zeiischrift  fitr  Binlogie,  1S91,  Bd.  28,  p.  245. 

*  Benchte  der  deutschen  chemischen  Gesellschaft,  1894,  Bd.26,  p.  2400. 


THE   CHEMISTRY   OF    THE  ANIMAL    BODY.  1007 

This  decomposition  probably  does  not  take  i)la<e  in  the  stomach.  Neither 
does  the  intestinal  juice  cause  tliis  transformation.'  Milk-sugar  is  probal)ly 
absorbed  unchanged,  and  is  not  a  glycogen-producer  except  indirectly  in  the 
sense  of  sparing  i)roteid  dextrose  which  may  become  glycogen.''  The  contrary 
view,  /.  e.  that  milk-sugar  is  converted  into  dextrose  and  galactose,  is  held  by 
^rinkowski"*  and  others.     The  question  is  not  definitely  settled. 

Isomaltose.— This  is  the  only  disaccharide  which  has  been  synthetically 
obtained,  having  been  produced  by  boiling  dextrose  with  hydrochloric  acid. 
It  ferments  with  difficulty  and  forms  an  osazone  which  melts  at  150°-153°. 
It,  wnth  dextrin,  is  a  product  of  the  action  of  diastase  and  of  the  diastatic 
enzymes  found  in  saliva,  pancreatic  juice,  intestinal  juice,  and  blood  upon 
starch  and  glycogen.  Through  further  action  of  the  same  ferments  isomaltose 
is  converted  into  maltose. 

Maltose.— ]Maltose  (and  dextrin)  are  the  end-products  of  the  action  of 
diastase  on  starch  and  glycogen,  the  process  being  one  of  hydrolysis : 

Maltose.  Dextrin. 

It  is  likewise  a  product  of  the  diastatic  action  of  ptyalin  (saliva),  amylopsin 
(pancreatic  juice),  and  of  ferments  in  the  intestinal  juice  and  in  the  blood. 
Maltose  readily  undergoes  alcoholic  fermentation  and  forms  an  osazone  which 
melts  at  206°.  It  is  converted  into  dextrose  by  boiling  with  acids.  Certain 
ferments  convert  maltose  (and  dextrin)  into  dextrose  (see  Starch). 

Cellulose  Group,  (CgHioOs)^. 

Cellulose.— This  is  a  highb'  polymerized  anhydride  of  dextrose,  perhaps  also  of  uian- 
nose.  It  forms  the  cell-wall  in  the  plant.  It  undergoes  putrefaction  in  the  intestinal 
canal,  especially  in  herbivora  (see  p.  976),  and  owing  to  the  production  of  fatty  acids  it  may 
have  value  as  a  food.  In  man  only  young  and  tender  cellulose  is  digested,  such  as  occurs 
in  lettuce  and  celery.  The  bulk  of  herbivorous  fecal  matter  consi.sts  of  cellulose.  Cellulose 
is  only  with  difficulty  attacked  by  acids  and  alkalies.  Tunicin,  found  among  the  tunicates, 
is  identical  with  cellulose,  so  that  the  substance  is  not  solely  characteristic  of  the  vegetable 
kingdom. 

Starch,  (C6Hio05)2o.— This  substance  on  boiling  with  dilute  acids  breaks 
down  by  hydrolysis  principally  to  dextrose.  It  is  found  in  plants,  and 
may  be  manufactured  by  them  from  cane-sugar,  dextrose,  levulose,  and  from 
other  sugars.  It  forms  a  reserve  food-stuff,  being  converted  into  sugar  as  the 
plant  requires  it— in  winter,  for  example.  Starch  gives  a  blue  color  with 
iodine.  According  to  recent  investigations  *  starch  is  said  to  be  broken  up  by 
diastase  into  five  successive  hydrolytic  cleavage-products  as  follow^s  :  (1)  Amylo- 
dcvtrin  (C22H2oOio)54,  a  substance  giving  a  deep-blue  color  with  iodine.  This 
is  next  changed  to  (2)  Erythrodextrin,  (Ci2H2oOio)i8  +  HgO,  or  (Ci2ll2oO,o)i7. 

1  Pregl  :  Pflugei's  Archiv,  1895,  Bd.  61,  p.  359.  '  C.  Voit,  Op.  cit.,  p.  260  et  seq. 

^  Archiv  fur  exper.  Pathologic  und  Pharviakologie,  1893,  B<1.  31,  p.  Kil  ;  Kausch  and  Socin,  ibid., 
1893,  Bd.  31,  p.  398. 

*  Lintner  and  Diill :  Berichte  der  deulschen  cJiemi^chen  Gctellschajt,  1893,  Bd.  26,  p.  2533. 


1008         AN   A  mi:  RICA  jY    TEXT-JiOOK    OF    PHYSTOLOGY. 

(CiJIjaO,,),  ^vlli(•ll  is  roailily  suluble  in  water  ami  givc-s  with  iodine  a  reildi.sh- 
hrown  eolor.  Erythrodextrin  is  converted  into  (3)  Adiroodexirin,  {^\nyi^Oy^^ 
+  HgO,  or  (C,2Tl2uO,u)5.Ci2H220ji,  wliioh  is  likewise  very  soluble,  tastes  slightly 
sweet,  but  gives  no  coloration  with  iodine.  Achroodcxtrin  now  breaks  up 
into  (4)  I.s(»nalios(',  which  through  change  in  configuration  is  transformed  to  its 
isomere  (5)  Maltose. 

Products  similar  to  these  are  formed  by  the  various  diastatic  ferments  in 
the  body,  and  in  addition  also  some  dextrose.  Ptyalin  ^  acts  rapidly  on  starch, 
producing  dextrin  antl  maltose,  but  very  little  dextrose.  Amylopsin,  from  the 
pancreas,  acts  still  more  rapidly  than  ptyalin,  and  with  the  production  of  con- 
siderable dextrose.  The  diastatic  ferment  of  intestinal  juice  acts  very  slowly 
on  starch,  forming  dextrin,  maltose,  and  a  little  dextrose,  while  the  ferment  in 
blood-scrum  likewise  acts  slowly  but  with  complete  transformation  of  all  the 
maltose  and  dextrin  formed,  into  dextrose. 

The  above  facts  lead  Hamburger  to  suggest  that  the  diastatic  ferments  of  the  body 
consist  of  mixtures,  in  different  proportions,  of  diastase,  which  forms  dextrin  and  maltose 
from  starch,  and  of  glucase,  which  converts  these  into  dextrose.  This,  however,  is  merely 
an  hypothesis,  and  glucase  has  never  been  prepared.  The  vegetable  diastase  is  not  iden- 
tical with  that  found  in  the  body.  Thus  ptyalin,  like  cmulsin,  breaks  up  salicin  into  sali- 
cylic alcohol  and  dextrose,  of  which  action  vegetable  diastase  is  incapable.  But  ptyalin, 
again,  is  not  identical  with  emulsin,  for  it  will  not  act  on  amygdalin. 

Glycog-en,  or  Animal  Starch. — Recent  investigations  have  shown  that  in 
all  the  juu'ticulars  of  diastatic  decomposition  glycogen  is  identical  with  vege- 
table starch.^  Glycogen  is  soluble  in  water,  giving  an  opalescent  fluid.  The 
blood  has  a  normal  composition  which  does  not  greatly  vary.  After  a  hearty 
meal  excess  of  fat  is  deposited  in  fatty  tissue,  excess  of  proteid  in  the  nui.scular 
tissue,  while  excess  of  sugar  is  stored  in  the  muscles  and  especially  in  the  liver- 
cells  in  the  less  combustible  and  less  diffusible  form  of  glycogen.  About  one- 
half  of  the  total  quantity  of  glycogen  is  found  in  the  muscles,  the  remainder 
in  the  liver,  where  it  may  even  amount  to  40  per  cent,  of  the  dry  solids. 
When  the  blood  becomes  poor  in  sugar,  the  store  of  glycogen  is  drawn  upon  to 
such  an  extent  that  in  hunger  the  body  becomes  glycogen-free.  Muscular  work 
likewise  causes  the  rapid  conversion  of  glycogen  into  sugar.  The  sources  of 
glycogen  are  certain  ingested  carbohydrates,  and  also  the  dextrose  derived  from 
proteid.  If  large  quantities  of  proteid  be  fed,  glycogen  may  be  stored.  If 
milk-sugar  and  galactose  be  burned  in  the  cells  of  an  otherwise  starving  animal, 
the  dextrose  from  proteid  is  economized  and  glycogen  is  found.  If  dextrose 
or  levulose  (or  anything  which  produces  dextrose,  e.  g.  cane-sugar,  maltose)  be 
fed,  there  is  a  direct  conversion  of  the  sugar  into  glycogen.  Voit'  has  called 
attention  to  the  fact  that  only  directly  fermentable  sugars  are  convertible  into 
glycogen,  Cremer  *  shows  that  yeast-cells  contain  nmch  glycogen  when  cul- 
tivated in  media  which  they  ferment,  not,  however,  when  cultivated  in  milk- 

»  See  Hamburger:  Pflilger'a  Archiv,  1895,  Bd.  60,  p.  573. 
'  Kulz  and  Vogel ;  Zeitschrift  fur  Biologie,  1895,  Bd.  31,  p.  108. 
»  Zeitschrift  fur  Biologie,  1891,  Bd.  28,  p.  270. 
*  Ibid.,  1895,  Bd.  31,  p.  188. 


THE    CHEMISTRY    OF   THE   ANIMAL    BODY.  1009 

sugar,  for  example.  So  perhaps,  in  Icvulose-fennentation  the  first  step  may 
be  conversion  into  glycioj^en  or  the  anhydride  of"  dextrose.  Cremer  maintains 
that  the  pentoses  are  burned  in  the  body,  but  are  oidy  indirectly  glycogen- 
producers. 

Dextrins. — These  have  been  described  under  starch. 

H    H    Oil  II 
(^-Glucuronic  Acid,  or  Glycuronic  Acid,  HOOC  C     C      C     C    CIIO. 

OHOHH     OH 

— Obtained  by  reducing-  (/-saccharic  acid  with  nascent  hydrogen.  After  feed- 
ing chloral  hydrate,  naphthalin,  camphor,  terpentine,  ])lienol,  ortho-nitrotoluol, 
and  other  bodies,  they  appear  in  the  urine  (usually  having  been  first  converted 
into  alcohol)  in  combination  with  glycuronic  acid.  Urochloralic  acid,  naphthol- 
glycuronic  acid,  campho-glycuronic  acid,  terpene-glycuronic  acid,  etc.,  all  rotate 
polarized  light  to  the  left.  It  seems  that  these  ingested  substances  unite  in  the 
body  with  the  aldehyde  group  of  dextrose,  at  the  same  time  protecting  all  but 
one  group  of  the  dextrose  molecule  from  further  oxidation  (Fischer).  Glycu- 
ronic acid,  which  is  easily  separated  by  hydrolysis  from  its  aromatic  combina- 
tion, itself  rotates  polarized  light  to  the  right,  reduces  alkaline  copper  solutions, 
and  might  be  confounded  with  dextrose  except  that  it  d(jes  not  ferment  with 
yeast.  Glycuronic  acid  is  likewise  found  in  the  urine  after  administration  of 
curare,  morphine,  and  after  chloroform-narcosis,  perhaps  paired  with  aromatic 
bodies  formed  in  the  organization. 

Combustion  in  the  Cell,  in  General. — Experiments^  show  that  taking 
the  proteid  decomposition  in  the  starving  dog  as  1,  it  is  necessary  to  feed  three 
to  four  times  that  amount  of  proteid  taken  alone  in  order  to  attain  nitrogenous 
equilibrium,  1.6  to  2.1  times  that  amount  of  proteid  when  fed  with  fat,  and  1  to 
1.2  times  that  amount  when  fed  with  carbohydrates.  The  physiological  proteid 
minimum  is  in  these  cases  never  less  than  the  amount  required  in  starvation. 
Only  after  feeding  gelatin  with  proteid  may  the  proteid  fed  be  below  the 
amount  decomposed  in  starvation.  The  above  shows  what  is  well  known,  that 
sugar  spares  proteid  from  decomposition  more  than  fat  does.  E.  Voit  ^  states 
these  two  propositions:  (1)  The  part  played  by  these  several  food-stuffs  in  the 
total  metabolism  depends  on  the  composition  of  the  fluid  feeding  the  cell. 
The  greater  the  amount  of  one  of  these  food-stuffs,  the  greater  its  decompo- 
sition and  the  less  the  decomposition  of  the  others,  so  long  as  the  total  decom- 
position suffers  no  change.  (2)  The  several  food-stuffs  do  not  act  wholly  on 
account  of  their  quantity  in  the  fluid  surrounding  the  cell,  but  especially  accord- 
ing to  the  chemical  affinity  of  the  cell-substance  for  them  individually.  First 
in  this  regard  comes  proteid,  then  carbohydrates,  and  lastly  fat. 

The  excessive  proteid  decomposition  in  diabetes  is  due  to  the  non-combus- 
tion of  the  proteid  protecting  sugars^  and  the  same  is  true  in  fever  where  a 
small  supply  of  carbohydrates  reaches  the  blood.^ 

*  E.  Voit  and  Korknnoff:  Zeitsehrift  fur  Biologk,  1895.  Bd.  32,  p.  117. 

^  Op.  cit.,  pp.  128  and  135.  =•  Lusk:  Zeitsehrift  fur  Biologic,  1890,  Bd.  27,  p.  459. 

*  May :  Ibid.,  1894,  Bd.  30,  p.  1. 


1010         AN  AMERICAN    TEXT-BOOK    OF  PHYSIOLOGY. 

For  further  discussion  of  carbohydrates  in  the  body  see  under  the  indi- 
vidual sugars,  and  under  Fat  in  the  liudy. 

Benzol  Derivatives  or  Aromatic  Compounds. 
The  aromatic  compouuds  are  characterized  by  a  configuration  in  which  six 
atoms  of  carbon  are  linked  together  in  a  circle  called  the  benzol  ring.     The 
type  of  this  is  benzol,  a  hydrocarbon  found  in  coal-tar  and  having  the  formula, 

{! 

H— C  C— H 


H— C  C— H 

\    // 


3 


C  4 

H 

The  hvdroiren  atoms  mav  be  substituted  for  others,  substitution  of  one  OH 

group,    for   example,    forming   phenol,  CgHg — OH.     If,  however,  two   OH 

groups  are  substituted,  three  different  bodies,  corresponding  to  the  different 

arrangements  on  the  ring,  become  possible.     If  the  two  OH  groups  occupy 

the  positions  1   and  2  the  substance  is  orf/io-dioxybenzol ;  if  1  and  3,  meta- 

dioxybenzol ;  and  if  1  and  4,  para-dioxybenzol. 

It  is  possible  to  convert  bodies  of  the  fatty  series  into  those  of  the  aro- 
matic. Acetylene  passed  through  red-hot  tubes  yields  benzol.  On  the  other 
hand,  aromatic  bodies  may  be  converted  into  those  of  the  fatty  series.  If 
phenol  in  aqueous  solution  be  subjected  to  electrolysis  by  an  alternating  cur- 
rent under  which  circumstances  hydrogen  and  oxygen  are  alternately  liberated 
on  the  same  pole,  the  effect  of  this  intermittent  oxidation  and  reduction  is  to 
break  up  the  phenol  into  caproic  acid,  and  finally,  after  passing  through  acids 
of  lower  carbon  contents,  into  carbonic  acid  and  water. 

The  aromatic  compounds  found  in  the  urine  are  normally  exclusively 
derived  from  the  products  of  proteid  putrefaction  in  the  intestines.  It  is 
admitted  that  neither  fats  nor  carbohydrates  play  any  part  in  their  formation. 

Benzol,  CfiHg.— This  body  if  fed  is  absorbed  and  afterward  converted  into  oxybenzol 
or  phenol,  with  subsequent  behavior  similar  to  phenol. 

Phenol  (Carbolic  Acid,  Oxybenzol,  Phenyl-hydroxide),  CgHpH. — 
This  is  an  aromatic  alcohol.  A  5  per  cent,  solution  precipitates  proteid,  and  a 
ranch  weaker  solution  produces  irritation  of  the  tissues,  and  especially  those 
of  the  kidney,  M'here  its  excretion  takes  place.  It  is  strange  that  a  strong 
antiseptic  like  j)henol  should  be  a  normal  product  of  proteid  putrefaction. 
Phenol  is  obtainable  from  tyrosin,  by  processes  of  cleavage  and  oxidation  (see 
Tyrosin),  and  in  the  intestinal  canal  is  probably  derived  from  tyrosin.  A 
small  amount  of  the  phenol  ordinarily  absorbed  is  converted  by  the  organism 
into  pyrocatechin,  a  dioxybenzol.  These  two  substances  are  found  in  normal 
urine  in  ethereal  combination  with  sulphuric  acid,  CgH^O.SOj.OH  (or  as  an 
alkaline  ethereal  sulphate).     This  synthesis,  accomplished  by  the  union  of  the 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  1011 

phenol  and  .sulphuric  at'i<l  with  loss  of  water,  has  heen  obtained  by  electrolysis, 
using  alt('rnatint»;  electric  currents.'  [f  phenol  be  administered  in  more  than 
a  very  small  amount,  hydroqiiinone  likewise  a})pears  in  the  urine,  paired  like 
the  others  with  sulphuric  acid,  and  should  the  plienol  administered  exceed  at 
any  time  the  available  sulphate,  it  forms  to  a  certain  extent -a  synthesis  with 
glycuronic  acid,  and  so  combined  appears  in  the  urine. 

Phenol  ffivcs  with  jMillon's  rea.ireiit  (niorcuric  nitrate  in  nitric  acid  with  some  nitrous 
acid)  a  brilliant  red  coloration.  This  is  given  by  all  bodies  liaving  an  hydroxyl  group  on  the 
benzol  ring,  of  which  substance  tyrosin  may  be  mentioned  as  an  example.  It  is  likewise 
given  by  proteid,  slowly  in  the  cold,  more  rapidly  on  warming,  and  this  fact  together 
with  the  cleavage  putrefactive  products  has  given  foundation  to  the  belief  that  the  oxy- 
benzol  ring  exists  preformed  in  the  proteid  molecule. 

Pyrocatechin,  C6H4(OH)2. — This  is  ortho-dioxybenzol.  For  its  forma- 
\'\(^\\  see  under  Phenol. 

Hydroquinone,  C6H4(OH)2. — Para-dioxy benzol.  Found  in  the  urine 
especially  in  cases  of  carbolic-acid  poisonuig  (see  Phenol).  If  such  urine  be 
shaken  in  the  air,  it  is  turned  black,  owing  to  the  oxidation  of  hydroquinone 

to  quinone,  CgH/    |  . 

p-Cresol,  CgH^.OH.CHs. — This  is  a  product  of  intestinal  putrefaction,  and  is 
derived  from  tyrosin  (which  see).     It  is  found  in  the  urine  as  an  ethereal  sulphate. 

Benzoic  Acid,  CgHsCOOH. — Salts  of  this  acid  and  analogous  bodies 
are  found  especially  in  plants.  In  the  urine  of  herbivora  therefore  is  found  a 
considerable  amount  of  hijppurie  acid,  COOH.CHg.NH.CO.CgHg,  the  com- 
bination of  benzoic  acid  and  glycocoU  (see  Glycocoll,  p.  981).  On  feeding 
jjhenifl-acetie  acid,  CgHsCHgCOOH,  phenaceturic  acid,  COOH.CHg.  ISTH.- 
CO.CHj.CgHj,  appears  in  the  urine,  while  the  higher  benzyl  acids,  such  as 
phenyl-propionic  acid,  suffer  the  oxidation  of  the  side  chain  in  the  body,  and 
ordinary  hippuric  acid  is  formed.  After  eating  apple-parings  and  other  vege- 
table substances,  hippuric  acid  is  found  in  human  urine.  It  is  further  stated 
that  j)henyl-acetic  acid  and  phenyl-propionic  acids  are  normal  products  of 
proteid  putrefaction,  though  in  very  small  quantities ;  hippuric  acid  and  phen- 
aceturic acid  must  therefore  be  constantly  present  in  traces  in  human  urine. 
Hippuric  acid  is  split  into  its  constituents  by  hydrolysis  through  the  action  of 
the  Micrococcus  urccv. 

p-Oxyphenyl-acetic  Acid,  C6H4.OH.CH2COOH. — This  is  a  product  of 
the  intestinal  putrefaction  of  proteid  and  of  tyrosin  (which  see).  It  occurs 
in  the  urine  either  paired  with  sulphuric  acid  or  as  an  alkaline  salt  of  oxyphenyl- 
acetic  acid.^ 

j^-Hydrocumaric  Acid,  CgH4.0H.C2ll4COOII. — This  second  oxy-  acid  is 
likewise  derived  from  proteid  and  tyrosin  (which  see)  putrefaction.  Its  occur- 
rence in  the  urine  is  similar  to  the  above  oxy-  acid. 

Tyrosin,   Amido-hydrocumaric   Acid,  p-Oxyphenyl-amido-propionic 

^  Drechsel :  Journal  Jar  praktische  Cliemie,  Bd.  29,  p.  229  ;  abstr.  Jtihresbericht  ilber  Thierchemief 
1884,  p.  77.  '  Baumann  :  Zeitschrijl  fur  physiologische  Chemie,  1886,  Bd.  10,  p.  125. 


1012         A.X   AMERICAA'    TEXT-BOOK    OF  PHYSIOLOGY. 

Acid,  (.'eH^.OH.CsHsNHaCOOlI.— Tyri)sin  is  a  coiistant  product  ol'tlic  putre- 
iiu^tion  of  all  proteid  bodies  (except  gelatin),  and  is  therefore  found  in  cheese. 
It  may  be  formed  in  large  quantities  by  boiling  horn-shavings  with  sul- 
phuric acid.  Leucin  is  always  formed  whenever  tyrosin  is.  Tyrosin  forms 
characteristic  sheaf-shaped  bundles  of  crystals.  All  the  aromatic  bodies  thus 
far  described  have  been  eliminated  in  the  urine  with  their  benzol  nucleus 
intact.  Tyrosin,  however,  may  be  completely  burned  in  the  body.  This 
seems  to  be  because  of  the  presence  of  the  aniido-  group  on  the  side  chain,  for 
phenyl-amido-propionic  acid  is  likewise  destroyed.  Tyrosin  is  found  in  the 
urine  in  vellow  atrophy  of  the  liver,  in  phosphorus-poisoning,  etc.  (see  Leucin, 
p.  1)83).  Through  cleavage,  oxidation,  or  reduction,  the  following  reactions 
take  place,  phenol  being  the  final  product.^  The  substances  not  found  in  intes- 
tinal putrefaction  are  named  in  italics : 

CcH,.0H.C,H3NH,C00H  +  H^    =    C6H,.0II.C,H,C00H  +  NH3 

jj-IIydrocumaric  acid. 

C6H,.0n.aH,C0()H    =    C«H,.0H.aH5  +  CO, 

p-Ethyl[)henol. 

C6H,.OH.C.,H5  +  30    =    CeH.OH.CH^COOH  +  H,0 

p-Oxyphenyl-acetic  acid. 

CeH^.OH.CH.COOH     =    C«H,.OH.CII:,  +  CO^ 

p-Crcsol. 

C6H,.OH.CH3  +  30     =    C«H,OH  COOH  +  H,0 

p-Oxybeiizoic  acid. 

CeH^.OH.COOH     =    CsH.OH  +  CO, 

Phenol. 

It  has  never  been  shown  that  tyrosin  is  a  normal  product  of  proteid  metabolism 
within  the  tissues.  With  leucin  it  is  said  to  be  a  normal  product  of  pancreatic  di- 
gestion (see  p.  983),  being  derived  only  from  hemipeptone  (Kiihne,  Chittenden). 

Pyridin.— This  body  has  the  accompanying  formula,  one  of  the  CH  groups  in  benzol 
H 
C 

^\ 
HC      CH  .,,,.,. 

bein<' substituted  by  N:       I         II    •  When  pyridin  is  fed,  met hyl-pyndm   ammonium 
HC      CH 

V 

hydroxide,  OH.CH3.NC5HS,  is  excreted  in  the  urine.'^  This  is  another  case,  besides  those 
of  selenium  and  tellurium,  of  methylation  in  the  body. 

H      H 

C      C 

HC      C      CH 

Chinolin.— The  accompanying  formula       I        II        I       illustrates   the   composition 

HC       C       CH 

N      C 
H 
of  this  body.    Several  of  the  methyl-chinolins  burn  readily  in  the  body.' 

'  Bauraann:  Berichle  da-  deutschen  chemischen  GeselMinfl,  1879,  Bd.  12,  p.  1450. 
-  His:  Archil'  fiir  exper.  Pathologie  und  Plumnakolorjie,  1S87,  Bd.  22,  p.  253. 
^  Cohn  :  Zeitschrift  Jur  physiologisehe  Chemie,  1894,  Bd.  20,  p.  210. 


THE    CHEMISTRY   OF    THE   ANIMAL    BODY.  1013 

Cynurenic  Acid,  (-.jH5N.OH.COOH. — This  is  oxychinolin  carbonic  acid ;  it  is  found 
normally  in  iloir's  urine,  beins  derived  from  proteid  metabolism.  This  form  of  the  chinolin 
prouj)  is  therefore  not  burned  in  the  body. 

Indol,  or  Benzopyrol,  CgH^N. — The  source  of  iiulol  i.s  surely  from 
proteid  putrefaction ;  it  may  also  be  obtained  by  melting  proteid  with  potash. 

H  H 

C  C 

^  \    /\  //\    /\ 

HC         C         CH  HC         C         COH 

I  II  II  I  II  II 

HC         C         CH  HC         C         CH 

% /\/  % /\/ 

C         N  C         N 

H        H  H        H 

Indol.  Indoxyl. 

After  its  absorption  it  receives  an  oxy-  group  just  as  benzol  does,  and  like 
benzol  pairs  with  sulphuric  acid  with  the  loss  of  a  molecule  of  water,  and 
appears  as  ethereal  sulphate  in  the  urine.  In  preparing  indol  from  feces  the 
fecal  odor  clings  to  it.  Pure  indol,  however,  has  no  smell.  An  alcoholic 
solution  of  indol  mixed  with  hydrochloric  acid  colors  fir-wood  cherry-red. 
If  urine  be  mixed  with  an  equal  volume  of  hydrochloric  acid,  chloroform 
added,  and  then  gradually  an  oxidizing  agent  (chloride  of  lime),  any  indoxyl- 
sulphuric  acid  present  will  be  oxidized  to  indigo-blue,  which  gives  a  blue  color 
to  the  chloroform  in  which  it  dissolves. 

Skatoi;  or    /3-Methyl    Indol,    CgHjCHaNH.— The    history   of    skatol, 

H 

C 
^  \    /\ 
HC         C         CCH3 
I  II  II        , 

HC         C         CH 
^  /\/ 
C         N 
H        H 

Skatol. 

is  the  same  as  that  of  indol.  Its  source  is  from  proteid  putrefaction  ;  after  ab- 
sorption it  unites  with  an  oxy-  group,  and  the  skatoxyl  thus  produced  pairs  with 
sulphuric  acid,  and  appears  in  the  urine  as  ethereal  skatoxyl-sulphuric  acid. 

Aromatic  Bodie.s  in  the  Urine. — There  have  been  named  above  as 
appearing  in  normal  human  urine  the  ethereal  sulphates  of  phenol,  p-cresol, 
pyrocatechin,  indoxyl,  skatoxyl,  hydroparacu marie  acid,  and  oxyphenyl-acetic 
acid,  of  which,  however,  the  last  two  appear  likewise  as  their  salts  without 
being  combined  with  sulphuric  acid.^  These,  are  derived  from  proteid  putre- 
factive products  formed  almost  entirely  in  the  large  intestine  (see  p.  988), 
which  are  partially  absorbed  and  partially  pass  into  the  feces.  The  amount 
'  Baiiniann  :  Zeitschrift  fur  pkysiologische  Chemie,  1886,  Bd.  10,  p.  125. 


1014         .LV   AAfl'JRICAN    TEXT-BOOK    OF    PHYSIOLOGY. 

of  etlieroal  sulphate  in  tlie  urine  ^ivcs  an  indication  of  the  amount  of  intes- 
tinal putrciac'tion.  It  does  not  disappear  in  starvation,  mucin  and  nucleo- 
proteitl  of  bile  and  intestinal  juice  furnishing  material.*  If  the  intestinal 
tract  be  treated  so  as  to  make  it  antiseptic,  the  ethereal  sulphates  disa])pear 
from  the  urine.^  Diarrluea  likewise  decreases  their  amount,  obviously  from 
the  short  time  given  for  putrefaction. 

Inosit.— This  is  the  hexatomic  jjhenol  of  hexahydrobenzol,  0,;Hg(OH)g. 
It  was  long  mistaken  for  a  carbohydrate.  It  has  been  found  in  muscle,  liver, 
spleen,  suprarenals,  lungs,  brain,  and  testicles;  likewise  in  plants,  in  unripe 
peas  and  beans.  After  drinking  nnich  water  it  may  be  washed  out  in  the 
urine,  and  perhaps  for  this  reason  is  often  found  in  the  voluminous  urine  of 
the  diabetic.  When  fed  it  is  burned ;  also  by  the  diabetic.  ^  Its  origin  is 
unknown. 

Substances  of  Unknown  Composition. 

Coloring  Matters  in  the  Body. 

Haemoglobin,  C-iJIii.joN.^uFeSjO^^  (Ziiioffsky's  forimila  for  lisemojrlobin  in  horse's 
blood). —  Ibcuioglobin  is  found  in  the  red  blood-corpuscle.  United  with  oxygen  it  forms 
oxyhemoglobin,  which  gives  the  scarlet  color  to  arterial  blood ;  h;«moglobin  itself  is  darker, 
more  bluish,  and  therefore  venous  blood  is  of  a  less  brilliant  red.  Methods  for  i)reparing 
oxyhacmoglobin  crystals  are  numerous,  but  all  depend  on  getting  the  haemoglobin  into  solu- 
tion. If  the  corpuscles  in  cruor  be  washed  with  physiological  salt-solution,  then  treated 
with  distilled  water,  the  HbO  will  be  dissolved  ;  on  shaking  with  a  little  etiier  the  stroma 
will  likewise  dissolve  ;  after  decantation  and  evaporation  of  the  ether,  at  the  room's  tem- 
perature, the  solution  is  cooled  to  — 10°  and  a  one-fi)urth  volume  of  alcohol  at  the  same 
temperature  added ;  after  a  few  days  rhombic  crystals  of  oxyhgemoglobin  may  be  collected, 
redissolved  in  water,  and  reprecipitated  for  purification.  The  crystals  may  be  dried  m 
vacuo  over  sulpliuric  acid.  Once  dry  they  may  be  heated  to  100°  without  decomposition, 
but  in  aqueous  solution  they  are  decomjiosed  at  70°  into  a  globulin  and  hacmatin,  the  latter 
having  a  brown  color.  This  difference  in  color  gives  the  divStinction  between  "rare  "  and 
"well-done  "  roast-beef  Gastric  and  pancreatic  digestion  likewise  convert  oxyhajmoglobin 
into  a  globulin,  which  may  be  absorbed,  and  haematin,  which  passes  into  the  feces.  Hjemo- 
globin  is  without  doubt  formed  in  the  body  from  simple  proteids  by  a  synthetic  process. 
(For  further  information  see  pp.  973  a!id  101,'"),  and  likewise  under  the  section  on  Blood.) 
CO-Hsemoglobin  (see  p.  960). 
NO-Hsemoglobin  (see  p.  956). 

Methaemoglobin.— This  has  the  same  composition  as  oxyhaemoglobin.  It  is  found 
in  blood-stains,  and  may  be  considered  as  oxyhfemoglobin  which  has  undergone  a  chemical 
change  whereby  its  oxygen  is  more  firmly  bound  in  the  molecule. 

Haematin,  C.TiH:,.,N,04Fe.— This  is  a  cleavage-product  of  haemoglobin  in  the  presence 
of  oxygen.  (See  above,  under  Haemoglobin).  It  is  not  itself  a  constituent  of  the  body. 
It  is  insoluble  in  dilute  acids,  alcohol,  ether,  or  chloroform,  but  is  soKible  in  alkalies  or  in 
acidified  alcohol  or  ether,  showing  characteristic  absorption-l)ands.  If  a  little  dry  blood 
be  placed  on  a  microscope  slide  with  NaCl  and  moistened  with  glacial  acetic  acid,  and 
warmed,  characteristic  brown  microscopic  crystals  ofhcpmin,  C;«H3oN4Fe03.H('l,  crystallize 
out.  If  these  crystals  and  the  spectroscopic  test  be  obtained,  one  can  be  absolutely  posi- 
tive of  the  presence  of  blood. 

Haemochromogen,  (>„n;,fiN4Fe05.— If  reduced  haemoglobin  be  heated  in  sealed  tubes 
with  dilute  acids  or  alkali  in  absence  of  oxygen,  a  i)uri)le-red  comjiound  is  i)roduced  called 
1  Von  Noorden  :  Patholocjie  des  Stoffwechsela,  1893,  p.  163.  '■'  Baumann,  Op.  cit.,  p.  129. 


Tifi':  ciiEMisTin'  or  tiik  animal  body.  1015 

hjeniochroni()i,u-ii,  which  is  a  crystallizuldo  cleavage-product  of  hncmoglobin.  According 
to  lloppo  Soyk'r  the  ()xy.ii:cMi  inox.vha'inoirlohin  is  bound  to  the  hiuniochronioiren  irroup. 
HiXMnuchromogou  treated  with  a  .stroiii;  dehydratinjr  agent  is  converted,  with  ehmination 
of  iron,  into  hcrmafoporphi/rin,  C^iJlmN^Oo,  an  isomer  of  biHniltin.  ILx'uiatoporijhyrin 
is  said  to  occur  in  normal  urine/  Iljcmatoporphyrin  treated  with  nascent  hydrogen  is 
converted  into  a  body  believed  to  be  identical  with  hydro-  or  urobilirubin.  Analogous  to 
this  is  the  work  of  the  liver  in  the  body,  manufacturing  the  biliary  coloring  matter  from 
haMnoglobiii,  and  retaining  the  separated  iron  for  tlie  synthesis  of  fresh  hemoglobin 
(see  p.  073).  I/iniKifoidin,  found  in  old  blood-stains,  is  believed  to  be  identical  with 
bilirubin. 

The  Bile-pigments.— The  ordinary  coloring  matter  of  yellow  human  bile  is  hilirubin, 
C3.,HsbN406.  The  next  higher  oxidation-product  is  the  green  biUcerdin,  CajHssN^Ob, 
which  is  the  usual  dominant  color  in  the  bile  of  herbivora.  In  gall-stones  have  been  found 
the  following  coloring  matters,  to  which  have  been  ascribed  the  accompanying  formulae  : 

Bilirubin  (red),  C.^H^eNA ; 

Biliverdin  (green),  QiiHsBN^Og; 

Bilifuscin  (brown), .  C3.2H4oN408; 

Biliprasin  (green),  Q^HuN^Oia ; 
Bilihumin  (brown),  ? 

Bilicyanin  (blue),  ? 

Choletelin  (black),  C32H3BN4O12. 

If  nitric  acid  containing  a  little  nitrous  acid  be  added  to  a  solution  of  bilirubin,  a  play  of 
colors  is  observed  at  the  juncture  of  the  two  fluids,  undoubtedly  depending  upon  various 
stages  of  oxidation.  Above  is  a  ring  of  green  (biliverdin),  then  blue  and  violet  (bilicya- 
nin), red,  yellowish-brown  (choletelin).  Cholotelin  is  the  highest  oxidation-product.  The 
above  is  known  as  Gmcliiis  tesf.'^ 

If  bilirubin  or  biliverdin  is  subjected  to  the  action  either  of  nascent  hydrogen  or 
of  putrefaction  it  is  reduced  to  hydrobilirubin,  C32H44N4O7.  This  substance  is  therefore 
formed  in  the  intestinal  tract,  is  in  part  absorbed,  and  appears  in  the  urine,  where  it  is 
called  urobilin,  though  the  two  are  identical.  Urobilin  gives  a  yellowish  coloration  to  the 
urine.  Injection  into  the  blood-vessels  of  distilled  water,  ether,  chloroform,  the  biliary 
salts,  or  arsenuretted  hydrogen,  produces  a  solution  of  the  red  blood-corpuscles  and  conver- 
sion of  haemoglobin  into  biliary  coloring  matters  which  are  thrown  out  in  the  urine  (see 
p.  988).     Bilirubin,  biliverdin,  and  bihcyanin  give  characteristic  spectra. 

Melanins. — Under  this  name  are  classed  the  pigments  of  the  skin,  of  the  retina,  and 
of  the  iris.  They  contain  iron,  and  their  source  has  been  attributed  to  haemoglobin.  In 
n>elanosis  and  kindred  diseases  they  are  deposited  in  black  granules.  There  are  melanins 
of  different  composition.  In  a  case  of  melanotic  sarcoma  the  haemoglobin  was  one  quar- 
ter, the  number  of  blood-corpuscles  one-half,  the  normal,  indicating  perhaps  the  source 
of  melanin.' 

Tryptophan. — This  is  said  to  be  a  cleavage-product  of  hemipeptone  in  tryptic  diges- 
tion ;  *  it  gives  a  red  color  with  chlorine  and  a  violet  color  with  bromine,  due  to  halogen- 
addition  compounds. 

Lipochromes. — These  include  Infein,  the  yellow  pigment  of  the  corpus  luteum,  of 
blood-plasma,  butter,  egg-yolk,  and  of  fat ;  likewise  viswd  jntrple  of  the  retina,  which  is 
bleached  by  light.  Solutions  of  the  pure  visual  purple  from  rabbits  or  dogs  become  clear 
as  water  on  exposure  to  light.* 

1  Garrod  :  Journal  of  Physioloyy,  1894,  vol.  17,  p.  348. 

"^  For  a  delicate  modification  of  tliis  test  see  Jolles  :  Zeitschrift  fur  physioloffische  Chemie,  1895> 
Bd.  20,  p.  461. 

3  Brandl  und  Pfeiffer  :  Zeitschrift  fur  Biologic,  1890,  Bd.  26,  p.  348. 

*  Stadelmann  :  Ibid.,  1890,  Bd.  26,  p.  491.  *  Kubne  :  Ibid.,  1895,  Bd.  32,  p.  26. 


1016         ^l^V   AMERICAN    TKXT-liOOK    OF   PHYSIOLOGY. 

Cholesterin. 

Cholesterin,  CafiH4:,0n. — Tliis  is  I'oiind  in  all  animal  and  vegetable  cells  and  in  the 
milk.'  It  is  es|)ecially  present  in  nervous  tissue,  in  blood-cdriiuseles.  and  in  the  bile.  It  may 
be  prepared  by  dissolvinjr  ^'all-stones  in  alcohol,  from  which  solution  the  cholesterin  crys- 
tallizes on  coolinsr  in  characteristic  plates.  It  is  insoluble  in  water  or  acids,  but  soluble 
in  the  biliary  salts,  alcohol,  and  ether.  It  is  probably  excreted  unabsorbed  in  the  feces, 
("holesterin  feels  like  a  fat  to  the  touch,  but  is  in  reality  a  monatomic  alcohol.  With  con- 
centrated sulphuric  acid  it  yields  a  hydrocarbon,  cholesferilin ,  C2eH4„  coloring  the  sul- 
jdiuric  acid  red  (Salkowski's  reaction).  Iso-cholesterin.  an  isomere,  is  found  combined  as 
an  ester  with  fatty  acid  in  wool-fat  or  lanolin.  The  physiological  importance  of  cholesterin 
is  unknown. 

The  Proteids. 

Consideration  of  the  proteids  from  a  purely  chemical  standpoint  is  impos- 
sible, for  their  composition  is  unknown.  There  exist  only  the  indices  of  cora- 
po.sition  furnished  bv  tlie  jn'oducts  of  cleavage  and  di.^integration.  Bodies  at 
present  classed  as  individuals  may  .sometimes  be  sho\vn  to  be  identical,  \vith 
characterizing  impurities.  It  remains  for  the  chemist  to  do  for  the  proteid 
o-rouji  what  Emil  Fischer  with  phenyl-hydrazin  has  accomplished  for  the 
sugars. 

As  a  characteristic  proteid,  egg-albumin  may  be  mentioned.  Proteid  forms 
(after  water)  the  largest  part  of  the  organized  cell,  and  i.-j  found  in  all  the 
fluids  of  the  body  except  in  urine,  sweat,  and  bile.  Proteid  contains  carbon, 
hydrogen,  nitrogen,  oxygen,  sulphur,  sometimes  phosphorus  and  iron. 

General  Reactions. — A  neutral  solution  of  proteid  (with  the  exception  of 
the  jieptones  and  proteoses)  is  partially  precipitated  on  boiling,  and  is  quite 
completely  precipitated  on  careful  addition  of  an  acid  (acetic)  to  the  boiling 
solution.  Proteids  are  precipitated,  in  the  cold  by  nitric  and  the  other  com- 
mon mineral  acids,  by  metaphosphoric  but  not  by  orthophosphoric  acid. 
Metallic  salts,  such  as  lead  acetate,  copper  sulphate,  and  mercuric  chloride, 
precipitate  proteid ;  as  do  ferro-  and  ferricyanide  of  potassium  in  acetic-acid 
solution.  Further,  saturation  of  acid  solutions  of  proteid  with  neutral  salts 
(XaCl,  Na2S04,  (NHJ2SOJ  precipitates  them,  as  does  likewise  alcohol  in 
neutral  or  acid  solutions.  Proteid  is  also  precipitated  by  tannic  acid  in  acetic- 
acid  solutions,  by  phospho-tungstic  and  phospho-molybdic  acids  in  the  presence 
of  free  mineral  acids,  by  picric  acid  in  solutions  acidified  by  organic  acids.^ 

Of  the  color-reactions  the  action  of  ^Slillon's  reagent  has  been  described 
(see  p.  992).  Soluble  proteids  give  the  biuret  test  (see  p.  1011).  With  concen- 
trated sulphuric  acid  and  a  little  cane-sugar  a  pink  color  is  given  when  proteid 
is  present  (.see  p.  988).  Proteid  heated  with  moderately  concentratcxl  nitric 
acid  gives  yellow  flakes,  changing  to  orange-yellow  on  addition  of  alkalies 
(xaiitho-proteid  reaction).  Proteid  in  a  mixture  of  one  part  of  concentrated 
suli)huric  acid  and  two  parts  of  glacial  acetic  acid  gives  a  rwldish-vioiet  color 
(Adamkiewicz),  a  reaction  accelerated  by  heating.     Finally,  proteid  dissolves 

'  Schmidt-Muhlheim :  Pfluger's  Archiv,  1888,  Bd.  30,  p.  384. 

■^  The  above  list  is  given  bv  Hammai-sten,  Physiological  Chemistry,  translated  by  Mandel, 
p.  18. 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  1017 

after  heating  with  concentrated  hydrochloric  acid,  forming  a  violet-colored 
solution  (Licborniann). 

The  following,  taken  in  part  from  Chittenden/  is  submitted  as  a  general 
classification  of  the  proteids  : 

SiMPi.E  Proteids. 
r  Serum-albumin ; 

I   Egg-albumin ; 

Albumins       ^   t     *      n 

Lacto-albunnn; 


GhbnJin.s 


Myo-albumin. 

Scrum-globulin ; 

Fibrinogen  ; 

Myosin  ; 

Myo-globulin ; 

Paramyosinogen ; 

^  Cell-globulin. 

. ,,       .     ,      f  Acid-albumin ; 
Albuminates  {    , ,,    ,.    „       . 
(.  Alkali-albumm. 

Proteoses  and  Peptones. 

Coagulated  Proteids  <    _  ,       '        ,       ,  . , 

I  Other  coagulated  proteids. 

Combined  Proteids. 

r  Haemoglobin ; 

Histo-haematins ; 
Chromo-proteids  ^  Chlorocruorin  ; 

Hsemerythrin ; 

^  Hsemocyanin. 

x^,  .  •  7       r  Mucins 

{jrlyGo-proteids 


Mucoids. 

{Casein ; 
Pyin  ; 
i.yui:ito-proieta>i  <.  Vitellin. 

'^  2.  Those  yielding  true  nuclein  <   ^  „        ,  .       ' 
^  t  Cell-nuciem. 

Phospho-glyco-proieids.     Hel  i  co-pro  teid. 

Albuminoids. 
Collagen  (gelatin). 
Elastin. 
Keratin  and  Neurokeratin.    ^ 

Albumins.— Bodies  of  this  group  are  soluble  in  water  and  precipitated  by  boiling,  or 
on  standing  with  alcohol.  Serum-albumin  is  the  principal  proteid  constituent  of  blood- 
plasma,  while  lacto-albumin  and  myo-albumin  are  similar  bodies  found  respectively  in 
milk  and  muscle. 

*  "  Digestive  Proteolysis,"  Oartwright  Lectures,  1895,  p.  30 


1018         ^.Y  AMERICAN    TEXT-BOOK   OF   PHYSIOLOGY. 

Globulins. — These  are  insoluble  in  water,  but  soluble  in  dilute  salt-solutions.  They 
are  coagulated  on  heating.  If  blood-serum  be  dialyzed  with  distilled  water  to  remove  the 
salts  present,  seruui-globulin  formerly  held  in  solution  separates  in  flakes.  Fibrinogen  and 
serum-globulin  are  in  blood-plasma  and  the  lymph.  Myosin  is  the  principal  constituent 
of  dead  muscles ;  in  the  living  muscle  myosin  is  said  to  be  present  in  the  form  of  myosin- 
ogen.  jMyoglobulin  in  muscle  is  akin  to  serum-globulin  in  plasma.  I'aramyosinogen  in 
muscle  is  characterized  by  the  low  temperature  at  which  it  coagulates  (+47°).  Cell- 
globulin  is  also  found  in  the  animal  cell. 

The  globulins  of  vegetable  cells  are  interesting  as  having  been  obtained  in  well-deflned 
crystalline  form  and  in  great  purity  of  composition.^  These  are  not  generally  coagulable 
by  heat,  and  indeed  vegetable  proteids  show  many  points  of  divergence  from  those  of  the 
animal. 

Albuminates. — If  any  of  the  above  native  animal  proteids  or  any  coagulated  proteid 
be  treated  with  an  alkaline  solution,  alkali  albuminate  is  formed.  In  this  way  the  alkali 
of  the  intestine  acts  upon  proteid.  If  hydrochloric  acid  acts  on  proteid,  there  is  a  gelatin- 
ization  and  slow  conversion  into  acid  albuminate,  a  process  accelerated  by  the  presence 
of  pepsin.  This  takes  place  in  the  stomach.  Both  alkali  and  acid  albuminates  are  in- 
soluble in  water,  but  both  are  soluble  in  dilute  acid  or  alkali,  without  loss  of  individual 
identity. 

Proteoses  and  Peptones. — These  are  bodies  obtained  from  the  digestion  of  proteids, 
through  a  process  of  hydrolysis.  They  are  non-coagulable  by  heat.  If  a  mixture  of  pro- 
teoses and  peptones  be  saturated  with  ammonium  sulphate  the  proteoses  are  said  to  be 
precipitated,  while  true  peptone  remains  in  solution.  The  chemical  identity  of  this  true 
peptone  is  still,  however,  to  be  established.  In  gastric  digestion  are  said  to  exist  four 
varieties  of  proteoses:  (1)  Dysproteose,  insoluble  in  water  and  dilute  NaCl  solutions,  (2) 
hetero-proteose,  insoluble  in  water  and  soluble  in  NaCl  solution,  (3)  proto-proteose,  soluble 
in  water  and  in  NaCl  solution,  (4)  deutero-proteose,  which  is  also  soluble  in  water  and  in 
NaCl  solution,  but  is  distinguished  by  the  fact  that  w'hile  the  first-named  three  are  pre- 
cipitated by  saturating  the  neutral  solution  with  NaCl,  deutero-proteose  is  only  partly 
precipitated,  the  rest  coming  down  on  addition  of  an  acid.  Proteoses  are  converted  into 
amphopeptones,  a  mixture  of  hemi-  and  antipeptone.  According  to  Kiihne  proteid  con- 
sists of  a  hemi-  and  an  anti-  group,  which  separate  into  distinct  hemi-  and  anti-  bodies  in 
proteolysis.  Of  the  final  products,  hemi-  and  antipeptone,  only  the  former  jdelds  leucin 
and  tjTosin  in  tryptic  proteolysis.  This  is  the  only  radical  difference  between  the  two 
peptones,  hence  hemipeptone  has  never  been  isolated. 

Coagulated  Proteids. —These  are  insoluble  in  water,  salt-solutions,  alcohol,  dilute 
acids  and  alkalies,  but  soluble  in  strong  acids  and  alkalies,  pepsin-hydrochloric  acid, 
and  alkaline  solutions  of  trypsin.  The  chemical  or  physical  change  which  is  efiected  in 
coagulation  of  proteid  is  imknown. 

Combined  Proteids. — These  consist  of  proteid  united  to  non-proteid  bodies  such  as 
haemochromogen.  carbohydrates,  and  nucleic  acid. 

Chromo-proteids. — These  are  compounds  of  proteid  with  an  iron-  or  copper-contain- 
ing pigment,  like  hoemoglobin,  which  has  already  been  described.  IIistoli(V)nat!ns  are 
iron-containing  pigments  found  especially  in  muscle.  That  which  is  found  in  muscle  is 
called  myohfematin,  and  resembles  h.nemochromogen  somewhat  in  its  spectroscopic  appear- 
ance, and  is  believed  to  be  present  in  two  forms  corresponding  to  htemoglobin  and  oxyhaemo- 
globin.  It  has  been  regarded  as  an  oxygen-carrier  to  the  tissues.  Among  the  inverte- 
brates the  blood  often  contains  only  white  corpuscles  with  sometimes  a  colored  plasma. 
Thus  the  blood-serum  of  the  common  earth-worm  contains  dissolved  haemoglobin,  that 
of  some  other  invertebrates  a  green  respiratory  pigment,  chlorocruorin,  whose  charac- 
terizing component  seems  similar  to  haematin  ;  hcemo-ythnn  occurs  in  the  pinkish  corpus- 

'  Osborne:  Journal  of  American  Chemical  Society,  1894,  vol.  xvi.,  Xos.  9,  10;  and  other  arti- 
cles in  the  same  journal  by  the  same  author. 


THE    CHEMISTRY   OF    THE   ANUTAL    BODY.  1019 

cles  of  SipH)icult(s,  wliile  the  bloutl  of  crabs,  snails,  and  other  animals  (mollusks  and 
arthropods)  is  colored  blue  by  a  pigment,  hcenwcyanin,  which  contains  copper  instead  of 
iron. 

Glyco-proteids. — Those  consist  of  protcids  conibiiic(l  with  a  carbohydrate.  They  are 
insoliililc  ill  water,  but  soluble  in  very  weak  alkalies.  On  boiling  with  dilute  mineral  acids 
they  yield  a  reducing  substance. 

Mucins  are  found  in  mucous  glands,  goblet  cells,  in  the  cement  substance  of  epithelium 
and  in  the  connective  tissues.  Of  the  nearly  related  mucoids  maybe  named  colloid.,  a  sub- 
stance appearing  like  a  gelatinous  glue  in  certain  tumors;  pacndo-mucoicl.,  the  slimy  body 
which  gives  its  chai-actcr  to  the  liquid  in  ovarian  cysts ;  and  chondro-mucoid,  found  as  a 
constituent  of  cartilage.  On  boiling  chondro-mucoid  with  dilute  sulphuric  acid  it  yields 
acid-albuminate,  a  peptone  substance,  and  chondroitic  acid.  The  last  is  a  nitrogenous 
ethereal  sulphuric  acid,  yielding  a  carboh3'drate  on  decomposition,  and  found  preformed  in 
every  cartilage'  and  in  the  amyloid  livci'.'^     It  is,  of  course,  not  a  proteid. 

Nucleo-proteids,  or  Nucleo-albumins.'— These  are  compounds  of  proteid  with 
nuclein,  which  latter  yields  phosphoric  acid  on  decomposition.  If  nucleo-proteid,  which 
is  found  in  every  cell,  be  digested  with  pepsin-hydrochloric  acid,  there  remains  a  residue 
of  insoluble  nuclein,  likewise  insoluble  in  water  but  soluble  in  alkalies.  If  this  nuclein 
yields  xanthin  bases  on  further  decomposition  it  is  called  true  nuclein,  if  it  fails  to  yield 
these  bases  it  is  called  paranuclein.*  Nucleo-proteids  yielding  proteid  and  paranuclein  on 
decomposition  include  the  casein  of  milk,  pyin  of  the  pleural  cavity,  vitellin  of  the  Qgii., 
Bunge's*  iron-containing  h?ematogen  of  the  eg§,  as  well  as  nucleo-proteids  found  in  all 
protoplasm.  They  all  contain  iron.  Paranuclein  is  probably  absorbable  (see  p.  958). 
It  is  considered  by  Liebermann  to  be  a  combination  of  proteid  and  metaphosphoric  acid 
(see  p.  958). 

A  second  group  of  nucleo-proteids  yields  true  nuclein  on  decomposition.  This  group 
includes  the  various  nucleo-proteids  which  are  constituents  of  different  cell-nuclei.  The 
nuclein  here  obtained  yields  on  decomposition  nucleic  acid,  from  which  xanthin  bases  are 
always  to  be  derived.  These  xanthin  bases  vary  in  proportion  and  kind  in  the  different 
nucleic  acids.  Nucleic  acid  of  yeast  nuclein  yields  guanin  and  adenin,  that  of  a  bull's 
testicle  adenin,  hypoxanthin,  and  xanthin,  that  of  the  thymus  adenin  alone.  Kossel® 
calls  this  latter  "adenylic  acid,"  and  speaks  likewise  of  "guanj'lic,"  "xanthylic,"'  etc., 
acids,  as  provisional  names  for  separate  nucleic  acids.  Each  one  of  this  family  of  acids  is 
capable  of  combining  with  any  soluble  proteid  to  form  nuclein,  hence  it  is  readily  seen 
that  nucleins  may  exist  in  great  variety.  Another  constituent  of  nucleic  acid  Kossel  finds 
to  be  thymin  (a  body  derived  from  paranucleic  acid,  which  latter,  according  to  Kossel,  is  a 
component  of  paranuclein).  Some  nucleic  acids,  such  as  those  derived  from  j'east,  pan- 
creas, and  the  lactic  glands,  yield  a  reducing  carbohydrate,  while  others  (calf's  thymus) 
show  the  presence  of  the  carbohydrate  group  only  in  the  production  of  levulic  acid  after 
very  thorough  decomposition,  and  still  others  (fish-sperm)  fail  to  indicate  any  carbohydrate 
radical  as  being  present.  A  clearer  idea  of  these  relations  is  afforded  by  the  following 
schematic  view  of  the  decomposition  of  the  nucleohiston,  the  constituent  of  blood-plates 
and  of  the  nuclei  of  leucocytes.' 

^  Morner  :  Zeitschrift  fiir  physiologische  Chemie,  1895,  Bd.  20,  p.  357. 

^  Oddi:  Archil' fiir  exper.  Pathologie  und  Phnrmakologie,  1894,  Bd.  33,  p.  376. 

^  These  two  terms  are  used  here  as  synonymous,  though  Hammarsten  would  confine  the 
term  nucleo-albumin  to  those  proteids  which  yield  paranuclein.  It  is  difficult  to  give  a  definite 
classification  of  these  bodies,  as  the  whole  subject  at  present  is  in  a  transition  stage. 

*  Kossel :  Yerhandlungen  der  Berliner  physiologischen  Gesellschaft,  Archivjur  Physiologie, 
1894,  p.  194. 

^  Physiologische  Chemie,  3d  ed.,  1894  p.  92.  *  Loc.  cit. 

'  Lilienfeld  :  Zeitschrift  fiir  physiologische  Chemie,  1895,  Bd.  20,  p.  106. 


1020         .l.V  AMERICAN    TEXT-BOOK    OF   PHYSIOLOOY. 

Nucleoht'ston,  soluble  in  H.^0, 
decomposed  by  HCl  or  BalOH)^  into 


Jfiston,  a  [)rolci(l.  LeuconucUin,  an  acid  ; 

decomposed  by  strong  alkali  into 


Proteid.  Adenylic  acid  (nucleic  acid),  which  on  lieating 

with  mineral  acids  yields  adenin,  thymin, 
levulic  acid,  and  phosphoric  acid. 

( For  the  respective  offices  of  histon  and  leuconuclein  in  the  coagulation  of  the  blood, 
see  section  on  the  Blood. ) 

In  the  sperm  of  salmon  is  found  only  i'ree  nucleic  acid  uncombined  with  proteid. 
According  to  Kossel  other  nuclei  may  at  times  contain  free  nucleic  acids. 

Phospho-glyco-proteids. — This  class  is  represented  by  Hammarsten's  hch'co-proteid, 
which  yields  paranucleiu,  and,  unlike  other  nucleo-proteids  of  the  paranuclein  class,  it 
yields  a  reducing  carbohydrate  on  boiling  with  acids. 

The  Albuminoids. — These  are  bodies  derived  from  true  i)roteid  in  the  body,  but  not 
themselves  convertible  into  proteid.  They  are  resistant  to  the  ordinary  jnoteid  solvents, 
and  as  a  rule  exist  in  the  solid  state  when  in  the  body. 

Collagen. — This  is  the  chief  constituent  of  the  fibres  of  connective  tissue,  of  the 
organic  matter  of  bone  (ossein)  and  is  likewise  one  of  the  constituents  of  cartilage.  Col- 
lagen is  insolul)le  in  water,  dilute  acids  and  alkalies.  On  boiling  with  water  it  forms 
gelatin  through  hydration,  which  is  soluble  in  hot  water,  but  gelatinizes  on  cooling  (as  in 
bouillon).  Dry  gelatin  swells  when  brought  into  cold  water.  By  continuous  boiling  or  by 
gastric  or  tryptic  digestion  further  hydration  takes  place  with  the  formation  of  soluble 
gelatin  peptone.  Gelatin  fed  will  not  take  the  place  of  proteid,  but,  like  sugar,  only  more 
effectively,  it  may  prevent  proteid  waste  by  being  burned  in  its  stead.  ^  Gelatin  yields  leucin 
and  glycocoll  on  decomposition,  but  no  tyrosin.  It  therefore  gives  the  biuret  reaction,  but 
none  with  Millon's  reagent.  It  contains  but  little  sulphur.  It  yields  about  the  same 
ami<l()-  acids  as  ordinary  proteid. 

Elastin. — This  is  very  insoluble  in  almost  all  reagents  and  in  boiling  water.  On 
decomposition  it  yields  leucin,  tyrosin,  glycocoll,  and  lysatin.  It  is  slowly  hydrated  by 
boiling  with  dilute  acids,  and  by  pepsin  hydrochloric  acid.  It  contains  very  little  sulphur, 
and  gives  IMillon's  teat.  It  is  found  in  various  connective  tissues,  and  especially  in  the 
cervical  ligament. 

Keratin  and  Neuro-keratin. — These  arc  insoluble  in  water,  dilute  acids  and  alkalies ; 
insoluble  in  i)epsin  hydrochloric  acid,  and  alkaline  solutions  of  trypsin.  Keratin  is  found 
in  all  horny  structures,  in  epidermis,  hair,  wool,  nails,  hoofs,  horn,  feathers,  tortoise-shell, 
whalebone,  etc.  Neuro-keratin  has  been  discovered  in  the  brain,  and  in  the  medullary 
sheath  of  nerve-fibres.''  On  decomposition  with  hydrochloric  acid  keratin  yields  all  the 
l)roducts  given  Ijy  simple  proteids.  It  contains  more  sulphur  than  simple  jiroteid  and 
yields  more  tyrosin.  DrechseP  believes  that  it  is  transfonncd  from  simi)le  proteid  by  the 
substitution  of  sulphur  for  some  of  the  oxygen  and  of  tyrosin  for  leucin  or  other  amido- 
acid.  Part  of  the  sulphur  is  loosely  combined,  and  a  lead  comb  turns  hair  black,  due  to 
the  formation  of  lead  sulphide.  There  are  different  keratins,  and  their  sulphur  content 
varies  greatly. 

General  Remarks  on  the  Proteids. — It  has  been  impo.-^sible  within 
the  limits  set  to  more  than  glance  at  tlie  proteid  bodies.  Many  facts  concern- 
ing the  behavior  of  proteids  have  been   mentioned  throughout  the  text,  and 

'  Voit:  Zeitschrift  fur  Bioloc/ie,  1872,  Bd.  8,  p.  297. 

■^  Kiihne  and  Chittenden  :  Zeitschrift  fiiv  Biologie,  1890,  Kd.  2(3,  p.  291. 

'  Ladenburg's  Handwbrlerbuch  der  Chemie,  1885,  Bd.  3,  p.  571. 


THE    CHEMISTRY    OF    THE   ANIMAL    BODY.  1021 

cannot  be  classified  here.  A  list  of  the  priiicipal  products  of  the  digestion 
and  putrefaction  of  proteid  may  not  b(;  out  of  place.  It  iuchidcs  albunioses, 
peptones,  leucin,  tyrosin,  lysin  and  lysatinin,  aspartic  acid,  glutamic  acid,  amido- 
valerianic  acid,  volatile  fatty  acids ;  ph('nyl-pro[)ionic,  phenyl-acetic,  ^j-oxy- 
phenyl-acetic,  and  p-hydrocumaric  acids ;  /j-cresol,  phenol,  indol,  skatol ;  and 
the  gases,  ammonia,  carbonic  oxide,  sulphuretted  hydrogen,  nictiiyl  mercaptan, 
hydrogen,  and  methane 

The  size  of  the  proteid  molecule  must  be  very  great,  and  one  computation 
shows  the  following  figures:^ 

Egg-albumin.  Proteid  from  heemoglobin  (dog). 

It  is  well,  perhaps,  finally,  to  speak  of  experiments  which,  however  incom- 
plete, at  least  throw  some  light  on  the  possibilities  of  the  problem  of  the  syn- 
thesis of  proteid.  Lilienfeld  -  through  the  condensation  of  the  ethyl-ester  of 
glycocoU  has  obtained  a  body  insoluble  in  water,  but  swelling  in  it,  forming  a 
gelatinous  mass.  The  substance  gives  the  biuret  reaction,  is  insoluble  in 
alcohol  and  dilute  hydrochloric  acid,  but  dissolves  in  pepsin-hydrochloric 
acid.  These  reactions  show  its  kinship  to  gelatin.  Lilienfeld  likewise  de- 
scribes a  synthetically  formed  peptone  and  a  coagulable  proteid,^  the  peptone 
formed  principally  through  condensation  of  the  above-described  product  with 
the  ethyl-esters  of  the  amido-  bodies,  leucin  and  tyrosin,  the  proteid  from  the 
same  with  addition  of  formic  aldehyde.  Griraaux  likewise  has  produced, 
with  other  reagents,  colloids  which  resemble  proteids.  Probably  none  of 
these  substances  are  native  proteids,  but  they  furnish  indications  of  lines  of 
attack  for  the  future  mastery  which  in  time  is  sure. 

^  Bunge :  Physiologische  Cheniie,  3d  ed.,  1893,  p.  56. 

'^  Verhandlungen  der  Berliner  physiologischen  Gesellschaft,  Archiv  fiir  Phydologie,  1894, 
p.  383. 

^  Ibid.,  p.  555.  ^ 


INDEX. 


Aberration.  760,  761 
Absorption,  250-259 

bile  ill,  physiological  importance  of,  265,  266 

by  diti'iisiou  and  osmosis,  250 

in  the  large  intestine,  2o4 

in  the  small  intestine,  253 

in  the  stomach,  252 

of  fats,  257 

of  proteids,  255 

of  sugars,  257 

of  water  and  salts,  258 

phenomena  of,  27 

spectra.    See  Spectrum. 
Accommodation.  See  Eye. 
Acetone,  982 
Acetonitril,  985 
Achroodextrin,  223,  1008 
Acid,  acetic,  980 

aceto-acetic,  980 

acetyl-acetic,  980 

amido-acetic,  981 

amido-ethyl  sulphonic,  986 

amido-hydrocumaric,  1011 

amido-succinic,  1000 
monamide  of,  1000 

«-amido-a-thiopropionic,  990 

a-lactic,  988 

a-€-diamido-caproic,  994 

aspartic,  1000 

p-oxybutyric,  991 

benzoic,  1011 

butyric,  normal,  245,  982 

capric,  984 

caproic,  983 

caprylic,  984 

carbamic,  991 

carbolic,  1010 

carbonic,  988 
amido-derivatives  of,  991 

choleic,  987 

cholic,  987 

cynurenic,  1013 

f?-glucuronic,  1009 

diamido-acetic,  994 

diamido-valeric,  994 

dithio-diamido-ethidene  lactic,  990 

fellic,  987 

formic,  978 

glutamic,  1000 

glycerin  phosphoric,  1001 

glycurtmic,  1009 

hippuric,  1.54.  279,  1011 

hydriodic,  9.53 

hydrobromic,  953 

hydrochloric,  952 

hydrocyanic,  985 

hydrofluoric,  954 

iso-butyl  amido-acetic,  983 

iso-butyric,  983 

iso-pentoic,  983 

iso-valerianic,  983 

lactic,  ethidene,  988 
of  gastric  juice,  226,  227 
production  of,  234 


Acid,  lactic,  sarco-  or  para-,  989 
source  of,  148 

levulic,  982 

malic,  1000 

metaphosphoric,  958 

metasilicic,  963 

methyl  amido-acetic,  982 
guanidin  acetic,  993 

oleic,  1002 

orthophosphoric,  958 
detection  of,  959 

oxalic,  999 

oxy-formic,  988 

oxy-succinic,  1000 

palmitic,  984 

phenaceturic,  1011 

phenyl-acetic,  1011 

jj-hydrocumaric,  1011 

^-oxyphenyl-acetic,  1011 

jj-oxyphenyl-amido-propionic,  1011 

propionic,  982 
I        /3-acetyl,  982 

stearic,  984 

succinic,  1000 

sulphuric,  950 

sulphurous,  950 

taurocholic,  263 

thiolactic,  990 

uric,  277,  278.  997 
dimethyl,  998 
murexid  test  for,  998 
preparation  and  properties,  997 

urochloralic,  980 
Acids,  action  of,  in  promoting  pancreatic  secre- 
tion,  177 

amido,  in  general.  981 

biliary,  Xeukomm's  test,  988 
Pettenkofer's  test,  988 

containing  more  than  five  carbon  atoms,  983 

dibasic,  diatomic,  999 

fatty,  976 
diamido-,  994 

lactic,  988 

mercapturic.  990 

monobasic.  970 

oxy-,  fatty,  988 

oxy-propionic.  988 

polysilicic.  963 

silicic,  963 

uric,  997.  998 
Acini.  1.53 
Adenin,  995 
Adipocere.  1002 

Adrenal  bodies,  internal  secretions  of,  210 
Adult,  body-temperature  of  female,  577 
male,  variations  in,  577 

heat-production  in  the,  estimates  of,  589 
After-birth,  the.  919 
Agamogenesis.  878 

Age,  changes  in  the  nervous  system  dependent 
upon.  715 

increase  in  brain-weight  with.  724 

intluence  of,  on  heat-dissipation,  .592 
on  heat-production,  590 

1023 


1024 


INDEX. 


Age,  iiifluenco  of.  on  tlie  respiratory  rate,  533 
on  till'  resjiiratory  tnu-t,  olfi 
old,  atrophy  of  I  he  hrain  in,  7~0,  726 
decrease  in  hniin-weijiht  in,  742 
metabolism  in  the  eerebellum  in,  743 
in  the  eneephalon  in,  743 
in  the  nerve-cells  in,  742 
recovery  of  vision  in,  7()0 
the  period  of,  t»2>s 
Air,  amount  of,  in  adult  human  lungs,  517 
dry  and   moist,     exposure     to,    physiological 

effect  of,  .'".78,  .'■>i)3,  59.-) 
expired,  ))roj)ortions  of  O  and  COa  in,  518 
quantity  of  N  iu,  518 

of  watery  vapor  given  oft'  by,  518 
temperature  of,  518 
volume  of.  51!) 
inspired   and   alveolar,  pressure  of  gases  in, 
.521 
constituents  of,  518 

eflFect  of,  on  the  respiratory  quotient,  .547 
efl'ects  of  alterations  of.  on  the  absorption 

and  elimination  of  gases,  543 
influence   of   alteration    iu    composition  of, 
upon  the  respiratory  rate,  .534 
proportions  of  O,  CO2,  and  N  iu  atmospheric, 

521,  523 
rarefied  and  compressed,  respiration  of,  effects 

of,  on  the  circulation,  559 
respired,  quantity  of,  .534,  .536 
Air-capacity,  alveolar,  of  the  lungs,  535 
of  the  trachea  aud  bronchi,  535 
vital,  .535,  .536 
Air-passages,  obstruction  of  the,  effects  of,  on 

the  circulation,  555) 
Air-vitiatiou  of  inhabited  rooius,  547 
Air-volumes,  respiratory,  Hutchinson's  classifi- 
cation, 534,  535 
— complemental  air,  535 
— residual,  535 
— stationary  air,  535 
— supplemental  or  reserve  air,  535 
Albumin,  acid-,  230 

serum-,  349 
Albuminates,  1018 
Albuminoids,  215,  1020 
action  of  gastric  .juice  on  the,  235 

of  trypsin  on  the,  243 
chemistry  of  the,  215 
nutritive  value  of,  to  the  body,  215,  288 
Albuminous  glands.     Sec  Glands. 
Albumins,  1017 
Albumose,  defined,  230,  n. 
Alcohol,  amyl,  983 
butvl,  poisonous  dose  of,  983 
cerotvl,  983 
cetvl,  983 
ethyl,  978 

poisonous  dose  of,  983 
excessive  use  of,  effect  of,  298 
in  the  body,  979 
iso-pentyl,'983 
melicyl,  983 

physiological  effect  of,  297 
propenyl,  1000 
propyl,  normal  or  primary,  982 

poisonous  dose  of,  983 
radicals,  compounds  of  the,  with  nitrogen,  984 
diatomic,  derivatives  of,  986 
monatomic,  975 
triatomic,  1000 
Alcohols    containing    more    than    five    carbon 
atoms,  983 
primary  general  reactions  for,  975 
secondary.  975 
tertiary,  975 
Aldehyde,  formic  (methyl),  977 


Aldehyde,  glycerin,  1001 
nietiiyl,  '.)~7 
paraforniic,  977 
Aldehydes,  behavior  and  preparation  of,  977 
Alimentar.v  canal,  bacteria  of  the,  248 

digestive  processes  in  the,  object  of,  213 
movements  of  the,  307-325 
— defecation,  .324 
—deglutition,  310 
— masticatiou,  310 
— movements,  intestinal,  320 
^movements  of  the  stomach,  315 
— vomiting,  325 
osmosis  of  tlie,  2.52 
Alkalies,  action  of.  in  promoting  pancreatic  se- 
cretion, 177 
AUantoin,  998 
Allochiria,  844 
Altitude,  influence  of,  on   the   number  of  red 

cor])Uscles  in  blood,  344 
Alveoli   and    the  blood,  iuterchange  of  C  and 
CO.'  lietween,  522-527 
of  resting  mammary  gland,  epithelial  cells  of, 

202 
of  the  lungs,  number  aud  size  of,  504 
of  the  pancreas,  172 
of  the  sebaceous  glands,  197 
secretory,  of  mammary  gland,  incompletel.v 
formed  before  pregnancy,  201,  204 
Amines,  the,  984 

of  the  olefines,  986 
Ammonia,  955 
Ammonium,  967 
carbonate,  218,  967 
cyanate.  98,5 
Amnion,  the,  911 
Amcrba,  33,  34 
Amphibia,  removal  of  cerebral  hemispheres  of, 

efiect  of,  706-709 
Ampho-iiei)tones,  231,  241 
Amygdalin,  985 
AmVlodextrin,  223,  1007 
Amylopsin,  243,  1008 
end-i)roducts  of,  243 
s]iecific  reaction  of,  243 
Anabolism  defined,  19 
Analysis,  chemical,  defined,  962 
Anatomy  of  the  ear,  807-824 
physiological,  of  the  central  nervous  system, 
644 
Anelectrotonus,  69 
Animal  "starch,"  266 

Animals,  cold-blooded,  bod.v-tenii)erature  of,  .575 
class  of,  57.5 

retentiou  of  vitality  of,  after  death,  39 
heat-production  in  various,  .590 
human  physiolog.v  founded  ui)on  experimen- 
tation on  lower,  .30 
nerve-cells  iu  different,  size  of.  609 
neurons  in  diflerent,  size  of,  609 
reflex  action  of  central  nervous  system  of,  704 
removal  of  cerebral  hemispheres  of,  result  of, 

compared,  705-710 
reproduction  in,  periods  of  desire  and  power 

of,  898 
sense  of  smell  in  lower,  851 
warm-blooded,  bod.v-temperature  of,  575 
class  of,  .575 
Anode,  electrical,  44 

])hysical  and  i)hysiological,  defined,  62 
Antalbuniid,  231,  n. 
Antipei)toue,  231,  241 
Anti-peristalsis.  317,  320 
Antrum  pylori,  315 
Apex-beat"  of  tile  heart,  409 
Aphasia,  697 
Apua'a,  548,  549 


INDEX. 


1025 


Apparatus,  electric,  43-4") 
Area,  visual,  cortical  subdivisious  of,  712. 
Areas,  cortical.     See  Bruin. 
Arteries  and  heart,  {leneral  changes  in,  404 
blood-speed  in  tiie,  iSMH 

coronary,  closnre  oC  the,  ehanjj;es  in  the  heart- 
beat from,  IT.'S 
excilinji  cause  of  ventricular  arrest  from, 

474 
frequency  and  results  of  ventricular  ar- 
rest from,  473 
in  the  do;;,  471 
terminal  nature  of,  472 
great,  ciianges  in  the,  in  the  open  chest,  407 
Articulation,  defined,  874 
Articulations,  the,  85.") 

of  the  auditorj'  ossicles,  812 
Asparagin,  l(KH) 
Asphyxia  defined,  548 

stages  of,  552,  553 
As.similation.    See  Nutrition. 
Astigmatism,  763-7(i5 
Atavism,  933 
Atropiu,  action  of,  upon  the  salivary  glands  and 

their  secretions,  170 
Auditory  meatus,  external,  807 
ossicles,  HIO 

sensation,  tjieory  of,  824 
Auricle  a  feeble  force-pump,  427 
are  the  venous  openings  into  the,  closed  during 

its  systole?  430 
changes  in  the,  from  vagus  excitation,  455 
connections  of  the,  426 
function  of  the,  428 
is  the,  emptied  by  its  systole?  430 
pressure  of  the  systole  of  the,  427 
withiu  the,  negative,  429 
Auricles,  beating,  changes  in  size  of,  404,  405 
changes  in  the,  in  the  open  chest,  407 
color  of  the,  407 

functions  of  the,  426.     See  also  Heart. 
Auricular  cycle,  relations  of  time  of  the,  413 
Auscultation,  inventor  of,  410 
Automatism,  muscle,  defined,  35 
Axilla,  temperature  of  the,  mean,  577 
Axis-cylinder  of  nerve,  36,  151 

Bacteria,  intestinal,  248-250 
pathogenic,  destruction  of,  by  the  leucocytes 
of  the  blood,  346 
Basilar  membrane,  cochlear,  821,  824 

fibres  of  the,  number  of,  824 
Basophiles,  345 

Baths,  influence  of  hot  and  cold,  on  body-tem- 
perature, 579 
Beats  in  notes  or  tones,  production  of,  830 
Benzol,  1010 
Benzopyrol,  1013 
Bidder's  ganglion,  440 
Bile,  261 
absorption  spectrum  of,  262 
analysis  of,  chemical,  261 
anti.septic  properties  of,  266 
circulation  of  the,  263 
color  of,  185,  186,  262 
constituents  of,  186,  261-265 
— bile-acids,  263 
— bile-pigments,  262 
— cholesterin,  264 
—fats,  265 
—lecithin,  265 
— nucleo-albuniin,  265 
ejection  of,  from  the  gall-bladder,  process  of, 
188 
normal  mechanism  of,  189 
formation  of,  action  of  secretory  nerve-fibres 
upon  the,  188 


Bile,  formation  of,  during  the  digestive  process, 
189 
not  controlled  by  the  nervous  system,  185 
function  of,  1.54 

importance  of,  physiological,  265 
inlliiiiicc  (if,  in  th<'  eniulsidcatiou  of  fats,  246 
in  llie  l)lood,  action  of  the  presence  of,  187 
method  of  obtaining,  261 
quantity  of,  secreted,  186,  261 
reaction  and  specific  gravity  of,  262 
Bile-acids,  2(i3,  2()4 

Bile-capillaries,  relations  of  the,  to   the  liver- 
cells,  185 
Bile-duct,  complete  occlusion  of  the,  effect  of, 

189 
Bile-ducts,  lining  epithelium  of,  relationship  be- 
tween the  liver-cells  and  the,  185 
Bile-pigments,  262,  1015 

Gmelin's  test  for,  262,  1015 
reabsorption  of,  265 
relationship  of  hajmoglobin  to,  343 
Bile-salts,  1.54 

Bile-secretion,  conditions  influencing  the  amount 
of,  187      ■ 
digestive  function  of,  265 
normal  mechanism  of,  189 
quantity  of,  186 

relation  of,  to  the  blood-flow  in  the  liver, 
187 
Bile-vessels,  motor  nerves  of  the,  188 
Bilirubin,  262,  1015 
Biliverdin,  262,  1015 
Birth.     See  Parturition. 
body-growth  before  and  after,  924,  925 
length  and  weight  of  fetal  body  at,  925 
Birth-rate,  relative,  of  the  two  sexes,  922,  923 
Births,  multiple,  920,  921 

periods  of  largest  number  of,  899,  n. 
Bladder,    changes  in   size   of  the,  from   reflex 
stimulation,  329 
contraction  of  the,  influence  of  the  force  of, 

upon  the  urinary  stream,  328 
contractions  of  the,  physiological  mechanism 

of,  329 
mechanism  of  the,  nervous,  330 

of  urinary  injection  into  the,  327 
movements  of  the,  328 
nerve-fibres  of  the,  sensory  and  motor,  330 
nerves  of  the,  vaso-motor,  500 
"Blind  spot,"  retinal,  774 
Blood,  absorption-coefficient  of,  for  O,  523 
alkalinity  of,  degree  of  and  test  for,  332 
ammonia  carbamate  of  the,  276 
appearance  of,  in  asphyxiation,  .553 
arterial,  gases  of,  alterations  in  the,  519 
per  cent,  of,  of  various  animals,  519 
proportions  of  O  and  CO2  in,  519 
pulmonary,  color  of,  519 
speed  ancf  pressure  of,  compared,  .393 
bile  in  the,  pre.sence  of,  action  of  the,  187 
capillary,  speed  and  pressure  of,  compared,  393 
CO2  in  the,  influence  of  the  quantity  of,  551 
composition  of,  chemical,  347 
gaseous,  effects  of,  on  the  respiratory  move- 
ments, .548 
importance  of,  ui)on  the  respirations,  566 
defibrinated,  331,  332 
defibrination  of,  3.52,  .3.53 
functions  of  the,  73,  331 
gases  in  the,  alterations  in  the,  519 

extraction  of,  528 
haemoglobin  in,  amount  of,  336 
in  the  body,  distribution  of,  .sto,  361 

quantity  of,  360 
in  the  central  system,  734-736 
"  laky,"  3:53 
menstrual,  amount  of,  discharged,  896 


1026 


INDEX. 


Bloud.  nu'ii8triial,  ihaiacter  of  the,  896 
uiovt'iuLMit  of  (lie,  ill  i'!i]ii Maries,  uiiuute  arte- 
ries and  veins,  371-377 
of  preKiiaiicy,  i'KJ 

of  various  animals,  nutritive  value  of,  482 
of  tile  niaininalian  heart,  482 
jieptoiU'S  and  jiroti'oses  in,  'I'-AS 
jiroperties  of  tiie,  general,  331-347 
reaetion  of,  33'J 

regeneration  of,  after  hemorrhage,  361 
solutions  of,  isotonic.  .334 
sjieeilie  gravity  of,  332 
sjieetra  of.  absorj)tion,  338 
structure  of,  histological.  331 
sugar  of  the.  form  of.  2r)7 
tenijierature  of  the,  577 

time  spent  by  the,  in  a  systemic  capillary,  395 
transfusion  t)f,  3(i'2 
urea  present  in  the,  amount  of,  275 
venous,  iiroportions  of  ()  and  COa  in,  519,  520 
speed  and  jiressure  of.  compared,  393,  394 
Blood  and  the  alveoli,  interchange  of  C  aud  CO2 
between  the.  .522-.527 
and  the  tissues,  interchange  of  O  and  CO2  be- 
tween the,  .527 
Hlood-circulation.     See  CirculKtion. 
Hlood-clottiug.     See  Coiujulniion. 
Blood-cor])uscles.     See  Corpusclex. 
Blood-tlovv,  cai)illary,  372 
causes  of  the,  369 
course  of  the,  368 
ill  the  small  ves.sels,  direct  observation  of, 

372 
sumniary  of,  377 
through  the  kidneys,  195 

the  lungs,  395 
venous,  subsidiary  forces  assisting  the,  387 
Blood-li'ucocytes.     See  Leucoq/tes. 
Blood-jiassages  in  the  frog's  heart,  471 
Blood-path,  circle  of  the,  368 

jmlmonary,  .370 
Blood-plasma.     See  PlaKma. 
Bluod-iilates,  347 
Blood-pressure,  aortic,  377-383 

arterial,  capiJlarv,  and  venous.  377-383 
causes  of,  .383-389 
causation  of,  383,  385 
arterial     and    venous,     manometric     and 
graphic,  method  of  studying,  .377-380 
manometric  trace  of,  381,  382 
<-apillary,  376,  438 

why  pulseless?  387 
cardiac,    eflect   of   stimulation    of    cardiac 

nerve-fibres  on  the,  46.3-467 
changes  in,  from  stimulation  of  the  brain, 

due  to  reflex  action,  494 
effects  of  resj)iratory  movements  on,  .5.55 
intracranial,  735,  7.36 

symptoms  of  bleeding  in  relation  to,  383 
the  mean  arterial,  ca]tillary,  and  venous,  382 
venous,  causation  of.  ;i86 
Blood-pressures  within  the  ventricles,  416 
Blood-proteids  of  Ivmph,  363 
JMood-serum,  .331-334 

action  of,  bactericidal,  334 
globulicidal,  334 
Blood-s[)ced  and  ])ressure  compared,  393 

in  arteries,  capillaries,  and  veins,  390-395 
in  large  vessels,  measurement  of,  390,  392 
in  the  arteries,  .393 
in  tlic  caiiillaries.  .393 
in  the  minute  vessels,  .375 
in  the  veins,  393 

varies  inversely  as  the  collective  sectional 
area  of  its  ])ath,  394 
Blood-stream,  evidence  of  the  more  rapid  move- 
ment of  the  central  part  of,  373 


Blood-stream,  iiulmonary,  3i(5,  3f)6 
Blood-supjily  and  heartbeat,  relation  of,  in  the 
coronary  circulation,  477 
eHect  of  the,  on  nerve  and  muscle,  73 
importance  of  the,  ujioii  the  respirations,  .566 
inliuence  of  the,  011  bodv-tenipcrature,  579 
of  the  brain,  723.  734-7:i(> 
Blood-vessels,  chorionic,  912 

clotting  within  the,  production  of,  3.58 
condition  of  the,  due  to  asphyxiation,  .553 
contractility    of    the,    early    experimental 

deuKMist rations  of.  482-486 
innervation  of  the,  482-.")01 
large,  sjieed  of  the  blood  in,  390-392 
minute.  s]>eed  of  the  blood  in,  .375 
lilacental,  912 
retinal.  767 

small,  How  in  the,  direct  observation  of,  372 
why  blood    does  not  clot  within  the,  359. 
See  Arterie.1,  Ciipilldries,  ]'eins. 
Body,  chemistry  of  the,  943-1021 
equilibrium,  dynamic,  833,  843,  845-849 

static.  849 
locomotion  of  the,  860 
"  Body  of  Aranzi,"  404 
Bodv-activitv,  influence  of,  on  heat-productiou, 

592 
Body-fat,  origin  of,  theories  of,  290,  291 
Body-heat.     See  Heat,  also  Temperature. 
chemic  production  of,  302 
specific.  948 
Body-growth  before  and  after  birth.  924,  925 
diminution  of,  progressive.  926,  928 
influence  of  race  upon,  926 
ra])iditvof,  relative,  in  both  sexes.  926 
Body-metabolism,  282-302 
Bodv-stirface    in    relation   to   heat-dissipation, 

594,  .5!)5 
Bodv-tenii)erature.     See  Temperature. 
Body-weight  in  death,  9.30 

influence  of,  on  heat-production,  590 
loss  of,  from  starvation,  .301 
relations  between  weight  of  centi'al  nervous 
system  and  the,  719 
Bone  a  mineral,  969 

Bones,  action  of  muscles  upon  the,  method  of, 
8.57 
in  human  skeleton,  number  of,  855 
muscles  of,  contraction  and  reaction  of,  107 
of  the  skull,  conduction   of  sound-sensation 

through  the, 815 
union  of.     See  Articulations. 
"  Border  cells,"  178 

Brain,  atroi)hy  of  the,  in  old  age,  720,  726 
blood-supiily  of  the,  7.34 
frontal  lol)es  of,  effect  of  removal  of,  703 
growth  of  the,  724 

hemis|)lien's  of   the,  effect  of   injury  to    the 
two,  ()99,  700 
nervous  pathways  within  the,  696-702 
nerves  of  the,  vaso-motor,  494 
relations  of  the,  to  vaso-motor  centres,  493 
removal  of  the,  in  animals,  result  of,  705-715 
sensory  and  motor  regions  of  the,  684-687 
specific  gravity  of  the,  716 
"speech-centre  "  of  the.  698.  702 
water  in  the.  })ercentage  of,  7](> 
weighing  the,  method  of,  718,  719 
white  matter  of.  composition  of,  150.    See  also 
Eiici'phitlon. 
Brain-weight  among  the  insane,  722 
at  birth,  726 
comparative,  718,  719 

of  eminent  men.  Manouvrier's  table,  721 
decrease  in,  in  old  age,  742,  928 
differences  in,  conditions  determining,  718 
increase  in,  with  age,  724 


INDEX. 


1027 


IJiaiii-weight,  iiillufiice  of  social  enviroumeut 
on,  7J1 
interpretation  of,  720 
of  i-riniinals,  7'^"J 
of  (liircriMit  races,  722 

variations  in,  acoiirdinK  to  age,  sex  and  stat- 
ure, 7 IS,  71!»,  720 
llrain-weijiiit  and  weight  of  the  pia  and  fluid, 
71(i 
of  tlie  s|iinal  cord,  715-724 
IJreathing.     Sei-  liespi ration. 

nasal,  value  of,  517 
Hroniine,  9515 
"  BuUy  coat,"  :}53 

Hulbus  arteriosus,  action  on  the,  from  vagus  ex- 
citation, 455 
Huliniia,  K((j 
Butyl  compounds,  98 

Cadaverin,  986 
Catlein,  99(i 
(.■alcium,  967 

carbonates,  968 

chloride,  967 

detection  of.  968 

fluoride,  967 

in  the  body.  969 

phos)>hates,  967 

sulphate,  967 
Calorie,  or  heat  unit,  584,  948 
Calorimeter,  Eeichert's,  586 
Calorimeters,  classes  of,  585 
Cane-sugar,  218,  247,  1006 

chemical  action  of  invertiu  on,  220 

inversion  of.  257 

relation  of,  to  glycogen-formation,  267,  268 
Cai)illaries,  blood-flow  of  the,  .377,  379 

blood  in  the,  movement  of,  371 

blood-pressure  of  the,  376 

blood-speed  in  the,  393 

calibre  of  the,  371,  376 

characters  of  the,  .371 

of  the  lungs,  .504 

red  corpuscles  of  the,  behavior  of,  373 
deformity  of,  373 

"systemic,"  369 
Capillary,  structure  of  the,  histological,  372 

systemic,  time  spent  by  the  blood  in  a,  395 
Capsules,  suprarenal,  removal  of  the,  symptoms 

preceding  death  from,  210 
Carbamate  of  ammonia,  derivation  of  urea  from, 

275,  276 
Carbamide,  991 
Carbohydrates,  215,  861,  1003 

absorption  of  the,  257 

action  of  gastric  juice  on,  235 
of  intestinal  secretion  on,  247 

combustion  equivalents  of,  303 

effect  of,  on  the  amount  of  glycogen  in  the 
liver,  267 

nutritive  importance  of,  to  the  body,  215,  292 

oxidation  of,  292 

potential  energy  of,  determination  of,  303 

production  of  fat  by  the,  291 

]iroper  regulation  of,  to  the  tissues,  essential 
to  health,  269 
Carbon,  960 

atom,  asymmetric,  989 

compounds,  chemistrv  of,  974 

dioxide,  961 

detection  of.  962 

elementary,  960 

equilibrium  defined,  284 

metabolism  of,  962 

monoxide,  960 
Carbonate,  ammonium,  967 
Carbonates,  calcium,  968 


Carlxinates,  magnesium,  971 
potassium,  !)ili 
sodium.  !lii6 
Cardia<'  centre,  augmentor,  localization  of,  469 
inliibitory,  localization  of,  467,  468 
cycle.  <leliii"ed,  :5!»6,  414 

relations  in  time  of  the  main  events  of,  413 
cycles,  brevity  and  varialjility  of  each,  414 

freciuency  of  the.  412 
excitation-wave,  443 
fibres,  inhil)itory,  origin  of,  468 
"impulse,"  405,409 
nerve-centres,  467-470 
nerves,  450 
Cardiogram,  the,  409 
Cardiometer.  the,  398 
Cardio-pneumatic  movements,  520 
Carnin,  998 

Caitilages  of  the  larynx,  865 
— of  Santorini,  865 
—of  Wrisberg,  865 
— the  arytenoid,  865 
— tlie  cricoid,  865 
— the  thyroid,  865 
Casein,  234 
Caseinogen,  2.34 
Castration,  pbvsiological  changes  due  to,  871, 

872.  900,  933 
Cataleptic  rigor,  145 
Catalysis  of  enzymes,  220,  947 
Cell,  combustion  in  tlie,  in  general,  1009 
death  of  the.  somatic,  943 
the,  the  unit  of  structure  of  living  organisms, 
20 
Cell-bodies,    nerve,  change   in,   resulting  from 
stimulation,  629-633 
relation  of  in  the  cerebral  cortex,  729,  730 
Cell-diflTerentiation,  22,  37 
Cell-division,  20 
Cell-granules,  157 
Cell-groups,  localization  of,  in  cerebral  cortex, 

682-696 
Cell-protoplasm,  conductivity  of,  81 

irritability    of,    conditions    determining 
the,  65 
Cell-reproduction,  asexual,  879 
Cells,  auditory,  classes  of,  818 
"border,"  function  of,  178,  179 
capillary,  372 
daughter-,  20 
dineuric,  defined.  607 
embryonic,  growth  of,  924 

■epithelial,    glomerular,    influence   of  the,    in 
urinary  secretion,  193,  194 
influence  of,  in  the  secretorv  processes,  154, 

155 
of  resting  mammary  gland,  202 
erythroblastic,  of  red  marrow,  formation  of 
red  blood-corpuscles  by  the,  343,  344 
ganglion-,  iiitracardiac,  440 
gland-,  sebaceous,  197 
goblet,  secretorv,  157 

hair-,  auditory,' of  Corti,  818,  822,  824,  825 
hepatic,  relations  of  the,  to  the  ducts,  184,  185 
mononeuric,  defined,  607 
mucous  (secretory),  157 
muscle-tissue,  of  alimentary  canal,  307 
nerve-,  classes  of,  defined,  641 
gustatory,  851 
tactile,  8.53 
vaso-motor,  488.  489 
of  Langerhans,  172 

of  mucous  gland,  appearance  of,  after  stimu- 
lation. 169 
in  a  resting  state,  169 
of  pancreas,  appearance  of.  during  fasting,  174 
during  the  stages  of  digestion,  175 


1028 


INDEX. 


Cells  of  pancreas,  histological  changes  in,  during 
activity.  174 
characters  of,  172 
of  parotid,  appearance  of,  after  stimulation, 
l(i8 
in  a  fresh  state,  IfiS 
in  a  restin;r  condition,  l(i7 
of  tuhules  of  kidney,  secretory  functions  of, 

definite.  1!)2.  1!« 
of  the  cortex.     .See  Cortex. 
of  the  gastric  glands,  histological  changes  in, 
during  secretion,  1S"J 
histological  characteristics  of,  178 
of  the  intestinal  glands.  184 
olfactory,  8o0 
"oxyntic."  178 
"parietal,"  178,  179 

secretory,  appearances  of,  histological,  157 
lumen  of  the,  101 
of  sweat-glands,  198 
spindle-shaped,  of  j)lain  muscle-tissue,  307 
sustentacular,  auditory,  818 
"  wandering,''  346 
Cellulose,  1C)07 

Centre  of  gravity  of  the  human  body,  859 
Centres,  nerve-,  cardiac,  407-470 
of  the  cortex.     See  Cortex. 
thermogenic,  598,  600.  601 
tiicrmo-inhibitory.  .599,  601 
vaso-motor.  489-49.'5 
Centrosome,  20.  22,  908 
Cephalization  defined,  703 
Cerebellum,  changes  in  the,  in  old  age,  743 

removal  of,  effect  of,  714 
Cerebral  cortex.     See  Cortex. 

hemispheres,  bilateral  symmetry  of  the,  723 
blood-supply  to  the,  723 
functions  in  the,  localization  of,  704,  705 

of  the  two,  relative,  699 
nervous  pathways  within  the,  696 
removal  of  the,  705-715 
Cerebri  n,  1001 
Cerumen,  198 
Charcot's  crystals,  884,  885 
Chemical  tonus,  133,  134 
Chemicals  and  drugs.     See  Drugs. 
Chemistry  of  digestion  and  nutrition,  213-304 
of  muscle  and  nerve,  144-151 
of  the  body,  943-1021 
Chemotaxis  or  chemotropism,  904 
Chest,  opened,  efi'ects  on  the  heart  and  vessels 
of  the.  407 
observation  of  heart  and  vessels  in  the,  405 
unopened,    probable    changes   in    the   heart's 
position  and  form  in   the,  408.     See 
Thorax. 
Chief-cells,   changes  during  secretion   in,  182, 
183 
of  the  gastric  glands  of  the  stomach,  function 
of,  178,  179 
Chinolin,  1012 
Chloral  hydrate,  980 
Chloride,  calcium,  967 
sodiun),  965 
potassium,  963 
Chlorides  of  the  urine,  quantity  of,  280 
Chlorine,  951 

in  the  body,  9.52 
Chlorocruorin,  1018 
Chloroform,  977 

Chocolate,  physiological  effect  of,  297 
Cliolesterilin.'lOKi 
Cholcsterin,  264.  1016 
elimi'.iation  of.  264,  265 
formation  and  distribution  of,  264 
Cholin,  986 
Chondro-mucoid,  1019 


Cin»rion,  the.  911,912 
Ciiromatin,  22,  28,  8b9,  892 
Ciiromo-proteids.  1018 
Chromosomes.  22,  28,  884,  889 

numbir  of,  in  fertilized  ovum,  908 
(.nironogra]))!,  the,  100 
Chyme,  237,  318 
"  CJirculating  proteid,"  285 
Circulation  (blood),  cerebral.  495 

circuit  of,  time  retinircd  to  complete  the,  371 
coronary,  blood-supply  and  heart-beat,  477 

volume  of,  476 
course  of  the,  368 
defined,  .368 

discovery  of  the,  362,  '.UiH 
effects  of  obstruction  of  the  air-passages  on 
the,  .")59 
of  the  respiration  of  rarefied  and  compressed 

air  on,  .")9 
of  the  resi)iratory  movements  on  the,  5.55 
influence  of,  on  heat-dissipation,  595 

on  heat-production,  590 
influences  of  intrathoracic  and  intrapulmon- 

ary  pressure  ui)on  the,  517 
in  the  central  nervous  system,  conditions  con- 
trolling the,  734,  735 
mechanics  of  the.  .371 
placental,  912,  913 
proofs  that  the  heart  unaided  can  maintain 

the,  .•i9() 
rapidity  of  the,  371 
I'etinal,  768 
Climacteric,  the.  898,  927 
changes  of.  pathological,  physical,  and  psychi- 
cal, 927 
Climate,  effect  of,  on  sexual  maturity,  927 
influence  of.  on  body-temperature,  578 
on  heat-dissipation.  .593 
on  heat-production.  .591 
Clothing,  influence  of,  on  heat-dissipation,  .593 
Clotting.     See  Codiiulotiou. 
CO2,  effect  of  respiration  of,  547.  .548 

elimination  of,  during  muscular  work.  299 
during  sleep,  300 

from  variations  in  temperature,  300.  301 
excretion  of,  from  the  skin,  282 
exhaled  through  the  skin,  quantity  of,  .530 
tension  of.  .524 
CO^-dyspncea,  cause  of,  550,  .551 
Coagulation,  blood,  352 

conditions  necessary  for,  Schmidt's  classi- 
fication, 355 
intravascular,  358,  .359 
means  of  hastening  or  retarding,  359 
— by  action  of  albuminose  solutions,  360 
— by  action  of  neutral  salts,  360 
— by  action  of  oxalate  solutions,  360 
— by  cooling,  3.59 
— by  use  of  leech  extracts,  360 
mechanism  of,  3.52 
necessity  of  calcium  salts  to,  296 
physiological  value  of,  35.3 
process  of  normal,  356 
relation  of  calcium  salts  to,  355 
theories  of,  3.53 

— Hannnarsten's  theory,  354 
— Lilienfeld's  theory,  .3.56 
— Pekel baring's  theory,  355 
— relation  of  .salts  to,  3.55 
— Schmidt's  older  theory,  354 
— Schmidt's  recent  theory,  354 
time  of  clotting,  .3.5.3 
lymph,  3(i3 

milk,  rcnnin  process  of,  2.34 
muscle,  in  rigor,  146,  147 
Coats,  muscular,  of  the  bladder,  328 
of  the  stomach,  315 


INDEX. 


1029 


Coats  of  till-  iiriters,  327 
Coflik'ii,  aiialiiiiiv  of  tlic,  {loncral,  R19 
nu'iiibranoiis,  ,sl7,  J^l!',  f^~l 
osseous  stnu'tiirc  of,  Hl(» 
Cotfeo,  pliysiolofjtical  fll'i-ct  of,  *2!)7 
Cold  and  warm  points,  cntanoous,  841 

application  of,  to  the  bodv,  reactions  produced 

by,  (iO;5 
efl'ect  of,  on  nuiscle-protoplasni,  147 
on  muscular  contraction,  127 
on  the  development  of  rigor,  145 
OoUaccn,  288,  1020 
Colloid,  101!) 

of  the  thyroids,  formation  of,  207 
Color  contrast,  retinal,  792 
sensation,  778,  779 

theory  of,  llering's,  782 
Mrs.  Franklin's,  783 
Yonng-Hehnholtz,  781,  782 
vision,  cerebral  centre  for,  785 
Color-blindness,  784 

practical  importance  of  determining,  785 
test  for,  Holmgren  method,  785 
Color-mixture,  spectral,  779 
Color-reactions  of  proteids,  1016 
Color-sensations,  778,  779 
Color-theories,  781 
Colorimetry,  584 

Colors,  binocular,  combination  of,  803 
"complementary,"  defined,  780 
luminosity  of  different,  78(> 
mixture  of,  physiological,  780,  781 
Colostrum,  204 

corpuscles,  origin  of,  203 
"Combustion  equivalent,"  303 
Commutator,  mercury,  Pohl,  51 
Conceptions,  multiple,  920 

periods  of  the  largest  number  of,  899,  n. 
Concha,  the,  807 
Concord,  musical,  perfect,  831 
Condiments  and  flavors,  influence  of,  on  diges- 
tion, 298 
Conduction,  influences  which  alter  the  rate  and 
strength  of  the  process,  92-96 
of  muscles  and  nerves  in  both  directions,  86 
influences    which    alter    the    rate    and 

strength  of  the  process,  92 
isolated,  83 

nature  of  the  process,  97 
protoplasmic  continuity  essential  to,  82 
rate  of,  88 
Conductivity,  21,  3.5,  81-98 
Consciousness,  28,  29  • 

existence  of,  in  animal  life,  29 
phenomena  of  the  central  nervous  system  in- 
volving, 606 
Consonants,  classification  of,  876,  877 

phonatiou  of,  876,  877 
Contiuuity,'protoplasmic,  of  muscles  and  nerves, 

82 
Contractility,  20,  32,  98-134 

power  of,  in  simple  living  organisms,  34,  35 
Contraction,  anodic,  50,  63,  68,  69 
cardiac,  441-450 
idiomuscular,  42,  93 
isometric,  108 
isotonic,  108 
kathodic,  50,  63,  68,  69 
law  of,  Pfliiger's,  60 

muscular,  alterations  in  the  form  of  the  myo- 
gram,   from    mechanical   conditions, 
108 
amount  of  irritation  process  developed,  esti- 
mated from  the  amount  of  the,  63 
as  effected  by  heat,  66 
duration  of,  differences  in,  106 
effect  of  cold  on,  127 


Contraction,  muscular,  effect  of  drugs  and  chem- 
icals on,  128 
of  temperature  on,  127,  128 
of  veratria  on,  128 

of  body-weigiit  on  the  form  of  the  myo- 
gram, 108 
influences  affecting  the  activity  and  charac- 
ter of  the,  106 
latent  p(-riod  of,  101,  113,  114 
law  of,  53,  (iO 

liberation  of  energy  by,  129-132 
method  of  recording,  49 
inyoj^rain  of,  simi)le,  101 
nature  of,  in  rigor,  146 
normal    and    rigor    mortis,    differences    in 

forms  of,   146 
of  rigor,  changes  resulting  from,  148 
of  the  bladder,  mechanism  of,  329 

sjiinal  centre  of  reflex,  330 
of  the  intestines,  309 
of  the  oesophagus,  312-314 
of  the  stomach  during  digestion,  316,  317 
of  the  ureters,  309,  327 
of  the  viscera,  mode  of,  310 
rate  of,  in  difl'erent  muscles,  107 
theories  of  chemical  changes  and  alterations 
of  form  in,  104 
of  muscle-tissue,  variation  in  rate  of,  308 
of  striped  muscle,  rapidity  of,  308 
spasmodic,  of  the  abdominal  muscles,  the  prin- 
cipal factor  in  vomiting,  325 
ventricular,  force  of  the,  399 
vermicular,  defined,  310 
"Contraction-ring,"  917 

Contraction-wave,  "  antiperistaltic,"  of  the  stom- 
ach, 317 
cardiac,  443 

peristaltic,  intestinal,  321 
Contractions,  fibrillary,  cardiac,  from  closure  of 
coronary  arteries,  473,  475 
from  closure  of  coronary  veins,  476 
recovery  from,  475 
muscular,  98-134,  737 

effect  of  fatigue  on.  111,  112,  126 

of  increase  of  strength   of  electric  cur- 
rent, 54,  ,55 
of  making  and  breaking  the  direct  elec- 
tric current,  50 
of  support  on  the  height  of,  119,  120 
of  tension  on  the  activity  of,  131,  132 
of  the  strength  of  electric  irritation  on, 
53,  54 
fatigue  from,  77 

of  voluntary,  126 
functions  of,  32,  33 
post-mortem,  144-147 
recording  of,  method,  98,  99 
separate,  effect  of  excitation  upon  the  form 

of,  113,  114 
simple,  studied  by  the  graphic  method,  98 
"staircase."  72,  110 

starting-points  of  excitation  in  the  irrita- 
tion process  of  making  and  breaking 
electric  currents,  50-53 
of  the  bladder,  influence  of  the  force  of,  upon 

the  urinary  stream,  328 
of  the  spleen,  272 
physiological,  normal,  124 
rhythms  of,  daily,  738 
uterine,  917-920 

duration  and  nature  of,  918-920 
ventricular,  369 
"Contracture"  (muscle),  115, 116 
Contrast,  auditory,  831,  832 

color,  retinal,  792 
Copulation,  902 
act  of  ejaculation  in,  902,  903 


1030 


INDEX. 


Copulation,  sexual  exciteiuent  of,  coiiUKirative, 

902 
Cord,   spinal,   hemist'ction   of,   degeneration  of 
nerve-fibres  after,  !)()!) 
efleet  of.  (iTl  tiT."!,  (iTii 
nerve-impulses  iu  tiie,  allereut  pathways  of, 

(>7o 
plates  of  the,  dorsiil  and  ventral,  (i45 
segmentation  of  the,  (ilT) 
Corpora  Araritii  of  semilunar  valves,  404 
Corpuseles,  l>l((oil-,  averajje  life  of,  343 
eomposition  of,  .■}47-34!) 
isotonie  relations  of,  334,  3;?5 
number  of,  variations  in.  eonditions  affect- 
ing the,  344 
red,  333 

behavior  of.  373 

blood-si)eed  measured  bj'  the  speed  of  the, 

375 
eolor  of.  333 
composition  of,  333 
destruction  of.  by  ingestion,  343 
evidences  of  friction  of,  373 
form  of  the,  330 
formation  of,  by  the  erythroblastic  cells 

of  red  marrow,  343,  344 
function  of,  333 
ha-moglobin  of,  condition  of  the,  333 

nature  and  amount  of,  335 
movement  of.  observation  of,  372 
number  of.  333.  344 
orii^in  and  fate  of.  343 
reproduction  of  the,  343 
specific  gravity  of,  333 
varieties  of,  331 
colostrum,  203,  204 
salivary,  161,  221 
touch-,  H.36 
Corpus  luteum,  893 

Cortex  (cerebral),  afferent  impulses  of  the,  com- 
posite character  of,  700 
y)ath\vays  through  gray  matter  of  the,  702 
variations  iu  association  of,  701 
area  of  the,  729 

areas  of  the,  centres  and,  separateness  of.  091 
latent,  702 

localization  of,  082,  683 
result  of  stimulation  upon,  683 
mapi»ing  of  the,  684,  689 
.sensory  and  motor.  683-687,  693 

determination  of,  696 
size  of  the,  090 
subdivisions  of,  690 
as.sociation-fibres  of.  697 
centre  for  color-vision  in  the,  785 
fibres  of  the,  increase  in  the,  729 
impulses  leaving  the,  course  of.  695 
metabolism  of  the,  iu  old  age.  743 
movements  from  the,  control  of.  094,  695 
relation  of  cell-bodies  in  the.  729,  730 
visual  area  of  the,  subdivision  of,  712 
Corti,  cells  of,  822 
organ  of,  821 
rods  of,  821-823,  825 
Coughing.  .562 

diagnostic  imimrtance  of,  563 
Covvper's  glands,  887 
secretion  of.  885 
"Crazy  bone."  the.  65 
Oeatin.  278,  993 
Creatinin.  278,  994 
Cresol.  formula.  280 

Cretinism,  sporadic,  feeding  of  thyroids  in,  ef- 
fect of,  737 
Criminals,  brain-weight  of,  722 
Crving.  .5^)2 
Crypts  of  Lieberkuhn,  184,  246 


Crystals,  Charcot's,  884,  885 

Inemctglobin,  337,  3;i8 
Cumre  experiment  on  the  independent  irrita- 
bility of  muscle,  41 
Cyanamide,  9f^5 
Cyanate,  ammonium,  985 
Cyanide,  meth.vl,  985 

potassium,  9b.5 
Cyste'in,  990 
Cystin,  990 
Cytology,  30 
Cytoplasm,  20,  81 

difiercntiation  of,  from  protoplasm  of  the  cell- 
nucleus,  22 

f?-FKUCTOsp:.  1005 
(/-galactose.  1006 
rf-glucose,  1005 
"  Dangerous  region,"  389 
Daniell  cell,  the,  43 
Deafness,  cause  of.  090 

Death  from  extirpation  of  the  thyroids,  208 
symptoms  [)receding,  208 

from  removal  of  sujjrarenal  cajisules.  40 

of  living  protoplasm,  molecular  alteration,  23 

of  the  tissues.  92ft 

rise  of  bodv-temperature  after,  cau.satiou,  604 

somatic,  929,  930 
Death-processes,  effect  of,  on  conduction,  92 
Decidufp,  the,  909-912 
Decomposition,  bacterial,  intestinal,  248 
Decussation  of  nerve-fibres,  647,  680,  681,  768 
Defecation,  324 

involuntary  factor  in,  324 

mechanism  of.  324.  325 

voluntary  factor  in,  324,  325 
Degeneration,  nerve-,  Wallerian.  033 

of  nerve-fibres,  of  the  central  system,  634 
secondary.  687 

of  non-medullated  nerve-fibres.  633 

of  nucleated  portion  of  nerve-fibres,  6.35 
Deglutition,  310 

kronecker-Meltzer  theory  of.  313 

nervous  c(mtrol  of,  314 

oesophageal,   number   and   time    elap,siug  be- 
tween. 3i:5.  314 

sound,  312,  313 

stages  of,  310.  311 
Demilunes  (cells),  100 
Dendrons,  neuric.  007 
Depth-perception.  801 
Deutero-proteoses.  230 
Deutoplasm,  S8.s.  ,Hb9 
Dextrose,  21h.  1005 
Diabetes  mellitus,  200,  207,  293 

sugar  in  the  urine  in,  268 
Dialysis  defined,  251 
Diaphragm,  movements  of  the,  respiratory,  506 

.structure  of  the,  50(),  .507 
Dia.stase,  218 
Diastole,  auricular.  .370.  .396 

ventricular,  .'!?!>,  390,  405 
Diet,  accessory  articles  of,  296,  298 

composition  of  healthy,  305 

effect  of.  <m  resi)iratory  quotient.  .545 

influence  ot'.  on  body-temperature,  578 
on  heat-i>ro<luction.  .591 
Dietetics,  object  of.  304 
I  Diets,  effect  of  various,  on  gastric  secretion.  181 
1  Digestion,  action  of  steapsin   in.  physiological 
value  of.  245 
of  nnoriranized  and  organized  ferments  on, 
'  219 

albuminoid.  2ss 

bile  in.  i)hysiological  importance  of,  26.5,  266 
'      carbohydnite.  292 
1      di-Siicciia rides  of,  247 


INDEX. 


1031 


Digestion,  effect  of  coudimcnts  aud  (liivors  upou, 

of  stimulants  upon,  •JH7 
foruiiition  of  l>ile  during,  189 
gastric,  "J^o-J.iT 

proteoses  of,  lOlrt 
influence  of,  on  boily-teuipenilure,  578 
on  lieat-produclion,  591 
on  the  viiluine  of  gases  respired,  539 
intestinal,  -J-l-i-'JlS 
action  of  the  intestinal  juice  upon,  247 
secretions  acting  in,  2;W 
normal,  tiow  of  gastric  secretion  during,  cause 
of,  181 
physiolofiical  value  of  saliva  on,  224 
object  of  tin?  processes  of,  in  the  alimentary 

canal,  213 
of  fats,  235,  2S9 
pepsin-hydrochloric  acid,  229,  240 

product  of,  255 
peptic,  240 

action  of  bile  on,  266 
end-products  of,  229,  230 
in  the  stomach,  228 
steps  in,  230 
study  of  artificial,  229 
physiology  of,  217 
products    of,    routes    of    absorption    of    the, 

250 
proteid,  285 

end-products  of,  255,  350,  1021 
proteolytic,  Kiihne's  theory  of,  231,  n. 

Xeumeister's  schema,  243,  n. 
salivary,  220,  221 

stonmch,  movements  of  the,  during,  316 
of  carbohydrates,  235 
of  fats,  235 

processes  of,  schema  of,  242 
products  of,  240,  255 
the.  not  essential  in,  237 
tryptic,  240 
Digestion  aud  nutrition,  chemistry  of,  213-304 
Dioptric  system,  74<}-748 
Dioxide,  carbon,  961 

silicon,  963 
Dioxyacetone,  1001 
Disaccharides,  the,  247,  1006 
Discord,  831 

Diseases,  infectious,  transmission  of,  935,  936 
Distance-perception,  retinal,  799 
D^ess,  adaptation  of,  to  climate,  factoi-s  in,  593 
Drowning,  death  from,  causation,  553 
Drugs,  action  of,  upon  the  salivary  glands  and 
their  secretions.  170 
application  of,  to  the  eye,  effects  of,  771 

upon  the  mechanism  of  eye-accommoda- 
tion, 757 
effect  of,  upon  body-temperature,  580 
upon  heat-dissipation,  .596 
upon  heat-i)roduction,  592 
upon  intestinal  movements,  323 
upon  the  sweat-glands,  200 
Drugs  aud  chemicals,   effect  of,  on  conduction, 
94 
upon  muscular  contraction,  128 
upon  the  irritabilitv  of  nerve  and  muscle, 
67 
Drum-skin  (ear),  809 

Du  Bois-Eeymond  law  of  electric  nerve  irrita- 
tion, 47 
Duct  of  Bartholin.  158 
of  Wirsung,  172 
of  the  gastric  gland,  179 
Ducts,  gland-.     See  Gland-ducts. 
lymphatic,  362,  437 
of  Rivinus.  158 
of  the  testis,  886 


Ducts  of  the  mammse,  201 

pancreatic,  172 
See  Secretion. 
Dumbness,  871 
Dyslysin,  987 
Dyspna-a,  cardiac,  555 

CO'i,  cause  of,  550,  551 

delined,  .548 

forms  and  eaussition  of,  550,  552 

hemorrhagic,  555 

Ear,  analysis  of  composite  tones  by  the,  828 
anatomy  and  histology  of,  807-824 
of  external,  807 
— external  auditory  meatus,  807 
— the  concha,  H(t7 
— the  pinna  or  auricle,  807 
of  internal,  815-824 
of  middle,  810-815 

— auditory  ossicles,  810 
— Eustachian  tube,  814 
— muscles  of  the  middle  ear,  814 
— tym])anic  membrane,  809 
— tympanum,  808 
different  parts  of  the,  functions  of,  832 
fatigue  of  the,  to  sound,  831 
imperfections  of  the,  to  sound-perception,  832 
judgment  of  direction  and  distance  by  the,  833 
muscles  of  the  middle,  814 
perception  of  time-intervals  by  the,  832 
sensitiveness  of  the,  to  difference  in  musical 
pitch,  829 
Elasticity,  muscle-,  104-106 
Elastin,  1020 
Electric  circuiting,  45 
current  as  an  irritant,  conditions  determining 
the  efficiency  of  the,  43-64 
effect  of,  43-60 
constant,  effect  of.  on  conduction,  94 

effect  of  the,  on  the  irritability  and  con- 
ductivity of  muscle  and  nerve,  61 
direct,   stimulating    effect    of  making  and 
breaking  the,  on  muscle  and  nerve,  .50 
effect  of  opening  and  closing  the,  on  normal 
human  nerve,  63 
of  rate  of  alternations  of,  Tessla's  experi- 
ments, .58 
upon  muscles,  68 
upon  nerves.  69 

upon  the  irritability  of  nerve  and  muscle, 
67 
irritating  effect  of,  on  mu.scle  and  nerve,  43 
— angle  of  application.  .58 
— density  of  current,  56 
— direction  of  flow.  60 
— duration  of  application,  .56 
— rate  at  which  the  intensity  changes,  46 
— strength  of  current.  54 
Gralvani  and  Volta's  experiments,  43 
relation  of  the  method  of  application  of. 

to  the,  .59 
relative  efficacy  of  the  different  methods 
of  application  upon  the  power  of,  59 
strength  of,  altering  the,  methods  of,  55,  56 
Electric  currents,  effect  of,  upon  normal  human 
nerves,  62 
induced,  irritating  effect  of,  on  muscle  and 

nerve.  48 
practical  application  of  alterations  produced 

by,  on  conduction,  95 
reaction  of  muscles  and  nerves  to,  57 
key,  Du  Bois-Reymond,  45 
Electrode,  the,  44  ' 
Electrometer,  capillary,  136 
Electrotonus,  69 

Elements  (chemic).  metallic,  of  the  body  : 
— ammonium,  967 


1032 


INDEX. 


Elements,  metallic: 
— calcium,  OfJT 
— iron,  !t71 
— mafjncsiiim,  970 
— potassium,  9G3 
— sodium,  JXi.^j 
— strontium,  970 
non-metallic : 

— bromine,  9.53 
— carbon,  fXiO 
— chlorine,  951 . 
— fluorine,  9.53 
— hydrogen,  943 
— iodine,  9.53 
— nitrojien,  9.54 
— oxygen,  944 
— phosi)liorus,  957 
— silicon,  9(52 
— sulphur,  949 
Embryo,  development  of  the,  911 
growth  of  the  cells,  tissues,  and  organs  of,  924 
length  and  weight  of  tlio  human,  at  ditfercnt 

ages,  924 
nutrition  of  the,  913 

sex  of  the,  factors  determining  the,  921-923 
Emnlsification,  245 
Emulsin,  21S,  985 
Emulsion,  1002 
Encephalon  defined, 717 
growth  of  body  and,  relation  between,  727 
in  old  age,  changes  in  the.  743 
nomenclature  of,  according  to  weight,  718 
section  of  the,  functional  disturbances  follow- 
ing, 713 
specific  gravity  of,  716 
the  "stem  "  of  the,  717,  719 
weight  of  the.  717 
at  different  ages,  726 
in  sane  ])ersons,  table,  718 
weights  01  different  portions  of,  721 
Encephalon  and  spinal  cord,  weight  of,  716. 

See  also  Brain. 
End-bulbs  of  sensory  nerve-fibres,  835 
End-organs,  nerve,  importance  of,  in  cutaneous 
sensation,  839 
transmission  of  excitation  by,  to  muscles 
and  nerves,  85,  86 
Endosmosis,  251 
"  Endosmotic  equivalent,"  251 
End-plates,  motor,  41 
Enemata,  absorption  of,  255 
Energy,  bodv-,  influence  of  inorganic  salts  on, 
294 
muscular,  electrical,  amount  developed,  135 
liberation  of,  129 
— mechanical,  130 
— thermal,  132 
source  of,  215,  298,  299,  302 
nerve,  .specific.  842 
potential,  liberation  of,  302-304 

direct  and    indirect  conversion   of,  into 
heat,  .582 
Enzyme,  176,  944 
fat-splitting,  pancreatic,  244 
glycolytic,  293 

zymogen  and,  of  pancreatic  secretion,  176 
Enzymes,  217 
action  of  the,  incompleteness  of,  219. 

theories  of  the  manner  of,  219 
classification  of.  218 
— amylolytic.  218 
— coagulating,  218 
—fat-splitting.  218 
— glucoside-si)littiug,  218 
— inverting,  218 
— proteolytic,  218 
— urea-splitting,  218 


Enzymes,  "diastatic,"  218 
of  gastric  juice,  226 
of  intestinal  secretion,  247,  248 
of  the  secretion  of  the  gastric  mucous  mem- 
brane, 179 
pancreatic,  2.39 
reaction  of,  218 

— effect  of  temperature,  219 

— incompleteness  of  action,  219 

— relation  of  the  amount  of  enzyme  to 

the  effect  it  produces,  219 
—solubility,  219 
Eosinophiles.  .345 
Epiglottis,  the,  861,  862 

movements  of  the,  in  swallowing,  311 
Equilibrium,  body-,  maintenance  of,  8.59,  960. 

See  Body-eqnUihrium. 
Ervthrodextrin,  223,  1007 
Ether,  ethyl,  980 

Ether  molecules,  rate  of  vibrations  of,  777 
waves,  retinal  changes  jjroduced  by,  777 
synonymous  terms  used,  777,  778 
Ethers,  mixed,  preparation  of,  980 
Ethyl  alcohol,  978 
compounds,  978 
ether,  980 
hydroxide,  978 
Ethylamine,  985 
Eudiometer,  the,  529 
Eupnoea  defined,  .548 

Eustachian  tube,  structure  and  function,  814 
Excitation,  cardiac,  electrical  variation  in,  454, 
4.55 
propagation  of  the,  454 
in  muscle,  rate  of  transmission  and  direction 
of,  66 
of  contraction-wave,  88 
of  muscle  and  nerve,  conditions  which  deter- 
mine the  eflTect  of,  42 
muscular.     See  Muscle. 
nerve,  rate  of,  122 
respiratory,    due    to    products    of   muscular 

activity  given  to  the  blood,  .552 
vagus,  inhibitory  power  of,  on  the  heart,  453- 
457 
Excitation-wave,  cardiac,  443-446 
Excitations,  muscular,  effect  of  double,  118,  119 
voluntary,  more  effective   than   electrical, 
126 
Excretion,  formula  of,  260 
Excretion  of  COi  by  the  skin,  amount,  282 
Excretions  defined,  154 

of  the  skin,  281 
Exercise,  effect  of,  80,  81 
muscular,    effect   of  preliminary   movements 
on,  112 
heat-production  from,  amount  of  energy  of, 

132,  1.33 
promoting  endurance  and  strength  of  mus- 
cles, 80 
Exosmosis,  251 
Expiration,  mechanism  of,  .506 

muscular  movements  of,  514,  515 
Extracts,  adrenal,  phvsiological  action  of  the, 
210 
testicular,  phvsiological  action  of,  211 
thyroid,  therapeutic  value  of,  208,  209,  901 
Eye  aberration,  760,  761 
accommodation,  752 
"astigmatic,"  755 

axial,  757,  7.58  __     _^ 

changes  produced  by  the  act  of,  7.55,  757 
theories  of  the  mechanism  tif,  7.55.  756 
diminished  ]iower  of,  with  age,  7(>0 
for  distant  olyects.  752-758 
for  near  objects,  752-758 
focal,  752-757 


TXDEX. 


1033 


Eyt',  ac'coiiiinoddtion,  nicchanism  of,  758 
iiilhuMico  of  drujjs  upon  the,  T")? 

jHipillary,  7.")7,  ITiS 

range  of,  in  uiyopicand  liypernietropiceyes, 
7(jl) 
normal,  7">8 

to  various  amounts  of  lifilit,  771,  772 
astifjimatic,  7ti3,  7tJ5 

blood-vessels  of,  methods  of  observing,  767 
centre  of  rotation  of  the,  744 
constants,  methods  of  determining,  749 
curvature  of  refracting  surfaces  of  the,  meth- 
ods of  determining,  750 
defined,  744 

dioptric  apparatus  of  the,  746-748,  760 
"far-point"  of  the,  758,  760 
hypermetropic,  75!l,  760 
images  of  the,  intraocular,  765 
iris  of  the,  768.     See  Iris. 
movements  of  the,  mechanical,  744 
muscse  volitantes  of  the,  766 
muscles  of  the,  745,  746 
myopic,  759 
"near-point,"  758,  760 
nodal  point  of  the,  jwsition  of,  751 
perception  of  time  intervals  by  the,  832 
positions  of  the,  axial,  745 
presbyopic,  760 
"reduced,"  750 
refracting  media  of  the,  748 
retina  of  the.     See  Retina,  also  Vision. 

Face,  respiratory  movements  of  the,  516 
Fallopian  tube,  the,  894 

entrance  of  the  spermatozoa  into  the,  mode 

of,  903 
reception  of  the  ovum  by  the,  mechanism 

of,  894 
structure  and  function  of,  894 
Fat  in  the  body,  1002 
formation  of,  290 
subcutaneous,  influence  of,  on  heat-dissipation, 
593 
Fatigue,  eflFect  of,  on  muscular  contraction,  111, 
112, 127 
loss  of  conductivity  of  muscle  by,  95 
muscular,  76 

decline  of  functional  activity  from,  79 
eflect  of  nutriment  on,  78 
from  functional  activity,  77 
recuperation  from,  time  required  for,  78 
of  nerves,  79,  80,  97 

of  voluntary  muscular  contractions,  126 
of  the  ear  to  sound,  831 
of  the  nervous  sj'stem,  737  , 

of  the  retina,  790 
Fatigue-prodticts  of  the  blood,  78 
Fats  of  the  body,  215 
absorption  of,  2.57 

from  the  stomach,  253 
action  of  gastric  juice  on,  235 

of  steapsin  in  the  decomposition  of,  244 
combustion  equivalent  of,  303 
emulsification  of,  245 

energy  of,  potential,  determination  of,  303 
nutritive  value  of,  215,  289 
Feces,  color  of,  359,  260 
composition  of,  qualitative,  259,  260 
— cholesterin,  260 
— excretiu,  260 
— indigestible  material,  259 
— inorganic  salts,  260 
— micro-organisms,  260 
— mucus,  and  epithelial  cells,  260 
— pigments,  260 

— products  of  bacterial  decomposition,  260 
— undigested  material,  259 


Feces,  composition  of,  quantitative,  259 
odor  of,  derivation  of  the,  ;i60 
weight  of,  259 
Ferments,  digestive,  217 
Ferratin,  972 
Ferrosulphide,  972 

Fertilization  (impregnation),  process  of,  904-906 
Fetal  membranes,  911 
Fetus,  ])osition  of,  at  end  of  pregnancy,  917 

respiratory  centre  in  the,  condition  of,  572 
Fever,  body-temperature  in,  .580 
Fevers,  influence  of,  on  heat-dissipation,  597 

on  heat-production,  592 
Fibres,  muscle-,  form  and  arrangement  of,  32 
secretory,  eflect  of  stimulation  on  the,  163, 164 
proofs  of  definite,  163 
stimulation  of,  eflect  of,  on  the  nature  of 

secretion,  163,  164 
to  the  sweat-glands,  199 
Fibrin  defined,  352 
ferment,  3.54,  355,  357 
solubility  of,  148 
"  Fibrin-globulin,"  354 
Fibrinogen,  351 

amount  of,  in  the  blood,  352 
coagulation-temperature  of,  351 
composition  of,  351 
occurrence  and  origin  of,  351,  352 
reactions  of,  351 
value  of,  physiological,  352 
"Fibroplastin,"  354 
"Fictitious  meal,"  experimental,  180 
Fission,  878,  879 

Fistulse,  pancreatic,  methods  of  making,  238 
Fluoride,  calcium,  967 
Fluorine,  953 

circulation  of,  in  the  body,  9.54 
Food,  absorption  of  food-stuffs  in  articles  of,  ex- 
tent of,  306 
calcium  salts  in  the,  importance  of,  296 
circuit  taken   by  and  the  effect  upon  the,  in 

the  digestive  process,  318 
deglutition  of,  normal  process  of,  311,  312 
digestion  of.     See  Difiestion. 
influence  of,  on  heat-production,  .591 
passage  of,  along  the  intestines,  time  required, 

254 
potential  energy  of,  302 
proteid,  necessity  of,  to  the  body,  214,  286 
value  of  inorganic  salts  as  constituents  of,  294 
variations  in  character  of  human,  213 
Food-consumption,  effect  of  muscular  work  upon, 

298 
Foods,  animal  and  vegetable,  analyses  of,  216 
composition  of,  213-219 
energy -yielding,  302 
"nitrogenous,"  214 
Food-stuff,  amount  of  energy  in  a,  determina- 
tion of,  302 
capacity  of,  for  digestion  and  absorption,  .305 
heat  given  off  by  any  one,  amount  of,  303 
Food-stuffs,  absorption  of,  in  articles  of  food,  ex- 
tent of,  305,  306 
albuminoid,  nutritive  value  of,  288 
average  amount  of,  required  by  an  adult  male, 

305 
carbohydrates  of,  nutritive  value  of,  292 
classification  of,  213-217 
— albuminoids,  215 
— carbohydrates,  215 
—fats,  215 
— proteids,  214 
— water  and  salts,  213,  214 
defined, 213 

energv-vielding,  constituents  of,  582 
fats  of,  nutritive  value  of,  289,  290 
nutritive  value  of,  285-294 


1034 


INDEX. 


Food  .stulls,  nutritive  value  of,  methods  of  de- 
tonuiiiiii};,  'Ir^^l 
plastic  or  respinitory.  defiiu'd,  2S6 
potential  ciierKV  of,  liberatiou  of,  302 
})rotcid,  nutritive  value  of,  285 

Korniose,  977 

Fovea?  centrales,  804 

"  Fraunliof'er  lines,"  33tt 

Fruit-sugar,  1005 

Furfurol,  264 

Gall-bi.aubkk,  motor  nerve-fibres  of  tlie,  188 
Galvani,  ex])criment  of,  on  the  irritating  efl'ect 

of  the  electric  current,  43 
Galvanometer,  the,  136 
Galvanotonus,  64,  123 
Gamogeuesis,  879 
Ganglion-cells,  intracardiac,  440 
sympathetic,  position  of,  Langley's  method  of 
determining  the,  501 
Gas,  cyanogen,  985 

intestinal,  composition  of,  260 
Gases  in  the  lungs,  blood,  and  tissues,  517 
of  saliva,  amount  of,  162 
respiration  of,  various,  eflects  of,  548 
respired  (O,  CO2),  conditions  afl'ectiug  the  vol- 
ume of,  536 
— age,  sex,  and  constitution,  538 
— atmospheric  pressure,  542 
— body-weight  and  l)<)dy-surface,  537,  538 
— comjtosition  of  insjjired  air,  543 
— diurnal  variations,  539 
— food  and  digestion,  539 
— muscular  activity,  541 
— nervous  sys'tem,  542 
— rate  and    depth   of   respiratory  move- 
ments, 538 
— species,  537 
—sunlight,  539 
— temperature,  540 
Gastric  juic(%  acid  of,  226 

action  of,  digestive,  beginning  of  the,  225 
on  carbohydrates  and  fats,  235 
on  the  albuminoids,  235 
analvsis  of,  226 
artificial,  229 
chlorides  of,  reaction  in  decomposition  of 

the,  228 
color,  reaction,  and  order  of,  226 
free  acid  of,  22(),  227 
free  mineral  acids  of,  color  tests  for,  227 
non-digestion  of  the  stomach  by  the,  236 
non-jmtrefaction  of,  226 
normal,  methods  of  obtaining,  225 
origin  of  the  HCl  of,  227 
properties  and  composition  of,  226 
specific  gravity  of,  226.     See  also  Secretion. 
Gelatin  a  typical  albuminoid,  215 

nutritive  value  of,  288,  289 
Gelatoses,  235 

Generative  organs.     See  Orgmis. 
Germ-cells  of  the  female.     See  Ova. 
of  the  male.     See  Spermatozoa. 
-plasm,  9.36,  937 
Gestation,  duration  of,  916 
Gland,  adrenal,  210 

mammary,  epithelial  cells  of  resting,  202 

influence  of  the  uterus  on  the,  204 
pancreatic,    histological   changes    in,    during 
activity,  174 
histological  characters  of,  172 
parotid,  cerebral  fibres  of  the,  course  of,  159 
histological  structure  of,  160 
nerve-fibres  of  the,  159 
position  of  the,  158 
pituitary,  211 
prostate,  886 


Gland,  salivary,  electrical  changes  in,  during 
activity  of,  172 
secretory,  defined.  152 
sublingual,  histological  structure  of,  160 

])osition  of,  15K 
submaxillary,  histological  structure  of,  160 

position  of,  158 
tubular,  comi)ound,  153 
and  racemose,  153 
Gland-cells,  connection  between  the  secretory 
nerve-fibres  and,  161 
fundic,  of  the  stomach,  histological  character- 
istics of,  178 
of  the  gastric  mucous  membrane,  histological 

characteristics  of,  17^ 
participation   of,  in  the  formation  of  secre- 
tions, 155 
pyloric,  histological  characteristics,  178 
Gland-ducts,  cutaneous,  197 

pancreatic,  238 
Gland-secretion,  153,  154 

of  organic  material,  conditions  determining 
the,  164.  1()5 
Glands,  albuminous,  156 

histological  changes  in,  during  activity,  167 
cutaneous,  secretory,  197 
gastric,  histological   changes   in  the,  during 

secretion,  182' 
influence  of  the,  on  the  growth  of  the  nervous 

system,  737 
intestinal,  secretion  of  the,  246 
mammary,  201-205 

histological  changes  during  secretion,  202 
histology  of  the,  201 
mucous,  1.56 

changes  in,  during  activity,  167,  169 
of  Brunner,  184 
of  C'owper,  885,  887 
of  Lieberkiihn,  184 
of  Littre,  886 

of  the  gastric  mucous  membrane,  178 
of  the  kidney,  189-195 
of  the  liver,  secretory,  184-189 
of  the  stomach,  secretory,  172,  178-182 
salivary,  1.58-172 

action  of  drugs  u]ion  the,  170 

changes  in,  electrical,  during  activity,  172 

histological,  during  activity,  167 
nerve-fibres  of  the,  159 
number  of,  158 
secretions  of,  character  of,  160,  220 

method. of  obtaining,  162 
structure  of,  160 
sebaceous,  characteristics  of,  197 

distribution  of,  281 
secretory,  albuminous,  examples  of,  157 
classification  of,  153,  156,  157 
mucous,  exampk\s  of,  157 
of  the  intestines,  181 

secretions  of   the,  chemical  difl'erences  in, 
157 
seminal,  885 
stomach,  changes  in,  during  secretion,  182 

characteristics  of,  178 
sublingual,  uerve-libres  of  the,  160 
subniaxillarv,  nerve-fibres  of,  160 
sweat-,  198-200 
testicular,  211 

thyroid,  secretions  of,  207,  209,  210 
Glauber's  salt,  9()6 
Globulins,  .33.5,  1018 
Globulose  defined,  230,  11. 
(Glomerulus,  histology  of,  190 
Glutamin,  1000 
Glutoses,  235 
Glycerin,  1000 
aldehyde,  1001 


INDEX. 


1035 


GlvcLiin,    relation    of,    to  glycoKeu-lonuaiion, 

2tJSt 
Cxlycerose,  lUOl 
Glvcocoll,  J»yl 
Glycogen,  -'(itJ,  UIO.').  10()8 

conversion  (»1",  to  dextrose,  how  eftected,  209 

derived  from  earboliydrates,  functions  of,  2G9 
from  proteid  foods,  functions  of,  270 

end -prod  nets  of,  2()(j 

formula,  2t)(> 

function  of.  209.  270 

in  animal  and  vegetable  bodies,  extent  of  dis- 
tribution of,  270 

in  the  human  body,  270 

in  the  liver,  20."),  2(i7-270 

in  the  muscles  and  other  tissues,  value  of,  270 

muscle,  conditions  atlecting  the  suyiply  in,  270 

origin  of,  2(>7 

reaction  of,  26(5 
Glycogen-consumptiou  in  muscular  work,  300 

in  starvation,  301 
Glycogen-formation  defined,  269 
Glycogenic  theory,  269 
Glycolysis,  293 
Glyco-pioteids.  1019 
Glycoses,  the,  1004 

Glycosuria  from  removal  of  pancreas,  206,  207 
Goitre,  treatment  of,  with  thyroid  extracts,  209 
Graatian  follicles,  b92 
Grammeter,  584 

Granules,  cell,  of  the  gastric  glands,  183 
of  the  pancreatic  glands,  172 
of  the  parotid.  167-169 

zymogen,  169,  183 
Grape-sugar,  1005 

Growth-changes  of  the  body,  influence  of  thy- 
roid gland  on,  737 
of  the  brain,  724-732 
Guanidin,  993 

glvcolvl  methyl,  994 
Guanin,'996 

H^MATix,  335,  342,  1014 
Hsematogeu,  295 
Hismatoidin,  342,  1015 
Hajmatopoiesis,  343 
Haematoporphyriu,  312.  1015 
Haemerythriu.  1018 
Hsemin*  342,  1014 

medico-legal  value  of.  342 
Haemochroiuogeu,  335,  342,  1014 

molecular  formula  of,  336 
Haemoglobin,  335,  1014 
carbon -monoxide,  336 

absorption  spectrum  of,  342 
composition  of,  .3;i5  , 

compounds  of,  derivative,  342 

— bile-,  and  urinary  pigments,  343 
— hsematin,  .'i42 
— hsematoidin,  .342 
— hffimatoporphyrin,  342 
— hsemin,  342 
— hffimoehromogen,  342 
— histohsematins,  342 
— methsemoglobin,  342 
with  oxygen  and  other  gases,  366 
condition  of  the,  in  red  blood-corpuscles,  333 
crystallization  of,  337 
decomposition-products  of,  335 
distribution  of,  33.5 
molecule  of,  formula,  335 

presence  of  iron  in  the,  337 
nature  and  amount  of,  in  red  blood-corpuscles, 

335 
"reduced,"  336 
absorption  spectrum  of,  340,  341 
Hair-cells  of  Corti,  822,  824,  825 


Hand,  contractions  of,  fatigue  from  muscular,  77 

Harmony,  831 

"  Harveian  circulation,"  368 

Hawking,  .5(>2 

IICI,  origin  of,  in  the  gastric  juice.  227 

Head,  Vii-so-motor  nerves  of  the,  496 

Hearing,  sense  of,  807-i"^33 

cortical  centres  for  the,  696,697 
special  n<-rve  of,  679 
Heart,  beating.     See  Heart-beat. 
method  of  exjiosing  the,  405 
position  and  form  of,  changes  in,  404 
blood-pas.sages  in  the  frog's,  471 
changes  in  form  and  size  of,  during  ventric- 
ular systole  and  diastole,  406 
conduction  in  the,  means  of.  85 
contractions  of  the,  in  heat-production,  400, 
597 
without  fatigue,  77 
contraction-wave  of  the,  443 
cords  of  tlie,  tendinous,  and  their  uses,  401 
excitation-wave  of  the,  443-446 
impulse  or  apex-beat  of  the,  409 
innervation  of  the,  440-470 
irritability  of  the,  diminished  by  vagus  exci- 
tation, 455 
lymphatics  of  the,  477 
mammalian,  constituents  of  blood  of,  482 

nutrition  of  the,  482 
muscle-fibres  of  the,  84,  85 
nerves  of  the,  450 
centres  of,  467-470 
inhibitory,  452 
sensory,  463,  466 
vaso-motor,  497 
ventricular,  163 
nutrition  of  the,  471-482 
pulse-volume  of  the,  397,  .398 
pumping  mechanism  of  the,  370 
the  "  pause  "  or  "  repose  "  of  the,  414 
vagus  influence  on  the,  nature  of,  457 
stimulation  on  the.  effect  of,  4.53-457 
— action  on  bulbus  arteriosus,  455 
— arrest  in  systole,  456 
— changes  in  the  auricle,  455 
— changes  in  the  ventricle,  453 
— comparative  inhibitory  power,  456 
— diminished   irritability   of   the  heart, 

455 
— effects  of  varying  the  stimulus,  4.55 
— nature  of  vagus  influence  on  the  heart, 

457 
— septal  nerves  in  the  frog,  456 
valves  of  the,  mechanism  of,  400-404 
ventricle  of,  average    pulse-volume    of    the 

human,  398 
voluntary  control  of  the,  defined,  469. 
.See  also  Auricles,  Ventricles. 
Heart  and  arteries,  general  changes  in  the,  404 
and  vessels,  observation  of  changes  of  the,  in 
the  open  chest,  405 
— changes  in  the  beating  auricles,  407 
— changes  in  the  great  arteries,  407 
— clianges  in  the  great  veins,  407 
— changes  of  position  in  the  beating  ven- 
tricles, 406 
— changes  of  size  and  form  in  the  beating 
ventricles,  40.5 
Heart-beat,  alterations  in  the,  by  vagus  excita- 
tion. 4.52-458 
changes  in  the,  from  closure  of  the  coronary 

arteries,  473 
conditions  influencing  the,  413 
effect  of  carbon  dioxide  on  the.  481 

of  stimulation  of  augmentor  nerves,  460 
following  cessation  of  respiration,  553 
influence  of  oxygen  on  the,  481 


1036 


IXDEX. 


Heart-beat,  influence  of  sex  and  age  on  the,  412, 
413 
inhibition  of  the,  .vagus,  453^.">7 
maintenance  of  the,  artificial,  Martin's  ex- 
periment, 75 
"negative  impulse"  of  the,  409 
of  pregnancy,  91G 
phenomena  of  the,  396 
refractory  period  and  compensating  pause  of 

the,  447 
rhythmic,  cause  of,  440 
solutions  maintaining  the,  477,  479,  480,481 
precautions  to  be  observed  in  testing,  479 
stopping  of  the,  a  gradual  process,  929 
theory  of  muscular,  442 
nerve-,  of,  441 
Heart-beat  and  blood-supi)ly,  relation  of,  in  the 
coronary  circulation,  477 
and  bodv-temperature,  relationship  between, 
579 
Heart-beats,  frequency  of,  412. 
Heart-muscle,  failure  of  tetanus  in,  122 

function  and  contraction  of,  107 
Heart-muscles,  papillary,  and  their  uses,  402 
Heart-nerve,  depressor,  4fi4 

symi)athetic,  467 
Heart-nerves,  inhibitory  centre  of,  467 
irradiation,  468 
origin  of  the  nerve-fibres,  468 
tonus  of,  468 
Heart-sound,  first,  acoustic  analysis  of,  411,  412 

second,  cause  of,  410. 
Heat,  animal  body-,  575-604 

body-,  575-580.     See  Temperature. 
sexual,  animal.  898 
Heat-centres,  599,  713,  714 
Heat-dissipation,  channels  of,  592 
mechanism  of,  601 
physiology  of,  584-597 
Heat-dyspncea,  causation  of,  550 
Heat-production  after  death,  cause  of,  604 
by  muscular  energy,  amount  of,  132 
mechanism  of,  .59< 
physiology  of,  .597 
Heat-regulation  of  the  body.  602 
Helico-proteids,   1020 
Hemianopsia,  697 
Hemi-peptone,  231,  241 
Hemorrhage,  extent  of,  with  safe  recovery,  361 

regeneration  of  blood  after,  361 
Heredity.  22,  28,  931-942 
Hetero-jiroteose,  2.30 
Heteroxanthin,  996 
Hexoses.  1004 

Hibernation,   absorption    and    elimination    of 
gases  during,  542,  546 
effect  on  heat-production  of,  592 
Hiccough,  .563 
Histoha-matins,  342,  1018 

Histon.  action  of,  in  prevention  of  blood-coagu- 
lation, 356 
Homothemious  animals,  575 
Horopter,  804 
Hunger,  sense  of,  845 
Hydrate,  chloral,  980 
Hydration,  947 
Hydrazones,  977 
Hydrobilirubin.  1015 

of  the  feces,  260,  263 
Hvdroearbons  or  parafiins,  saturated,  975 
Hydrogen.  943.  944 
peioxide  of,  919 

preparation  and  properties  of,  943,  944 
sulphuretted,  950 
Hydrolysis,  94K 

of  enzymes  defined,  219 
Hydroquinone,  1011 


Hydroxide,  ethyl,  978 
Hypermetropia,  7.59 
Hyjierpnua  defined,  .548 
Hypoxanthin,  278,  995 

Illusions  op  touch,  840 

oi>tical,  794-803 
Images,  after-,  retinal,  791 

intraocular,  765 
Imbibition,  948 
Imidosarcin,  995 
Imido-xanthin,  996 
Impulse  or  apex-beat  of  the  heart,  409 
Incus,  the,  810,  811 
Indol,  260,  280,  lOlS 

P-methyl.  1013 
Induction  apparatus,  48,  54 
Inheritance,  facts  of,  931 

of  acquired  characters,  934 

of  disease,  9.35 

of  latent  characters,  932,  933 

theories  of,  936 
Inhibition,  cardiac,  seat  of  the  power  of,  4.52 
vagus,  4.52-457 

of  reflex  action  of  central  system,  667 

respiratory,  567,  570,  571 
Innervation,  dermal,  673 

of  the  blood-vessels,  482-501 

of  the  heart,  440-470 

of  the  jaw-muscles,  310 

of  the  lungs,  573 
Inosit,  1014 

Insane,  brain-weight  of  the,  722 
Inspiration,  mechanism  of,  506 

muscles  of.  .506,  513 
Inspiration  and  expiration,  relative  periods  o^ 

variations  in,  .532 
Intensit.v  of  light,  778,  785 
Intestine,  large,  absorption  in  the,  254 
digestion  in  the,  248 
gas  of  the,  composition  of,  260 

muscl(!-tissue  of  the,  contraction -wave  of,  309 

secretion  of  the,  246 

small,  absorption  in  the,  253 
Intestines,  decomposition  in  the,  bacterial,  248 

glands  of  the.  secretory,  184 

movements  of  the,  320 

— jiendular  movements,  322 
— I.eristalsis,  320-322 
conditions  influencing  the,  323 

nerves  of  the,  extrinsic,  322 
vaso-motor,  498 
Iodine,  9.53 
Iris,  the,  768 

movements  of  the,  muscular,  <  il 

muscles  of  the,  769 
Iron,  971 

compounds  of,  detection  of,  972 

in  animal  and  vegetable  foods,  absorption  and 
excretion  of,  295 

in  hsemoglobin,  presence  of,  337 

in  the  body,  972 

in  the  production  of  liaMuoglobin,  26.3,  295 
"  Iron-free  "  ha-matin,  .342 
Irradiation,  retinal,  794 
Irritability,  38-81 

alterations  of  electrotonic,  71 

induced  by  anelcctrotonic  and  katelectro- 
tonic  changes,  71 

anodic,  6f<,  69.  70,  72 

degree  of.  method  of  ascertaining,  38 

dependent  ujion  oxygen-supply,  73,  74 

duration  of,  as  aflected  by  temperature,  66 

efl'ect  of  enforced  rest  on,  81 
of  exercise  on,  80 

of  fretjnencv  of  application  of  stimulus  ou, 
72 


INDEX. 


lO'M 


Irritability,  effect  on,  from  separation  of  nerves 
from  the  ffiitral  mrvoiis  system,  75 
efficacy  ot"  tlic  hlood  to  preserve,  74,  75 
influence  of  tlie  lilood  on,  73 
kathodic,  ti«,  m,  70,  72 
loss  of,  by  separation  of  muscles,  76 

by  separation  of  nerves,  75,  7t> 
of  muscle,  defined,  :{."> 

curare  experinunt,  41 
independent,  40 
of  muscles  and  nerves,  conditions  which  deter- 
mine, (>4 
effect  of  heat  and  cold  on,  66 
of  nerves,  '^S-A 

— chemical  irritation,  40 
— electriial  irritation,  40 
— mechanical  irritation,  40 
— thermal  irritation,  40 
curare,  experiment  for  determining,  40,  41 
influence  of  constant ,  electric  currents  on 
the,  G9 
result  of  change  in  the  chemical  constitution 

of  muscles  and  nerves,  67,  68 
vital,  definition  of,  18 
Irritability  and  conductivity  of  nerve-fibres,  624 

and  contractility  of  ova,  37,  38 
Irritant,  electric  current  as  a  muscle  and  nerve, 

43-60.     See  Electric  current. 
Irritants,  classes  of,  38 
effect  of,  study  rf  the,  39 
efficiency  of,  on  muscles  and  nerves,  43 
influence  of,  upon  the  irritability  of  muscle 
and  nerve,  6.5 
— effect  of  chemicals  and  drugs,  67 
— effect  of  electric  current  upon  the  mus- 
cles, 68 
— effect  of  electric  current  upon  nerves,  69 
— effect  of  temperature,  66 
— effect  of  the  frequent  application  of  the 

stimulus  on  irritability,  72 
— mechanical  agencies,  65 
relative  value  of  different,  38 
Irritation,  direct,  of  muscle-protoplasm,  proofs 
of,  42 
nerve,  by  electric  current,  Du  Bois-Reymond's 
law,  47 
frequency  of  stimuli  and  effect  of,  65 
of   nerve  and  muscle,    result  of,  conditions 
determining,  42 
"Isodynamic  equivalent,"  304 
Isomaltose,  1007 
Iso-nitril,  an,  defined,  985 

Jauxdice,  causation  of,  189 

Jaw  movements,  muscles  concerned  in  the,  310 

Joint-movements,  classes  of,  856 

— ball-and-socket  joint,  857 

— hinge  joints,  856 

— saddle  joint,  857 

— sliding  joints,  856 
Joints,  union  of  bones  by,  855 

Kaeyokinesis  defined,  19,  20 
Katabolism  defined,  20 

of  animal  protoplasm,  20 
Katelectrotonus,  69 
Kathode  defined,  44 

phvsical  and  phvsiological  defined,  62  ' 
Kera'tin,  1020 
Ketone,  dimethvl,  982 
Kidney,  189,  273 

Kidneys,  blood-flow  through  the,  195 
action  of  dinretics  on  the,  195 
regulation  of,  by  the  vaso-motor  nerves, 
196,  197 

glands  of  the,  secretory,  189-195 

nerves  of  the,  vaso-motor,  498 


Knee-kick,   muscular    reaction    involved,  649- 
652 
reinforced  nerve-impulses  of,  665-686 
Kymograph,  the,  381 

Labor,  nature  of,  919,  920 

stages  of,  917-919.    See  also  Parturition. 
Labor-pains.  918 
Labyrinth,  the,  815 
meml)ranons,  815 
fluids  of,  .517 

transmission  of  vibrations  through  the,  820 
osseous,  structure  of,  815,  816 
Lactates  in  human  urine.  278 
Lacteals,  absorption  of  fat  by  the,  258 
Lactose,  202,  1006 

relations  of,  to  glycogen-formation,  268 
Laiiguuge  defined,  874 
Lanolin,  198 

Larynx,  appearance  of  the,  laryngoscopic,  869 
cartilages  of  the,  865 
movements  of  the,  516 
muscles  of  the,  865-868 
nerve-supply  of  the,  868 
self-examination  of,  method  of,  869 
stricture  of,  861-869 
ventricular  bands  of,  862,  863 
Latent  cliaracters,  inherited  human,  932 
heat,  iMrt 
period  defined,  101 

differentiation  of  electrical  and  mechanical, 

102 
in  retinal  sensation,  789 
of  muscular  contraction,  113,  114 
Laughing,  562 
Lecithin,  265,  1001 
Lens,  achromatic,  discoverv  of  the  principle  of 

the,  762 
Leucin,  242,  983 

Leucocytes,  blood-,  action  of,  346,  374 
classification  of,  345,  346 
— lymphocytes,  345 
— mononuclear,  346 
— polymorphous  or  poly  nucleated,  346 
emigration  of,  346,  376 
functions  of,  C  '5,  346 
movements  of,  35 

amoeboid,  346 
origin  of,  .347 
physiology  of,  345 
"  Leuconuclein,"  356 
Levulose,  218,  1005 

Life,  phenomena  of,  hypotheses  of,  25,  26 
Light,  "dispersion"  of,  778 
intensity  of,  778,  785 
modifications  r^',  779 
— color,  77j 
— color-blindness,  784 
— color-mixture,  779 
— color-theories,  781 
— intensity,  785 
— luminosity  of  colors,  786 
— saturation,  788 
retinal,  changes  produced  by,  776 
saturation  of,  7 .  .O,  7C8 
sensation  of,  retinal,  777,  778 
Limbs,  nerves  of  the,  vaso-motor,  501 
Lipochromes,  1015 
Liquor  amnii,  function  of,  911 

quantity  and  composition  of,  911 
Liver,  blood-flow  in  the,  relation  of  the  secretion 
of  bile  to  the,  187 
existence  of  secretory  nerves  to  the,  188 
extirpation  of,  effect  of,  on  urea  formation,  276, 

277 
functions  of  the,  260 
glands  of  the,  secretory,  184-189 


1038 


INDEX. 


Liver,  glycogen  in  tlio,  conditions  affecting  the 
.sujiply  of.  270 
function  of,  "Jfiii 
occurrence  and  origin  of,  "JOO,  267 

nerves  of  the,  vaso-iuotor,  49H 

relations  of  tlie,  to  the  circulation,  276 

secretions  of  the,  IK"),  'JO.j 

structure  of  the,  histological,  184 

urea  in  the.  formation  of,  271 

urea-forming  power  of  the,  271,  272 
Liver  and  sjileen,  physiology  of,  260-272 
Liver-cells.  t)lood-sui)ply  of,  sources  of,  187 

chemical  changes  hy  the,  184 

formation  of  urea  by  the,  271,  272,  275 

glvcogen  of  the,  267 

pllvsiologv  of  the,  260.  261 

relations  of  the,  to  the  ducts,  184,  185 

secretions  formed  by  the,  205,  206 
Locomotion,  body-,  860 

of  the  spermatozoa,  883,  903 

mechanisms  of,  8.")5-861 
Loop  of  Ilenle,  189.  190,  192 
Lumen  of  the  secretory  cells,  161 
Lung-pressure,  .')04,  .^05,  514,  516 
Lung-ventilation,  artificial,  laboratory  method 

of,  7m.\,  554,  561 
Lungs,  action  of  the  continuous  pull  of  the,  on 
the  blood-fiow,  387 

air  in  the,  admixture  and  jjurification  of,  522 
amount  of,  in  adult  human.  517 

alveoli  of  the.  number  and  size  of,  504 

blood-tluw  through  the,  395 

cai>illaries  of  the,  504 

elasticity  of  the,  504 

expansion  of,  in  the  new-born.  .504,  573 

fetal,  atelectatic  condition  of,  504 
in  utero,  573 

gases  in  the,  alterations  in  the,  517 

inflation  of  the,  artificial,  554 

iunervation  of  the,  .573 

nerves  of  the,  vaso-motor.  466 

O  and  CO2  absorbed  and  eliminated  by  the, 
quantity  of.  519 
diffusion  in  the.  forces  concerned  in,  520 

structure  of  the.  .504 
Lunuhe  of  the  semilunar  valves,  403 
Lutein,  1015 
Lymi>h,  .36.3-367 

aspiration  of,  thoracic,  439 

composition  of,  363 

formation   of,  filtration-and-diffusion  theory 
of,  362-367 

movement  of,  362,  363,  4.37-439 

occurrence  of,  .362 

origin  of  the,  4.3H 
Lymph-flow,  influence  of  body-movements  upon 

the,  4.39 
Lymph-hearts,  absence  of,  in  man.  438 
Lymph-pressure,  differences  of,  4:J8 
Lymph-valves,  body-movements  and  the,  439 
Lymphatic  system,  437 
Lymphocvtes,  345 
Lvsatin,  994 
Lvsatinin,  277,  994 
Lysin,  994 

Magnesium,  970 

carbonates.  971 

phf>sphates.  971 
Malleus,  the,  810,  811 
Maltose.  218,  247.  1007 
Mammalia,  removal  of  cerebral  hemispheres  of, 

effect  of,  710 
Mammary  glands.     See  Glandn. 
Man,  reproductive  power  of,  waning  period,  927 
Manometer,  differential,  422,  423 

elastic,  418,  419 


Manometer,  mercurial,  379,  380 

Manometers,  Uales',  378 

Marsh-gas,  976 

Mas.sage.  effect  of,  on  muscular  fatigue,  79 

Mastication,  310 

normal  salivary  flow  during,  the  result  of  re- 
flex action,  171 

taste-perception  developed  b3',  852 
Maturation  of  the  ovum.  889.  891 

of  the  spermatozoon.  Ks4.  892 
Meats  as  a  source  of  proteid-supply,  305 
Meconium,  biliary  salts  in,  987 
Medullary  sheath,  36.  151 
Medullation  in  central  nervous  .system,  616 

of  nerve-fibres.  614,  615 
significance  of,  729 
Melanins.  1015 
Menopause,  the,  898,  927 
Menstruation.  895 

amount  of  blood  discharged,  896 

appearance  of,  time  of.  927 

c(»nditions  aflecting.  897 

duration  and  onset.  896-898 

physiology  of.  comparative,  898 

process  oC  895,  896 

theory  of,  898,  899 
Mercaptan.  methvl.  9/< 
Metabolism,  bcKly-.  20,  282.  .302 
conditions  influencing.  298 
— effect  of  muscular  work,  298 
— effect  of  starvation,  301 
— efl'ect  of  variations  in  tem])erature,  300 
— metabolism  during  sleep,  .300 
total,  determination  of,  282-284 

in  the  ence]dialon  in  old  age,  743 

in  the  nerve-cells  in  old  age,  742 

of  carbon,  962 

of  cell-body,  626 

of  sulphur,  951 
Methffimoglobin,  342,  1014 
Methane.  975,  976 
Methyl  aldehyde,  977 

compounds.  976 

cyanide,  985 

mercaptan,  977 

seleuide,  978 

telluridc.  978 
Methylamine,  984 
"  Micellfe."  25 

Microcei)halics.  the  brain  of,  711,  720 
Micturition,  .327 

control  of  the  process  of,  329 

mechanism  of  normal.  32H 

— movements  of  the  bladder,  328 
— movements  of  the  ureters,  327 
— nervous  mechanism  of  the  bladder,  330 

normal,  a  reflex  act,  .329,  330 
" ilicturition-centre."  .329 
Milk.  conipositi(m  of,  201 

secretion  of  normal,  204 
Milk-coagulation,  rennin  process,  234 
Milk-<lucts  of  the  mamniiP,  201 
Milk-fat.  constituents  and  formation  of,  201,  203 
Milk-formation,  changes  in  the  cells  of  alveoli 

of  mammary  gland  during,  202 
Milk-plasma,  constituents  of.  201,  202 
Milk-sjilts.  secretion  of,  epithelial.  202 
Milk-sugar  or  lacto.se,  202,  247,  1006 
Mitosis.  20 
Molecule,  protoid.  size  of,  1021 

protoplasmic,  instability  of,  23,  24 
^Monoxide,  carbon,  fKiO 
Morula.  fHl9 

Mouth,  temperature  of  the.  577 
Mucin.  261 

bile.  265 

formation  and  function  of,  221 


INDEX. 


1039 


Mucin  of  >fol'li'l-f<'ll'<.  formation  of,  157,  15ti 

of  saliva,  amount  of,  I(j-J 
Mucins.  lOlil 

Mucous  glands.     See  Glands. 
membrane,  gastric,  composition  of  the  secre- 
tion of,  179 
glands  of  the,  structure,  178 
irritation    of,    ti  ininrature-sensation    not 

discriminated  by,  842 
irritation  of,  touch-sensation  not  induced 

by,  840 
olfactory,  850 
Murexid,  998 
Muscpe.  volitantes,  766 
Musearin,  986 

action  of,  on  the  lieart,  442 
Muscle,  "after-loaded,"  108 

altered  condition  of,  after  contraction,  109 
change  in,  iu  rigor  mortis,  144 
conijiosition  of,  '.i'Z 
conduction  in  both  directions  in,  86 
conductivity  of,  loss  and  recovery  of,  83 
contraction  of.     See  Contmction. 
contraction-wave   of,    length  of,  methods  of 
determining,  90 
rate  of  transmission  of,  88-90 
death  of,  chemical  change  in,  144 
digastric,  function  of,  310 
dying,  circumscribed  contraction  of,  42 
etlect  of  mechanical  stimulus  on,  93 
elasticity  of,  104 

changes  in  the.  conditions  influencing,  105 
excitation  of,   effect  of  rate,  on  height  and 
form  of  contraction,  109 
— continuous  contractions  caused  by  con- 
tinuous excitation,  123 
— effect  of    frequent    excitation    on  the 
height  of  separate  muscular  contrac- 
tions, 109 
— eflect  of  frequent  excitation  to  produce 

tetanus,  114 
— effect  of  frequent  excitations  upon  the 

form  of  separate  contractions,  113 
— effect  of  exceedingly  rapid  excitations, 

122 
— effect  of  gradually  increasing  the  rate 

of  excitation,  121 
— eflect  of,  upon  the  form  of  separate  con- 
tractions, 113,  114 
— explanation    of    the    great    height    of 

tetanic  contractions,  118 
— number  of  excitations  required  to  tetan- 

ize,  121 
— relative  intensity  of  tetanus  and  single 

contractions,  122 
— summary  of  the  efl'ects  of  rapid  excita- 
tion that  produce  tetanus,  121 
excitations,  double,  effect  of,  118,  119 
extensibility  and  elasticity  of,  104-106 

a  protection  against  injury,  106 
gases  of,  150 

glycogenetic  function  of,  270 
importance  of  the  blood-supply  to  the,  75 

of  the  circulation  to  the,  73 
injured,  "diminution  effect"  upon,  141 

tetanized,  changes  of  electric  potential  in, 
140 
intestinal,  of  the  fly,  structure  of,  84 
irritability  of,  independent,  40-42 
curare  experiment,  41 
conditions  which  determine  the  effect  of,  42 
"loaded,"  108 

masseter,  function  of  the,  310 
omohyoid  and  pectoralis,  of  turtle,  contraction 

and  function  of,  107 
phenomena,  electric,  theories  of,  1.38 
pterygoid,  external,  function  of,  310 


Muscle,  pterygoid,  internal,  function,  310 
reaction    of    human,   to  electric    currents,  a 

means  of  diagnosis,  58 
rest  of,   neces.sjiry   to    restoration  of   normal 

condition,  109 
stapediu.s,  814 

stretching  of,  effect  of,  on  irritability,  G6 
striated,  conductivity  of,  82 

optical  pr<jperties  of,  during  rest  and  action, 

102 
contraction  of,  rapidity  of,  308 
temporal,  functifjii  of,  310 
tensor-lynipani,  Ml4 

tetanized,  amount  of  shortening. in,  122 
Muscle  and  nerve,  chemistry  of,  144-151 

conditions  which  determine  the  efficiency  of 

irritants  on,  43 
effect   of   constant   electric   current  on  the 

irritability  and  conductivity  of,  61 
electrical  phenomena  in,  i:j4-143 
excitation   of.  conditions  which   determine 

the  eflect  of,  42 
influences  favoring  the  maintenance  of  the 
normal  physiological  condition  of,  73 
irritability   of,  influence  of  irritants  upon 

the,  65 
irritant,   electric  i^urrent  as  an,   effect  of, 

43-60 
irritating  effect  of  induced  electric  currents, 
48 
of  the  electric  current,  43 
result  of,  conditions  determining  the,  42 
physiology  of,  general,  32 
reflex  movements  of,  41 
stimulating  effects  of  making  and  breaking 
the  direct  electric  current,  50 
Muscle -contraction,    influences    affecting    the 
activity  and  character  of  the,  106 
latent  period'  of,  101,  113,  114.     See  Contrac- 
tion. 
Muscle-contractions,  graphic  method  of  study, 

98-101 
Muscle-fibre,  structure  of,  histological,  103 
Muscle-fibres,  condtiction  in,  rate  of,  92 
Muscle-injury,  electrical  current  of,  138 
Muscle-plasma,  146,  147 

Muscle-protoplasm,  direct  irritation  of,  proofs  of, 
42 
irritability  of,  35,  40-42 
Muscle-serum,  constituents  of,  148-150 
Muscle-sounds,  124 
iluscle-spindles,  845 

Muscle-tissue  of  the  bladder,  histology  of,  328 
of  the  intestines,  contraction -wave  of,  309 
of  the  ureter,  contraction-wave  of,  309 
plain,  of  the  alimentary  canal,  307 
contraction  of,  308,  310 
"  tone  "  of,  defined,  309 
smooth,  conductivity  of,  82 
structure  of,  32,  33 
Muscle-tonus,  133 

Muscles,   abdominal,    contraction    of  the,   spas- 
modic, influence  of,  in  vomiting,  325 
functions  of,  515 
action  of  the,  in  standing,  859  _ 

upon  the  bones,  method  of,  857 
capacity  of  the,  for  work  or  exercise,  77 
chemical  changes  in,  73 
classes  of,  33 
concerned  in  the  act  of  vomiting,  326 

in  the  movements  of  the  jaw,  310 
condition   of,  following  removal  of  the  cere- 
bellum, 714 
conduction  in,  84 

rate  of,  88-90 
contraction  in   different,  rate  of,  with   their 
function,  107 


1040 


INDEX. 


Musclrs,  ort'iitin  «>f,  279 
ett'ect  of  electric  current  upon,  68 
endurance  of,  cU-lined,  80 
enforced  rest  of,  etlect  of,  81 
expinitory,  cliief,  525 

actioUfi  of,  515 
eye,  745,  74G 

nerve-supply  of  the,  746 
fatigue  of,  etlect  of,  7li 
glycotieu  in,  value  of,  270 
inspiratory  and  expiratory,  chief,  506,  513 
intercostal,  actions  of,  exemplitied,  510-512 

functions  of,  510,  512,  513,  515 
intestinal,  histology  of,  320 
intrinsic    laryngeal,    actions    and    origin   of, 

8()6-8(!8 
involuntary,  delined,  33 
jaw,  innervation  of,  mode  of,  310 
laryngeal,  intrinsic,  86t>-868 

— aryteno-epiglottidian,  867,  868 
— arytenoid,  867 
— crico-arytenoid,  lateral,  866 
— crico-arytenoid,  posterior,  866,  867 
— crico-thyroid,  866 
— thyro-arytenoid,  868 
levator,  functions  of  the,  510,  513 

ani,  function  of,  515 
movements  of  the  rib,  controlling  the,  509 
myosin  of,  1018 
nerves  of  the,  vaso-motor,  501 
non-striated,  33 
of   inspiration,  contraction  of,  action  on  the 

blood-flow  of,  387 
of  the  iris,  769 
of  the  larynx,  865-868 
of  the  middle  ear,  814 
of  the  vagina,  900 
oxidization  jjroccsses  of,  73,  74 
quadrati  luniborum,  function  of,  507,  513 
reaction  of.  to  electric  current,  57 
rectiil,  physiology  of,  324 
recuperative  power  of,  77-79 
relations  between   separate    contractions  and 

tetanus  of,  123 
scaleni,  function  of,  509,  513 
serrati  postici,  functions  of,  510-513 
skeletal,  84 
and  the  venous  valves,  action  on  the  blood- 
flow  of,  387 
relation  of,  to  heat-production,  597 
striated  or  striped,  33 

apj)earance  of,  after  contraction,  104 
contractions  of,  diflerences  in  duration  of. 

106 
excitation  of,  rate  of,  122 
function  of,  98 

properties  of,  optical,  during  rest  and  action, 
102 
structure  of,  102-104 
ten.sion  of.  sense-perception  of  the,  844 
thoracic,  512,  513 

triangulares  sterni,  function  of,  515 
uterine,  895 

use  and  disuse  of,  efiect  of,  80 
voluntary,  defined,  3.3 
Muscles  and  nerves,  changes  in.  influenced  by 
the  eflects  of  batterj*  currents,  69 
conduction     of,      protoplasmic     continuity 
essential  to,  82 
in  both  directions,  86 
influences    which      alter    the    rate    and 

strength  of  the  process,  92 
isolated,  83 
rate  of,  88 
efiect  of  influences  which  result  from  func- 
tional activity  of,  76 
— ett'ect  of  enforced  rest,  81 


Muscles  and  nerves : 

— eflect  of  use  and  disuse,  80 
— fatigue  of  muscles,  76 
— fatigue  of  nerves,  79 
irritabilitv  of,  conditions  which  determine 
the,  64 
etfect  of  heat  and  cold  on  the,  66 
transmission  of  excitation  to,  by  end-organs, 
H5 
Muscular  activity,  dyspncua  of,  552 

eflict  of,  on  tiie  resi)iratory  quotient,  546 
influence  of,  on  body-temperature,  578 
influence  of,  on  heat-dissiiiation,  595 
on  the  volume  of  gases  respired,  .541 
mechanisms,  s])ecial  ])liysiology  of,  85.5-877 
Musical  note,  highest,  number  of  impulses  pro- 
ducing the,  778 
Mydriatics,  771 
Myogram,  the,  50,  101 

of  simple  muscle-contraction,  101 
Myogniph,  50,  51,  99 

double,  experiments  with  the,  52 
Myopia,  759 
Myosin,  147,  148 
Myotics.  771 
Myrosin,  218 

Myxoedema,  treatment  of,  with  thyroid  extracts, 
208,  209 

Nativk  albumins,  349 
"  Negative  variation  current,"  140 
Nerve,  auditory,  679,  818 
chorda  tympani,  course  of  the,  159,  160 
conductivity  of,  effect  of  .stretching  on,  93 
depressor,  effects  of  stimulation  of  the,  464 
dying,  eflect  of  mechanical  stimulation  on,  93 
end-organs  of,  importance  of.  839 
glosso-pharyngeal,  excitation  of  the,  eflect  on 

respiratory  movements  of,  570 
irritation  of,  chemical,  40 

conditions  determining  the  eflect  of,  42 
electrical,  40 
mechanical,  40 
temperatural,  47 
thermal,  40 
layngeal,  superior,  excitation  of  the,  eflect  of^ 

on  respiratory  movements,  570 
of  Jacobson,  159 
olfactory,  682 
optic,  679 

relations  of  afferent  fibres  in  the,  680 
pressure  upon  a.  irritating  eflect  of.  47 
reaction  of  a,  eflect  of  making  and  breaking 

induction  shocks  on  the,  49 
relation  of  the  strength  of  a  current  to  the 

irritating  eflect  upon  a.  test  of.  54 
sen.sory,  excitation  of,  efl'ect  of  mechanical,  65 
separation  of  a.  break  in  conductivity  by,  82 
stretching  a.  effect  of.  on  irritability,  65 
sympathetic,  effect  of  stimulation  of  the,  467 
ulnar,  effect  of  jiressurc  on  the.  93 

excifcition  of  the,  eflect  of  ice-water  on  the,66 
vagus,  of  the  dog,  morphology  of,  450 
Nerve  and  mn.scle  protoplasm,  resemblance  of, 

30,  37 
Nerve-cell,  anatomical  characteristics  of,  607 
bodies,  sizes  and  shai>es  of,  607,  608 

volume  relations  of,  608 
body,  im])ulses  on  the,  effect  of,  622 
metabolism  of.  6C<» 
points  of  the.  at  which  the  nerve-impulse 

can  be  aroused,  624 
shape  of,  sigTiificance  of,  622 
structure  of,  608 
chemical  changes  in,  626 
defined,  607 
fatigue  of,  influence  of,  628 


INDEX. 


1041 


Nerve-cell,  maturing  of  the,  611 

nutritiuii  of  thi',  iufluciices  acting  on  the, 

62U  «:«» 
physiology  of  the,  (iOT-fi.'JJt 
single,  nerve-iMipiilso,  vvitliin  a,  618 
spinal-cord,  volume  of,  (!11 
stimuli   neeessary  to  elicit  a  response  in  a, 

nuinlter  of,  62.") 
tropiiic  iulliieiices  on  the,  627 
Nerve-cells,  ehanges  in,  due  to  age,  617 
classes  of,  defined,  641 
cytoplasm  of,  ciuinges  in  the,  617 
disuse  of,   elfeet  of,  upon   reflex  action   of 

nerve-lihres,  iii'A^ 
efferent,  sympathetic  relations  of  the,  654 
forms  of,  (>07 

groups  of,  in  central  nervous  system,  639 
growtii  of,  610 

impulses  of,  rate  of  discharge  of,  623 
in  central  nervous  system,  number  of,  731 
increase  in  the  mass  of,  731 

in  the  number  of,  in  central  nervous  sys- 
tem, 727,  728 
location  of,  3() 
medulJation  of,  614 
metal>olism  in,  in  old  age,  742 
peculiarilics  of,  6(t8 
size  and  function  of,  (ilO 

in  ditfcreiit  animals,  609 
types  of,  612,  613 
unipolar,  441 
vaso-motor,  4H8,  489 
Nerve-elements,  classification  of,  641 

degeneration  and  regeneration  of,  633 
enlargement  in  tlie,  average,  731 
functional,  increase  in  the  number  of,  in 
central  system,  727 
Nerve-fibre,  axis-cylinder,  conductivity  of,  82 
branches,  growth  of,  613 
chemical  reaction  of,  151 
composition  of,  150,  151 
defined,  607 

degeneration  and  regeneration  of,  52,  82 
injured,  absorption-process  following,  82,  83 

recovery,  functional,  83 
irritability  and  conductivity  of,  624 
Nerve-fibres,  afferent  or  centripetal,  36 
of  spinal  cord,  645 
arrangement  of,  36 
association,  cortical,  697 
auditory,  of  the  cochlea,  821 

terminations  of,  815-818 
cardiac  inhibitory,  origin  of,  468 
cerebral,  of  the  salivary  glands,  1.59,  160 

varieties  of,  729 
cholesterin  of,  264 
classes  of,  36 

— medullated,  36 
— non-mednllatud,  36 
constrictor,  of  the  pupils,  769,  770 
cortical,  increase  in  the,  729 
decussation  of,  647,  680,  681,  768 
degeneration  of,  after  hemisection  of  cord, 
669 
in  the  central  system,  6.34 
of  non-medulla'ted,  633 
of  nucleated  portion  of,  635 
secondary,  of  cortical,  687 
dependence  of,  on  the  blood-supply,  74 
diameters  of  the  neurons  of,  613 
dilator,  of  the  pupils,  769,  770 
dorsal  root,  number  of,  673 
efferent  or  centrifugal,  ,36 
extrinsic,  intestinal,  .322,  323 

of  the  stomach  muscles,  316,  319,  320 
function  of,  36 
"germinal,"  688 


Nerve-fibres,  glyco-secretory,  188 

growth  of  the  medullary  sheath  of,  615 

lecithin  of,  265 

meduilation  of,  <)14,  til."),  729 

motor,  of  the  gall-bladder,  188 

of  liver-ci^lls,  existence  of,  185 

of  salivary  glands,  l.">9 

of  sweat-glands,   199 

of  the  bladder,  330 

of  tlu!  eye-muscles,  746 

of  the  jiarotid,  159 

of  the  skin,  281,  835 

of  the  sphincter  ani,  324 

of  the  spleen,  272,  273 

of  the  stomach,  316 

olfactory,  8.50 

optic,  insensibility  of,  to  light,  774 

number  of,  770 
pressor  and  dejjressor,  494 
regeneration  of,  .58,  82,  6.36 
relation  of  medullary  sheath  and  axis-cyl- 
inder of,  to  the  central  system,  (il6 
to  the  p(5ri)theral  nervous  system,  615 
secretory,  action  of,  upon  the  formation  of 
bile,  188 
connection  between  the  gland-cells  and 

the,  l6l 
in  the  pancreas,  ])roof  of,  173,  174 
normal    function   of   the,   in   the  sympa- 
thetic, 171 
of  the  kidney,  191 
termination  of,  161 
theory  of,  1<)5,  166 
varieties  of,  l.")5 
sensory,  ending  of,  in  the  .skin,  835 

of  the  tongue,  8.52 
stimulation  and  changes  in  temperature  on, 

effect  of,  614,  615 
structure  of,  36 
trophic,  theory  of,  16.5,  166 
thermogenic,  598 
vaso-constrictor  of  the  kidneys,  action  of, 

196,  197 
vaso-dilator  of  the  kidneys,  action  of,  196, 

197 
vaso-motor  of  the  lungs,  574 
Nerve-impulse,  afferent,  of  the  cortex  composite 
character  of,  700 
defined,  40,  611 
direction  of  the,  619 
extension   of  the,  conditions  surrounding 

the,  619 
pathways  of  the,  double,  621 
points  in  the  cell-body  at  which  the,  can  be 

aroused,  624 
rate  of,  618,  738,  7.39 

theories  of  the  passage  of  the,  in  the  cen- 
tral system,  644 
within  a  single  nerve-cell,  618 
Nerve-impulses,  arrangement  of,  in  the  central 
system,  621 
course  of  the,  on  leaving  the  cortex,  695 
effect  of,  on  the  cell-body,  622 
efferent,  reaction  of,  660 
olfactorv,  pathwav  of,  682' 
pathways  of  the,  (318,  647-657,  668,  682 
sensory,  pathways  of,  668 
Nerve-injury,  electrical  current  of,  139 
Nerve-muscle  preparation,  49 
Nerve-roots,  afferent,  644,  645 
Nerve-supply  of  the  larynx,  868 
Nerve-theory  of  heart-beat,  441 
Nerve-tissnes,  specific  gravity  of,  7.32 
Nerve-tracts  in  the  central  system,  668 
Nerve-trunks,  direct   irritation   of,  excites  no 
sensations  of  temperature  and  touch, 
841,  842 


1042 


INDEX. 


Nene-tniiiks,  conduction  in,  83 
Nerves,  action  of  the,  on  the  pancreatic  secre- 
tion, 173 
auditory,  of  the  cochlea,  ftJl 
aufimentor,  course  of,  in  various  animals,  459 

stiniuhition  of,  ettects  of,  4(30 
branchiii};  of,  84 
cardiac,  430 

— au^nientor  nerves,  458 
— centrifugal  nerves,  462 
— centriin'tal  nerves,  463 
— inhibitory  nerves,  452 
centres  of  the,  467-47U 
— augnientor  centre,  469 
— inhibitory  centre,  467 
— intra-ventricular  centre,  470 
— peripheral  reflex  centres,  470 
division  of  the,  451 
inhibitory,  452 
chemical  chaufjes  in,  by  conduction,  96 
chemistry  of,  150 
concerned  in  the  reflex  action  of  deglutition, 

314 
conduction  in  both  directions  in,  86 

experimental  methods  of  determining,  87 
rate  of,  90 

— in  motor  nerves,  91 
— in  sensory  nerves,  92 
conductivity  of,  efl'ect  of  pressure  upon,  93 

effect  of  temperature  on  the,  93 
cutaneous,   excitation   of  the,  effect  on   the 

respiratory  movements  of,  571 
effect  of  electric  current  upon,  69 
on  normal  humaTi,  62 
of  sudden   alterations  in  the  intensity  of 
stimuli,  4(),  47 
electro-motive  force  of,  139 
extrinsic,  of  the  intestines,  322 

to  the  stomach  muscles,  319 
fatigue  of,  l)y  conduction,  79,  97 
influence  of  the,  ou  the  gastric  secretion,  180 
inhibitory,  defined,  36 
and  augmentor.  Pawlow's  classification,  462 
effect  of  simultaneous  stimulation  of,  461 
intracardiac,  440 

effects  of  stimulation  of  the,  463 
irritability  of,  38-40 

testing  anelectrotonic  and  katelectrotonic 
alterations  of,  69,  70 
irritation  of,  by  electrical  current,  Du  Bois- 

Reymond's  law,  47 
liberation  of  heat  in,  by  conduction,  96 
motor,  conduction  in  human,  91,  92 
defined,  36 

of  the  bile-vessels,  188 
of  common  sensation,  843 
of  special  sense,  effect  of  stimulation  of  the, 

467 
of  the  eye,  769-772 
of  the  spleen,  499 
olfactory,  excitation  of  the,  effect  of,  on  the 

respiratory  movements,  571 
pancreatic,  172 

phrenic,  result  of  section  of,  571 
pueumogastric,  573 
functions  of,  568-570 
pulnumary  branches  of,  573,  574 
reaction  of,  to  currents  of  gradually  increas- 
ing strength,  64 
respiratory,  afferent,  568 

efferent,  571 
sciatic  and  sensory,  excitation  of  the,  effect 

of,  on  respiration,  571 
secretory,  36.  162-164 

action  of  drugs  upon  the,  170 
existence  of,  to  the  liver,  188 
of  the  pancreas,  173 


Nerves,  sensory,  defined,  36 
of  the  muscles,  844,  845 
stimulation  of  the,  effect  of,  466 
septal,  effect  of  vagus  excitation  on  tlie,  of  a 

frog,  456 
splanchnic,  excitation  of  the,  effect  of,  on  the 

respiration,  571 
sweat-,  19!» 

sympathetic,  pulmonary,  574 
temperature,  840-842 
thermogenic,  598 
trigeminal,  excitation  of  the,  effect  on   the 

respiration  of,  591 
"  trophic."  defined,  36 
vagus,  stimulation  of  the,  effects  of,  463 
vaso-dilator,  early  demonstration  of,  484 
vaso-motor,  defined,  36 

differences    between    the   constrictors    and 

dilators  of  the,  487 
early  exi)erimental  demonstrations  of,  482- 

486 
observation  of,  methods  of,  486 
origin  and  course  of,  488 
reflex  excitation  of,  492 
topography  of,  494 
— of  the  back,  501 
—of  tlie  bladder,  500 
— of  the  brain,  494 

— of  the  external  generative  organs,  499 
—of  the  head,  496 
—of  the  heart,  497 

— of  the  internal  generative  organs,  500 
— of  the  intestines,  498 
—of  the  kidnevs,  498 
—of  the  limbs,  501 
—of  the  liver,  498 
— of  the  lungs,  496 
— of  the  muscles,  501 
— of  the  portal  system,  501  ' 

— of  the  spleen,  499 
—of  the  tail.  501 
ventricular,  463 
distribution  of,  440 
Nerves  and   muscles  of  cold-blooded   animals, 
effect  of  irritants  l)est  studied  l).y,  39 
Nervous  system,  alterations  in  the,  due  to  preg- 
nancy, 916 
central,  605-743 

activities  of  the,  summary  of,  656 

anatomy  of  the,  physiological,  644 

architecture  of,  general,  639 

asymmetry  of,  723 

cells  in  the,  number  of,  731 

circulation  in  the,  734-737 

conditions  of  the,  during  sleep,  740 

conditions  of  the,  favoring  sleep,  739 

connections  between  cells  in  the,  643 

constituents  of  the,  716 

development   in   different  parts  of   the, 

relative,  642 
development  of  the,  defective,  734 
effect  of  fatigue  on  the,  737 
effect  of  loss  of  .sleep  on  the,  742 
effect  of  removal  of  cerebral  hemispheres, 

705-715 
effect  of  starvation  on  the,  737 
influence  of  tlie.  on  gastric  secretion,  180 
growth  and  organization,  606 
growtii  of,  influence  of  glands  on  the,  737 
medullation  in,  616 
nerve-elements   of  the,  cla.ssification   of, 

641 
nerve-elements  of  the,  increa.se  in  num- 
ber of  functional.  727 
nerve-fibres  in  the,  degeneration  of,  634, 

669,  670 
nerve-impulses  of  tlie,  arrangement  of,621 


TNDEX. 


i()4;i 


NtTVOussvstL'iii,  mrvi'-iniiuilsfs  of  tlu',  diffusion 
'of,  (MS,  (;r)-2,  (i.j:{ 
nerve-iinimlsis  i»l'  tlie,  evideucc  of  con- 
tinuous outfjoing  of,  6.55 
uerve-impulses  of    tlit-,    theories   of  the 

passage  of  till',  (>44 
ncrve-traots  in  tht-,  (ids 
nerves  of  the,  specific  afferent,  673 
— auditory,  67!> 
— olfacfory,  682 
— optic,  <)7y 

— special  nerves  of  pain,  674 
old  age  of  the,  742,  743 
organization  of,  642,  734 
organization  and  nutrition  of  the,  732-739 
pathways  of  the,  64s.  670,  67.5 
phenomena  of  the,  involving  conscious- 
ness, 60(i 
physiology  of  the,  comparative,  703-705 
pn'ncsscs  in  the,  time  taken  in,  738 
reaction  of  the  efferent  impulses,  660 
reactions  of,  from  fractures  of  the  spinal 

cord,  660 
reactions  of,  during  sleep,  740,  741 
reactions  of  the  spinal  cord,  segmental, 6.58 
reflex  action  of,  6.57-667 
relations  between  body-weight  and,  719 
stimulation  of  the.  conditions  of,  647 
strength  of  stimulus  and  strength  of  re- 
sponses of.  64S 
subdivisions  of,  60.5 
symmetry  of,  bilateral,  645,  723 
unity  of  "the,  60.5,  639 
sweat-centres  in,  200 
volume  of  the,  731 
changes  in  the,  dependent  upon  age,  715 
control  of  the  mammary  secretion  by  the, 

203 
disturbances  of  the,  influence  of,  on  body- 
temperature,  580 
influence  of  the,  on  functional  activity,  81 

on  heat-dissipation,  596 
physiology  of  the,  as  a  whole,  715 
sympathetic,  nerve-impulses  in  the 

sion  of,  6.54 
weight  of  the,  interpretations  of,  717 
Neuridin,  986 
Neurilemma,  36,  150 
Neurin,  986 

Neuroblast,  the,  610,  611 
Neuroblasts,  polarization  of,  611 
Neuro-keratin,  151,  1020 

Neuron,  axis-cylinder  of  the,  constitution  of, 614 
defined,  607 

form  of  the,  as  a  means  of  classification,  611 
structure  of  the,  607 
volume  of  the,  609 
Neurons,  medullation  of,  614-616 

size  of.  in  different  animals,  609 
Neutrophiles,  345 

New-born,  body-temperature  of,  .577 
expansion  of  the  lungs  in,  504,  573 
respiratory  movements  of,  573 
Nicotin,  action  of,  upon  the  salivary  glands  and 

their  secretions,  ITT) 
Nipple,  origin  of  the,  201 
Nitril  defined,  985 
Nitrogen,  954 
compounds  of  the  alcohol  radicals  with,  984 

with  oxygen,  9.56 
effect  of  respiration  of.  .548 
equilibrium,  defined,  284 
in  the  body,  956 
tension  of,  .525 
Nitrogenous  material,  determination  of  amount 

destroyed  in  the  body,  282 
"  Nceud  vital,"  564 


diffu- 


Noises,  832 

Non-nitrogenous    material,   determination    ot 

amount  destroyed  in  the  body,  283 
Nose,  tracts  of  tlie,  849 
Notes,  musical,  quality  of,  827,  828 
Nuclein,  1019 
Nucleo-albuniins,  1019 
Nucleo-histon,  347,  .356,  1019,  1020 
Nucleo-proteids,  1019 
Nucleus,  cell-,  protoplasm  of  the,  differentiation 

from  cytoplasm  of,  22 
Nutriment,  effect  of,  on  muscular  fatigue,^  78 
Nutrition,  body-,  bile  not  essential  for,  261 
defined.  18,  19,  213 

of  the  embryo,  913 

of  the  placental  process  of,  914,  915 

of  the  heart,  461-482 

Odors,  detection  of,  by  sensations  of  smell,  8.50, 

851 
skin,  racial  and  individual,  851 
(l^sophagus,  deglutition  in  the,  312 
Oil,  emulsions  of,  artificial,  245 
Old  age.     See  Age. 
Olefines,  amines  of  the,  986 
Oncometer,  Roy's,  196 
Ophthalmometer,  the,  7.50,  765 
Ophthalmoscope,  the,  772 
"  Optogram,"  776 
Organ  of  Corti.     See  Corti. 
Organization.     See  Central  Nervous  System. 
Organs,  reproductive,  female,  887-901 
male,  882-887 

mechanical  and  pathological  changes  in  the 
female,  due  to  pregnancy,  915,  916 
respiratory.  .503 
secretory,  internal,  205-211 
sexual,  classification  of,  882 
'      vocal,  107,  870-877 
Ornithin.  994 
Osazones,  1004 
Osmometer,  251 
Osmosis,  2.50-252 
Ossicles,  auditory,  810 
function  of,  813 
ligaments  of  the,  811 
Otoliths  or  otoconia,  819,  849 
Ova,  irritability  and  contractility  of,  37,  38 
movements  of,  amoeboid,  37,  38 
primitive,  number  of,  in  the  ovaries,  892 
Ovaries,  primitive  ova  in,  number  of,  892 

structure  of  the,  892 
Ovary,  the,  892 
Overtones,  musical,  827 

inharmonic,  830 
Ovulation,  892-894 
Ovum,  the,  888 

action  of  the  spermatozoa  in  entering  the,  904 
chemistry  of  the,  889 

chromosomes  of,  power  of  hereditary  transmis- 
sion due  to  the,  22,  28 
fertilization  of,  904-906 
growth  of  the,  uterine,  911 
human  and  fowl's,  compared,  888,  913 
discovery  of,  888 
form  and  size  of,  888 
structure  of,  888,  889 
impregnation  of,  movements  during  the,  37, 38 
maturation  of  the,  889-891 
nucleolus  of  the,  889 
nucleus  of  the,  888 
nutrition  of  the,  mode  of,  37 
protoplasm  of,  37 

reception  of  the,  by  the  Fallopian  tube,  894 
segmentation  of  the,  907,  908 
Oxidation,  body-,  Hoppe-Seyler's  theory  of,  949 
Traube's  theory  of  causation,  946 


1044 


INDEX. 


Oxick'.  iiitrif,  95(1 

uitroiis, !)")() 
Oxvl'eii/.ol,  KtlO 
Oxyrholiii.  Of^U 
Oxytri'ii,  !>ll 
jibsorptioii-ciiinK'itios  of  tissues  for,  530 

-coi'lliciiiit  of  blood  lor,  523 
conipouiuls,  5)56,  958 
ottict  of  nspiration  of,  548 
iiiflueiu'c  of,  on  the  heart-beat,  481 
of  uuisclo,  150 

preparation  and  properties  of,  945 
reduction  defined,  946 
Oxygen   and   CO2,  ditfusion   of,  in    the  luugs, 
forces  concerned  in,  520 
interchange  of,  between  the  alveoli  and  the 
blood,  522,  525 
between  the  blood  and  tissues,  527 
jtroportion  of,  in  the  blood,  519 

in  room-ventilation,  547 
([uantity  of,  absorbed  and  eliminated,  518 
tension  of,  523 

volumes  of,  respired,  53fi 
Oxygen,  CO2,  and  N,  absorption-coefficients  of 
water  for,  522 
and  other  gases,  compounds  of  haemoglobin 
with,  33(5 
Oxygeu-dysimcea,  cause  of,  550,  551 
()xyhtemoglol)iii,  336 

absorption  spectrum  of,  339,  340 
Oxyphiles,  345 
Ozone,  946,  947 

Pacinian  bodies,  836 
Pain,  842,  843 

special  nerves  of,  674 
Pains,  "sympathetic"  or  transferred,  844 
Pancreas,  172-17f> 

anatomical  relations  of  the,  172 
changes  during  activity  in  the,  174 
characters  of  the,  172 
consumption  of  sugar  by  the,  293 
removal  of  the,  result  of  the,  206 
secretion  of  the.     See  Secretion. 
Pancreatic  diabetes,  293 
juice,  action  of,  in  the  emulsification  of  fats, 
24() 
artificial,  240 
composition  of,  238,  239 
enzymes  of,  238-244 
— amylopsin,  243 
— steapsin,  244 
— trypsin,  239 
flow  of,  during  digestion,  rapidity  of,  176 
obtaining  the,  methods  of,  238 
Papilla;  of  the  tongue,  851,  K52 

sensitiveness  of,  to  stimuli,  854 
Paraffins  or  hydrocarbons,  saturated,  975 
Paraglobulin,  350 

amount  of,  in  the  blood,  351 
coagulation-temperature  of,  .351 
composition  and  reaction  of,  350,  351 
function  of,  351 
occurrence  and  origin  of,  351 
Paralvsis  agitaiis,  73,  743 
Paraiiuclein,  1019 
Parapcptone,  230 
Parathyroids,  207 
Paraxanthin,  !J'J6 

Parotid,  appearance  of,  after  stimulation,  168 
in  a  fresh  state,  16H 
in  a  resting  condition,  167 
changes  in,  following  stimulation,  167 
nerve-fibres  of  the,  159 
position  of,  15H 
structure  of,  160 
Parturition,  contractions  in,  uterine,  919,  920 


Parturition,  date  of,  estimating  the,  916 

mechanism  of,  917-919 
pate  de  foie  gras,  1002 
Pause,  resi)iratorv,  50(;,  532 
P-cresol,  1011 
Penis,  the,  H,>7 

erection  of,  mechanism  of,  902,  903 
Pen  tame  thy  lene-diamine,  986 
Pentyl  compounds,  983 
Pepsin,  action  of,  235 
on  proteids,  219 

nature  and  properties  of,  228 

preparations  of,  Briicke's  method,  229 
commercial  and  laboratory,  228 
Pepsin  and  trypsin,  ditt'erences  in  action  of,  241 
Peptones,  232,  1018 

absorption  of,  from  the  stomach,  253 

diftusibilitv  of,  233 

formation  of,  230-232 

])roperties  and  reactions  of,  232 
Peptones  and  proteoses,  analysis  of,  233 

conversion  of,  into  serum-albumin,  350 
Peristalsis  defined,  310 

intestinal,  320-322 

of  the  oesophagus  in  deglutition,  312 

of  the  stomach  during  digestion,  317 

of  the  ureters,  causation,  327 
Peroxide,  phosjihorus,  958 
Perspiration,  198,  281 
"  Pettenkofer's  test,"  988 
Phagocytes,  346 

Phagocytosis  theory  of  Metschnikoff,  346 
Phakoscope,  the,  754 
Pharynx,  deglutition  in  the,  311 

respiratorv  movements  of  the,  516 
Phenol,  280,"  1010 

Millon's  reagent,  1011 
Phenyl-hydroxide,  1010 
Phonation,  874 
Phosphate,  ferric,  972 

sodium-ammonium,  967 
Phosphates,  calcium,  967 

excreted,  derivation  of,  959 

magnesium,  971 

of  urine,  280 

potassium,  903 

sodium,  966 
Phospheues,  751 ,  777 
Phosphorus,  957 

compounds  of,  with  oxygen,  958 

detection  of,  958 

in  the  body,  959 
Phosphorus-i)oisouing,  957 
Physiology  defined,  17 

divisions  of,  17 

special,  ditlerentiation  of,  from  gt'ueral,  29,  30 

study  of,  experimental  methods  used  and  pre- 
liminary knowledge  required  in,  30,31 
Pia  and  fluid,  weight  of,  716 
Pigments,  bile.     See  BUe-piiimcntn. 

urinary,  i-elationship  of  hivmoglobin  to,  343 
Pilocarpine,  action  of,  upon  the  salivary  glands 

and  their  secretions,  170 
Pince  myograiihique  and  recording  tambour,  89 
Pinna  or  auricle,  807 
Pitch,  musical,  825,  826 
Pituitary  body,  internal  secretions  of,  211 
Placenta,  the,"  912 

relationship  of  the,  to  euibrvonic   nutrition, 
914,  915 
Plant-cell  assimilation,  18 
Plant-cells,  conductivity  in,  84 
Plants  and  animals,  structural  dissimilarity  of, 
17,  18 

enzymes  of,  218 
Plasma  (blood-),  coagulation  of,  147,  148 

composition  of,  347-349 


INDEX. 


1045 


Plasma,  "inert  laver  "  of,  in  small  blood- vessels, 
374 
proteids  of,  .'Mit 

pure,  method  of  obtaining,  360 
rogeneiation  of,  after  hemorrhage,  361 
"salted,"  :jr)7,  360 
structure  ami  color  of,  331 
I'Kiuroncctidic,  clironiotoblasts  of,  35 
l'ncuMH>»rapli  of  .Mai'cy,  r>31 
I'oikilotliermous  aninials,  575 
I'oisoninfj,  pliosi)lu)rus,  !)57 
Polymerization,  23 
I'olvpno'a,  causation  of,  550 
Tolyspcrmy,  !»()!» 

Portal  system,  vaso-motor  nerves  of  the,  501 
Post-mortem  rise  of  body-temperature,  145,  604 
Potassium,  i)(i3 
carbonates,  !)(i4 
chloride,  !»(>3 
cyanide,  9H5 
in  the  body,  f)64 
phosphates,  9()3 
sulphocyaiiidc,  221,  222 
thiocyauide,  !/\S(i 
Pregnancy,    influence    of,    on    the    mammary 
glands,  204,  915 
multiple,  920,  921 

physiological  eflects  upon  the  mother  of,  915 
position  of  fetus  at  end  of,  917 
sign  of,  urinary  coat  as  a,  968 
Presbyopia,  7()0 
Pressure,  blood-,  and  speed,  compared,  393 

arterial  and  venous,  method  of  studying, 

377 
capillarj-,  causation,  385 
symptoms  of  bleeding  in  relation  to,  383 
the  mean  arterial,  capillary,  and  venous, 

382 
venous,  causation,  386 
intrapulmonary,  505,  516 
intrathoraci  ,  505,  516 
sense  of.     See  Touch. 
upon  a  nerve,  irritating  effect  of,  47 
Pressure-curve,  ventricular,  and  the  auricular 
systole,  422 
and  the  valve-play,  422 
ventricular,  general  chai'acters  of,  419 
Pressure-points,  cutaneous,  839 
Pressure-sense,  tympanic  membrane  as  an  organ 

of,  826 
Propeptone,  230 
Prostate,  secretion  of  the,  885 
Protagon,  1001 
of  nerve,  151 
Proteid,  composition  of,  1016 
digestion,  products  of,  1021 
loss  of,  during  starvation,  302 
molecule,  size  of,  1021 
oxidization  of,  power  of  tissue  in,  286 
putrefaction,  products  of,  1021 
supply,  value  of  meats  as,  305 
synthesis,  experiments,  1021 
Proteids,  214,  1016 
absorption  of,  intestinal  and  stomach,  252-254 
action,  of  pepsin-hydrochloric  acid  on,  229 
bacterial,  upon  the,  products  of,  249 
of  pepsin  on,  products  of  digestion  in,  219 
animal-food,  digestibility  of,  217 
blood-,  346 

of  lymph,  363 
chromo-,  1018 
coagulated,  1018 
combined,  1018 
digestion  of,  214,  1021 
effect  of,  on  glycogen-formation  in  the  liver, 

268 
glyco-,  1019 


Proteids,  importance  of  nutritive,  to  the  body, 
211,285 
luxus  consumption  of,  288 
of  milk,  201 

of  muscle,  fractional   heat-coagulation  to  de- 
termine the,  148,  149 
nucleo  ,  1019 
of  tiie  l)lood-plasma,  349 
— fii)riiiogen,  3.50 
— paraglobulin,  350 
— serum  albumin,  349 
phos])ho-glyco-,  1020 
potential  energy  of,  303 
production  of  fiits  by  the,  290,  291 

of  glycogen  from,  2()8 
properties  of,  dependent  upon  the  presence  of 

inorganic  salts,  294 
putrefaction  of,  bacterial,  249 
reaction  of,  general,  1016 
remarks  on  the,  general,  1021 
vegetable,  digestibility  of,  217 
Proteose  defined,  230,  n. 
Proteoses,  230,  lOlH 
Protoplasm,  animal,  katabolism  of,  20 
synthetic  properties  of,  18 
cell,  continuity  of,  84,  85 
conductivity  of,  35 
contractu  itv  of,  32-35 
defined,  17,^943 

dying,  chemical  changes  in,  9.30 
irritability  of,  35 
irritating  effect  of  irritants   upon   different 

forms  of,  39 
living  and  dead,  differentiation,  18 
death  of,  molecular  change  in,  23 
divisions  of,  17 
instability  of,  23,  24 

specialization    of   function    of,    in    highly 
organized  animals,  21,  22 
muscle,  35,  40-42 
necessity  of  pi-oteids  for  the  formation  and 

preservation  of,  214 
nerve  and  muscle,  resemblance  of,  36,  37 
plant,  nutrition  of,  215 
primitive,  immortality  of,  930 
properties  of,  fundamental,  21 
structure  of,  molecular,  23-25 
vegetable,  synthetic  properties  of,  18 
Proto-proteose,  230 
Pseudo-mucoid,  1019 
Ptyalin,  218,  222,   1008 
action  of,  222 

conditions  influencing  the,  224 
— conditions  of  the  starch,  224 
— effect  of  reaction,  224 
— temperature,  224 
of  acids  on,  224 
specific,  in  saliva,  162 
Puberty,  926 
changes  at,  anatomical  and  physiological,  927 

voice,  871,  872 
period  of,  in  the  female  and  male,  927 
Pulsation,  cardiac.     See  Heart-heat. 
Pulse,  arterial,  385,  431 

celerity  of  stroke  of,  432 
dicrotic  wave  of,  435 
extinction  of  the,  386 
frequency  and  regularity  of,  432 
investigation  of  the,  by  the  finger,  432 
nature  and  importance  of,  431 
size  of  the,  433 
tension  of,  433 
transmission  of,  4.32 
"bounding."  defined,  433 
compressible  and  incompressible,  433 
"dicrotic,"  435 
digital  examination  of,  in  diagnosis,  432 


1046 


INDEX. 


Pulse,  effects  of  resjii ration  ou  the,  559 

resj)iratory,  in  the  veins  near  the  diest,  388 
varieties  of,  \'.V.\ 
venous,  Ut? 
Pulse-rate,  intlueneo  of  variations  in  body-tem- 
l)erature  on  the,  57!> 
relation  of  frequency  of   respirations  and 
the,  534 
Pulse-trace,  arterial,  434 

Pulse-volume,  average,  of  the  human  ventriclej 
3!),S 
defined,  3S)7 
force  exerted  upon  the  ventricles,  during 

each  systt)le,  3f»!) 
measuring  the,  methods  of.  397,  398 
of  the  heart,  variation  in,  397 
Pulse-wave,  dicrotic,  435 

transmission  of,  rate  of,  432 
Pupil,  changes  in  size  of,  method  of  observing, 
7()8 
contraction  and  dilatation  of,  769-771 
effects  of  drugs  ujion  the,  771 
reflex  action  of,  to  light,  7(59-772 
Purkiiije's  i)henomenou,  787,  788 
Putrefaction.  945 
liroteid,  intestinal,  248,  249 
products  of,  1021 
Putre.scin,  986 
"Pyramid  of  light,"  810 
Pyridin,  1012 
Pyrocatechin,  1011 

Race,  influence  of,  upon  body-growth,  926 
Races,  brain-weight  of  different,  722 

skin  odors  of,  851 
Radiation,  coetlicient  of,  596 
Reaction,  biuret,  of  urea,  992 

of  a  nerve,  effect  of  making  and  breaking  in- 
duction shocks  on  the,  49 

of  blood,  332 

of  efferent  nerve-impulses,  660 

of  muscle  in  rigor,  cause  of,  964 

of  muscles  and  nerves  to  electric  currents,  57 

of  nerve-tibre,  chemical,  151 

of  saliva,  221,  224 

of  sweat,  199,  281 

of  the  efferent  impulses  of  central  system,  660 

of  urine,  273,  274,  280 

produced  by  application  of  cold  to  the  body, 
603 
Reactions  of  enzymes,  218,  219 

of  intestinal  secretion,  247 

of  nervous  system,  involuntary,  651-667 
voluntary,  667-682 

proteid,  1016 
Rectum,  absorption  by  the,  2.55 

mu.scles  of  the,  function  of,  324 
Rectum  and  colon,  nerve-supply  of,  323 
Reflex  action  of  light  upon  the  jiupil,  769-772 
of  deglutition,  nerves  concerned  in  the,  314 
of  muscle  and  nerve,  41 
of  normal  salivary  flow  during  mastication, 

171 
of  the  central  nervous  system,  657-667 

contractions  of  uterus  during  labor,  919,  920 

excitation  of  vaso-motor  nerves.  492 

movements  of  muscle  and  nerve.  41 

of  spinal  cord,  in  lower  vertebrates,  703-705 
Reflex  and  voluntary  actions,  difference  between, 

667 
Regeneration  of  blood  after  hemorrhage,  361 

of  nerve-fibres.  .58,  82,  636 

pathological.  933 

physiological.  933 
Relief,  perception  of.  800 
Rennin,  218.  23.3,  234 

extracts,  method  of  obtaining,  234 


Reniiin-zymogen,  2.34 
Rei)rodu("tiou,  877-942 
asexual,  878 
bv  conjugation,  879 
defined,  IH.  20 
desire  and  power  of,  jjcriods  in  animals  of  the, 

898,  899 
double  function  of,  28 
organs  of,  female,  882,  887-901 

male,  882-887 
periods  of,  seasonal,  899 
process  of.  901-923 
sexual,  879 
theories  of,  880,  881 
Resemblances,  congenitiil,  hereditary,  932 

variations  in,  938 
Resonators,  829 
Respiration,  .503-.574 

appearance  of  the  larynx  in,  869 
artificial,  553 

laboratory  method  of,  .553,  554,  561 
average  rate  in  man,  533 
centre  of,  cxi)iratory,  565 
insi)irat<irv.  565 
ill  the  fitiis.  condition  of,  572 
location  of  the.  .563 
rhythmic  activity  of,  .566 
discharges  from  the,  causation,  567 
centres,  .56.3-567 
subsidiary,  565 
"Cheyne-Stokes,"  .532 
cutaneous,  530 

quantity  of  QO-i  exhaled,  .530 
influence  of.  internal  or  tissue-,  530 
on  licat-dissi])ati(>ii.  595 
on  heat-production.  590 
movements  r)f.  .503-516 

centre  of  the,  location  of,  563,  564 
effects  of  the  gaseous  composition  of  the  blood 
(m  the,  548 
on  blood-pressure,  555 
on  the  circulation,  555 
on  the  pulse,  5.5.5 
frequency  of,  533 

increase  in  dejith  of,  in  C'( )2-dyspn(Ea,  551 
influence  of  rate  and  depth  of  the  volume 

of  gases  exjiii'ed  on,  .538 
instrumental  recording  of,  531 
nervous  mechanism  of,  563 
of  the  new-born.  .573 

relative  periods  in,  variations  in  the,  532 
rhythm  of.  .5;',] 

jjcriodical  alterations  in,  .532,  533 
sequence  of,  rhythmic,  causation,  .566 
special,  561 

— coughing,  562 
— crying,  562 
—gargling,  563 
—hawking.  562 
— hiccough.  .563 
— laughing,  562 
— sneezing.  5(52 
— snoring.  563 
— sobbing,  562 
— yawning,  .562 
object  of,  517,  530 
of  various  gases,  effect  of,  548 
organs  of,  .503 
rate  of.  518 
conditions  affecting  the,  533,  534 
—age,  53.3 

— atmospheric  pressure,  .5.34 
— composition  of  inspired  air,  534 
— diurnal  changes.  5.33 
— emotions  and  will-power,  .534 
— posture,  533 
— respiratory  centres  and  nerves.  5.34 


INDEX. 


1047 


Respiration,  rate  of,  coiulitious  affecting  the : 
— season,  534 
— species,  fiUIJ 
— temperature,  5:51 
types  of,  5()() 
Kespinitor,  Ileriiiji's,  557 
Kespiratory  (luotient,  51S,  544 
conditions  afl'ectiug  the,  545 
— age,  546 

— conii)osition  of  the  inspired  air,  547 
—diet,  545 

— diurnal  variation,  546 
—muscular  activity,  546 
— species,  545 
— temperature,  546 
sounds,  517 
tract,  function  of,  849 
Rest,  muscular,  eflect  of  enforced,  81 

electrical  currents  of,  137-139 
Resuscitation  from  drowning,  553 
Retina,  the,  773 
activity  of  the,  oscillatory,  790 
after-images  of  the,  791 
"blind  spot"  in  the,  774 
blood-circulation  in  the,  768 
blood-vessels  of  the,  767 
changes  produced  in  the,  by  light,  776 
color  contrast  of  the,  792,  793 
sensations  upon  the,  778-788 
distance-perception  of  the,  799 
fatigue  of,  790 
irradiation  of,  794 
projection  of  inverted  images  on,  751 

of  a  shadow  on,  751 
rods  nnd  cones  of,  function  of,  773,  787 

structure  of,  775 
sensation  of  the,  persistence  of,  791 

of  light  on  the,  777,  778 
space-percei)tion  of  the,  793,  796 
structure  of  the,  773,  775 
stimulation  of,  phenomena  of,  788-791 
— after-effects,  791 
—fatigue,  790 
— latent  period,  789 
— rise  to  maximum  of  sensation,  789 
visual  purple  of  the,  776,  784,  1015 
Retinal  image,  size  of,  750 
Reversion,  hereditary,  932,  933 
Rheocord,  the,  56 
Rheometer,  the,  391 
Rheonome,  46 

Rheoscope,  physiological,  140 
Rheostat,  the,  55 
Rhythm  of  respiration,  531-533 
of  muscular  contractions,  738 
Ribs,  axes  of  rotation  of,  obliquity  of,  508 
eversiou  of  the,  508 
movements  of  the,  respiratory,  508 
of  the  intercostal  spaces,  509 
Rigor  caloris,  66 
"cataleptic,"  145 
mortis,  144 

appearance  and  duration,  145,  146 
disappearance  of,  147 
heat-production  during  development  of, 
influence  of  nerve-impulses  upon,  656 
reaction  of  muscle  in,  cause  of,  964 
Rima  glottidis  or  glottis,  863 

respiratoria,  863 
Ritter-Valli  law  of  irritability,  75 
"Rivalry  of  the  fields  of  vision,"  803 
Rods  and  cones.     See  Corti  and  Retina. 
Running,  mechanism  of,  861 

Saccharose,  1006 
Saliva,  action  of  ptyalin  on  the,  222 
conditions  influencing,  224 


Saliva,  anmunt  of,  secreted,  221 
analysis  of,  162,  221 
appearance  and  specific  gravity,  161 
glands  forming  tiie,  159 
origin  of  tlu-,  220 
physiological  value  of,  224 
properties  and  composition  of  mixed,  221 
reaction  of,  normal,  221,  224 
salts  of,  inorganic,  221 
specific  gravity  of,  161,  221 
Salivary  glands.     See  (Hands. 
Salt,  use  of,  by  herbivora  and  carnivora,  295 
Salt-solution,  physiological,  362 
Salts,  biliary,  9H7 

calcium,  excretion  of,  by  the  body,  296 

importance  of,  in  food,  296 
inorganic,  nutritive  value  of,  294 

reactions  of,  294 
iron,  importance  of,  to  body-metabolism,  295 
Saponification,  1000 
Saprin,  986 
Sarcin,  995 
Sarcolemma,  .32,  103 
Sarcoplasm,  conductivity  of,  82 
Sarcosin,  982 

Saturation  of  light,  779,  788 
Schneiderian  membrane,  849 
Sebum,  composition  of,  198 
Secretion,  152-211 
biliary,  activity  of,  formative,  186,  187 
digestive  function  of,  265 
normal  mechanism  of,  189 
physiology  of,  261 
quantity  of,  186,  187 

variations  in  ejection   from  the  liver,  186, 
187 
centre,  salivary,  171 

changes  in  the  gastric  glands  during,  182 
cutaneous,  197-204 

digestive,  exemption  of  tissues  from,  237 
double,  of  the  liver,  184 
effect  of  stimulation   of  secretory  fibres  on, 

163,  164 
from  stimulation  of  secretory  fibres,  nature 

of,  163,  164 
gastric,  cause  of,  during  normal  digestion,  181 
effect  of  chemical  stimulus  on  the,  182 

of  various  diets  on,  181 
influence  of  the  central  system  on,  180 
quantity  of,  variation  in,  181,  182 
rapidity  of  the,  during  digestion,  176,  177 
gland,  of  organic  material,  conditions  deter- 
mining, 164,  165 
internal,  of  reproductive  glands,  901 
intestinal,  action  of,  digestive,  246-248 
color  and  reaction  of,  247 
composition  of,  247 
method  of  obtaining,  246 
quantity  of,  184,  246,  247 
mammary,  composition  of,  201 
conditions  controlling  the,  203 
control  of  the,  by  the  nervous  system,  203 
influence  of  artificial  nerve-stimulation  on, 
204 
604  normal,  204 

of  seminal  vesicles,  885 
of  small  intestine,  246 

of  the  gastric  juice,  normal  mechanism  of,  181 
of  the  gastric  mucous  membrane,  acidity  of, 
226 
digestive  action  of,  225 
methods  of  obtaining,  225 
properties  and  composition,  179,  226 
of  the  liver,  composition  of,  185 
of  the  sweat-glands,  physiological  value,  281 
of  the  testis,  211 
pancreatic,  206,  238 


1048 


INDEX. 


Secretion,  pancreatic,  action  of  nerves  on,  173 
aniylolytic,  24:{,  244 
analysis  of,  173,  239 
characters  ol"  the,  238 
enzyme  and  zymogen  of,  176 
enzymes  of,  173 
normal  mechanism  of,  17(5 
properties  of,  238 
putrefaction  of,  239 
rellex  excitation  of,  by  stimuli,  177 
specific  gravity  of,  239 
jiyloric,  composition  of,  179 
relation  of  the  strength  of  stimulation  to  the 

cou>])(isition  of.  1(!4 
salivary,  antiparalytic  oraulilytic,  171 
composition  of.  Hil 
normal  n)echanism  of,  171 
paralytic.  170 
sebaceous,  197.  2H2 
composition  of,  282 
of  the  skin,  198 

of  un)pygal  glands  of  birds,  function  of,  198 
physiological  value  of,  282 
uriiuvry,  amount  of,  191 

conditions  inlhieiwiiig  the,  197 
nitrogenous  elements  of  the,  of  birds,  192 
of  water  and  siilts,  193,  194 
theoretical  considerations,  191-195 
Secretion  and  absorption,  i)henonieua,  27 
Secretions,  animal,  pro])erties  of,  27 
therapeutic  value  of,  210 
formation  of,  154 
gland,  composition  of,  153,  154 
internal,  2(tri-211 

—adrenal  bodies,  210 
—liver,  205 
■ — pancreas,  20G 
— pituitary  body,  211 
—testis,  211 
— thyroid,  207 
organs  of,  152 
of  the  gastric  mucous  membrane,  226-228 
of  the  liver,  205  > 

of  the  male  acces.sorv  sexual  organs,  885 
of  the  thyroids,  207-210,  901 
salivary,  action  of  drugs  on  the,  170 
method  of  obtaining,  1()2 
Segmentation  of  the  ovum,  907,  90S 
Selenide,  methyl,  978 
Semen,  the,  884 

amount  ejected,  884 
composition  of,  chemical,  804 
derivation  of.  884 

ejaculation  of,  in  copulation,  902,  903 
Semicircular  canals,  function  of,  846,  848 

structure  of,  816 
Seminal  vesicles,  885,  886 
Senescence,  928 

Sensation,  auditory,  theory  of,  824 
color,  phenomena  of,  779 
co-ordinated  movements  of,  83,  84 
muscular,  b34,  844 
of  light,  retinal,  777 

qualitative  modifications,  778 
retinal,  latent  ])eriod  in,  789 
of  white,  787 
persistence  of,  791 
rise  to  maximum  of,  789 
touch.     See  Toueh-sensation. 
Sen.sations,  common,  843 

c\itaneous  and  muscular,  694,  8.34-846 

of  consciousness  of  surrounding  objects,  826, 

834 
painful,  localization  of,  842 
temperature,  of  the  skin,  840-842 
Sense  of  equilibrium,  846 
of  hearing,  807-833 


Sense  of  pain,  842 

of  posture,  843 

of  .smell,  849 

of  taste,  851 

of  temperature,  840 

of  touch, 836-840 

of  vision,  696,  697,  744-806 
Sense-organs.     Sec  Eiid-or(ians  or  End-bulbs. 

functional  independence  of,  845 
Senses,  special,  744-854 
Sensibilitj',  cutaneous,  674 
Serum.    Sec  Blood-nerum. 

muscle,  148-150 
Serum-albumin,  349,  3.50 
Sex,  characters  of,  i)rimary  and  secondary,  881 

determination  of,  Hofacker-.Sadler  law,  922 

influence  of,  on  heat-dissi])ation,  592 

of  the  embryo,  determination  of,  821-923 

origin  of,  880 
Sexes,  body-growth  in  both,  relative  rapidity  of,  • 
926 

stature  and  weight  of  both,  after  birth,  925 
Sight.     Sec  Vision. 
Silica,  963 
Silicon,  962 

dioxide,  963 
"Sinuses"  of  Valsalva,  403 
Skatol,  260,  280,  1013 
"  Skiascopy,"  765 
Skin,  cold  and  warm  points  of,  841 

excretions  of  the,  281,  282 

functions  of  the,  281 

greasing  the,  ettect  of,  593 

nerve-fibres  in  the,  281.  H.'i") 

pressure-i)oints  of  the.  839  • 

pressure-sensibility     of     the,     discriminating 
diflerences  of,  tests,  836,  837 

respiration  of.     See  liespirafion. 

secretions  of,  197-204 
•    sensations  of  the,  cla.ssification  of,  834 

sense-perception  of  the,  diflerences  in,  841 

sensitiveness  of  the,  to  temperature,  840 

"tactile  areas"  of  the,  8:J8,  839 

temperature  of  the,  of  various  points  of  the 
body,  576 

temperaturc-seuse  of,  840 

touch-sensation  of  the,  8.36 
Skin-tenderness,    topographical    association    of, 

with  visceral  diseases,  844 
Sleep,  739-742 

body-metiibolism  during,  300 

body-temperature  during,  578 

cause  of,  740 

conditions  favoring,  7.39,  740 

loss  of,  742 
Smegma  prjeputii,  198 
Smell,  sense  of,  696,  849-851 
Sneezing,  .562 
Snoring,  .56.3 
Sobbing,  .562 
Sodium,  965-967 

carbonates,  966 

chloride,  965 

phosi>hates.  966 

sulphate,  96(> 
Sodium-ammonium  jihosphate.  967 
Solutions,  carbon-monoxide  haemoglobin,  prepa- 
rati(jn  of,  342 

maintaining  the  heart-beat,  4//-481 

oxyha-moglobin,    conversion    of.    into   haemo- 
globin solutions,  341 
"  Somacules,"  25 

Sound,   relation    l)etween  physical   and   physi- 
ological, 825-8.34.     See  Tone. 
Sound-perception,    functions  of  difl'erent  parts 
of  the  ear  to.  relative,  Ki2 
judgment  of  direction  and  distance  by,  833 


INDEX. 


1049 


Soiiud-sensatiou,  vibration-rate  necessary  to  pro- 
duce, fcf-J(> 
Sound-wavi's.  production  of,  825 
Sounds,  audible,  liuiit.s  of,  826 
heart-,  -110 

praitiial  ai)plication  of  observation  of,  410 
musieal,  analysis  of,  829 
respiratory,  517 
Spaee-perce|>tion,  illusions  of,  79(3-799 
Specilic  heat  of  the  body,  itl8 
Species,  elfect  of,  on  resj)iratory  (juotient,  545 
intluenee  of,  on  heat-dissipation,  592 
on  heat-])ro(luetion,  590 
on  the  respiratory  rate,  5.'J3 
on  the  voliinie  of  gases  resi)ired,  537 
Spectroscojje,  the,  '.V.\A,  339 
Spectrum,  absorption  of  bile,  262 
of  blood,  338 

of  carbon-monoxide  hajmoglobiu,  342 
of  Invmatin,  312 
of  methienioglobiu,  342 
of  oxyhiemoglol)in,  339,  340 
of  reduced  ha-moglobin,  340,- 341 
colors,  number  of,  778 
defined,  338 

intensity  of  the,  distribution  of  the,  786 
Speech,  861-877 

impairment  of,  cause  of,  698 
Speech  and  hearing  centres,  relations  of,  871 
"  Speech-centre,"  Broca's,  698 
Spermatocyte,  884 
Spermatozoa,  the,  882 

action  of  the,  in  entering  the  ovum,  904 
contractility  of,  35 
di.scovery  of,  882,  936 
duration  of  life  of  the,  903,  904 
locomotion  of  the,  883,  903 
maturation  of,  884 

passage  of  the,  time  required  in,  903 
presence  of,  in  the  testes  of  the  aged,  885 
production  of,  average,  883 
structure  of  human,  882,  883 
Spermatozoon  and  ovum,  place  of  union,  903 
Spermine,  211,  884 
Sphincter  ani  pylorici,  315 
of  the  cardiac  oriiice,  312 
pyloric,  315,  319 
urethras,  328 
vesicffi  internus,  328 
Sphincters,  rectal,  function  of,  324 
"  Sphygmogram,"  the,  434-436 
Sphygniograph,  the,  434 
Sphygmomanometer,  the,  433 
Spinal  cord,  nerve-libres  in  the,  ending  of,  85 
reactions  of  portions  of  the,  704 
weight  of  the,  723 
and  of  the  brain,  715-724 
Spirometer,  the,  535 
Spleen,  composition  of,  chemical,  273 
extirpation  of,  result  of,  272 
functions  of  the,  272,  273 
movements  of  the,  272 
nerves  of  the,  vaso-motor,  499 
theory  of   reproduction  of  blood-corpuscles, 
343 
"  Staircase  contractions,"  72,  110 
Standing,  muscular  action  in,  846,  859 
Stapedius  (muscle),  814 
Stapes,  the,  810,  812 
Starch,  1007 
action  of  amylolopsin  on,  243,  244 
animal,  1008 

conversion  of,  223.  224,  257 
digestion  of,  intestinal,  247 
Starvation,  effect  of,  on  body-metabolism,  301 

on  the  nervous  system,  737 
Stature,  decrease  of,  in  old  age,  929 


Stature  and  weight  of  both  sexes  at  birtb,  925 
Steapsin,  244 

action  of,  influence  of  temperature  on,  245 

reaction  of,  244 

value  of,  in  digesti<jn  and  absorption  of  fats, 
245 
Stenson's  duct,  1.58 
Stereoscope,  the,  801 
Sternum,  respiratory  movements  of,  509 
Stimulants,  action  of,  upon  the  pancreatic  secre- 
tion, 177 

as  articles  of  diet,  297 
Stimulation,  electrical,  of  the  cut  vagus,  results 
of,  568,  569 

muscle,   effect   of   artificial,   compared    with 
normal,  126 

nerve,  relation  of  tlie  composition  of  the  secre- 
tion to  the  strength  of,  164 

of  secretory  nerve-fibres,  effect  of,  163,  164 

retinal,  788,  791 

vagus,  effect  of,  on  the  heart,  453-457 
Stimuli,  number  of,  necessary  to  elicit  a  response 
in  a  nerve-cell,  625 

rapidly-repeated,   eflect    of,    on    muscle    and 
nerve,  72,  73 

reaction  to.    See  Reflex  action. 
Stokes'  reagent,  341,  u. 
Stomach,  absorption  in,  252,  2.53 

bacteria  of  the,  248 

coats  of  the,  315 

contents,  ejection  of  the,  318,  319,  325,  326 

digestion  in  the,  i)ei)tic,  228-232 

functions  of  the,  237 

glands  of  the,  secretory,  178-182 

movements  of  the,  315,  316 

muscles  of  the,  315,  319 

not  essential  in  digestion,  237 

physiology  of  the,  237 

secretions  of,  acidity  of,  226-228 

self-digestion  of,  exemption  from,  236 
Striae  gravidarum,  915 
Stromuhr,  the,  391 
Strontium,  970 
Strychnin,  influence  of,  on  the  dififusibility  of 

nerve  impulse,  652 
Succus  entericus,  184,  286 
Suffocation.     See  Asphyxia. 
Sugar  of  the  body,  292,  293 
Sugars,  absorption  of,  253,  257 
Sulphate,  calcium,  967 

sodium,  966 
Sulphates  of  urine,  conjugated,  279 

quantity  of,  280 
Sulphide,  ferro-,  972 
Sulphur,  949 

detection  of,  950 

metabolism  of,  951 
Suprarenal  capsules,  210 
Sutures,  union  of  bone  by,  855 
Swallowing,  act  of,  nervous  control  of,  314 

mechanism  of,  311-313,  866 

stages  of,  310,  311 
Sweat,  198-200,  281 

color  and  odor  of,  281 

composition  of,  198,  199,  281 

elimination  of  urea  in,  275 

influence  of,  on  heat-dissipation,  595 

reaction  of,  199,  281 

specifi(?gravity  of,  199,  281 
Sweat-centres,  in  central  system,  200 
Sweat-glands,  action  of  nerve-fibres  on,  199 

•    distribution  of  the,  281 
effect  of  drugs  on  the,  200 
effect  of  temperature  on  the,  200 
histology  of,  198 
number  of  human,  198 
secretion  of  the,  198-200 


1050 


INDEX. 


Sweat-nerves,  lt)i) 

Sweatiii);,  inol'iise,  cause  of,  200 

Sympathetic  jiaius,  844 

vibratiou,  ^29 
Symphyses,  85") 
Syiulesiuoses,  855 
Synovial  fluid,  855 
Synthesis,  962 

proteiil,  experiments,  1021 
Syntoniu,  2;50 

Syphilis,  transmission  of,  936 
Svstole.  arrest  of,  from  vafjus  stimulus,  456 
"auricular,  370,  396,  422,  427 

ventricular,  370,  396,  399,  415 
Systole  anil  diastole,  auricular,  relative  duration 
of  the,  and  of  the  pause,  416 
time  relations  of  the,  428 

Taste,  sense  of,  851 

cortical  centre  for  the,  696 
Taste-buds,  structure  of,  851 
Taste- perceptions  modified  by  sight  and  smell, 

852 
Taste-sensation,  contrasts  of,  854 
destruction  of,  854 
intensified  bv  mastication  and  swallowing, 

852 
primary,  853 
sensitiveness  of,  853 
Taurin,  951,  986 
Tea,  physiological  eflect  of,  297 
Teeth,  tartar  on  the,  968 
Telluride,  methyl,  978 
Temperature,  body,  575-604 
alniormal,  580 
conditions  afl'ecting,  577 
conduction  of,  from  part  to  part,  576 
constant,  defined,  581 
diminished,  defined,  58 
dissipation  of,  584-588,  592 
eflfect  of,  on  respiratory  quotient,  546 
evolution  of,  581.  582 
expenditure  and  income  of,  581-584 
increased,  defined,  581 
influence  of,  on  heat-dissipation,  594 

on  the  volume  of  gases  respired,  540 
mechanism  of,  597,  601 
of  animals,  methods  of  taking  the,  575 
of  different  regions  of  the  body,  576 
of  the  new-born,  577 
origin  of,  302 

post-mortem  rise  of,  145,  604 
production  of,  302,  584,  588,  589 
regulation  of,  580 
rise  and  fall  of,  576,  577 
specific,  948 
effect  of  on  conduction,  93 
on  muscular  contraction,  127 
on  elasticity  of  muscle,  105 
on  the  development  of  rigor,  145 
on  the  irritability  of  muscle  and  nerve,  65 
on  the  reaction  of  enzymes,  219 
external,  changes  in,  effect  on  irritability  and 
conductivity  of  nerve-fibres,  614,  615 
effect  of,  on  the  respiratory  quotient,  546 

on  the  sweat-glands,  200 
influence  of,  on  heat-dissipation,  594 
on  heat-production,  591 
on  the  volume  of  gases  respired,  540,  541 
upon  the  respirations,  566 
upon  the  respiratory  rate,  534 
reactions  produced  by,  603 
sense-perceptions  of,  840-842 
variations  in,  on  body-metabolism,  300 
on  the  oxidation  of  non-proteid  material 
in  the  body,  300 
of  blood  of  the  brain,  736 


Temperature  of  ex])ired  air,  518 
Temperature-sense  of  the  skin,  674,  840-842 
Tension,   muscular,   effect  on    the  extent  and 

course  of  contraction  of,  108 
Tessla,  experiment   of,  on   the  effect  of  rapid 

alternations  of  electric  currents,  58 
Testes,  embryonic,  structure  of,  885 
Testicular  extracts,  effect  of  injections  of,  on 

the  neuro-muscular  system,  901 
Testis,  the,  885,  886 

internal  secretion  of,  211 
Tetanus.  65,  73 

closing,  Wundt's,  52,  68,  123 

complete,  conditions  necessary  to  effect,  122 

continuous,  causation,  123 

duration  of  contracture  of,  122 

effect  of  double  excitation  on,  118-120 

of  frequent  excitations  to  produce,  114,  116 
effect  of  gradually  increasing  the  rate  of  ex- 
citation, 121 
effect  of  rai)id  excitations  to  produce,  117, 118, 

122 
explanation  of  the  great  height  of  contrac- 
tions in, 118-120 
height  and  strength  due  to  intensity  of  stimu- 
lus, 123 
incomplete,  effect  of  frequent  stimuli  to  pro- 
duce, 115 
and  contracture,  development  of,  by  indi- 
rect stimulation,  117 
intensity  of,  relative,  and  single  contractions, 

122 
method  of  exciting,  by  breaking  induction- 
shocks,  121 
number  of  excitations  required  to  produce,  121 
opening,  Rittcr's,  52,  68,  123 
production  of,  factors  in  the,  121 
secondary, 140 

summary  of  the  effects  of  rapid  excitation,  121 
"  Tetanus  muscles,"  122 
Tetramethvlene-diamine,  986 
Thein,  996" 
Theobromin,  996 
Theophyllin.  996 

Thermo-accelerator  centres,  599-601 
Thermogenesis,  .597 
Thermolysis,  .597,  601  . 
Thermoi)ile,  the,  133 
Thermo]iolvpnflca,  550 
Thermotaxis,  .597,  602-604 
Thiocyanide,  potassium,  986 
Thirst,  sense  of,  845 
"Thiry-Vvlla  fistula,"  246,  321 
Thorax,  .505 

inspiratory  changes  in  form  of  the,  .506 
muscles  of  the,  512 
Tlu-onihin,  218,  .355 
Thrombosin,  .356 
Thrombus  (blood),  3.58 
Thyreo-antitoxin,  210 

Thvroid  extracts,  therapeutic  value  of,  208.  209, 
901 
glands,  influence  on  growth-changes  of  the 

body  of,  737 
secretions  of  the,  internal,  207-210 
Thyroidalbumin,  210 
Thyroidectomy,  results  following,  208 
Thyroids,  207,"  208 

function  of  the,  208,209 
Thyro-iodin,  209,  953 
"Tidal  air"  (respiration),  534 
Tissue  differentiation,  22,  23 
Tissue- proteid,  285 
Tissue-respiration,  .530 
Tissues,  absorption-capacities  of,  for  O,  530 
death  of  the,  929 
effect  of  depriving,  of  blood,  73 


INDEX. 


1051 


Tissues,  embryonic,  growth  of,  924 
glycogen  in  the,  value  of,  270 
influence  of  activity  of,  on  body-temperature, 

57H 
musck'.     ^va  Muscle. 
nerve-,  si)ecilic  gravity  of,  732 
temperature  of  dillerent,  variations  in,  577 
thermogenic,  r)!)7 
Tissues  and  tlie  bh)()d,  interchange  of  O  and  CO2 
hetween  the,  527 
and  fluids  of  the  body,  importance  of  the  in- 
organic salts  to  the,  294 
and  organs,  efl'ect  of  starvation  upon,  301 
Tone,  musical,  diflerential,  831 
fundamental,  815,  827 
sensation  of,  production  of,  825 
"Tone"  of  muscle-tissue,  309 
Tones,  musical,  832 

combinational,  831,  832 
complex,  827 

composite,  analysis  of,  by  the  ear,  828 
concordant  and  discordant,  831 
factors  (letcrniining,  s;;! 
production  of  l)eats  in,  830 
Tongue,  nerves  of  the,  sensory,  852 
papilla^  of  the,  851,  852 

sensitivi'uess  of,  to  stimuli,  854 
tastc-iicrcciition  ))v  the,  points  of,  854 
"Touogi-aphs,"  419* 
Touch,  illusions  of,  840 
pressure  sensibility  to,  836,  837 
sense  of,  83(5-840 
Touch-corpuscles,  836 

Touch-sensation  and  stimulus,  relations  of,  836 
importance  of  the  nerve  end-organ  in,  839 
localization  of,  838,  839 
Tracts,  pyramidal,  size  of,  695 
Transfusion,  l)lood,  danger  attending,  362 
Transmissii)n,  hereditary,  22,  28,  931-942 
Traube-Hering  waves,  492 
Tremors,  muscle,  124 
Trichlormethane,  977 
Trimethvlamine,  985 
Trioses,  'lOOl 
Trypsin,  231,  239-241 

extracts,  methods  of  preparing,  240 
Trypsinogen,  176,  240 
Tryptophan,  1015 

Tubules,  uriniferous,  histologj'  of,  189,  190 
Tympanic  membrane,  809 

as  an  organ  of  pressure-sense,  826 
function  of,  815 

perforation  or  extirpation  of,  efi"ect  of,  815 
vibrations  of,  815,  820 
Tvmpanum,  the,  808 
Tyrosin,  242,  1011 

Units,  calorimetric,  584 

Urates,  deposition  of,  in  the  kidneys,  by  ligation 

of  ureters,  192 
Urea,  274,  991 

biuret  reaction  of,  992 

combustion-equivalent  of,  303 

derivation  of,  205,  206,  274-276 

elimination  from  urine  of,  192 
in  sweat,  275 
process  and  rate  of,  195 

formation  of,  in  the  liver,  271,  272,  275 

in  milk,  202,  275 

in  sweat,  199,  281 

in  the  body,  992 

in  the  urine,  274 

preparation  and  properties,  991,  992 

quantity  of,  eliminated,  274 
Ureter,  muscle-tissue  of  the,  contractioii-wave 

of,  309 
Ureters,  movements  of,  327 


Urethra,  the,  886 
Urination.     See  Micturition. 
Urine,  accunuilation  of,  in  the  bladder,  328 
amount  s«'creted,  191,  274 
color  of  the,  191,  273 
constituents  of.  191,  274-280 
— conjugated  suliihatcs,  279 
— creatinin,  278 
— hippuric  acid,  279 
— urea,  274 
— uric  acid,  277 
— water  and  salts,  280 
— xanthin  bodies,  277 
creatinin  in,  278,  279 

elimination  of  nrea  and  related  bodies  of,  192 
fermentation  of  the,  ammoniacal,  956 
hippuric  acid  of,  279 
injecting  the,  into  the  bladder,  mechanism  of, 

327 
lactates  in  human,  presence  of,  278 
phosphatic  coating  of,  as  a  sign  of  pregnancy, 

968 
reaction  of,  273,  274.  280 
salts  of,  inorganic,  280 
secretion  of,  191-193 
specific  gravity  of,  191,  273 
sulphur  in,  form  eliminated,  279 
urea  in  the,  274 
uric  acid  in,  272,  273,  277,  278 
Urobilin,  1015 
Uterus,  the,  895 
changes  in  the,  during  menstruation,  896,  897 

iu  early  gestation,  909,  910 
enti'ancc  of  spermatozoa  into,  mode  of,  903 

V'agina,  the,  900 
Vagus,  the,  463 

stimulation  of  the,  results  of,  568 
Valve,  auriculo-veutricular,  400 
Valve-play,  cardiac,  method  of  recording,  423- 

425 
Valves,  heart-,  mechanism  of,  400-404 

semilunar,  mechanism  of,  402-404 
"  Valvulte  couniventes,"  254 
Vas  deferens,  the,  886 
Vaseline,  975 

Vaso-constrictor  centre,  bulbar,  489-492 
Vaso-motor  centre,  bulbar,  489 

centres,  relation  of  cerebrum  to,  490-493 
cerebral,  495 
spinal,  490 
reflexes,  492 

spinal,  discovery  of,  490 
Vein,  wounded,  entrance  of  air  into  a,  danger 

of,  389 
Veins,  blood-flow  in,  subsidiary  forces  assisting 
the,  387 
blood-pressure  in,  causation,  386 
blood-speed  in  the,  393 
coronary,  closure  of  the,  results  of,  476 
great,  changes  in  the,  iu  the  open  chest,  407 

contraction  of  the,  rhythmic,  407 
valves  of  the.     See  Valves. 
Ventilation,  principles  of,  547 
Ventricle,  changes  in  the,  from  vagus  excita- 
tion, 453 
— force  of  the  contraction,  453 
— periodicity  of  contraction,  453 
• — the  diastolic  pressure,  454 
— the  output  and  input,  454 
— the  ventricular  tonus,  454 
— the  volume  of  blood,  454 
closure  of  the,  two  periods  of  complete,  425 
the  auricle  a  mechanism  for  the  quick-charg- 
ing of,  428 
Ventricles,  changes  in  size  of,  during  the  heart- 
beat, 404,  405 


1052 


INDEX. 


Ventricles,  beatiuR,  changes  in  size  and  foi-m  of, 
in  the  open  chest,  405 
of  position  in  the  open  chest,  406 
contracting,  force  of,  398,  399 
of  .Morgagni,  .S(i3 
pressure  within  the,  416-418 

negative,  425 
suction  within  the,  387,  426.    See  also  Heart. 
Ventricular  hands  of  larynx,  862,  863 
cycle,  perioils  of  the,  425 
relations  in  time  of  the,  413 
Vernix  caseosa,  198 
Vestibule,  auditory,  816 

Vertebrates,  comparative  physiology  of  the  cen- 
tral nervous  system  in,  703-705 
Viscera,  abdominal,  cardiac  cflfect  of  stimulating 
the,  4C7 
muscular  contraction  of  the,  310 
Villi,  chorionic,  912 

intestinal,  254,  258 
Vision,  binocular  and  monocular,  compared,  801 
defective,  097,  759,  760,  763 
physiology  of,  744 

caution  in  the  study  of,  806 
points  of,  corresponding,  803 
pseudoscopic,  802 
sense  of,  696,  697,  744-806 
stereoscopic,  801-803 
"  Vital  force  "  of  life.  25,  26 
Vocal  cords,  false  and  true,  862.  863 
in  voice-production,  870-8/  / 
structure  of,  863,  864 
Vocal  organs,  muscles  of,  reaction  and  contrac- 
tion of,  107 
Voice,  the,  870-877 

— changing  the  pitch,  872 
— speech,  874 
— vocal  machinery,  870 
— vowel  and  consonantal  sounds,  874-877 
— whispering,  875 
changes  in  the.  at  puberty,  871,  872,  927 
characters  of  the : 
— loudness,  870 
—pitch,  870 
— quality,  870 
eflFect  of  castration  on  the,  871,  872 
pitch  of  the,  872 
range  of  the,  872,  873 
registers  of  the,  872-874 


Voice,  speaking  and  singing,  distinguished,  874 

Voice  and  speech,  861-877 

Voice-i)roduction,  861,  870 

Voices,  classification  of,  873 

Voltaic  pile,  invention  of,  43 

Vomiting,  nervous  mechanism  of,  325,  32() 

centre,  lociition  of  .i,  .'12() 
Von  Frey's  experiment  of  artificially  preserving 

the  irritability  of  muscle,  74 
Vorticella,  .34.  35 
Vowel  sounds,  difference  in  quality  of,  829 

mechanism  of  i)roduction  of,  874-876 
Vowels,  phonation  of,  874-876 
Vulva,  the,  and  its  parts,  900 

Walking,  mechanism  of,  860,  861 
Water,  947 

deprivation   of,  effect   of  continued,  on   the 

body,  294 
distilled,  preparation  of,  947 
drinking-,  948 
elimination  from   the  body  of,  channels   of, 

280,  293 
in  the  brain,  percentage  of,  716 
Water  and  salts,  absorption  of,  258 
from  the  stomach,  253 
intestinal,  254,  259 
in  secretions,  theories  of  the  formation  of, 

1.5.5,  1.56 
necessity  of,  to  the  body,  214 
of  food-stuffs,  213,  214 
of  urine,  193,  280 
value  of,  nutritive,  293,  294 
Waves,  sound-,  jiroduction  of,  825 
Wharton's  duct.  1.58 
Whispering,  876 
Whistling  register,  873 
Womb,  the,  895 

Women,  sexual  period  in,  of  reproductive  power, 
927 

Xanthin,  277,  278,  996 
dimethyl,  996 
monoraethyl,  996 
trimethyl,'99() 

Zymogen,  176 
cell-granules,  169,  183 


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Money  may  be  sent  at  the  risk  of  the  publisher  in  either  of  the  followmg  ways :  A  post- 
office'  money  order,  an  express  money  order,  a  bank  check,  and  in  a  registered  letter.  Money 
sent  in  any  other  way  is  at  the  risk  of  the  sender. 

See  pages  30,  31,  for  a  List  of  Contents  classified  according  to  subjects. 


LATEST  PUBLICATIONS. 

American  Text-Book  of  Dis.  of  Eye,  Ear,  Nose,  and  Throat.    Page  3. 
American  Text-Book  of  Genito-Urinary  and  Skin  Diseases,    Page  4. 
American  Text-Book  of  Diseases  of  Children— Rev.  Edition.     Page  3. 
American  Text-Book  of  Gynecology— Revised  Edition.     See  page  4. 
American  Year-Book  of  Medicine  and  Surgery.     See  page  6. 
Anders^  Practice  of  Medicine — Revised  Edition.     See  page  6. 
Vierordf  s  Medical  Diagnosis— Fourth  (Revised)  Edition.     See  page  29. 
Van  Valzah  and  Nisbet's  Diseases  of  the  Stomach.     See  page  28. 
Church  and  Peterson's  Nervous  and  Mental  Diseases.     See  page  8. 
Da  Costa's  Surgery — Revised  and  Enlarged  Edition.     See  page  10. 
Saunders*  Medical  Hand-Atlases.     See  page  2. 
Griffith  on  The  Baby— Revised  Edition.     See  page  12. 
Butler's  Materia  Medica  and  Therapeutics— Revised  Edition.     Page  8. 
De  Schweinitz'  Diseases  of  the  Eye— Revised  Edition.     See  page  10. 
Vecki's  Sexual  Impotence.    See  page  28. 
Stoney's  Materia  Medica  for  Nurses.    See  page  28. 
Penrose's  Diseases  of  Women— Second  Edition.     See  page  J8. 
McFarland's  Pathogenic  Bacteria— Revised  Edition.    See  page  J7, 
American  Pocket  Medical  Dictionary.    See  page  10. 
Stengel's  Text-Book  of  Pathology.     See  page  26. 
Hirst's  Text-Book  of  Obstetrics.    See  page  13. 
Grafstrom's  Massage  and  Medical  Gymnastics.     Page  12. 
Saunders'  Pocket  Formulary— Fifth  ( Revised )  Edition.    See  page  24. 
Stevens'  Practice  of  Medicine— Fifth  (Revised)  Edition.    See  page  27, 


SAUNDERS'  MEDICAL  HAND-ATLASES. 

The  series  of  books  included  under  this  title  consists  of  auiliorized  translations  into 
English  of  the  world  famous  Lehmann  Medicinische  Handatlanten,  which  for  sci- 
cntif  c  accuracy,  pictorial  beauty,  compactness,  aiul  cheapness  surjiass  any  similar 
volumes  ever  published.  Each  volume  contains  from  50  to  100  colored  plates,  executed 
by  the  most  skilful  German  lilhographers,  besides  numerous  illustrations  in  the  text.  There 
is  a  full  and  appropriate  description  of  each  plate,  and  each  book  contains  a  condensed 
but  adequate  outline  of  the  subject  to  which  it  is  devoted. 

One  of  the  most  valuable  features  of  these  atlases  is  that  they  offer  a  ready  and  satis- 
factory substitute  for  clinical  observation.  To  those  unable  to  attend  important  clinics 
these  books  will  be  absolutely  indispensable. 

In  planning  this  series  ot  books  arrangements  were  made  with  representative  puljlishers 
in  the  chief  medical  centers  of  the  world  for  the  publication  of  translations  of  the  atlases 
into  nine  different  languages,  the  lithographic  plates  for  all  these  editions  being  made  in  Ger- 
many, where  work  of  this  kind  has  been  brought  to  the  greatest  perfection.  The  expense  of 
making  the  plates  being  shared  by  the  various  publishers,  the  cost  to  each  one  was  materially 
reduced.  Thus  by  reason  of  their  universal  translation  and  reproduction,  the  publish- 
ers have  been  enabled  to  secure  for  these  atlases  the  best  artistic  and  professional 
talent,  to  produce  them  in  the  most  elegant  style,  and  yet  to  offer  them  at  a  price 
heretofore  unapproached  in  cheapness.  The  success  of  the  undeitakinij  is  demon- 
strated bv  the  fact  that  the  volumes  have  already  appeared  in  nine  different  languages 
— German,  English,  French,  Italian,  Russian,  Spanish,  Danish,  Swedish,  and  Hungarian. 

In  view  of  the  striking  success  of  these  works,  Mr.  Saunders  has  contracted  with  the 
publisher  of  the  original  German  edition  for  one  hundred  thousand  copies  of  the  atlases. 
In  consideration  of  this  enormous  undertaking,  the  publisher  has  been  enabled  to  prepare 
and  furnish  special  additional  colored  plates,  making  the  series  even  handsomer  and  more 
complete  than  was  originally  intended. 

As  an  indication  of  the  practical  value  of  the  atlases  and  of  the  favor  with  which  they 
have  been  received,  it  should  be  noted  that  the  Medical  Department  of  the  U.  S.  Army 
has  adopted  the  "  Atlas  of  Operative  Surgery  "  as  its  standard,  and  has  ordered  the  book  in 
large  quantities  for  distribution  to  the  various  regiments  and  army  posts. 

The  same  careful  and  competent  editorial  supervision  has  been  secured  in  the 
English  edition  as  in  the  originals,  the  translations  being  edited  by  the  leading  American 
specialists  in  the  different  subjects. 

NOW  READY. 

Atlas  oi  Internal  Medicine  and  Clinical  Diagnosis.  By  Dr.  Chr.  Jakob,  of  Erlanjj:en.  Edited 
by  Augustus  A.  Hshnek,  M.D.,  Professor  of  Cliiiicril  Medicine  in  tlie  Philadelpliia  Polyclinic;  At- 
tending Physician  to  the  Philadelphia  Hospital.  68  colored  plates,  and  64  illustrations  in  the  text. 
Cloth,  5300  net. 

Atlas  of  Legal  Medicine.  By  Dr.  E.  R.  von  Hofmann,  of  Vienna.  Edited  by  Freukrick  Peter- 
son. M.D.,  Clinical  Professor  of  Mental  Diseases,  Woman's  Medical  College,  New  York;  Chiel 
of  Clinic,  Nervous  Dept.,  College  of  Physicians  and  Surgeons,  New  York.  With  120  colored  fig- 
ures on  56  plates,  and  193  beautiful  hall-lone  illustrations.     Cloth,  J3.50  net. 

Atlas  of  Diseases  of  the  Larynx.  V>\  Uk.  L.  Grijnwald,  of  Munich.  Edited  by  Charles  P. 
Grayson,  M.D.,  Lecturer  on  Laixngology  and  Khinology  in  the  University  of  Pennsylvania; 
Physician-in-Charge,  Throat  and  Nose  Department,  Hospital  of  the  University  of  Pennsylvania. 
With  107  colored  figures  on  44  plates,  and  25  text-illustrations.    Cloth,  $2.50  net. 

Atlas   of  Operative    Surgery.     Bv  Dr.  O.   Zuckkrkandl,  of  Vienna.     Edited   by  J.  Chalmers 

DaCosta,  M.D.,  Cluneal  Professor  of  Singeiy,  JefteVbon  Medical  College,  Philadelphia  ;  Surgeon 
to  the  Philadelphia  Hospital.     With  i'4  colored  plates,  and  217  text  illustrations.     Cloth,  $3.00  net. 

Atlas  of  Syphilis  and  the  Venereal  Diseases.  By  Prof.  Dr.  Franz  Mrackk,  of  Vienna.  Edited 
by  L.  BoLTO.v  Bangs,  M.D.,  late  Professor  of  Genito-Urinary  and  Venereal  Diseases,  New  York 
Posl-Graduate  Medical  School  and  Hospital.  With  71  colored  plates  from  original  water-colors, 
and  16  black-and-white  illustrations.     Cloth,  $3.50  net. 

IN  PREPARATION. 

Atlas  of  External  Diseases  of  the  Eye.  By  Dr.  O.  Haab,  of  Zurich.  Edited  by  G.  E. 
DE  ScHvvKiNiTZ,  M.D.,  Professor  of  Ophthalmology,  Jeflferson  Medical  College,  Philadelphia. 
With  100  colored  illustrations. 

Atlas  of  Skin  Diseases.  By  Prof.  Dr.  Franz  Mra?kk,  of  Vienna.  Edited  by  Henry  W.  Stelvvagon, 
JVI.  D.,  Clinical  Professor  of  Dermatology,  Jeflferson  Medical  College,  Philada.    80  colored  plates. 

Atlas  of  Pathological  Histology.  Atlas  of  Operative  Gynecology. 

Atlas  of  Orthopedic  Surgery.  Atlas  of  Psychiatry. 

Atlas  of  General  Surgery.  Atlas  of  Diseases  of  the  Ear. 


THE  AMERICAN  TEXT-BOOK  SERIES. 

AN  AMERICAN  TEXT=BOOK  OF  APPLIED  THERAPEUTICS. 

By  43  Distinguished  Practitioners  and  Teachers.  Edited  by  James  C. 
Wilson,  M.D.,  Professor  of  the  Practice  of  Medicine  and  of  Clinical 
Medicine  in  the  Jefferson  Medical  College,  Philadelphia.  One  hand- 
some imperial  octavo  volume  of  1326  pages.  Illustrated.  Cloth, 
I7.00  net;  Sheep  or  Half  Morocco,  ^8.00  net.     Sold  by  Subscription. 

"  As  a  work  either  for  study  or  reference  it  will  be  of  great  value  to  the  practitioner,  as 
it  is  virtually  an  exposition  of  such  clinical  therapeutics  as  experience  has  taught  to  be  of 
the  most  value.  Taking  it  all  in  all,  no  recent  publication  on  therapeutics  can  be  compared 
with  this  one  in  practical  value  to  the  working  physician." — Chicago  Clinical  Review. 

"The  whole  field  of  medicine  has  been  well  covered.  The,  work  is  thoroughly  prac- 
tical, and  while  it  is  intended  for  practitioners  and  students,  it  is  a  better  book  for  the  general 
practitioner  than  for  the  student.  The  young  practitioner  especially  will  find  it  extremely 
suggestive  and  helpful." — The  Indian  Lancet. 

AN  AMERICAN  TEXT=BOOK  OF  THE  DISEASES  OF  CHILDREN. 
Second  Edition,  Revised. 

By  65  Eminent  Contributors.  Edited  by  Louis  Starr,  M.  D.,  Con- 
sulting Pediatrist  to  the  Maternity  Hospital,  etc.  ;  assisted  by  Thomp- 
son S.  Westcott,  M.  D.,  Attending  Physician  to  the  Dispensary 
for  Diseases  of  Children,  Hospital  of  the  University  of  Pennsyl- 
vania. In  one  handsome  imperial  octavo  volume  of  1244  pages, 
profusely  illustrated.  Cloth,  $7.00  net;  Sheep  or  Half  Morocco, 
$8.00  net.     Sold  by  Subsct'iption. 

"This  is  far  and  away  the  best  text-book  on  children's  diseases  ever  published  in  the 
English  language,  and  is  certainly  the  one  which  is  best  adapted  to  American  readers. 
We  congratulate  the  editor  upon  the  result  of  his  work,  and  heartily  commend  it  to  the 
attention  of  every  student  and  practitioner." — American  Journal  of  the  Medical  Sciences. 

AN  AMERICAN  TEXT=BOOK  OF  DISEASES  OF  THE  EYE,  EAR, 
NOSE,  AND  THROAT. 

By  58  Prominent  Specialists.  Edited  by  G.  E.  de  Schweinitz,  M.D.  , 
Professor  of  Ophthalmology  in  the  Jefferson  Medical  College,  Phila- 
delphia ;  and  B.  Alexander  Randall,  M.D.,  Professor  of  Diseases 
of  the  Ear  in  the  University  of  Pennsylvania.  Imperial  octavo,  1251 
pages;  766  illustrations,  59  of  them  in  colors.  Cloth,  ;^7.oo  net;  Sheep 
or  Half  Morocco,  $8.00  net.     Sold  by  Subscription. 

Illustrated  Catalogue  of  the  ** American  Text-Books'*  sent  free  upon  application. 


4  Medical  Publications  of  W.  B.  Saunders. 

AN  AMERICAN   TEXT-BOOK    OF   GENITO-URINARY  AND  SKIN 
DISEASES. 

By  47  Eminent  Specialists  and  Teachers.  Edited  by  L.  Bolton 
Bangs,  M.D.  ,  Late  Professor  of  Genito-Urinary  and  Venereal  Diseases, 
New  York  Post-Graduate  Medical  School  and  Hospital ;  and  W. 
A.  Hardaway,  M.D.,  Professor  of  Diseases  of  the  Skin,  Missouri 
Medical  College.  Imperial  octavo  volume  of  1229  pages,  with  300  en- 
gravings and  20  full-page  colored  plates.  Cloth,  $7.00  net;  Sheep 
or  Half  Morocco,  $8.00  net.     Sold  by  Subscription. 

"This  volume  is  one  of  the  best  yet  issued  of  the  publisher's  series  of '  American  Text- 
Books.'  The  list  of  contributors  represents  an  extraordinary  array  of  talent  and  extended 
experience.  The  book  will  easily  take  the  place  in  comprehensiveness  and  value  of  the 
half  dozen  or  more  costly  works  on  these  subjects  which  have  heretofore  been  necessary  to 
a  well-equipped  library." — N^etv  York  Polyclinic. 

AN  AMERICAN  TEXT=BOOK  OF  GYNECOLOGY,  MEDICAL  AND 
SURGICAL.     Second  Edition,  Revised. 

By  10  of  the  Leading  Gynecologists  of  America.     Edited  by  J-   M. 
Baldv,  M.  D.,  Professor  of  Gynecology  in  the  Philadelphia  Polyclinic, 
etc.     Handsome  imperial  octavo  volume  of  718  pages,  with  341  illus- 
trations in  the  text,  and  38  colored  and  half-tone  plates.      Cloth,  $6.00 
net;  Sheep  or  Half  Morocco,  $7.00  net.     Sold  by  Subscription. 
"  It  is  practical  from  beginning  to  end.     Its  descriptions  of  conditions,  its  recommen- 
dations for  treatment,  and   above  all  the   necessary  technique  of  different  operations,  are 
clearly  and  admirably  presented.     .     .     .     It  is  well  up  to  the  most  advanced  views  of  the 
day,  and  embodies  all  the  essential  points  of  advanced  American  gynecology.     It  is  destined 
to  make  and  hold  a  place  in  gynecological    literature  which  will  be  peculiarly  its  own." — 
Medical  Record,  New  York. 

AN  AMERICAN  TEXT=BOOK  OF  LEGAL  MEDICINE  AND  TOXI- 
COLOGY. 

Edited  by  Frederick  Peterson,  M.D.,  Clinical  Professor  of  Mental 
Diseases  in  the  Woman's  Medical  College,  New  York;  Chief  of  Clinic, 
Nervous  Department,  College  of  Physicians  and  Surgeons,  New  York ; 
and  Walter  S.  Haines,  M.D.,  Professor  of  Chemistry,  Pharmacy, 
and  Toxicology  in  Rush  Medical  College,  Chicago.     In  Preparation. 

AN  AMERICAN  TEXT=BOOK  OF  OBSTETRICS. 

By  15  Eminent  American  Obstetricians.     Edited  by  Richard  C.  Nor- 

ris,  M.D.;  Art  Editor,  Robert  L.  Dickinson,  M.D.     One  handsome 

imperial  octavo  volume  of  1014  ])ages,  with  nearly  900  beautiful  colored 

and  half-tone  illustrations.     Cloth,  $7.00  net ;  Sheep  or  Half  Morocco, 

$8.00  net.     Sold  by  Subscription. 

"  Permit  me  to  say  that  your  American  Text-Book  of  Obstetrics  is  the  most  magnificent 

medical  work  that  I  have  ever  seen.    I  congratulate  you  and  thank  you  for  this  superb  work, 

which  alone  is  sufficient  to  place  you  first  in  the  ranks  of  medical  publishers." — Alexander 

J.  C.  .Skenk,  Professor  of  Gynecology  in  the  Long  Island  College  Hospital,  Brooklyn,  N.  V. 

"  This  is  the  most  sumptuously  illustrated  work  on  midwifery  that  has  yet  appeared.   In 

the  number,  the  excellence,  and  the  beauty  of  production  of  the  illustrations  it  far  surpasses 

every  other  book  upon  the  subject.     This  feature  alone  makes  it  a  work  which  no  medical 

library  should  omit  to  purchase." — British  Medical  Journal. 

"  As  an  authority,  as  a  book  of  reference,  as  a  '  working  book  '  for  the  student  or  prac- 
titioner, we  commend  it  because  we  believe  there  is  no  better." — American  Journal  of  the 
Medical  Sciences. 

Illustrated  Catalogue  of  the  "American  Tczt-Books  "  sent  free  upon  application. 


Medical  Publications  of  W.  B.  Saunders.  5 

AN  AMERICAN  TEXT-BOOK  OF  PATHOLOGY. 

Edited  by  John  Guiteras,  M.D.,  Professor  of  General  Pathology  and 
of  Morbid  Anatomy  in  the  University  of  Pennsylvania;  and  David 
RiESMAN,  M.D. ,  Demonstrator  of  Pathological  Histology  in  the 
University  of  Pennsylvania.     In  Preparation. 

AN  AMERICAN  TEXT-BOOK  OF  PHYSIOLOGY. 

By  ID  of  the  Leading  Physiologists  of  America.  Edited  by  William 
H.  Howell,  Ph.D.,  M.D.,  Professor  of  Physiology  in  the  Johns  Hop- 
kins University,  Baltimore,  Md.  One  handsome  imperial  octavo 
volume  of  1052  pages.  Illustrated.  Cloth,  $6.00  net ;  Sheep  or  Half 
Morocco,  $7.00  net.     Sold  by  Subscription. 

"  We  can  commend  it  most  heartily,  not  only  to  all  students  of  physiology,  but  to  every 
physician  and  pathologist,  as  a  valuable  and  comprehensive  work  of  reference,  written  by 
men  who  are  of  eminent  authority  in  their  own  special  subjects." — London  Lancet. 

"  To  the  practitioner  of  medicine  and  to  the  advanced  student  this  volume  constitutes, 
we  believe,  the  best  exposition  of  the  present  status  of  the  science  of  physiology  in  the 
English  language." — Amen'can  Journal  of  the  Medical  Sciences. 

AN  AMERICAN  TEXT=BOOK  OF  SURGERY.     Second  Edition. 

By  13  Eminent  Professors  of  Surgery.  Edited  by  William  W.  Keen, 
M.D.,  LL.D.,  and  J.  William  White,  M.D.,  Ph.D.  Handsome 
imperial  octavo  volume  of  1250  pages,  with  500  wood-cuts  in  the  text, 
and  39  colored  and  half-tone  plates.  Thoroughly  revised  and  enlarged, 
with  a  section  devoted  to  "  The  Use  of  the  Rontgen  Rays  in  Surgery." 
Cloth,  ^7.00  net;  Sheep  or  Half  Morocco,  $8.00  net.  Sold  by  Sub- 
scription. 

*'  Personally,  I  should  not  mind  it  being  called  THE  Text-Book  (instead  of  A  Text- 
Book)  ,  for  I  know  of  no  single  volume  which  contains  so  readable  and  complete  an  account 
of  the  science  and  art  of  Surgery  as  this  does." — Edmund  Owen,  F.R.C.S.,  Member  of 
the  Board  of  Examiners  of  the  Royal  College  of  Surgeons,  England. 

"  If  this  text-book  is  a  fair  reflex  of  the  present  position  of  American  surgery,  we  must 
admit  it  is  of  a  very  high  order  of  merit,  and  that  English  surgeons  will  have  to  look  very 
carefully  to  their  laurels  if  they  are  to  preserve  a  position  in  the  van  of  surgical  practice." — 
London  Lancet. 

AN  AMERICAN  TEXT=BOOK  OF  THE  THEORY  AND  PRACTICE 
OF  MEDICINE. 

By  12  Distinguished  American  Practitioners.  Edited  by  William 
Pepper,  M.D.,  LL.D.,  Professor  of  the  Theory  and  Practice  of  Medi- 
cine and  of  Clinical  Medicine  in  the  University  of  Pennsylvania.  Two 
handsome  imperial  octavo  volumes  of  about  1000  pages  each.  Illus- 
trated. Prices  per  volume  :  Cloth,  $5.00  net ;  Sheep  or  Half  Morocco, 
$6.00  net.     Sold  by  Subscription. 

"  I  am  quite  sure  it  will  commend  itself  both  to  practitioners  and  students  of  medicine, 
and  become  one  of  our  most  popular  text-books." — Alfred  Loomis,  M.D.,  LL.D.,  Pro- 
fessor of  Pathology  and  Practice  of  Medicine,  University  of  the  City  of  New  York. 

"  V.'e  reviewed  the  first  volume  of  this  work,  and  said  :  '  It  is  undoubtedly  one  of  the 
best  text-books  on  the  practice  of  medicine  which  we  possess.'  A  consideration  of  the 
second  and  last  volume  leads  us  to  modify  that  verdict  and  to  say  that  the  completed  work 
is  in  our  opinion  the  best  of  its  kind  it  has  ever  been  our  fortune  to  see." — A^ew  York  Medical 
Journal. 

Illustrated  Catalogue  of  the  **  American  Text-Books*'  sent  free  upon  application* 


Medical  Publications  of  W.  B.  Saunders, 


AN  AMERICAN  YEAR-BOOK  OF  MEDICINE  AND  SURGERY. 

A  Yearly  Digest  of  Scientific  Progress  and  Authoritative  Opinion  in  all 
branches  of  Medicine  and  Surgery,  drawn  from  journals,  monographs, 
and  text-books  of  the  leading  American  and  Foreign  authors  and 
investigators.  Collected  and  arranged,  with  critical  editorial  com- 
ments, by  eminent  American  specialists  and  teachers,  under  the  general 
editorial  charge  of  Geor(;e  M.  Gould,  M.D.  One  handsome  imperial 
octavo  volume  of  about  1200  pages.  Uniform  in  style,  size,  and 
general  make-up  with  the  "American  Text-Book"  Series.  Cloth, 
$6.50  net;  Half  Morocco,  $7.50  net.     So/d  by  Subscription. 

"  It  is  difficult  to  know  which  to  admire  most — the  research  and  industry  of  the  distin- 
guished band  of  experts  whom  Dr.  Gould  has  enlisted  in  the  service  of  the  Year-Book,  or  the 
wealth  and  abundance  of  the  contributions  to  every  department  of  science  that  have  been 
deemed  worthy  of  analysis.  .  .  .  It  is  much  more  than  a  mere  compilation  of  abstracts, 
for,  as  each  section  is  entrusted  to  experienced  and  able  contributors,  the  reader  has  the 
advantage  of  certain  critical  commentaries  and  expositions  .  .  .  proceeding  from  writers 
fully  qualified  to  perform  these  tasks.  ...  It  is  emphatically  a  book  which  should  find 
a  place  in  ever)-  medical  library,  and  is  in  several  respects  more  useful  than  the  famous 
'Jahrbiicher'  of  Geiinany." — London  Lancet. 

THE  AMERICAN   POCKET  MEDICAL  DICTIONARY. 

[See  Borland' s  Pocket  Dictionary,  page  10.] 

ANDERS'  PRACTICE  OF  MEDICINE.    Second  Edition. 

A  Text-Book  of  the  Practice  of  Medicine.  By  James  M.  Anders, 
M.D.,  Ph.D.,  LL.D.,  Professor  of  the  Practice  of  Medicine  and  of 
Clinical  Medicine,  Medico-Chirurgical  College,  Philadelphia.  In  one 
handsome  octavo  volume  of  1287  pages,  fully  illustrated.  Cloth, 
$5.50  net;  Sheep  or  Half  Morocco,  $6.50  net. 

"  It  is  an  excellent  book, — concise,  comprehensive,  thorough,  and  up  to  date.  It  is  a 
credit  to  you  ;  but,  more  than  that,  it  is  a  credit  to  the  profession  of  Philadelphia— to  us." 
James  C.  Wilson,  Professor  of  the  Practice  of  Medicine  and  Clinical  Medicine,  Jefferson 
Medical  College,  Philadelphia. 

ASHTON'S  OBSTETRICS.     Fourth  Edition,  Revised. 

Essentials  of  Obstetrics.  By  W.  Easterly  Ashton,  M.D.,  Pro- 
fessor of  Gynecology  in  the  Medico-Chirurgical  College,  Philadelphia. 
Crown  octavo,  252  pages;  75  illustrations.  Cloth,  $1.00;  interleaved 
for  notes,  $1.25. 

[See  Saunders'   Question- Cotnpends,  page  21.] 
"  Embodies  the  whole  subject  in  a  nut-.shell.     We  cordially  recommend  it  to  our  read 
ers." — Chicago  Medical  Times. 

BALL'S  BACTERIOLOGY.     Third  Edition,  Revised. 

Essentials  of  Bacteriology  ;  a  Concise  and  Systematic  Introduction 
to  the  Study  of  Micro-organisms.  By  M.  V.  Ball,  M.D.,  Bacteriol- 
ogist to  St.  Agnes'  Hospital,  Philadelphia,  etc.  Crown  octavo,  218 
pages;  82  illustrations,  some  in  colors,  and  5  plates.  Cloth,  ,^i.oo; 
interleaved  for  notes,  $1.25. 

[See  Saunders'  Question- Compends,  page  21.] 
««  The  student  or  practitioner  can  readilv  obtain  a  knowledge  of  the  subject  from  a  perusal 

of  this  book.     The  illustrations  are  clear  and  satisfactory."— il/<?a'jVa/  Record,  New  York. 


Medical  Publications  of  W.  B.  Saunders. 


BASTIN'S  BOTANY. 

Laboratory  Exercises  in  Botany.  By  Edson  S.  Bastin,  M.A., 
late  IMofessor  of  Materia  Medica  and  Botany,  Philadelphia  College  of 
Pharmacy.    Octavo  volinne  of  536  pages,  with  87  plates.    Cloth,  ^2.50. 

"It  is  unquestionably  the  best  textbook  on  the  subject  that  has  yet  appeared.  The 
work  is  eminently  a  practical  one.  We  regard  the  issuance  of  this  book  as  an  important 
event  in  the  history  of  pharmaceutical  teaching  in  this  country,  and  predict  for  it  an  unquali- 
fied success." Alumni  Report  to  the  Philadelphia  College  of  Pharmacy. 

"There  is  no  work  like  it  in  the  pharmaceutical  or  botajiical  literature  of  this  country, 
and  we  predict  for  it  a  wide  circulation." — American  Journal  of  Pharmacy. 

BECK'S  SURGICAL  ASEPSIS. 

A  Manual  of  Surgical  Asepsis.  By  Carl  Beck,  M.D.,  Surgeon  to 
St.  Mark's  Hospital  and  the  New  York  German  Poliklinik,  etc.  306 
pages;  65  text-illustrations,  and  12  full-page  plates.     Cloth,  $1.25  net. 

"  An  excellent 'exposition  of  the  '  very  latest'  in  the  treatment  of  wounds  as  practised 
by  leading  German  and  American  surgeons." — Birmingham  (Eng.)  Medical  Review. 

"This  little  volume  can  be  recommended  to  any  who  are  desirous  of  learning  the  details 
of  asepsis  in  surgery,  for  it  will  serve  as  a  trustworthy  guide." — London  Lancet. 

BOISLINIERE'S  OBSTETRIC  ACCIDENTS,  EMERGENCIES,  AND 
OPERATIONS. 
Obstetric  Accidents,  Emergencies,  and  Operations.     By  L.  Ch. 

BoisLiNiERE,  M.D.,  late  Emeritus  Professor  of  Obstetrics,  St.  Louis 
Medical  College.    381  pages,  handsomely  illustrated.     Cloth,  $2.00  net. 

"  It  is  clearly  and  concisely  written,  and  is  evidently  the  work  of  a  teacher  and  practi- 
tioner of  large  experience." — British  Medical  Journal. 

"  A  manual  so  useful  to  the  student  or  the  general  practitioner  has  not  been  brought  to 
our  notice  in  a  long  time.  The  field  embraced  in  the  title  is  covered  in  a  terse,  interesting 
way." —  Yale  Medical  Journal. 

BROCKWAY'S  MEDICAL  PHYSICS.     Second  Edition,  Revised. 
Essentials  of   Medical   Physics.     By  Fred  J.  Brockway,  M.D., 
Assistant  Demonstrator  of  Anatomy  in  the  College  of  Physicians  and 
Surgeons,  New  York.     Crown  octavo,  330  pages  ;   155  fine  illustrations. 
Cloth,  51.00  net ;  interleaved  for  notes,  ^1.25  net. 

[See  Saunders'  Question- Compends,  page  21.] 

"  The  student  who  is  well  versed  in  these  pages  will  certainly  prove  qualified  to  com 
prehend  with  ease  and  pleasure  the  great  majority  of  questions  involving  physical  principles 
likely  to  be  met  with  in  his  medical  studies." — American  Practitioner  and  News. 

<'We  know  of  no  manual  that  affords  the  medical  student  a  better  or  more  concise 
exposition  of  physics,  and  the  book  may  be  commended  as  a  most  satisfactory  presentation 
of  those  essentials  that  are  requisite  in  a  course  in  medicine." — Nezv  York  Medical  Jourttal. 

"  It  contains  all  that  one  need  know  on  the  subject,  is  well  written,  and  is  copiously 
illustrated." — Medical  Record,  New  York. 

BURR  ON  NERVOUS  DISEASES. 

A  Manual  of  Nervous  Diseases.     By  Charles  W.   Burr,  M.D., 

Clinical  Professor  of  Nervous  Diseases,  Medico-Chirurgical  College, 
Philadelphia;  Pathologist  to  the  Orthopedic  Hospital  and  Infirmary 
for  Nervous  Diseases;  Visiting  Physician  to  St.  Joseph's  Hospital,  etc. 
Jn  Preparation. 


8  Medical  Publications  of  W.  B.  Saunders. 

BUTLER'S  MATERIA  MEDICA,  THERAPEUTICS,  AND  PHAR- 
MACOLOGY. Second  Edition,  Revised. 
A  Text-Book  of  Materia  Medica,  Therapeutics,  and  Pharma- 
cology. By  Georcje  ¥.  ikriLER,  Ph.G.,  M.D.,  Professor  of  Materia 
Medica  and  of  Clinical  Medicine  in  the  College  of  Physicians  and 
Surgeons,  Chicago ;  Professor  of  Materia  Medica  and  Therapeutics, 
Northwestern  University,  Woman's  Medical  School,  etc.  Octavo,  860 
pages,  illustrated.     Cloth,  $4.00  net ;    Sheep,  $5.00  net. 

*'  Taken  as  a  whole,  the  book  may  fairly  be  considered  as  one  of  the  most  satisfactory 
of  any  single-volume  works  on  materia  medica  in  the  market." — Journal  of  the  Avierican 
Medical  Association. 

CERNA  ON  THE  NEWER  REMEDIES.  Second  Edition,  Revised. 
Notes  on  the  Newer  Remedies,  their  Therapeutic  Applications 
and  Modes  of  Administration.  By  David  Cekna,  M.D.,  Ph.D., 
formerly  Demonstrator  of  and  Lecturer  on  Experimental  Therapeutics 
in  the  University  of  Pennsylvania;  Demonstrator  of  Physiology  in  the 
Medical  Department  of  the  University  of  Texas.  Rewritten  and 
greatly  enlarged.     Post-octavo,   253  pages.     Cloth,  ;^  1.25. 

"  The  appearance  of  this  new  edition  of  Dr.  Cerna's  very  valuable  work  shows  that  it 
is  properly  appreciated.  The  book  ought  to  be  in  the  possession  of  every  practising  physi- 
cian."— Netu  York  Medical  Journal. 

CHAPIN  ON  INSANITY. 

A  Compendium  of  Insanity.  By  John  B.  Chapin,  M.D.,  LL.D., 
Physician-in-Chief,  Pennsylvania  Hospital  for  the  Insane ;  late  Physi- 
cian-Superintendent of  the  Willard  State  Hospital,  New  York ;  Hon- 
orary Member  of  the  Medico-Psychological  Society  of  Great  Britain, 
of  the  Society  of  Mental  Medicine  of  Belgium.  lamo,  234  pages, 
illustrated.     Cloth,  $1.25  net. 

"  The  practical  parts  of  Dr.  Chapin's  book  are  what  constitute  its  distinctive  merit.  We 
desire  especially  to  call  attention  to  the  fact  that  on  the  subject  of  therapeutics  of  insanity 
the  work  is  exceedingly  valualjle.  It  is  not  a  made  book,  hut  a  genuine  condensed  thesis, 
which  has  all  the  value  of  ripe  opinion  and  all  the  charm  of  a  vigorous  and  natural  style." — 
Philadelphia  Medical  Journal. 

CHAPMAN'S  MEDICAL  JURISPRUDENCE  AND  TOXICOLOGY. 
Second  Edition,  Revised. 
Medical  Jurisprudence  and  Toxicology.  By  Henry  C.  Chapman, 
M.D.,  Professor  of  Institutes  of  Medicine  and  Medical  Jurisprudence 
in  the  Jefferson  Medical  College  of  Philadelphia.  254  pages,  with  55 
illustrations  and  3  full-page  plates  in  colors.     Cloth,  $1.50  net. 

"The  best  book  of  its  class  for  the  undergraduate  that  we  know  of." — A^ew  York 
Medical  Times. 

CHURCH  AND  PETERSON'S  NERVOUS  AND  MENTAL  DISEASES. 
Nervous  and  Mental  Diseases.  By  Archii.ai.u  Church,  M.  D., 
Professor  of  Mental  Diseases  and  Medical  Jurisprudence  in  the  North- 
western University  Medical  School,  Chicago;  and  Frederick  Peter- 
son, M.  D.,  Clinical  Professor  of  Mental  Diseases,  Woman's  Medical 
College,  N.  Y.;  Chief  of  Clinic,  Nervous  Dept.,  College  of  Physi- 
cians and  Surgeons,  N.  Y.  Handsome  octavo  volume  of  843  pages, 
profusely  illustrated.     Cloth,  ;;^5.oo  net;  Half  Morocco,  56.00  net. 


Medical  Publications  of  W.  B.  Saunders. 


CLARKSON'S  HISTOLOGY. 

A   Text-Book    of    Histology,    Descriptive   and    Practical.      By 

Arthur  Clakkson,  M.B.,  CM.  Edin.,  formerly  Demonstrator  of 
Physiology  in  the  Owen's  College,  Manchester;  late  Demonstrator  of 
Physiology  in  Yorkshire  College,  Leeds.  Large  octavo,  554  pages; 
22  engravings  in  the  text,  and  174  beautifully  colored  original  illustra- 
tions.     Cloth,  strongly  bound,  $6.00  net. 

"  The  work  must  be  considered  a  valuable  addition  to  the  list  of  available  textbooks, 
and  is  to  be  highly  recommended." — Ne7v  York  Medical  Journal. 

'« Tliis  is  one  of  the  best  works  for  students  we  have  ever  noticed.  We  predict  that  the 
book  will  attain  a  well-deserved  poinilarity  amongom  'iiwA&nXs:'— Chicago  Medical  Recorder. 

CLIMATOLOGY. 

Transactions  of  the  Eighth  Annual  Meeting  of  the  American 
Climatological  Association,  held  in  Washington,  September  22-25, 
1 89 1.  Forming  a  handsome  octavo  volume  of  276  pages,  uniform  with 
remainder  of  series.      (A  limited  quantity  only.)     Cloth,  $1.50. 

COHEN  AND  ESHNER'S  DIAGNOSIS. 

Essentials  of  Diagnosis.  By  Solomon  Solis-Cohen,  M.D.,  Pro- 
fessor of  Clinical  Medicine  and  Applied  Therapeutics  in  the  Philadel- 
phia Polyclinic  ;  and  Augustus  A.  Eshner,  M.D.,  Professor  of  Clinical 
Medicine  in  the  Philadelphia  Polyclinic.  Post-octavo,  382  pages;  55 
illustrations.     Cloth,  ^1.50  net. 

[See  Saunders'   Question- Compends,  page  21.] 

"We  can  heartily  commend  the  book  to  all  those  who  contemplate  purchasing  a  'com- 
pend  '  It  is  modern  and  complete,  and  will  give  more  satisfaction  than  many  other  works 
which  are  perhaps  too  prolix  as  well  as  behind  the  \\m^%:'— Medical  Review,  St.  Louis. 

CORWiN'S  PHYSICAL  DIAGNOSIS. 

Essentials  of  Physical  Diagnosis  of  the  Thorax.  By  Arthur 
M.  CoRWiN,  A.M.,  M.D.,  Demonstrator  of  Physical  Diagnosis  in  Rush 
Medical  College,  Chicago  ;  Attending  Physician  to  Central  Free  Dis- 
pensary, Department  of  Rhinology,  Laryngology,  and  Diseases  of  the 
Chest,  Chicago.    200  pages,  illustrated.   Cloth,  flexible  covers,  ^i.  25  net. 

"It  is  excellent.  The  student  who  shall  use  it  as  his  guide  to  the  careful  study  of 
physical  exploration  upon  normal  and  abnormal  subjects  can  scarcely  fail  to  acquire  a  good 
working  knowledge  of  the  subject." — Philadelphia  Polyclinic. 

"A  most  excellent  little  work.  It  brightens  the  memory  of  the  differential  diagnostic 
signs,  and  it  arranges  orderly  and  in  sequence  the  various  objective  phenomena  to  logical 
solution  of  a  careful  diagnosis."— >2/r«a/  of  Nervous  and  Mental  Diseases. 

CRAGIN'S  GYN/ECOLOGY.     Fourth  Edition,  Revised. 

Essentials  of  Gynaecology.  By  Edwin  B.  Cr.^gin,  M.  D.,  Lecturer 
in  Obstetrics,  College  of  Physicians  and  Surgeons,  New  York.  Crown 
octavo,  200  pages;  62  illustrations.     Cloth,  $1.00  ;  interleaved  for  notes, 

^  1 .  2  ^ . 

[See  Sajmders'  Question- Canpends,  page  21.] 
«  A  handy  volume,  and  a  distinct  improvement  on  students'  compends  in  general.     No 
author  who  was  not  himself  a  practical  gynecologist  could  have  consulted  the  student's  needs 
so  thoroughly  as  Dr.  Cragin  has  d.ont."— Medical  Record,  New  York. 


10  Medical  Publications  of  W.  B.  Saunders. 

CROOKSHANK'S  BACTERIOLOGY.     Fourth  Edition,  Revised. 

A  Text-Book  of  Bacteriology.  By  Edgar  M.  Crookshank,  M.B., 
Professor  of  Comparative  I'athology  and  Bacteriology,  King's  College^ 
London.  Octavo  volume  of  700  pages,  with  273  engravings  and  22 
original  colored  plates.     Cloth,  $6.50  net;   Half  Morocco,  57.50  net. 

"  To  the  student  who  wishes  to  obtain  a  good  resume  of  what  has  been  done  in  bacteri- 
ology, or  wlio  wishes  an  accurate  account  of  the  various  methods  of  research,  the  book  may 
be  recommended  with  confidence  that  he  will  find  there  what  he  requires."  —  London  Lancet. 

DaCOSTA'S  surgery.  Second  Ed.,  Revised  and  Greatly  Enlarged. 
Modern  Surgery,  General  and  Operative.  By  John  Chalmers 
DaCosta,  M.D.,  Clinical  Professor  of  Surgery,  Jefferson  Medical 
College,  Philadelphia;  Surgeon  to  the  Philadelphia  Hospital,  etc. 
Handsome  octavo  volume  of  900  pages,  profusely  illustrated.  Cloth, 
;^4.oo  net;  Half  Morocco,  55.00  net. 

"We  know  of  no  small  work  on  surgery  in  the  English  language  which  so  well  fulfils- 
the  requirements  of  the  modern  student." — ALeJico-Chiruigical Journal,  Bristol,  England. 

DE  SCHWEINITZ  ON  DISEASES  OF  THE  EYE.      Third  Edition, 
Revised, 
Diseases  of   the  Eye.     A  Handbook   of   Ophthalmic   Practice. 

By  G.  E.  DE  ScHWEiNiTZ,  M.D.,  Professor  of  Ophthalmology  in  the 
Jefferson  Medical  College,  Philadelphia,  etc.  Handsome  royal  octavo 
volume  of  696  pages,  with  256  fine  illustrations  and  2  chromo-litho- 
graphic  plates.     Cloth,  54.00  net;  Sheep  or  Half  Morocco,  55- 00  net. 

"  A  clearly  written,  comprehensive  manual.  One  which  we  can  commend  to  students 
as  a  reliable  text-book,  written  with  an  evident  knowledge  of  the  wants  of  those  entering 
upon  the  study  of  this  special  branch  of  medical  science." — British  Medical  JournaL 

"  A  work  that  will  meet  the  requirements  not  only  of  the  specialist,  but  of  the  general 
practitioner  in  a  rare  degree.  I  am  satisfied  that  unusual  success  awaits  it." — William 
Pepper,  M.D.,  Professor  of  the  Theory  and  Practice  of  jMedicine  and  Clinical  Medicine, 
University  of  Pennsylvania. 

DORLAND'S  DICTIONARY. 

The  American  Pocket  Medical  Dictionary.  Containing  the  Pro- 
nunciation and  Derivation  of  over  26,000  words  and  phrases,  and  a  large 
number  of  useful  tables.  Edited  by  W.  A.  Newman  Dorland,  M.  D., 
Assistant  Demonstrator  of  Obstetrics,  LIniversity  of  Pennsylvania  ;  Fel- 
low of  the  American  Academy  of  Medicine.  518  pages;  handsomely 
bound  in  full  leather,  limp,  with  gilt  edges.      Price,  51.25  net. 

DORLAND'S  OBSTETRICS. 

A  Manual  of  Obstetrics.  By  W.  A.  Newman  Dorland,  M.D., 
Assistant  Demonstrator  of  Obstetrics,  University  of  Pennsylvania; 
Instructor  in  Gynecology  in  the  Philadelphia  Polyclinic.  760  pages; 
163  illustrations  in  the  text,  and  6  full-page  plates.     Cloth,  $2.50  net. 

"By  far  the  best  book  on  this  subject  that  has  ever  come  to  our  notice." — American 
Medical  Review. 

"  It  has  rarely  been  our  duty  to  review  a  book  which  has  given  us  more  pleasure  in  its 
perusal  and  more  satisfaction  in  its  criticism.  It  is  a  veritable  encyclopedia  of  knowledge, 
a  gold  mine  of  practical,  concise  thoughts." — American  Medico-Surgical  Bulletin. 


Medical  Publications  of  W.  B.  Saunders.  11 


FROTHINGHAM'S  GUIDE  FOR  THE  BACTERIOLOGIST. 

Laboratory  Guide  for  the  Bacteriologist.  By  Langdon  Froth- 
in(;ham,  M.D.V.,  Assistant  in  Bacteriology  and  Veterinary  Science, 
Sheffield  Scientific  School,  Yale  University.    Illustrated.    Cloth,  75  cts. 

"  It  is  a  convenient  and  useful  little  work,  and  will  more  than  repay  the  outlay  neces- 
sary for  its  ]HUchase  in  the  saving  of  time  which  would  otherwise  be  consumed  in  looking 
up  the  various  points  of  technique  so  clearly  and  concisely  laid  down  in  its  pages." — Ameri- 
can Medico- Surgical  BuUelin. 

GARRIGUES'  DISEASES  OF  WOMEN.  Second  Edition,  Revised. 
Diseases  of  Women.  By  Henry  J.  Garrigues,  A.M.,  M.D.,  Pro- 
fessor of  Gynecology  in  the  New  York  School  of  Clinical  Medicine ; 
Gynecologist  to  St.  Mark's  Hospital  and  to  the  German  Dispensary, 
New  York  City,  etc.  Handsome  octavo  volume  of  728  pages,  illus- 
trated by  335  engravings  and  colored  plates.  Cloth,  $4.00  net; 
Sheep  or  Half  Morocco,  ^5.00  net. 

"  One  of  the  best  text-books  for  students  and  practitioners  which  has  been  published  in 
the  English  language  ;  it  is  condensed,  clear,  and  comprehensive.  The  profound  learning 
and  great  clinical  experience  of  the  distinguished  author  find  expression  in  this  book  in  a 
most  attractive  and  instructive  form.  Young  practitioners  to  whom  experienced  consultants 
may  not  be  available  will  find  in  this  book  invaluable  counsel  and  help." — Thad.  A. 
Reamv,  M.D.,  LL.D.,  Professor  of  Clinical  Gymecology,  Medical  College  of  Ohio. 

GLEASON'S  DISEASES  OF  THE  EAR.  Second  Edition,  Revised. 
Essentials  of  Diseases  of  the  Ear.  By  E.  B.  Gleason,  S.B., 
M.D.,  Clinical  Professor  of  Otology,  Medico-Chirurgical  College, 
Philadelphia  ;  Surgeon-in-Charge  of  the  Nose,  Throat,  and  Ear  Depart- 
ment of  the  Northern  Dispensary,  Philadelphia.  208  pages,  with 
114  illustrations.  Cloth,  ^i.oo  ;  interleaved  for  notes,  $1.25. 
[See  Saunders'   Question- Compends,  page  21.] 

"  It  is  just  the  book  to  put  into  the  hands  of  a  student,  and  cannot  fail  to  give  him  a 
useful  introduction  to  ear-affections  ;  while  the  style  of  question  and  answer  which  is  adopted 
throughout  the  book  is,  we  believe,  the  best  method  of  impressing  facts  permanently  on  the 
mind. " — Liverpool  Medico-  Chiru7gical  Journal. 

GOULD  AND  PVLE'S  CURIOSITIES  OF  MEDICINE. 

Anomalies  and  Curiosities  of  Medicine.  By  George  M.  Gould, 
M.D.,  and  Walter  L.  Pyle,  M.D.  An  encyclopedic  collection  of 
rare  and  extraordinary  cases  and  of  the  most  striking  instances  of 
abnormality  in  all  branches  of  Medicine  and  Surgery,  derived  from  an 
exhaustive  research  of  medical  literature  from  its  origin  to  the  "present 
day,  abstracted,  classified,  annotated,  and  indexed.  Handsome  im- 
perial octavo  volume  of  968  pages,  with  295  engravings  in  the  text, 
and  12  full-page  plates.  Cloth,  $6.00  net;  Half  Morocco,  $7.00  net. 
Sold  by  Subscription. 

"  One  of  the  most  valuable  contributions  ever  made  to  medical  literature.  It  is,  so  far 
as  we  know,  absolutely  unique,  and  every  page  is  as  fascinating  as  a  novel.  Not  alone  for 
the  medical  profession  has  this  volume  value :  it  will  serve  as  a  book  of  reference  for  all  who 
are  interested  in  general  scientific,  sociologic,  or  medico-legal  topics." — Brooklyn  Medical 
Journal. 

"This  is  certainly  a  most  remarkable  and  interesting  volume.  It  stands  alone  among 
medical  literature,  an  anomaly  on  anomalies,  in  that  there  is  nothing  like  it  elsewhere  in 
medical  literature.  It  is  a  book  full  of  revelations  from  its  first  to  its  last  page,  and  cannot 
but  interest  and  sometimes  almost  horrify  its  readers." — Atnerican  Medico- Surgical  Bulletin. 


12  Medical  Publications  of  W.  B.  Saunders. 


QRAFSTROM'S   MECHANO-THERAPY. 

A  Text-Book  of  Mechano-Therapy  (Massage  and  Medical  Gym- 
nastics). I'.y  AxKi,  V.  CiRAi'STKOM,  H.  Sc,  M.  D.,  late  Lieutenant  in 
the  Royal  Swedish  Army  ;  late  House  Physician  City  Hos])ital,  Ijlack- 
well's  Island,  New  York.    i2nio,  139  pages,  illustrated,    ("loth,  ;f!i.oonet. 

GRIFFITH  ON  THE  BABY.     Second  Edition,  Revised. 

The  Care  of  the  Baby.  By  J.  P.  Ckozer  Griffith,  M.D.,  Clini- 
cal Professor  of  Diseases  of  Children,  University  of  Pennsylvania; 
Physician  to  the  Children's  Hospital,  Philadelphia,  etc.  i2mo,  404 
pages,  with  67  illustrations  in  the  text,  and  5  plates.      Cloth,  $1.50. 

"  Tlie  best  book  for  the  use  of  the  young  mother  with  which  we  are  acquainted.  .  .  . 
There  are  very  few  general  practitioners  who  could  not  read  the  book  through  with  advan- 
tage."— Archives  of  Pediatrics. 

"The  whole  book  is  characterized  by  rare  good  sense,  and  is  evidently  written  liy  a 
master  liand.  It  can  be  read  with  benefit  not  only  by  mothers  but  by  medical  students  and 
by  any  practitioners  who  have  not  had  large  opportunities  for  observing  children." — Ameri- 
can Journal  of  Obstetrics. 

GRIFFITH'S  WEIGHT  CHART. 

Infant's  Weight  Chart.  Designed  by  J.  P.  Crozer  Griffith,  M.D., 
Clinical  Professor  of  Diseases  of  Children  in  the  University  of  Penn- 
sylvania, etc.      25  charts  in  each  pad.      Per  pad,  50  cents  net. 

A  convenient  blank  for  keeping  a  record  of  the  child's  weight  during  the  first  two  years 
of  life.  Printed  on  each  chart  is  a  curve  representing  the  average  weight  of  a  healthy  infant, 
so  that  any  deviation  from  the  normal  can  readily  be  detected. 

GROSS,  SAMUEL  D.,  AUTOBIOGRAPHY  OF. 

Autobiography  of  Samuel  D.  Gross,  M.D.,  Emeritus  Professor  of 
Surgery  in  the  Jefferson  Medical  College,  Philadelphia,  with  Remi- 
niscences of  His  Times  and  Contemporaries.  Edited  by  his  Sons, 
Samuel  W.  Gross,  M.D.,  LL.D.,  late  Professor  of  Principles  of  Sur- 
gery and  of  Clinical  Surgery  in  the  Jefferson  Medical  College,  and 
A.  Haller  Gross,  A.M.,  of  the  Philadelphia  Bar.  Preceded  by  a 
Memoir  of  Dr.  Gross,  by  the  late  Austin  Flint,  M.D.,  LL.D.  In 
two  handsome  volumes,  each  containing  over  400  pages,  demy  octavo, 
extra  cloth,  gilt  tops,  with  fine  Frontispiece  engraved  on  steel.  Price 
per  volume,  $2.50  net. 

"  Dr.  Gross  was  perhaps  the  most  eminent  exponent  of  medical  science  tiiat  America 
has  yet  produced.  His  Autobiography,  related  as  it  is  with  a  fulness  and  completeness 
seldom  to  be  found  in  such  works,  is  an  interesting  and  valuable  book.  He  conmients  on 
many  things,  especially,  of  course,  on  medical  men  and  medical  practice,  in  a  very  interest- 
ing way." — IJie  Spectator,  London,  England. 

HAMPTON'S  NURSING.  Second  Edition,  Revised  and  Enlarged. 
Nursing:  Its  Principles  and  Practice.  By  Isabel  Adams  Hami- 
TON,  Ciraduate  of  the  New  York  Training  School  for  Nurses  attached 
to  Bellevue  Hospital ;  late  Superintendent  of  Nurses  and  I'rincipal  of 
the  Training  School  for  Nurses,  Johns  Hopkins  Hospital,  Baltimore, 
Md.     12  mo,  512  pages,  illustrated.     Cloth,  $2.00  net. 

"  Seldom  have  we  perused  a  book  upon  the  subject  that  has  given  us  so  much  pleasure 
as  the  one  before  us.  We  would  strongly  urge  upon  the  members  of  our  own  profession  the 
need  of  a  book  like  this,  for  it  will  enable  each  of  us  to  become  a  training  school  in  him- 
self."—  Ontario  Medical  Journal. 


Medical  Publications  of  W.  B.  Saunders.  13 


HARE'S  PHYSIOLOGY.  Fourth  Edition,  Revised. 

Essentials  of  Physiology.  ]}y  H.  A.  Hakk,  M.I).,  Professor  of 
'Ihcrapcutics  and  Materia  Mcdica  in  the  Jefferson  Medical  College  of 
Phihulclphia.  Crown  octavo,  230  pages.  Cloth,  $1.00  net;  inter- 
leaved for  notes,  $1.25  net. 

[See  Saunders'  Question- Compends,  page  21.] 

"  The  best  condensation  of  physiological  knowledge  we  have  yet  seen." — Medical 
Record,  New  York. 

HART'S  DIET  IN  SICKNESS  AND  IN  HEALTH. 

Diet  in  Sickness  and  in  Health.  By  Mrs.  Ernest  Hart,  formerly 
Student  of  the  Faculty  of  Medicine  of  Paris  and  of  the  London  School 
of  Medicine  for  Women ;  with  an  Introduction  by  Sir  Hknrv 
Thompson,  F.R.C.S.,  M.D.,  London.     220  pages.      Cloth,  $1.50. 

"  We  recommend  it  cordially  to  the  attention  of  all  practitioners ;  both  to  them  and  to 
their  patients  it  may  be  of  the  greatest  service." — New  York  Medical  Journal. 

HAYNES'  ANATOMY. 

A  Manual  of  Anatomy.  By  Irving  S.  Havnes,  M.D.,  Adjunct 
Professor  of  Anatomy  and  Demonstrator  of  Anatomy,  Medical  Depart- 
ment of  the  New  York  University,  etc.  680  pages,  illustrated  with  42 
diagrams  in  the  text,  and  134  full-page  half-tone  illustrations  from 
original  photographs  of  the  author's  dissections.      Cloth,  $2.50  net. 

"  This  book  is  the  work  of  a  practical  instructor — one  who  knows  by  experience  the 
requirements  of  the  average  student,  and  is  able  to  meet  these  requirements  in  a  very  satisr- 
factory  way.      The  book  is  one  that  can  be  commended." — Medical  Record,  New  York. 

HEISLER'S  EMBRYOLOGY. 

A  Text=Book  of  Embryology.  By  John  C.  Heisler,  M.D.,  Pro- 
fessor of  Anatomy  in  the  Medico-Chirurgical  College,  Philadelphia. 
hi  Preparation. 

HIRST'S  OBSTETRICS. 

A  Text=Book  of  Obstetrics.  By  Barton  Cooke  Hirst,  M.D., 
Professor  of  Obstetrics  in  the  University  of  Pennsylvania.  Handsome 
octavo  volume  of  848  pages,  with  618  illustrations,  and  a  number  of 
colored  plates.     Cloth,  $5.00  net;  Sheep  or  Half  Morocco,  $6.00  net. 

This  work  represents  the  very  latest  teaching  in  the  practice  of  obstetrics  by  a  man  of 
extended  experience  and  recognized  authority.  The  book  emphasizes  especially,  as  a  work 
on  obstetrics  should,  the  practical  side  of  the  subject,  and  to  this  end  presents  an  unusually 
large  collection  of  illustrations,  the  majority  of  them  original. 

HYDE  AND  MONTGOMERY  ON  SYPHILIS  AND  THE  VENEREAL 
DISEASES. 
Syphilis  and  the  Venereal  Diseases.  By  James  Nevins  Hyde, 
M.D.,  Professor  of  Skin  and  Venereal  Diseases,  and  Frank  H.  Mont- 
gomery, M.D.,  Lecturer  on  Dermatology  and  Genito-L'rinary  Diseases 
in  Rush  Medical  College,  Chicago,  111.  618  pages,  profusely  illustrated. 
Cloth,  $2.50  net. 

"  We  can  commend  this  manual  to  the  student  as  a  help  to  him  in  his  study  of  venereal 
diseases. ' ' — Liverpool  Medico-  Chirurgical  Journal. 

"The  best  student's  manual  which  has  appeared  on  the  subject." — St.  Louis  Medical 
and  Surgical  Journal. 


14  Medical  Publications  of  W.  B.  Saunders. 


JACKSON  AND  QLEASON'S  DISEASES  OF  THE  EYE,  NOSE,  AND 
THROAT.  Second  Edition,  Revised. 
Essentials  of  Refraction  and  Diseases  of  the  Eye.  By  Edward 
Jackson,  A.M.,  M.D.,  Professor  of  Diseases  of  the  Eye  in  the  Phila- 
delphia Polyclinic  and  College  for  Graduates  in  Medicine;  and — 
Essentials  of  Diseases  of  the  Nose  and  Throat.  By  E.  Bald- 
win Gleason,  M.D.,  Surgeon-in-Charge  of  the  Nose,  Throat,  and 
Ear  Department  of  the  Northern  Dispensary  of  Philadelphia.  Two 
volumes  in  one.  Crown  octavo,  290  pages;  124  illustrations.  Cloth, 
$1.00;  interleaved  for  notes,  $1.25. 

[See  Saunders'  Question- Compends,  page  21.] 

"  Of  great  value  to  the  beginner  in  these  branches.  The  authors  are  both  capable  men, 
and  know  what  a  student  most  needs." — Medical  Record,  New  York. 

KEATINQ'S  DICTIONARY.     Second  Edition,  Revised. 

A  New  Pronouncing  Dictionary  of  Medicine,  with  Phonetic 
Pronunciation,  Accentuation,  Etymology,  etc.  Bv  John  M. 
Keating,  M.D.,  LL.D.,  Fellow  of  the  College  of  Physicians  of  Phila- 
delphia ;  Vice-President  of  the  American  Psediatric  Society ;  Editor 
"Cyclopaedia  of  the  Diseases  of  Children,"  etc.;  and  Henry 
Hamilton,  Author  of  '-'A  New  Translation  of  Virgil's  ^neid  into 
English  Rhyme,"  etc.;  with  the  collaboration  of  J.  Chalmers  Da- 
Costa,  M.D.,  and  Frederick  A.  Packard,  M.D.  With  an  Appendix 
containing  Tables  of  Bacilli,  Micrococci,  Leucomaines,  Ptomaines; 
Drugs  and  Materials  used  in  Antiseptic  Surgery ;  Poisons  and  their 
Antidotes ;  Weights  and  Measures ;  Thermometric  Scales ;  New 
Official  and  Unofficial  Drugs,  etc.  One  volume  of  over  800  pages. 
Prices,  with  Denison's  Patent  Ready-Reference  Index:  Cloth,  $5.00 
net;  Sheep  or  Half  Morocco,  $6.00  net;  Half  Russia,  $6.50  net. 
Without  Patent  Index:  Cloth,  $4.00  net;  Sheep  or  Half  Morocco, 
$5.00  net. 

"  I  am  much  pleased  witli  Keathig's  Dictionary,  and  shall  take  pleasure  in  recommend' 
ing  it  to  my  classes." — Henry  M.  Lyman,  M.D.,  Professor  of  the  Principles  and  Practict 
of  Medicine,  Rush  Medical  College,  Chicago,  III. 

"  I  am  convinced  that  it  will  be  a  very  valuable  adjunct  to  my  study-table,  convenient 
in  size  and  sufficiently  full  for  ordinary  use." — C.  A.  Lindslev,  M.D.,  Professor  of  the 
Theory  and  Practice  of  Medicine,  Medical  Dept.    Yale  University. 

KEATINQ'S  LIFE  INSURANCE. 

How  to  Examine  for  Life  Insurance.  By  John  M.  Keating, 
M.D.,  Fellow  of  the  College  of  Physicians  of  Philadelphia;  Vice- 
President  of  the  American  Pediatric  Society  ;  Ex-President  of  the 
Association  of  Life  Insurance  Medical  Directors.  Royal  octavo,  2H 
pages ;  with  two  large  half-tone  illustrations,  and  a  plate  prepared  by 
Dr.  McClellan  from  special  dissections ;  also,  numerous  other  illustra- 
tions.    Cloth,  $2.00  net. 

"  This  is  by  far  the  raost  useful  book  which  has  yet  appeared  on  insurance  examination, 
a  subject  of  growing  interest  and  importance.  Not  the  least  valuable  portion  of  the  volume 
is  Part  II,  which  consists  of  instructions  issued  to  their  examining  physicians  by  twenty-four 
representative  companies  of  this  country.  If  for  these  alone,  the  book  should  be  at  the  right 
hand  of  every  physician  interested  m  this  special  branch  of  medical  science." — The  Medical 
News. 


Medical  Piihlicntions  of  W,  B.  Saunders.  15 


KEEN  ON  THE  SURGERY  OF  TYPHOID  FEVER. 

The    Surgical   Complications  and   Sequels  of   Typhoid    Fever. 

By  Wm.  W.  Kkkn,  M.D.,  LI-.D.,  I'rofcssor  of  the  I'rinciplcs  of  Sur- 
gery and  of  Clinical  Surgery,  Jefferson  Medical  College,  Phila(ie]i)liia ; 
Corresponding  Member  of  the  Societe  de  Chirurgie,  Paris;  Honorary 
Member  of  the  Soci6t6  Beige  de  Chirurgie,  etc.  (Jctavo  volume  of 
386  pages,  illustrated.     Cloth,  113.00  net. 

"  This  is  probably  the  first  and  only  work  in  the  Knglish  language  that  gives  the  reader 
a  clear  view  of  what  typlioid  fever  really  is,  and  what  it  does  and  can  do  to  the  human 
organism.  This  book  should  be  in  the  possession  of  every  medical  man  in  America." — 
Atiurican  MeiiiiO-Sur;^ic(il  Hullitin. 

KEEN'S  OPERATION  BLANK.  Second  Edition,  Revised  Form. 
An  Operation  Blank,  with  Lists  of  Instruments,  etc.  Required 
in  Various  Operations,  rrejjared  by  W.  W.  Kken,  M.D.,  LL.D., 
Professor  of  the  Principles  of  Surgery  in  Jefferson  Medical  College, 
Philadelphia.  Price  per  pad,  containing  blanks  for  fifty  operations, 
50  cents  net. 

KYLE  ON  THE  NOSE  AND  THROAT. 

Diseases  of  the  Nose  and  Throat.  By  D.  Braden  Kyle,  M.D., 
Clinical  Professor  of  Laryngology  and  Rhinology,  Jefferson  Medical 
College,  Philadelphia;  Consulting  Laryngologist,  Rhinologist,  and 
Otologist,  St.  Agnes'  Hospital ;  Bacteriologist  to  the  Philadelphia 
Orthopedic  Hospital.     ///  Preparation. 

LAINE'S  TEMPERATURE  CHART. 

Temperature  Chart.  Prepared  by  D.  T.  Laine,  M.D.  Size  8  x  13^ 
inches.  A  conveniently  arranged  Chart  for  recording  Temperature, 
with  columns  for  daily  amounts  of  Urinary  and  Fecal  Excretions, 
Food,  Remarks,  etc.  On  the  back  of  each  chart  is  given  in  full  the 
method  of  Brand  in  the  treatment  of  Typhoid  Fever.  Price,  per  pad 
of  25  charts,  50  cents  net. 

"  To  the  busy  practitioner  this  chart  will  be  found  of  great  value  in  fever  cases,  and 
especially  for  cases  of  typhoid." — Indian  Lancet,  Calcutta. 

LOCKWOOD'S  PRACTICE  OF  MEDICINE. 

A  Manual  of  the  Practice  of  Medicine.  By  George  Roe  Lock- 
wood,  M.D.,  Professor  of  Practice  in  the  Woman's  Medical  College 
of  the  New  York  Infirmary,  etc.  935  pages,  with  75  illustrations  in 
the  text,  and  22  full-page  plates.      Cloth,  $2.50  net. 

•'  Gives  in  a  most  concise  manner  the  points  essential  to  treatment  usually  enumerated 
in  the  most  elaborate  works." — Massachusetts  Medical  Journal. 

LONG'S  SYLLABUS  OF  GYNECOLOGY. 

A  Syllabus  of  Gynecology,  arranged  in  Conformity  with  «'  An 
American  Text=Book  of  Gynecology."  By  J.  W.  Long,  M.D., 
Professor  of  Diseases  of  Women  and  Children,  Medical  College  of 
Virginia,  etc.      Cloth,  interleaved,  $1.00  net. 

"  The  book  is  certainly  an  admirable  ristimt  of  what  every  gynecological  student  and 
practitioner  should  know,  and  will  prove  of  value  not  only  to  those  who  have  the  '  American 
Text-Book  of  Gynecology,'  but  to  others  as  well." — Brooklyn  Medical  Journal. 


16  Medical  Publications  of  W.  B.  Saunders. 


MACDONALD'S  SURGICAL  DIAGNOSIS   \ND  TREATMENT. 

Surgical  Diagnosis  and  Treatment.  By  J.  W.  Macdonald,  M.D. 
Edin.,  F.R.C.S.,  Edin.,  Professor  of  the  Practice  of  Surgery  and  of 
Clinical  Surgery  in  Hamline  University;  Visiting  Surgeon  to  St. 
Barnabas'  Hospital,  Minneapolis,  etc.  Handsome  octavo  volume  of 
800  pages,  profusely  illustrated.  Cloth,  $5.00  net;  Half  Morocco, 
$6.00  net. 

"  A  thorough  and  complete  work  on  surgical  diagnosis  and  treatment,  free  from  pad- 
ding, full  of  valuable  material,  and  in  accord  with  the  surgical  teaching  of  the  day." — 7'ke 
Medical  Ne-vs,  Nrw  York. 

"The  work  is  brimful  of  just  the  kind  of  practical  information  that  is  useful  alike  to 
students  and  practitioners.  It  is  a  pleasure  to  commend  the  book  because  of  its  intrinsic 
value  to  the  medical  practitioner." — Cincinnati  Lancet- Clinic. 

MALLORY  AND  WRIGHT'S  PATHOLOGICAL  TECHNIQUE. 

Pathological  Technique.  A  Practical  Manual  for  Laboratory  Work 
in  Pathology,  Bacteriology,  and  Morbid  Anatomy,  with  chapters  on 
Post-Mortem  Technique  and  the  Performance  of  Autopsies.  By  Frank 
B.  Mallory,  A.M.,  M.D.,  Assistant  Professor  of  Pathology,  Harvard 
University  Medical  School,  Boston;  and  James  H.  Wright,  A.M., 
M.D.,  Instructor  in  Pathology,  Harvard  University  Medical  School, 
Boston.  Octavo  volume  of  396  pages,  handsomely  illustrated.  Cloth, 
$2.50  net. 

"  I  have  been  looking  forward  to  the  publication  of  this  book,  and  I  am  glad  to  say  that 
I  find  it  to  be  a  most  useful  laboratory  and  post-mortem  guide,  full  of  practical  information, 
and  well  up  to  date." — William  II.  Welch,  Professor  of  Pathology,  Johns  Hopkins  Uni- 
versity, Baltimore,  Md. 

MARTIN'S  MINOR  SURGERY,  BANDAGING,  AND  VENEREAL 
DISEASES.  Second  Edition,  Revised. 
Essentials  of  Minor  Surgery,  Bandaging,  and  Venereal 
Diseases.  By  Edward  Martin,  A.M.,  M.D.,  Clinical  Professor  of 
Genito- Urinary  Diseases,  University  of  Pennsylvania,  etc.  Crown 
octavo,  166  pages,  with  78  illustrations.  Cloth,  $1.00  ;  interleaved  for 
notes,  $1.25. 

[See  Satinders'  Question- Compends,  page  21.] 

"A  very  practical  and  systematic  study  of  the  subjects,  and  shows  the  author's  famil- 
iarity with  the  needs  of  students." — Therapeutic  Gazette. 

MARTIN'S  SURGERY.     Sixth  Edition,  Revised. 

Essentials  of  Surgery.  Containing  also  Venereal  Diseases,  Surgi- 
cal Landmarks,  Minor  and  Operative  Surgery,  and  a  complete  de- 
scription, with  illustrations,  of  the  Handkerchief  and  Roller  Bandages. 
By  Edward  Martin,  A.M.,  M.D.,  Clinical  Professor  of  Genito- 
urinary Diseases,  University  of  Pennsylvania,  etc.  Crown  octavo,  338 
pages,  illustrated.  With  an  Appendix  containing  full  directions  for  the 
preparation  of  the  materials  used  in  Antiseptic  Surgery,  etc.  Cloth, 
$1.00;  interleaved  for  notes,  $1.25. 

[See  Saunders'  Question- Compends,  page  21.] 

"Contains  all  necessary  essentials  of  modem  surgery  in  a  comparatively  small  space. 
Its  style  is  interesting,  and  its  illustrations  are  admirable." — Medical  and  Surgical  Reporter. 


Medical  Publications  of  W.  B.  iSaunders.  17 


McFARLAND'S  PATHOGENIC  BACTERIA.  Second  Edition,  Re- 
vised and  Greatly  Enlarged. 
Text-Book  upon  the  Pathogenic  Bacteria.  By  Joseph  McFar- 
LAND,  M.  D.,  Professor  of  Pathology  and  Bacteriology  in  the  Medico- 
Chirurgical  College  of  Philadelphia,  etc.  Octavo  volume  of  497  pages, 
finely  illustrated.     Cloth,  $2.50  net. 

"  Dr.  McFarland  lias  treated  the  subject  in  a  systematic  manner,  and  has  succeeded  in 
presenting  in  a  concise  and  readable  form  the  essentials  of  bacteriology  up  to  date.  Alto- 
gether, the  book  is  a  satisfactory  one,  and  I  shall  take  pleasure  in  recommending  it  to  the 
students  of  Trinity  College."— H.  B.  Anderson,  M.D. ,  Professor  of  Pathology  and Bac- 
teriologv.  Trinity  JMedical  College,  Toronto. 

MEIGS  ON  FEEDING  IN  INFANCY. 

Feeding  in  Early  Infancy.     By  Arthur  V.  Meigs,  M.D.     Bound 

in  limp  cloth,  flush  edges,  25  cents  net. 

"This  pamphlet  is  worth  many  times  over  its  price  to  the  physician.  The  author's 
experiments  and  conclusions  are  original,  and  have  been  the  means  of  doing  much  good." — 
Medical  Bulletin. 

MOORE'S  ORTHOPEDIC  SURGERY. 

A  Manual  of  Orthopedic  Surgery.  By  James  E.  Moore,  M.D., 
Professor  of  Orthopedics  and  Adjunct  Professor  of  Clinical  Surgery, 
University  of  Minnesota,  College  of  Medicine  and  Surgery.  Octavo 
volume  of  356  pages,  handsomely  illustrated.     Cloth,  $2.50  net. 

"  A  most  attractive  work.  The  illustrations  and  the  care  with  which  the  book  is  adapted 
to  the  wants  of  the  general  practitioner  and  the  student  are  worthy  of  great  praise." — Chicago 
Medical  Recorder. 

"  A  very  demonstrative  work,  every  illustration  of  which  conveys  a  lesson.  The  work  is 
a  most  excellent  and  commendable  one,  which  we  can  certainly  endorse  with  pleasure." — 
St.  Louis  Aledical  and  Surgical  Journal. 

MORRIS'S  MATERIA  MEDICA  AND  THERAPEUTICS.  Fifth 
Edition,  Revised. 
Essentials  of  Materia  Medica,  Therapeutics,  and  Prescription- 
Writing.  By  Henry  Morris,  M.D.,  late  Demonstrator  of  Thera- 
peutics, Jefferson  Medical  College,  Philadelphia;  Fellow  of  the  College 
of  Physicians,  Philadelphia,  etc.  Crown  octavo,  288  pages.  Cloth, 
$1.00;  interleaved  for  notes,  $1.25. 

[See  Saunders'  Question- Compe?ids,  page  21.] 

"  This  work,  already  excellent  in  the  old  edition,  has  been  largely  improved  by  revii- 
sion." — American  Practitioner  and  News. 

MORRIS,  WOLFF,  AND  POWELL'S  PRACTICE  OF  MEDICINE, 
Third  Edition,  Revised. 
Essentials  of  the  Practice  of  Medicine.  By  Henry  Morris,  M.D.^ 
late  Demonstrator  of  Therapeutics,  Jefferson  Medical  College,  Phila- 
delphia ;  with  an  Appendix  on  the  Clinical  and  Microscopic  Examina- 
tion of  Urine,  by  Lawrence  Wolff,  M.D. ,  Demonstrator  of  Chemistry,. 
Jefferson  Medical  College,  Philadelphia.  Enlarged  by  some  300  essen- 
tial formulae  collected  and  arranged  by  William  M.  Powell,  M.D.. 
Post-octavo,  488  pages.      Cloth,  ^2.00. 

[See  Saunders'  Question- Compends,  page  21.] 

"  The  teaching  is  sound,  the  presentation  graphic  ;  matter  full  as  can  be  desired,  and 
style  attractive." — American  Practitioner  and  News. 


18  Medical  Publications  of  W,  B.  Saunders. 


MORTEN'S  NURSE'S  DICTIONARY. 

Nurse's  Dictionary  of  Medical  Terms  and  Nursing  Treat- 
ment. Containing  Definitions  of  the  Principal  Medical  and  Nursing 
Terms  and  Abbreviations ;  of  the  Instruments,  Drugs,  Diseases,  Acci- 
dents, Treatments,  Operations,  Foods,  Appliances,  etc.  encountered 
in  the  ward  or  in  the  sick-room.  By  Honnor  Morten,  author  of 
"  How  to  Become  a  Nurse,"  etc.     i6mo,  140  pages.      Cloth,  $1.00. 

"  A  liandy,  compact  little  volume,  containing  a  large  amount  of  general  information,  all 
of  which  is  arranged  in  dictionary  or  encyclopedic  form,  thus  facilitating  (piick  reference. 
It  is  certainly  of  value  to  those  for  whose  use  it  is  published." — Chicago  Clinical  Kernew. 

NANCREDE'S  ANATOMY.     Fifth  Edition. 

Essentials  of  Anatomy,  including  the  Anatomy  of  the  Viscera. 
By  Charles  B.  Nancrede,  M.D.,  Professor  of  Surgery  and  of  Clini- 
cal Surgery  in  the  University  of  Michigan,  Ann  Arbor.  Crown  octavo, 
388  pages;  180  illustrations.  With  an  Appendix  containing  over  60 
illustrations  of  the  osteology  of  the  human  body.  Based  upon  Gray' s 
Anatomy.  Cloth,  $1.00;  interleaved  for  notes,  $i.2c^. 
[See  Satmders'  Question- Compends,  page  21.] 

"  For  self-quizzing  and  keeping  fresh  in  mind  the  knowledge  of  anatomy  gained  at 
school,  it  would  not  be  easy  to  speak  of  it  in  terms  too  favorable." — American  Practitioner. 

NANCREDE'S  ANATOMY  AND  DISSECTION.     Fourth  Edition. 
Essentials  of  Anatomy  and    Manual  of    Practical    Dissection. 

By  Charles  B.  Nancrede,  M.D.,  Professor  of  Surgery  and  of  Clinical 
Surgery,  University  of  Michigan,  Ann  Arbor.  Post-octavo  ;  500  pages, 
with  full-page  lithographic  plates  in  colors,  and  nearly  200  illustrations. 
Extra  Cloth  (or  Oilcloth  for  the  dissection-room),  ^2.00  net. 

"  It  may  in  many  respects  be  considered  an  epitome  of  Gray's  popular  work  on  general 
anatomy,  at  the  same  time  having  some  distinguishing  characteristics  of  its  own  to  commend 
it.  The  plates  are  of  more  than  ordinary  excellence,  and  are  of  especial  value  to  students 
in  their  work  in  the  dissecting  room." — Journal  of  the  American  Aledical  Association. 

NORRIS'S  SYLLABUS  OF  OBSTETRICS.  Third  Edition,  Revised. 
Syllabus  of  Obstetrical  Lectures  in  the  Medical  Department 
of  the  University  of  Pennsylvania.  By  Richard  C.  Norris, 
A.M.,  M.D.,  Demonstrator  of  Obstetrics,  University  of  Pennsylvania. 
Crown  octavo,  222  pages.     Cloth,  interleaved  for  notes,  $2.00  net. 

"This  work  is  so  far  superior  to  others  on  the  same  subject  that  we  take  pleasure  in 
calling  attention  briefly  to  its  excellent  features.  It  covers  the  subject  thoroughly,  and  will 
prove  invaluable  both  to  the  student  and  the  practitioner." — Medical  Record,  New  York. 

PENROSE'S  DISEASES  OF  WOMEN.     Second  Edition,  Revised. 
A  Text=Book  of  Diseases  of  Women.     By  Charles  B.  Penrose, 
M.D.,  Ph.D.,  Professor  of  Gynecology  in  the  University  of  Pennsyl- 
vania ;    Surgeon    to    the   Gynecean    Hospital,    Philadelphia.     Octavo 
volume  of  529  pages,  handsomely  illustrated.      Cloth,  ^3.50  net. 

<'I  shall  value  very  highly  the  copy  of  Penrose's  'Diseases  of  Women'  received. 
I  have  already  recommended  it  to  my  class  as  THE  BEST  book."— Howard  A.  Kelly. 
Professor  of  Gynecology  and  Obstetrics,  Johns  Hopkins  University,  Baltimore,  Md. 

"  The  book  is  to  be  commended  without  reserve,  not  only  to  the  student  but  to  the 
general  practitioner  who  wishes  to  have  the  latest  and  best  modes  of  treatment  explained 
with  absolute  clearness." — Therapeutic  Gazette. 


Medical  Publications  of  W.  B.  Saunders.  19 

POWELL'S  DISEASES  OF  CHILDREN.     Second  Edition. 

Essentials  of  Diseases  of  Children.  By  William  M.  Powell, 
M.D.,  Attending  Physician  to  the  Mercer  House  for  Invalid  Women 
at  Atlantic  City,  N.  J.  ;  late  Physician  to  the  Clinic  for  the  Diseases  of 
Children  in  the  Hospital  of  the  University  of  Pennsylvania.  Crown 
octavo,  222  pages.     Cloth,  j^i-oo;  interleaved  for  notes,  $1.25. 

[See  Saunders'  Question- Compends,  page  21.] 

"Contains  the  gist  of  all  the  best  works  in  the  department  to  which  it  relates."— 
American  Practitioner  and  News. 

PRINQLE'S  SKIN  DISEASES  AND  SYPHILITIC  AFFECTIONS. 
Pictorial  Atlas  of  Skin  Diseases  and  Syphilitic  Affections 
(American  Edition).  Translation  from  the  French.  Edited  by 
J.  J.  Pringle,  M.B.,  F.R.C.P.,  Assistant  Physician  to  the  Middlesex 
Hospital,  London.  Photo-lithochromes  from  the  famous  models  in 
the  Museum  of  the  Saint-Louis  Hospital,  Paris,  with  explanatory  wood- 
cuts and  text.  In  12  Parts.  Price  per  Part,  $3.00.  Complete  in 
one  volume,  Half  Morocco  binding,  $40.00  net. 

**  I  strongly  recommend  this  Atlas.  The  plates  are  exceedingly  well  executed,  and 
will  be  of  great  value  to  all  studying  dermatology." — Stephen  Mackenzie,  M.D. 

"The  introduction  of  explanatory  wood-cuts  in  the  text  is  a  novel  and  most  important 
feature  which  greatly  furthers  the  easier  understanding  of  the  excellent  plates,  than  which 
nothing,  we  venture  to  say,  has  been  seen  better  in  point  of  correctness,  beauty,  and  general 
merit." — AWc  Vori  Aledical  Journal. 

PYE'S  BANDAGING. 

Elementary  Bandaging  and  Surgical  Dressing.  With  Direc- 
tions concerning  the  Immediate  Treatment  of  Cases  of  Emergency. 
For  the  use  of  Dressers  and  Nurses.  By  Walter  Pye,  F.R.C.S.,  late 
Surgeon  to  St.  Mary's  Hospital,  London.  Small  i2mo,  with  over  80 
illustrations.      Cloth,  flexible  covers,  75  cents  net. 

"  The  directions  are  clear  and  the  illustrations  are  good." — London  Lancet. 
"  The  author  writes  well,  the  diagrams  are  clear,  and  the  book  itself  is  small  and  port- 
able, although  the  paper  and  type  are  good." — British  Medical  Journal. 

RAYMOND'S  PHYSIOLOGY. 

A  Manual  of  Physiology.  By  Joseph  H.  Raymond,  A.M.,  M.D., 
Professor  of  Physiology  and  Hygiene  and  Lecturer  on  Gynecology  in 
the  Long  Island  College  Hospital;  Director  of  Physiology  in  the 
Hoagland  Laboratory,  etc.  382  pages,  with  102  illustrations  in  the 
text,  and  4  full-page  colored  plates.      Cloth,  ^1.25  net. 

'•  Extremely  well  gotten  up,  and  the  illustrations  have  been  selected  with  care.  The 
text  is  fully  abreast  with  modern  physiology." — British  Medical  Journal. 

RONTGEN  RAYS. 

Archives  of  the  Rontgen  Ray  (Formerly  Archives  of  Clinical 
Skiagraphy).  Edited  by  Sydney  Rowland,  M.A.,  M.R.C.S.,  and 
W.  S.  Hedley,  M.D.,  M.R.C.S.  A  series  of  collotype  illustrations, 
with  descriptive  text,  illustrating  the  applications  of  the  new  photo- 
graphy to  Medicine  and  Surgery.  Price  per  Part,  $1.00.  Now  ready: 
Vol.  I  ,  Parts  I.  to  IV.;  Vol.  II.,  Parts  I.,  II. 


Saunders' 
Question 
compends 


Arranged  in  Question  and 
Answer  Form, 

npHE  MOST  COMPLETE  AND  BEST 
ILLUSTRATED  SERIES  OF 


COMPENDS  EVER  ISSUED. 

Now  the  Standard  Authorities  in  Medical  Literature  .... 

with  Students  and  Practitioners  in  every  City  of  the  United  States  and  Canada. 


•<3 


^    OVER  ^  65,000  COPIES  SOLD.    ^ 
THE  REASON  WHY, 

They  are  the  advance  guard  of  "Student's  Helps" — that  DO  HELP.  They  are  the 
leaders  in  their  special  line,  well  and  authoritatively  written  by  able  men,  who,  as  teachers  in 
the  large  colleges,  know  exactly  what  is  wanted  by  a  student  preparing  for  his  examinations. 
The  judgment  exercised  in  the  selection  of  authors  is  fully  demonstrated  by  their  professional 
standing.  Chosen  from  the  ranks  of  Demonstrators,  Quiz-masters,  and  Assistants,  most  of 
them  have  become  Professors  and  Lecturers  in  their  respective  colleges. 

Each  book  is  of  convenient  size  (5x7  inches),  containing  on  an  average  250  pages, 
profusely  illustrated,  and  elegantly  printed  in  clear,  readable  type,  on  fine  paper. 

The  entire  series,  numbering  twenty-three  volumes,  has  been  kept  thoroughly  revised 
and  enlarged  when  necessary,  many  of  the  books  being  in  their  fifth  and  sixth  editions. 

TO  SUM  UP> 

Although  there  are  numerous  other  Quizzes,  Manuals,  Aids,  etc.  in  the  market,  none  of 
them  approach  the  "  Blue  Series  of  Question  Compends;"  and  the  claim  is  made  for  the 
following  points  of  excellence  : 

1.  Professional  distinction  and  reputation  of  authors. 

2.  Conciseness,  clearness,  and  soundness  of  treatment. 

3.  Quality  of  illustrations,  pajier,  printing,  and  binding. 

Any  of  these  Compends  will  be   mailed  on  receipt  of  price  (see  next  page  for  .List). 


Saunders^  Question-Compend  beries* 

Price»  Cloth,  $1.00  per  copy,  except  when  otherwise  noted, 

"Where   Ihe  work   of  prepariiiR   students'  manuals   is   to  end  we   cannot   say,  but  the 
Saunders  Series,  in  our  opinion,  bears  off  the  palm  at  present."— iV^zt/  Vork  Medical  Record. 


1.  ESSENTIALS  OF  PHYSIOLOGY.     By  H.  A.  Hare,  M.D.    Fourth  edition, 

revised  and  enlarged.      ($l.oo  net.) 

2.  ESSENTIALS   OF   SURGERY.     By  Edward  Martin,  M.D.      Sixth  edition, 

revisetl,  with  an  Appendix  on  Antiseptic  Surgery. 

3.  ESSENTIALS   OF   ANATOMY.      By  Charlks   B.    Nancrede,   M.D.     Fifth 

edition,  with  an  Appendix. 

4.  ESSENTIALS  OF  MEDICAL  CHEMISTRY,  ORGANIC  AND  INORGANIC. 

By  Lawrence  Wolfe,  M.D.     Fourth  edition,  revised,  with  an  Appendix. 

5.  ESSENTIALS  OF  OBSTETRICS.     By  W.  Easterly  Ashton,  M.D.     Fourth 

edition,  revised  and  enlarged. 

6.  ESSENTIALS  OF  PATHOLOGY  AND  MORBID  ANATOMY.     By  C.  E. 

Armand  Semple,  M.D. 

7.  ESSENTIALS  OF  MATERIA  MEDICA,  THERAPEUTICS,  AND   PRE- 

SCRIPTION=WRITING.    By  Henry  Morris,  M.D.       Fifth  edition,  revised. 

8.  9.    ESSENTIALS   OF    PRACTICE    OF    MEDICINE.      By   Henry   Morris, 

M.D.     An  Appendix  on  Urine  Examination.     By  Lawrence  Wolff,  M.D. 

Third  edition,  enlarged  by  some  300  Essential  Formulae,  selected  from  eminent 

authorities,  by  Wm.  "^M.  Powell,  M.D.     (Double  number,  ^2.00.) 
10.    ESSENTIALS  OF  GYNECOLOGY.      By  Edwin  B.  Cragin,  M.D.      Fourth 

edition,  revised. 
U.    ESSENTIALS  OF  DISEASES  OF  THE  SKIN.     By  Henry  W.  Stelwagon, 

M.D.      Third  edition,  revised  and  enlarged.      ($1.00  net.) 

12.  ESSENTIALS  OF  MINOR  SURGERY,  BANDAGING,  AND  VENEREAL 

DISEASES.     By  Edward  Martin,  M.D.     Second  ed.,  revised  and  enlarged. 

13.  ESSENTIALS  OF  LEGAL  MEDICINE,  TOXICOLOGY,  AND  HYGIENE. 

By  C.  E.  Armand  Semple,  M.D. 
14     ESSENTIALS  OF   DISEASES  OF  THE   EYE,  NOSE,  AND  THROAT. 

By  Edward  Jackson,  M.D.,  and  E.  B.  Gleason,  M.D.     Second  ed.,  revised. 

15.  ESSENTIALS  OF  DISEASES  OF  CHILDREN.     By  William  M.  Powell, 

M.  D.      Second  edition. 

16.  ESSENTIALS  OF   EXAMINATION    OF   URINE.     By   Lawrence  Wolff, 

M.D.      Colored  "  VoGEL  Scale."      (75  cents.) 

17.  ESSENTIALS  OF  DIAGNOSIS.     By  S.  Solis  Cohen,  M.D.,  and  A.  A.  Eshner, 

M.D.      ($1.50  net.) 

18.  ESSENTIALS  OF  PRACTICE   OF   PHARMACY.     By   Lucius   E.    Sayre. 

Second  edition,  revised  and  enlarged. 

20.  ESSENTIALS  OF  BACTERIOLOGY.     By  M.  V.  Ball,  M.D.     Third  edition, 

revised. 

21.  ESSENTIALS  OF  NERVOUS  DISEASES  AND  INSANITY.     By  John  C. 

Shaw,  M.D.     Third  edition,  revised. 

22.  ESSENTIALS  OF   MEDICAL  PHYSICS.      By   Fred  J.    Brockway,    M.D. 

Second  edition,  revised.      ($1.00  net.) 

23.  ESSENTIALS  OF  MEDICAL  ELECTRICITY.    By  David  D.  Stewart,  M.D., 

and  Edward  S.  Lawrance,  M.D. 

24.  ESSENTIALS  OF  DISEASES  OF  THE   EAR.      By  E.  B.  Gleason,  M.D 

Second  edition,  revised  and  greatly  enlarged. 


PampWet  containing  specimen  pages,  etc  sent  free  upon  application. 


I 

1- 


Saunders' 

New  Series 
of  Manuals 


for  Students 
and 
Practitioners. 


■*  I  'HAT  there  exists  a  need  for  thoroughly  reliable  hand-books  on  the  leading  branches 
of  Medicine  and  Surgery  is  a  fact  amply  demonstrated  by  the  favor  with  which 
the  SAUNDERS  NEW  SERIES  OF  MANUALS  have  been  received  by  medical 
students  and  practitioners  and  by  the  Medical  Press.  These  manuals  are  not  merely 
condensations  from  present  literature,  but  are  ably  w^ritten  by  w^ell-known  authors 
and  practitioners,  most  of  them  being  teachers  in  representative  American  colleges* 
Each  volume  is  concisely  and  authoritatively  w^ritten  and  exhaustive  in  detail,  without 
being  encumbered  -with  the  introduction  of  "cases,"  which  so  largely  expand  the 
ordinary  text-book.  These  manuals  will  therefore  form  an  admirable  collection  of 
advanced  lectures,  useful  alike  to  the  medical  student  and  the  practitioner:  to  the 
latter,  too  busy  to  search  through  page  after  page  of  elaborate  treatises  for  w^hat  he 
wants  to  know^,  they  w^ill  prove  of  inestimable  value ;  to  the  former  they  will  afford 
safe  guides  to  the  essential  points  of  study. 

The  SAUNDERS  NEW  SERIES  OF  MANUALS  are  conceded  to  be  superior 
to  any  similar  books  now  on  the  market.  No  other  manuals  afford  so  much  infor- 
mation in  such  a  concise  and  available  form.  A  liberal  expenditure  has  enabled  the 
publisher  to  render  the  mechanical  portion  of  the  w^ork  worthy  of  the  high  literary 
standard  attained  by  these  books. 

Any  of  these  Manuals  w^ill  be  mailed  on  receipt  of  price  (see  next  page  for  List). 


Saunders^  New  Series  of  Manuals* 


VOLUMES    PUBLISHED. 

PHYSIOLOGY.  By  Joski>h  Howard  Raymond,  A.M.,  M.D.,  Professor  of  Physiology 
and  Hygiene  and  Lecturer  on  Gynecology  in  the  Long  Island  College  Hospital; 
Director  of  Physiology  in  the  Hoagland  Laboratory,  etc.     Illustrated.     Cloth,  jgl.aj;  net. 

SURGERY,  General  and  Operative.  IJy  John  Chai.mkks  DaCosta,  M.D.,  Clini- 
cal I'rolcssor  of  Surgery,  Jelierson  Medical  College,  Philadelphia;  Surgeon  to  the 
Philadelphia  Hos]iilal,  etc.  Second  edition,  thoroughly  revised  and  greatly  enlarged. 
Octavo,  911  pages,  profusely  illustrated.      Cloth,  M-OO  net ;   Half  Morocco,  $5.00  net. 

DOSE=BOOK    AND    MANUAL    OF    PRESCRIPTION-WRITING.      By   E.    Q. 

TiioKNToN,    M.I).,   Demonstrator  of  Therapeutics,  Jeffer.son   Medical  College,  Phila- 
(lel[ihia.      Illustrated.      Cloth,  $1.25  net. 

SURGICAL  ASEPSIS.  By  Car t.  Beck,  M.D.,  Surgeon  to  St.  Mark's  Hospital  and 
to  the  New  York  German  PoliUlinik,  etc.     Illustrated.     Cloth,  ;?1.25  net. 

MEDICAL  JURISPRUDENCE.  By  Henry  C.  Chapman,  M.D.  Professor  of  Insti- 
tutes of  Medicine  and  Medical  Jurisprudence  in  the  Jeffenson  Medical  College  of  Phila- 
delphia.     Illustrated.      Cloth,  #1.50  net. 

SYPHILIS  AND  THE  VENEREAL  DISEASES.  By  James  Nevins  Hyde,  M.D., 
Professor  of  Skin  and  Venereal  Diseases,  and  Frank  H.  Montgomery,  M.D., 
Lecturer  on  Dermatology  and  Genito-Urinary  Diseases  in  Rush  Medical  College, 
Chicago.     Profusely  illustrated.     Cloth,  ^2.50  net. 

PRACTICE  OF  MEDICINE.  By  George  Roe  Lockwood,  M.D.,  Professor  of 
Practice  in  the  Woman's  Medical  College  of  the  New  York  Infirmary ;  Instructor  in 
Physical  Diagnosis  in  the  Medical  Department  of  Columbia  College,  etc.  Illustrated. 
Cloth,  ^2.50  net. 

MANUAL  OF  ANATOMY.  By  Irving  S.  Haynes,  M.D.,  Adjunct  Professor  of 
Anatomy  and  Demonstrator  of  Anatomy,  Medical  Department  of  the  New  York 
University,  etc.      Beautifully  illustrated.      Cloth,  $2.50  net. 

MANUAL  OF  OBSTETRICS.  By  W.  A.  Newman  Dorland,  M.D.,  Assistant 
Demonstrator  of  Obstetrics,  University  of  Pennsylvania  ;  Chief  of  Gynecological  Dis- 
pensary, Pennsylvania  Hospital,  etc.     Profusely  illustrated.     Cloth,  ^2.50  net. 

DISEASES  OF  WOMEN.  By  J.  Bland  Sutton,  F.  R.  C.  S.,  Assistant  Surgeon  to 
Middlesex  Hospital  and  Surgeon  to  Chelsea  Hospital,  London;  and  Arthur  E. 
Giles,  M.  D.,  B.  Sc.  Lond.,  F.R.C.S.  Edin.,  Assistant  Surgeon  to  Chelsea  Hospital, 
London.     Handsomely  illustrated.     Cloth,  ^2.50  net. 


VOLUMES  IN  PREPARATION. 

NOSE  AND  THROAT.  By  D.  Braden  Kyle,  M.D.,  Clinical  Professor  of  Laryn- 
gology and  Rhinology,  Jefferson  Medical  College,  Philadelphia ;  Consulting  Laryngolo- 
gist,  Rhinologist,  and  OtologLst,  St.  Agnes'  Hospital;  Bacteriologist  to  the  Philadel- 
phia Orthopedic  Hospital  and  Infirmary  for  Nervous  Diseases,  etc. 

NERVOUS  DISEASES.  By  Charles  W.  Burr,  M.D.,  Clinical  Professor  of  Nervous 
Diseases,  Medico-Chirurgical  College.  Philadelphia;  Pathologist  to  the  Orthopaedic 
Hospital  and  Infirmary  for  Nervous  Diseases;  Visiting  Physician  to  the  St.  Joseph 
Hospital,  etc. 

***  There  will  be  published  in  the  same  series,  at  short  intervals,  carefully-prepared  works 
on  various  subjects  by  prominent  specialists. 


Pamphlet  containing  specimen  pages,  etc.  sent  free  upon  application. 


24  Medical  Publications  of  W.  B.  Saunders. 


SAUNDBY'S  RENAL  AND  URINARY  DISEASES. 

Lectures  on  Renal  and  Urinary  Diseases.  P>y  Robert  Saundby, 
M.D.  Edin.,  Fellow  of  the  Royal  College  of  Physicians,  London,  and 
of  the  Royal  Medico-Chirurgical  Society  ;  Physician  to  the  General 
Hospital  ;  Consulting  Physician  to  the  Eye  Hospital  and  to  the  Hos- 
pital for  Diseases  of  Women;  Professor  of  Medicine  in  Mason  College, 
Birmingham,  etc.  Octavo  volume  of  434  pages,  with  numerous  illus- 
trations and  4  colored  plates.     Cloth,  $2.50  net. 

"  The  volume  makes  a  favorable  impression  at  once.  The  style  is  clear  and  succinct. 
We  cannot  find  any  part  of  the  subject  in  which  the  views  expressed  are  not  carefully  thought 
out  and  fortified  by  evidence  drawn  from  the  most  recent  sources.  The  book  may  be  cordially 
recommended." — British  IMedical  Jonrnal. 

5AUNDERS'  MEDICAL  HAND=ATLASES. 

This  series  of  books  consists  of  authorized  translations  into  English  of 
the  world-famous    Lehmann    Medicinische    liandatlanten.     I<2ach 

volume  contains  from  50  to  100  colored  lithographic  ])lates,  besides 
numerous  illustrations  in  the  te.xt.  There  is  a  full  description  of  each 
plate,  and  each  book  contains  a  condensed  but  adequate  outline  of  the 
subject  to  which  it  is  devoted.  For  full  description  of  this  series,  with 
list  of  volumes  and  prices,  see  page  2. 

"Lehmann  Medicinische  liandatlanten  belong  to  that  class  of  books  that  arc  too  good 
to  be  appropriated  by  any  one  nation." — Journal  of  Eye,  Ear,  and  T/iroat  Diseases. 

'•  The  appearance   of  these  works  marks  a  new  era  in   illustrated   English  medical 

works."' — Thr  Canaiiian  Practitioner. 

5AUNDERS'   POCKET  MEDICAL   FORMULARY.      Fifth   Edition, 
Revised. 

By  William  M.  Powell,  M.D.,  Attending  Physician  to  the  Mercer 
House  for  Invalid  Women  at  Atlantic  City,  N.  J.  Containing  i8qo 
ibrmulce  selected  from  the  best-known  authorities.  With  an  Appen- 
dix containing  Posological  Table,  Formulae  and  Doses  for  Hypo- 
dermic Medication,  Poisons  and  their  Antidotes,  Diameters  of  the 
Female  Pelvis  and  Foetal  Head,  Obstetrical  Table,  Diet  List  for  Various 
Diseases,  Materials  and  Drugs  used  in  Antiseptic  Surgery,  Treatment 
of  Asphyxia  from  Drowning,  Surgical  Remembrancer,  Tables  of 
Incompatibles,  Eruptive  Fevers,  Weights  and  Measures,  etc.  Hand- 
somely bound  in  flexible  morocco,  with  side  index,  wallet,  and  flap. 
$1.75  net. 

"  This  little  book,  that  can  be  conveniently  carried  in  the  pocket,  contains  an  immense 
amount  of  material.  It  is  very  useful,  and,  as  the  name  of  the  author  of  each  jirescription 
is  given,  is  unusually  reliable." — Medical  Record,  New  York. 

SAYRE'S  PHARMACY.     Second  Edition,  Revised. 

Essentials  of  the  Practice  of  Pharmacy.  By  Lucius  E.  Sayre, 
M.D.,  Professor  of  Pharmacy  and  Materia  Medica  in  the  University  of 
Kansas.  Crown  octavo,  200  pages.  Cloth,  $1.00;  interleaved  for 
notes,  $1.25. 

[See  Saunders''  Question- Coftipends,  page  21.] 

"  The  topics  are  treated  in  a  simple,  practical  manner,  and  the  work  forms  a  very  useful 
Student's  manual." — Boston  iMedical  and  Stiigical  Journal. 


Medical  Publications  of  W.  B.  Saunders.  25 


SEMPLE'S  LEGAL  MEDICINE,  TOXICOLOGY,  AND  HYGIENE. 

Essentials  of    Legal    Medicine,  Toxicology,  and   Hygiene.     By 

C.  E.  Armanu  Skmi'Lk,  B.  A.,  M.  1}.  Cantab.,  M.  R.C.I'.  Lond., 
Physician  to  the  Northeastern  Hospital  for  Children,  Hackney,  etc. 
Crown  octavo,  212  pages;  130  illustrations.  Cloth,  ;gi. 00;  interleaved 
for  notes,  Si.  25. 

[See  Saunders'  Question- Compends,  page  21.] 

"  No  general  practitioner  or  student  can  afiord  to  be  without  this  valuable  work.  The 
subjects  are  dealt  with  by  a  masterly  hand." — Loudon  Hospital  Gazette. 

SEMPLE'S  PATHOLOGY  AND  MORBID  ANATOMY. 

Essentials    of    Pathology    and    Morbid    Anatomy.      By  C.   E. 

Armand  Semple,  B.A.,  M.B.  Cantab.,  M.R.C.P.  Lond.,  Physician  to 
the  Northeastern  Hospital  for  Children,  Hackney,  etc.     Crown  octavo, 
174  pages;  illustrated.      Cloth,  $1.00;   interleaved  for  notes,  $i.  25. 
[See  Saunders'  Question- Compends,  page  21.] 

"  Should  take  its  place  among  the  standard  volumes  on  the  bookshelf  of  both  student 
and  practitioner." — London  Hospital  Gazette. 

SENN'S  GENITO=URINARY  TUBERCULOSIS. 

Tuberculosis  of  the  Genito-Urinary  Organs,  Male  and  Female. 

By  Nicholas  Senn,  M.D.,  Ph.D.,  LL.D.,  Professor  of  the  Practice  of 
Surgery  and  of  Clinical  Surgery,  Rush  Medical  College,  Chicago. 
Handsome  octavo  volume  of  320  pages,  illustrated.     Cloth,  $3.00  net. 

"  An  important  book  upon  an  important  subject,  and  written  by  a  man  of  mature  judg- 
ment and  wide  experience.  The  author  has  given  us  an  instructive  book  upon  one  of  the 
most  important  subjects  of  the  day." — Clinical  Reporter. 

"  A  work  which  adds  another  to  the  many  obligations  the  profession  owes  the  talented 
author." — Chicago  Medical  Recorder. 

SENN'S  SYLLABUS  OF  SURGERY. 

A  Syllabus  of  Lectures  on  the  Practice  of  Surgery,  arranged 
in  conformity  with  "  An  American  Text=Book  of  Surgery."    By 

Nicholas  Senn,  M.D.,  Ph.D.,  Professor  of  the  Practice  of  Surgery  and 
of  Clinical  Surgery  in  Rush  Medical  College,  Chicago.     Cloth,  ;^2.oo. 

"  This  syllabus  will  be  found  of  service  by  the  teacher  as  well  as  the  student,  the  work 
being  superbly  done.     There  is  no  praise  too  high  for  it.     No  surgeon  should  be  without 

it. " — Ne7v  York  Medical  Times. 

SENN'S  TUMORS. 

Pathology  and  Surgical  Treatment  of  Tumors.  By  N.  Senn, 
M.D.,  Ph.D.,  LL.D.,  Professor  of  Surgery  and  of  Clinical  Surgery, 
Rush  Medical  College ;  Professor  of  Surgery,  Chicago  Polyclinic ; 
Attending  Surgeon  to  Presbyterian  Hospital ;  Surgeon-in-Chief,  St. 
Joseph's  Hospital,  Chicago.  Octavo  volume  of  710  pages,  with  515 
engravings,  including  full-page  colored  plates.  Cloth,  $6.00  net; 
Half  Morocco,  $7.00  net. 

"  The  most  exhaustive  of  any  recent  book  in  Engush  on  this  subject.  It  is  well  illus- 
trated, and  will  doubtless  remain  as  the  principal  monograph  on  the  subject  in  our  language 
for  some  years.  The  book  is  handsomely  illustrated  and  printed,  and  the  author  has  given  a 
notable  and  lasting  contribution  to  surgery. "—_/(?«/-««/  of  the  American  Medical  Association. 


26  Medical  Publications  of  W.  B.  Saunders. 


SHAW'S  NERVOUS  DISEASES  AND  INSANITY.  Third  Edition, 
Revised. 
Essentials  of  Nervous  Diseases  and  Insanity.  By  John  C. 
Shaw,  M.D.,  Clinical  Professor  of  Diseases  of  the  Mind  and  Nervous 
System,  Long  Island  College  Hospital  Medical  School ;  Consulting 
Neurologist  to  St.  Catherine's  Hospital  and  to  the  Long  Island  College 
Hospital.  Crown  octavo,  186  pages;  48  original  illustrations.  Cloth, 
$1.00  ;  interleaved  for  notes,  $1.25. 

[See  Saunders'  Question- Compends,  page  21.] 

"Clearly  and  intelligently  written." — Boston  Medical  atiJ  Surgical  Journal. 

"There  is  a  mass  of  valuable  material  crowded  into  this  small  compass." — American 
Medico-Surgical  Bulletin. 

STARR'S  DIETS  FOR  INFANTS  AND  CHILDREN. 

Diets  for  Infants  and  Children  in  Health  and  in  Disease.     By 

Louis  Starr,  M.D. ,  Editor  of  "An  American  Text-Book  of  the 
Diseases  of  Children."  230  blanks  (pocket-book  size),  perforated 
and  neatly  bound  in  flexible  morocco.      $1.25  net. 

The  first  series  of  blanks  are  prepared  for  the  first  seven  months  of  infant  life  ;  each 
blank  indicates  the  ingredients,  but  not  the  quantities,  of  the  food,  the  latter  directions  being 
left  for  the  physician.  After  the  seventh  month,  modifications  being  less  necessary,  the  diet 
lists  are  printed  in  full.      Formulas  for  the  preparation  of  diluents  and  foods  are  appended. 

STELW AGON'S  DISEASES  OF  THE  SKIN.  Third  Edition,  Revised. 
Essentials  of  Diseases  of  the  Skin.  By  Henry  W.  Stelwagon, 
M.D.,  Clinical  Professor  of  Dermatology  in  the  Jefferson  Medical 
College,  Philadelphia;  Dermatologist  to  the  Philadelphia  Hospital; 
Physician  to  the  Skin  Dei)artnient  of  the  Howard  Hospital,  etc. 
Crown  octavo,  270  pages;  86  illustrations.  Cloth,  $1.00  net;  inter- 
leaved for  notes,  $1.25  net. 

[See  Saunders'  Question- Compends,  page  21.] 
"  The  best  student's  manual  on  skin  diseases  we  have  yet  seen." — Times  and  Register. 

STENGEL'S  PATHOLOGY. 

A  Text=Book  of  Pathology.  By  Alfred  Stenoei.,  M.  D.,  Physician 
to  the  Philadeli)hia  Hospital ;  Clinical  Professor  of  Medicine  in  the 
Woman's  Medical  College  ;  Physician  to  the  Children's  Hospital ; 
late  Pathologist  to  the  German  Hosi)ital,  Philadelphia,  etc.  Handsome 
octavo  volume  of  848  ])ages,  with  nearly  400  illustrations,  many  of  them 
in  colors.     Cloth,  $4.00  net;   Half  Morocco,  $5.00  net. 

STEVENS'   MATERIA    MEDICA    AND   THERAPEUTICS.      Second 
Edition,  Revised. 
A  Manual  of   Materia   Medica   and  Therapeutics.      By  A.  A. 

Stevens,  A.M.,  M.D.,  Lecturer  on  Terminology  and  Instructor  in 
Physical  Diagnosis  in  the  University  of  Pennsylvania  ;  Professor  of 
Pathology  in  the  Woman's  Medical  College  of  Pennsylvania.  Post- 
octavo,  445  pages.     Flexible  leather,  $2.25. 

"The  author  has  faithfully  presented  modern  therapeutics  in  a  comprehensive  work, 
and,  while  intended  particularly  for  the  use  of  students,  it  will  be  found  a  reliable  guide  and 
sufficiently  comprehensive  for  the  physician  in  practice." — University  Medical  Magazine. 


Medical  Publications  of  W.  B.  Saunders.  27 


STEVENS'  PRACTICE  OF  MEDICINE.     Fifth  Edition,  Revised. 
A  Manual  of  the  Practice  of  Medicine.     \',y  A.  A.  Si  kvkns,  A.M., 
M.  1).,  IxctuiLT  on   Icrminology  and  Instructor  in   Physical  Diagnosis 
in   the    University   of    Pennsylvania;     J'rofessor    of    Pathology   in    the 
Woman's    Medical  College  of   Pennsylvania.     Speciallv  intended    for 
students    preparing  for   graduation  and    hospital  examinations.      Posi- 
octavo,  519  pages;   illustrated.     Fle.xible  leather,  $2.00  net. 
"The  frequency  with  which  new  editions  of  this  manual  are  demanded  bespeaks  its 
popularity.     It  is  an  excellent  condensation  of  the  essentials  of  medical  practice  for  the 
student,  and  maybe  found  also  an  excellent  reminder  for  the  busy  physician." — Buffalo 
Medical  Jounial.  ^  ■" 

STEWART'S  PHYSIOLOGY.      Third  Edition,  Revised. 

A  Manual  of  Physiology,  with  Practical  Exercises.  For 
Students  and  Practitioners.  By  G.  N.  Stewart,  M.A.,  M.D., 
D.Sc,  lately  Examiner  in  Physiology,  University  of  Aberdeen,  and 
of  the  New  Museums,  Cambridge  University ;  Professor  of  Physiology 
in  the  Western  Reserve  University,  Cleveland,  Ohio.  Octavo  volume 
of  848  pages;  300  illustrations  in  the  text,  and  5  colored  i>lates. 
Cloth,  $3.75  net. 

"  It  will  make  its  way  by  sheer  force  of  merit,  and  amply  deserves  to  do  so.  It  is  one 
of  the  very  best  English  text-books  on  the  subject." — London  Lancet. 

"Of  the  many  text-books  of  physiology  published,  we  do  not  know  of  one  that  so 
nearly  comes  up  to  the  ideal  as  does  Prof.  Stewart's  volume." — British  Medical  Journal. 

STEWART  AND  LAWRANCE'S  MEDICAL  ELECTRICITY. 

Essentials  of  Medical  Electricity.  By  D.  D.  Stewart,  M.D., 
Demonstrator  of  Diseases  of  the  Nervous  System  and  Chief  of  the 
Neurological  Clinic  in  the  Jefferson  Medical  College ;  and  E.  S. 
Lawrance,  M.D.,  Chief  of  the  Electrical  Clinic  and  Assistant  Demon- 
strator of  Diseases  of  the  Nervous  System  in  the  Jefferson  Medical 
College,  etc.  Crown  octavo,  158  pages;  65  illustrations.  Cloth, 
;^i.oo  ;  interleaved  for  notes,  $1.25. 

[See  Saunders'  Question- Compends,  page  21.] 

"  Throughout  the  whole  brief  space  at  their  command  the  authors  show  a  discriminating 
knowledge  of  their  subject." — Medical  News. 

STONEY'S  NURSING.     Second  Edition,  Revised. 

Practical  Points  in  Nursing.     For  Nurses  in  Private  Practice, 

By  Emily  A.  M.  Stoney,  Graduate  of  the  Training-School  for  Nurses, 
Lawrence,  Mass.;  late  Superintendent  of  the  Training-School  for 
Nurses,  Carney  Hospital,  South  Boston,  Mass.  456  pages,  illustrated 
with  73  engravings  in  the  text,  and  8  colored  and  half-tone  plates. 
Cloth,  $1.75  net. 

"  There  are  few  books  intended  for  non-professional  readers  which  can  be  so  cordially 
endorsed  by  a  medical  journal  as  can  this  one." — Therapeutic  Gazette. 

"  This  is  a  well-written,  eminently  practical  volume,  which  covers  the  entire  range  of 
private  nursing  as  distinguished  from  hospital  nursing,  and  instructs  the  nurse  how  best  to 
meet  the  various  emergencies  which  may  arise,  and  how  to  prepare  everything  ordinarily 
needed  in  the  illness  of  her  patient." — American  Journal  of  Obstetrics  and  Diseases  of 
Women  and  Children. 

"  It  is  a  work  that  the  physician  can  place  in  the  hands  of  his  private  nurses  with  the 
assurance  of  benefit." — Ohio  Aledical Journal. 


28  Medical  Publications  of  W.  B.  Saunders. 


STONEY'S   MATERIA   MEDICA    FOR   NURSES. 

Materia  Medica  for  Nurses.  P.y  Kmii.y  A.  M.  Stoney,  Graduate  of 
the  'rraining-School  lor  Nurses,  Lawrence,  Mass.  ;  late  Superintendent 
of  the  Training-School  for  Nurses,  Carney  Hospital.  South  Boston,  Mass. 
Handsome  octavo  volume  of  about  300  pages.     Cloth,  $1.50  net. 

The  present  book  differs  from  other  similar  works  in  several  features,  all  of  which  are 
intended  to  render  it  more  practical  and  generally  useful.  The  general  plan  of  the  contents 
follows  the  lines  laid  down  in  training-schools  for  nurses,  but  the  book  contains  much  use- 
ful matter  not  usually  included  in  works  of  this  character,  such  as  Poison-emergencies, 
Ready  Dose-list,  Weights  and  Measures,  etc.,  as  well  as  a  Glossary,  defining  all  the  terms 
used  in  Materia  Medica,  and  describing  all  the  latest  drugs  and  remedies,  which  have  been 
generally  neglected  by  other  books  of  the  kind. 

SUTTON  AND  GILES'  DISEASES  OF  WOMEN. 

Diseases  of  Women.  By  J.  Bland  Sutton,  F.R.C.S.,  Assistant 
Surgeon  to  Middlesex  Hospital,  and  Surgeon  to  Chelsea  Hospital, 
London;  and  Arthur  E.  Giles,  M.D.,  B.Sc.  Lond.,  F.R.C.S.  Edin., 
Assistant  Surgeon  to  Chelsea  Hospital,  London.  436  pages,  hand- 
somely illustrated.      Cloth,  $2.50  net. 

"The  text  has  been  carefully  prepared.  Nothing  essential  has  been  omitted,  and  its 
teachings  are  those  recommended  by  the  leading  authorities  of  the  day.'"— Journal  of  tkt 
Avieiican  Medical  Association. 

THOMAS'S  DIET  LISTS  AND  SICK=ROOM  DIETARY. 

Diet  Lists  and  Sick=Room  Dietary.  By  Jerome  B.  Thomas, 
M.D.,  Visiting  Physician  to  the  Home  for  Friendless  Women  and 
Children  and  to  the  Newsboys'  Home  ;  Assistant  Visiting  Physician 
to  the  Kings  County  Hospital.      Cloth,  $1.50.     Send  for  sample  sheet. 

THORNTON'S  DOSE=BOOK  AND  PRESCRIPTION=WRITING. 

Dose=Book  and  Manual  of    Prescription=Writing.       By   E.    Q. 

Thornton,  M.D.,  Demonstrator  of  Therapeutics,  Jefferson  Medical 
College,  Philadelphia.      334  pages,  illustrated.      Cloth,  $1.25  net. 

"Full  of  practical  suggestions;  will  take  its  place  in  the  front  rank  of  works  of  this 
sort." — Medical  Record,  New  York. 

VAN  VALZAH  AND  NISBET'S  DISEASES  OF  THE  STOMACH. 
Diseases  of  the  Stomach.  By  Willl\m  W.  Van  Valzah,  M.D.  , 
Professor  of  General  Medicine  and  Diseases  of  the  Digestive  System 
and  the  Blood,  New  Vork  Polyclinic;  and  J.  Douglas  Ntsbet,  M.D., 
Adjunct  Professor  of  General  Medicine  and  Diseases  of  the  Digestive 
System  and  the  Blood,  New  Vork  Polyclinic.  Octavo  volume  of  674 
pages,  illustrated.     Cloth,  $3-50  net. 

"  Its  chief  claim  lies  in  its  clearness  and  general  adaptability  to  the  practical  needs  of 
the  general  practitioner  or  student.  In  these  relations  it  is  probal)ly  the  best  of  the  recent 
special  works  on  diseases  of  the  stomach." — Chicago  Clinical  Review. 

VECKI'S   SEXUAL   IMPOTENCE. 

The  Pathology  and  Treatment  of  Sexual  Impotence.  By  Victor 
G.  Vecki,  M.D.  From  the  second  German  edition,  revised  and  en- 
larged.    Demi-octavo,  about  300  pages.     Cloth,  $2.00  net. 

The  subiect  of  impotence  has  seldom  been  treated  in  this  country  in  the  truly  scientific 
spirit  that  it  deserves.  Dr.  Vecki's  work  has  long  been  favorably  known,  and  the  German 
book  has  received  the  highest  consideration.  This  edition  is  more  than  a  mere  translation, 
for,  although  based  on  the  German  edition,  it  has  been  entirely  rewritten  in  English. 


Medical  Publications  of  W.  B.  Saunders.  29 

VIERORDT'S  MEDICAL  DIAGNOSIS.  Fourth  Edition,  Revised. 
Medical  Diagnosis.  By  Dr.  Oswald  Vierordt,  Professor  of  Medi- 
cine at  the  University  of  Heidelberg.  Translated,  with  additions, 
from  the  fifth  enlarged  German  edition,  with  the  author's  permission, 
by  Francis  H.  Stuart,  A.  M.,  M.  D.  Handsome  royal  octavo  volume 
of  603  pages;  194  fine  wood-cuts  in  text,  many  of  them  in  colors. 
Cloth,  $4.00  net;  Sheep  or  Half  Morocco,  $5.00  net. 

"  A  treasury  of  practical  information  which  will  be  found  of  daily  use  to  every  busy 
practitioner  who  will  consult  it." — C.  A.  LlNDSLEY,  M.D.,  Professor  of  the  Theory  and 
Practice  of  Medicine,   Yale  University . 

"  Rarely  is  a  book  published  with  which  a  reviewer  can  find  so  little  fault  as  with  the 
volume  before  us.  Each  particular  item  in  the  consideration  of  an  organ  or  apparatus,  which 
is  necessary  to  determine  a  diagnosis  of  any  disease  of  that  organ,  is  mentioned ;  nothing 
seems  forgotten.  The  chapters  on  diseases  of  the  circulatory  and  digestive  apparatus  and 
nervous  system  are  especially  full  and  valuable.  The  reviewer  would  repeat  that  the  book  is 
one  of  the  best — probably  the  best — which  has  fallen  into  his  hands." — University  Medical 
Magazine. 

WARREN'S  SURGICAL  PATHOLOGY  AND  THERAPEUTICS. 

Surgical  Pathology  and  Therapeutics.  By  John  Collins  Warren, 
M.D.,  LL.D.,  Professor  of  Surgery,  Medical  Department  Harvard 
University;  Surgeon  to  the  Massachusetts  General  Hospital,  etc. 
Handsome  octavo  volume  of  832  pages;  136  relief  and  lithographic 
illustrations,  33  of  which  are  printed  in  colors,  and  all  of  which  were 
drawn  by  William  J.  Kaula  from  original  specimens.  Cloth,  $6.00 
net;   Half  Morocco,  $7.00  net. 

"There  is  the  work  of  Dr.  Warren,  which  I  think  is  the  most  creditable  book  on 
Surgical  Pathology,  and  the  most  beautiful  medical  illustration  of  the  bookmaker's  art,  that 
has  ever  been  issued  from  the  American  press." — Dr.  Roswell  Park,  in  the  Harvard 
Graduate  Magazine. 

"  The  handsomest  specimen  of  bookmaking  that  has  ever  been  issued  from  the  American 
medical  press." — American  Journal  of  the  Medical  Sciences. 

"  A  most  striking  and  very  excellent  feature  of  this  book  is  its  illustrations.  Without 
e.xception,  from  the  point  of  accuracy  and  artistic  merit,  they  are  the  best  ever  seen  in  a  work 
of  this  kind.  Many  of  those  representing  microscopic  pictures  are  so  perfect  in  their  coloring 
and  detail  as  almost  to  give  the  beholder  the  impression  that  he  is  looking  down  the  barrel 
of  a  microscope  at  a  well-mounted  section." — Annals  of  Surgery. 

WOLFF  ON  EXAMINATION  OF  URINE. 

Essentials  of  Examination  of  Urine.  By  Lawrence  Wolff,  M.D., 
Demonstrator  of  Chemistry,  Jefferson  Medical  College,  Philadelphia, 
etc.  Colored  (Vogel)  urine  scale  and  numerous  illustrations.  Crown 
octavo.      Cloth,  75  cents. 

[See  Saunders'  Question- Compends,  page  21.] 

"  A  very  good  work  of  its  kind — very  well  suited  to  its  purpose." — Times  and  Register. 

WOLFF'S  MEDICAL  CHEMISTRY.     Fourth  Edition,  Revised. 
.  Essentials    of    Medical    Chemistry,   Organic    and    Inorganic. 

Containing  also  Questions  on  Medical  Physics,  Chemical  Physiology, 
Analytical  Processes,  Urinalysis,  and  Toxicology.  By  Lawrence 
Wolff,  M.D.,  Demonstrator  of  Chemistry,  Jefferson  Medical  College, 
Philadelphia,  etc.  Crown  octavo,  218  pages.  Cloth,  ^i.oo;  inter- 
leaved for  notes,  ^1.25. 

[See  Saunders'  Question- Compends,  page  21.] 

"The  scope  of  this  work  is  certainly  equal  to  that  of  the  best  course  of  lectures  on 
Medical  Chemistry." — Pharmaceutical  Era. 


CLASSIFIED    LIST 


Medical  Publications 


W.  B.  SAUNDERS, 

925  Walnut  Street,  Philadelphia. 


ANATOMY,  EMBRYOLOGY, 
HISTOLOGY. 

Clarkson — A  Text-Book  of  Histology,  9 
Haynes — A  Manual  of  Anatomy,  .  .  .  13 
Heisler — A  Text- Book  of  Embryology,  13 
Nancrede — Essentials  of  Anatomy,  .  .  18 
Nancrede — Essentials  of  Anatomy  and 

Manual  of  Practical  Dissection,  .  .  .  18 
Semple — Essentials   of   Pathology  and 

Morbid  Anatomy 25 

BACTERIOLOGY. 

Ball — Essentials  of  Bacteriology,  ...      6 
Crookshank — A  Text- Book  of  Bacteri- 
ology,   10 

Frothingham  — Laboratory  Guide,  .  .  11 
Mallory    and    Wright — Pathological 

Technique, 16 

McFarland — Pathogenic  Bacteria,    .    .    17 

CHARTS,  DIET-LISTS,  ETC. 

Griffith — Infant's  Weight  Chart,     ...  12 

Hart — Diet  in  Sickness  and  in  Health,  .  13 

Keen — Operation  Blank, 15 

Laine — Temperature  Chart,    ....  15 

Meigs — Feeding  in  Early  Infancy,     .    .  17 

Starr — Diets  for  Infants  and  Children,  .  26 
Thomas — Diet-Lists     and    Sick-Room 

Dietary, 28 

CHEMISTRY  AND  PHYSICS. 

Brockway — Essentials  of  Medical  Phys- 
ics,   7 

Wolff — Essentials  of  Medical  Chemistry,  29 

CHILDREN. 

An  American  Text-Book  of  Diseases 

of  Children,    .    .             3 

Griffith — Care  of  the  Baby 12 

Griffith — Infant's  Weight  Chart,   ...  12 

Meigs — Feeding  in  Early  Infancy,    .    .  17 

Powell — Essentials  of  Dis.  of  Children,  19 

Starr — Diets  for  Infants  and  Children,  .  26 

DIAGNOSIS. 

Cohen  and  Eshner  — Essentials  of  Di- 
agnosis  9 

Corwin — Physical  Diagnosis,      ....      9 

Macdonald — Surgical  Diagnosis  and 
Treatment,      16 

Vierordt — Medical  Diagnosis,    ....    29 

DICTIONARIES. 

Dorland — Pocket  Dictionary,     ....  10 

Keating — Pronouncing  Dictionary,    .    .  14 

Morten — Nurse's  Dictionary,     ....  18 


EYE,  EAR,  NOSE,   AND  THROAT. 

An  American  Text- Book  of  Diseases 

of  the  Eye,  Ear,  Nose,  and  Throat,  .  3 
De  Schweinitz — Diseases  of  the  Eye. .  10 
Gleason — Essentials  of  Dis.  of  the  Ear,  il 
Jackson   and    Gleason — Essentials  of 

Diseases  of  the  Eye,  Nose,  and  Throat,  14 
Kyle — Diseases  of  the  Nose  and  Throat,  15 

GENITO=URINARY. 

An  American  Text-Book  of  Genito- 
urinary and  Skin  Diseases, 4 

Hyde  and  Montgomery — Syphilis  and 

the  Venereal  Diseases, 13 

Martin — Essentials   of  Minor   Surgery. 

Bandaging,  and  Venereal  Diseases,  .  16 
Saundby — Renal  and  Urinary  Diseases,  24 
Senn — Genito-Urinary  Tuberculosis,  .  25 
Vecki — Sexual  Impotence, 28 

GYNECOLOGY. 

American  Text- Book  of  Gynecology,  4 
Cragin — Essentials  of  Gynecology,  .  .  9 
Garrigues — Diseases  of  Women,  ...  11 
Long — Syllabus  of  Gynecology,  ...  15 
Penrose — Diseases  of  Women,  .  ...  18 
Sutton  and  Giles — Diseases  of  Women,  28 

MATERIA  MEDICA,  PHARMACOL- 
OGY, AND  THERAPEUTICS. 

An  American  Text-Book  of  Applied 

Therapeutics 3 

Butler — Text-Book  of  Materia  Medica, 

Therapeutics  and  Pharmacology,  .  .  .  8 
Cerna — Notes  on  the  Newer  Remedies,  8 
Griffin — Materia  Med.  and  Therapeutics,  12 
Morris — P'ssentials  of    Materia   Medica 

and  Therapeutics,  .    .  17 

Saunders'  Pocket  Medical  Formulary,  24, 
Sayre — Essentials  of  Pharmacy,  .  .  24 
Stevens — Essentials  of  Materia  Medica 

and  Therapeutics ...    26 

Stoney — Materia  Medica  for  Nurses,  .  28 
Thornton — Dose-Book  and   Manual  of 

Prescription-Writing, 28 

MEDICAL   JURISPRUDENCE    AND 
TOXICOLOGY. 

An  American  Text-Book  of  Legal 
Medicine  and  Toxicology, 4 

Chapman — Medical  Jurisprudence  and 
Toxicology, 8 

Semple — Essentials  of  Legal  Medicine, 
Toxicology,  and  Hygiene, 25 


Medical  Publications  of  W.  B.  Saunders. 


31 


NERVOUS  AND  MENTAL 
DISEASES,  ETC. 

Burr — Nervous  Diseases, 7 

Chapin — Compendium  of  Insanity,  .  .  8 
Church    and    Peterson — Nervous  and 

Mental  Diseases, 8 

Shaw — Essentials  of  Nervous  Diseases 

and  Insanity, 26 

NURSING. 

An  American  Text-Book  of  Nursing,  29 

Griffith — The  Care  of  the  Baby,    ...  12 

Hampton — Nursing, 12 

Hart — Diet  in  Sickness  and  in  Health,  13 

Meigs — Feeding  in  Early  Infancy,    ,    .  17 

Morten — Nurse's  Dictionary,     ....  18 

Stoney — Practical  Points  in  Nursing,    .  27 

OBSTETRICS. 

An  American  Text-Book  of  Obstetrics, 
Ashton — Essentials  of  Obstetrics,  .  .  . 
Boisliniere — Obstetric  Accidents,  Emer 

gencies,  and  Operations,  .... 
Dorland — Manual  of  Obstetrics,  . 
Hirst — Text-Book  of  Obstetrics,  . 
Norris — Syllabus  of  Obstetrics,  .    . 

PATHOLOGY. 

An  American  Text-Book  of  Pathology,  5 
Mallory    and    Wright  —  Pathological 

Technifjue, 16 

Semple — Essentials   of    Pathology  and 

Morbid  Anatomy,  .    .         25 

Senn — Pathology  and  Surgical  Treat- 
ment of  Tumors, 25 

Stengel — Text- Book  of  Pathology,    .    .    26 
Warren — Surgical  Pathology  and  Thera- 
peutics,    29 

PHYSIOLOGY. 

An  American  Text-Book  of  Physi- 
ology,    5 

Hare — Essentials  of  Physiology,    .    .    .  13 

Raymond — Manual  of  Physiology,   .    .  19 

Stewart — Manual  of  Physiology,  ...  27 

PRACTICE  OF  MEDICINE. 

An  American  Text-Book  of  the  The- 
ory and  Practice  of  Medicine,  ....      5 

An  American  Year-Book  of  Medicine 
and  Surgery,  6 

Anders — Text-Book  of  the  Practice  of 
Medicine, ...      6 

Lockwood — Manual  of  the  Practice  of 
Medicine, 15 

Morris — Essentials  of  the  Practice  of 
Medicine, 17 

Rowland  and  Hedley  —  Archives  of 
the  Roentgen  Ray, 19 

Stevens — Manual  of  the  Practice  of 
Medicine, 27 

SKIN  AND  VENEREAL. 

An  American  Text-Book  of  Genito- 
urinary and  Skin  Diseases, 3 


Hyde  and  Montgomery — .Syphilis  and 
the  Venereal  Diseases, 13 

Martin — Essentials  of  Minor  Surgery, 
Bandaging,  and  Venereal  Diseases,    .    16 

Pringle — Pictorial  Atlas  of  Skin  Dis- 
eases and  Syphilitic  Affections,    ...    19 

Stelwagon — Essentials  of  Diseases  of 
the  .Skin, 26 

SURGERY. 

An  American  Text-Book  of  Surgery,     5 
An  American  Year-Book  of  Medicine 

and  Surgery 6 

Beck — Manual  of  Surgical  Asepsis,  .    .      7 
DaCosta — Manual  of  Surgery,  ....    10 

Keen  — Operation  Blank, 15 

Keen — The  Surgical  Complications  and 

Sequels  of  Typhoid  Fever, 15 

Macdonald — Surgical    Diagnosis    and 

Treatment, 16 

Martin — Essentials   of    Minor  Surgery, 

Bandaging,  and  Venereal  Diseases,    .    16 
Martin — Essentials  of  .Surgery, ....    16 

Moore — Orthopedic  Surgery, 17 

Pye — Elementary  Bandaging  and  Surgi- 
cal Dressing, 19 

Rowland    and    Hedley— Archives  of 

the  Roentgen  Ray, 19 

Senn — Genito-Urinary  Tuberculosis,     .    25 

Senn— Syllabus  of  Surgery, 25 

Senn — Pathology  and  Surgical  Treat- 
ment of  Tumors, 25 

Warren — Surgical  Pathology  and  Ther- 
apeutics,       29 

URINE  AND  URINARY  DISEASES. 

Saundby — Renal  and  Urinary  Diseases,  24 
Wolff — Essentials   of    Examination    of 
Urine, 29 


MISCELLANEOUS. 

Bastin — Laboratory    Exercises    in    Bot- 
any,      7 

Gould  and  Pyle — Anomalies  and  Curi- 
osities of  Medicine, ir 

Grafstrom — Massage,     .......     12 

Keating — Howr   to    Examine    for    Life 

Insurance, ,      I4 

Rowland    arid    Hedley — Archives   of 

the  Roentgen  Ray, I9 

Saunders'  Medical  Hand-Atlases,  .  .  2 
Saunders'  New  Series  of  Manuals,  22,  23 
Saunders'  Pocket  Medical  Formulary,  .  24 
Saunders'  Question-Compends,  .  .  20,  21 
Senn — Pathology  and  Surgical  Treat- 
ment of  Tumors, -25 

Stewart  and  Lawrance — Essentials  of 

Medical  Electricity, 27 

Thornton — Dose-Book  and  Manual  of 

Prescription-Writing, 28 

Van  Valzah  and  Nisbet — Diseases  of 
the  Stomach, 28 


In  Preparation  for  Early  Publication. 


THE  INTERNATIONAL  TEXT=BOOK  OF  SURGERY.     In  two  volumes. 

By  American  and  Briiish  authors.  Edited  by  J.  CoLLiNS  Warren,  M.  D.,  LL.D.^ 
Professor  of  Surgery,  Harvard  Medical  School,  Boston;  Surgeon  to  the  Massachusetts 
General  Hospital ;  and  A.  Pearck  Gould,  M.  S.,  F.  R.  C.  S.,  England,  Lecturer  on 
Practical  Surgery  and  Teacher  of  Operative  Surgery,  Middlesex  Hospital  Medical 
School;    Surgeon  to  the  Middlesex  Hospital,  I^ondon,  England. 

AN  AMERICAN  TEXT-BOOK  OF  PATHOLOGY. 

Edited  by  John  Guiteras,  M.D.,  Professor  of  General  Pathology  and  of  Morbid 
Anatomy  in  the  University  of  Pennsylvania;  and  David  Riesman,  M.D.,  Demon- 
strator of  Pathological  Histology  in  the  University  of  Pennsylvania. 

AN  AMERICAN  TEXT=BOOK  OF  LEGAL  MEDICINE  AND  TOXICOLOGY. 

Edited  by  Frederick  Peterson,  M.D.,  Clinical  [Professor  of  Mental  Diseases  in 
the  Woman's  Medical  College,  New^  York;  Chief  of  Clinic,  Nervous  Department, 
College  of  Physicians  and  Surgeons,  New  York;  and  Walter  S.  Haines,  M.D., 
Professor  of  Chemistry,  Pharmacy,  and  Toxicology  in  Rush  Medical  College,  Chicago, 
Illinois. 

AN  AMERICAN  TEXT=BOOK  OF  DIAGNOSIS. 

Edited  by  ALFRED  STENGEL,  M.  D.,  Physician  to  the  Philadelphia  Hospital ;  Professor 
of  Clinical  Medicine  in  the  Woman's  Medical  College;  Physician  to  the  Children's 
Hospital ;   late  Pathologist  to  the  German  Hospital,  Philadelphia,  etc. 

HEISLER'S  EMBRYOLOGY. 

A  Text=Book  of  Embryology.  By  John  C.  Heisler,  M.D.,  Professor  ot 
Anatomy  in  the  Medico-Chirurgical  College,  Philadelphia. 

KYLE  ON  THE  NOSE  AND  THROAT. 

Diseases  of  the  Nose  and  Throat.  By  D.  Braden  Kyle,  M.  D.,  Clinical  Pro- 
fessor of  Laryngology  and  Rhinology,  Jefferson  Medical  College,  Philadelphia;  Con- 
sulting Laryngologist,  Rhinologist,  and  Otologist,  St.  Agnes'  Hospital ;  Bacteriologist 
to  the  Philadelphia  Orthopedic  Hospital  and  Infirmary  for  Nervous  Diseases,  etc. 

PRYOR— PELVIC  INFLAMMATIONS. 

The  Treatment  of  Pelvic  Inflammations  through  the  Vagina.     By  W.  R. 

Pryor,  M.  D.,  Professor  of  Gynecology  in  the  New  York  Polyclinic. 

WEST'S  NURSING. 

An  American  Text=Book  of  Nursing.  By  American  Teachers.  Edited  by 
RoBERiA  M.  West,  late  Superintendent  of  Nurses  in  the  Hospital  of  the  University 
of  Pennsylvania. 


/  ^. 


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